Ecosystem transformation upon Aptian seawater ingress into the Proto-South Atlantic Ocean

Ecosystem transformation upon Aptian seawater ingress into the Proto-South Atlantic Ocean | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Article Ecosystem transformation upon Aptian seawater ingress into the Proto-South Atlantic Ocean Jian Ma, Leonardo Cury, Anelize Rumbelsperger, Heidi Albrecht, and 7 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-4463807/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 26 Jan, 2025 Read the published version in Communications Earth & Environment → Version 1 posted You are reading this latest preprint version Abstract The early evolution of the South Atlantic Ocean following the Cretaceous break-up of Gondwana is extensively recorded in rift basins along the conjugate margins of Africa and Brazil. For the Brazil margin, divergent views of the source and pathway of the initial seawater incursion persist due to a paucity of recognized transitional sequences that document marine transgressive deposits over the continental interior. To address this, we conducted a high-resolution sedimentological and geochemical study through a core in the Campos Basin that encompasses the key lithologic switch from lacustrine carbonate to marine evaporite settings. Steroid lipid biomarkers, derived from marine algae, make a striking appearance in concert with a pronounced negative shift of 87Sr/86Sr ratios and coincident with the appearance of anhydrite. Importantly, the sulfur-sequestered biomarkers reveal a dynamic system where redox-stratified and anoxic conditions were amplified along with a deepening chemocline through the marine transition. Gondwana seawater incursion biomarker desulfurization ecosystem Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Introduction The early Cretaceous breakup of the western Gondwana Supercontinent marks the birth of the South Atlantic Ocean (SAO) and instigated a range of other impacts on the Earth system 1 , 2 , 3 , 4 , 5 . Specifically, the Aptian–Albian stage is a critical interval in terms of the development of a new oceanic gateway and the initiation of the central SAO between the rifting South America and Africa plates 6 , 7 , 8 , 9 . As a consequence, seawater ingress along with marine organisms transformed the pre-existing saline lacustrine ecosystems 10 . The widespread Aptian–Albian sea/seaways in the plate interiors led to the development of restricted and hypersaline environments 11 and ubiquitous thick deposits of salt with organic-rich layers along the Brazilian-African conjugate margins 11 , 12 . Concomitantly, the Aptian–Albian transgression was sufficiently extensive to produce the propagation of marine biotas 13 , 14 , 15 . In turn, sedimentary and fossil records in the conjugate margins of Brazil and West Africa provide fundamental constraints for paleogeographic reconstruction. Despite numerous reports of marine incursions, however, there are divergent views on the source and pathways taken by the first marine transgression into these intracratonic basins, hindering our understanding of paleogeographic and ecosystem reconstruction. On the Brazil side, it is postulated that a long-distance Aptian–Albian transgression, originated from the equatorial Atlantic Tethyan Ocean, spreading southwards 8 , while tectonic evolution analyses support northward Aptian–Albian marine ingressions from the austral SAO 16 , 17 , 18 , 19 . Pathways of marine ingressions are further complicated by conflicting results based on paleocurrent data and marine biota comparisons between NE and SE Brazilian basins 7 , 20 . The conundrum persists, as the paucity of transitional sedimentary sequences that represent marine transgressive deposits over the continental interior hinder the interpretation of ecosystem impacts. Discriminating between non-marine and marine-influenced settings, especially in the absence of body fossils, is heavily reliant on sedimentology and geochemistry. Even so, much of the available toolkit is unable to unequivocally discriminate between marine and saline lacustrine deposition. Conversely, fossil lipids—biomarkers—represent geologically stable molecules derived from the diagenetic modification of microbially-derived precursors thereby fingerprinting parent organisms and, by extension, the depositional environment they once inhabited 21 , 22 , 23 . Of particular significance here, 24- n -propylcholestane (24-npc) is a steroidal lipid derived from the diagenetic transformation of 24- n -propylcholesterol—the major sterol constituent of modern marine pelagophyte algae 24 . Given that contemporary pelagophyte algae are exclusively marine organisms, and the ubiquity of 24-npc in marine-derived organic matter 25 , 26 , 24-npc is widely applied as a diagnostic indicator of marine-influenced sedimentation 27 , 28 , 29 . Hitherto, most biomarker-based paleoenvironmental interpretations have focused on ‘free’ lipids from organic extracts of rocks. On the other hand, chemolysis studies have demonstrated that organic molecules with multiple unsaturations (double bonds) and/or particular functional groups are prone to rapidly react with reduced inorganic sulfur species (e.g., H 2 S) under anoxic and sulfidic conditions to become incorporated via S-S and S-C crosslinking into the polar or macromolecular fractions of sedimentary organic matter 30 , 31 . Thereby, organic sulfurization can lead to selective sequestration of specific biomarker precursors affording investigation of diverse complex species that are not readily amenable to conventional lipid analysis 32 , 33 , 34 and resolve biases in paleoenvironmental reconstruction 35 , 36 . Given widespread anoxic environments in Aptian–Albian strata of Brazilian marginal basins 7 , 11 , both free and sulfurized lipids of organic extracts need to be evaluated before a complete biomarker picture can be visualized. In an independent yet complementary approach, the radiogenic Sr isotopic composition ( 87 Sr/ 86 Sr) of sediments is sensitive to the weathering inputs into a basin. In a lacustrine environment, the 87 Sr/ 86 Sr isotopic composition is set by the radiogenic 87 Sr/ 86 Sr isotopic of the specific combination of bedrock within upstream catchments. In the case of the Brazilian lacustrine systems, it has been postulated that extremely radiogenic Precambrian cratonic bedrock on both the South American and African margins determined the 87 Sr/ 86 Sr isotopic composition of the lacustrine rift system 37 , 38 . In contrast the 87 Sr/ 86 Sr isotopic composition of marine waters is well mixed and yields a coherent marine 87 Sr/ 86 Sr isotope curve through time 39 . Reconstructing the 87 Sr/ 86 Sr isotopic composition of South Atlantic sediments can, therefore, yield an independent record of marine transgression into the lacustrine system. Herein, we report free and sulfurized lipid biomarkers and Sr isotope analyses, along with carbon, oxygen, and clumped isotopes and sedimentological descriptions of a core retrieved from the SE Brazilian Campos Basin that reveal the initial Aptian marine ingress therein and associated ecosystem perturbation. The succession cored by the Fragata borehole, located in the northwest of the basinal depocenter (Fig. 1 ), encompasses lacustrine carbonates of the upper Macabu Fm. and interbedded anhydrite, halite within carbonate sequences of the Retiro Fm., thus providing a sedimentological record and opportunity to explore preserved organic matter associated with the event. Our findings address the knowledge gap about the impact of the marine transgression in the western conjugate margin by documenting its environmental consequences and ecosystem responses. Results and discussion 3.1 Seawater ingress into the Campos Basin The Macabu Fm. in the Campos Basin is dominated by carbonate successions, which developed in an alkaline lacustrine setting under an arid climate 40 , 41 , 42 . The overlying Albian aged Macaé Group in the Campos Basin clearly records sedimentation in a marine environment, as evidenced by foraminiferal biozonation and carbonate microfacies 43 . Contrastingly, the Retiro Fm. is typified by evaporites, which represents the transitional phase between successions in the Macabu Formation and the Albian-aged Macaé Group, and may record the initial marine incursions in the Campos Basin. Both carbonate clumped isotope (Δ47) values and the stereochemical configurations of biomarkers have reveal a moderate thermal history of the study area (SI). A wide array of lipid biomarkers, including n -alkanes, acyclic isoprenoids, terpanes, steranes, hopanes and carotenoids, were present in both free and desulfurized fractions (Fig. S5) from the Fragata core samples (Fig. 1 ). Of particular significance among the sterane biomarkers is the detection of 24- n -propylcholestane (24-npc) in both free non-polar (free-NP) and a second set of non-polar fractions generated by Raney Ni desulfurization (RN-NP) (Fig. 2 ). As a geological derivative of 24- n -propylidenecholesterol 24 , 25 , 24-npc is the major sterane diagnostic for marine chrysophyte/pelagophyte algae 44 , 45 . Accordingly, 24-npc is ubiquitously detected in marine environments and has been widely adopted as a diagnostic marker of marine or marine-influenced strata in the geological record 26 , 27 , 28 , 29 , 46 . However, the detection of 24-npc may be confounded when in low relative abundance due to an interference signal from 4α-methyl-24-ethylcholestane (4α-methylstigmastane, 4-Me24Et) 21 that partially co-elutes on most GC liquid phases. Strict criteria are followed for the rigorous identification of 24-npc in the Fragata samples and include the relative signal intensities and the small but reproducible retention time difference between 24-npc and 4α-methyl-24-ethylcholestane 27 . Ratios of 24-npc and 4-Me24Et (denoted as 24-npc ratio) are elevated in samples shallower than 5024.3 m in the Fragata core (26.7% ± 8.8%, 1σ, Table S2). This allows positive identification of 24-npc, since the 24-npc/4-Me24Et ratios in seawater-influenced settings are expected to exceed 10% 21, 28 . Additionally, a reproducible offset of ~ 0.1 mins in the chromatographic peaks in the 414 → 217 and 414 → 231 Da transitions on GC-QQQ-MS (Fig. 2 ) further verified the marine signature of 24-npc at the top of the Fragata core. Significantly, 24-npc peaks are also recognized in the desulfurized RN-NP fractions (Fig. 2 ) with elevated signal intensities. Above 5024.3 m the 24-npc ratios rise to 73.0% (51.8% on average, Table S2). Accordingly, the occurrence of 24-npc in both free and sulfurized fractions, restricted to the entire interval above 5024.3 m in Fragata core, and upwards from the first appearance of anhydrite at the base of the Retiro Fm. indicates that marine waters had intruded into Campos Basin during the late Aptian (< 116 Ma). Notable variations of 87 Sr/ 86 Sr were captured in the interval above 5024.3 m in the Fragata core (Fig. 3 ). The findings delineate distinct groups characterized by ratios falling within the ranges of 0.712–0.714 and 0.709–0.710. The initial interval, previously identified in several studies 40 , 47 , 48 , is attributed to distinctly continental sources, serving as a significant geochemical indicator supporting the interpretation of the carbonate succession as having a lacustrine origin in the Campos and Santos basins. Despite the limited understanding of the paleo-tectonic context, the notable variability in the strontium isotope signal indicates a depositional system influenced by a range of sources, including continental cratonic rocks and contemporaneous basaltic volcanism as potential contributors 37 , 49 . The second interval, however, exhibits notably reduced radiogenic Sr values, predominantly around 0.709, indicating a distinct decrease in radiogenic sources entering the basin. Influx of marine waters would be reasonable, given that the anticipated average 87 Sr/ 86 Sr ratio for seawater during the Aptian period is approximately 0.707 50 , with a projected rise in radiogenic Sr attributed to the evolution of the Paraná-Etendeka Large Igneous Province, as posited elsewhere 51 . A mix between internally-drained solutes and marine influx would produce a hybrid brine with a new 87 Sr/ 86 Sr ratio under hydrological equilibrium. Considering fluctuations in water levels within a shallow environment, with a water/Sr mass balance sensitive to source variations, it may be possible to explain the variation in radiogenic strontium within the Macabu Formation due to changes in sources that are influenced by tectonic activity. The excursions of 87 Sr/ 86 Sr ratio are indicative of sources related to mafic volcanic rocks and/or marine incursions. While other strontium excursions are observed in the lower intervals of the pre-salt carbonates 47 , 52 , a significant shift at the top of the succession, near the contact with the Retiro Formation, suggests this point as the onset of predominant marine influx. Paleontological evidence has implied that seawater infiltrated from the NE Brazilian marginal basins, including the Sao Luís, Parnaíba and Araripe basins during the transition of Aptian–Albian; Furthermore, a Tethyan ingression is suggested by the presence of several fossil taxa 8 , 13 , 14 , 15 . However, there is a lack of unequivocal marine evidence in the SE Brazilian marginal basins (e.g., Campos and Santos Basins). Accordingly, a series of southward marine transgressions from the equatorial Tethys Ocean was hypothesized 7 , 8 divergent from the tectonic evidence of a marine pathway extending from south to north on the basis of sea-floor spreading patterns and geodynamic reconstructions 16 , 17 , 18 , 19 , recently acquired geochronological data 37 , 49 and from evidence gathered from the conjugate margins of West Africa 9 . 3.2 A switch to a marine-influenced ecosystem Numerous examples have illustrated how seawater entry into lacustrine ecosystems alters their hydrography, water chemistry and biology. Ingressions can result from subtle changes in relative sea level on glacial-interglacial timescales (e.g. 53 ) or from tectonism on geological timescales 27 , 28 , 29 , 53 . The salinity and depth of a water body, together with basin shape, will influence the tendency towards density stratification. Relative abundances of methyltrimethyltridecylchromans (MTTCs) isomers (e.g., methylated MTTCs) have been proposed to be a reliable indicator for paleosalinity in aquatic surface-layers 54 , 55 , especially recording the periodic incursions of marine waters and subsequent evaporation 56 . Here, the Fragata core records enhanced MTTCs ratios (0.02 vs. 0.16 on average, with the highest value to 0.42, Table S2, Fig. 3 ), pointing to a rapid elevation in salinity above 5025.12 m. Subsequently, the elevated abundance of gammacerane (denoted by the gammacerane index, GI) is additionally indicative of enhanced water column stratification, given that its precursor, tetrahymanol, is a signal for bacterivorous ciliates living at redox transitions 57 , 58 . Stratification reduces mixing and thus promotes oxygen-depletion in deeper waters, as evidenced by concomitant reduction in the pristane/phytane (Pr/Ph) ratio and enhancement of C 35 Homohopane Index (C 35 HHI) at the top of the section (Fig. 3 ). Pr/Ph is regarded as a redox-sensitive proxy due to the preferential formation of phytane over pristane derived from the phytol side-chains of chlorophylls under anoxic conditions 59 . Although additional factors including salinity, organic matter sources, and diagenetic process may affect Pr/Ph 60 , 61 values below 1 are considered diagnostic for pervasive anoxia. Similarly, the C 35 HHI is a robust proxy for tracing anoxic conditions 21 , considering that the C5 side-chains of its precursor compounds, C 35 bacteriohopanepolyols, are best preserved under the anoxic and H 2 S-rich conditions that follow from enhancement of sulfate levels from seawater incursions 62 , 63 . Together, the evolution of multiple biomarker proxies documents a hydrographically dynamic system, capturing the establishment of enhanced anoxic/euxinic, saline and stratified conditions in the Retiro Formation. Given the enhancement of anoxia induced by the marine incursion, reductive sulfurization of organic matter under euxinic conditions 33 becomes an issue that may complicate or inhibit the identification of some biological precursor lipids 64 . In fact, here, the patterns of n -alkanes, and of sterane and hopane stereoisomers released by the RN treatment (Fig. S5–S6), illustrate how specific biomarkers have been sequestered into the S-bound macromolecular component of sedimentary organic matter. High abundances of phytane and C 35 homohopanes released during desulfurization (Fig. 4 -D) further confirm their preferential preservation under anoxic and sulfidic conditions 59 , 63 . Despite striking differences in the patterns of the free-NP and RN-NP fractions, however, the key biomarker proxies all move in a consistent direction concomitant with the marine incursion. Both free and sulfurized lipids also reveal a dynamic system: Here, the ingress of seawater strengthened stratification within this sector of the Campos Basin, fostering the development of water column anoxia, as evidenced by elevated values of GI, C 35 HHI and MTTC (Fig. 5 ). Accordingly, hydrographic changes induced by seawater ingress have prompted ecosystem re-structuring as recorded in its biochemostratigraphy. A striking and progressive elevation in sterane/hopane ratios (S/H) (up to 10.6, Table S2), a proxy based on the diagenetic products of sterols and hopanoids diagnostic for eukaryotes and bacteria respectively 21 , 65 , suggests this environmental shift appears to have favored photosynthetic algae, allowing their proliferation at the expense of bacteria. Consistent with transgressive records in other basins 23 , 27 , the elevated S/H document the ingress of seawater providing algae with an advantage over the bacterial community whether by addition of nutrients or other factors associated with the water chemistry. Among all steroid derivatives, stigmastane (C 29 sterane) becomes dominant over cholestane, its C 27 counterpart, after the marine incursion (Fig. 4 -C; Fig. 5 ). Given their mostly biological source from Chlorophyceae and Rhodophyceae, respectively 66 , 67 , the enhanced stigmastane represents the likely prevalence of green algae over other taxa in the immediate aftermath of the transition. 3.3 A progressive deepening of the chemocline with marine ingress Despite the detection of the array of carotenoids in the free biomarker fractions (Table S2), diverse inventories of aliphatic and aromatic carotenoids are released upon desulfurization of the polar fractions (Fig. 4 -A, B). In the free-NP fractions, the predominant compounds in all samples are β-carotane and isorenieratane, together with minor β-isorenieratane and C 38 carotenoids. However, in the RN-NP fractions, relatively high abundances of isorenieratane, chlorobactane and okenane that have been sequestered into macromolecules by sulfurization supports the notion that they represent indigenous signals for phototrophic sulfur bacteria. As strict anaerobes, these phototrophic sulfur bacteria, comprising green sulfur bacteria (i.e., GSB, Chlorobiaceae ) and purple sulfur bacteria (i.e. PSB, Chromatiaceae ), utilize sulfide and other reduced sulfur species as electron donors for photosynthesis 68 . Because of their dual requirements for illumination and sulfide, the GSB and PSB are considered index species for photic zone euxinia (PZE) where the light penetrates a sulfide-containing water column 69 . Thus, their biomarker lipids have been applied as PZE biosignatures in both modern environments and in paleoenvironmental reconstruction 64 , 65 , 70 , 71 , 72 , 73 . Being the most widely recorded aromatic carotenoid in marine sediments 71 , 74 , isorenieratane is the diagenetic product of isorenieratene that is derived from low-light-adapted brown strains of phototrophic green sulfur bacteria (GSB). These GSB are known to be well adapted to lower light intensities and therefore deeper waters (~ 100 m) 69 , 75 . In comparison, green-colored strains that produce chlorobactene, the biological precursor of chlorobactane, require higher light intensity and accordingly are concentrated at shallower (∼15–30 m) chemocline depths 76 . In contrast, the okenone-synthesizing PSB can proliferate as plankton within a shallow chemocline (~ 20 m; 77 ), in benthic microbial mats, as aggregates with sulfate reducing bacteria in the water column 78 or, perhaps reflecting their slightly higher tolerance for oxygen, as observed in the ‘pink berry consortia’ that are found in tidally-influenced marginal marine environments 79 . In the present study, by comparing the sedimentary lipids of the free and S-bound fractions, we observe a novel switch in the assemblages of aromatic carotenoids upon initial marine ingress into the Campos Basin. At the base of the anhydrite-bearing layer that marks the onset of the incursion, a peak in PSB-derived okenane (up to 33.0%, Fig. 6 , Table S2) implies extremely shallow PZE or microbial mat facies. Okenane then declines coincident with a peak in the abundance of GSB-derived chlorobactane (3.8%) and elevated isorenieratane. After this, isorenieratane becomes the dominant aromatic carotenoid identifying the brown-pigmented GSB as the predominant anoxygenic phototroph and a deepening chemocline. In addition, the composition of C 38 aromatic carotenoids decrease markedly (6.4% vs. 18.2%, p < 0.001, Table S2). These C 38 aromatic carotenoids are the diagenetic products of synechoxanthin which is a C 40 aromatic carotenoid with dual carboxylic acid functionalities prevalent in non-marine or euryhaline cyanobacteria 22 , 70 , 80 , 81 . Thus, reductive sulfurization and decarboxylation affords the C 38 diagenetic products together with C 39 counterparts diagnostic for cyanobacteria that are prevalent while lacustrine conditions prevail. Their decline coincides with the increases in phototrophic sulfur bacteria that accompany the ingress of seawater. In other words, the marine incursions instigated an overturn of the photosynthetic community, including a proliferation of eukaryotic algae together with GSB concomitant with a decline in primary productivity by the synechoxanthin-producing cyanobacteria. In summary, both the less radiogenic 87 Sr/ 86 Sr ratio and 24-npc biomarker results indicate marine incursion associated with the deposition of the Retiro Formation, associated with a fundamental transformation in the biological community. Materials and Methods Petrology inspection and organic extraction. In total 40 core samples of carbonates and mudstones, with a 2–4 m resolution of depths, were selected from the Fragata core in the Campos Basin (Fig. 1 -A, B) covering a depth range of 5026.320 m to 5148.695 m (Fig. 1 -D, red dots). Core slabs and core plugs were prepared for sedimentology and organic–inorganic geochemistry analyses. Specifically, petrographic microscopic observations were carried out under plane-polarized, crossed-polarized and cathodoluminescence (CL) illumination on polished thin-sections. Several aliquots of bulk-rock powders were prepared for mineral (X-ray diffraction, XRD), isotopic and organic geochemistry analyses. To mitigate possible inorganic or organic contamination, the outer parts of core plugs were removed using a diamond blade saw. The inner parts, after gentle polishing, were then placed in a combusted jar and sonicated repeatedly with DI water for 15 seconds to remove the trace slurry on the fresh surfaces. Upon drying within a low-temperature oven (40°C) they were ground in a puckmill. This was cleaned between samples to remove any potential cross-contaminating organic residues by first grinding an aliquot of combusted sand and then rinsing with DI water, MeOH and DCM (3X). For each biomarker sample, approximately 2 g powdered sample was weighed and extracted (4X for 25 mins at 100°C) with dichloromethane (DCM): methanol (MeOH) (9:1;v:v) in a MARS 6 Microwave Digestion System at the Massachusetts Institute of Technology. The extracts were transferred into combusted 60 ml glass tubes using combusted pipettes, combined, and concentrated at room temperature under a gentle stream of N 2 on the TurboVap followed by transfer into combusted 4 ml vials with DCM rinsing and sonication. Elemental sulfur was removed by reaction with activated copper shot. The resultant extracts were dried to ~ 100µl and fractionated using a silica gel column. Solvent mixtures of hexane: DCM (4:1; v:v) and DCM: MeOH (4:1;v:v) were used to elute the non-polar (free-NP) and polar fractions, sequentially. Raney nickel desulfurization. For desulfurization reactions, ‘T-1’ Raney-Nickel (RN) catalyst was prepared. Specifically, 40 g non-activated nickel aluminum alloy (1:1) was reacted with 600 ml of 10% sodium hydroxide for 1 hour at the temperature of 95°C under a gentle N 2 stream. Subsequently, the aqueous component was decanted and the residue washed with Milli-Q water (3X), and then activated by distilled absolute ethanol (3X). Natural ignition of dry Raney-Ni slurry verified the efficiency of prepared catalyst prior to use. Meanwhile, a procedure blank and an oil standard were subject to the procedure in each set of RN reactions. For desulfurization reactions, ~ 7 mg of the polar fraction of a TLE was dissolved in 20 ml distilled absolute ethanol together with 3 ml ‘T-1’ RN slurry and the mixture heated to 80°C under N 2 reflux for 2 h. The products were extracted into DCM with sonication (4X). After subsequent centrifugation and drying, aliquots of RN-treated new extracts were subjected to further silica gel column chromatography to obtain a second pair of NP (RN-NP) and polar fractions. RN reactivity and an absence of contamination were verified the recovery yields from an oil standard and the purity of blanks. Lipid biomarker analysis. Both free-NP and RN-NP fractions were subjected to GC-MS analysis using a 7890B Agilent gas chromatograph coupled to a 5975C Agilent MSD and a 7010A Agilent triple quadrupole MS (GC-QQQ-MS) operated in full scan or multiple reaction monitoring (MRM) modes, respectively. All the GC’s were equipped with a multi-mode injector at an initial injection temperature of 45°C which was ramped at a rate of 720°/min to 340°C. A DB-5MS column (60 m×250 µm×0.25 µm) was installed with each GC with an oven temperature held isothermally at 40° for 2 mins, ramped to 320°C at a rate of 4°/min, and then held at this temperature for 22 mins. The transfer lines and source temperatures in GC-MS and GC-QQQ-MS were set to 320°C and 250°C, respectively. The electron energy of GC-QQQ-MS was 70 eV to ensure a standard signal for the precursor-product transitions. All biomarker data are processed using MassHunter software. In GC-QQQ-MS, each compound was identified and integrated under MRM mode within a narrow retention time window (0.5 mins). in situ 87 Sr/ 86 Sr analysis. The 87 Sr/ 86 Sr results were obtained by the LA-ICP-MS method at the University of Paraná, Brazil, with analytical resolution for the characterization of different phases, resolving micro structures varying between 2 µm and 150 µm. Results were obtained with excimer ArF laser ablation Analyte Excite CETAC Teledyne, generating beams with wavelength of 193 nm, which is sufficient energy to sample different carbonate microfacies. The ablation was carried out in raster mode, with sampling lines using laser beams with spot dimensions of 40µm, in a path length of 700 µm, scanning speed of 10 µm/s, frequency of 7 Hz, and energy of 6.26 J/cm². The analyzes were carried out on ~ 1 mm fragments extracted from drill core plugs, which were previously analyzed by back-scattered electron (BSE) imaging using scanning electron microscopy analysis. The BSE images made it possible to accurately identify variations in composition such as silica replacement, clay minerals, fractures, and other relevant constituents for selecting the sampling area. Reproducibility was tested with three counter-tests per sample. Furthermore, samples from sample populations with end-member 87 Sr/ 86 Sr results were selected using the in-situ method, for further analysis and confirmation by ID-TIMS. The measurements were carried out in a multi collector ICP-MS Thermo Fischer Neptune Plus, monitoring the species 83 Kr (L4 amplifier 10ˆ11), 167 Er +2 (L3 amplifier 10ˆ13), 84 Sr (L2 amplifier 10ˆ11), 85 Rb (L1 amplifier 10ˆ11), 86 Sr (H1 amplifier 10ˆ11), 173 Yb 2+ (H2 amplifier 10ˆ13), 87 Sr (H3 amplifier 10ˆ11) and 88 Sr (H4 amplifier 10ˆ11). As a reference standard, the coral JCp-1 was analyzed, which has an accepted 87 Sr/ 86 Sr ratio in the literature of 0.709160 ± 0.000020. The coral JCp-1 yielded a variable intensity of 88 Sr, the most abundant isotope, between 15 and 20V measured with a 10ˆ11 amplifier, equivalent to an estimated a Sr concentration from 7000 ppm to 2000 ppm, reflecting the heterogeneous distribution of strontium as it is a natural standard. δ 13 C, δ 18 O and clumped isotope (Δ 47 ) analysis of carbonate. Stable isotopic measurements of δ 13 C, δ 18 O, and carbonate clumped isotope (Δ 47 ) analyses were completed to contextualize the biomarker and 87 Sr/ 86 Sr results. Sample δ 13 C, δ 18 O, and Δ 47 were measured from January 2020 to June 2021 at the MIT Carbonate Research Laboratory on a Nu Perspective dual-inlet isotope ratio mass spectrometer with a Nu Carb automated sample preparation unit held at 70°C. Calcite samples weighing ~ 400–600 µg were reacted for 25 minutes in individual glass vials with 150 µl orthophosphoric acid (ρ = 1.94 g/cm 3 ). Evolved CO 2 gas was purified cryogenically and by passive passage through a Porapak trap (1/4" ID; 0.4 g 50/80 mesh Porapak Q) held at − 30°C. The initial voltage was 8–20 V on the m/z 44 beam with 2x10 8 Ω resistors and depleted by approximately 50% over the course of an analysis (60 cycles with 20-minute total integration time). Sample and standard CO 2 gases depleted at equivalent rates from microvolumes over the analysis time. Mass spectrometry methods were nearly identical to those reported in Anderson et al. (2021). ETH-1–4 and IAEA-C2 were used as anchors; IAEA-C1 and Merck were treated as unknowns. Unknown anchor ratio was 1:1 for each 50 run. The reference side of the dual-inlet was refilled with reference gas after every 10 analyses. In total, unknowns were measured 1–4 times over the study interval (76 total unknown analyses; 118 InterCarb standards). Raw mass spectrometer data were first processed by removing cycles (i.e., single integration cycles of mass spectrometer measurement) with raw Δ 47 values more than 5 "long-term" standard deviations (0.50‰; the mean of the respective cycle-level SD for ETH-1–4 over a 3-month period was 0.10‰) away from the median Δ 47 measurement for the analysis. Analyses were removed if more than 10 cycles (out of 60 total cycles) fell outside the 5 long-term SD threshold. Analyses with transducer pressure below 15 mbar, typically corresponding to sample collection issues, incomplete digestion, or low carbonate content, and analyses that ran misbalanced by > 1% were also removed. No pressure baseline correction was applied. After removal of cycle-level outliers, data were processed using the 'D47crunch' Python package using IUPAC 17 O parameters 82 , and projected to the I-CDES with values for ETH-1–4 and IAEA-C2 anchors from the InterCarb project 83 , 84 . Raw Δ 47 measurements were converted to the I-CDES using a pooled-regression approach that accounts for the relative mapping of all samples in δ 47 -Δ 47 space 84 . Analytical uncertainty and error associated with the creation of the reference frame were fully propagated through the dataset. A full description of the data reduction procedure used in D47crunch is detailed in 84 . Each sample carousel (typically 50 analyses) was treated as a single analytical session. IAEA-C1 and Merck standards were treated as unknowns and used as an internal consistency check (IAEA-C1 mean Δ47 = 0.308‰ vs. nominal Δ47 = 0.302‰, 1SD = 0.012‰; Merck mean Δ47 = 0.525‰ vs. nominal Δ47 = 0.514‰, 1SD = 0.016‰). Long-term external repeatability (1SD) of Δ 47 for all analyses (anchors and unknowns) after the data processing described above, including error introduced by the reference frame, is 0.029‰. Declarations Data availability All data generated from this study are included in the article and Supplementary Inventory. Acknowledgements Financial support at the Massachusetts Institute of Technology (MIT) was provided by an MIT Energy Initiative grant funded by Shell with additional support from the Simons Foundation Collaboration on the Origins of Life that provided instrumentation needed for this work. Funding support at Shanghai Jiao Tong University (SJTU) is provided by the SJTU startup grant (WH220544005) and the National Natural Science Foundation of China (42203030, 42273075). Author Contributions J.M. and R.E.S. designed the research; J.M., R.E.S., X.C. and H.L.A. performed the biomarker analysis; L.F.C. and K.S conducted Sr isotopic analysis; K.D.B., A.M.B.R., E.W.A., J.E.A., A.G.C. performed C, O, clumped isotopic and petrographic analyses. J.M. and R.E.S. wrote the draft, and all authors have contributions on revising the manuscript. Competing interests The authors declare no competing interests. References Larson RL, Ladd JW. Evidence for the opening of the South Atlantic in the Early Cretaceous. Nature 246 , 209-212 (1973). Dias-Brito D. Global stratigraphy, palaeobiogeography and palaeoecology of Albian–Maastrichtian pithonellid calcispheres: impact on Tethys configuration. Cretac Res 21 , 315-349 (2000). Le Pichon X, Fox PJ. Marginal offsets, fracture zones, and the early opening of the North Atlantic. J Geophys Res 76 , 6294-6308 (1971). Leandro C , et al. Astronomical tuning of the Aptian stage and its implications for age recalibrations and paleoclimatic events. Nature Communications 13 , 1-12 (2022). Santos A , et al. Earlier onset of the Early Cretaceous Equatorial humidity belt. Global and Planetary Change 208 , 103724 (2022). Chaboureau A-C, Guillocheau F, Robin C, Rohais S, Moulin M, Aslanian D. Paleogeographic evolution of the central segment of the South Atlantic during Early Cretaceous times: Paleotopographic and geodynamic implications. Tectonophysics 604 , 191-223 (2013). Bastos LPH , et al. Organic geochemical evidence for the transition of Aptian-Albian hypersaline environments into marine restricted seas: The South Atlantic oceanic northern gateway and its implications for the pre-salt deposits. Marine and Petroleum Geology 140 , 105632 (2022). Arai M. Aptian/Albian (Early Cretaceous) paleogeography of the South Atlantic: a paleontological perspective. Brazilian Journal of Geology 44 , 339-350 (2014). Cui X, Wignall B, Freeman KH, Summons RE. Early Cretaceous marine incursions into South Atlantic rift basins originated from the south. Communications Earth & Environment 4 , 6 (2023). Sanjines AES, Viviers MC, Costa DS, dos Anjos Zerfass GdS, Beurlen G, Strohschoen Jr O. Planktonic foraminifera from the Aptian section of the Southeastern Brazilian Atlantic margin. Cretac Res 134 , 105141 (2022). Bastos LPH, Pereira E, da Costa Cavalcante D, Alferes CLF, de Menezes CJ, Rodrigues R. Expression of Early Cretaceous global anoxic events in Northeastern Brazilian basins. Cretac Res 110 , 104390 (2020). Davison I. Geology and tectonics of the South Atlantic Brazilian salt basins. Geological Society, London, Special Publications 272 , 345-359 (2007). Araripe RC, Oliveira DH, Tome ME, de Mello RM, Barreto AM. Foraminifera and Ostracoda from the lower Cretaceous (Aptian–lower Albian) Romualdo formation, Araripe basin, northeast Brazil: Paleoenvironmental inferences. Cretac Res 122 , 104766 (2021). Michels FH, de Souza PA, Premaor E. Aptian-Albian palynologic assemblages interbedded within salt deposits in the Espírito Santo Basin, eastern Brazil: Biostratigraphical and paleoenvironmental analysis. Marine and Petroleum Geology 91 , 785-799 (2018). Melo RM, Guzmán J, Almeida-Lima D, Piovesan EK, Neumann VHdML. New marine data and age accuracy of the Romualdo Formation, Araripe Basin, Brazil. Scientific reports 10 , 1-15 (2020). Dingle R. Walvis Ridge barrier: its influence on palaeoenvironments and source rock generation deduced from ostracod distributions in the early South Atlantic Ocean. Geological Society, London, Special Publications 153 , 293-302 (1999). Heine C, Zoethout J, Müller RD. Kinematics of the South Atlantic rift. Solid Earth 4 , 215-253 (2013). Eagles G. New angles on South Atlantic opening. Geophysical Journal International 168 , 353-361 (2007). Moulin M, Aslanian D, Unternehr P. A new starting point for the South and Equatorial Atlantic Ocean. Earth-Science Reviews 98 , 1-37 (2010). Assine ML, Quaglio F, Warren LV, Simões MG. Comments on paper by M. Arai" Aptian/Albian (Early Cretaceous) paleogeography of the South Atlantic: a paleontological perspective". Brazilian Journal of Geology 46 , 03-07 (2016). Peters KE, Walters CC, Moldowan JM. The Biomarker Guide . Cambridge University Press (2005). Summons RE, Welander PV, Gold DA. Lipid biomarkers: molecular tools for illuminating the history of microbial life. Nature Reviews Microbiology 20 , 174-185 (2022). Roussel A, Cui X, Summons RE. Biomarker stratigraphy in the Athel Trough of the South Oman Salt Basin at the Ediacaran‐Cambrian Boundary. Geobiology 18 , 663-681 (2020). Moldowan JM. C 30 -steranes, novel markers for marine petroleums and sedimentary rocks. Geochimica et Cosmochimica Acta 48 , 2767-2768 (1984). Moldowan JM , et al. Sedimentary 12-n-propylcholestanes, molecular fossils diagnostic of marine algae. Science 247 , 309-312 (1990). McCaffrey MA , et al. Paleoenvironmental implications of novel C 30 steranes in Precambrian to Cenozoic age petroleum and bitumen. Geochimica et Cosmochimica Acta 58 , 529-532 (1994). Ma J, Wu C, Uveges BT, Ding W, Summons RE, Cui X. Biomarkers reveal Eocene marine incursions into the Qaidam Basin, north Tibetan Plateau. Organic Geochemistry , 104380 (2022). Xu H, George SC, Hou D. The occurrence of isorenieratane and 24-n-propylcholestanes in Paleogene lacustrine source rocks from the Dongying Depression, Bohai Bay Basin: Implications for bacterial sulfate reduction, photic zone euxinia and seawater incursions. Organic Geochemistry 127 , 59-80 (2019). Hu J , et al. Seawater incursion events in a Cretaceous paleo-lake revealed by specific marine biological markers. Scientific reports 5 , 1-6 (2015). Kohnen ME, Damsté JSS, Kock-van Dalen A, Jan WDL. Di-or polysulphide-bound biomarkers in sulphur-rich geomacromolecules as revealed by selective chemolysis. Geochimica et Cosmochimica acta 55 , 1375-1394 (1991). Richnow H, Jenisch A, Michaelis W. Structural investigations of sulphur-rich macromolecular oil fractions and a kerogen by sequential chemical degradation. Organic Geochemistry 19 , 351-370 (1992). Schouten S, Eglinton TI, Sinninghe Damsté JS, de Leeuw JW. Influence of sulphur cross-linking on the molecular-size distribution of sulphur-rich macromolecules in bitumen.). ACS Publications (1995). Hebting Y , et al. Biomarker evidence for a major preservation pathway of sedimentary organic carbon. Science 312 , 1627-1631 (2006). Adam P , et al. Structural investigation of nonpolar sulfur cross-linked macromolecules in petroleum. Geochimica et Cosmochimica Acta 57 , 3395-3419 (1993). Kohnen ME, Sinninghe Damste JS, De Leeuw JW. Biases from natural sulphurization in palaeoenvironmental reconstruction based on hydrocarbon biomarker distributions. Nature 349 , 775-778 (1991). Schaeffer P, Ocampo R, Callot H, Albrecht P. Extraction of bound porphyrins from sulphur-rich sediments and their use for reconstruction of palaeoenvironments. Nature 364 , 133-136 (1993). Lawson M , et al. New age and lake chemistry constraints on the Aptian pre-salt carbonates of the central South Atlantic. Bulletin 135 , 595-607 (2023). Pietzsch R , et al. Palaeohydrology of the Lower Cretaceous pre-salt lacustrine system, from rift to post-rift phase, Santos Basin, Brazil. Palaeogeography, Palaeoclimatology, Palaeoecology 507 , 60-80 (2018). Jones CE, Jenkyns HC. Seawater strontium isotopes, oceanic anoxic events, and seafloor hydrothermal activity in the Jurassic and Cretaceous. Am J Sci 301 , 112-149 (2001). Lima BEM, De Ros LF. Deposition, diagenetic and hydrothermal processes in the Aptian Pre-Salt lacustrine carbonate reservoirs of the northern Campos Basin, offshore Brazil. Sedimentary Geology 383 , 55-81 (2019). Wright VP, Barnett AJ. The textural evolution and ghost matrices of the Cretaceous Barra Velha Formation carbonates from the Santos Basin, offshore Brazil. Facies 66 , 7 (2020). Muniz M, Bosence D. Lacustrine carbonate platforms: facies, cycles, and tectonosedimentary models for the presalt Lagoa Feia Group (Lower Cretaceous), Campos Basin, Brazil. AAPG Bulletin 102 , 2569-2597 (2018). Caetano-Filho S, Dias-Brito D, Rodrigues R, de Azevedo RLM. Carbonate microfacies and chemostratigraphy of a late Aptian–early Albian marine distal section from the primitive South Atlantic (SE Brazilian continental margin): Record of global ocean-climate changes? Cretac Res 74 , 23-44 (2017). Giner JL, Zhao H, Boyer GL, Satchwell MF, Andersen RA. Sterol chemotaxonomy of marine pelagophyte algae. Chemistry and Biodiversity 6 , 1111-1130 (2009). Volkman J. Sterols in microorganisms. Appl Microbiol Biotechnol 60 , 495-506 (2003). Holba A , et al. Application of tetracyclic polyprenoids as indicators of input from fresh-brackish water environments. Organic Geochemistry 34 , 441-469 (2003). Pietzsch R, Tedeschi LR, Oliveira DM, dos Anjos CWD, Vazquez JC, Figueiredo MF. Environmental conditions of deposition of the Lower Cretaceous lacustrine carbonates of the Barra Velha Formation, Santos Basin (Brazil), based on stable carbon and oxygen isotopes: a continental record of pCO2 during the onset of the Oceanic Anoxic Event 1a (OAE 1a) interval? Chemical Geology 535 , 119457 (2020). Farias F, Szatmari P, Bahniuk A, França AB. Evaporitic carbonates in the pre salt of Santos Basin: Genesis and tectonic implications–A reply. Marine and Petroleum Geology 133 , 105201 (2021). Louback VS, de Castro Valente S, de Almeida CN, Ross J, Borghi L. Aptian flood basalts in Bacalhau oil and gas field: petrogenesis and geodynamics of post-rift tholeiites in the pre-salt sequence of Santos Basin, Brazil. Contrib Mineral Petrol 178 , 1-25 (2023). Bralower T, Fullagar P, Paull C, Dwyer G, Leckie R. Mid-Cretaceous strontium-isotope stratigraphy of deep-sea sections. Geological Society of America Bulletin 109 , 1421-1442 (1997). Bodin S, Meissner P, Janssen NM, Steuber T, Mutterlose J. Large igneous provinces and organic carbon burial: Controls on global temperature and continental weathering during the Early Cretaceous. Global and Planetary Change 133 , 238-253 (2015). Farias F, Szatmari P, Bahniuk A, Franca AB. Evaporitic carbonates in the pre-salt of Santos Basin–Genesis and tectonic implications. Marine and Petroleum Geology 105 , 251-272 (2019). Coolen MJ , et al. Evolution of the plankton paleome in the Black Sea from the Deglacial to Anthropocene. Proceedings of the National Academy of Sciences 110 , 8609-8614 (2013). Sinninghe Damsté JS, Kock-Van Dalen A, de Leeuw JW, Schenck P, Guoying S, Brassell SC. The identification of mono-, di-and trimethyl 2-methyl-2-(4,8,12-trimethyltridecyl) chromans and their occurrence in the geosphere. Geochimica et Cosmochimica Acta 51 , 2393-2400 (1987). Tulipani S , et al. Molecular proxies as indicators of freshwater incursion-driven salinity stratification. Chemical Geology 409 , 61-68 (2015). Sinninghe Damsté JK, Brendan J, Betts SE, Baas M, Maxwell JR, de Leeuw JW. Variations in abundances and distributions of isoprenoid chromans and long-chain alkylbenzenes in sediments of the Mulhouse Basin: a molecular sedimentary record of palaeosalinity. Organic Geochemistry 20 , 1201-1215 (1993). Harvey HR, Mcmanus GB. Marine ciliates as a widespread source of tetrahymanol and hopan-3β-ol in sediments. Geochimica et Cosmochimica Acta 55 , 3387-3390 (1991). Sinninghe Damsté JS , et al. Evidence for gammacerane as an indicator of water column stratification. Geochimica et Cosmochimica Acta 59 , 1895-1900 (1995). Didyk B, Simoneit B, Brassell St, Eglinton G. Organic geochemical indicators of palaeoenvironmental conditions of sedimentation. Nature 272 , 216-222 (1978). Grice K, Schouten S, Nissenbaum A, Charrach J, Damsté JSS. Isotopically heavy carbon in the C21 to C25 regular isoprenoids in halite-rich deposits from the Sdom Formation, Dead Sea Basin, Israel. Organic Geochemistry 28 , 349-359 (1998). Tulipani S, Grice K, Greenwood P, Schwark L. A pyrolysis and stable isotopic approach to investigate the origin of methyltrimethyltridecylchromans (MTTCs). Organic geochemistry 61 , 1-5 (2013). Sinninghe Damsté JS, Kok MD, Köster J, Schouten S. Sulfurized carbohydrates: an important sedimentary sink for organic carbon? Earth and Planetary Science Letters 164 , 7-13 (1998). Sinninghe Damsté J, Van Duin AC, Hollander D, Kohnen ME, De Leeuw JW. Early diagenesis of bacteriohopanepolyol derivatives: Formation of fossil homohopanoids. Geochimica et Cosmochimica Acta 59 , 5141-5157 (1995). Ma J, French KL, Cui X, Bryant DA, Summons RE. Carotenoid biomarkers in Namibian shelf sediments: Anoxygenic photosynthesis during sulfide eruptions in the Benguela Upwelling System. Proceedings of the National Academy of Sciences 118 , (2021). Sinninghe Damsté J, Koopmans M. The fate of carotenoids in sediments: an overview. Pure and Applied Chemistry 69 , 2067-2074 (1997). Schwark L, Empt P. Sterane biomarkers as indicators of Palaeozoic algal evolution and extinction events. Palaeogeography, Palaeoclimatology, Palaeoecology 240 , 225-236 (2006). Kirst G. Salinity tolerance of eukaryotic marine algae. Annu Rev Plant Biol 41 , 21-53 (1990). Imhoff JF. Taxonomy and physiology of phototrophic purple bacteria and green sulfur bacteria. In: Anoxygenic photosynthetic bacteria ). Springer (1995). Repeta D, Simpson D, Jorgensen B, Jannasch H. Evidence for anoxygenic photosynthesis from the distribution of bacterio-chlorophylls in the Black Sea. Nature 342 , 69-72 (1989). Cui X , et al. Niche expansion for phototrophic sulfur bacteria at the Proterozoic–Phanerozoic transition. Proceedings of the National Academy of Sciences 117 , 17599-17606 (2020). French K, Rocher D, Zumberge J, Summons R. Assessing the distribution of sedimentary C 40 carotenoids through time. Geobiology 13 , 139-151 (2015). Ma J, Cui X. Aromatic carotenoids: Biological sources and geological implications. Geosystems and Geoenvironment , 100045 (2022). Summons RE, Powell TG. Chlorobiaceae in Palaeozoic seas revealed by biological markers, isotopes and geology. Nature 319 , 763-765 (1986). Sinninghe Damsté JS, Schouten S, Van Duin AC. Isorenieratene derivatives in sediments: possible controls on their distribution. Geochimica et Cosmochimica Acta 65 , 1557-1571 (2001). Overmann J, Cypionka H, Pfennig N. An extremely low‐light adapted phototrophic sulfur bacterium from the Black Sea. Limnology and Oceanography 37 , 150-155 (1992). Vila X, Abella C. Effects of light quality on the physiology and the ecology of planktonic green sulfur bacteria in lakes. Photosynthesis research 41 , 53-65 (1994). Block KR, O'Brien JM, Edwards WJ, Marnocha CL. Vertical structure of the bacterial diversity in meromictic Fayetteville Green Lake. MicrobiologyOpen 10 , e1228 (2021). Peduzzi S, Tonolla M, Hahn D. Isolation and characterization of aggregate-forming sulfate-reducing and purple sulfur bacteria from the chemocline of meromictic Lake Cadagno, Switzerland. FEMS microbiology ecology 45 , 29-37 (2003). Wilbanks EG , et al. Microscale sulfur cycling in the phototrophic pink berry consortia of the S ippewissett S alt M arsh. Environmental microbiology 16 , 3398-3415 (2014). Graham JE, Bryant DA. The biosynthetic pathway for synechoxanthin, an aromatic carotenoid synthesized by the euryhaline, unicellular cyanobacterium Synechococcus sp. strain PCC 7002. Journal of bacteriology 190 , 7966-7974 (2008). Graham JE, Lecomte JT, Bryant DA. Synechoxanthin, an aromatic C40 xanthophyll that is a major carotenoid in the cyanobacterium Synechococcus sp. PCC 7002. Journal of natural products 71 , 1647-1650 (2008). Kim S-T, O’Neil JR, Hillaire-Marcel C, Mucci A. Oxygen isotope fractionation between synthetic aragonite and water: Influence of temperature and Mg2+ concentration. Geochimica et Cosmochimica Acta 71 , 4704-4715 (2007). Bernasconi SM , et al. InterCarb: A community effort to improve interlaboratory standardization of the carbonate clumped isotope thermometer using carbonate standards. Geochemistry, Geophysics, Geosystems 22 , e2020GC009588 (2021). Daëron M. Full propagation of analytical uncertainties in Δ47 measurements. Geochemistry, Geophysics, Geosystems 22 , e2020GC009592 (2021). Seifert WK, Moldowan JM. The effect of biodegradation on steranes and terpanes in crude oils. Geochimica et Cosmochimica Acta 43 , 111-126 (1979). Sandison CM, Alexander R, Kagi RI. The analysis of polar fractions from sediment extracts and crude oils using reaction-gas chromatography–mass spectrometry. Organic geochemistry 34 , 1373-1389 (2003). Additional Declarations There is NO Competing Interest. Supplementary Files FragataManuscriptSI.docx Cite Share Download PDF Status: Published Journal Publication published 26 Jan, 2025 Read the published version in Communications Earth & Environment → Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-4463807","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":307841294,"identity":"b8bf2811-2af4-4583-bb8c-5af264cf5b0d","order_by":0,"name":"Jian Ma","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA+UlEQVRIiWNgGAWjYHCChAMQmvkAgwREgGgtbAkMEgnEaYEBHgOoagJadNsPPDzwcweDXT97z+cPlj8OM/Cz5xgwAEVwArMzCQkHe88wJM/sObtNQiLhMINkzxsDRqAIbi0HEhIO8LYxJBvcyN3GANJicCPHgJmxDY+W8w8SDv4FarG/kfP4A0iLPUEtNxISDgNtsTOQyGEAOwzIIKTlQcJh2TaGBIkzx8wkJNLSeSTOPCs42IvXYTnJH9+2Mdjztzc//ixhYy3H35688cFPPFqA0ZEAJP4nNgBJZmDs84DEDuDTwMDADpa3BxGMH/ArHQWjYBSMghEKALHUVU16EBs+AAAAAElFTkSuQmCC","orcid":"https://orcid.org/0000-0001-8600-1749","institution":"Shanghai Jiao Tong University","correspondingAuthor":true,"prefix":"","firstName":"Jian","middleName":"","lastName":"Ma","suffix":""},{"id":307841295,"identity":"83b7bbc9-485c-4f03-b874-a0e454fc46d6","order_by":1,"name":"Leonardo Cury","email":"","orcid":"","institution":"","correspondingAuthor":false,"prefix":"","firstName":"Leonardo","middleName":"","lastName":"Cury","suffix":""},{"id":307841296,"identity":"ca8ff716-7d3a-4069-ad73-7b5dfe8e7555","order_by":2,"name":"Anelize Rumbelsperger","email":"","orcid":"","institution":"","correspondingAuthor":false,"prefix":"","firstName":"Anelize","middleName":"","lastName":"Rumbelsperger","suffix":""},{"id":307841297,"identity":"b42e49c2-d62a-4514-bf03-46bfc1d9b589","order_by":3,"name":"Heidi Albrecht","email":"","orcid":"","institution":"","correspondingAuthor":false,"prefix":"","firstName":"Heidi","middleName":"","lastName":"Albrecht","suffix":""},{"id":307841298,"identity":"070d475e-32d9-4677-97e9-2df8f15c2dd5","order_by":4,"name":"Erwin Adams","email":"","orcid":"","institution":"","correspondingAuthor":false,"prefix":"","firstName":"Erwin","middleName":"","lastName":"Adams","suffix":""},{"id":307841299,"identity":"70c376e4-d716-4f07-ae57-c71c366832d7","order_by":5,"name":"Joachim Amthor","email":"","orcid":"","institution":"","correspondingAuthor":false,"prefix":"","firstName":"Joachim","middleName":"","lastName":"Amthor","suffix":""},{"id":307841300,"identity":"26abb8f3-c3a0-4b8b-b979-04f2a9f4a233","order_by":6,"name":"Xingqian Cui","email":"","orcid":"https://orcid.org/0000-0001-6705-7595","institution":"Shanghai Jiao Tong University","correspondingAuthor":false,"prefix":"","firstName":"Xingqian","middleName":"","lastName":"Cui","suffix":""},{"id":307841301,"identity":"89a3ef6d-29a5-45d2-9bda-1e5ce9c5000c","order_by":7,"name":"Antoine Cremiere","email":"","orcid":"https://orcid.org/0000-0001-7382-2097","institution":"","correspondingAuthor":false,"prefix":"","firstName":"Antoine","middleName":"","lastName":"Cremiere","suffix":""},{"id":307841302,"identity":"a97c6c49-682a-4e9b-a573-125329f302c1","order_by":8,"name":"Kei Sato","email":"","orcid":"","institution":"","correspondingAuthor":false,"prefix":"","firstName":"Kei","middleName":"","lastName":"Sato","suffix":""},{"id":307841303,"identity":"f6e35bf0-33a3-4ebf-84cf-30ee4ec9af81","order_by":9,"name":"Kristin Bergmann","email":"","orcid":"https://orcid.org/0000-0002-6106-2059","institution":"Massachusetts Institute of Technology","correspondingAuthor":false,"prefix":"","firstName":"Kristin","middleName":"","lastName":"Bergmann","suffix":""},{"id":307841304,"identity":"e525f6cb-20db-41ba-a85e-1f09d413de48","order_by":10,"name":"Roger Summons","email":"","orcid":"https://orcid.org/0000-0002-7144-8537","institution":"Massachusetts Institute of Technology","correspondingAuthor":false,"prefix":"","firstName":"Roger","middleName":"","lastName":"Summons","suffix":""}],"badges":[],"createdAt":"2024-05-23 03:00:37","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-4463807/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-4463807/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1038/s43247-025-02029-2","type":"published","date":"2025-01-26T05:00:00+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":58148295,"identity":"eab37d2d-52cd-4a6b-a79a-dc4dd01d255d","added_by":"auto","created_at":"2024-06-11 18:56:56","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":545223,"visible":true,"origin":"","legend":"\u003cp\u003eThe location of Fragata drill core within the geological map of Campos (B), SE Brazil (A). Northwest to southeast with change in dip direction to north-northeast seismic section (blue lines in B) in depth illustrating the geologic context of the Fragata core (6-DEV-018-RJS) in the Campos Basin (C, D). Blue arrows indicate the base of the Macabu Formation; The orange arrow and dotted line show the base of the Retiro Fm. The Fragata core is located at the edge of the external high with seismic reflector terminations (white arrows) indicating erosion along an escarpment setting. Outboard parallel, continuous reflectors are observed indicating a ponded and deeper lake system. Two wells (SEAT and BP) located in the East Graben in the outboard comprise pre-salt ostracod biostratigraphic data and calibrate the stratigraphy to the Jiquiá and Alagoas zones or Coqueiros and Macabu Formations, respectively.\u003c/p\u003e","description":"","filename":"Fig.1.png","url":"https://assets-eu.researchsquare.com/files/rs-4463807/v1/e69bb89d97999067e49e5b62.png"},{"id":58147976,"identity":"18d4074e-94d8-428b-832d-2ecd1700fd6d","added_by":"auto","created_at":"2024-06-11 18:48:56","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":72701,"visible":true,"origin":"","legend":"\u003cp\u003eSterane comparisons in free (A) and desulfurized lipids (B) for sample FGT 217 (5020.48 m). The marine algal signal can be detected in both free and RN fractions of rock extracts in samples above 5025m (e.g., FGT 217). Here, the chromatograms at the top of the A and B stacks show \u003cem\u003em/z \u003c/em\u003e217 from full scan GC-MSD data. Chromatograms for individual sterane carbon numbers are from GC-QQQ data; scales in each chromatogram are normalized to the highest peaks (shown as 100%). Peaks of 24-npc (24-\u003cem\u003en\u003c/em\u003e-propylcholestane, green peaks) are highlighted with red dashed line, with the reproducible offset of retention time at ~0.1 mins compared to the peaks of 4-Me24Et (4α-methyl-24-ethylcholestane). 24-npc ratios (24-npc/4-Me24Et) are 20.1% and 73.0% in free-NP and RN-NP fractions, respectively. Additionally, unconventional configurations of C\u003csub\u003e27\u003c/sub\u003e-C\u003csub\u003e30\u003c/sub\u003e steranes, which are denoted as 5α,14α,17β(H) 20R (ααβ, blue peaks marked with \u003cstrong\u003e*\u003c/strong\u003e in the right panel) and 5α,14β,17α(H) 20R (αβα, blue peaks marked with \u003cstrong\u003ex\u003c/strong\u003e in the right panel) (Fig. S7), were identified in this study. They are mostly detected in RN-NP fractions of marine influenced samples in the Fragata core and are predominant among all steranes. The identification of ααβ and αβα steranes are based on mass spectra (Fig. S7) \u003csup\u003e85\u003c/sup\u003e and retention times \u003csup\u003e86\u003c/sup\u003e. Abbreviation: free-NP: free non-polar fractions; RN-NP: non-polar fractions by Raney Ni treatment on polar fractions.\u003c/p\u003e","description":"","filename":"Fig.2.png","url":"https://assets-eu.researchsquare.com/files/rs-4463807/v1/d697703a10e961a75d148cb6.png"},{"id":58147982,"identity":"ade57030-c3c4-46c0-9bfd-d10f6b64f3c6","added_by":"auto","created_at":"2024-06-11 18:48:56","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":60621,"visible":true,"origin":"","legend":"\u003cp\u003eSr isotope and biomarker profiles of the Fragata core spanning the Upper Macabu Formation through the Lower Retiro Formation from 5017.3 m to 5048.7 m. 24-npc = 24-\u003cem\u003en\u003c/em\u003e-propylcholesterane (24-npc) / 4-methylsterane; MTTCI = Methyl MTTC (Methyltrimethyltridecylchromans) / trimethyl MTTC; GI = gammacerane / C\u003csub\u003e30\u003c/sub\u003e αβ hopane; Pr / Ph = pristane/phytane; HHI = C\u003csub\u003e35\u003c/sub\u003e homohopanes / C\u003csub\u003e30\u003c/sub\u003e αβ hopane.\u003c/p\u003e","description":"","filename":"Fig.3.png","url":"https://assets-eu.researchsquare.com/files/rs-4463807/v1/4ad5ea5704ed88e9b22f4410.png"},{"id":58147977,"identity":"01621628-7550-4931-aae5-b956cf062cb1","added_by":"auto","created_at":"2024-06-11 18:48:56","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":37681,"visible":true,"origin":"","legend":"\u003cp\u003eBiomarker comparisons of free lipid (free-NP, free non-polar fractions) and desulfurized lipid fractions (RN-NP, non-polar fractions obtained by Raney Ni treatment of polar fractions). A and B: As shown in the sample FGT-217 (5020.48 m), there are distinctive abundances of PSB-specific and GSB-specific carotenoids (i.e., okenane and chlorobactane respectively) after the desulfurization treatment; C and D: All marine-influenced samples are characterized by anoxic (high HHI and low Pr/Ph) and eukaryote dominance indicated by a high S/H and with C\u003csub\u003e29\u003c/sub\u003e sterane predominance.\u003c/p\u003e","description":"","filename":"Fig.4.png","url":"https://assets-eu.researchsquare.com/files/rs-4463807/v1/068e95e2f4ea0e0d173a5cd5.png"},{"id":58148296,"identity":"fb2ff032-8c81-4ac3-9aae-9324d7cb4f78","added_by":"auto","created_at":"2024-06-11 18:56:56","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":44904,"visible":true,"origin":"","legend":"\u003cp\u003eExpanded geochemical profile for the top of the Fragata core, recording the ecosystem reorganization upon ingress of seawater at \u0026lt;116 Ma. These changes coincide with the appearance of anhydrite in the sediment column. Both free and sulfurized biomarkers are self-consistent, especially for the detection of 24-npc, indicative of indigenous signals. 24-npc = 24-npc/4-methylsterane; S/H = C\u003csub\u003e27\u003c/sub\u003e-C\u003csub\u003e29\u003c/sub\u003e steranes/C\u003csub\u003e27\u003c/sub\u003e-C\u003csub\u003e35\u003c/sub\u003e hopanes; Steranes = C\u003csub\u003e27\u003c/sub\u003e or C\u003csub\u003e29\u003c/sub\u003e steranes/C\u003csub\u003e27\u003c/sub\u003e-\u003csub\u003e29\u003c/sub\u003e steranes; C\u003csub\u003e35\u003c/sub\u003e HHI = C\u003csub\u003e35\u003c/sub\u003e homohopanes/C\u003csub\u003e30\u003c/sub\u003e αβ hopane; GI = gammacerane/C\u003csub\u003e30\u003c/sub\u003e αβ hopane; MTTC = Methyl MTTC (Methyltrimethyltridecylchromans)/trimethyl MTTC. Biomarker data from samples below 5038.58 m (n=25) are summarized in the form of box and whisker plots.\u003c/p\u003e","description":"","filename":"Fig.5.png","url":"https://assets-eu.researchsquare.com/files/rs-4463807/v1/3e3f53917ec9dc6ac6965997.png"},{"id":58147983,"identity":"af32508c-5736-45f3-9598-d1340c24bf0d","added_by":"auto","created_at":"2024-06-11 18:48:56","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":40358,"visible":true,"origin":"","legend":"\u003cp\u003eEvolving carotenoid distributions following the onset of the marine transgression captured by the upper Macabu–Lower Retiro Formations within the Fragata core. Here, horizontal shaded bars illustrate the changes in the community of phototrophic bacteria following the intrusion of sulfate-bearing marine waters. Changes in the dominant carotenoids illustrate a clear progression from okenane (oke), through chlorobactane (chl) and subsequently to isorenieratane (iso) that reveals a shift from purple sulfur bacteria (PSB) at the initial seawater ingress, through green- and then brown-pigmented green sulfur bacteria (GSB). Red and blue datapoints identify trends in free and sulfurized lipids, respectively. The box and whisker plots summarized the carotenoid data from below 5038.58 m (n=25) (Figure 2; Table 1).\u003c/p\u003e","description":"","filename":"Fig.6.png","url":"https://assets-eu.researchsquare.com/files/rs-4463807/v1/8b95e0988df3525449973d8b.png"},{"id":74765925,"identity":"4e19081c-c923-4530-9264-985b67264bf0","added_by":"auto","created_at":"2025-01-26 08:09:19","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1781243,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-4463807/v1/decf4104-95d0-4382-873b-8cd660af9bfb.pdf"},{"id":58147979,"identity":"731f9736-f830-4870-954c-b2264d71a78a","added_by":"auto","created_at":"2024-06-11 18:48:56","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":2326559,"visible":true,"origin":"","legend":"","description":"","filename":"FragataManuscriptSI.docx","url":"https://assets-eu.researchsquare.com/files/rs-4463807/v1/4b1f26af784b1e082c2c09ce.docx"}],"financialInterests":"There is \u003cb\u003eNO\u003c/b\u003e Competing Interest.","formattedTitle":"Ecosystem transformation upon Aptian seawater ingress into the Proto-South Atlantic Ocean","fulltext":[{"header":"Introduction","content":"\u003cp\u003eThe early Cretaceous breakup of the western Gondwana Supercontinent marks the birth of the South Atlantic Ocean (SAO) and instigated a range of other impacts on the Earth system \u003csup\u003e\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e, \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e, \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e, \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e, \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e\u003c/sup\u003e. Specifically, the Aptian\u0026ndash;Albian stage is a critical interval in terms of the development of a new oceanic gateway and the initiation of the central SAO between the rifting South America and Africa plates \u003csup\u003e\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e, \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e, \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e, \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e\u003c/sup\u003e. As a consequence, seawater ingress along with marine organisms transformed the pre-existing saline lacustrine ecosystems \u003csup\u003e\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e\u003c/sup\u003e. The widespread Aptian\u0026ndash;Albian sea/seaways in the plate interiors led to the development of restricted and hypersaline environments \u003csup\u003e\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e\u003c/sup\u003e and ubiquitous thick deposits of salt with organic-rich layers along the Brazilian-African conjugate margins \u003csup\u003e\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e, \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e\u003c/sup\u003e. Concomitantly, the Aptian\u0026ndash;Albian transgression was sufficiently extensive to produce the propagation of marine biotas \u003csup\u003e\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e, \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e, \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e\u003c/sup\u003e. In turn, sedimentary and fossil records in the conjugate margins of Brazil and West Africa provide fundamental constraints for paleogeographic reconstruction. Despite numerous reports of marine incursions, however, there are divergent views on the source and pathways taken by the first marine transgression into these intracratonic basins, hindering our understanding of paleogeographic and ecosystem reconstruction. On the Brazil side, it is postulated that a long-distance Aptian\u0026ndash;Albian transgression, originated from the equatorial Atlantic Tethyan Ocean, spreading southwards \u003csup\u003e\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e\u003c/sup\u003e, while tectonic evolution analyses support northward Aptian\u0026ndash;Albian marine ingressions from the austral SAO \u003csup\u003e\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e, \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e, \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e, \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e\u003c/sup\u003e. Pathways of marine ingressions are further complicated by conflicting results based on paleocurrent data and marine biota comparisons between NE and SE Brazilian basins \u003csup\u003e\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e, \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e\u003c/sup\u003e. The conundrum persists, as the paucity of transitional sedimentary sequences that represent marine transgressive deposits over the continental interior hinder the interpretation of ecosystem impacts.\u003c/p\u003e \u003cp\u003eDiscriminating between non-marine and marine-influenced settings, especially in the absence of body fossils, is heavily reliant on sedimentology and geochemistry. Even so, much of the available toolkit is unable to unequivocally discriminate between marine and saline lacustrine deposition. Conversely, fossil lipids\u0026mdash;biomarkers\u0026mdash;represent geologically stable molecules derived from the diagenetic modification of microbially-derived precursors thereby fingerprinting parent organisms and, by extension, the depositional environment they once inhabited \u003csup\u003e\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e, \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e, \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e\u003c/sup\u003e. Of particular significance here, 24-\u003cem\u003en\u003c/em\u003e-propylcholestane (24-npc) is a steroidal lipid derived from the diagenetic transformation of 24-\u003cem\u003en\u003c/em\u003e-propylcholesterol\u0026mdash;the major sterol constituent of modern marine pelagophyte algae \u003csup\u003e\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e\u003c/sup\u003e. Given that contemporary pelagophyte algae are exclusively marine organisms, and the ubiquity of 24-npc in marine-derived organic matter \u003csup\u003e\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e, \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e\u003c/sup\u003e, 24-npc is widely applied as a diagnostic indicator of marine-influenced sedimentation \u003csup\u003e\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e, \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e, \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e\u003c/sup\u003e. Hitherto, most biomarker-based paleoenvironmental interpretations have focused on \u0026lsquo;free\u0026rsquo; lipids from organic extracts of rocks. On the other hand, chemolysis studies have demonstrated that organic molecules with multiple unsaturations (double bonds) and/or particular functional groups are prone to rapidly react with reduced inorganic sulfur species (e.g., H\u003csub\u003e2\u003c/sub\u003eS) under anoxic and sulfidic conditions to become incorporated via S-S and S-C crosslinking into the polar or macromolecular fractions of sedimentary organic matter \u003csup\u003e\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e, \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e\u003c/sup\u003e. Thereby, organic sulfurization can lead to selective sequestration of specific biomarker precursors affording investigation of diverse complex species that are not readily amenable to conventional lipid analysis \u003csup\u003e\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e, \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e, \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e\u003c/sup\u003e and resolve biases in paleoenvironmental reconstruction \u003csup\u003e\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e, \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e\u003c/sup\u003e. Given widespread anoxic environments in Aptian\u0026ndash;Albian strata of Brazilian marginal basins \u003csup\u003e\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e, \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e\u003c/sup\u003e, both free and sulfurized lipids of organic extracts need to be evaluated before a complete biomarker picture can be visualized.\u003c/p\u003e \u003cp\u003eIn an independent yet complementary approach, the radiogenic Sr isotopic composition (\u003csup\u003e87\u003c/sup\u003eSr/\u003csup\u003e86\u003c/sup\u003eSr) of sediments is sensitive to the weathering inputs into a basin. In a lacustrine environment, the \u003csup\u003e87\u003c/sup\u003eSr/\u003csup\u003e86\u003c/sup\u003eSr isotopic composition is set by the radiogenic \u003csup\u003e87\u003c/sup\u003eSr/\u003csup\u003e86\u003c/sup\u003eSr isotopic of the specific combination of bedrock within upstream catchments. In the case of the Brazilian lacustrine systems, it has been postulated that extremely radiogenic Precambrian cratonic bedrock on both the South American and African margins determined the \u003csup\u003e87\u003c/sup\u003eSr/\u003csup\u003e86\u003c/sup\u003eSr isotopic composition of the lacustrine rift system \u003csup\u003e\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e, \u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e\u003c/sup\u003e. In contrast the \u003csup\u003e87\u003c/sup\u003eSr/\u003csup\u003e86\u003c/sup\u003eSr isotopic composition of marine waters is well mixed and yields a coherent marine \u003csup\u003e87\u003c/sup\u003eSr/\u003csup\u003e86\u003c/sup\u003eSr isotope curve through time \u003csup\u003e\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e\u003c/sup\u003e. Reconstructing the \u003csup\u003e87\u003c/sup\u003eSr/\u003csup\u003e86\u003c/sup\u003eSr isotopic composition of South Atlantic sediments can, therefore, yield an independent record of marine transgression into the lacustrine system.\u003c/p\u003e \u003cp\u003eHerein, we report free and sulfurized lipid biomarkers and Sr isotope analyses, along with carbon, oxygen, and clumped isotopes and sedimentological descriptions of a core retrieved from the SE Brazilian Campos Basin that reveal the initial Aptian marine ingress therein and associated ecosystem perturbation. The succession cored by the Fragata borehole, located in the northwest of the basinal depocenter (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e), encompasses lacustrine carbonates of the upper Macabu Fm. and interbedded anhydrite, halite within carbonate sequences of the Retiro Fm., thus providing a sedimentological record and opportunity to explore preserved organic matter associated with the event. Our findings address the knowledge gap about the impact of the marine transgression in the western conjugate margin by documenting its environmental consequences and ecosystem responses.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e"},{"header":"Results and discussion","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e3.1 Seawater ingress into the Campos Basin\u003c/h2\u003e \u003cp\u003eThe Macabu Fm. in the Campos Basin is dominated by carbonate successions, which developed in an alkaline lacustrine setting under an arid climate \u003csup\u003e\u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e, \u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e, \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e\u003c/sup\u003e. The overlying Albian aged Macaé Group in the Campos Basin clearly records sedimentation in a marine environment, as evidenced by foraminiferal biozonation and carbonate microfacies \u003csup\u003e\u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e43\u003c/span\u003e\u003c/sup\u003e. Contrastingly, the Retiro Fm. is typified by evaporites, which represents the transitional phase between successions in the Macabu Formation and the Albian-aged Macaé Group, and may record the initial marine incursions in the Campos Basin.\u003c/p\u003e \u003cp\u003eBoth carbonate clumped isotope (Δ47) values and the stereochemical configurations of biomarkers have reveal a moderate thermal history of the study area (SI). A wide array of lipid biomarkers, including \u003cem\u003en\u003c/em\u003e-alkanes, acyclic isoprenoids, terpanes, steranes, hopanes and carotenoids, were present in both free and desulfurized fractions (Fig. S5) from the Fragata core samples (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). Of particular significance among the sterane biomarkers is the detection of 24-\u003cem\u003en\u003c/em\u003e-propylcholestane (24-npc) in both free non-polar (free-NP) and a second set of non-polar fractions generated by Raney Ni desulfurization (RN-NP) (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). As a geological derivative of 24-\u003cem\u003en\u003c/em\u003e-propylidenecholesterol \u003csup\u003e\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e, \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e\u003c/sup\u003e, 24-npc is the major sterane diagnostic for marine chrysophyte/pelagophyte algae \u003csup\u003e\u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e, \u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e45\u003c/span\u003e\u003c/sup\u003e. Accordingly, 24-npc is ubiquitously detected in marine environments and has been widely adopted as a diagnostic marker of marine or marine-influenced strata in the geological record \u003csup\u003e\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e, \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e, \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e, \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e, \u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e46\u003c/span\u003e\u003c/sup\u003e. However, the detection of 24-npc may be confounded when in low relative abundance due to an interference signal from 4α-methyl-24-ethylcholestane (4α-methylstigmastane, 4-Me24Et) \u003csup\u003e\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e\u003c/sup\u003e that partially co-elutes on most GC liquid phases. Strict criteria are followed for the rigorous identification of 24-npc in the Fragata samples and include the relative signal intensities and the small but reproducible retention time difference between 24-npc and 4α-methyl-24-ethylcholestane \u003csup\u003e\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e\u003c/sup\u003e. Ratios of 24-npc and 4-Me24Et (denoted as 24-npc ratio) are elevated in samples shallower than 5024.3 m in the Fragata core (26.7% ± 8.8%, 1σ, Table S2). This allows positive identification of 24-npc, since the 24-npc/4-Me24Et ratios in seawater-influenced settings are expected to exceed 10% \u003csup\u003e21, \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e\u003c/sup\u003e. Additionally, a reproducible offset of ~ 0.1 mins in the chromatographic peaks in the 414 → 217 and 414 → 231 Da transitions on GC-QQQ-MS (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e) further verified the marine signature of 24-npc at the top of the Fragata core. Significantly, 24-npc peaks are also recognized in the desulfurized RN-NP fractions (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e) with elevated signal intensities. Above 5024.3 m the 24-npc ratios rise to 73.0% (51.8% on average, Table S2). Accordingly, the occurrence of 24-npc in both free and sulfurized fractions, restricted to the entire interval above 5024.3 m in Fragata core, and upwards from the first appearance of anhydrite at the base of the Retiro Fm. indicates that marine waters had intruded into Campos Basin during the late Aptian (\u0026lt; 116 Ma).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eNotable variations of \u003csup\u003e87\u003c/sup\u003eSr/\u003csup\u003e86\u003c/sup\u003eSr were captured in the interval above 5024.3 m in the Fragata core (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e). The findings delineate distinct groups characterized by ratios falling within the ranges of 0.712–0.714 and 0.709–0.710. The initial interval, previously identified in several studies \u003csup\u003e\u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e, \u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e47\u003c/span\u003e, \u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e48\u003c/span\u003e\u003c/sup\u003e, is attributed to distinctly continental sources, serving as a significant geochemical indicator supporting the interpretation of the carbonate succession as having a lacustrine origin in the Campos and Santos basins. Despite the limited understanding of the paleo-tectonic context, the notable variability in the strontium isotope signal indicates a depositional system influenced by a range of sources, including continental cratonic rocks and contemporaneous basaltic volcanism as potential contributors \u003csup\u003e\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e, \u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e49\u003c/span\u003e\u003c/sup\u003e. The second interval, however, exhibits notably reduced radiogenic Sr values, predominantly around 0.709, indicating a distinct decrease in radiogenic sources entering the basin. Influx of marine waters would be reasonable, given that the anticipated average \u003csup\u003e87\u003c/sup\u003eSr/\u003csup\u003e86\u003c/sup\u003eSr ratio for seawater during the Aptian period is approximately 0.707 \u003csup\u003e50\u003c/sup\u003e, with a projected rise in radiogenic Sr attributed to the evolution of the Paraná-Etendeka Large Igneous Province, as posited elsewhere \u003csup\u003e\u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e51\u003c/span\u003e\u003c/sup\u003e. A mix between internally-drained solutes and marine influx would produce a hybrid brine with a new \u003csup\u003e87\u003c/sup\u003eSr/\u003csup\u003e86\u003c/sup\u003eSr ratio under hydrological equilibrium. Considering fluctuations in water levels within a shallow environment, with a water/Sr mass balance sensitive to source variations, it may be possible to explain the variation in radiogenic strontium within the Macabu Formation due to changes in sources that are influenced by tectonic activity. The excursions of \u003csup\u003e87\u003c/sup\u003eSr/\u003csup\u003e86\u003c/sup\u003eSr ratio are indicative of sources related to mafic volcanic rocks and/or marine incursions. While other strontium excursions are observed in the lower intervals of the pre-salt carbonates\u003csup\u003e\u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e47\u003c/span\u003e, \u003cspan citationid=\"CR52\" class=\"CitationRef\"\u003e52\u003c/span\u003e\u003c/sup\u003e, a significant shift at the top of the succession, near the contact with the Retiro Formation, suggests this point as the onset of predominant marine influx.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003ePaleontological evidence has implied that seawater infiltrated from the NE Brazilian marginal basins, including the Sao Luís, Parnaíba and Araripe basins during the transition of Aptian–Albian; Furthermore, a Tethyan ingression is suggested by the presence of several fossil taxa \u003csup\u003e\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e, \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e, \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e, \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e\u003c/sup\u003e. However, there is a lack of unequivocal marine evidence in the SE Brazilian marginal basins (e.g., Campos and Santos Basins). Accordingly, a series of southward marine transgressions from the equatorial Tethys Ocean was hypothesized \u003csup\u003e\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e, \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e\u003c/sup\u003e divergent from the tectonic evidence of a marine pathway extending from south to north on the basis of sea-floor spreading patterns and geodynamic reconstructions \u003csup\u003e\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e, \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e, \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e, \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e\u003c/sup\u003e, recently acquired geochronological data \u003csup\u003e\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e, \u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e49\u003c/span\u003e\u003c/sup\u003e and from evidence gathered from the conjugate margins of West Africa \u003csup\u003e\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e3.2 A switch to a marine-influenced ecosystem\u003c/h2\u003e \u003cp\u003eNumerous examples have illustrated how seawater entry into lacustrine ecosystems alters their hydrography, water chemistry and biology. Ingressions can result from subtle changes in relative sea level on glacial-interglacial timescales (e.g. \u003csup\u003e\u003cspan citationid=\"CR53\" class=\"CitationRef\"\u003e53\u003c/span\u003e\u003c/sup\u003e) or from tectonism on geological timescales \u003csup\u003e\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e, \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e, \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e, \u003cspan citationid=\"CR53\" class=\"CitationRef\"\u003e53\u003c/span\u003e\u003c/sup\u003e. The salinity and depth of a water body, together with basin shape, will influence the tendency towards density stratification. Relative abundances of methyltrimethyltridecylchromans (MTTCs) isomers (e.g., methylated MTTCs) have been proposed to be a reliable indicator for paleosalinity in aquatic surface-layers \u003csup\u003e\u003cspan citationid=\"CR54\" class=\"CitationRef\"\u003e54\u003c/span\u003e, \u003cspan citationid=\"CR55\" class=\"CitationRef\"\u003e55\u003c/span\u003e\u003c/sup\u003e, especially recording the periodic incursions of marine waters and subsequent evaporation \u003csup\u003e\u003cspan citationid=\"CR56\" class=\"CitationRef\"\u003e56\u003c/span\u003e\u003c/sup\u003e. Here, the Fragata core records enhanced MTTCs ratios (0.02 vs. 0.16 on average, with the highest value to 0.42, Table S2, Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e), pointing to a rapid elevation in salinity above 5025.12 m. Subsequently, the elevated abundance of gammacerane (denoted by the gammacerane index, GI) is additionally indicative of enhanced water column stratification, given that its precursor, tetrahymanol, is a signal for bacterivorous ciliates living at redox transitions \u003csup\u003e\u003cspan citationid=\"CR57\" class=\"CitationRef\"\u003e57\u003c/span\u003e, \u003cspan citationid=\"CR58\" class=\"CitationRef\"\u003e58\u003c/span\u003e\u003c/sup\u003e. Stratification reduces mixing and thus promotes oxygen-depletion in deeper waters, as evidenced by concomitant reduction in the pristane/phytane (Pr/Ph) ratio and enhancement of C\u003csub\u003e35\u003c/sub\u003e Homohopane Index (C\u003csub\u003e35\u003c/sub\u003e HHI) at the top of the section (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e). Pr/Ph is regarded as a redox-sensitive proxy due to the preferential formation of phytane over pristane derived from the phytol side-chains of chlorophylls under anoxic conditions \u003csup\u003e\u003cspan citationid=\"CR59\" class=\"CitationRef\"\u003e59\u003c/span\u003e\u003c/sup\u003e. Although additional factors including salinity, organic matter sources, and diagenetic process may affect Pr/Ph \u003csup\u003e\u003cspan citationid=\"CR60\" class=\"CitationRef\"\u003e60\u003c/span\u003e, \u003cspan citationid=\"CR61\" class=\"CitationRef\"\u003e61\u003c/span\u003e\u003c/sup\u003e values below 1 are considered diagnostic for pervasive anoxia. Similarly, the C\u003csub\u003e35\u003c/sub\u003e HHI is a robust proxy for tracing anoxic conditions \u003csup\u003e\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e\u003c/sup\u003e, considering that the C5 side-chains of its precursor compounds, C\u003csub\u003e35\u003c/sub\u003e bacteriohopanepolyols, are best preserved under the anoxic and H\u003csub\u003e2\u003c/sub\u003eS-rich conditions that follow from enhancement of sulfate levels from seawater incursions \u003csup\u003e\u003cspan citationid=\"CR62\" class=\"CitationRef\"\u003e62\u003c/span\u003e, \u003cspan citationid=\"CR63\" class=\"CitationRef\"\u003e63\u003c/span\u003e\u003c/sup\u003e. Together, the evolution of multiple biomarker proxies documents a hydrographically dynamic system, capturing the establishment of enhanced anoxic/euxinic, saline and stratified conditions in the Retiro Formation.\u003c/p\u003e \u003cp\u003eGiven the enhancement of anoxia induced by the marine incursion, reductive sulfurization of organic matter under euxinic conditions \u003csup\u003e\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e\u003c/sup\u003e becomes an issue that may complicate or inhibit the identification of some biological precursor lipids \u003csup\u003e\u003cspan citationid=\"CR64\" class=\"CitationRef\"\u003e64\u003c/span\u003e\u003c/sup\u003e. In fact, here, the patterns of \u003cem\u003en\u003c/em\u003e-alkanes, and of sterane and hopane stereoisomers released by the RN treatment (Fig. S5–S6), illustrate how specific biomarkers have been sequestered into the S-bound macromolecular component of sedimentary organic matter. High abundances of phytane and C\u003csub\u003e35\u003c/sub\u003e homohopanes released during desulfurization (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e-D) further confirm their preferential preservation under anoxic and sulfidic conditions \u003csup\u003e\u003cspan citationid=\"CR59\" class=\"CitationRef\"\u003e59\u003c/span\u003e, \u003cspan citationid=\"CR63\" class=\"CitationRef\"\u003e63\u003c/span\u003e\u003c/sup\u003e. Despite striking differences in the patterns of the free-NP and RN-NP fractions, however, the key biomarker proxies all move in a consistent direction concomitant with the marine incursion. Both free and sulfurized lipids also reveal a dynamic system: Here, the ingress of seawater strengthened stratification within this sector of the Campos Basin, fostering the development of water column anoxia, as evidenced by elevated values of GI, C\u003csub\u003e35\u003c/sub\u003e HHI and MTTC (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e). Accordingly, hydrographic changes induced by seawater ingress have prompted ecosystem re-structuring as recorded in its biochemostratigraphy. A striking and progressive elevation in sterane/hopane ratios (S/H) (up to 10.6, Table S2), a proxy based on the diagenetic products of sterols and hopanoids diagnostic for eukaryotes and bacteria respectively \u003csup\u003e\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e, \u003cspan citationid=\"CR65\" class=\"CitationRef\"\u003e65\u003c/span\u003e\u003c/sup\u003e, suggests this environmental shift appears to have favored photosynthetic algae, allowing their proliferation at the expense of bacteria. Consistent with transgressive records in other basins \u003csup\u003e\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e, \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e\u003c/sup\u003e, the elevated S/H document the ingress of seawater providing algae with an advantage over the bacterial community whether by addition of nutrients or other factors associated with the water chemistry. Among all steroid derivatives, stigmastane (C\u003csub\u003e29\u003c/sub\u003e sterane) becomes dominant over cholestane, its C\u003csub\u003e27\u003c/sub\u003e counterpart, after the marine incursion (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e-C; Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e). Given their mostly biological source from Chlorophyceae and Rhodophyceae, respectively \u003csup\u003e\u003cspan citationid=\"CR66\" class=\"CitationRef\"\u003e66\u003c/span\u003e, \u003cspan citationid=\"CR67\" class=\"CitationRef\"\u003e67\u003c/span\u003e\u003c/sup\u003e, the enhanced stigmastane represents the likely prevalence of green algae over other taxa in the immediate aftermath of the transition.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003e3.3 A progressive deepening of the chemocline with marine ingress\u003c/h2\u003e \u003cp\u003eDespite the detection of the array of carotenoids in the free biomarker fractions (Table S2), diverse inventories of aliphatic and aromatic carotenoids are released upon desulfurization of the polar fractions (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e-A, B). In the free-NP fractions, the predominant compounds in all samples are β-carotane and isorenieratane, together with minor β-isorenieratane and C\u003csub\u003e38\u003c/sub\u003e carotenoids. However, in the RN-NP fractions, relatively high abundances of isorenieratane, chlorobactane and okenane that have been sequestered into macromolecules by sulfurization supports the notion that they represent indigenous signals for phototrophic sulfur bacteria. As strict anaerobes, these phototrophic sulfur bacteria, comprising green sulfur bacteria (i.e., GSB, \u003cem\u003eChlorobiaceae\u003c/em\u003e) and purple sulfur bacteria (i.e. PSB, \u003cem\u003eChromatiaceae\u003c/em\u003e), utilize sulfide and other reduced sulfur species as electron donors for photosynthesis \u003csup\u003e\u003cspan citationid=\"CR68\" class=\"CitationRef\"\u003e68\u003c/span\u003e\u003c/sup\u003e. Because of their dual requirements for illumination and sulfide, the GSB and PSB are considered index species for photic zone euxinia (PZE) where the light penetrates a sulfide-containing water column \u003csup\u003e\u003cspan citationid=\"CR69\" class=\"CitationRef\"\u003e69\u003c/span\u003e\u003c/sup\u003e. Thus, their biomarker lipids have been applied as PZE biosignatures in both modern environments and in paleoenvironmental reconstruction \u003csup\u003e\u003cspan citationid=\"CR64\" class=\"CitationRef\"\u003e64\u003c/span\u003e, \u003cspan citationid=\"CR65\" class=\"CitationRef\"\u003e65\u003c/span\u003e, \u003cspan citationid=\"CR70\" class=\"CitationRef\"\u003e70\u003c/span\u003e, \u003cspan citationid=\"CR71\" class=\"CitationRef\"\u003e71\u003c/span\u003e, \u003cspan citationid=\"CR72\" class=\"CitationRef\"\u003e72\u003c/span\u003e, \u003cspan citationid=\"CR73\" class=\"CitationRef\"\u003e73\u003c/span\u003e\u003c/sup\u003e. Being the most widely recorded aromatic carotenoid in marine sediments \u003csup\u003e\u003cspan citationid=\"CR71\" class=\"CitationRef\"\u003e71\u003c/span\u003e, \u003cspan citationid=\"CR74\" class=\"CitationRef\"\u003e74\u003c/span\u003e\u003c/sup\u003e, isorenieratane is the diagenetic product of isorenieratene that is derived from low-light-adapted brown strains of phototrophic green sulfur bacteria (GSB). These GSB are known to be well adapted to lower light intensities and therefore deeper waters (~ 100 m) \u003csup\u003e\u003cspan citationid=\"CR69\" class=\"CitationRef\"\u003e69\u003c/span\u003e, \u003cspan citationid=\"CR75\" class=\"CitationRef\"\u003e75\u003c/span\u003e\u003c/sup\u003e. In comparison, green-colored strains that produce chlorobactene, the biological precursor of chlorobactane, require higher light intensity and accordingly are concentrated at shallower (∼15–30 m) chemocline depths \u003csup\u003e\u003cspan citationid=\"CR76\" class=\"CitationRef\"\u003e76\u003c/span\u003e\u003c/sup\u003e. In contrast, the okenone-synthesizing PSB can proliferate as plankton within a shallow chemocline (~ 20 m; \u003csup\u003e\u003cspan citationid=\"CR77\" class=\"CitationRef\"\u003e77\u003c/span\u003e\u003c/sup\u003e), in benthic microbial mats, as aggregates with sulfate reducing bacteria in the water column \u003csup\u003e\u003cspan citationid=\"CR78\" class=\"CitationRef\"\u003e78\u003c/span\u003e\u003c/sup\u003e or, perhaps reflecting their slightly higher tolerance for oxygen, as observed in the ‘pink berry consortia’ that are found in tidally-influenced marginal marine environments \u003csup\u003e\u003cspan citationid=\"CR79\" class=\"CitationRef\"\u003e79\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eIn the present study, by comparing the sedimentary lipids of the free and S-bound fractions, we observe a novel switch in the assemblages of aromatic carotenoids upon initial marine ingress into the Campos Basin. At the base of the anhydrite-bearing layer that marks the onset of the incursion, a peak in PSB-derived okenane (up to 33.0%, Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e, Table S2) implies extremely shallow PZE or microbial mat facies. Okenane then declines coincident with a peak in the abundance of GSB-derived chlorobactane (3.8%) and elevated isorenieratane. After this, isorenieratane becomes the dominant aromatic carotenoid identifying the brown-pigmented GSB as the predominant anoxygenic phototroph and a deepening chemocline. In addition, the composition of C\u003csub\u003e38\u003c/sub\u003e aromatic carotenoids decrease markedly (6.4% vs. 18.2%, p \u0026lt; 0.001, Table S2). These C\u003csub\u003e38\u003c/sub\u003e aromatic carotenoids are the diagenetic products of synechoxanthin which is a C\u003csub\u003e40\u003c/sub\u003e aromatic carotenoid with dual carboxylic acid functionalities prevalent in non-marine or euryhaline cyanobacteria \u003csup\u003e\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e, \u003cspan citationid=\"CR70\" class=\"CitationRef\"\u003e70\u003c/span\u003e, \u003cspan citationid=\"CR80\" class=\"CitationRef\"\u003e80\u003c/span\u003e, \u003cspan citationid=\"CR81\" class=\"CitationRef\"\u003e81\u003c/span\u003e\u003c/sup\u003e. Thus, reductive sulfurization and decarboxylation affords the C\u003csub\u003e38\u003c/sub\u003e diagenetic products together with C\u003csub\u003e39\u003c/sub\u003e counterparts diagnostic for cyanobacteria that are prevalent while lacustrine conditions prevail. Their decline coincides with the increases in phototrophic sulfur bacteria that accompany the ingress of seawater. In other words, the marine incursions instigated an overturn of the photosynthetic community, including a proliferation of eukaryotic algae together with GSB concomitant with a decline in primary productivity by the synechoxanthin-producing cyanobacteria. In summary, both the less radiogenic \u003csup\u003e87\u003c/sup\u003eSr/\u003csup\u003e86\u003c/sup\u003eSr ratio and 24-npc biomarker results indicate marine incursion associated with the deposition of the Retiro Formation, associated with a fundamental transformation in the biological community.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e"},{"header":"Materials and Methods","content":"\u003cp\u003e \u003cb\u003ePetrology inspection and organic extraction.\u003c/b\u003e In total 40 core samples of carbonates and mudstones, with a 2–4 m resolution of depths, were selected from the Fragata core in the Campos Basin (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e-A, B) covering a depth range of 5026.320 m to 5148.695 m (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e-D, red dots). Core slabs and core plugs were prepared for sedimentology and organic–inorganic geochemistry analyses. Specifically, petrographic microscopic observations were carried out under plane-polarized, crossed-polarized and cathodoluminescence (CL) illumination on polished thin-sections. Several aliquots of bulk-rock powders were prepared for mineral (X-ray diffraction, XRD), isotopic and organic geochemistry analyses. To mitigate possible inorganic or organic contamination, the outer parts of core plugs were removed using a diamond blade saw. The inner parts, after gentle polishing, were then placed in a combusted jar and sonicated repeatedly with DI water for 15 seconds to remove the trace slurry on the fresh surfaces. Upon drying within a low-temperature oven (40°C) they were ground in a puckmill. This was cleaned between samples to remove any potential cross-contaminating organic residues by first grinding an aliquot of combusted sand and then rinsing with DI water, MeOH and DCM (3X).\u003c/p\u003e\u003cp\u003eFor each biomarker sample, approximately 2 g powdered sample was weighed and extracted (4X for 25 mins at 100°C) with dichloromethane (DCM): methanol (MeOH) (9:1;v:v) in a MARS 6 Microwave Digestion System at the Massachusetts Institute of Technology. The extracts were transferred into combusted 60 ml glass tubes using combusted pipettes, combined, and concentrated at room temperature under a gentle stream of N\u003csub\u003e2\u003c/sub\u003e on the TurboVap followed by transfer into combusted 4 ml vials with DCM rinsing and sonication. Elemental sulfur was removed by reaction with activated copper shot. The resultant extracts were dried to ~ 100µl and fractionated using a silica gel column. Solvent mixtures of hexane: DCM (4:1; v:v) and DCM: MeOH (4:1;v:v) were used to elute the non-polar (free-NP) and polar fractions, sequentially.\u003c/p\u003e\u003cp\u003e \u003cb\u003eRaney nickel desulfurization.\u003c/b\u003e For desulfurization reactions, ‘T-1’ Raney-Nickel (RN) catalyst was prepared. Specifically, 40 g non-activated nickel aluminum alloy (1:1) was reacted with 600 ml of 10% sodium hydroxide for 1 hour at the temperature of 95°C under a gentle N\u003csub\u003e2\u003c/sub\u003e stream. Subsequently, the aqueous component was decanted and the residue washed with Milli-Q water (3X), and then activated by distilled absolute ethanol (3X). Natural ignition of dry Raney-Ni slurry verified the efficiency of prepared catalyst prior to use. Meanwhile, a procedure blank and an oil standard were subject to the procedure in each set of RN reactions. For desulfurization reactions, ~ 7 mg of the polar fraction of a TLE was dissolved in 20 ml distilled absolute ethanol together with 3 ml ‘T-1’ RN slurry and the mixture heated to 80°C under N\u003csub\u003e2\u003c/sub\u003e reflux for 2 h. The products were extracted into DCM with sonication (4X). After subsequent centrifugation and drying, aliquots of RN-treated new extracts were subjected to further silica gel column chromatography to obtain a second pair of NP (RN-NP) and polar fractions. RN reactivity and an absence of contamination were verified the recovery yields from an oil standard and the purity of blanks.\u003c/p\u003e\u003cp\u003e \u003cb\u003eLipid biomarker analysis.\u003c/b\u003e Both free-NP and RN-NP fractions were subjected to GC-MS analysis using a 7890B Agilent gas chromatograph coupled to a 5975C Agilent MSD and a 7010A Agilent triple quadrupole MS (GC-QQQ-MS) operated in full scan or multiple reaction monitoring (MRM) modes, respectively. All the GC’s were equipped with a multi-mode injector at an initial injection temperature of 45°C which was ramped at a rate of 720°/min to 340°C. A DB-5MS column (60 m×250 µm×0.25 µm) was installed with each GC with an oven temperature held isothermally at 40° for 2 mins, ramped to 320°C at a rate of 4°/min, and then held at this temperature for 22 mins. The transfer lines and source temperatures in GC-MS and GC-QQQ-MS were set to 320°C and 250°C, respectively. The electron energy of GC-QQQ-MS was 70 eV to ensure a standard signal for the precursor-product transitions. All biomarker data are processed using MassHunter software. In GC-QQQ-MS, each compound was identified and integrated under MRM mode within a narrow retention time window (0.5 mins).\u003c/p\u003e\u003cp\u003e \u003cb\u003ein situ\u003c/b\u003e \u003csup\u003e\u003cb\u003e87\u003c/b\u003e\u003c/sup\u003e\u003cb\u003eSr/\u003c/b\u003e\u003csup\u003e\u003cb\u003e86\u003c/b\u003e\u003c/sup\u003e\u003cb\u003eSr analysis.\u003c/b\u003e The \u003csup\u003e87\u003c/sup\u003eSr/\u003csup\u003e86\u003c/sup\u003eSr results were obtained by the LA-ICP-MS method at the University of Paraná, Brazil, with analytical resolution for the characterization of different phases, resolving micro structures varying between 2 µm and 150 µm. Results were obtained with excimer ArF laser ablation Analyte Excite CETAC Teledyne, generating beams with wavelength of 193 nm, which is sufficient energy to sample different carbonate microfacies. The ablation was carried out in raster mode, with sampling lines using laser beams with spot dimensions of 40µm, in a path length of 700 µm, scanning speed of 10 µm/s, frequency of 7 Hz, and energy of 6.26 J/cm². The analyzes were carried out on ~ 1 mm fragments extracted from drill core plugs, which were previously analyzed by back-scattered electron (BSE) imaging using scanning electron microscopy analysis. The BSE images made it possible to accurately identify variations in composition such as silica replacement, clay minerals, fractures, and other relevant constituents for selecting the sampling area. Reproducibility was tested with three counter-tests per sample. Furthermore, samples from sample populations with end-member \u003csup\u003e87\u003c/sup\u003eSr/\u003csup\u003e86\u003c/sup\u003eSr results were selected using the \u003cem\u003ein-situ\u003c/em\u003e method, for further analysis and confirmation by ID-TIMS. The measurements were carried out in a multi collector ICP-MS Thermo Fischer Neptune Plus, monitoring the species \u003csup\u003e\u003cspan citationid=\"CR83\" class=\"CitationRef\"\u003e83\u003c/span\u003e\u003c/sup\u003eKr (L4 amplifier 10ˆ11), \u003csup\u003e167\u003c/sup\u003eEr\u003csup\u003e+2\u003c/sup\u003e (L3 amplifier 10ˆ13), \u003csup\u003e\u003cspan citationid=\"CR84\" class=\"CitationRef\"\u003e84\u003c/span\u003e\u003c/sup\u003eSr (L2 amplifier 10ˆ11), \u003csup\u003e\u003cspan citationid=\"CR85\" class=\"CitationRef\"\u003e85\u003c/span\u003e\u003c/sup\u003eRb (L1 amplifier 10ˆ11), \u003csup\u003e\u003cspan citationid=\"CR86\" class=\"CitationRef\"\u003e86\u003c/span\u003e\u003c/sup\u003eSr (H1 amplifier 10ˆ11), \u003csup\u003e173\u003c/sup\u003eYb\u003csup\u003e2+\u003c/sup\u003e (H2 amplifier 10ˆ13), \u003csup\u003e87\u003c/sup\u003eSr (H3 amplifier 10ˆ11) and \u003csup\u003e88\u003c/sup\u003eSr (H4 amplifier 10ˆ11). As a reference standard, the coral JCp-1 was analyzed, which has an accepted \u003csup\u003e87\u003c/sup\u003eSr/\u003csup\u003e86\u003c/sup\u003eSr ratio in the literature of 0.709160 ± 0.000020. The coral JCp-1 yielded a variable intensity of \u003csup\u003e88\u003c/sup\u003eSr, the most abundant isotope, between 15 and 20V measured with a 10ˆ11 amplifier, equivalent to an estimated a Sr concentration from 7000 ppm to 2000 ppm, reflecting the heterogeneous distribution of strontium as it is a natural standard.\u003c/p\u003e\u003cp\u003e \u003cb\u003eδ\u003c/b\u003e \u003csup\u003e \u003cb\u003e \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e \u003c/b\u003e \u003c/sup\u003e \u003cb\u003eC, δ\u003c/b\u003e \u003csup\u003e \u003cb\u003e \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e \u003c/b\u003e \u003c/sup\u003e \u003cb\u003eO and clumped isotope (Δ\u003c/b\u003e \u003csub\u003e \u003cb\u003e47\u003c/b\u003e \u003c/sub\u003e \u003cb\u003e) analysis of carbonate.\u003c/b\u003e Stable isotopic measurements of δ\u003csup\u003e\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e\u003c/sup\u003eC, δ\u003csup\u003e\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e\u003c/sup\u003eO, and carbonate clumped isotope (Δ\u003csub\u003e47\u003c/sub\u003e) analyses were completed to contextualize the biomarker and \u003csup\u003e87\u003c/sup\u003eSr/\u003csup\u003e86\u003c/sup\u003eSr results. Sample δ\u003csup\u003e\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e\u003c/sup\u003eC, δ\u003csup\u003e\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e\u003c/sup\u003eO, and Δ\u003csub\u003e47\u003c/sub\u003e were measured from January 2020 to June 2021 at the MIT Carbonate Research Laboratory on a Nu Perspective dual-inlet isotope ratio mass spectrometer with a Nu Carb automated sample preparation unit held at 70°C. Calcite samples weighing ~ 400–600 µg were reacted for 25 minutes in individual glass vials with 150 µl orthophosphoric acid (ρ = 1.94 g/cm\u003csup\u003e3\u003c/sup\u003e). Evolved CO\u003csub\u003e2\u003c/sub\u003e gas was purified cryogenically and by passive passage through a Porapak trap (1/4\" ID; 0.4 g 50/80 mesh Porapak Q) held at − 30°C. The initial voltage was 8–20 V on the m/z 44 beam with 2x10\u003csup\u003e8\u003c/sup\u003e Ω resistors and depleted by approximately 50% over the course of an analysis (60 cycles with 20-minute total integration time). Sample and standard CO\u003csub\u003e2\u003c/sub\u003e gases depleted at equivalent rates from microvolumes over the analysis time. Mass spectrometry methods were nearly identical to those reported in Anderson et al. (2021). ETH-1–4 and IAEA-C2 were used as anchors; IAEA-C1 and Merck were treated as unknowns. Unknown anchor ratio was 1:1 for each 50 run. The reference side of the dual-inlet was refilled with reference gas after every 10 analyses. In total, unknowns were measured 1–4 times over the study interval (76 total unknown analyses; 118 InterCarb standards). Raw mass spectrometer data were first processed by removing cycles (i.e., single integration cycles of mass spectrometer measurement) with raw Δ\u003csub\u003e47\u003c/sub\u003e values more than 5 \"long-term\" standard deviations (0.50‰; the mean of the respective cycle-level SD for ETH-1–4 over a 3-month period was 0.10‰) away from the median Δ\u003csub\u003e47\u003c/sub\u003e measurement for the analysis. Analyses were removed if more than 10 cycles (out of 60 total cycles) fell outside the 5 long-term SD threshold. Analyses with transducer pressure below 15 mbar, typically corresponding to sample collection issues, incomplete digestion, or low carbonate content, and analyses that ran misbalanced by \u0026gt; 1% were also removed. No pressure baseline correction was applied. After removal of cycle-level outliers, data were processed using the 'D47crunch' Python package using IUPAC \u003csup\u003e\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e\u003c/sup\u003eO parameters \u003csup\u003e\u003cspan citationid=\"CR82\" class=\"CitationRef\"\u003e82\u003c/span\u003e\u003c/sup\u003e, and projected to the I-CDES with values for ETH-1–4 and IAEA-C2 anchors from the InterCarb project \u003csup\u003e\u003cspan citationid=\"CR83\" class=\"CitationRef\"\u003e83\u003c/span\u003e, \u003cspan citationid=\"CR84\" class=\"CitationRef\"\u003e84\u003c/span\u003e\u003c/sup\u003e. Raw Δ\u003csub\u003e47\u003c/sub\u003e measurements were converted to the I-CDES using a pooled-regression approach that accounts for the relative mapping of all samples in δ\u003csup\u003e\u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e47\u003c/span\u003e\u003c/sup\u003e-Δ\u003csub\u003e47\u003c/sub\u003e space \u003csup\u003e\u003cspan citationid=\"CR84\" class=\"CitationRef\"\u003e84\u003c/span\u003e\u003c/sup\u003e. Analytical uncertainty and error associated with the creation of the reference frame were fully propagated through the dataset. A full description of the data reduction procedure used in D47crunch is detailed in \u003csup\u003e\u003cspan citationid=\"CR84\" class=\"CitationRef\"\u003e84\u003c/span\u003e\u003c/sup\u003e. Each sample carousel (typically 50 analyses) was treated as a single analytical session. IAEA-C1 and Merck standards were treated as unknowns and used as an internal consistency check (IAEA-C1 mean Δ47 = 0.308‰ vs. nominal Δ47 = 0.302‰, 1SD = 0.012‰; Merck mean Δ47 = 0.525‰ vs. nominal Δ47 = 0.514‰, 1SD = 0.016‰). Long-term external repeatability (1SD) of Δ\u003csub\u003e47\u003c/sub\u003e for all analyses (anchors and unknowns) after the data processing described above, including error introduced by the reference frame, is 0.029‰.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003eData availability\u003c/p\u003e\n\u003cp\u003eAll data generated from this study are included in the article and Supplementary Inventory.\u003c/p\u003e\n\u003cp\u003eAcknowledgements\u003c/p\u003e\n\u003cp\u003eFinancial support at the Massachusetts Institute of Technology (MIT) was provided by an MIT Energy Initiative grant funded by Shell with additional support from the Simons Foundation Collaboration on the Origins of Life that provided instrumentation needed for this work. Funding support at Shanghai Jiao Tong University (SJTU) is provided by the SJTU startup grant (WH220544005) and the National Natural Science Foundation of China (42203030, 42273075).\u003c/p\u003e\n\u003cp\u003eAuthor Contributions\u003c/p\u003e\n\u003cp\u003eJ.M. and R.E.S. designed the research; J.M., R.E.S., X.C. and H.L.A. performed the biomarker analysis; L.F.C. and K.S conducted Sr isotopic analysis; K.D.B., A.M.B.R., E.W.A., J.E.A., A.G.C. performed C, O, clumped isotopic and petrographic analyses. J.M. and R.E.S. wrote the draft, and all authors have contributions on revising the manuscript.\u003c/p\u003e\n\u003cp\u003eCompeting interests\u003c/p\u003e\n\u003cp\u003eThe authors declare no competing interests.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n \u003cli\u003eLarson RL, Ladd JW. Evidence for the opening of the South Atlantic in the Early Cretaceous. \u003cem\u003eNature\u003c/em\u003e \u003cstrong\u003e246\u003c/strong\u003e, 209-212 (1973).\u003c/li\u003e\n \u003cli\u003eDias-Brito D. Global stratigraphy, palaeobiogeography and palaeoecology of Albian\u0026ndash;Maastrichtian pithonellid calcispheres: impact on Tethys configuration. \u003cem\u003eCretac Res\u003c/em\u003e \u003cstrong\u003e21\u003c/strong\u003e, 315-349 (2000).\u003c/li\u003e\n \u003cli\u003eLe Pichon X, Fox PJ. Marginal offsets, fracture zones, and the early opening of the North Atlantic. \u003cem\u003eJ Geophys Res\u003c/em\u003e \u003cstrong\u003e76\u003c/strong\u003e, 6294-6308 (1971).\u003c/li\u003e\n \u003cli\u003eLeandro C\u003cem\u003e, et al.\u003c/em\u003e Astronomical tuning of the Aptian stage and its implications for age recalibrations and paleoclimatic events. \u003cem\u003eNature Communications\u003c/em\u003e \u003cstrong\u003e13\u003c/strong\u003e, 1-12 (2022).\u003c/li\u003e\n \u003cli\u003eSantos A\u003cem\u003e, et al.\u003c/em\u003e Earlier onset of the Early Cretaceous Equatorial humidity belt. \u003cem\u003eGlobal and Planetary Change\u003c/em\u003e \u003cstrong\u003e208\u003c/strong\u003e, 103724 (2022).\u003c/li\u003e\n \u003cli\u003eChaboureau A-C, Guillocheau F, Robin C, Rohais S, Moulin M, Aslanian D. Paleogeographic evolution of the central segment of the South Atlantic during Early Cretaceous times: Paleotopographic and geodynamic implications. \u003cem\u003eTectonophysics\u003c/em\u003e \u003cstrong\u003e604\u003c/strong\u003e, 191-223 (2013).\u003c/li\u003e\n \u003cli\u003eBastos LPH\u003cem\u003e, et al.\u003c/em\u003e Organic geochemical evidence for the transition of Aptian-Albian hypersaline environments into marine restricted seas: The South Atlantic oceanic northern gateway and its implications for the pre-salt deposits. \u003cem\u003eMarine and Petroleum Geology\u003c/em\u003e \u003cstrong\u003e140\u003c/strong\u003e, 105632 (2022).\u003c/li\u003e\n \u003cli\u003eArai M. Aptian/Albian (Early Cretaceous) paleogeography of the South Atlantic: a paleontological perspective. \u003cem\u003eBrazilian Journal of Geology\u003c/em\u003e \u003cstrong\u003e44\u003c/strong\u003e, 339-350 (2014).\u003c/li\u003e\n \u003cli\u003eCui X, Wignall B, Freeman KH, Summons RE. Early Cretaceous marine incursions into South Atlantic rift basins originated from the south. \u003cem\u003eCommunications Earth \u0026amp; Environment\u003c/em\u003e \u003cstrong\u003e4\u003c/strong\u003e, 6 (2023).\u003c/li\u003e\n \u003cli\u003eSanjines AES, Viviers MC, Costa DS, dos Anjos Zerfass GdS, Beurlen G, Strohschoen Jr O. Planktonic foraminifera from the Aptian section of the Southeastern Brazilian Atlantic margin. \u003cem\u003eCretac Res\u003c/em\u003e \u003cstrong\u003e134\u003c/strong\u003e, 105141 (2022).\u003c/li\u003e\n \u003cli\u003eBastos LPH, Pereira E, da Costa Cavalcante D, Alferes CLF, de Menezes CJ, Rodrigues R. Expression of Early Cretaceous global anoxic events in Northeastern Brazilian basins. \u003cem\u003eCretac Res\u003c/em\u003e \u003cstrong\u003e110\u003c/strong\u003e, 104390 (2020).\u003c/li\u003e\n \u003cli\u003eDavison I. Geology and tectonics of the South Atlantic Brazilian salt basins. \u003cem\u003eGeological Society, London, Special Publications\u003c/em\u003e \u003cstrong\u003e272\u003c/strong\u003e, 345-359 (2007).\u003c/li\u003e\n \u003cli\u003eAraripe RC, Oliveira DH, Tome ME, de Mello RM, Barreto AM. Foraminifera and Ostracoda from the lower Cretaceous (Aptian\u0026ndash;lower Albian) Romualdo formation, Araripe basin, northeast Brazil: Paleoenvironmental inferences. \u003cem\u003eCretac Res\u003c/em\u003e \u003cstrong\u003e122\u003c/strong\u003e, 104766 (2021).\u003c/li\u003e\n \u003cli\u003eMichels FH, de Souza PA, Premaor E. Aptian-Albian palynologic assemblages interbedded within salt deposits in the Esp\u0026iacute;rito Santo Basin, eastern Brazil: Biostratigraphical and paleoenvironmental analysis. \u003cem\u003eMarine and Petroleum Geology\u003c/em\u003e \u003cstrong\u003e91\u003c/strong\u003e, 785-799 (2018).\u003c/li\u003e\n \u003cli\u003eMelo RM, Guzm\u0026aacute;n J, Almeida-Lima D, Piovesan EK, Neumann VHdML. New marine data and age accuracy of the Romualdo Formation, Araripe Basin, Brazil. \u003cem\u003eScientific reports\u003c/em\u003e \u003cstrong\u003e10\u003c/strong\u003e, 1-15 (2020).\u003c/li\u003e\n \u003cli\u003eDingle R. Walvis Ridge barrier: its influence on palaeoenvironments and source rock generation deduced from ostracod distributions in the early South Atlantic Ocean. \u003cem\u003eGeological Society, London, Special Publications\u003c/em\u003e \u003cstrong\u003e153\u003c/strong\u003e, 293-302 (1999).\u003c/li\u003e\n \u003cli\u003eHeine C, Zoethout J, M\u0026uuml;ller RD. Kinematics of the South Atlantic rift. \u003cem\u003eSolid Earth\u003c/em\u003e \u003cstrong\u003e4\u003c/strong\u003e, 215-253 (2013).\u003c/li\u003e\n \u003cli\u003eEagles G. New angles on South Atlantic opening. \u003cem\u003eGeophysical Journal International\u003c/em\u003e \u003cstrong\u003e168\u003c/strong\u003e, 353-361 (2007).\u003c/li\u003e\n \u003cli\u003eMoulin M, Aslanian D, Unternehr P. A new starting point for the South and Equatorial Atlantic Ocean. \u003cem\u003eEarth-Science Reviews\u003c/em\u003e \u003cstrong\u003e98\u003c/strong\u003e, 1-37 (2010).\u003c/li\u003e\n \u003cli\u003eAssine ML, Quaglio F, Warren LV, Sim\u0026otilde;es MG. Comments on paper by M. Arai\u0026quot; Aptian/Albian (Early Cretaceous) paleogeography of the South Atlantic: a paleontological perspective\u0026quot;. \u003cem\u003eBrazilian Journal of Geology\u003c/em\u003e \u003cstrong\u003e46\u003c/strong\u003e, 03-07 (2016).\u003c/li\u003e\n \u003cli\u003ePeters KE, Walters CC, Moldowan JM. \u003cem\u003eThe Biomarker Guide\u003c/em\u003e. Cambridge University Press (2005).\u003c/li\u003e\n \u003cli\u003eSummons RE, Welander PV, Gold DA. Lipid biomarkers: molecular tools for illuminating the history of microbial life. \u003cem\u003eNature Reviews Microbiology\u003c/em\u003e \u003cstrong\u003e20\u003c/strong\u003e, 174-185 (2022).\u003c/li\u003e\n \u003cli\u003eRoussel A, Cui X, Summons RE. Biomarker stratigraphy in the Athel Trough of the South Oman Salt Basin at the Ediacaran‐Cambrian Boundary. \u003cem\u003eGeobiology\u003c/em\u003e \u003cstrong\u003e18\u003c/strong\u003e, 663-681 (2020).\u003c/li\u003e\n \u003cli\u003eMoldowan JM. C\u003csub\u003e30\u003c/sub\u003e-steranes, novel markers for marine petroleums and sedimentary rocks. \u003cem\u003eGeochimica et Cosmochimica Acta\u003c/em\u003e \u003cstrong\u003e48\u003c/strong\u003e, 2767-2768 (1984).\u003c/li\u003e\n \u003cli\u003eMoldowan JM\u003cem\u003e, et al.\u003c/em\u003e Sedimentary 12-n-propylcholestanes, molecular fossils diagnostic of marine algae. \u003cem\u003eScience\u003c/em\u003e \u003cstrong\u003e247\u003c/strong\u003e, 309-312 (1990).\u003c/li\u003e\n \u003cli\u003eMcCaffrey MA\u003cem\u003e, et al.\u003c/em\u003e Paleoenvironmental implications of novel C\u003csub\u003e30\u003c/sub\u003e steranes in Precambrian to Cenozoic age petroleum and bitumen. \u003cem\u003eGeochimica et Cosmochimica Acta\u003c/em\u003e \u003cstrong\u003e58\u003c/strong\u003e, 529-532 (1994).\u003c/li\u003e\n \u003cli\u003eMa J, Wu C, Uveges BT, Ding W, Summons RE, Cui X. Biomarkers reveal Eocene marine incursions into the Qaidam Basin, north Tibetan Plateau. \u003cem\u003eOrganic Geochemistry\u003c/em\u003e, 104380 (2022).\u003c/li\u003e\n \u003cli\u003eXu H, George SC, Hou D. The occurrence of isorenieratane and 24-n-propylcholestanes in Paleogene lacustrine source rocks from the Dongying Depression, Bohai Bay Basin: Implications for bacterial sulfate reduction, photic zone euxinia and seawater incursions. \u003cem\u003eOrganic Geochemistry\u003c/em\u003e \u003cstrong\u003e127\u003c/strong\u003e, 59-80 (2019).\u003c/li\u003e\n \u003cli\u003eHu J\u003cem\u003e, et al.\u003c/em\u003e Seawater incursion events in a Cretaceous paleo-lake revealed by specific marine biological markers. \u003cem\u003eScientific reports\u003c/em\u003e \u003cstrong\u003e5\u003c/strong\u003e, 1-6 (2015).\u003c/li\u003e\n \u003cli\u003eKohnen ME, Damst\u0026eacute; JSS, Kock-van Dalen A, Jan WDL. Di-or polysulphide-bound biomarkers in sulphur-rich geomacromolecules as revealed by selective chemolysis. \u003cem\u003eGeochimica et Cosmochimica acta\u003c/em\u003e \u003cstrong\u003e55\u003c/strong\u003e, 1375-1394 (1991).\u003c/li\u003e\n \u003cli\u003eRichnow H, Jenisch A, Michaelis W. Structural investigations of sulphur-rich macromolecular oil fractions and a kerogen by sequential chemical degradation. \u003cem\u003eOrganic Geochemistry\u003c/em\u003e \u003cstrong\u003e19\u003c/strong\u003e, 351-370 (1992).\u003c/li\u003e\n \u003cli\u003eSchouten S, Eglinton TI, Sinninghe Damst\u0026eacute; JS, de Leeuw JW. Influence of sulphur cross-linking on the molecular-size distribution of sulphur-rich macromolecules in bitumen.). ACS Publications (1995).\u003c/li\u003e\n \u003cli\u003eHebting Y\u003cem\u003e, et al.\u003c/em\u003e Biomarker evidence for a major preservation pathway of sedimentary organic carbon. \u003cem\u003eScience\u003c/em\u003e \u003cstrong\u003e312\u003c/strong\u003e, 1627-1631 (2006).\u003c/li\u003e\n \u003cli\u003eAdam P\u003cem\u003e, et al.\u003c/em\u003e Structural investigation of nonpolar sulfur cross-linked macromolecules in petroleum. \u003cem\u003eGeochimica et Cosmochimica Acta\u003c/em\u003e \u003cstrong\u003e57\u003c/strong\u003e, 3395-3419 (1993).\u003c/li\u003e\n \u003cli\u003eKohnen ME, Sinninghe Damste JS, De Leeuw JW. Biases from natural sulphurization in palaeoenvironmental reconstruction based on hydrocarbon biomarker distributions. \u003cem\u003eNature\u003c/em\u003e \u003cstrong\u003e349\u003c/strong\u003e, 775-778 (1991).\u003c/li\u003e\n \u003cli\u003eSchaeffer P, Ocampo R, Callot H, Albrecht P. Extraction of bound porphyrins from sulphur-rich sediments and their use for reconstruction of palaeoenvironments. \u003cem\u003eNature\u003c/em\u003e \u003cstrong\u003e364\u003c/strong\u003e, 133-136 (1993).\u003c/li\u003e\n \u003cli\u003eLawson M\u003cem\u003e, et al.\u003c/em\u003e New age and lake chemistry constraints on the Aptian pre-salt carbonates of the central South Atlantic. \u003cem\u003eBulletin\u003c/em\u003e \u003cstrong\u003e135\u003c/strong\u003e, 595-607 (2023).\u003c/li\u003e\n \u003cli\u003ePietzsch R\u003cem\u003e, et al.\u003c/em\u003e Palaeohydrology of the Lower Cretaceous pre-salt lacustrine system, from rift to post-rift phase, Santos Basin, Brazil. \u003cem\u003ePalaeogeography, Palaeoclimatology, Palaeoecology\u003c/em\u003e \u003cstrong\u003e507\u003c/strong\u003e, 60-80 (2018).\u003c/li\u003e\n \u003cli\u003eJones CE, Jenkyns HC. Seawater strontium isotopes, oceanic anoxic events, and seafloor hydrothermal activity in the Jurassic and Cretaceous. \u003cem\u003eAm J Sci\u003c/em\u003e \u003cstrong\u003e301\u003c/strong\u003e, 112-149 (2001).\u003c/li\u003e\n \u003cli\u003eLima BEM, De Ros LF. Deposition, diagenetic and hydrothermal processes in the Aptian Pre-Salt lacustrine carbonate reservoirs of the northern Campos Basin, offshore Brazil. \u003cem\u003eSedimentary Geology\u003c/em\u003e \u003cstrong\u003e383\u003c/strong\u003e, 55-81 (2019).\u003c/li\u003e\n \u003cli\u003eWright VP, Barnett AJ. The textural evolution and ghost matrices of the Cretaceous Barra Velha Formation carbonates from the Santos Basin, offshore Brazil. \u003cem\u003eFacies\u003c/em\u003e \u003cstrong\u003e66\u003c/strong\u003e, 7 (2020).\u003c/li\u003e\n \u003cli\u003eMuniz M, Bosence D. Lacustrine carbonate platforms: facies, cycles, and tectonosedimentary models for the presalt Lagoa Feia Group (Lower Cretaceous), Campos Basin, Brazil. \u003cem\u003eAAPG Bulletin\u003c/em\u003e \u003cstrong\u003e102\u003c/strong\u003e, 2569-2597 (2018).\u003c/li\u003e\n \u003cli\u003eCaetano-Filho S, Dias-Brito D, Rodrigues R, de Azevedo RLM. Carbonate microfacies and chemostratigraphy of a late Aptian\u0026ndash;early Albian marine distal section from the primitive South Atlantic (SE Brazilian continental margin): Record of global ocean-climate changes? \u003cem\u003eCretac Res\u003c/em\u003e \u003cstrong\u003e74\u003c/strong\u003e, 23-44 (2017).\u003c/li\u003e\n \u003cli\u003eGiner JL, Zhao H, Boyer GL, Satchwell MF, Andersen RA. Sterol chemotaxonomy of marine pelagophyte algae. \u003cem\u003eChemistry and Biodiversity\u003c/em\u003e \u003cstrong\u003e6\u003c/strong\u003e, 1111-1130 (2009).\u003c/li\u003e\n \u003cli\u003eVolkman J. Sterols in microorganisms. \u003cem\u003eAppl Microbiol Biotechnol\u003c/em\u003e \u003cstrong\u003e60\u003c/strong\u003e, 495-506 (2003).\u003c/li\u003e\n \u003cli\u003eHolba A\u003cem\u003e, et al.\u003c/em\u003e Application of tetracyclic polyprenoids as indicators of input from fresh-brackish water environments. \u003cem\u003eOrganic Geochemistry\u003c/em\u003e \u003cstrong\u003e34\u003c/strong\u003e, 441-469 (2003).\u003c/li\u003e\n \u003cli\u003ePietzsch R, Tedeschi LR, Oliveira DM, dos Anjos CWD, Vazquez JC, Figueiredo MF. Environmental conditions of deposition of the Lower Cretaceous lacustrine carbonates of the Barra Velha Formation, Santos Basin (Brazil), based on stable carbon and oxygen isotopes: a continental record of pCO2 during the onset of the Oceanic Anoxic Event 1a (OAE 1a) interval? \u003cem\u003eChemical Geology\u003c/em\u003e \u003cstrong\u003e535\u003c/strong\u003e, 119457 (2020).\u003c/li\u003e\n \u003cli\u003eFarias F, Szatmari P, Bahniuk A, Fran\u0026ccedil;a AB. Evaporitic carbonates in the pre salt of Santos Basin: Genesis and tectonic implications\u0026ndash;A reply. \u003cem\u003eMarine and Petroleum Geology\u003c/em\u003e \u003cstrong\u003e133\u003c/strong\u003e, 105201 (2021).\u003c/li\u003e\n \u003cli\u003eLouback VS, de Castro Valente S, de Almeida CN, Ross J, Borghi L. Aptian flood basalts in Bacalhau oil and gas field: petrogenesis and geodynamics of post-rift tholeiites in the pre-salt sequence of Santos Basin, Brazil. \u003cem\u003eContrib Mineral Petrol\u003c/em\u003e \u003cstrong\u003e178\u003c/strong\u003e, 1-25 (2023).\u003c/li\u003e\n \u003cli\u003eBralower T, Fullagar P, Paull C, Dwyer G, Leckie R. Mid-Cretaceous strontium-isotope stratigraphy of deep-sea sections. \u003cem\u003eGeological Society of America Bulletin\u003c/em\u003e \u003cstrong\u003e109\u003c/strong\u003e, 1421-1442 (1997).\u003c/li\u003e\n \u003cli\u003eBodin S, Meissner P, Janssen NM, Steuber T, Mutterlose J. Large igneous provinces and organic carbon burial: Controls on global temperature and continental weathering during the Early Cretaceous. \u003cem\u003eGlobal and Planetary Change\u003c/em\u003e \u003cstrong\u003e133\u003c/strong\u003e, 238-253 (2015).\u003c/li\u003e\n \u003cli\u003eFarias F, Szatmari P, Bahniuk A, Franca AB. Evaporitic carbonates in the pre-salt of Santos Basin\u0026ndash;Genesis and tectonic implications. \u003cem\u003eMarine and Petroleum Geology\u003c/em\u003e \u003cstrong\u003e105\u003c/strong\u003e, 251-272 (2019).\u003c/li\u003e\n \u003cli\u003eCoolen MJ\u003cem\u003e, et al.\u003c/em\u003e Evolution of the plankton paleome in the Black Sea from the Deglacial to Anthropocene. \u003cem\u003eProceedings of the National Academy of Sciences\u003c/em\u003e \u003cstrong\u003e110\u003c/strong\u003e, 8609-8614 (2013).\u003c/li\u003e\n \u003cli\u003eSinninghe Damst\u0026eacute; JS, Kock-Van Dalen A, de Leeuw JW, Schenck P, Guoying S, Brassell SC. The identification of mono-, di-and trimethyl 2-methyl-2-(4,8,12-trimethyltridecyl) chromans and their occurrence in the geosphere. \u003cem\u003eGeochimica et Cosmochimica Acta\u003c/em\u003e \u003cstrong\u003e51\u003c/strong\u003e, 2393-2400 (1987).\u003c/li\u003e\n \u003cli\u003eTulipani S\u003cem\u003e, et al.\u003c/em\u003e Molecular proxies as indicators of freshwater incursion-driven salinity stratification. \u003cem\u003eChemical Geology\u003c/em\u003e \u003cstrong\u003e409\u003c/strong\u003e, 61-68 (2015).\u003c/li\u003e\n \u003cli\u003eSinninghe Damst\u0026eacute; JK, Brendan J, Betts SE, Baas M, Maxwell JR, de Leeuw JW. Variations in abundances and distributions of isoprenoid chromans and long-chain alkylbenzenes in sediments of the Mulhouse Basin: a molecular sedimentary record of palaeosalinity. \u003cem\u003eOrganic Geochemistry\u003c/em\u003e \u003cstrong\u003e20\u003c/strong\u003e, 1201-1215 (1993).\u003c/li\u003e\n \u003cli\u003eHarvey HR, Mcmanus GB. Marine ciliates as a widespread source of tetrahymanol and hopan-3\u0026beta;-ol in sediments. \u003cem\u003eGeochimica et Cosmochimica Acta\u003c/em\u003e \u003cstrong\u003e55\u003c/strong\u003e, 3387-3390 (1991).\u003c/li\u003e\n \u003cli\u003eSinninghe Damst\u0026eacute; JS\u003cem\u003e, et al.\u003c/em\u003e Evidence for gammacerane as an indicator of water column stratification. \u003cem\u003eGeochimica et Cosmochimica Acta\u003c/em\u003e \u003cstrong\u003e59\u003c/strong\u003e, 1895-1900 (1995).\u003c/li\u003e\n \u003cli\u003eDidyk B, Simoneit B, Brassell St, Eglinton G. Organic geochemical indicators of palaeoenvironmental conditions of sedimentation. \u003cem\u003eNature\u003c/em\u003e \u003cstrong\u003e272\u003c/strong\u003e, 216-222 (1978).\u003c/li\u003e\n \u003cli\u003eGrice K, Schouten S, Nissenbaum A, Charrach J, Damst\u0026eacute; JSS. Isotopically heavy carbon in the C21 to C25 regular isoprenoids in halite-rich deposits from the Sdom Formation, Dead Sea Basin, Israel. \u003cem\u003eOrganic Geochemistry\u003c/em\u003e \u003cstrong\u003e28\u003c/strong\u003e, 349-359 (1998).\u003c/li\u003e\n \u003cli\u003eTulipani S, Grice K, Greenwood P, Schwark L. A pyrolysis and stable isotopic approach to investigate the origin of methyltrimethyltridecylchromans (MTTCs). \u003cem\u003eOrganic geochemistry\u003c/em\u003e \u003cstrong\u003e61\u003c/strong\u003e, 1-5 (2013).\u003c/li\u003e\n \u003cli\u003eSinninghe Damst\u0026eacute; JS, Kok MD, K\u0026ouml;ster J, Schouten S. Sulfurized carbohydrates: an important sedimentary sink for organic carbon? \u003cem\u003eEarth and Planetary Science Letters\u003c/em\u003e \u003cstrong\u003e164\u003c/strong\u003e, 7-13 (1998).\u003c/li\u003e\n \u003cli\u003eSinninghe Damst\u0026eacute; J, Van Duin AC, Hollander D, Kohnen ME, De Leeuw JW. Early diagenesis of bacteriohopanepolyol derivatives: Formation of fossil homohopanoids. \u003cem\u003eGeochimica et Cosmochimica Acta\u003c/em\u003e \u003cstrong\u003e59\u003c/strong\u003e, 5141-5157 (1995).\u003c/li\u003e\n \u003cli\u003eMa J, French KL, Cui X, Bryant DA, Summons RE. Carotenoid biomarkers in Namibian shelf sediments: Anoxygenic photosynthesis during sulfide eruptions in the Benguela Upwelling System. \u003cem\u003eProceedings of the National Academy of Sciences\u003c/em\u003e \u003cstrong\u003e118\u003c/strong\u003e, (2021).\u003c/li\u003e\n \u003cli\u003eSinninghe Damst\u0026eacute; J, Koopmans M. The fate of carotenoids in sediments: an overview. \u003cem\u003ePure and Applied Chemistry\u003c/em\u003e \u003cstrong\u003e69\u003c/strong\u003e, 2067-2074 (1997).\u003c/li\u003e\n \u003cli\u003eSchwark L, Empt P. Sterane biomarkers as indicators of Palaeozoic algal evolution and extinction events. \u003cem\u003ePalaeogeography, Palaeoclimatology, Palaeoecology\u003c/em\u003e \u003cstrong\u003e240\u003c/strong\u003e, 225-236 (2006).\u003c/li\u003e\n \u003cli\u003eKirst G. Salinity tolerance of eukaryotic marine algae. \u003cem\u003eAnnu Rev Plant Biol\u003c/em\u003e \u003cstrong\u003e41\u003c/strong\u003e, 21-53 (1990).\u003c/li\u003e\n \u003cli\u003eImhoff JF. Taxonomy and physiology of phototrophic purple bacteria and green sulfur bacteria. In: \u003cem\u003eAnoxygenic photosynthetic bacteria\u003c/em\u003e). Springer (1995).\u003c/li\u003e\n \u003cli\u003eRepeta D, Simpson D, Jorgensen B, Jannasch H. Evidence for anoxygenic photosynthesis from the distribution of bacterio-chlorophylls in the Black Sea. \u003cem\u003eNature\u003c/em\u003e \u003cstrong\u003e342\u003c/strong\u003e, 69-72 (1989).\u003c/li\u003e\n \u003cli\u003eCui X\u003cem\u003e, et al.\u003c/em\u003e Niche expansion for phototrophic sulfur bacteria at the Proterozoic\u0026ndash;Phanerozoic transition. \u003cem\u003eProceedings of the National Academy of Sciences\u003c/em\u003e \u003cstrong\u003e117\u003c/strong\u003e, 17599-17606 (2020).\u003c/li\u003e\n \u003cli\u003eFrench K, Rocher D, Zumberge J, Summons R. Assessing the distribution of sedimentary C 40 carotenoids through time. \u003cem\u003eGeobiology\u003c/em\u003e \u003cstrong\u003e13\u003c/strong\u003e, 139-151 (2015).\u003c/li\u003e\n \u003cli\u003eMa J, Cui X. Aromatic carotenoids: Biological sources and geological implications. \u003cem\u003eGeosystems and Geoenvironment\u003c/em\u003e, 100045 (2022).\u003c/li\u003e\n \u003cli\u003eSummons RE, Powell TG. Chlorobiaceae in Palaeozoic seas revealed by biological markers, isotopes and geology. \u003cem\u003eNature\u003c/em\u003e \u003cstrong\u003e319\u003c/strong\u003e, 763-765 (1986).\u003c/li\u003e\n \u003cli\u003eSinninghe Damst\u0026eacute; JS, Schouten S, Van Duin AC. Isorenieratene derivatives in sediments: possible controls on their distribution. \u003cem\u003eGeochimica et Cosmochimica Acta\u003c/em\u003e \u003cstrong\u003e65\u003c/strong\u003e, 1557-1571 (2001).\u003c/li\u003e\n \u003cli\u003eOvermann J, Cypionka H, Pfennig N. An extremely low‐light adapted phototrophic sulfur bacterium from the Black Sea. \u003cem\u003eLimnology and Oceanography\u003c/em\u003e \u003cstrong\u003e37\u003c/strong\u003e, 150-155 (1992).\u003c/li\u003e\n \u003cli\u003eVila X, Abella C. Effects of light quality on the physiology and the ecology of planktonic green sulfur bacteria in lakes. \u003cem\u003ePhotosynthesis research\u003c/em\u003e \u003cstrong\u003e41\u003c/strong\u003e, 53-65 (1994).\u003c/li\u003e\n \u003cli\u003eBlock KR, O\u0026apos;Brien JM, Edwards WJ, Marnocha CL. Vertical structure of the bacterial diversity in meromictic Fayetteville Green Lake. \u003cem\u003eMicrobiologyOpen\u003c/em\u003e \u003cstrong\u003e10\u003c/strong\u003e, e1228 (2021).\u003c/li\u003e\n \u003cli\u003ePeduzzi S, Tonolla M, Hahn D. Isolation and characterization of aggregate-forming sulfate-reducing and purple sulfur bacteria from the chemocline of meromictic Lake Cadagno, Switzerland. \u003cem\u003eFEMS microbiology ecology\u003c/em\u003e \u003cstrong\u003e45\u003c/strong\u003e, 29-37 (2003).\u003c/li\u003e\n \u003cli\u003eWilbanks EG\u003cem\u003e, et al.\u003c/em\u003e Microscale sulfur cycling in the phototrophic pink berry consortia of the S ippewissett S alt M arsh. \u003cem\u003eEnvironmental microbiology\u003c/em\u003e \u003cstrong\u003e16\u003c/strong\u003e, 3398-3415 (2014).\u003c/li\u003e\n \u003cli\u003eGraham JE, Bryant DA. The biosynthetic pathway for synechoxanthin, an aromatic carotenoid synthesized by the euryhaline, unicellular cyanobacterium Synechococcus sp. strain PCC 7002. \u003cem\u003eJournal of bacteriology\u003c/em\u003e \u003cstrong\u003e190\u003c/strong\u003e, 7966-7974 (2008).\u003c/li\u003e\n \u003cli\u003eGraham JE, Lecomte JT, Bryant DA. Synechoxanthin, an aromatic C40 xanthophyll that is a major carotenoid in the cyanobacterium Synechococcus sp. PCC 7002. \u003cem\u003eJournal of natural products\u003c/em\u003e \u003cstrong\u003e71\u003c/strong\u003e, 1647-1650 (2008).\u003c/li\u003e\n \u003cli\u003eKim S-T, O\u0026rsquo;Neil JR, Hillaire-Marcel C, Mucci A. Oxygen isotope fractionation between synthetic aragonite and water: Influence of temperature and Mg2+ concentration. \u003cem\u003eGeochimica et Cosmochimica Acta\u003c/em\u003e \u003cstrong\u003e71\u003c/strong\u003e, 4704-4715 (2007).\u003c/li\u003e\n \u003cli\u003eBernasconi SM\u003cem\u003e, et al.\u003c/em\u003e InterCarb: A community effort to improve interlaboratory standardization of the carbonate clumped isotope thermometer using carbonate standards. \u003cem\u003eGeochemistry, Geophysics, Geosystems\u003c/em\u003e \u003cstrong\u003e22\u003c/strong\u003e, e2020GC009588 (2021).\u003c/li\u003e\n \u003cli\u003eDa\u0026euml;ron M. Full propagation of analytical uncertainties in \u0026Delta;47 measurements. \u003cem\u003eGeochemistry, Geophysics, Geosystems\u003c/em\u003e \u003cstrong\u003e22\u003c/strong\u003e, e2020GC009592 (2021).\u003c/li\u003e\n \u003cli\u003eSeifert WK, Moldowan JM. The effect of biodegradation on steranes and terpanes in crude oils. \u003cem\u003eGeochimica et Cosmochimica Acta\u003c/em\u003e \u003cstrong\u003e43\u003c/strong\u003e, 111-126 (1979).\u003c/li\u003e\n \u003cli\u003eSandison CM, Alexander R, Kagi RI. The analysis of polar fractions from sediment extracts and crude oils using reaction-gas chromatography\u0026ndash;mass spectrometry. \u003cem\u003eOrganic geochemistry\u003c/em\u003e \u003cstrong\u003e34\u003c/strong\u003e, 1373-1389 (2003).\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"nature-portfolio","isNatureJournal":true,"hasQc":false,"allowDirectSubmit":false,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"","title":"Nature Portfolio","twitterHandle":"","acdcEnabled":false,"dfaEnabled":false,"editorialSystem":"ejp","reportingPortfolio":"","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"Gondwana, seawater incursion, biomarker, desulfurization, ecosystem","lastPublishedDoi":"10.21203/rs.3.rs-4463807/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-4463807/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"The early evolution of the South Atlantic Ocean following the Cretaceous break-up of Gondwana is extensively recorded in rift basins along the conjugate margins of Africa and Brazil. For the Brazil margin, divergent views of the source and pathway of the initial seawater incursion persist due to a paucity of recognized transitional sequences that document marine transgressive deposits over the continental interior. To address this, we conducted a high-resolution sedimentological and geochemical study through a core in the Campos Basin that encompasses the key lithologic switch from lacustrine carbonate to marine evaporite settings. Steroid lipid biomarkers, derived from marine algae, make a striking appearance in concert with a pronounced negative shift of 87Sr/86Sr ratios and coincident with the appearance of anhydrite. Importantly, the sulfur-sequestered biomarkers reveal a dynamic system where redox-stratified and anoxic conditions were amplified along with a deepening chemocline through the marine transition.","manuscriptTitle":"Ecosystem transformation upon Aptian seawater ingress into the Proto-South Atlantic Ocean","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-06-11 18:48:51","doi":"10.21203/rs.3.rs-4463807/v1","editorialEvents":[],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"communications-earth-and-environment","isNatureJournal":true,"hasQc":false,"allowDirectSubmit":false,"externalIdentity":"commsenv","sideBox":"Learn more about [Communications Earth and Environment](https://www.nature.com/commsenv/)","snPcode":"","submissionUrl":"","title":"Communications Earth \u0026 Environment","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"ejp","reportingPortfolio":"Communications Series","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"0fdedf8c-5e06-4e8b-983b-6de56a7361c1","owner":[],"postedDate":"June 11th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2025-01-26T08:09:13+00:00","versionOfRecord":{"articleIdentity":"rs-4463807","link":"https://doi.org/10.1038/s43247-025-02029-2","journal":{"identity":"communications-earth-and-environment","isVorOnly":false,"title":"Communications Earth \u0026 Environment"},"publishedOn":"2025-01-26 05:00:00","publishedOnDateReadable":"January 26th, 2025"},"versionCreatedAt":"2024-06-11 18:48:51","video":"","vorDoi":"10.1038/s43247-025-02029-2","vorDoiUrl":"https://doi.org/10.1038/s43247-025-02029-2","workflowStages":[]},"version":"v1","identity":"rs-4463807","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-4463807","identity":"rs-4463807","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}