Neogene plant macrofossils from West Antarctica reveal persistence of Nothofagaceae forests into the Early Miocene

Neogene plant macrofossils from West Antarctica reveal persistence of Nothofagaceae forests into the Early Miocene | 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 Neogene plant macrofossils from West Antarctica reveal persistence of Nothofagaceae forests into the Early Miocene Joaquin Bastias-Silva, Marcelo Leppe, Bethany Fox, Matthias Magiera, and 10 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-6148923/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 26 Nov, 2025 Read the published version in Communications Earth & Environment → Version 1 posted You are reading this latest preprint version Abstract The extinction of woody vegetation in Antarctica remains difficult to constrain due to its fragmented macrofossil record. Despite its long-standing polar position, Antarctica hosted extensive vegetation throughout the Paleogene. This changed near the Eocene-Oligocene Transition (ca. 34 Ma) as glaciation led to vegetation decline. Sparse evidence suggests tundra-like forests persisted until the Pliocene in East Antarctica, but the Neogene record from West Antarctica is largely restricted to palynoflora data. Here, we report early Miocene plant macrofossils from West Antarctica, consisting of Nothofagus leaves. U-Pb zircon geochronology confirms tundra-like vegetation existed in this region during the early Miocene (ca. 22–20 Ma), representing the youngest macrofossil record of West Antarctica. These findings suggest that Nothofagus either persisted through Antarctica’s harsh Late Cenozoic Ice Age conditions or recolonised during intermittent warm periods. This significantly advances our understanding of West Antarctica’s vegetation history and extends the known record of Nothofagus in Antarctic ecosystems. Biological sciences/Evolution/Palaeontology Earth and environmental sciences/Climate sciences/Palaeoclimate Earth and environmental sciences/Climate sciences/Cryospheric science Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 1. Introduction One of the most enigmatic aspects of Antarctica's history is its transition from terrestrial ecosystems dominated by thriving forests in the early Cenozoic to its current configuration, with no tree or shrub layers and terrestrial biota limited to a few invertebrates, lichens, mosses, diatoms and microbial groups 1 – 3 . The present combination of low temperatures, lack of humidity and winter darkness results in a limited distribution and diversity of plant species 4 . However, throughout the Mesozoic and early Cenozoic, Antarctica was home to a wide variety of plant life 5 , despite already being situated at polar latitudes 6 . Although plant macrofossils are very sparse, it has been inferred that Antarctica may have been capable of supporting woody plants well into the Neogene 7 – 11 . A major challenge in assessing the evolution of vegetation dynamics in Antarctica is that nearly 98% of the continent is covered by ice 12 , resulting in a highly spatially and temporally fragmented fossil record. Consequently, the timing of the extirpation of woody vegetation across Antarctica remains poorly understood and is often interpreted through methods other than direct macrofossil evidence, such as palynological and molecular studies. Although ephemeral ice sheets appeared in Antarctica during the late Mesozoic 13 , driven by a significant gradual decrease in global temperatures 14 – 16 , a permanent ice sheet did not develop until the Eocene–Oligocene Transition 17 , 18 (EOT; ca . 34 Ma), which marked the initiation of the Late Cenozoic Ice Age 19 . The plant macrofossil record in Antarctica postdating the EOT suggests that some woody vegetation may have persisted in low-diversity Nothofagus -dominated tundra ecosystems 20 – 23 . Nothofagus is a genus of southern beech trees (family Nothofagaceae) that may have been able to inhabit latitudes up to 85°S 5 , 8 , 9 , 11 in East Antarctica until as late as the Pliocene. This implies that areas at lower latitudes were probably able to support this vegetation during the Neogene as well, although direct macrofossil evidence remains elusive. However, this remains controversial, as ice-cap models are not consistent with the presence of Antarctic vegetation after the EOT, particularly from the Miocene onwards 24 – 26 . The study of Nothofagus fossils in Antarctica is therefore fundamental for understanding when and how forests became extinct on the continent. The study of how woody vegetation disappeared from Antarctica is further complicated by significant differences in the fossil record between East and West Antarctica 21 . East Antarctica has yielded sporadic macrofossil discoveries that provide a broader basis for reconstructing past vegetation dynamics 4 , 5 . In contrast, the West Antarctic the macrofossil record is far more limited and primarily restricted to deposits dating to shortly after the EOT 5 , 21 . Furthermore, the evidence for the presence of tundra-like vegetation in West Antarctica during and after the Oligocene is largely drawn from palynological studies. The nature of pollen evidence is such that there is substantial uncertainty as to whether this vegetation was physically present in the same location as the fossil pollen finds, since (i) anemophilic pollen may be able to travel significant distances and (ii) tundra-like vegetation was present in proximal southern Patagonia during the mid- and late Cenozoic 27 , 28 , providing a potential source. In this study, we present Nothofagus leaf macrofossils from the Miocene-aged glaciomarine sedimentary rocks of the Cape Melville Formation, exposed on King George Island in the northeastern Antarctic Peninsula (Fig. 1 ). These represent the youngest macrofossil evidence of woody vegetation on record for West Antarctica. Our results are further supported by new U-Pb zircon geochronological data (LA-ICP-MS) collected from an ash-layer intercalated within the Cape Melville Formation, providing robust chronological control for the age of the fossils. Combined, this evidence provides unequivocal proof of tundra-like vegetation in West Antarctica during the Late Cenozoic Ice Age and enhances our understanding of how long these forests managed to persist during Antarctic glaciation. 2. The geology of Melville Peninsula, King George Island Melville Peninsula is located at the northeast extreme of King George Island (Fig. 2 ), which is the largest island in the South Shetland Islands. Although King George Island is mostly covered by an ice cap, the rocks that are exposed host an exceptional Cenozoic stratigraphic record 30 , 31 and therefore holds critical exposures for studies addressing the Cenozoic evolution of Antarctica. The South Shetland archipelago extends parallel to the northern Antarctic Peninsula on the western side (Fig. 1 ), separated from the peninsula by the Bransfield Strait, a relatively young back-arc rift basin formed during the last 4 Myr 32 . The archipelago of the South Shetland Islands is mainly composed of the products of the active margin developed as a result of the eastward subduction of the Phoenix Plate beneath the continental crust of the Antarctic Peninsula 29 , 33 – 36 . This archipelago records tectonic, global sea-level and climate change throughout the Mesozoic and Cenozoic 29 , which can be divided into three main stages: (i) deep marine sedimentation during the Jurassic and Early Cretaceous 33 , 37 ; (ii) subaerial arc volcanism and sedimentation with a proliferation of plants and fauna from ca . 140 to 34 Ma 23 , 33 , 35 , 38 – 40 ; and (iii) glacial and interglacial deposits from ca . 34 Ma 29 – 31 . While Jurassic and Early Cretaceous rocks are exposed in the southwest of the South Shetland Islands 29 , 36 , Cenozoic formations are confined to the northeast of the archipelago 41 , 42 . The latter are grouped into the Moby Dick Group, an Eocene to Miocene volcano-sedimentary succession 43 , 44 (Fig. 2 ) composed of three formations: (i) Sherratt Bay Formation, (ii) Destruction Bay Formation and (iii) Cape Melville Formation. The Sherratt Bay Formation consists of an andesitic-basaltic succession which is exposed on the eastern edge of the Melville Peninsula (Fig. 2 ). While this unit has been interpreted as a terrestrial plateau-basalt sheet at the base of the Moby Dick Group 45 , it has been argued that it may be instead be a doleritic sill 46 . Its age remains poorly constrained. A K-Ar date of ca. 18 Ma 8 , previously attributed to the Sherratt Bay Formation, is likely associated with the early Miocene dike intrusions that are widespread on the Melville Peninsula rather than the Sherratt Bay rocks themselves 47 . A stratigraphic hiatus separates the Sherratt Bay Formation from the overlying Oligocene fossiliferous Destruction Bay Formation. Although the presence of fossil wood has been mentioned for the Destruction Bay Formation 41 , no further details have been presented or documented. This formation consists of a ca . 40–100 m thick succession of volcaniclastic rocks, dominated by reworked basaltic material with horizons (mostly siltstones) rich in marine invertebrates 41 (Fig. 2 ). The sedimentary features of this unit suggest a nearshore depositional environment under non-glacial conditions 41 . The age of the Destruction Bay Formation is loosely bracketed between 25.3 ± 0.8 Ma (brachiopods, 87 Sr/ 86 Sr 48 ) and 23.6 ± 0.7 Ma (basaltic tuff, K-Ar 49 ). Overlying the Destruction Bay Formation is the Cape Melville Formation (Fig. 2 ), which is composed of glacio-marine sediments including sandstones, conglomerates, clay-shales and silty shales with occasional iceberg-rafted dropstones 41 . The dropstones often show glacial striae and glacially polished facets, thus giving primary evidence for the presence of a continental ice-sheet in Antarctica 41 , 42 . This glacial event has been correlated with the Mi-1 and Mi-1a glaciations 42 , 46 , which are the most significant glaciation events following the establishment of the ice-cap in Antarctica during the EOT 50 . However, it is possible that West Antarctica developed a comparatively smaller ice cap relative to East Antarctica 51 . An abundant fossil record is present in the Cape Melville Formation, with (i) a thriving community of marine invertebrates, which includes bivalvia, gastropoda, coral, decapoda, scaphopoda, bryozoa, brachiopoda, echinodermata, and polychaeta 52 , and (ii) reworked palynomorphs (spores and pollen), which include Nothofagus pollen 42 . The benthic foraminifera of the Cape Melville Formation suggest an early Miocene age 53 and an inferred Sr age of 22.6 ± 0.4 Ma was obtained from skeletal carbonate 48 . Recently, a tuff interbedded in the Cape Melville Formation has been dated ( 40 Ar/ 39 Ar on hornblende) to an age of 21.3 ± 3.1 Ma 46 . These two geochronological constraints have been used to suggest an early Miocene age for the Cape Melville Formation 46 . 3. Methods 3.1. Fieldwork and fossil preparation The fieldwork campaign took place on the Melville Peninsula during January and February 2023 as part of the Chilean Antarctic Institute’s ECA-59 expedition aboard the Betanzos Vessel. Plant macrofossils were found preserved as impressions at two localities, Notho1 (62.019°S, 57.633°W) and Notho2 (62.018°S, 57.632°W) (Fig. 3 ). These fossils are housed in the Palaeontological Collection of Antarctica and Patagonia at the Chilean Antarctic Institute (INACH) in Punta Arenas, Chile. They were examined under a Zeiss Stemi 2000-C stereo microscope, and photographic records were captured using a Sony Alpha 7 III camera with a macro lens. The systematic description followed standardised guidelines 54 . 3.2. LA-ICP-MS zircon U-Pb geochronology Zircon grains were separated from an ash-layer (23JB15) collected in the Cape Melville Formation using standard crushing, hydraulic, magnetic and heavy liquid procedures. They were then mounted and imaged by cathodoluminescence (CL) using a scanning electron microscope (SEM) at the ETH Zürich. Laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS) techniques were used to determine trace element abundances and U-Pb ages. A 193 nm Resonetics Resolution S155 laser ablation system was used coupled to a Thermo Element XR, Sector-field single collector ICP-MS 55 . Laser parameters include a 19 µm spot size, a repetition rate of 5 Hz and an energy density of ca. 2 J cm − 2 . The ablation aerosol was mixed in the fast washout S-155 ablation cell (Laurin Technic) with carrier gas consisting of helium (ca. 0.25 L min − 1 ) and make-up gas consisting of argon (ca. 1 L min − 1 ) and nitrogen (2 mL min − 1 ). The ablated aerosol was then homogenised by flushing through a squid device before introduction into the plasma torch. The single collector sector-field MS is equipped with a high-capacity (80 m 3 h − 1 ) interface pump to improve sensitivity. Before each analytical session the instrument was optimised with NIST SRM612 glass to achieve a detection efficiency in the range of 1% (on Pb, Th, U) while keeping a low oxides production ( 248 ThO + / 232 Th + ≤ 0.25%) and a U/Th ratio of ca. 1. Intensities were recorded for the following isotopes: 27 Al, 29 Si, 31 P, 89 Y, 91 Zr, 93 Nb, 137 Ba, 139 La, 140 Ce, 141 Pr, 146 Nd, 147 Sm, 153 Eu, 157 Gd, 159 Tb, 163 Dy, 165 Ho, 167 Er, 169 Tm, 173 Yb, 175 Lu, 178 Hf, 181 Ta, 202 Hg, 204 Pb, 206 Pb, 207 Pb, 208 Pb, 232 Th, 235 U, and 238 U. The full dataset can be found in Supplementary Data file XX, following the community-derived guidelines 56 . For U-Pb geochronology, GJ-1 was used as the primary calibration reference material (CRM). Validating reference materials (VRMs) included Plešovice (337 Ma 57 ), Temora (417 Ma 58 ) and 91500 (1062 Ma 59 ) zircons. The VRMs results show the achievable precision and accuracy of the method, which is in the range of 1.0%. The data was reduced using the software Iolite 4.5 60,61 with VizualAge 62 . No common-Pb correction was applied but integration intervals were set to exclude inclusions, common Pb and discordant parts of the signal. The long-term external uncertainty is in the range of 1.5% for 206 Pb/ 238 U ages and is composed of the uncertainty from the applied corrections, uncertainty of the decay constants, lacking common-Pb correction, the uncertainty on the true 206 Pb/ 238 U ratio of the primary standard GJ-1, and possible uncertainty from matrix effects. For trace element quantification we used Si as internal standard at 15.2 wt% SiO 2 in zircons, and SRM NIST610 as external CRM. Ti was quantified by zircon 91500 (Ti: 4.73 ± 0.15 mg g − 1 ) 63 . 4. Results 4.1. Systematic Nothofagus description Two samples containing fossilised leaves were collected from siltstone layers of the early Miocene Cape Melville Formation. These rocks are interpreted as part of a glacio-marine depositional environment, providing a rare and valuable insight into the Neogene vegetation of West Antarctica. The samples form the basis for the systematic description of Nothofagus . Class: Eudicotyledonea. Order: Fagales. Family: Nothofagaceae. Genus: Nothofagus Blume, 1851. Type: cf. Nothofagus sp. Figure: Fig. 3 A-B. Material: Palaeontological Collection of Antarctic and Patagonia CPAP 9105. Locality: Notho1, Cape Melville, King George Island, Antarctica. Description: Incomplete simple leaf, microphyll, measuring 2.0 cm in length and 2.1 cm in width. Apex acute and rounded; margin lobed to serrate. Venation pinnate with a primary vein that is straight and persistent to the apex. Secondary veins craspedodromous, regularly parallel, straight or slightly curved apically, opposite, and terminating in a probable tooth. Tertiary veins are not visible Class: Eudicotyledonea. Order: Fagales. Family: Nothofagaceae. Genus: Nothofagus Blume, 1851. Type: cf. Nothofagus sp. Figure: Fig. 3 C-D. Material: Palaeontological Collection of Antarctic and Patagonia - CPAP 9106. Locality: Notho2, Cape Melville, King George Island, Antarctica. Description: Fragmentary simple leaf, microphyll, approximately 2.5 cm in length and 2.3 cm wide. The apex is acute and rounded, with a margin ranging from lobed to serrate. Venation is pinnate, with a prominent primary vein extending straight to the apex. Secondary veins are craspedodromous, evenly spaced, straight or slightly curved towards the apex, opposite, and likely terminating in a tooth. Tertiary veins are not visible. 4.2. Geochronology The ash layer 23JB15, of andesitic composition, was sampled within a section of the sequence dominated by sandstones, approximately 70 m above the formation boundary with the Destruction Bay Formation (Fig. 4 a). Cathodoluminescence imaging of zircon grains revealed either (i) oscillatory zonation with distinct cores, or (ii) patchy and homogeneous zoning, with an absence of rim-core relationship, both textural varieties are typical of zircons crystallised in magmatic environment 64 , 65 (Fig. 4 b). Ablation of zircons yielded concordant analyses spanning 206 Pb/ 238 U ages from 19.3 ± 1.0 to 68.1 ± 3.1 Ma. From these, two main populations are observed: an older cluster that yielded ages between 63.1 ± 2.6 and 68.1 ± 3.1 Ma, and a younger group with concordant dates between 19.3 ± 1.0 and 22.3 ± 1.3 Ma (Fig. 4 c). The latter yields a weighted mean age of 20.97 ± 0.22 Ma (n = 27, MSWD = 1.2, Fig. 4 d). The full dataset is available in Supplementary Data file XX. 5. Discussion 5.1 Age of the Nothofagus leaves The Nothofagus leaves discovered in the early Miocene Cape Melville Formation are stratigraphically closely associated with the ash layer 23JB15 (Fig. 4 ). The latter contains zircon grains exhibiting internal oscillatory zoning and homogeneous U-Pb ages, indicating direct magmatic sourcing with minimal, if any, reworking or sedimentary input. Thus, the weighted mean age of 20.97 ± 0.22 Ma provides the best estimate for the depositional age of the ash layer and constrains the age of the Cape Melville Formation. No significant stratigraphic discordance or hiatus was identified between the ash layer and the fossiliferous horizon, nor within the entire Cape Melville Formation. Unfortunately, no ash bed has been found above the fossilised leaves to further bracket their age. However, the available evidence suggests that the leaves were deposited between 20 and 22 Ma, making this the youngest plant macrofossil record from West Antarctica. 5.2. Post-EOT vegetation evolution of Antarctica: east versus west Despite being located in a polar position since at least the Cretaceous 34 , 66 , East Antarctica maintained vegetation dominated by floristically rich forests prior to the EOT 21 . This vegetation was diverse in both composition and stature 67 , with forests dominated by Nothofagus , Araucaria and podocarps, including large trees 68 . This suggests that the climate was not extreme, and vegetation resembled the forests currently found in Patagonia, known vernacularly as ‘Valdivian Forest’ 69 – 71 . Temperatures fell at the end of the Eocene, leading to the collapse of these forests as a viable ecosystem 72 . The Oligocene pollen records suggest that southern beech forests grew locally, with minor components of podocarps, Proteaceae and other shrubby angiosperms 21 . This vegetation type is similar to the present-day Patagonian steppe of bunchgrasses and shrubs or the Nothofagus -podocarp forests of New Zealand. These Oligocene forests were dominated by Nothofagus 73 , which had become reduced in both stature and diversity compared to the pre-EOT vegetation 74 , 75 . Among these Oligocene vegetational assemblages, the extensive fossil record of Nothofagus subgenus Fuscospora suggests that it may have been the only species 21 , 76 . However, the palaeontological record, largely limited to pollen grains and spores, with very sparse wood and leaves, suggests that this low-diversity tundra-like vegetation persisted after the EOT only in favourable or refugial areas 21 , 73 , 77 , 78 . It is uncertain whether this vegetation persisted into the early Miocene, as most of the record is based on pollen evidence 21 , 75 , 76 . The cold, glacial climate of the Miocene was briefly interrupted by a warm period ca . 17 − 15 Ma (the Middle Miocene Climatic Optimum; MMCO) 79 . This warming resulted in a temporary increase in both the diversity and stature of East Antarctic vegetation 22 , 77 , 80 , which facilitated the return of several Nothofagus taxa 21 . However, this was immediately followed by abrupt cooling 81 , accompanied by the gradual disappearance of woody plants, although the continued presence of Nothofagus pollen suggests that they may have persisted in glacial refugia in a manner analogous to the glacial refugia detected through Pleistocene glaciations in southern Patagonia 82 , 83 , which explain the degree of endemism in this part of South America and the speed of subsequent recolonisation 80 , 84 . After the MMCO, the ice sheet expanded in Antarctica throughout the Neogene and Quaternary, preventing the establishment of woody plants, with the exception of one notable site with tundra-like vegetation of mid-Pliocene age. The latter is found at less than 500 km from the South Pole 5 , 21 , 85 , and had an assemblage similar to that in the modern-day southern Patagonia (Cape Horn) 21 , 40 . This vegetation consisted of cushion-forming mosses and vascular plants with deciduous Nothofagus and rare podocarps 9 , 21 , 86 . Notably, there is a lack of consensus on the age of the rocks that host these fossils 7 , 21 and on how these tundra-like forests may have persisted in East Antarctica during the middle Pliocene. To the west of the Transantarctic Mountains lies the West Antarctic region which, like East Antarctica, was already located in a polar position during the late Mesozoic 65 , 66 , 87 , 88 . Our understanding of the Cenozoic vegetation evolution of the Antarctic Peninsula has been mostly constrained from the outcrops exposed in King George Island 89 . These outcrops also hold most of the evidence for woody vegetation in West Antarctica 4 . Middle Eocene petrified forests are found in the centre-east of the island, revealing a once diverse ecosystem of Nothofagus and Araucaria conifers, among other species 67 , 90 , which resembles the modern fern bush communities of southern oceanic islands (e.g. Auckland Island). This vegetation survived until the late Eocene 4 , when King George Island was on the locus of the arc axis in the Antarctic Peninsula 29 , 36 . After the EOT, as the climate turned colder and drier 91 , the woody vegetation transitioned to tundra-like forests dominated by Nothofagus 21 . Although it has been suggested that from the Oligocene onwards there may have been a relatively extensive ice cap in the Antarctic Peninsula, the lateral extent of such an ice-cap remains unclear 31 . Nevertheless, the development of an ice-cap during the Oligocene may have caused the tundra-like vegetation to succumb, at least temporarily 4 . Evidence for woody vegetation is absent in West Antarctica after the early Oligocene, except for evidence from palynological studies on the early Miocene glacio-marine Cape Melville Formation on King George Island 31 , 42 , which suggest the presence of a monotypic Nothofagus assemblage. Prior to our study, it was not possible to determine whether the source of the Nothofagus pollen was autochthonous or allochthonous, given the anemophilous nature of its grains. Because Nothofagus pollen is so widely wind-dispersed, it is difficult to use palynological evidence alone to reconstruct possible species co-occurrences within local vegetation. However, the macrofossil record does not suffer from this problem, since it is likely that most Nothofagus macrofossils are deposited very close to their source plants 84 . While the Nothofagus leaves were found in the shallow marine Cape Melville Formation, suggesting transport before deposition, this does not preclude the presence of local vegetation, as they were recovered from a land-proximal marine environment 52 . 5.3. Miocene tectonic models of the Antarctic Peninsula and the proximity of other Nothofagus communities The Miocene tectonic history of the Antarctic Peninsula provides context for assessing the persistence of Nothofagus communities in West Antarctica during the early Miocene. The geological history of the Antarctic Peninsula is dominated by the development of a continental arc throughout the Mesozoic and part of the Cenozoic 65 , 92 , which was the result of the eastward subduction of the oceanic lithosphere of the Phoenix Plate 47 . This subduction system waned during the Cenozoic to eventually cease at ca . 20 Ma 34 , 47 , 93 . The sea floor remnants of the region and paleomagnetic studies have been used to reconstruct this sector of Antarctica and South America and suggest that during the Jurassic and Cretaceous, Patagonia was in juxtaposition to the north of the Antarctic Peninsula 87 , 93 . Therefore, during this period, there would have been a strong floral and faunal connection between these two regions 69 . However, during the Cenozoic the Antarctic Peninsula drifted to the south with respect to South America as a response to the formation of the Scotia Plate, a sliver of oceanic lithosphere located between the Antarctic and the South American plates 94 (Fig. 6 ). This extension led to the opening of the Drake Passage, which effectively disconnected Antarctica from South America, causing the isolation of the Antarctic continent from any other landmass and setting up the Antarctic Circumpolar Current 95 . This event, which occurred near to the EOT, marks the onset of the Late Cenozoic Ice Age 94 and is considered, at least in part, to have contributed to the initiation of this Earth period 96 . Throughout the Palaeogene the Antarctic Peninsula experienced counterclockwise rotation, which caused it to progressively further separate from Patagonia 93 . During the early Miocene, when the Cape Melville Formation was deposited, it is estimated that the Antarctic Peninsula, and thus King George Island as well, was more than 500 km to the south with respect to Patagonia 47 , 93 (Fig. 6 ). While anemophilic pollen may be able to travel significant distances 97 and tundra-like vegetation was present in southern Patagonia during the mid- and late Cenozoic 27 , 28 , it is unlikely that leaves could have been transported and preserved more than 500 km south. This supports our argument that the Nothofagus leaf fossils originated from an autochthonous tundra-like forest. 5.4. Survival or Recolonisation? The presence of Nothofagus -dominated tundra-like forests as recently as the early Miocene in West Antarctica (this work) and the mid-Pliocene in East Antarctica raises the question of whether these species were resilient and adapted to survive in glacial refugia to changing climatic conditions throughout the Neogene, or briefly recolonised Antarctica under particularly favourable conditions during warm intervals. From an autoecological perspective, Nothofagus seed dispersal is by gravity and wind (anemochory), while germination is generally epigeal and occurs not far from the seed-producing tree crown 98 . Although some authors argue that Nothofagus seeds can disperse over long transoceanic distances 98 , there is still a significant body of research that claims that their seeds are intolerant to seawater 99 – 101 , and so would have been unable to recolonise the Antarctic Peninsula from the southern tip of South America after the Drake Passage opened during the Paleogene 102 . The base of the Cape Melville Formation is marked by a glacial diamictite, suggesting that the ice grounding line extended into the marine realm. This glacial advance is generally correlated with the Mi-1 and Mi-1a events, which occurred close to the Oligocene-Miocene boundary 29 , 46 . Following this, the marine sedimentary succession evolved from to ice-proximal and then ice-distal conditions prior to the deposition of the rocks hosting the Nothofagus leaf macrofossils 9 , 12 , 31 . The presence of tundra-like forest thus coincides with evidence for a climate amelioration in this part of Antarctica. The evidence for extensive ice cover at the Oligocene-Miocene boundary indicates that this site is itself unlikely to have been a persistent glacial refugium. The sparse occurrence of Neogene woody macrofossils in Antarctica may indicate that Nothofagus recolonised Antarctica during warmer intervals in suitable locations via long-distance dispersal, rather than persisting without interruption. This is based on the premise that continuous persistence would have yielded, albeit locally, a continuous record of woody plant fossils. Episodic recolonisation from tundra-like vegetational relicts would result in a more fragmented fossil record, which better fits the observed macrofossil data. Tundra-like forests existed in regions subjected to glacial conditions during this period, including Patagonia and Oceania 103 , 104 , and potentially could have acted as seed sources for the resurgence of these forests in Antarctica. However, the absence of fossils does not necessarily disprove the presence of glacial refugia. Both the lack of appropriate sedimentation conditions and the inaccessibility of many sedimentary strata could produce a discontinuous and incomplete fossil record. In addition, the mechanism by which long-distance dispersal may have occurred remains unclear. The record of tundra-like vegetation in East Antarctica after the early Miocene is limited to two episodes: the MMCO 22 and the mid-Pliocene 9 , 12 (Fig. 5 ). The fossiliferous site dated to the latter is located less than 500 km from the South Pole. If such latitudes were populated by Nothofagus -dominated forest relicts during these periods, it is reasonable to assume that this vegetation was also present at lower latitudes of Antarctica. However, direct macrofossil evidence is absent in West Antarctica after the early Miocene. Although the evidence presented here represents a significant advance in our understanding of the Neogene vegetation history of West Antarctica, the question of persistence or recolonisation remains unresolved. 5. 5. Stability of the Neogene ice-cap The presence of low-diversity tundra-like vegetation either temporarily recolonising Antarctica during favourable conditions or persisting through the Late Cenozoic Ice Age has critical implications for understanding the stability of the Antarctic ice sheet. Although consecutive glaciations followed the EOT, during which the ice cap is conservatively estimated to have reached 80–110% of its modern volume 105 , the presence of tundra-like forests suggests that at least some sectors remained ice-free during warm periods or possibly throughout the Neogene, lasting as late as the Pliocene. These findings challenge the assumption of a stable Antarctic ice sheet since the EOT. Furthermore, evidence indicates that ice sheets could have melted rapidly during brief warm periods 106 – 109 , demonstrating their sensitivity to climate warming. This highlights the potential for rapid changes in the Antarctic ice cap under current global warming scenarios, where the return of woody vegetation could occur relatively quickly. 6. Conclusions The Nothofagus leaf imprints from the Cape Melville Formation on King George Island presented here (Fig. 5 ), combined with our geochronological results (Fig. 4 ), provide the first robust evidence for the presence of tundra-like vegetation in West Antarctica during the early Miocene, suggesting that tundra-like forests were present in the region at least between 22 and 20 Ma and potentially even before this period, establishing it as the youngest woody macrofossil record from West Antarctica. This new finding advances the debate surrounding palynoflora-based interpretations of Neogene tundra-like forests in West Antarctica. Furthermore, it fills critical gaps in our understanding of how woody vegetation became extinct in Antarctica and underscores the remarkable adaptability of Nothofagus within Antarctic ecosystems. Localised refugia with tundra-like vegetation in West Antarctica may have either survived numerous glaciations since the EOT or recolonised during warm interglacial periods. King George Island likely served as such an enclave during the early Miocene, suggesting a more complex climatic history than previously thought. This implies that Antarctic conditions may not have been uniformly harsh for woody vegetation, at least episodically. The biology of Nothofagus and its syndrome of reproduction argue against recolonisation from nearby areas (e.g. Patagonia). On the other hand, repopulation of tundra-like forests in Antarctica from glacial refugia is also uncertain, as the ice sheet should have reached volumes during the Late Cenozoic Ice Age that were similar to or greater than those of the present day. Therefore, whether tundra-like vegetation recolonised Antarctica or persisted under the harsh conditions of the Late Cenozoic Ice Age remains a challenging and open question, which should be the focus of future studies. The presence of early Miocene tundra-like vegetation in West Antarctica suggests that the vegetation dynamics may have been more synchronised between East and West Antarctica than previously assumed, highlighting the complex stability of Antarctica’s ice sheet. Declarations Acknowledgements JBS was funded by the Swiss National Science Foundation (project P5R5PN_217947) and the project RT-01-22 funded by the Chilean Antarctic Institute (INACH). LG was funded by the Natural Science Foundation of China (NSFC) (42322607 and 42076223). Fieldwork on the Antarctic Peninsula was supported by the Chilean Antarctic Institute. Especial thanks to the team supporting in the field Georgette Mell, Billy Wallace and Ignacio Reyes. References Green TGA, Schroeter B, Sancho LG (2007) Plant Life in Antarctica. in Functional Plant Ecology . CRC Allegrucci G, Carchini G, Todisco V, Convey P, Sbordoni V (2006) A molecular phylogeny of antarctic chironomidae and its implications for biogeographical history. Polar Biol 29:320–326 Convey P et al (2008) Antarctic terrestrial life – challenging the history of the frozen continent? Biol Rev 83:103–117 Cantrill DJ, Poole I (2012) The Vegetation of Antarctica through Geological Time. Cambridge University Press Francis JE et al (2007) 100 Million Years of Antarctic Climate Evolution: Evidence from Fossil Plants. 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Temuco","correspondingAuthor":false,"prefix":"","firstName":"Claudio","middleName":"","lastName":"Tapia","suffix":""}],"badges":[],"createdAt":"2025-03-03 20:05:08","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-6148923/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-6148923/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1038/s43247-025-02921-x","type":"published","date":"2025-11-26T05:00:00+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":81434998,"identity":"0ca545e4-4087-4fe6-85ba-efa52042b2de","added_by":"auto","created_at":"2025-04-26 11:09:32","extension":"jpg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":1907052,"visible":true,"origin":"","legend":"\u003cp\u003eCurrent tectonic configuration of the region encompassing the Scotia Plate, Patagonia, and the Antarctic Peninsula. The locations of the South Shetland Islands (SSI) and the Bransfield Strait (BS) are highlighted. Figure modified from\u003csup\u003e29\u003c/sup\u003e. Red box in the inset figure shows the location of the South Shetland Islands archipelago with King George Island in red. FZ = fault zone.\u003c/p\u003e","description":"","filename":"Figure1.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6148923/v1/72843e2630804c38223fb882.jpg"},{"id":81435073,"identity":"6d00adfc-eb1b-4c7a-bd61-297034b737a6","added_by":"auto","created_at":"2025-04-26 11:17:32","extension":"jpg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":1706267,"visible":true,"origin":"","legend":"\u003cp\u003eGeological map and stratigraphic log of Melville Peninsula, King George Island, modified from\u003csup\u003e29,42,46\u003c/sup\u003e. The fossil locations are indicated by stars.\u003c/p\u003e","description":"","filename":"Figure2.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6148923/v1/48c89fcb4e365b6a16f41b06.jpg"},{"id":81435004,"identity":"c1244594-571a-483b-813b-fc5692cfeaec","added_by":"auto","created_at":"2025-04-26 11:09:32","extension":"jpg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":1882826,"visible":true,"origin":"","legend":"\u003cp\u003eFragmentary leaf imprints of \u003cem\u003eNothofagus\u003c/em\u003e from the early Miocene Cape Melville Formation. (A) fossil leaf (CPAP 9105) showing the primary and second veins; (B) drawing with detail of secondary opposite venation; (C) fossil leaf (CPAP 9106) showing the primary and second veins; (D) drawing with detail of craspedodromous, evenly spaced venation.\u003c/p\u003e","description":"","filename":"Figure3.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6148923/v1/828c3e91d47eb934a82b9e98.jpg"},{"id":81435015,"identity":"2768511d-016b-4df6-81d3-24a79f0dbd99","added_by":"auto","created_at":"2025-04-26 11:09:33","extension":"jpg","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":713314,"visible":true,"origin":"","legend":"\u003cp\u003eStratigraphy (generalised) and geochronology of the Cape Melville Formation. (A) Composite stratigraphic section indicating the position of the sample analysed for U-Pb geochronology (23JB15) and the level where the leaf fossils were found. (B) Weighted mean \u003csup\u003e206\u003c/sup\u003ePb/\u003csup\u003e238\u003c/sup\u003eU dates of the volcanic ash-layer, sample 23JB15. Bars represent single ablation spots and represent 2σ uncertainty. (C) Wetherill concordia plot of zircon U–Pb data for the sample 23JB15. (D) Representative SEM-based cathodoluminescence images of the dated zircons with location of analytical spots, including \u003csup\u003e206\u003c/sup\u003ePb/\u003csup\u003e238\u003c/sup\u003eU ages.\u003c/p\u003e","description":"","filename":"Figure4.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6148923/v1/3f4ab0eb7ba21a3af7f52809.jpg"},{"id":81435079,"identity":"fcedb2dc-4869-4410-9eca-b75b1809d27a","added_by":"auto","created_at":"2025-04-26 11:17:33","extension":"jpg","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":1812051,"visible":true,"origin":"","legend":"\u003cp\u003eMacrofossil vegetation record in West and East Antarctica during the Eocene to Pliocene, based on this work and literature\u003csup\u003e7,9,12,21,40,69,73,76–78,80,90\u003c/sup\u003e.\u003c/p\u003e","description":"","filename":"Figure5.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6148923/v1/19847a4cb9b2ef56b2a58c04.jpg"},{"id":81435072,"identity":"e81bba77-01a3-48d6-b9ca-26a3a59a6805","added_by":"auto","created_at":"2025-04-26 11:17:32","extension":"jpg","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":575830,"visible":true,"origin":"","legend":"\u003cp\u003ePaleogeographic reconstruction of the Antarctic Peninsula and South America during the early Miocene, redrawn from reference\u003csup\u003e93\u003c/sup\u003e. ASSSZ: Ancestral South Sandwich Subduction zone.\u003c/p\u003e","description":"","filename":"Figure6.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6148923/v1/ff8b1680674ce974af1384d7.jpg"},{"id":96885686,"identity":"39e76350-5169-4fdf-b028-c768895625ef","added_by":"auto","created_at":"2025-11-27 08:13:09","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":7020437,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-6148923/v1/cb19da1b-7e73-47aa-8cb3-8fac66dfcdd1.pdf"},{"id":81434999,"identity":"2468ce48-d387-438b-8f14-56d261801791","added_by":"auto","created_at":"2025-04-26 11:09:32","extension":"jpg","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":393018,"visible":true,"origin":"","legend":"Science Illustration","description":"","filename":"draftScienceIllustration.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6148923/v1/a19d17487b1fa4beb15321c5.jpg"},{"id":81435003,"identity":"e6dc1fd0-3d69-45f3-8c57-2e0f5f682f81","added_by":"auto","created_at":"2025-04-26 11:09:32","extension":"zip","order_by":2,"title":"","display":"","copyAsset":false,"role":"supplement","size":11693033,"visible":true,"origin":"","legend":"Supplementary Dataset 1","description":"","filename":"SupplementaryMaterial.zip","url":"https://assets-eu.researchsquare.com/files/rs-6148923/v1/c9073a7d34f9bbafb8c19e42.zip"}],"financialInterests":"There is \u003cb\u003eNO\u003c/b\u003e Competing Interest.","formattedTitle":"Neogene plant macrofossils from West Antarctica reveal persistence of Nothofagaceae forests into the Early Miocene","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eOne of the most enigmatic aspects of Antarctica's history is its transition from terrestrial ecosystems dominated by thriving forests in the early Cenozoic to its current configuration, with no tree or shrub layers and terrestrial biota limited to a few invertebrates, lichens, mosses, diatoms and microbial groups\u003csup\u003e\u003cspan additionalcitationids=\"CR2\" citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e\u003c/sup\u003e. The present combination of low temperatures, lack of humidity and winter darkness results in a limited distribution and diversity of plant species\u003csup\u003e\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e\u003c/sup\u003e. However, throughout the Mesozoic and early Cenozoic, Antarctica was home to a wide variety of plant life\u003csup\u003e\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e\u003c/sup\u003e, despite already being situated at polar latitudes\u003csup\u003e\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e\u003c/sup\u003e. Although plant macrofossils are very sparse, it has been inferred that Antarctica may have been capable of supporting woody plants well into the Neogene\u003csup\u003e\u003cspan additionalcitationids=\"CR8 CR9 CR10\" citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e\u003c/sup\u003e. A major challenge in assessing the evolution of vegetation dynamics in Antarctica is that nearly 98% of the continent is covered by ice\u003csup\u003e\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e\u003c/sup\u003e, resulting in a highly spatially and temporally fragmented fossil record. Consequently, the timing of the extirpation of woody vegetation across Antarctica remains poorly understood and is often interpreted through methods other than direct macrofossil evidence, such as palynological and molecular studies.\u003c/p\u003e \u003cp\u003eAlthough ephemeral ice sheets appeared in Antarctica during the late Mesozoic\u003csup\u003e\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e\u003c/sup\u003e, driven by a significant gradual decrease in global temperatures\u003csup\u003e\u003cspan additionalcitationids=\"CR15\" citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e\u003c/sup\u003e, a permanent ice sheet did not develop until the Eocene\u0026ndash;Oligocene Transition\u003csup\u003e\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e,\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e\u003c/sup\u003e (EOT; \u003cem\u003eca\u003c/em\u003e. 34 Ma), which marked the initiation of the Late Cenozoic Ice Age\u003csup\u003e\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e\u003c/sup\u003e. The plant macrofossil record in Antarctica postdating the EOT suggests that some woody vegetation may have persisted in low-diversity \u003cem\u003eNothofagus\u003c/em\u003e-dominated tundra ecosystems\u003csup\u003e\u003cspan additionalcitationids=\"CR21 CR22\" citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e\u003c/sup\u003e. \u003cem\u003eNothofagus\u003c/em\u003e is a genus of southern beech trees (family Nothofagaceae) that may have been able to inhabit latitudes up to 85\u0026deg;S\u003csup\u003e\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e,\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e,\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e,\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e\u003c/sup\u003e in East Antarctica until as late as the Pliocene. This implies that areas at lower latitudes were probably able to support this vegetation during the Neogene as well, although direct macrofossil evidence remains elusive. However, this remains controversial, as ice-cap models are not consistent with the presence of Antarctic vegetation after the EOT, particularly from the Miocene onwards\u003csup\u003e\u003cspan additionalcitationids=\"CR25\" citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e\u003c/sup\u003e. The study of \u003cem\u003eNothofagus\u003c/em\u003e fossils in Antarctica is therefore fundamental for understanding when and how forests became extinct on the continent.\u003c/p\u003e \u003cp\u003eThe study of how woody vegetation disappeared from Antarctica is further complicated by significant differences in the fossil record between East and West Antarctica\u003csup\u003e\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e\u003c/sup\u003e. East Antarctica has yielded sporadic macrofossil discoveries that provide a broader basis for reconstructing past vegetation dynamics\u003csup\u003e\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e,\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e\u003c/sup\u003e. In contrast, the West Antarctic the macrofossil record is far more limited and primarily restricted to deposits dating to shortly after the EOT\u003csup\u003e\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e,\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e\u003c/sup\u003e. Furthermore, the evidence for the presence of tundra-like vegetation in West Antarctica during and after the Oligocene is largely drawn from palynological studies. The nature of pollen evidence is such that there is substantial uncertainty as to whether this vegetation was physically present in the same location as the fossil pollen finds, since (i) anemophilic pollen may be able to travel significant distances and (ii) tundra-like vegetation was present in proximal southern Patagonia during the mid- and late Cenozoic\u003csup\u003e\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e,\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e\u003c/sup\u003e, providing a potential source.\u003c/p\u003e \u003cp\u003eIn this study, we present \u003cem\u003eNothofagus\u003c/em\u003e leaf macrofossils from the Miocene-aged glaciomarine sedimentary rocks of the Cape Melville Formation, exposed on King George Island in the northeastern Antarctic Peninsula (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). These represent the youngest macrofossil evidence of woody vegetation on record for West Antarctica. Our results are further supported by new U-Pb zircon geochronological data (LA-ICP-MS) collected from an ash-layer intercalated within the Cape Melville Formation, providing robust chronological control for the age of the fossils. Combined, this evidence provides unequivocal proof of tundra-like vegetation in West Antarctica during the Late Cenozoic Ice Age and enhances our understanding of how long these forests managed to persist during Antarctic glaciation.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e"},{"header":"2. The geology of Melville Peninsula, King George Island","content":"\u003cp\u003eMelville Peninsula is located at the northeast extreme of King George Island (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e), which is the largest island in the South Shetland Islands. Although King George Island is mostly covered by an ice cap, the rocks that are exposed host an exceptional Cenozoic stratigraphic record\u003csup\u003e\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e,\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e\u003c/sup\u003e and therefore holds critical exposures for studies addressing the Cenozoic evolution of Antarctica. The South Shetland archipelago extends parallel to the northern Antarctic Peninsula on the western side (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e), separated from the peninsula by the Bransfield Strait, a relatively young back-arc rift basin formed during the last 4 Myr\u003csup\u003e\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e\u003c/sup\u003e. The archipelago of the South Shetland Islands is mainly composed of the products of the active margin developed as a result of the eastward subduction of the Phoenix Plate beneath the continental crust of the Antarctic Peninsula\u003csup\u003e\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e,\u003cspan additionalcitationids=\"CR34 CR35\" citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e\u003c/sup\u003e. This archipelago records tectonic, global sea-level and climate change throughout the Mesozoic and Cenozoic\u003csup\u003e\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e\u003c/sup\u003e, which can be divided into three main stages: (i) deep marine sedimentation during the Jurassic and Early Cretaceous\u003csup\u003e\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e,\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e\u003c/sup\u003e; (ii) subaerial arc volcanism and sedimentation with a proliferation of plants and fauna from \u003cem\u003eca\u003c/em\u003e. 140 to 34 Ma\u003csup\u003e\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e,\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e,\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e,\u003cspan additionalcitationids=\"CR39\" citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e\u003c/sup\u003e; and (iii) glacial and interglacial deposits from \u003cem\u003eca\u003c/em\u003e. 34 Ma\u003csup\u003e\u003cspan additionalcitationids=\"CR30\" citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e\u003c/sup\u003e. While Jurassic and Early Cretaceous rocks are exposed in the southwest of the South Shetland Islands\u003csup\u003e\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e,\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e\u003c/sup\u003e, Cenozoic formations are confined to the northeast of the archipelago\u003csup\u003e\u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e,\u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e\u003c/sup\u003e. The latter are grouped into the Moby Dick Group, an Eocene to Miocene volcano-sedimentary succession\u003csup\u003e\u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e43\u003c/span\u003e,\u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e\u003c/sup\u003e (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e) composed of three formations: (i) Sherratt Bay Formation, (ii) Destruction Bay Formation and (iii) Cape Melville Formation.\u003c/p\u003e \u003cp\u003eThe Sherratt Bay Formation consists of an andesitic-basaltic succession which is exposed on the eastern edge of the Melville Peninsula (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). While this unit has been interpreted as a terrestrial plateau-basalt sheet at the base of the Moby Dick Group\u003csup\u003e\u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e45\u003c/span\u003e\u003c/sup\u003e, it has been argued that it may be instead be a doleritic sill\u003csup\u003e\u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e46\u003c/span\u003e\u003c/sup\u003e. Its age remains poorly constrained. A K-Ar date of ca. 18 Ma\u003csup\u003e\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e\u003c/sup\u003e, previously attributed to the Sherratt Bay Formation, is likely associated with the early Miocene dike intrusions that are widespread on the Melville Peninsula rather than the Sherratt Bay rocks themselves\u003csup\u003e\u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e47\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eA stratigraphic hiatus separates the Sherratt Bay Formation from the overlying Oligocene fossiliferous Destruction Bay Formation. Although the presence of fossil wood has been mentioned for the Destruction Bay Formation\u003csup\u003e\u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e\u003c/sup\u003e, no further details have been presented or documented. This formation consists of a \u003cem\u003eca\u003c/em\u003e. 40\u0026ndash;100 m thick succession of volcaniclastic rocks, dominated by reworked basaltic material with horizons (mostly siltstones) rich in marine invertebrates\u003csup\u003e\u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e\u003c/sup\u003e (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). The sedimentary features of this unit suggest a nearshore depositional environment under non-glacial conditions\u003csup\u003e\u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e\u003c/sup\u003e. The age of the Destruction Bay Formation is loosely bracketed between 25.3\u0026thinsp;\u0026plusmn;\u0026thinsp;0.8 Ma (brachiopods, \u003csup\u003e87\u003c/sup\u003eSr/\u003csup\u003e86\u003c/sup\u003eSr\u003csup\u003e48\u003c/sup\u003e) and 23.6\u0026thinsp;\u0026plusmn;\u0026thinsp;0.7 Ma (basaltic tuff, K-Ar\u003csup\u003e\u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e49\u003c/span\u003e\u003c/sup\u003e).\u003c/p\u003e \u003cp\u003eOverlying the Destruction Bay Formation is the Cape Melville Formation (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e), which is composed of glacio-marine sediments including sandstones, conglomerates, clay-shales and silty shales with occasional iceberg-rafted dropstones\u003csup\u003e\u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e\u003c/sup\u003e. The dropstones often show glacial striae and glacially polished facets, thus giving primary evidence for the presence of a continental ice-sheet in Antarctica\u003csup\u003e\u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e,\u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e\u003c/sup\u003e. This glacial event has been correlated with the Mi-1 and Mi-1a glaciations\u003csup\u003e\u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e,\u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e46\u003c/span\u003e\u003c/sup\u003e, which are the most significant glaciation events following the establishment of the ice-cap in Antarctica during the EOT\u003csup\u003e\u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e50\u003c/span\u003e\u003c/sup\u003e. However, it is possible that West Antarctica developed a comparatively smaller ice cap relative to East Antarctica\u003csup\u003e\u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e51\u003c/span\u003e\u003c/sup\u003e. An abundant fossil record is present in the Cape Melville Formation, with (i) a thriving community of marine invertebrates, which includes bivalvia, gastropoda, coral, decapoda, scaphopoda, bryozoa, brachiopoda, echinodermata, and polychaeta\u003csup\u003e\u003cspan citationid=\"CR52\" class=\"CitationRef\"\u003e52\u003c/span\u003e\u003c/sup\u003e, and (ii) reworked palynomorphs (spores and pollen), which include \u003cem\u003eNothofagus\u003c/em\u003e pollen\u003csup\u003e\u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e\u003c/sup\u003e. The benthic foraminifera of the Cape Melville Formation suggest an early Miocene age\u003csup\u003e\u003cspan citationid=\"CR53\" class=\"CitationRef\"\u003e53\u003c/span\u003e\u003c/sup\u003e and an inferred Sr age of 22.6\u0026thinsp;\u0026plusmn;\u0026thinsp;0.4 Ma was obtained from skeletal carbonate\u003csup\u003e\u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e48\u003c/span\u003e\u003c/sup\u003e. Recently, a tuff interbedded in the Cape Melville Formation has been dated (\u003csup\u003e40\u003c/sup\u003eAr/\u003csup\u003e39\u003c/sup\u003eAr on hornblende) to an age of 21.3\u0026thinsp;\u0026plusmn;\u0026thinsp;3.1 Ma\u003csup\u003e\u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e46\u003c/span\u003e\u003c/sup\u003e. These two geochronological constraints have been used to suggest an early Miocene age for the Cape Melville Formation\u003csup\u003e\u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e46\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e"},{"header":"3. Methods","content":"\u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e3.1. Fieldwork and fossil preparation\u003c/h2\u003e \u003cp\u003eThe fieldwork campaign took place on the Melville Peninsula during January and February 2023 as part of the Chilean Antarctic Institute\u0026rsquo;s ECA-59 expedition aboard the Betanzos Vessel. Plant macrofossils were found preserved as impressions at two localities, Notho1 (62.019\u0026deg;S, 57.633\u0026deg;W) and Notho2 (62.018\u0026deg;S, 57.632\u0026deg;W) (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e). These fossils are housed in the Palaeontological Collection of Antarctica and Patagonia at the Chilean Antarctic Institute (INACH) in Punta Arenas, Chile. They were examined under a Zeiss Stemi 2000-C stereo microscope, and photographic records were captured using a Sony Alpha 7 III camera with a macro lens. The systematic description followed standardised guidelines\u003csup\u003e\u003cspan citationid=\"CR54\" class=\"CitationRef\"\u003e54\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003e3.2. LA-ICP-MS zircon U-Pb geochronology\u003c/h2\u003e \u003cp\u003eZircon grains were separated from an ash-layer (23JB15) collected in the Cape Melville Formation using standard crushing, hydraulic, magnetic and heavy liquid procedures. They were then mounted and imaged by cathodoluminescence (CL) using a scanning electron microscope (SEM) at the ETH Z\u0026uuml;rich. Laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS) techniques were used to determine trace element abundances and U-Pb ages. A 193 nm Resonetics Resolution S155 laser ablation system was used coupled to a Thermo Element XR, Sector-field single collector ICP-MS\u003csup\u003e\u003cspan citationid=\"CR55\" class=\"CitationRef\"\u003e55\u003c/span\u003e\u003c/sup\u003e. Laser parameters include a 19 \u0026micro;m spot size, a repetition rate of 5 Hz and an energy density of ca. 2 J cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e. The ablation aerosol was mixed in the fast washout S-155 ablation cell (Laurin Technic) with carrier gas consisting of helium (ca. 0.25 L min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) and make-up gas consisting of argon (ca. 1 L min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) and nitrogen (2 mL min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e). The ablated aerosol was then homogenised by flushing through a squid device before introduction into the plasma torch. The single collector sector-field MS is equipped with a high-capacity (80 m\u003csup\u003e\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e\u003c/sup\u003e h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) interface pump to improve sensitivity. Before each analytical session the instrument was optimised with NIST SRM612 glass to achieve a detection efficiency in the range of 1% (on Pb, Th, U) while keeping a low oxides production (\u003csup\u003e248\u003c/sup\u003eThO\u003csup\u003e+\u003c/sup\u003e/ \u003csup\u003e232\u003c/sup\u003eTh\u003csup\u003e+\u003c/sup\u003e \u0026le; 0.25%) and a U/Th ratio of ca. 1. Intensities were recorded for the following isotopes: \u003csup\u003e\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e\u003c/sup\u003eAl, \u003csup\u003e\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e\u003c/sup\u003eSi, \u003csup\u003e\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e\u003c/sup\u003eP, \u003csup\u003e\u003cspan citationid=\"CR89\" class=\"CitationRef\"\u003e89\u003c/span\u003e\u003c/sup\u003eY, \u003csup\u003e\u003cspan citationid=\"CR91\" class=\"CitationRef\"\u003e91\u003c/span\u003e\u003c/sup\u003eZr, \u003csup\u003e\u003cspan citationid=\"CR93\" class=\"CitationRef\"\u003e93\u003c/span\u003e\u003c/sup\u003eNb, \u003csup\u003e137\u003c/sup\u003eBa, \u003csup\u003e139\u003c/sup\u003eLa, \u003csup\u003e140\u003c/sup\u003eCe, \u003csup\u003e141\u003c/sup\u003ePr, \u003csup\u003e146\u003c/sup\u003eNd, \u003csup\u003e147\u003c/sup\u003eSm, \u003csup\u003e153\u003c/sup\u003eEu, \u003csup\u003e157\u003c/sup\u003eGd, \u003csup\u003e159\u003c/sup\u003eTb, \u003csup\u003e163\u003c/sup\u003eDy, \u003csup\u003e165\u003c/sup\u003eHo, \u003csup\u003e167\u003c/sup\u003eEr, \u003csup\u003e169\u003c/sup\u003eTm, \u003csup\u003e173\u003c/sup\u003eYb, \u003csup\u003e175\u003c/sup\u003eLu, \u003csup\u003e178\u003c/sup\u003eHf, \u003csup\u003e181\u003c/sup\u003eTa, \u003csup\u003e202\u003c/sup\u003eHg, \u003csup\u003e204\u003c/sup\u003ePb, \u003csup\u003e206\u003c/sup\u003ePb, \u003csup\u003e207\u003c/sup\u003ePb, \u003csup\u003e208\u003c/sup\u003ePb, \u003csup\u003e232\u003c/sup\u003eTh, \u003csup\u003e235\u003c/sup\u003eU, and \u003csup\u003e238\u003c/sup\u003eU. The full dataset can be found in Supplementary Data file XX, following the community-derived guidelines\u003csup\u003e\u003cspan citationid=\"CR56\" class=\"CitationRef\"\u003e56\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eFor U-Pb geochronology, GJ-1 was used as the primary calibration reference material (CRM). Validating reference materials (VRMs) included Plešovice (337 Ma\u003csup\u003e\u003cspan citationid=\"CR57\" class=\"CitationRef\"\u003e57\u003c/span\u003e\u003c/sup\u003e), Temora (417 Ma\u003csup\u003e\u003cspan citationid=\"CR58\" class=\"CitationRef\"\u003e58\u003c/span\u003e\u003c/sup\u003e) and 91500 (1062 Ma\u003csup\u003e\u003cspan citationid=\"CR59\" class=\"CitationRef\"\u003e59\u003c/span\u003e\u003c/sup\u003e) zircons. The VRMs results show the achievable precision and accuracy of the method, which is in the range of 1.0%. The data was reduced using the software Iolite 4.5\u003csup\u003e60,61\u003c/sup\u003e with VizualAge\u003csup\u003e\u003cspan citationid=\"CR62\" class=\"CitationRef\"\u003e62\u003c/span\u003e\u003c/sup\u003e. No common-Pb correction was applied but integration intervals were set to exclude inclusions, common Pb and discordant parts of the signal. The long-term external uncertainty is in the range of 1.5% for \u003csup\u003e206\u003c/sup\u003ePb/\u003csup\u003e238\u003c/sup\u003eU ages and is composed of the uncertainty from the applied corrections, uncertainty of the decay constants, lacking common-Pb correction, the uncertainty on the true \u003csup\u003e206\u003c/sup\u003ePb/\u003csup\u003e238\u003c/sup\u003eU ratio of the primary standard GJ-1, and possible uncertainty from matrix effects. For trace element quantification we used Si as internal standard at 15.2 wt% SiO\u003csub\u003e2\u003c/sub\u003e in zircons, and SRM NIST610 as external CRM. Ti was quantified by zircon 91500 (Ti: 4.73\u0026thinsp;\u0026plusmn;\u0026thinsp;0.15 mg g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003csup\u003e63\u003c/sup\u003e.\u003c/p\u003e \u003c/div\u003e"},{"header":"4. Results","content":"\u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003e4.1. Systematic \u003cem\u003eNothofagus\u003c/em\u003e description\u003c/h2\u003e \u003cp\u003eTwo samples containing fossilised leaves were collected from siltstone layers of the early Miocene Cape Melville Formation. These rocks are interpreted as part of a glacio-marine depositional environment, providing a rare and valuable insight into the Neogene vegetation of West Antarctica. The samples form the basis for the systematic description of \u003cem\u003eNothofagus\u003c/em\u003e.\u003c/p\u003e \u003cp\u003eClass: Eudicotyledonea.\u003c/p\u003e \u003cp\u003eOrder: Fagales.\u003c/p\u003e \u003cp\u003eFamily: Nothofagaceae.\u003c/p\u003e \u003cp\u003eGenus: \u003cem\u003eNothofagus\u003c/em\u003e Blume, 1851.\u003c/p\u003e \u003cp\u003eType: \u003cem\u003ecf. Nothofagus\u003c/em\u003e sp.\u003c/p\u003e \u003cp\u003eFigure: Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eA-B.\u003c/p\u003e \u003cp\u003eMaterial: Palaeontological Collection of Antarctic and Patagonia CPAP 9105.\u003c/p\u003e \u003cp\u003eLocality: Notho1, Cape Melville, King George Island, Antarctica.\u003c/p\u003e \u003cp\u003eDescription: Incomplete simple leaf, microphyll, measuring 2.0 cm in length and 2.1 cm in width. Apex acute and rounded; margin lobed to serrate. Venation pinnate with a primary vein that is straight and persistent to the apex. Secondary veins craspedodromous, regularly parallel, straight or slightly curved apically, opposite, and terminating in a probable tooth. Tertiary veins are not visible\u003c/p\u003e \u003cp\u003eClass: Eudicotyledonea.\u003c/p\u003e \u003cp\u003eOrder: Fagales.\u003c/p\u003e \u003cp\u003eFamily: Nothofagaceae.\u003c/p\u003e \u003cp\u003eGenus: \u003cem\u003eNothofagus\u003c/em\u003e Blume, 1851.\u003c/p\u003e \u003cp\u003eType: \u003cem\u003ecf. Nothofagus\u003c/em\u003e sp.\u003c/p\u003e \u003cp\u003eFigure: Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eC-D.\u003c/p\u003e \u003cp\u003eMaterial: Palaeontological Collection of Antarctic and Patagonia - CPAP 9106.\u003c/p\u003e \u003cp\u003eLocality: Notho2, Cape Melville, King George Island, Antarctica.\u003c/p\u003e \u003cp\u003eDescription: Fragmentary simple leaf, microphyll, approximately 2.5 cm in length and 2.3 cm wide. The apex is acute and rounded, with a margin ranging from lobed to serrate. Venation is pinnate, with a prominent primary vein extending straight to the apex. Secondary veins are craspedodromous, evenly spaced, straight or slightly curved towards the apex, opposite, and likely terminating in a tooth. Tertiary veins are not visible.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003e4.2. Geochronology\u003c/h2\u003e \u003cp\u003eThe ash layer 23JB15, of andesitic composition, was sampled within a section of the sequence dominated by sandstones, approximately 70 m above the formation boundary with the Destruction Bay Formation (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ea). Cathodoluminescence imaging of zircon grains revealed either (i) oscillatory zonation with distinct cores, or (ii) patchy and homogeneous zoning, with an absence of rim-core relationship, both textural varieties are typical of zircons crystallised in magmatic environment\u003csup\u003e\u003cspan citationid=\"CR64\" class=\"CitationRef\"\u003e64\u003c/span\u003e,\u003cspan citationid=\"CR65\" class=\"CitationRef\"\u003e65\u003c/span\u003e\u003c/sup\u003e (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eb). Ablation of zircons yielded concordant analyses spanning \u003csup\u003e206\u003c/sup\u003ePb/\u003csup\u003e238\u003c/sup\u003eU ages from 19.3\u0026thinsp;\u0026plusmn;\u0026thinsp;1.0 to 68.1\u0026thinsp;\u0026plusmn;\u0026thinsp;3.1 Ma. From these, two main populations are observed: an older cluster that yielded ages between 63.1\u0026thinsp;\u0026plusmn;\u0026thinsp;2.6 and 68.1\u0026thinsp;\u0026plusmn;\u0026thinsp;3.1 Ma, and a younger group with concordant dates between 19.3\u0026thinsp;\u0026plusmn;\u0026thinsp;1.0 and 22.3\u0026thinsp;\u0026plusmn;\u0026thinsp;1.3 Ma (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ec). The latter yields a weighted mean age of 20.97\u0026thinsp;\u0026plusmn;\u0026thinsp;0.22 Ma (n\u0026thinsp;=\u0026thinsp;27, MSWD\u0026thinsp;=\u0026thinsp;1.2, Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ed). The full dataset is available in Supplementary Data file XX.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e"},{"header":"5. Discussion","content":"\u003cdiv id=\"Sec10\" class=\"Section2\"\u003e \u003ch2\u003e5.1 Age of the \u003cem\u003eNothofagus\u003c/em\u003e leaves\u003c/h2\u003e \u003cp\u003eThe \u003cem\u003eNothofagus\u003c/em\u003e leaves discovered in the early Miocene Cape Melville Formation are stratigraphically closely associated with the ash layer 23JB15 (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e). The latter contains zircon grains exhibiting internal oscillatory zoning and homogeneous U-Pb ages, indicating direct magmatic sourcing with minimal, if any, reworking or sedimentary input. Thus, the weighted mean age of 20.97\u0026thinsp;\u0026plusmn;\u0026thinsp;0.22 Ma provides the best estimate for the depositional age of the ash layer and constrains the age of the Cape Melville Formation. No significant stratigraphic discordance or hiatus was identified between the ash layer and the fossiliferous horizon, nor within the entire Cape Melville Formation. Unfortunately, no ash bed has been found above the fossilised leaves to further bracket their age. However, the available evidence suggests that the leaves were deposited between 20 and 22 Ma, making this the youngest plant macrofossil record from West Antarctica.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003e5.2. Post-EOT vegetation evolution of Antarctica: east versus west\u003c/h2\u003e \u003cp\u003eDespite being located in a polar position since at least the Cretaceous\u003csup\u003e\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e,\u003cspan citationid=\"CR66\" class=\"CitationRef\"\u003e66\u003c/span\u003e\u003c/sup\u003e, East Antarctica maintained vegetation dominated by floristically rich forests prior to the EOT\u003csup\u003e\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e\u003c/sup\u003e. This vegetation was diverse in both composition and stature\u003csup\u003e\u003cspan citationid=\"CR67\" class=\"CitationRef\"\u003e67\u003c/span\u003e\u003c/sup\u003e, with forests dominated by \u003cem\u003eNothofagus\u003c/em\u003e, \u003cem\u003eAraucaria\u003c/em\u003e and podocarps, including large trees\u003csup\u003e\u003cspan citationid=\"CR68\" class=\"CitationRef\"\u003e68\u003c/span\u003e\u003c/sup\u003e. This suggests that the climate was not extreme, and vegetation resembled the forests currently found in Patagonia, known vernacularly as \u0026lsquo;Valdivian Forest\u0026rsquo;\u003csup\u003e\u003cspan additionalcitationids=\"CR70\" citationid=\"CR69\" class=\"CitationRef\"\u003e69\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR71\" class=\"CitationRef\"\u003e71\u003c/span\u003e\u003c/sup\u003e. Temperatures fell at the end of the Eocene, leading to the collapse of these forests as a viable ecosystem\u003csup\u003e\u003cspan citationid=\"CR72\" class=\"CitationRef\"\u003e72\u003c/span\u003e\u003c/sup\u003e. The Oligocene pollen records suggest that southern beech forests grew locally, with minor components of podocarps, Proteaceae and other shrubby angiosperms\u003csup\u003e\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e\u003c/sup\u003e. This vegetation type is similar to the present-day Patagonian steppe of bunchgrasses and shrubs or the \u003cem\u003eNothofagus\u003c/em\u003e-podocarp forests of New Zealand. These Oligocene forests were dominated by \u003cem\u003eNothofagus\u003c/em\u003e\u003csup\u003e\u003cspan citationid=\"CR73\" class=\"CitationRef\"\u003e73\u003c/span\u003e\u003c/sup\u003e, which had become reduced in both stature and diversity compared to the pre-EOT vegetation\u003csup\u003e\u003cspan citationid=\"CR74\" class=\"CitationRef\"\u003e74\u003c/span\u003e,\u003cspan citationid=\"CR75\" class=\"CitationRef\"\u003e75\u003c/span\u003e\u003c/sup\u003e. Among these Oligocene vegetational assemblages, the extensive fossil record of \u003cem\u003eNothofagus\u003c/em\u003e subgenus Fuscospora suggests that it may have been the only species\u003csup\u003e\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e,\u003cspan citationid=\"CR76\" class=\"CitationRef\"\u003e76\u003c/span\u003e\u003c/sup\u003e. However, the palaeontological record, largely limited to pollen grains and spores, with very sparse wood and leaves, suggests that this low-diversity tundra-like vegetation persisted after the EOT only in favourable or refugial areas\u003csup\u003e\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e,\u003cspan citationid=\"CR73\" class=\"CitationRef\"\u003e73\u003c/span\u003e,\u003cspan citationid=\"CR77\" class=\"CitationRef\"\u003e77\u003c/span\u003e,\u003cspan citationid=\"CR78\" class=\"CitationRef\"\u003e78\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eIt is uncertain whether this vegetation persisted into the early Miocene, as most of the record is based on pollen evidence\u003csup\u003e\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e,\u003cspan citationid=\"CR75\" class=\"CitationRef\"\u003e75\u003c/span\u003e,\u003cspan citationid=\"CR76\" class=\"CitationRef\"\u003e76\u003c/span\u003e\u003c/sup\u003e. The cold, glacial climate of the Miocene was briefly interrupted by a warm period \u003cem\u003eca\u003c/em\u003e. 17\u0026thinsp;\u0026minus;\u0026thinsp;15 Ma (the Middle Miocene Climatic Optimum; MMCO)\u003csup\u003e\u003cspan citationid=\"CR79\" class=\"CitationRef\"\u003e79\u003c/span\u003e\u003c/sup\u003e. This warming resulted in a temporary increase in both the diversity and stature of East Antarctic vegetation\u003csup\u003e\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e,\u003cspan citationid=\"CR77\" class=\"CitationRef\"\u003e77\u003c/span\u003e,\u003cspan citationid=\"CR80\" class=\"CitationRef\"\u003e80\u003c/span\u003e\u003c/sup\u003e, which facilitated the return of several \u003cem\u003eNothofagus\u003c/em\u003e taxa\u003csup\u003e\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e\u003c/sup\u003e. However, this was immediately followed by abrupt cooling\u003csup\u003e\u003cspan citationid=\"CR81\" class=\"CitationRef\"\u003e81\u003c/span\u003e\u003c/sup\u003e, accompanied by the gradual disappearance of woody plants, although the continued presence of \u003cem\u003eNothofagus\u003c/em\u003e pollen suggests that they may have persisted in glacial refugia in a manner analogous to the glacial refugia detected through Pleistocene glaciations in southern Patagonia\u003csup\u003e\u003cspan citationid=\"CR82\" class=\"CitationRef\"\u003e82\u003c/span\u003e,\u003cspan citationid=\"CR83\" class=\"CitationRef\"\u003e83\u003c/span\u003e\u003c/sup\u003e, which explain the degree of endemism in this part of South America and the speed of subsequent recolonisation\u003csup\u003e\u003cspan citationid=\"CR80\" class=\"CitationRef\"\u003e80\u003c/span\u003e,\u003cspan citationid=\"CR84\" class=\"CitationRef\"\u003e84\u003c/span\u003e\u003c/sup\u003e. After the MMCO, the ice sheet expanded in Antarctica throughout the Neogene and Quaternary, preventing the establishment of woody plants, with the exception of one notable site with tundra-like vegetation of mid-Pliocene age. The latter is found at less than 500 km from the South Pole\u003csup\u003e\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e,\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e,\u003cspan citationid=\"CR85\" class=\"CitationRef\"\u003e85\u003c/span\u003e\u003c/sup\u003e, and had an assemblage similar to that in the modern-day southern Patagonia (Cape Horn)\u003csup\u003e\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e,\u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e\u003c/sup\u003e. This vegetation consisted of cushion-forming mosses and vascular plants with deciduous \u003cem\u003eNothofagus\u003c/em\u003e and rare podocarps\u003csup\u003e\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e,\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e,\u003cspan citationid=\"CR86\" class=\"CitationRef\"\u003e86\u003c/span\u003e\u003c/sup\u003e. Notably, there is a lack of consensus on the age of the rocks that host these fossils\u003csup\u003e\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e,\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e\u003c/sup\u003e and on how these tundra-like forests may have persisted in East Antarctica during the middle Pliocene.\u003c/p\u003e \u003cp\u003eTo the west of the Transantarctic Mountains lies the West Antarctic region which, like East Antarctica, was already located in a polar position during the late Mesozoic\u003csup\u003e\u003cspan citationid=\"CR65\" class=\"CitationRef\"\u003e65\u003c/span\u003e,\u003cspan citationid=\"CR66\" class=\"CitationRef\"\u003e66\u003c/span\u003e,\u003cspan citationid=\"CR87\" class=\"CitationRef\"\u003e87\u003c/span\u003e,\u003cspan citationid=\"CR88\" class=\"CitationRef\"\u003e88\u003c/span\u003e\u003c/sup\u003e. Our understanding of the Cenozoic vegetation evolution of the Antarctic Peninsula has been mostly constrained from the outcrops exposed in King George Island\u003csup\u003e\u003cspan citationid=\"CR89\" class=\"CitationRef\"\u003e89\u003c/span\u003e\u003c/sup\u003e. These outcrops also hold most of the evidence for woody vegetation in West Antarctica\u003csup\u003e\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e\u003c/sup\u003e. Middle Eocene petrified forests are found in the centre-east of the island, revealing a once diverse ecosystem of \u003cem\u003eNothofagus\u003c/em\u003e and \u003cem\u003eAraucaria\u003c/em\u003e conifers, among other species\u003csup\u003e\u003cspan citationid=\"CR67\" class=\"CitationRef\"\u003e67\u003c/span\u003e,\u003cspan citationid=\"CR90\" class=\"CitationRef\"\u003e90\u003c/span\u003e\u003c/sup\u003e, which resembles the modern fern bush communities of southern oceanic islands (e.g. Auckland Island). This vegetation survived until the late Eocene\u003csup\u003e\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e\u003c/sup\u003e, when King George Island was on the locus of the arc axis in the Antarctic Peninsula\u003csup\u003e\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e,\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e\u003c/sup\u003e. After the EOT, as the climate turned colder and drier\u003csup\u003e\u003cspan citationid=\"CR91\" class=\"CitationRef\"\u003e91\u003c/span\u003e\u003c/sup\u003e, the woody vegetation transitioned to tundra-like forests dominated by \u003cem\u003eNothofagus\u003c/em\u003e\u003csup\u003e\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e\u003c/sup\u003e. Although it has been suggested that from the Oligocene onwards there may have been a relatively extensive ice cap in the Antarctic Peninsula, the lateral extent of such an ice-cap remains unclear\u003csup\u003e\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e\u003c/sup\u003e. Nevertheless, the development of an ice-cap during the Oligocene may have caused the tundra-like vegetation to succumb, at least temporarily\u003csup\u003e\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eEvidence for woody vegetation is absent in West Antarctica after the early Oligocene, except for evidence from palynological studies on the early Miocene glacio-marine Cape Melville Formation on King George Island\u003csup\u003e\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e,\u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e\u003c/sup\u003e, which suggest the presence of a monotypic \u003cem\u003eNothofagus\u003c/em\u003e assemblage. Prior to our study, it was not possible to determine whether the source of the \u003cem\u003eNothofagus\u003c/em\u003e pollen was autochthonous or allochthonous, given the anemophilous nature of its grains. Because \u003cem\u003eNothofagus\u003c/em\u003e pollen is so widely wind-dispersed, it is difficult to use palynological evidence alone to reconstruct possible species co-occurrences within local vegetation. However, the macrofossil record does not suffer from this problem, since it is likely that most \u003cem\u003eNothofagus\u003c/em\u003e macrofossils are deposited very close to their source plants\u003csup\u003e\u003cspan citationid=\"CR84\" class=\"CitationRef\"\u003e84\u003c/span\u003e\u003c/sup\u003e. While the Nothofagus leaves were found in the shallow marine Cape Melville Formation, suggesting transport before deposition, this does not preclude the presence of local vegetation, as they were recovered from a land-proximal marine environment\u003csup\u003e\u003cspan citationid=\"CR52\" class=\"CitationRef\"\u003e52\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec12\" class=\"Section2\"\u003e \u003ch2\u003e5.3. Miocene tectonic models of the Antarctic Peninsula and the proximity of other \u003cem\u003eNothofagus\u003c/em\u003e communities\u003c/h2\u003e \u003cp\u003eThe Miocene tectonic history of the Antarctic Peninsula provides context for assessing the persistence of \u003cem\u003eNothofagus\u003c/em\u003e communities in West Antarctica during the early Miocene. The geological history of the Antarctic Peninsula is dominated by the development of a continental arc throughout the Mesozoic and part of the Cenozoic\u003csup\u003e\u003cspan citationid=\"CR65\" class=\"CitationRef\"\u003e65\u003c/span\u003e,\u003cspan citationid=\"CR92\" class=\"CitationRef\"\u003e92\u003c/span\u003e\u003c/sup\u003e, which was the result of the eastward subduction of the oceanic lithosphere of the Phoenix Plate\u003csup\u003e\u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e47\u003c/span\u003e\u003c/sup\u003e. This subduction system waned during the Cenozoic to eventually cease at \u003cem\u003eca\u003c/em\u003e. 20 Ma\u003csup\u003e\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e,\u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e47\u003c/span\u003e,\u003cspan citationid=\"CR93\" class=\"CitationRef\"\u003e93\u003c/span\u003e\u003c/sup\u003e. The sea floor remnants of the region and paleomagnetic studies have been used to reconstruct this sector of Antarctica and South America and suggest that during the Jurassic and Cretaceous, Patagonia was in juxtaposition to the north of the Antarctic Peninsula\u003csup\u003e\u003cspan citationid=\"CR87\" class=\"CitationRef\"\u003e87\u003c/span\u003e,\u003cspan citationid=\"CR93\" class=\"CitationRef\"\u003e93\u003c/span\u003e\u003c/sup\u003e. Therefore, during this period, there would have been a strong floral and faunal connection between these two regions\u003csup\u003e\u003cspan citationid=\"CR69\" class=\"CitationRef\"\u003e69\u003c/span\u003e\u003c/sup\u003e. However, during the Cenozoic the Antarctic Peninsula drifted to the south with respect to South America as a response to the formation of the Scotia Plate, a sliver of oceanic lithosphere located between the Antarctic and the South American plates\u003csup\u003e\u003cspan citationid=\"CR94\" class=\"CitationRef\"\u003e94\u003c/span\u003e\u003c/sup\u003e (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e). This extension led to the opening of the Drake Passage, which effectively disconnected Antarctica from South America, causing the isolation of the Antarctic continent from any other landmass and setting up the Antarctic Circumpolar Current\u003csup\u003e\u003cspan citationid=\"CR95\" class=\"CitationRef\"\u003e95\u003c/span\u003e\u003c/sup\u003e. This event, which occurred near to the EOT, marks the onset of the Late Cenozoic Ice Age\u003csup\u003e\u003cspan citationid=\"CR94\" class=\"CitationRef\"\u003e94\u003c/span\u003e\u003c/sup\u003e and is considered, at least in part, to have contributed to the initiation of this Earth period\u003csup\u003e\u003cspan citationid=\"CR96\" class=\"CitationRef\"\u003e96\u003c/span\u003e\u003c/sup\u003e. Throughout the Palaeogene the Antarctic Peninsula experienced counterclockwise rotation, which caused it to progressively further separate from Patagonia\u003csup\u003e\u003cspan citationid=\"CR93\" class=\"CitationRef\"\u003e93\u003c/span\u003e\u003c/sup\u003e. During the early Miocene, when the Cape Melville Formation was deposited, it is estimated that the Antarctic Peninsula, and thus King George Island as well, was more than 500 km to the south with respect to Patagonia\u003csup\u003e\u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e47\u003c/span\u003e,\u003cspan citationid=\"CR93\" class=\"CitationRef\"\u003e93\u003c/span\u003e\u003c/sup\u003e (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e). While anemophilic pollen may be able to travel significant distances\u003csup\u003e\u003cspan citationid=\"CR97\" class=\"CitationRef\"\u003e97\u003c/span\u003e\u003c/sup\u003e and tundra-like vegetation was present in southern Patagonia during the mid- and late Cenozoic\u003csup\u003e\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e,\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e\u003c/sup\u003e, it is unlikely that leaves could have been transported and preserved more than 500 km south. This supports our argument that the \u003cem\u003eNothofagus\u003c/em\u003e leaf fossils originated from an autochthonous tundra-like forest.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec13\" class=\"Section2\"\u003e \u003ch2\u003e5.4. Survival or Recolonisation?\u003c/h2\u003e \u003cp\u003eThe presence of \u003cem\u003eNothofagus\u003c/em\u003e-dominated tundra-like forests as recently as the early Miocene in West Antarctica (this work) and the mid-Pliocene in East Antarctica raises the question of whether these species were resilient and adapted to survive in glacial refugia to changing climatic conditions throughout the Neogene, or briefly recolonised Antarctica under particularly favourable conditions during warm intervals. From an autoecological perspective, \u003cem\u003eNothofagus\u003c/em\u003e seed dispersal is by gravity and wind (anemochory), while germination is generally epigeal and occurs not far from the seed-producing tree crown\u003csup\u003e\u003cspan citationid=\"CR98\" class=\"CitationRef\"\u003e98\u003c/span\u003e\u003c/sup\u003e. Although some authors argue that \u003cem\u003eNothofagus\u003c/em\u003e seeds can disperse over long transoceanic distances\u003csup\u003e\u003cspan citationid=\"CR98\" class=\"CitationRef\"\u003e98\u003c/span\u003e\u003c/sup\u003e, there is still a significant body of research that claims that their seeds are intolerant to seawater\u003csup\u003e\u003cspan additionalcitationids=\"CR100\" citationid=\"CR99\" class=\"CitationRef\"\u003e99\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR101\" class=\"CitationRef\"\u003e101\u003c/span\u003e\u003c/sup\u003e, and so would have been unable to recolonise the Antarctic Peninsula from the southern tip of South America after the Drake Passage opened during the Paleogene\u003csup\u003e\u003cspan citationid=\"CR102\" class=\"CitationRef\"\u003e102\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eThe base of the Cape Melville Formation is marked by a glacial diamictite, suggesting that the ice grounding line extended into the marine realm. This glacial advance is generally correlated with the Mi-1 and Mi-1a events, which occurred close to the Oligocene-Miocene boundary\u003csup\u003e\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e,\u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e46\u003c/span\u003e\u003c/sup\u003e. Following this, the marine sedimentary succession evolved from to ice-proximal and then ice-distal conditions prior to the deposition of the rocks hosting the \u003cem\u003eNothofagus\u003c/em\u003e leaf macrofossils\u003csup\u003e\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e,\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e,\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e\u003c/sup\u003e. The presence of tundra-like forest thus coincides with evidence for a climate amelioration in this part of Antarctica. The evidence for extensive ice cover at the Oligocene-Miocene boundary indicates that this site is itself unlikely to have been a persistent glacial refugium.\u003c/p\u003e \u003cp\u003eThe sparse occurrence of Neogene woody macrofossils in Antarctica may indicate that \u003cem\u003eNothofagus\u003c/em\u003e recolonised Antarctica during warmer intervals in suitable locations via long-distance dispersal, rather than persisting without interruption. This is based on the premise that continuous persistence would have yielded, albeit locally, a continuous record of woody plant fossils. Episodic recolonisation from tundra-like vegetational relicts would result in a more fragmented fossil record, which better fits the observed macrofossil data. Tundra-like forests existed in regions subjected to glacial conditions during this period, including Patagonia and Oceania\u003csup\u003e\u003cspan citationid=\"CR103\" class=\"CitationRef\"\u003e103\u003c/span\u003e,\u003cspan citationid=\"CR104\" class=\"CitationRef\"\u003e104\u003c/span\u003e\u003c/sup\u003e, and potentially could have acted as seed sources for the resurgence of these forests in Antarctica. However, the absence of fossils does not necessarily disprove the presence of glacial refugia. Both the lack of appropriate sedimentation conditions and the inaccessibility of many sedimentary strata could produce a discontinuous and incomplete fossil record. In addition, the mechanism by which long-distance dispersal may have occurred remains unclear.\u003c/p\u003e \u003cp\u003eThe record of tundra-like vegetation in East Antarctica after the early Miocene is limited to two episodes: the MMCO\u003csup\u003e\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e\u003c/sup\u003e and the mid-Pliocene\u003csup\u003e\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e,\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e\u003c/sup\u003e (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e). The fossiliferous site dated to the latter is located less than 500 km from the South Pole. If such latitudes were populated by \u003cem\u003eNothofagus\u003c/em\u003e-dominated forest relicts during these periods, it is reasonable to assume that this vegetation was also present at lower latitudes of Antarctica. However, direct macrofossil evidence is absent in West Antarctica after the early Miocene. Although the evidence presented here represents a significant advance in our understanding of the Neogene vegetation history of West Antarctica, the question of persistence or recolonisation remains unresolved.\u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003e5. 5. Stability of the Neogene ice-cap\u003c/h3\u003e\n\u003cp\u003eThe presence of low-diversity tundra-like vegetation either temporarily recolonising Antarctica during favourable conditions or persisting through the Late Cenozoic Ice Age has critical implications for understanding the stability of the Antarctic ice sheet. Although consecutive glaciations followed the EOT, during which the ice cap is conservatively estimated to have reached 80\u0026ndash;110% of its modern volume\u003csup\u003e\u003cspan citationid=\"CR105\" class=\"CitationRef\"\u003e105\u003c/span\u003e\u003c/sup\u003e, the presence of tundra-like forests suggests that at least some sectors remained ice-free during warm periods or possibly throughout the Neogene, lasting as late as the Pliocene. These findings challenge the assumption of a stable Antarctic ice sheet since the EOT. Furthermore, evidence indicates that ice sheets could have melted rapidly during brief warm periods\u003csup\u003e\u003cspan additionalcitationids=\"CR107 CR108\" citationid=\"CR106\" class=\"CitationRef\"\u003e106\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR109\" class=\"CitationRef\"\u003e109\u003c/span\u003e\u003c/sup\u003e, demonstrating their sensitivity to climate warming. This highlights the potential for rapid changes in the Antarctic ice cap under current global warming scenarios, where the return of woody vegetation could occur relatively quickly.\u003c/p\u003e"},{"header":"6. Conclusions","content":"\u003cp\u003eThe \u003cem\u003eNothofagus\u003c/em\u003e leaf imprints from the Cape Melville Formation on King George Island presented here (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e), combined with our geochronological results (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e), provide the first robust evidence for the presence of tundra-like vegetation in West Antarctica during the early Miocene, suggesting that tundra-like forests were present in the region at least between 22 and 20 Ma and potentially even before this period, establishing it as the youngest woody macrofossil record from West Antarctica. This new finding advances the debate surrounding palynoflora-based interpretations of Neogene tundra-like forests in West Antarctica. Furthermore, it fills critical gaps in our understanding of how woody vegetation became extinct in Antarctica and underscores the remarkable adaptability of \u003cem\u003eNothofagus\u003c/em\u003e within Antarctic ecosystems.\u003c/p\u003e \u003cp\u003eLocalised refugia with tundra-like vegetation in West Antarctica may have either survived numerous glaciations since the EOT or recolonised during warm interglacial periods. King George Island likely served as such an enclave during the early Miocene, suggesting a more complex climatic history than previously thought. This implies that Antarctic conditions may not have been uniformly harsh for woody vegetation, at least episodically. The biology of \u003cem\u003eNothofagus\u003c/em\u003e and its syndrome of reproduction argue against recolonisation from nearby areas (e.g. Patagonia). On the other hand, repopulation of tundra-like forests in Antarctica from glacial refugia is also uncertain, as the ice sheet should have reached volumes during the Late Cenozoic Ice Age that were similar to or greater than those of the present day. Therefore, whether tundra-like vegetation recolonised Antarctica or persisted under the harsh conditions of the Late Cenozoic Ice Age remains a challenging and open question, which should be the focus of future studies.\u003c/p\u003e \u003cp\u003eThe presence of early Miocene tundra-like vegetation in West Antarctica suggests that the vegetation dynamics may have been more synchronised between East and West Antarctica than previously assumed, highlighting the complex stability of Antarctica\u0026rsquo;s ice sheet.\u003c/p\u003e"},{"header":"Declarations","content":"\u003ch2\u003eAcknowledgements\u003c/h2\u003e \u003cp\u003eJBS was funded by the Swiss National Science Foundation (project P5R5PN_217947) and the project RT-01-22 funded by the Chilean Antarctic Institute (INACH). LG was funded by the Natural Science Foundation of China (NSFC) (42322607 and 42076223). Fieldwork on the Antarctic Peninsula was supported by the Chilean Antarctic Institute. Especial thanks to the team supporting in the field Georgette Mell, Billy Wallace and Ignacio Reyes.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eGreen TGA, Schroeter B, Sancho LG (2007) Plant Life in Antarctica. in \u003cem\u003eFunctional Plant Ecology\u003c/em\u003e. CRC\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eAllegrucci G, Carchini G, Todisco V, Convey P, Sbordoni V (2006) A molecular phylogeny of antarctic chironomidae and its implications for biogeographical history. Polar Biol 29:320\u0026ndash;326\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eConvey P et al (2008) Antarctic terrestrial life \u0026ndash; challenging the history of the frozen continent? Biol Rev 83:103\u0026ndash;117\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eCantrill DJ, Poole I (2012) The Vegetation of Antarctica through Geological Time. 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Nature 413:719\u0026ndash;723\u003c/span\u003e\u003c/li\u003e\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":"","lastPublishedDoi":"10.21203/rs.3.rs-6148923/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-6148923/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThe extinction of woody vegetation in Antarctica remains difficult to constrain due to its fragmented macrofossil record. Despite its long-standing polar position, Antarctica hosted extensive vegetation throughout the Paleogene. This changed near the Eocene-Oligocene Transition (ca. 34 Ma) as glaciation led to vegetation decline. Sparse evidence suggests tundra-like forests persisted until the Pliocene in East Antarctica, but the Neogene record from West Antarctica is largely restricted to palynoflora data. Here, we report early Miocene plant macrofossils from West Antarctica, consisting of Nothofagus leaves. U-Pb zircon geochronology confirms tundra-like vegetation existed in this region during the early Miocene (ca. 22\u0026ndash;20 Ma), representing the youngest macrofossil record of West Antarctica. These findings suggest that \u003cem\u003eNothofagus\u003c/em\u003e either persisted through Antarctica\u0026rsquo;s harsh Late Cenozoic Ice Age conditions or recolonised during intermittent warm periods. This significantly advances our understanding of West Antarctica\u0026rsquo;s vegetation history and extends the known record of \u003cem\u003eNothofagus\u003c/em\u003e in Antarctic ecosystems.\u003c/p\u003e","manuscriptTitle":"Neogene plant macrofossils from West Antarctica reveal persistence of Nothofagaceae forests into the Early Miocene","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-04-26 11:09:27","doi":"10.21203/rs.3.rs-6148923/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":"64e4b72f-4ff5-44e1-aadd-e9ac67a2fba3","owner":[],"postedDate":"April 26th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[{"id":45927469,"name":"Biological sciences/Evolution/Palaeontology"},{"id":45927470,"name":"Earth and environmental sciences/Climate sciences/Palaeoclimate"},{"id":45927471,"name":"Earth and environmental sciences/Climate sciences/Cryospheric science"}],"tags":[],"updatedAt":"2025-11-27T08:13:00+00:00","versionOfRecord":{"articleIdentity":"rs-6148923","link":"https://doi.org/10.1038/s43247-025-02921-x","journal":{"identity":"communications-earth-and-environment","isVorOnly":false,"title":"Communications Earth \u0026 Environment"},"publishedOn":"2025-11-26 05:00:00","publishedOnDateReadable":"November 26th, 2025"},"versionCreatedAt":"2025-04-26 11:09:27","video":"","vorDoi":"10.1038/s43247-025-02921-x","vorDoiUrl":"https://doi.org/10.1038/s43247-025-02921-x","workflowStages":[]},"version":"v1","identity":"rs-6148923","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-6148923","identity":"rs-6148923","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}