Compaction of organic-rich carbonate and siliceous mud: mechanism, rate, typical structures. Case studies from Domanik Formation (Russia).

Compaction of organic-rich carbonate and siliceous mud: mechanism, rate, typical structures. Case studies from Domanik Formation (Russia). | 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 Research Article Compaction of organic-rich carbonate and siliceous mud: mechanism, rate, typical structures. Case studies from Domanik Formation (Russia). Roman Viktorovich Mirnov This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-8412682/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 4 You are reading this latest preprint version Abstract This article examines the compaction of organic-rich siliceous-carbonate sediments, using Upper Devonian-Lower Carboniferous deposits in the southeastern East European Platform as an example. The study is based on the analysis of deep-well core samples containing rocks with varying organic carbon contents. The methodology includes petrographic analysis of thin sections and sedimentological study of the core. Typical features of compaction were identified: the formation of folded calcite veins filled with calcite, the development of saucer-shaped concretions, and flat-pebble breccias. It was established that the degree of rock compaction can exceed threefold. Particular attention is paid to the study of deformation structures arising during compaction. It was found that specific structures reflecting the plastic state of the sediment are formed in layers with high organic matter contents. The mechanisms of silica and calcite redistribution during compaction, as well as the interactions between compacting and early lithified layers, were studied. The results obtained provide a better understanding of sedimentary rock transformation processes and can be used to reconstruct depositional environments and subsequent diagenetic transformations. This study contributes to our understanding of the mechanisms of deformation structure formation in organic-rich sediments. compaction deformation structures fractures flat-pebble breccias Domanik Formation hydrocarbon migration Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 Introduction The transformation of sediment into rock is accompanied by its dehydration and volume reduction. The degree of sediment compaction depends on its initial composition; clayey and carbonate silts undergo maximum compaction. The most stable sediments are those composed of initially solid components — sands, pebbles, and, especially, reef carbonates, which are characterized by lithification that virtually occurs during their life. Sediment compaction has been studied by many scientists since the early twentieth century. One of the first works devoted to analyzing the causes of compaction was the work of the US geologist H.K. Sorby (Sorby, 1908), who proposed the dependence of porosity on pressure and rock age. Work on compaction can be roughly divided into three groups. The first group of studies is based on the study of the porosity of already compacted rocks in deep wells. Thus, one of the first compaction curves for clay rocks with depth (Hedberg, 1926, Hedberg, 1936) was constructed based on porosity measurements of Cenozoic clays in a well section in Venezuela. This was later criticized by N.B. Vassoevich (Vassoevich, 1960) for underestimating the influence of eroded sediments. Instead, a curve constructed using data from the Alexandria borehole, drilled in a zone of sustainable tectonic subsidence, was proposed. This revealed a nearly twofold increase in dry rock density upon submersion to a depth of 5 km (from 1.4 g/cm3 to 2.7 g/cm3). The second group involves studying the surface layer of bottom sediments. Such studies have been known since the middle of the last century (Rittenberg, 1952, Bruevich, 1945, Lisitsyn, 1956 etc.). One modern study on the compaction of varve lake sediments in Northern Sweden (Maier et al., 2013) presents data on a 70% reduction in clay layer thickness upon submersion to a depth of 12 cm over 33 years. The third group of studies is based on laboratory experiments on rock compression under pressure. P. Trask (1931) first conducted laboratory experiments centrifuging marine bottom sediments of varying grain sizes and found that the coarser-grained varieties were less susceptible to compaction than microgranular silts, which shrank more than twofold in volume. Similar experiments were later conducted on carbonate rocks (Croizé et al., 2013). Methods for monitoring the degree of flattening of small-sized objects deserve special mention. For example, measuring the asymmetry of cross-sections of burrows (Railsback, 1993) or the relationship of early diagenetic formations (carbonate nodules, pyrite concretions, etc.) to the thickness of the enclosing layer (Abu-Mahfouz, 2023). The object of this study is siliceous-carbonate rocks enriched in dispersed organic matter. They contain virtually no clay minerals, so the compaction processes in them differ significantly from those in clays, which have been the subject of numerous published studies (Vassoevich, 1960, Nesterov, 1965, Mukhin, 1965, Buryakovskiy, 1991, etc.). J. M. Weller (Weller, 1959) noted the complexity of the problem and the insufficient study of the nature of sediment compaction, including its dependence on composition. It is common to distinguish between mechanical compaction ("squeezing out" water) and dissolution under pressure, but these processes are often inextricably linked, making the problem even more complex. In the succinct words of N. M. Strakhov, "The driving force of diagenesis is the internal contradictions in the material composition of the sediment, gradually eliminated through the transformation of the mineralogical form of reactive substances and their adaptation to one another" (Strakhov, 1960). Dispersed organic matter serves as an important actor for diagenetic transformations (reactive matter). Therefore, rocks with high organic matter content are of particular interest. The study of compaction processes has not only theoretical but also practical significance. Uneven compaction of sediments with different compositions during subsidence (differential compaction) can cause the formation of anticlinal structures above carbonate buildups, sandstone lenses, etc., without the influence of tectonic factors. For example, a significant number of oil deposits in the Upper Devonian and Carboniferous of the Volga-Ural petroleum province are confined to such anticlinal traps above Frasnian-Lower Famennian reefs (Mkrtchyan, 1980; Bera and Carminati, 2012; etc.). Compaction processes must be studied to reconstruct the original rock thickness and accurately calculate the paleodepths of the basin, which, in turn, can be used for facies reconstructions, basin modeling, etc. In recent years, an increasing number of publications have appeared on the threat of flooding of vast territories in areas of modern deltas as a result of sediment compaction (Teatini et al., 2011; Zoccarato et al., 2018). Thus, the processes being studied can have a direct impact on human economic activity. Any reduction in rock volume leads to the emergence of new textural features that must be correctly interpreted. Taking this factor into account may be key to understanding the genesis of mysterious and not fully deciphered structures, common, among other things, in Precambrian rocks. Rocks enriched in organic matter (OM) are always considered a potential source of hydrocarbon generation. Despite numerous studies on the geochemical study of these rocks, the mechanism of fluid migration itself remains an incompletely understood process. The relationship between the compaction of petroleum source rocks and the removal of hydrocarbon fluids from them remains an open question. Thus, sediment compaction is associated with a wide variety of scientific fields. Materials and Methods The material for this study was deep-well core collected from the Domanik Formation in the southeastern East European Platform. A stratotype outcrop near the Domanik Stream was also studied. A sedimentological study of the core was conducted, with particular attention paid to deformation structures. Microscopic examination of 300 thin sections was performed using a Zeiss Axiolab A1 microscope. The mineralogy of the rocks was determined using X-ray diffraction (XRD) on each sample. To exclude erroneous interpretation of deformation structures, the absence of deep faults in the study area was previously confirmed using seismic data and borehole microimagers. In addition to studying the Domanik Formation, core from the Proterozoic Kaltasinskaya Suite in well 1VAK was also studied. The study revealed that some structures, previously interpreted as the result of compaction, are also found in Precambrian rocks. These structures were systematized and also served as material for studying compaction processes. To analyze the degree of compaction and construct a compaction curve, wells drilled in the zone of facies replacement of isolated carbonate reefs by Domanik Formation sediments were selected. Interwell correlation was conducted for subsequent analysis of thickness variations. In this article, the term "reef" is used in the sense of "seismic reef" and does not include analysis of reef paleoecology. The term "organic-rich shales" refers to thin-bedded rocks with a high content of organic matter, but not clay material. Geological settings The Domanik Formation is developed in the eastern part of the East European Platform and spans the Frasnian-Tournaisian stratigraphic interval. The Domanik Formation is thickest (up to 300 m) and most stratigraphically complete in the axial parts of the Kama-Kinel trough system. Its name derives from the Domanik Creek, where the stratotype of the Middle Frasnian Domanik horizon is located (Fig. 1 ). The rocks of the Domanik Formation are characterized by a siliceous-carbonate composition and a high content of dispersed organic matter, which ranges from tenths of a percent to 30% or more of the rock volume. The highest organic matter concentrations are observed in the stratigraphic interval of the Middle Frasnian Domanik horizon. Most researchers agree that the rocks of the Domanik Formation are the main oil-producing rocks of the Volga-Ural petroleum province. In the study area, the Domanik Formation is relatively immature: Tmax values range from 430–435 degrees Celsius. The organic matter of Domanik appears to be of type II-S. Faunal remains include tentaculites, radiolarians, ostracods, and, to a lesser extent, brachiopods, foraminifera, gastropods, nautiloids, and ammonoids. Tentaculites are predominantly characteristic of the Domanik horizon and typically occur as flattened and thinned shells oriented along the bedding plane. Radiolarians are often very poorly preserved, with the exception of calcified varieties with a regular isometric shape. One of the typical features of the rocks is the frequent alternation of millimeter-thick interlayers of varying compositions with sharply variable organic carbon content. Thin interlayers enriched in tuffaceous material are found in the section. Rocks of the Lower Riphean Kaltasinskaya suite were studied in the core of the well 1 VAK (Vostochno-Askinskaya). They share features with rocks of the Domanik Formation: elevated organic carbon content, minimal clay mineral content, and frequent alternation of thin interlayers of varying lithology. The organic matter of the Kaltasinskaya suite rocks is represented by non-pyrolyzable carbon. Results Folded Veins One of the most striking indications of significant compaction of Domanik sediments is the presence of folded veins mineralized by calcite (Fig. 2 ). They range in length from tenths of a millimeter to a few centimeters, gradually decreasing in width toward the bottom. Folded veins are found in interlayers of siliceous-carbonate rocks or limestones, which are particularly rich in organic matter. Sometimes, cracks intersect several layers with different lithology. In such cases, they are straight and subvertical in layers of organic-poor limestones and cherts, continuing in a crumpled form in low-siliceous layers enriched in organic matter (Fig. 2 C). Typically, such fractures originate at the boundary between layers with different lithologies and attenuate both at the layer boundaries and within the OM-rich layer. Folded veins have smooth outlines, indicating the plastic state of the calcite filling them during compression. Figure 2 , A shows a folded vein, between whose bends are remnants of lighter limestone, preserved before significant compaction and an increase in the OM concentration in the matrix. Vein breaks likely formed during further compaction of the rock after the final crystallization of the calcite filling the fracture. Measurements of the ratio of the length of a folded vein (3 mm) to the thickness of the host layer (0.97 mm) (Fig. 2 B) in two dimensions (in three dimensions, it will be even greater) in thin section show that from the time the fracture formed until its lithification, the rock compacted more than threefold. Considering the presence of veins, the degree of further compaction can be roughly estimated. Another example (Fig. 2 C, 2 D) shows a fracture intersecting several thin layers. In a layer of light-colored limestone, it appears as a subvertical straight line, then begins to meander in the underlying organic-rich layer. Here, the degree of compaction of the host rock after calcite crystallization in the "crumpled" fracture can be estimated by the change in layer thickness along the fracture (11.7 mm) and further away from it (7 mm). In this case, the crystallized fracture acts as a "spacer" for the layer, preventing it from further compaction. The final visible compaction of the rock is 26 mm/7 mm (3.7 times). The "straightening" of cracks where they intersect light-colored limestones and cherts indicates a significantly earlier lithification of the latter. Concretions Another picturesque example of the relationship between compacted and lithified rocks during the early stages of diagenesis are the loaf-shaped concretions of light-colored limestones, occurring among the thinly layered, OM-rich rocks that envelop them (Fig. 3 ). Concretions are located at discontinuous layers in the section, and the "swells," located linearly along the stratification are convenient to use as benchmarks when describing outcrops. They have a slightly flattened shape and range in size from a few centimeters to several tens of centimeters. Large ammonoid or nautiloid shells are often serving as crystallization centers within the nodules. The nodules are composed of tentaculite limestones or calcified radiolarites. Remnants of parallel lamination, preserved from the initial sediment to compaction, can often be observed within the nodules (Fig. 3 B, 3 C). When comparing the internal structure of the nodules with the host rocks, the latter are distinguished by a significantly higher organic matter content and the shape of the calcite shell fragments. These are significantly thinned and flattened to form indefinable filiform veinlets. The organic-rich rocks enclosing the nodules in different parts vary in morphology and the number of calcite fossils. Near the widest part, they occur as isolated, very thin relics, increasing in number and thickness fan-shaped toward the periphery of the nodule (Fig. 3 D, 3 E). Similar concretions have been described in many clayey and limestone strata, with high organic carbon content. The ratio of the thickness of the central part of the nodule to the thickness of the corresponding horizontal layer is often used by various authors to calculate the degree of compaction. In Domanik deposits, this ratio reaches 10 (Fig. 3 A). It should be noted that chert nodules are also found in these deposits, but they are significantly less widespread and thickness. Redistribution of Silica and Calcite During Compaction Short, subvertical mineralized fractures are common in Domanik Formation, which can be mistakenly interpreted as the result of tectonic activity. These fractures, obviously formed by rock compaction, are evidence of a multistage redistribution of calcite and silica. The fractures are developed in limestone interbeds, and are longest in intervals where organic-rich rocks occur as thin, centimeter-size interbeds within the main mass of wackstones (Fig. 4 ). Thinned shell remains similar to those described above are observed within the organic-rich layers. The layers themselves have variable thickness, and the fractures originate at points of localized thickening (at "breakthrough points"). Most often, the fractures are directed from bottom to top, although thinner fractures directed from top to bottom are also present. At the sites of fracture attenuation, significant areas of silicification are observed within the limestone layer, reminiscent of smoke escaping from a factory chimney or fluid injected under pressure from a thin syringe needle (Fig. 4 A). Furthermore, silicification is observed along the fracture margins, indicating its earlier deposition compared to the calcite filling the fracture. The calcite itself is represented by several generations, the most recent of which exhibits a brownish color and bitumen admixtures (Fig. 4 B, 4 C; Fig. 5 C, 4 D). Importantly, the OM does not fill the pores, but rather colors the crystals themselves, indicating the release of hydrocarbons during fracture mineralization (during compaction). Thus, we observe multiple reactivations of fractures after their formation as a result of rupture of the overlying layer under fluid pressure. The crack appeared as a result of a breakthrough of a solution saturated with silica, after which, in the process of further compaction, the stages of crystallization of silica and calcite alternated. With more frequent intercalation of limestones and OM-rich siliceous-carbonate rocks, a variety of fracture combinations are observed (Fig. 6 ), demonstrating the multistage nature of silica and calcite redistribution during diagenesis. Folded veins are observed exclusively in low-siliceous layers enriched in OM. When such fractures intersect radiolarite layers (Fig. 6 C), they retain a straight shape, indicating significantly earlier crystallization of cherts. Straight fractures in limestones mineralized with calcite always point upward, which is likely due to the lower density of the overlying sediments compared to the underlying sediments. Limestones contain not only mineralized fractures but also fractures partially filled with organic-rich siliceous-carbonate material pressed in from the adjacent layer (Fig. 6 B). Compaction-Related Deformation Structures Domanik-type rocks accumulated under conditions of uncompensated sedimentation and remoteness of the provenances of terrigenous and carbonate material. Therefore, they exhibit virtually no resuspension or slumping structures, with a predominantly fine parallel stratification. However, they do exhibit ductile deformation structures, related to compaction of the rocks (Fig. 7 ). Limestone layers embedded in siliceous-carbonate rocks, which are highly enriched in organic matter (15% or more), exhibit unusual structures—mushroom-shaped intrusions of organic-rich rocks into the limestone. These intrusions are most often directed upward, and when they are directed toward each other, the intrusions at the base of the limestone have a greater amplitude (Fig. 7 A, 7 B). 7C shows a photograph of a core sample showing deformed clusters of tentaculite shells forming thin laminae. Such structures can hardly be interpreted as primary sedimentation. They indicate elevated pressure in rocks enriched in organic matter, which acted on the as-yet-unlithified sediment and led to the development of ductile deformations. Discussion Breccia Formation by Compaction Along with the ductile deformations that occurred before sediment lithification, brittle deformation structures are also encountered, formed by the interaction of thin layers of lithified carbonates and still ductile organic-rich shales. Such structures can be called "compaction breccias." They are found in rocks richest in organic matter, where they host thin (1–3 cm) early-lithified limestone layers (Fig. 8 ). Figure 8 A shows a photograph of a core section showing brittle deformations of the initial (lower part) and final (upper part) stages of breccia formation. Brittle deformations are manifested in numerous cracks that cut through the limestone layer from below and above, some of which have encroached the host rock. The breccia interlayer lies among completely undisturbed thin-layered rocks and shows no signs of ordering of the fragments, imbrication or gradational sorting. These breccias clearly show that the fragments lack any signs of rounding and represent parts of a single layer, which can be mentally connected like pieces of a construction set (Fig. 8 D, 8 E). Figure 8 C shows a photograph of a core sample, which, as in the examples shown above, shows the intrusion of organic-rich rocks into the overlying limestone layer. However, in this case, they do not deform this limestone layer, but partially fragment it, forming an unusual breccia in which the fragments, seemingly defying the laws of gravity, are located at the top of the layer. It is important to note another observation: bitumen segregations are present in the "compaction breccias," namely, in the filler (Fig. 7 C). This clearly indicates a connection between deformation (compaction) processes and the transformation of organic matter. The described "compaction breccias" have morphological similarities to flat-pebble breccias common in Precambrian rocks. Figure 9 , using Proterozoic (Lower Riphean) deposits from well 1VAK as an example, shows deformation structures identical to those recorded in Domanik Formation. The fragments (“clasts”) in the flat-pebble breccias (Fig. 9 D) are unrounded fragments of thin layers separated by compaction. Within the intervals of flat-pebble breccia development, one can observe ductile deformations (Fig. 9 A), straight mineralized fractures emerging from thin layers of organic-rich rocks, and intrusions of host rocks into limestones (Fig. 9 B). The studied intervals containing flat-pebble breccias are represented by frequent alternation of thin (1–3 cm) layers of light-colored limestones and dark-colored organic-rich carbonates. The small thickness of the limestone interlayers and their early lithification are likely the main cause of the formation of flat-pebble breccias as a result of compaction. A similar mechanism for their formation has been considered by some authors (Chen et al., 2010, Chen et al., 2015); however, they did not provide similar examples from Phanerozoic deposits. The material presented in this article allows for a more substantiated interpretation of these ambiguous structures as the result of compaction of carbonate organic-rich mud. Differential compaction can also lead to breccia formation. Figure 10 shows an example of a natural object ideally suited for studying the mechanism of differential compaction. The correlation diagram of wells located no more than a kilometer apart shows that the interval of Domanik Formation in wells 78 and 91 (Fig. 9 D) corresponds to a non-radioactive interval of reef carbonate rocks in well 92 In addition, the reef is covered by a similar layer of Domanik-type rocks. This relationship between the rocks can be explained by the sedimentation and compaction diagram shown in Fig. 10 A, 10 B, 10 C. As a result of rising relative sea level, the reef ceased was submerged, after which it was buried for a long time under condensed organic-rich sediments. The modern structure arose after the compaction of the latter. During compaction and tensile forces applied to the organic-rich rock unit in borehole 92, structures virtually indistinguishable from tectonic breccias were formed (Fig. 10 E). It should be noted that seismic and borehole data show no signs of any faults in the studied area, therefore, the presence of tectonic breccias is excluded. The organic-rich interval in borehole 92 is represented by carbonate-siliceous rocks and cherts, which underwent earlier lithification than the low-siliceous varieties. Further compaction of the surrounding rocks resulted in brittle deformations and breccia development. Calculating the Degree and Rate of Compaction This article attempts to calculate the degree and rate of compaction with subsidence using the high-amplitude Volkovskiy reef, located in the South-East part of the East-European Platform, as an example. In the well that penetrated reef body (Fig. 11 , Well No. 230), reef carbonates occur in the Upper Frasnian-Famennian interval of the section, while in the nearest well, No. 42 (located 3,280 m from well No. 230), this interval is characterized by Domanik type organic-rich rocks. An anticlinal structure forms above the organogenic structure, which is evident throughout the entire interval of the overlying Carboniferous-Permian sediments. This allows us to estimate the change in compaction rates with time and the thickness of the overlying sediments. This object is well suited for calculations because The Middle and Upper Devonian deposits below the stratigraphic interval of the reef are at the same absolute elevations. This fact excludes the influence of local tectonic movements, which would undoubtedly lead to deformation of the entire section, not just its upper portion. Even if we accept the postulate that reef rocks are virtually unaffected by mechanical compaction (Anderson, 1996, Brown, 1995), the extent of pressure solution, evidence of which is recorded in boundstones by the presence of stylolite sutures, remains unaccounted for. Therefore, this calculation shows the relative compaction rates of organic-rich (Domanik) shales and reef. This calculation is based on the following assertion. The sediments overlying the Upper Devonian-Tournaisian interval of the section are represented by relatively shallow-marine varieties, with evidence of subaerial exposure at all levels. Therefore, the difference in the thicknesses of these sediments in the two wells reflects changes in the accommodation space resulting from compaction of organic-rich shales. To plot the relative compaction curve in the two wells, a correlation (Table 1 ) was performed using the most clearly defined well-logging benchmarks (marked with blue circles and numbered from bottom to top in Fig. 11 ). The thicknesses of the intervals between the closest benchmarks (between 2 and 3, between 3 and 4, etc.) were then calculated in both wells. By subtracting the resulting thicknesses in well No. 42 from the corresponding thicknesses in well No. 230, the rates of accommodation space change due to compaction were calculated (Table 2 ). To plot the diagram, the thickness difference values are plotted on the horizontal axis, and the absolute elevations of the identified benchmarks in well No 230 are plotted on the vertical axis. The resulting curve is a very convenient tool for analyzing compaction rates. To correctly interpret it, it is necessary to pay attention to the composition of the rocks overlying the compacted interval. While the upper part of the section (between benchmarks 3 and 15) is composed predominantly of carbonates and is virtually identical in composition to wells No. 230 and No. 42, facies substitutions are observed in the lower part (between benchmarks 1 and 3). Because the reef is overlain by a carbonate clinoforms, its upper boundary cannot be accurately determined from log data. Therefore, the analysis is conducted starting from the first, most distinct benchmark—the top of the Tournaisian, where limestones abruptly change to siliclastic (predominantly clayey) rocks of the Lower Visean. The interval of Domanik shales in well No 230 is 143 m (excluding the Domanik horizon, which are identical in both wells). The difference in thickness between benchmarks 1 and 2 is 142 m. This value coincides with the current amplitude of the anticline structure along the Tournaisian surface. The section of borehole No. 230 shows changes in the composition of the Kosvin deposits — the appearance of clay layers (Fig. 11 , shown by blue arrows). Clearly, during sedimentation, due to the additional accommodation space formed by compaction, clay material was transported to lower-lying areas of the relief. At the same time, the increased clay content of these deposits in borehole No. 230 increased their degree of compaction compared to borehole No. 42. The difference in thickness between benchmarks 3 and 2 (Bobrik horizon) is 27 m (4 m and 31 m, respectively). Because they are clays, they were also compacted, creating additional accommodation space in the borehole No. 230 section. The compaction curve in the interval between benchmarks 1–4 exhibits a bend (shown by green arrows in the Fig.), which is associated with a distortion in the thickness of the analyzed clay deposits of the Kosvinsky and, especially, the Bobrikov horizons. Table 1 Absolute benchmark elevations in wells No. 42 and No. 230 Benchmark Stratigraphy TVD, m (Well No. 42) TVD, m (Well No. 230) 1 D3f2 -1886 -1887 2 C1t2 -1384 -1527 3 C1v1 -1380 -1496 4 C1v2 -1327 -1433 5 C1v2 -1238 -1326 6 C1s1 -1179 -1252 7 C1s2 -1090 -1152 8 C2b -966 -1020 9 C2m -776 -824 10 C3k -483 -523 11 C3g -317 -356 12 P1a -215 -251 13 P1s -133 -175 14 P1ar -95 -134 15 P1k -46 -85 16 P1k 8 -25 Table 2 Calculation of compaction in well No. 230 Thicknesses between benchmarks In well No. 42 In well No.. 230 Thickness difference, m Total compaction 1–2 502 360 -142 - 2–3 4 31 27 27 3–4 53 63 10 37 4–5 89 107 18 55 5–6 59 74 15 70 6–7 89 100 11 81 7–8 124 132 8 89 8–9 190 196 6 95 9–10 293 301 8 103 10–11 166 167 1 104 11–12 102 105 3 107 12–13 82 76 -6 101 13–14 38 41 3 104 14–15 49 49 0 104 15–16 54 60 6 110 In the section, we observe the final clay thickness, which was clearly greater during sedimentation. By benchmark 4, the compaction curve levels out, which can be interpreted as the end of the main stage of clay compaction. However, compaction of the organic-rich sediments continued for a long time. The compaction curve smoothly straightens out toward benchmark 11 (the Carboniferous-Permian boundary), after which fluctuations begin, which are most likely related to tectonic reorganization of the region and the uplift of the Ural Mountains. The resulting compaction curve can be roughly divided into three stages. The first, spanning the entire Carboniferous period, is characterized by compaction rates of 2.17 m per million years for the Domanik sequence, or compaction of the Domanik shale interval with a current thickness of 143 m by 89 m, with an overlying sediment thickness of 590 m. During the second stage, rocks compacted at a rate of 0.95 m per million years, or an additional 18 m, with an overlying sediment thickness of 796 m. Due to the absence of Mesozoic-Cenozoic deposits in the study area, the third stage cannot be analyzed in detail. However, a final compaction of 142 m can be recorded (meaning that the Domanik shales were compacted at least twice as much—142 m by 143 m of their current thickness). Thus, the third stage of compaction is characterized by compaction rates of 0.12 m per million years, or 35 m for a thickness of 548 m of preserved overlying sediments (considering tectonic activation). Compaction Factors Analysis of thickness changes in selected wells showed that compaction of clayey rocks (Bobrik and Kosvinsky horizons) occurs quite rapidly. Many authors note that the main, most rapid part of this process occurs in the first few meters, after which its rate drops sharply. However, organic-rich rocks can compact over very long periods. This is confirmed by both the calculations performed and structural evidence of their plastic state after lithification of carbonates and cherts. An assessment of the degree of compaction of Domanik shales based on the ratio of the transverse size of loaf-shaped concretions to the thickness of the enclosing layer reveals compaction values of 3–5 times or more. These values likely reflect the actual compaction of the primary sediment, as concretions are the earliest lithified formations. Such concretions or nodules (Selles, Martines, 1996) are common in many organic-rich formations worldwide (including those of clayey composition). Most authors attribute their development to the microbial decomposition of organic matter in the underlying rocks at the upper boundary of the bacterial methanogenesis zone during breaks in sedimentation (Lash, Blood, 2003, Otharán, 2020). Much rarer stuctures— folded calcite veins — apparently are a typical feature of organic-rich radiolarite mud. Identical fractures in Mesozoic-Cenozoic deposits of the Muwwaqar Formation ("Jordan Shales") have been the subject of detailed studies (Hooker et al., 2017, Abu-Mahfouz et al., 2019, Hooker et al., 2019), leading the authors to conclude that the main cause of rock compaction is the diagenetic transformation of silica in radiolarian skeletons from opal A to quartz. It should be noted that the "Jordan Shales" are the closest analogue of Domanik-type rocks. Both are characterized by a low clay content, an abundance of radiolarians, and an extremely high organic matter content. This compositional similarity resulted in the presence of identical structures — nodules, "crumpled" fractures, and straight fractures mineralized by calcite, similar to those shown in Figs. 4 – 6 . Undoubtedly, the transformation of opal A into quartz and the compaction of the initially highly porous radiolarian skeletons are among the causes of sediment volume changes. This process is likely a key factor in the formation of such unusual structures as folded calcite veins. However, compaction can also occur without the participation of radiolarians, as evidenced by the significant compaction of Proterozoic (Lower Riphean) organic-rich shales. Probably, one of the main factors for such a long stay of sediments in a non-lithified state is organic matter. It also serves as a catalyst for various diagenetic processes (Ricken, 1992). The presence of traces of hydrocarbons in cracks mineralized by calcite (Figs. 4 , 5 ) indicates an early transformation of organic matter in compacted rocks (squeezing of hydrocarbon fluids from pores in the literal sense (Magara, 1982)). The relationship between deformation structures and changes in OM is also recorded in the bitumen shows in compaction breccias. E. Lichtfouse and J. Rullkötter (Lichtfouse, Rullkötter, 1994), studying sediments of the Sea of Japan, by analyzing the ratio of hopanes and steranes of OM in diagenetic cracks and in the parent rock deduced that compaction under silica diagenesis conditions can accelerate the transformation of OM. Similar conclusions were reached by researchers studying the "Jordanian shales" (Abu-Mahfouz et al., 2019, Abu-Mahfouz et al., 2020) following a detailed petrographic and geochemical study of Muwwaqar Formation rocks. This mechanism may explain the presence of hydrocarbons in immature sediments. For example, Domanik shales in studied area have low maturity based on Tmax (less than 430°C). At the same time, oil samples from numerous fields show a genetic link specifically to Domanik rocks. Conclusion Carbonate and low clay organic-rich shales retain plasticity for long periods during submergence and can be compacted several times. With such significant volume reduction, the rocks acquire specific compaction structures: folded veins, flat-pebble breccias, saucer-shaped concretions (nodules), etc. The process of differential compaction plays a crucial role in the formation of anticlinal structures in sediments enveloping reefs. The proposed methods for calculating changes in compaction rates and constructing a relative compaction curve can be successfully applied in petroleum geology. For example, by intersecting an enveloping structure in the Middle Carboniferous interval, the amplitude of the structure in the Lower Carboniferous and Upper Devonian can be calculated, allowing one to assess the feasibility of further drilling. Differential compaction creates localized stresses in rocks, which can lead to faults. If thin seals are ruptured, this will lead to the disintegration of the deposit, and if reservoir rocks are affected, this will improve their filtration properties due to decompression and/or the formation of fractures. Rock compaction and diagenetic alterations of silica probably accelerate the conversion of kerogen to hydrocarbons. Furthermore, prolonged compaction of source rocks can drive the migration of hydrocarbon fluids into the reservoir. All structures associated with compaction are observed in rocks enriched in organic matter. Therefore, the presence of such structures may indicate good petroleum-bearing properties of the host rocks even in cases of highly transformed organic matter. For example, in deep-seated Precambrian deposits, where only residual organic carbon can be detected by pyrolysis. Thus, the conducted studies have demonstrated the great theoretical and practical significance of compaction processes in organic-rich rocks. They must be considered in structural analysis, paleotectonic analysis, basin modeling, etc. Failure to account for compaction can lead to misinterpretations of deformation structures as a result of tectonic activity. Rock compaction is an important factor in increasing accommodation space, and therefore must be considered in sequence stratigraphic interpretations of sections (Mirnov, Chanysheva, 2025). Failure to account for compaction processes leads to misinterpretations of paleodepths in sedimentation basins (Ershov, 2016). Thus, the analyzed materials indicate that Domanik shales accumulated at relatively shallow depths (tens of meters), and pinnacle reefs appeared as minor protrusions in the relief during sedimentation, acquiring their colossal dimensions compared to the host rocks only during subsequent compaction. References Abu‑Mahfouz IS, Cartwright J, Idiz E, Hooker J, Robinson SA (2020) Silica diagenesis promotes early primary hydrocarbon migration. Geology Abu‑Mahfouz IS, Meng Q, Hooker J, Cartwright J (2019) Fractures in mudrocks: advances in constraining timing and understanding mechanisms. Journal of Structural Geology Abu‑Mahfouz IS, Cartwright J, Idiz E, Hooker JN, Robinson SA, van den Boorn SH (2019) Genesis and role of bitumen in fracture development during early catagenesis. Petroleum Geoscience 25:371–388. DOI: 10.1144/petgeo2018‑179 Abu‑Mahfouz IS (2023) Diagenesis, compaction strain and deformation associated with chert and carbonate concretions in organic‑rich marl and phosphorite; Upper Cretaceous to Eocene, Jordan. Sedimentology. DOI: 10.1111/sed.13085 Anderson NL (1996) A seismic analysis of differential compaction in the Frasnian Duhamel reef, south‑central Alberta. Computers & Geosciences 22(3):345–354 Bera F, Carminati E (2012) Differential compaction and early rock fracturing in high‑relief carbonate platforms: numerical modelling of a Triassic case study (Esino Limestone, Central Southern Alps, Italy). Basin Research 24:1–17. DOI: 10.1111/j.1365‑2117.2012.00542.x Brown RJ, Anderson NL, Cederwall DA, Sun Z, Manning PM, Zhang Q (1995) Duhamel: a seismic analysis of differential compaction in a Leduc reef. CREWES Research Report 7 Bruevich SV (1945) Soil moisture content of the Caspian Sea. DAN SSSR 47(4) (In Russ) Buryakovskiy LA (1991) Mathematical simulation of sediment compaction. Journal of Petroleum Science and Engineering 5(2) Chen J (2015) Origin of the Furongian limestone breccias in the North China Platform. Sci China Earth Sci 58:770–775 Chen J, Han Z, Zhang X et al. (2010) Early diagenetic deformation structures of the Furongian ribbon rocks in Shandong Province of China—a new perspective of the genesis of limestone conglomerates. Sci China Earth Sci 53:241–252. DOI: 10.1007/s11430‑010‑0010‑6 Croizé D, Renard F, Gratier J‑P (2013) Compaction and porosity reduction in carbonates: a review of observations, theory, and experiments. Advances in Geophysics 54. ISSN 0065‑2687. DOI: 10.1016/B978‑0‑12‑380940‑7.00003‑2 Ershov SV (2016) Paleobathymetry of the Late Jurassic‑Neocomian basin in northern West Siberia and the impact of natural processes. Russian Geology and Geophysics 57(8):1221–1238. DOI: 10.1016/j.rgg.2016.08.008 Hedberg HD (1926) The effect of gravitational compaction on the structure of sedimentary rocks. AAPG Bulletin 10:1035–1072. DOI: 10.1306/3D932750‑16B1‑11D7‑8645000102C1865D Hedberg HD (1936) Gravitational compaction of clays and shales. American Journal of Science, Ser 5, 31:241–287. DOI: 10.2475/AJS.S5‑31.184.241 Hooker JN, Huggett JM, Cartwright J, Hussein MA (2017) Regional‑scale development of opening‑mode calcite veins due to silica diagenesis. Geochemistry, Geophysics, Geosystems 18:2580–2600. DOI: 10.1002/2017GC006888 Hooker J, Abu‑Mahfouz IS, Meng Q, Cartwright J (2019) Fractures in mudrocks: advances in constraining timing and understanding mechanisms. Journal of Structural Geology Lash GG, Blood D (2004) Geochemical and textural evidence for early (shallow) diagenetic growth of stratigraphically confined carbonate concretions, Upper Devonian Rhinestreet black shale, western New York. Chemical Geology 206(3–4):407–424. DOI: 10.1016/j.chemgeo.2003.12.017 Lichtfouse E, Rullkötter J (1994) Accelerated transformation of organic matter below the silica transition zone in immature sediments from the Japan Sea. Organic Geochemistry 21:517–523. DOI: 10.1016/0146‑6380(94)90102‑3 Lisitsyn AP (1956) Bottom sediment moisture content of the Western Bering Sea. DAN SSSR 107(2) (In Russ) Magara K (1978) Compaction and fluid migration: practical petroleum geology. Nauka, Moscow, 318 p Maier DB, Rydberg J, Bigler C, Renberg I (2013) Compaction of recent varved lake sediments. Geologiska Foreningen 135:231–236. DOI: Mirnov RV, Chanysheva LN (2025) Experience of applying sequence‑stratigraphic approach for detailed study of Upper Devonian‑Tournaisian clinoform complex of Aktanysh‑Chishminsky trough. Georesources 27(1):284–298. DOI: 10.18599/grs.2025.1.28 Mkrtchyan OM (1980) Patterns of structural form distribution in the Eastern Russian Plate. Nauka, Moscow, 135 p (In Russ) Mukhin YuV (1965) Processes of clay sediment compaction. Nedra, Moscow, 200 p (In Russ) Mukhin YuV (1965) On the role of geological time in the compaction of clay sediments. Lithology and Useful Fossils, pp 126–130 (In Russ) Nesterov IN (1965) Compaction of clayey rocks. Sovetskaya Geologiya (12):69–80 (In Russ) Otharán G (2020) Sedimentología y análisis de facies de la Formación Vaca Muerta (Tithoniano‑Valanginiano), Cuenca Neuquina. El rol de los flujos de fango en la depositación de espesas sucesiones de lutitas. Ph.D. thesis in Geology. DOI: 10.13140/RG.2.2.32858.67520/1 Railsback LB (1993) Original mineralogy of Carboniferous worm tubes: evidence for changing marine chemistry and biomineralization. Geology 21 Ricken W (1992) A volume and mass approach to carbonate diagenesis: the role of compaction and cementation. In: Developments in Sedimentology 47:291–315. DOI: 10.1016/S0070‑4571(08)70568‑5 Selles‑Martines J (1996) Concretion morphology, classification and genesis. Earth‑Science Reviews 41(3):177–210 Sorby HC (1908) On the application of quantitative methods to the study of the structure and history of rocks. Quarterly Journal of the Geological Society of London 64:171–233 Strakhov NM (1960) Fundamentals of the theory of lithogenesis. Volume 1. Types of lithogenesis and their location on the Earth’s surface. Publishing House of the USSR Academy of Sciences, Moscow, 210 p Trask PD (1931) Compaction of sediments. AAPG Bulletin 15(3):271–276. DOI: 10.1306/3D93298A‑16B1‑11D7‑8645000102C1865D Vassoevich NB (1960) Experience in constructing a typical curve of gravity compaction of clayey sediments. News of Oil Technology. Geology, pp 11–15 (In Russ) Weller JM (1959) Compaction of sediments. AAPG Bulletin 43(2):273–310 Cite Share Download PDF Status: Under Review Version 1 posted Reviewers agreed at journal 24 Feb, 2026 Reviewers invited by journal 24 Feb, 2026 Editor assigned by journal 24 Dec, 2025 First submitted to journal 22 Dec, 2025 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-8412682","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":596232444,"identity":"e3a9056d-a4d1-4b12-9304-e5b5490a3b07","order_by":0,"name":"Roman Viktorovich Mirnov","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA2ElEQVRIiWNgGAWjYBACg8MINuMDIMHDR0iLJZIWZgOQFjZCWuwPINhsEmCSkBaz47zPHnxsuyen2372WOXXHDsZNgbmh49u4NNymN3ccGZbsbHZmby027LbkoEOYzM2zsGrhY1NmudMQuK2AzlmtyW3MQO18LBJ49NiANdy/o1ZseS2emK1VAC13MgxY/y47TBxWiRnVCQYm914YyzNuO04DxszAb8YnD/GJvHBIEHO7HyO4cef26rt+dmbHz7GpwUFMPOASWKVgwDjD1JUj4JRMApGwYgBAPy7QwbVSkuiAAAAAElFTkSuQmCC","orcid":"https://orcid.org/0000-0002-7665-7338","institution":"Ufa State Petroleum Technological University: Ufimskij gosudarstvennyj neftanoj tehniceskij universitet","correspondingAuthor":true,"prefix":"","firstName":"Roman","middleName":"Viktorovich","lastName":"Mirnov","suffix":""}],"badges":[],"createdAt":"2025-12-20 14:09:08","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-8412682/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-8412682/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":103588865,"identity":"f970fc15-d16a-49d6-90fc-e0442f6250dc","added_by":"auto","created_at":"2026-02-27 11:48:54","extension":"jpeg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":206940,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cem\u003eOverview map of studied area.\u003c/em\u003e\u003c/p\u003e","description":"","filename":"floatimage1.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-8412682/v1/7445dc8495c922f1e7736acb.jpeg"},{"id":103588871,"identity":"bf146ef5-63f9-4820-ab86-5c4f31c4feac","added_by":"auto","created_at":"2026-02-27 11:48:54","extension":"jpeg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":494747,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cem\u003eGeometry of folded calcite veins. A – a folded vein in organic-rich rocks in thin section. Relics of limestone with lower OM content are preserved between the fracture bends (yellow arrows). Vein breaks are visible (red arrows). Domanik horizon. Cross polarized light (CPL). B – Schematic representation of the fracture indicating its length and the observed thickness of the host layer. C – A straight fracture passing through a limestone interlayer, continuing into a folded (“crumpled”) vein in a layer of organic-rich rocks. Kosvinsky horizon. D – Schematic representation of the fracture indicating its length and the observed thicknesses of the host layer.\u003c/em\u003e\u003c/p\u003e","description":"","filename":"floatimage2.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-8412682/v1/1d2fdbe3d6390f5d0772a006.jpeg"},{"id":103588866,"identity":"b27412a6-e76f-4e3f-ae8b-834fdf4a9a8a","added_by":"auto","created_at":"2026-02-27 11:48:54","extension":"jpeg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":935383,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cem\u003eCarbonate nodules in the Domanik Horizon deposits. A – Large nodule, gradually tapering towards the margins. Conformable enveloping of thin-bedded organic-rich rocks is visible (red arrows). B – Elements of relict horizontal bedding preserved within the nodule. c – Character of transition of the nodule into organic-rich shales. A, B – outcrop on the Domanik Stream, C – well core (Blagoveshchenskaya Depression). D, E – Gradual change in the number and size of tentaculite remains (yellow arrows) near the nodule. Photo of thin sections. Plane polarized light (PPL).\u003c/em\u003e\u003c/p\u003e","description":"","filename":"floatimage3.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-8412682/v1/c3bac98c0fa5c771cc1c6fa3.jpeg"},{"id":103588868,"identity":"f20ded31-e291-4284-8167-8071e49228c6","added_by":"auto","created_at":"2026-02-27 11:48:54","extension":"jpeg","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":485479,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cem\u003eCracks in the Kosvinsky Horizon deposits formed by the compaction of organic-rich rocks. A: a straight vertical crack mineralized by silica and calcite of several generations (shown by black arrows). B: a branched crack mineralized by calcite of several generations. The red rectangle shows an enlarged fragment of C. Red arrows indicate the crack initiation points.\u003c/em\u003e\u003c/p\u003e","description":"","filename":"floatimage4.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-8412682/v1/64165df00f30d698eab501dc.jpeg"},{"id":104398560,"identity":"722f7cd8-53a8-41ba-b7b5-7133789c4b52","added_by":"auto","created_at":"2026-03-11 12:02:54","extension":"jpeg","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":613593,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cem\u003eCracks filled with several generations of chalcedony and calcite. A, C – PPL, B, D – CPL. Orange arrows indicate the area of the earliest silicification of the host limestone, yellow arrows – coarse-crystalline calcite contaminated with hydrocarbon admixture filling the crack, red arrows – the latest generation of chalcedony.\u003c/em\u003e\u003c/p\u003e","description":"","filename":"floatimage5.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-8412682/v1/0f0ceb6d9736e060cccbbdfd.jpeg"},{"id":104399256,"identity":"025be5fe-7703-44dd-9ef2-46cbd7146874","added_by":"auto","created_at":"2026-03-11 12:05:15","extension":"jpeg","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":623108,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cem\u003eRelationships between different mineralized veins. A – Folded veins mineralized by calcite (red arrows); straight fractures mineralized by chalcedony (purple arrows) and chert lenses (black arrows) from which straight fractures mineralized by calcite originate (blue arrow). B – Straight upward-directed fractures mineralized by calcite (blue arrows); straight downward-directed fracture with impressed \u003c/em\u003eorganic-rich\u003cem\u003emud (black arrow). C – Folded vein intersecting organic-rich limestone interlayers (yellow arrows) and a thin chert interlayer (orange arrow), thin section, PPL. Red arrows indicate fracture breaks. D – Straight fracture mineralized by calcite extending upward from a chert lens.\u003c/em\u003e\u003c/p\u003e","description":"","filename":"floatimage6.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-8412682/v1/dc155f9e01f6352b58e87bc6.jpeg"},{"id":103588873,"identity":"60cd3ece-aef3-450a-9007-f4557a9272ec","added_by":"auto","created_at":"2026-02-27 11:48:54","extension":"jpeg","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":403224,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cem\u003eDuctile deformations in Domanik-type rocks. A — Limestone layer in organic-rich rocks, in which mushroom-shaped intrusions of host rocks directed from bottom to top (arrows) are noted. B — Limestone layers with intrusions of host rocks from bottom to top and from top to bottom. C — Deformed, thin layers of tentaculites in a highly organic-rich interlayer.\u003c/em\u003e\u003c/p\u003e","description":"","filename":"floatimage7.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-8412682/v1/f439d099fc409f27d8bb4eca.jpeg"},{"id":103588874,"identity":"6029ea2f-41ce-4225-9cac-64b51cc7df4c","added_by":"auto","created_at":"2026-02-27 11:48:54","extension":"jpeg","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":759420,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cem\u003eBreccias formed by compaction of Domanik-type rocks. Domanik horizon. A — Various stages of breccia formation in a single core section. The orange arrow shows a crack filled with host rock, which does not completely cut the limestone layer. Yellow arrows indicate areas of completely fragmented limestone. Red squares indicate the areas from which thin sections d and e were taken. B — Flat-pebble compaction breccia in a thin interlayer of organic-rich rocks. Arrows indicate bitumen segregations. C — Intrusion of the underlying layer into the limestone layer with its partial fragmentation (arrow). D, E — Breccias in thin sections (PPL). Red arrows indicate cracks from the initial stage of limestone fragmentation.\u003c/em\u003e\u003c/p\u003e","description":"","filename":"floatimage8.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-8412682/v1/388113d9583fb05190b894e1.jpeg"},{"id":104808235,"identity":"c4428ce9-996b-4636-97df-5aa82e5a2248","added_by":"auto","created_at":"2026-03-17 12:34:06","extension":"jpeg","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":401099,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cem\u003eCompaction-related deformations in the core of borehole 1 East Askinskaya (Kaltasinskaya Formation, Lower Riphean). A, B — thin carbonate interlayers in organic-rich rocks with mineralized fractures (red arrows). Intrusions of host rocks into the fractures are noted with yellow arrow. C — fracture fragmented as a result of compaction (compacted fragments are shown by arrows). D — flat-pebble breccia. Fragments of a single layer, moved away from each other, are visible (arrows).\u003c/em\u003e\u003c/p\u003e","description":"","filename":"floatimage9.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-8412682/v1/944262b34963bf3f98329d89.jpeg"},{"id":103588869,"identity":"981ef9cc-1d57-47ce-a31c-9a698e7e7c7e","added_by":"auto","created_at":"2026-02-27 11:48:54","extension":"jpeg","order_by":10,"title":"Figure 10","display":"","copyAsset":false,"role":"figure","size":2285025,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cem\u003eA, B, C – mechanism of formation of depression rocks above the reef. a – cessation of bioherm growth as a result of a sharp rise in relative sea level; B – compaction of organic-rich rocks; C – modern ratio of rocks uncovered by wells. The black arrow indicates the interval with the provided core photo. 1 –organic-rich rocks; 2 – limestones; 3 – reef limestones and dolomites; 4 – Domanik horizon, 5 – Voronezh horizon, 6 – Upper Famennian; 7 – well projections. D – profile of wells through the reef. The Domanik Formation subjected to compaction are highlighted in color. E – Photograph of a core from the Domanik Formation overlying the reef in well No. 92. Visible are breccias with acute-angled fragments (yellow arrows), calcite-mineralized fractures (red arrow), and inclined layer contacts (orange arrow).\u003c/em\u003e\u003c/p\u003e","description":"","filename":"floatimage10.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-8412682/v1/2e66c746670f2d99e103bc90.jpeg"},{"id":104399395,"identity":"674239fb-bba7-4d74-9266-653aaaa20eb6","added_by":"auto","created_at":"2026-03-11 12:05:55","extension":"jpeg","order_by":11,"title":"Figure 11","display":"","copyAsset":false,"role":"figure","size":338107,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cem\u003eRelative compaction curve for Domanik-type rocks (interval highlighted in purple) and rocks composing the organogenic structure (approximate interval highlighted in yellow). Blue arrows indicate intercalations of Kosvin clays, and the yellow arrow indicates the Visean clay interval. Explanations in the text.\u003c/em\u003e\u003c/p\u003e","description":"","filename":"floatimage11.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-8412682/v1/0570d1b7977562a93cb36057.jpeg"},{"id":104835297,"identity":"c3d21607-fd52-4f4e-91f5-4d3043e4c137","added_by":"auto","created_at":"2026-03-17 17:43:13","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":8202879,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-8412682/v1/2771054b-8b39-403d-8271-7580d8dbdb81.pdf"}],"financialInterests":"","formattedTitle":"Compaction of organic-rich carbonate and siliceous mud: mechanism, rate, typical structures. Case studies from Domanik Formation (Russia).","fulltext":[{"header":"Introduction","content":"\u003cp\u003eThe transformation of sediment into rock is accompanied by its dehydration and volume reduction. The degree of sediment compaction depends on its initial composition; clayey and carbonate silts undergo maximum compaction. The most stable sediments are those composed of initially solid components \u0026mdash; sands, pebbles, and, especially, reef carbonates, which are characterized by lithification that virtually occurs during their life. Sediment compaction has been studied by many scientists since the early twentieth century. One of the first works devoted to analyzing the causes of compaction was the work of the US geologist H.K. Sorby (Sorby, 1908), who proposed the dependence of porosity on pressure and rock age.\u003c/p\u003e \u003cp\u003eWork on compaction can be roughly divided into three groups.\u003c/p\u003e \u003cp\u003eThe first group of studies is based on the study of the porosity of already compacted rocks in deep wells. Thus, one of the first compaction curves for clay rocks with depth (Hedberg, 1926, Hedberg, 1936) was constructed based on porosity measurements of Cenozoic clays in a well section in Venezuela. This was later criticized by N.B. Vassoevich (Vassoevich, 1960) for underestimating the influence of eroded sediments. Instead, a curve constructed using data from the Alexandria borehole, drilled in a zone of sustainable tectonic subsidence, was proposed. This revealed a nearly twofold increase in dry rock density upon submersion to a depth of 5 km (from 1.4 g/cm3 to 2.7 g/cm3).\u003c/p\u003e \u003cp\u003eThe second group involves studying the surface layer of bottom sediments. Such studies have been known since the middle of the last century (Rittenberg, 1952, Bruevich, 1945, Lisitsyn, 1956 etc.). One modern study on the compaction of varve lake sediments in Northern Sweden (Maier et al., 2013) presents data on a 70% reduction in clay layer thickness upon submersion to a depth of 12 cm over 33 years.\u003c/p\u003e \u003cp\u003eThe third group of studies is based on laboratory experiments on rock compression under pressure. P. Trask (1931) first conducted laboratory experiments centrifuging marine bottom sediments of varying grain sizes and found that the coarser-grained varieties were less susceptible to compaction than microgranular silts, which shrank more than twofold in volume. Similar experiments were later conducted on carbonate rocks (Croiz\u0026eacute; et al., 2013).\u003c/p\u003e \u003cp\u003eMethods for monitoring the degree of flattening of small-sized objects deserve special mention. For example, measuring the asymmetry of cross-sections of burrows (Railsback, 1993) or the relationship of early diagenetic formations (carbonate nodules, pyrite concretions, etc.) to the thickness of the enclosing layer (Abu-Mahfouz, 2023).\u003c/p\u003e \u003cp\u003eThe object of this study is siliceous-carbonate rocks enriched in dispersed organic matter. They contain virtually no clay minerals, so the compaction processes in them differ significantly from those in clays, which have been the subject of numerous published studies (Vassoevich, 1960, Nesterov, 1965, Mukhin, 1965, Buryakovskiy, 1991, etc.).\u003c/p\u003e \u003cp\u003eJ. M. Weller (Weller, 1959) noted the complexity of the problem and the insufficient study of the nature of sediment compaction, including its dependence on composition. It is common to distinguish between mechanical compaction (\"squeezing out\" water) and dissolution under pressure, but these processes are often inextricably linked, making the problem even more complex. In the succinct words of N. M. Strakhov, \"The driving force of diagenesis is the internal contradictions in the material composition of the sediment, gradually eliminated through the transformation of the mineralogical form of reactive substances and their adaptation to one another\" (Strakhov, 1960). Dispersed organic matter serves as an important actor for diagenetic transformations (reactive matter). Therefore, rocks with high organic matter content are of particular interest.\u003c/p\u003e \u003cp\u003eThe study of compaction processes has not only theoretical but also practical significance. Uneven compaction of sediments with different compositions during subsidence (differential compaction) can cause the formation of anticlinal structures above carbonate buildups, sandstone lenses, etc., without the influence of tectonic factors. For example, a significant number of oil deposits in the Upper Devonian and Carboniferous of the Volga-Ural petroleum province are confined to such anticlinal traps above Frasnian-Lower Famennian reefs (Mkrtchyan, 1980; Bera and Carminati, 2012; etc.). Compaction processes must be studied to reconstruct the original rock thickness and accurately calculate the paleodepths of the basin, which, in turn, can be used for facies reconstructions, basin modeling, etc.\u003c/p\u003e \u003cp\u003eIn recent years, an increasing number of publications have appeared on the threat of flooding of vast territories in areas of modern deltas as a result of sediment compaction (Teatini et al., 2011; Zoccarato et al., 2018). Thus, the processes being studied can have a direct impact on human economic activity.\u003c/p\u003e \u003cp\u003eAny reduction in rock volume leads to the emergence of new textural features that must be correctly interpreted. Taking this factor into account may be key to understanding the genesis of mysterious and not fully deciphered structures, common, among other things, in Precambrian rocks.\u003c/p\u003e \u003cp\u003eRocks enriched in organic matter (OM) are always considered a potential source of hydrocarbon generation. Despite numerous studies on the geochemical study of these rocks, the mechanism of fluid migration itself remains an incompletely understood process. The relationship between the compaction of petroleum source rocks and the removal of hydrocarbon fluids from them remains an open question. Thus, sediment compaction is associated with a wide variety of scientific fields.\u003c/p\u003e"},{"header":"Materials and Methods","content":"\u003cp\u003eThe material for this study was deep-well core collected from the Domanik Formation in the southeastern East European Platform. A stratotype outcrop near the Domanik Stream was also studied. A sedimentological study of the core was conducted, with particular attention paid to deformation structures. Microscopic examination of 300 thin sections was performed using a Zeiss Axiolab A1 microscope. The mineralogy of the rocks was determined using X-ray diffraction (XRD) on each sample. To exclude erroneous interpretation of deformation structures, the absence of deep faults in the study area was previously confirmed using seismic data and borehole microimagers.\u003c/p\u003e \u003cp\u003eIn addition to studying the Domanik Formation, core from the Proterozoic Kaltasinskaya Suite in well 1VAK was also studied. The study revealed that some structures, previously interpreted as the result of compaction, are also found in Precambrian rocks. These structures were systematized and also served as material for studying compaction processes.\u003c/p\u003e \u003cp\u003eTo analyze the degree of compaction and construct a compaction curve, wells drilled in the zone of facies replacement of isolated carbonate reefs by Domanik Formation sediments were selected. Interwell correlation was conducted for subsequent analysis of thickness variations.\u003c/p\u003e \u003cp\u003eIn this article, the term \"reef\" is used in the sense of \"seismic reef\" and does not include analysis of reef paleoecology. The term \"organic-rich shales\" refers to thin-bedded rocks with a high content of organic matter, but not clay material.\u003c/p\u003e \u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003eGeological settings\u003c/h2\u003e \u003cp\u003eThe Domanik Formation is developed in the eastern part of the East European Platform and spans the Frasnian-Tournaisian stratigraphic interval. The Domanik Formation is thickest (up to 300 m) and most stratigraphically complete in the axial parts of the Kama-Kinel trough system. Its name derives from the Domanik Creek, where the stratotype of the Middle Frasnian Domanik horizon is located (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThe rocks of the Domanik Formation are characterized by a siliceous-carbonate composition and a high content of dispersed organic matter, which ranges from tenths of a percent to 30% or more of the rock volume. The highest organic matter concentrations are observed in the stratigraphic interval of the Middle Frasnian Domanik horizon. Most researchers agree that the rocks of the Domanik Formation are the main oil-producing rocks of the Volga-Ural petroleum province. In the study area, the Domanik Formation is relatively immature: Tmax values range from 430\u0026ndash;435 degrees Celsius. The organic matter of Domanik appears to be of type II-S.\u003c/p\u003e \u003cp\u003eFaunal remains include tentaculites, radiolarians, ostracods, and, to a lesser extent, brachiopods, foraminifera, gastropods, nautiloids, and ammonoids. Tentaculites are predominantly characteristic of the Domanik horizon and typically occur as flattened and thinned shells oriented along the bedding plane. Radiolarians are often very poorly preserved, with the exception of calcified varieties with a regular isometric shape.\u003c/p\u003e \u003cp\u003eOne of the typical features of the rocks is the frequent alternation of millimeter-thick interlayers of varying compositions with sharply variable organic carbon content. Thin interlayers enriched in tuffaceous material are found in the section.\u003c/p\u003e \u003cp\u003eRocks of the Lower Riphean Kaltasinskaya suite were studied in the core of the well 1 VAK (Vostochno-Askinskaya). They share features with rocks of the Domanik Formation: elevated organic carbon content, minimal clay mineral content, and frequent alternation of thin interlayers of varying lithology. The organic matter of the Kaltasinskaya suite rocks is represented by non-pyrolyzable carbon.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e"},{"header":"Results","content":"\u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003eFolded Veins\u003c/h2\u003e \u003cp\u003eOne of the most striking indications of significant compaction of Domanik sediments is the presence of folded veins mineralized by calcite (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). They range in length from tenths of a millimeter to a few centimeters, gradually decreasing in width toward the bottom.\u003c/p\u003e \u003cp\u003eFolded veins are found in interlayers of siliceous-carbonate rocks or limestones, which are particularly rich in organic matter. Sometimes, cracks intersect several layers with different lithology. In such cases, they are straight and subvertical in layers of organic-poor limestones and cherts, continuing in a crumpled form in low-siliceous layers enriched in organic matter (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eC).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eTypically, such fractures originate at the boundary between layers with different lithologies and attenuate both at the layer boundaries and within the OM-rich layer. Folded veins have smooth outlines, indicating the plastic state of the calcite filling them during compression. Figure\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e, A shows a folded vein, between whose bends are remnants of lighter limestone, preserved before significant compaction and an increase in the OM concentration in the matrix. Vein breaks likely formed during further compaction of the rock after the final crystallization of the calcite filling the fracture. Measurements of the ratio of the length of a folded vein (3 mm) to the thickness of the host layer (0.97 mm) (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eB) in two dimensions (in three dimensions, it will be even greater) in thin section show that from the time the fracture formed until its lithification, the rock compacted more than threefold. Considering the presence of veins, the degree of further compaction can be roughly estimated.\u003c/p\u003e \u003cp\u003eAnother example (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eC, \u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eD) shows a fracture intersecting several thin layers. In a layer of light-colored limestone, it appears as a subvertical straight line, then begins to meander in the underlying organic-rich layer. Here, the degree of compaction of the host rock after calcite crystallization in the \"crumpled\" fracture can be estimated by the change in layer thickness along the fracture (11.7 mm) and further away from it (7 mm). In this case, the crystallized fracture acts as a \"spacer\" for the layer, preventing it from further compaction. The final visible compaction of the rock is 26 mm/7 mm (3.7 times).\u003c/p\u003e \u003cp\u003eThe \"straightening\" of cracks where they intersect light-colored limestones and cherts indicates a significantly earlier lithification of the latter.\u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003eConcretions\u003c/h3\u003e\n\u003cp\u003eAnother picturesque example of the relationship between compacted and lithified rocks during the early stages of diagenesis are the loaf-shaped concretions of light-colored limestones, occurring among the thinly layered, OM-rich rocks that envelop them (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e). Concretions are located at discontinuous layers in the section, and the \"swells,\" located linearly along the stratification are convenient to use as benchmarks when describing outcrops. They have a slightly flattened shape and range in size from a few centimeters to several tens of centimeters.\u003c/p\u003e \u003cp\u003eLarge ammonoid or nautiloid shells are often serving as crystallization centers within the nodules. The nodules are composed of tentaculite limestones or calcified radiolarites. Remnants of parallel lamination, preserved from the initial sediment to compaction, can often be observed within the nodules (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eB, \u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eC).\u003c/p\u003e \u003cp\u003eWhen comparing the internal structure of the nodules with the host rocks, the latter are distinguished by a significantly higher organic matter content and the shape of the calcite shell fragments. These are significantly thinned and flattened to form indefinable filiform veinlets. The organic-rich rocks enclosing the nodules in different parts vary in morphology and the number of calcite fossils. Near the widest part, they occur as isolated, very thin relics, increasing in number and thickness fan-shaped toward the periphery of the nodule (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eD, \u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eE).\u003c/p\u003e \u003cp\u003eSimilar concretions have been described in many clayey and limestone strata, with high organic carbon content. The ratio of the thickness of the central part of the nodule to the thickness of the corresponding horizontal layer is often used by various authors to calculate the degree of compaction. In Domanik deposits, this ratio reaches 10 (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eA). It should be noted that chert nodules are also found in these deposits, but they are significantly less widespread and thickness.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e\n\u003ch3\u003eRedistribution of Silica and Calcite During Compaction\u003c/h3\u003e\n\u003cp\u003eShort, subvertical mineralized fractures are common in Domanik Formation, which can be mistakenly interpreted as the result of tectonic activity. These fractures, obviously formed by rock compaction, are evidence of a multistage redistribution of calcite and silica.\u003c/p\u003e \u003cp\u003eThe fractures are developed in limestone interbeds, and are longest in intervals where organic-rich rocks occur as thin, centimeter-size interbeds within the main mass of wackstones (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e). Thinned shell remains similar to those described above are observed within the organic-rich layers. The layers themselves have variable thickness, and the fractures originate at points of localized thickening (at \"breakthrough points\"). Most often, the fractures are directed from bottom to top, although thinner fractures directed from top to bottom are also present.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eAt the sites of fracture attenuation, significant areas of silicification are observed within the limestone layer, reminiscent of smoke escaping from a factory chimney or fluid injected under pressure from a thin syringe needle (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eA). Furthermore, silicification is observed along the fracture margins, indicating its earlier deposition compared to the calcite filling the fracture. The calcite itself is represented by several generations, the most recent of which exhibits a brownish color and bitumen admixtures (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eB, \u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eC; Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eC, \u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eD). Importantly, the OM does not fill the pores, but rather colors the crystals themselves, indicating the release of hydrocarbons during fracture mineralization (during compaction).\u003c/p\u003e \u003cp\u003eThus, we observe multiple reactivations of fractures after their formation as a result of rupture of the overlying layer under fluid pressure. The crack appeared as a result of a breakthrough of a solution saturated with silica, after which, in the process of further compaction, the stages of crystallization of silica and calcite alternated.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eWith more frequent intercalation of limestones and OM-rich siliceous-carbonate rocks, a variety of fracture combinations are observed (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e), demonstrating the multistage nature of silica and calcite redistribution during diagenesis. Folded veins are observed exclusively in low-siliceous layers enriched in OM. When such fractures intersect radiolarite layers (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003eC), they retain a straight shape, indicating significantly earlier crystallization of cherts. Straight fractures in limestones mineralized with calcite always point upward, which is likely due to the lower density of the overlying sediments compared to the underlying sediments. Limestones contain not only mineralized fractures but also fractures partially filled with organic-rich siliceous-carbonate material pressed in from the adjacent layer (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003eB).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003eCompaction-Related Deformation Structures\u003c/h2\u003e \u003cp\u003eDomanik-type rocks accumulated under conditions of uncompensated sedimentation and remoteness of the provenances of terrigenous and carbonate material. Therefore, they exhibit virtually no resuspension or slumping structures, with a predominantly fine parallel stratification. However, they do exhibit ductile deformation structures, related to compaction of the rocks (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eLimestone layers embedded in siliceous-carbonate rocks, which are highly enriched in organic matter (15% or more), exhibit unusual structures\u0026mdash;mushroom-shaped intrusions of organic-rich rocks into the limestone. These intrusions are most often directed upward, and when they are directed toward each other, the intrusions at the base of the limestone have a greater amplitude (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003eA, \u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003eB). 7C shows a photograph of a core sample showing deformed clusters of tentaculite shells forming thin laminae.\u003c/p\u003e \u003cp\u003eSuch structures can hardly be interpreted as primary sedimentation. They indicate elevated pressure in rocks enriched in organic matter, which acted on the as-yet-unlithified sediment and led to the development of ductile deformations.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e"},{"header":"Discussion","content":"\u003cdiv id=\"Sec10\" class=\"Section2\"\u003e \u003ch2\u003eBreccia Formation by Compaction\u003c/h2\u003e \u003cp\u003eAlong with the ductile deformations that occurred before sediment lithification, brittle deformation structures are also encountered, formed by the interaction of thin layers of lithified carbonates and still ductile organic-rich shales.\u003c/p\u003e \u003cp\u003eSuch structures can be called \"compaction breccias.\" They are found in rocks richest in organic matter, where they host thin (1\u0026ndash;3 cm) early-lithified limestone layers (Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003eA shows a photograph of a core section showing brittle deformations of the initial (lower part) and final (upper part) stages of breccia formation. Brittle deformations are manifested in numerous cracks that cut through the limestone layer from below and above, some of which have encroached the host rock. The breccia interlayer lies among completely undisturbed thin-layered rocks and shows no signs of ordering of the fragments, imbrication or gradational sorting.\u003c/p\u003e \u003cp\u003eThese breccias clearly show that the fragments lack any signs of rounding and represent parts of a single layer, which can be mentally connected like pieces of a construction set (Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003eD, \u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003eE).\u003c/p\u003e \u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003eC shows a photograph of a core sample, which, as in the examples shown above, shows the intrusion of organic-rich rocks into the overlying limestone layer. However, in this case, they do not deform this limestone layer, but partially fragment it, forming an unusual breccia in which the fragments, seemingly defying the laws of gravity, are located at the top of the layer.\u003c/p\u003e \u003cp\u003eIt is important to note another observation: bitumen segregations are present in the \"compaction breccias,\" namely, in the filler (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003eC). This clearly indicates a connection between deformation (compaction) processes and the transformation of organic matter.\u003c/p\u003e \u003cp\u003eThe described \"compaction breccias\" have morphological similarities to flat-pebble breccias common in Precambrian rocks. Figure\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003e, using Proterozoic (Lower Riphean) deposits from well 1VAK as an example, shows deformation structures identical to those recorded in Domanik Formation.\u003c/p\u003e \u003cp\u003eThe fragments (\u0026ldquo;clasts\u0026rdquo;) in the flat-pebble breccias (Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003eD) are unrounded fragments of thin layers separated by compaction. Within the intervals of flat-pebble breccia development, one can observe ductile deformations (Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003eA), straight mineralized fractures emerging from thin layers of organic-rich rocks, and intrusions of host rocks into limestones (Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003eB). The studied intervals containing flat-pebble breccias are represented by frequent alternation of thin (1\u0026ndash;3 cm) layers of light-colored limestones and dark-colored organic-rich carbonates. The small thickness of the limestone interlayers and their early lithification are likely the main cause of the formation of flat-pebble breccias as a result of compaction. A similar mechanism for their formation has been considered by some authors (Chen et al., 2010, Chen et al., 2015); however, they did not provide similar examples from Phanerozoic deposits. The material presented in this article allows for a more substantiated interpretation of these ambiguous structures as the result of compaction of carbonate organic-rich mud.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eDifferential compaction can also lead to breccia formation. Figure\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003e shows an example of a natural object ideally suited for studying the mechanism of differential compaction. The correlation diagram of wells located no more than a kilometer apart shows that the interval of Domanik Formation in wells 78 and 91 (Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003eD) corresponds to a non-radioactive interval of reef carbonate rocks in well 92 In addition, the reef is covered by a similar layer of Domanik-type rocks. This relationship between the rocks can be explained by the sedimentation and compaction diagram shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003eA, \u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003eB, \u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003eC.\u003c/p\u003e \u003cp\u003eAs a result of rising relative sea level, the reef ceased was submerged, after which it was buried for a long time under condensed organic-rich sediments. The modern structure arose after the compaction of the latter. During compaction and tensile forces applied to the organic-rich rock unit in borehole 92, structures virtually indistinguishable from tectonic breccias were formed (Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003eE).\u003c/p\u003e \u003cp\u003eIt should be noted that seismic and borehole data show no signs of any faults in the studied area, therefore, the presence of tectonic breccias is excluded.\u003c/p\u003e \u003cp\u003eThe organic-rich interval in borehole 92 is represented by carbonate-siliceous rocks and cherts, which underwent earlier lithification than the low-siliceous varieties. Further compaction of the surrounding rocks resulted in brittle deformations and breccia development.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003eCalculating the Degree and Rate of Compaction\u003c/h2\u003e \u003cp\u003eThis article attempts to calculate the degree and rate of compaction with subsidence using the high-amplitude Volkovskiy reef, located in the South-East part of the East-European Platform, as an example. In the well that penetrated reef body (Fig.\u0026nbsp;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e11\u003c/span\u003e, Well No. 230), reef carbonates occur in the Upper Frasnian-Famennian interval of the section, while in the nearest well, No. 42 (located 3,280 m from well No. 230), this interval is characterized by Domanik type organic-rich rocks.\u003c/p\u003e \u003cp\u003eAn anticlinal structure forms above the organogenic structure, which is evident throughout the entire interval of the overlying Carboniferous-Permian sediments. This allows us to estimate the change in compaction rates with time and the thickness of the overlying sediments. This object is well suited for calculations because The Middle and Upper Devonian deposits below the stratigraphic interval of the reef are at the same absolute elevations. This fact excludes the influence of local tectonic movements, which would undoubtedly lead to deformation of the entire section, not just its upper portion.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eEven if we accept the postulate that reef rocks are virtually unaffected by mechanical compaction (Anderson, 1996, Brown, 1995), the extent of pressure solution, evidence of which is recorded in boundstones by the presence of stylolite sutures, remains unaccounted for. Therefore, this calculation shows the relative compaction rates of organic-rich (Domanik) shales and reef.\u003c/p\u003e \u003cp\u003eThis calculation is based on the following assertion. The sediments overlying the Upper Devonian-Tournaisian interval of the section are represented by relatively shallow-marine varieties, with evidence of subaerial exposure at all levels. Therefore, the difference in the thicknesses of these sediments in the two wells reflects changes in the accommodation space resulting from compaction of organic-rich shales. To plot the relative compaction curve in the two wells, a correlation (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e) was performed using the most clearly defined well-logging benchmarks (marked with blue circles and numbered from bottom to top in Fig.\u0026nbsp;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e11\u003c/span\u003e). The thicknesses of the intervals between the closest benchmarks (between 2 and 3, between 3 and 4, etc.) were then calculated in both wells. By subtracting the resulting thicknesses in well No. 42 from the corresponding thicknesses in well No. 230, the rates of accommodation space change due to compaction were calculated (Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eTo plot the diagram, the thickness difference values are plotted on the horizontal axis, and the absolute elevations of the identified benchmarks in well No 230 are plotted on the vertical axis. The resulting curve is a very convenient tool for analyzing compaction rates. To correctly interpret it, it is necessary to pay attention to the composition of the rocks overlying the compacted interval. While the upper part of the section (between benchmarks 3 and 15) is composed predominantly of carbonates and is virtually identical in composition to wells No. 230 and No. 42, facies substitutions are observed in the lower part (between benchmarks 1 and 3).\u003c/p\u003e \u003cp\u003eBecause the reef is overlain by a carbonate clinoforms, its upper boundary cannot be accurately determined from log data. Therefore, the analysis is conducted starting from the first, most distinct benchmark\u0026mdash;the top of the Tournaisian, where limestones abruptly change to siliclastic (predominantly clayey) rocks of the Lower Visean.\u003c/p\u003e \u003cp\u003eThe interval of Domanik shales in well No 230 is 143 m (excluding the Domanik horizon, which are identical in both wells). The difference in thickness between benchmarks 1 and 2 is 142 m. This value coincides with the current amplitude of the anticline structure along the Tournaisian surface. The section of borehole No. 230 shows changes in the composition of the Kosvin deposits \u0026mdash; the appearance of clay layers (Fig.\u0026nbsp;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e11\u003c/span\u003e, shown by blue arrows). Clearly, during sedimentation, due to the additional accommodation space formed by compaction, clay material was transported to lower-lying areas of the relief. At the same time, the increased clay content of these deposits in borehole No. 230 increased their degree of compaction compared to borehole No. 42.\u003c/p\u003e \u003cp\u003eThe difference in thickness between benchmarks 3 and 2 (Bobrik horizon) is 27 m (4 m and 31 m, respectively). Because they are clays, they were also compacted, creating additional accommodation space in the borehole No. 230 section. The compaction curve in the interval between benchmarks 1\u0026ndash;4 exhibits a bend (shown by green arrows in the Fig.), which is associated with a distortion in the thickness of the analyzed clay deposits of the Kosvinsky and, especially, the Bobrikov horizons.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eAbsolute benchmark elevations in wells No. 42 and No. 230\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"4\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eBenchmark\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eStratigraphy\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eTVD, m (Well No. 42)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eTVD, m (Well No. 230)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eD3f2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e-1886\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e-1887\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eC1t2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e-1384\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e-1527\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eC1v1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e-1380\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e-1496\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eC1v2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e-1327\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e-1433\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eC1v2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e-1238\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e-1326\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eC1s1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e-1179\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e-1252\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eC1s2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e-1090\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e-1152\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eC2b\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e-966\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e-1020\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eC2m\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e-776\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e-824\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eC3k\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e-483\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e-523\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e11\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eC3g\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e-317\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e-356\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e12\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eP1a\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e-215\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e-251\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e13\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eP1s\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e-133\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e-175\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e14\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eP1ar\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e-95\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e-134\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e15\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eP1k\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e-46\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e-85\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e16\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eP1k\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e-25\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eCalculation of compaction in well No. 230\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"5\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eThicknesses between benchmarks\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eIn well No. 42\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eIn well No.. 230\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eThickness difference, m\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eTotal compaction\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e1\u0026ndash;2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e502\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e360\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e-142\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e2\u0026ndash;3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e31\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e27\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e27\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e3\u0026ndash;4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e53\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e63\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e37\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e4\u0026ndash;5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e89\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e107\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e18\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e55\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e5\u0026ndash;6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e59\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e74\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e15\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e70\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e6\u0026ndash;7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e89\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e100\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e11\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e81\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e7\u0026ndash;8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e124\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e132\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e89\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e8\u0026ndash;9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e190\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e196\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e95\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e9\u0026ndash;10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e293\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e301\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e103\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e10\u0026ndash;11\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e166\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e167\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e104\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e11\u0026ndash;12\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e102\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e105\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e107\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e12\u0026ndash;13\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e82\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e76\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e-6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e101\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e13\u0026ndash;14\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e38\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e41\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e104\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e14\u0026ndash;15\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e49\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e49\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e104\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e15\u0026ndash;16\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e54\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e60\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e110\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eIn the section, we observe the final clay thickness, which was clearly greater during sedimentation. By benchmark 4, the compaction curve levels out, which can be interpreted as the end of the main stage of clay compaction. However, compaction of the organic-rich sediments continued for a long time.\u003c/p\u003e \u003cp\u003eThe compaction curve smoothly straightens out toward benchmark 11 (the Carboniferous-Permian boundary), after which fluctuations begin, which are most likely related to tectonic reorganization of the region and the uplift of the Ural Mountains.\u003c/p\u003e \u003cp\u003eThe resulting compaction curve can be roughly divided into three stages. The first, spanning the entire Carboniferous period, is characterized by compaction rates of 2.17 m per million years for the Domanik sequence, or compaction of the Domanik shale interval with a current thickness of 143 m by 89 m, with an overlying sediment thickness of 590 m. During the second stage, rocks compacted at a rate of 0.95 m per million years, or an additional 18 m, with an overlying sediment thickness of 796 m. Due to the absence of Mesozoic-Cenozoic deposits in the study area, the third stage cannot be analyzed in detail. However, a final compaction of 142 m can be recorded (meaning that the Domanik shales were compacted at least twice as much\u0026mdash;142 m by 143 m of their current thickness).\u003c/p\u003e \u003cp\u003eThus, the third stage of compaction is characterized by compaction rates of 0.12 m per million years, or 35 m for a thickness of 548 m of preserved overlying sediments (considering tectonic activation).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec12\" class=\"Section2\"\u003e \u003ch2\u003eCompaction Factors\u003c/h2\u003e \u003cp\u003eAnalysis of thickness changes in selected wells showed that compaction of clayey rocks (Bobrik and Kosvinsky horizons) occurs quite rapidly. Many authors note that the main, most rapid part of this process occurs in the first few meters, after which its rate drops sharply. However, organic-rich rocks can compact over very long periods. This is confirmed by both the calculations performed and structural evidence of their plastic state after lithification of carbonates and cherts.\u003c/p\u003e \u003cp\u003eAn assessment of the degree of compaction of Domanik shales based on the ratio of the transverse size of loaf-shaped concretions to the thickness of the enclosing layer reveals compaction values of 3\u0026ndash;5 times or more. These values likely reflect the actual compaction of the primary sediment, as concretions are the earliest lithified formations. Such concretions or nodules (Selles, Martines, 1996) are common in many organic-rich formations worldwide (including those of clayey composition). Most authors attribute their development to the microbial decomposition of organic matter in the underlying rocks at the upper boundary of the bacterial methanogenesis zone during breaks in sedimentation (Lash, Blood, 2003, Othar\u0026aacute;n, 2020).\u003c/p\u003e \u003cp\u003eMuch rarer stuctures\u0026mdash; folded calcite veins \u0026mdash; apparently are a typical feature of organic-rich radiolarite mud. Identical fractures in Mesozoic-Cenozoic deposits of the Muwwaqar Formation (\"Jordan Shales\") have been the subject of detailed studies (Hooker et al., 2017, Abu-Mahfouz et al., 2019, Hooker et al., 2019), leading the authors to conclude that the main cause of rock compaction is the diagenetic transformation of silica in radiolarian skeletons from opal A to quartz.\u003c/p\u003e \u003cp\u003eIt should be noted that the \"Jordan Shales\" are the closest analogue of Domanik-type rocks. Both are characterized by a low clay content, an abundance of radiolarians, and an extremely high organic matter content. This compositional similarity resulted in the presence of identical structures \u0026mdash; nodules, \"crumpled\" fractures, and straight fractures mineralized by calcite, similar to those shown in Figs.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e\u0026ndash;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e.\u003c/p\u003e \u003cp\u003eUndoubtedly, the transformation of opal A into quartz and the compaction of the initially highly porous radiolarian skeletons are among the causes of sediment volume changes. This process is likely a key factor in the formation of such unusual structures as folded calcite veins. However, compaction can also occur without the participation of radiolarians, as evidenced by the significant compaction of Proterozoic (Lower Riphean) organic-rich shales.\u003c/p\u003e \u003cp\u003eProbably, one of the main factors for such a long stay of sediments in a non-lithified state is organic matter. It also serves as a catalyst for various diagenetic processes (Ricken, 1992). The presence of traces of hydrocarbons in cracks mineralized by calcite (Figs.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e, \u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e) indicates an early transformation of organic matter in compacted rocks (squeezing of hydrocarbon fluids from pores in the literal sense (Magara, 1982)). The relationship between deformation structures and changes in OM is also recorded in the bitumen shows in compaction breccias. E. Lichtfouse and J. Rullk\u0026ouml;tter (Lichtfouse, Rullk\u0026ouml;tter, 1994), studying sediments of the Sea of Japan, by analyzing the ratio of hopanes and steranes of OM in diagenetic cracks and in the parent rock deduced that compaction under silica diagenesis conditions can accelerate the transformation of OM. Similar conclusions were reached by researchers studying the \"Jordanian shales\" (Abu-Mahfouz et al., 2019, Abu-Mahfouz et al., 2020) following a detailed petrographic and geochemical study of Muwwaqar Formation rocks.\u003c/p\u003e \u003cp\u003eThis mechanism may explain the presence of hydrocarbons in immature sediments. For example, Domanik shales in studied area have low maturity based on Tmax (less than 430\u0026deg;C). At the same time, oil samples from numerous fields show a genetic link specifically to Domanik rocks.\u003c/p\u003e \u003c/div\u003e"},{"header":"Conclusion","content":"\u003cp\u003eCarbonate and low clay organic-rich shales retain plasticity for long periods during submergence and can be compacted several times. With such significant volume reduction, the rocks acquire specific compaction structures: folded veins, flat-pebble breccias, saucer-shaped concretions (nodules), etc.\u003c/p\u003e \u003cp\u003eThe process of differential compaction plays a crucial role in the formation of anticlinal structures in sediments enveloping reefs. The proposed methods for calculating changes in compaction rates and constructing a relative compaction curve can be successfully applied in petroleum geology. For example, by intersecting an enveloping structure in the Middle Carboniferous interval, the amplitude of the structure in the Lower Carboniferous and Upper Devonian can be calculated, allowing one to assess the feasibility of further drilling.\u003c/p\u003e \u003cp\u003eDifferential compaction creates localized stresses in rocks, which can lead to faults. If thin seals are ruptured, this will lead to the disintegration of the deposit, and if reservoir rocks are affected, this will improve their filtration properties due to decompression and/or the formation of fractures.\u003c/p\u003e \u003cp\u003eRock compaction and diagenetic alterations of silica probably accelerate the conversion of kerogen to hydrocarbons. Furthermore, prolonged compaction of source rocks can drive the migration of hydrocarbon fluids into the reservoir.\u003c/p\u003e \u003cp\u003eAll structures associated with compaction are observed in rocks enriched in organic matter. Therefore, the presence of such structures may indicate good petroleum-bearing properties of the host rocks even in cases of highly transformed organic matter. For example, in deep-seated Precambrian deposits, where only residual organic carbon can be detected by pyrolysis.\u003c/p\u003e \u003cp\u003eThus, the conducted studies have demonstrated the great theoretical and practical significance of compaction processes in organic-rich rocks. They must be considered in structural analysis, paleotectonic analysis, basin modeling, etc. Failure to account for compaction can lead to misinterpretations of deformation structures as a result of tectonic activity.\u003c/p\u003e \u003cp\u003eRock compaction is an important factor in increasing accommodation space, and therefore must be considered in sequence stratigraphic interpretations of sections (Mirnov, Chanysheva, 2025). Failure to account for compaction processes leads to misinterpretations of paleodepths in sedimentation basins (Ershov, 2016). Thus, the analyzed materials indicate that Domanik shales accumulated at relatively shallow depths (tens of meters), and pinnacle reefs appeared as minor protrusions in the relief during sedimentation, acquiring their colossal dimensions compared to the host rocks only during subsequent compaction.\u003c/p\u003e "},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eAbu‑Mahfouz IS, Cartwright J, Idiz E, Hooker J, Robinson SA (2020) Silica diagenesis promotes early primary hydrocarbon migration. Geology\u003c/li\u003e\n\u003cli\u003eAbu‑Mahfouz IS, Meng Q, Hooker J, Cartwright J (2019) Fractures in mudrocks: advances in constraining timing and understanding mechanisms. Journal of Structural Geology\u003c/li\u003e\n\u003cli\u003eAbu‑Mahfouz IS, Cartwright J, Idiz E, Hooker JN, Robinson SA, van den Boorn SH (2019) Genesis and role of bitumen in fracture development during early catagenesis. Petroleum Geoscience 25:371\u0026ndash;388. DOI: 10.1144/petgeo2018‑179\u003c/li\u003e\n\u003cli\u003eAbu‑Mahfouz IS (2023) Diagenesis, compaction strain and deformation associated with chert and carbonate concretions in organic‑rich marl and phosphorite; Upper Cretaceous to Eocene, Jordan. Sedimentology. DOI: 10.1111/sed.13085\u003c/li\u003e\n\u003cli\u003eAnderson NL (1996) A seismic analysis of differential compaction in the Frasnian Duhamel reef, south‑central Alberta. Computers \u0026amp; Geosciences 22(3):345\u0026ndash;354\u003c/li\u003e\n\u003cli\u003eBera F, Carminati E (2012) Differential compaction and early rock fracturing in high‑relief carbonate platforms: numerical modelling of a Triassic case study (Esino Limestone, Central Southern Alps, Italy). Basin Research 24:1\u0026ndash;17. DOI: 10.1111/j.1365‑2117.2012.00542.x\u003c/li\u003e\n\u003cli\u003eBrown RJ, Anderson NL, Cederwall DA, Sun Z, Manning PM, Zhang Q (1995) Duhamel: a seismic analysis of differential compaction in a Leduc reef. CREWES Research Report 7\u003c/li\u003e\n\u003cli\u003eBruevich SV (1945) Soil moisture content of the Caspian Sea. DAN SSSR 47(4) (In Russ)\u003c/li\u003e\n\u003cli\u003eBuryakovskiy LA (1991) Mathematical simulation of sediment compaction. Journal of Petroleum Science and Engineering 5(2)\u003c/li\u003e\n\u003cli\u003eChen J (2015) Origin of the Furongian limestone breccias in the North China Platform. Sci China Earth Sci 58:770\u0026ndash;775\u003c/li\u003e\n\u003cli\u003eChen J, Han Z, Zhang X et al. (2010) Early diagenetic deformation structures of the Furongian ribbon rocks in Shandong Province of China\u0026mdash;a new perspective of the genesis of limestone conglomerates. Sci China Earth Sci 53:241\u0026ndash;252. DOI: 10.1007/s11430‑010‑0010‑6\u003c/li\u003e\n\u003cli\u003eCroiz\u0026eacute; D, Renard F, Gratier J‑P (2013) Compaction and porosity reduction in carbonates: a review of observations, theory, and experiments. Advances in Geophysics 54. ISSN 0065‑2687. DOI: 10.1016/B978‑0‑12‑380940‑7.00003‑2\u003c/li\u003e\n\u003cli\u003eErshov SV (2016) Paleobathymetry of the Late Jurassic‑Neocomian basin in northern West Siberia and the impact of natural processes. Russian Geology and Geophysics 57(8):1221\u0026ndash;1238. DOI: 10.1016/j.rgg.2016.08.008\u003c/li\u003e\n\u003cli\u003eHedberg HD (1926) The effect of gravitational compaction on the structure of sedimentary rocks. AAPG Bulletin 10:1035\u0026ndash;1072. DOI: 10.1306/3D932750‑16B1‑11D7‑8645000102C1865D\u003c/li\u003e\n\u003cli\u003eHedberg HD (1936) Gravitational compaction of clays and shales. American Journal of Science, Ser 5, 31:241\u0026ndash;287. DOI: 10.2475/AJS.S5‑31.184.241\u003c/li\u003e\n\u003cli\u003eHooker JN, Huggett JM, Cartwright J, Hussein MA (2017) Regional‑scale development of opening‑mode calcite veins due to silica diagenesis. Geochemistry, Geophysics, Geosystems 18:2580\u0026ndash;2600. DOI: 10.1002/2017GC006888\u003c/li\u003e\n\u003cli\u003eHooker J, Abu‑Mahfouz IS, Meng Q, Cartwright J (2019) Fractures in mudrocks: advances in constraining timing and understanding mechanisms. Journal of Structural Geology\u003c/li\u003e\n\u003cli\u003eLash GG, Blood D (2004) Geochemical and textural evidence for early (shallow) diagenetic growth of stratigraphically confined carbonate concretions, Upper Devonian Rhinestreet black shale, western New York. Chemical Geology 206(3\u0026ndash;4):407\u0026ndash;424. DOI: 10.1016/j.chemgeo.2003.12.017\u003c/li\u003e\n\u003cli\u003eLichtfouse E, Rullk\u0026ouml;tter J (1994) Accelerated transformation of organic matter below the silica transition zone in immature sediments from the Japan Sea. Organic Geochemistry 21:517\u0026ndash;523. DOI: 10.1016/0146‑6380(94)90102‑3\u003c/li\u003e\n\u003cli\u003eLisitsyn AP (1956) Bottom sediment moisture content of the Western Bering Sea. DAN SSSR 107(2) (In Russ)\u003c/li\u003e\n\u003cli\u003eMagara K (1978) Compaction and fluid migration: practical petroleum geology. Nauka, Moscow, 318 p\u003c/li\u003e\n\u003cli\u003eMaier DB, Rydberg J, Bigler C, Renberg I (2013) Compaction of recent varved lake sediments. Geologiska Foreningen 135:231\u0026ndash;236. DOI: \u003c/li\u003e\n\u003cli\u003eMirnov RV, Chanysheva LN (2025) Experience of applying sequence‑stratigraphic approach for detailed study of Upper Devonian‑Tournaisian clinoform complex of Aktanysh‑Chishminsky trough. Georesources 27(1):284\u0026ndash;298. DOI: 10.18599/grs.2025.1.28\u003c/li\u003e\n\u003cli\u003eMkrtchyan OM (1980) Patterns of structural form distribution in the Eastern Russian Plate. Nauka, Moscow, 135 p (In Russ)\u003c/li\u003e\n\u003cli\u003eMukhin YuV (1965) Processes of clay sediment compaction. Nedra, Moscow, 200 p (In Russ)\u003c/li\u003e\n\u003cli\u003eMukhin YuV (1965) On the role of geological time in the compaction of clay sediments. Lithology and Useful Fossils, pp 126\u0026ndash;130 (In Russ)\u003c/li\u003e\n\u003cli\u003eNesterov IN (1965) Compaction of clayey rocks. Sovetskaya Geologiya (12):69\u0026ndash;80 (In Russ)\u003c/li\u003e\n\u003cli\u003eOthar\u0026aacute;n G (2020) Sedimentolog\u0026iacute;a y an\u0026aacute;lisis de facies de la Formaci\u0026oacute;n Vaca Muerta (Tithoniano‑Valanginiano), Cuenca Neuquina. El rol de los flujos de fango en la depositaci\u0026oacute;n de espesas sucesiones de lutitas. Ph.D. thesis in Geology. DOI: 10.13140/RG.2.2.32858.67520/1\u003c/li\u003e\n\u003cli\u003eRailsback LB (1993) Original mineralogy of Carboniferous worm tubes: evidence for changing marine chemistry and biomineralization. Geology 21\u003c/li\u003e\n\u003cli\u003eRicken W (1992) A volume and mass approach to carbonate diagenesis: the role of compaction and cementation. In: Developments in Sedimentology 47:291\u0026ndash;315. DOI: 10.1016/S0070‑4571(08)70568‑5\u003c/li\u003e\n\u003cli\u003eSelles‑Martines J (1996) Concretion morphology, classification and genesis. Earth‑Science Reviews 41(3):177\u0026ndash;210\u003c/li\u003e\n\u003cli\u003eSorby HC (1908) On the application of quantitative methods to the study of the structure and history of rocks. Quarterly Journal of the Geological Society of London 64:171\u0026ndash;233\u003c/li\u003e\n\u003cli\u003eStrakhov NM (1960) Fundamentals of the theory of lithogenesis. Volume 1. Types of lithogenesis and their location on the Earth\u0026rsquo;s surface. Publishing House of the USSR Academy of Sciences, Moscow, 210 p\u003c/li\u003e\n\u003cli\u003eTrask PD (1931) Compaction of sediments. AAPG Bulletin 15(3):271\u0026ndash;276. DOI: 10.1306/3D93298A‑16B1‑11D7‑8645000102C1865D\u003c/li\u003e\n\u003cli\u003eVassoevich NB (1960) Experience in constructing a typical curve of gravity compaction of clayey sediments. News of Oil Technology. Geology, pp 11\u0026ndash;15 (In Russ)\u003c/li\u003e\n\u003cli\u003eWeller JM (1959) Compaction of sediments. AAPG Bulletin 43(2):273\u0026ndash;310\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"facies","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"faci","sideBox":"Learn more about [Facies](http://link.springer.com/journal/10347)","snPcode":"10347","submissionUrl":"https://www.editorialmanager.com/faci/default2.aspx","title":"Facies","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"compaction, deformation structures, fractures, flat-pebble breccias, Domanik Formation, hydrocarbon migration","lastPublishedDoi":"10.21203/rs.3.rs-8412682/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-8412682/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThis article examines the compaction of organic-rich siliceous-carbonate sediments, using Upper Devonian-Lower Carboniferous deposits in the southeastern East European Platform as an example. The study is based on the analysis of deep-well core samples containing rocks with varying organic carbon contents. The methodology includes petrographic analysis of thin sections and sedimentological study of the core. Typical features of compaction were identified: the formation of folded calcite veins filled with calcite, the development of saucer-shaped concretions, and flat-pebble breccias. It was established that the degree of rock compaction can exceed threefold. Particular attention is paid to the study of deformation structures arising during compaction. It was found that specific structures reflecting the plastic state of the sediment are formed in layers with high organic matter contents. The mechanisms of silica and calcite redistribution during compaction, as well as the interactions between compacting and early lithified layers, were studied. The results obtained provide a better understanding of sedimentary rock transformation processes and can be used to reconstruct depositional environments and subsequent diagenetic transformations. This study contributes to our understanding of the mechanisms of deformation structure formation in organic-rich sediments.\u003c/p\u003e","manuscriptTitle":"Compaction of organic-rich carbonate and siliceous mud: mechanism, rate, typical structures. Case studies from Domanik Formation (Russia).","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-02-27 11:48:49","doi":"10.21203/rs.3.rs-8412682/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"reviewerAgreed","content":"","date":"2026-02-24T19:26:39+00:00","index":0,"fulltext":""},{"type":"reviewersInvited","content":"","date":"2026-02-24T10:49:59+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-12-24T09:21:26+00:00","index":"","fulltext":""},{"type":"submitted","content":"Facies","date":"2025-12-22T11:41:03+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"facies","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"faci","sideBox":"Learn more about [Facies](http://link.springer.com/journal/10347)","snPcode":"10347","submissionUrl":"https://www.editorialmanager.com/faci/default2.aspx","title":"Facies","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"7a657a71-12f0-40e3-b3f1-3c211e0a91ac","owner":[],"postedDate":"February 27th, 2026","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2026-02-27T11:48:49+00:00","versionOfRecord":[],"versionCreatedAt":"2026-02-27 11:48:49","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-8412682","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-8412682","identity":"rs-8412682","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}