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Carbonates have been known to act as hydrocarbon source rocks, but their basic geochemical and associated hydrocarbon generation characteristics remain not well understood as they occur with argillaceous source rocks in most cases, and the hydrocarbon generation from each rock type is difficult to distinguish, forming one of puzzling issues within the field of petroleum geology and geochemistry. To improve the understanding of this critical issue, this paper reviews recent advances in this field and provides a summary of key areas that can be studied in future. Results show that carbonate source rocks are generally associated with high-salinity environments with low amounts of terrestrial inputs and low dissolved oxygen contents. Petrographically, these source rocks are dark gray or black, fine-grained, stratified, and contain bacterial and algal bioprecursors along with some other impurities. They generally have low organic matter contents, although these can vary significantly in different cases (e.g., the total organic carbon contents of marine and lacustrine carbonate source rocks in China are generally 0.1%–1.0% and 0.4%–4.0%, respectively). These rocks contain type I and type II kerogen, meaning there is a lack of vitrinites. This means that assessment of the maturity of the organic matter in these sediments needs to use non-traditional techniques rather than vitrinite reflectance. In terms of molecular geochemistry, carbonate source rocks have typical characteristics indicative of generally reducing and saline environments and lower organism-dominated bioprecursors of organic matter, e.g., high contents of sulfur compounds, low Pr/Ph ratios, and dominance of n -alkanes. Most of the carbonate source rocks are typically dominated by D-type organic facies in an oxidized shallow water mass, although high-quality source rocks generally contain A- and B-type organic facies in saline lacustrine and marine-reducing environments, respectively. The hydrocarbon generation model for the carbonate source rocks can involve early, middle, and late stages, with a diversity of hydrocarbons within these rocks, which can be aggregated, adsorbed, enclosed within minerals, or present as inclusions. This in turn implies that the large-scale hydrocarbon expulsion from these rocks is reliant on brittle deformation caused by external forces. Finally, a number of aspects of these source rocks remain unclear and need further study, including the effectiveness of carbonates as hydrocarbon source rocks, bioprecursors, and hydrocarbon generation models of carbonate source rock, and the differences between marine and lacustrine carbonate source rocks.

Background Lepidosauria (lizards, snakes, tuatara) is a globally distributed and ecologically important group of over 9,000 reptile species. The earliest fossil records are currently restricted to the Late Triassic and often dated to 227 million years ago (Mya). As these early records include taxa that are relatively derived in their morphology (e.g. Brachyrhinodon ), an earlier unknown history of Lepidosauria is implied. However, molecular age estimates for Lepidosauria have been problematic; dates for the most recent common ancestor of all lepidosaurs range between approximately 226 and 289 Mya whereas estimates for crown-group Squamata (lizards and snakes) vary more dramatically: 179 to 294 Mya. This uncertainty restricts inferences regarding the patterns of diversification and evolution of Lepidosauria as a whole. Results Here we report on a rhynchocephalian fossil from the Middle Triassic of Germany (Vellberg) that represents the oldest known record of a lepidosaur from anywhere in the world. Reliably dated to 238–240 Mya, this material is about 12 million years older than previously known lepidosaur records and is older than some but not all molecular clock estimates for the origin of lepidosaurs. Using RAG1 sequence data from 76 extant taxa and the new fossil specimens two of several calibrations, we estimate that the most recent common ancestor of Lepidosauria lived at least 242 Mya (238–249.5), and crown-group Squamata originated around 193 Mya (176–213). Conclusion A Early/Middle Triassic date for the origin of Lepidosauria disagrees with previous estimates deep within the Permian and suggests the group evolved as part of the faunal recovery after the end-Permain mass extinction as the climate became more humid. Our origin time for crown-group Squamata coincides with shifts towards warmer climates and dramatic changes in fauna and flora. Most major subclades within Squamata originated in the Cretaceous postdating major continental fragmentation. The Vellberg fossil locality is expected to become an important resource for providing a more balanced picture of the Triassic and for bridging gaps in the fossil record of several other major vertebrate groups.

Unconventional resources such as tight, fractured and hybrid shale gas and oil plays as well as oil or kerogen shale systems, are considered exploitable self-contained source and reservoir rocks. A better understanding of the thermal cracking of sedimentary organic matter, hydrocarbons generation, expulsion, storage and retention mechanisms constitutes a key point, estimating the oil and gas in-place, free or adsorbed, for their exploration and exploitation. Herein, we introduce a new “ready to use” method of analysis and interpretation for the Rock-Eval 6 device for better assessment of free or sorbed hydrocarbons in unconventional shale plays. This method was developed at IFP Energies nouvelles (France) and was tested on 15 actual or potential unconventional shale samples from Silurian Shale (Algeria), Mississippian Barnett Shale (USA), Early Jurassic Shale (France), Late Jurassic Bazhenov Shale (Russia) and Eocene Green River Shale at different thermal maturity stages. Results indicate a better quantification of free and/or sorbed hydrocarbons (Sh0 and Sh1 peaks) as well as a more accurate determination of the Rock-Eval Tmax maturity parameter. Les ressources non conventionnelles, en particulier les hydrocarbures de roches mères et les schistes bitumineux sont actuellement considérées comme des roches réservoirs pétroliers exploitables. Une meilleure compréhension sur le craquage thermique de la matière organique sédimentaire, sur les mécanismes de production/génération, d’expulsion, de stockage et de rétention des hydrocarbures constitue un point essentiel à la fois pour l’estimation mais également pour l’exploration et l’estimation du pétrole et du gaz en place (libre ou adsorbé) présents dans ces systèmes. Ici, nous présentons une nouvelle méthode d’analyse et d’interprétation pour le Rock-Eval 6 permettant une meilleure estimation/évaluation des hydrocarbures libres ou adsorbés au sein d’une roche mère non conventionnelle. Cette méthode, développée à l’IFP Energies nouvelles (France), a été élaborée et testée sur 15 échantillons de schistes actuels ou potentiels provenant : du Silurien Shale (Algérie), du Mississippien Barnett Shale (USA), du Jurassique Inférieur du Bassin de Paris (France), du Jurassique Supérieur Bazhenov Shale (Russie) et de l’Eocène Green River Shale (USA) et ce, à des stades différents de maturité thermique. Les résultats indiquent une meilleure quantification d’hydrocarbures libres et/ou adsorbés (pics Sh0 et Sh1) ainsi qu’une détermination plus précise du paramètre de maturité thermique le Tmax du Rock-Eval.

Geometric morphometrics (GM) and finite element analysis (FEA) are increasingly common techniques for the study of form and function. We show how principles of quantitative evolution in continuous phenotypic traits can link the two techniques, allowing hypotheses about the relative importance of different functions to be tested in a phylogenetic and evolutionary framework. Finite element analysis is used to derive quantitative surfaces that describe the comparative performance of different morphologies in a morphospace derived from GM. The combination of two or more performance surfaces describes a quantitative adaptive landscape that can be used to predict the direction morphological evolution would take if a combination of functions was selected for. Predicted paths of evolution also can be derived for hypotheses about the relative importance of multiple functions, which can be tested against evolutionary pathways that are documented by phylogenies or fossil sequences. Magnitudes of evolutionary trade-offs between functions can be estimated using maximum likelihood. We apply these methods to an earlier study of carapace strength and hydrodynamic efficiency in emydid turtles. We find that strength and hydrodynamic efficiency explain about 45% of the variance in shell shape; drift and other unidentified functional factors are necessary to explain the remaining variance. Measurement of the proportional trade-off between shell strength and hydrodynamic efficiency shows that throughout the Cenozoic aquatic turtles generally sacrificed strength for streamlining and terrestrial species favored stronger shells; this suggests that the selective regime operating on small to mid-sized emydids has remained relatively static.

Flight first The Green River formation in Wyoming has produced many important fossils, including Icaronycteris index , which for over 40 years has been regarded as the oldest known bat. Its cranial features suggest that it could locate its insect prey by echolocation. This fuelled a spirited debate between proponents of the 'flight-first', 'echolocation-first' and 'tandem-development' hypotheses of bat evolution. New Green River bat fossils — including two near-complete skeletons, a cast of one of which is shown on the cover — looks to have settled the matter in favour of flight first. The new species is the most primitive bat known. It had fully developed wings and was clearly capable of powered flight, but the morphology of the ear region suggests that it could not echolocate, making it a possible intermediate link between bats and their non-flying, non-echolocating mammalian ancestors. Limb characteristics, including robust hind legs and retention of tiny claws on all of its elongate fingers, indicate that the new bat may have been an agile climber. Bats (Chiroptera) represent one of the largest and most diverse radiations of mammals, accounting for one-fifth of extant species 1 . Although recent studies unambiguously support bat monophyly 2 , 3 , 4 and consensus is rapidly emerging about evolutionary relationships among extant lineages 5 , 6 , 7 , 8 , the fossil record of bats extends over 50 million years, and early evolution of the group remains poorly understood 5 , 7 , 8 , 9 . Here we describe a new bat from the Early Eocene Green River Formation of Wyoming, USA, with features that are more primitive than seen in any previously known bat. The evolutionary pathways that led to flapping flight and echolocation in bats have been in dispute 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , and until now fossils have been of limited use in documenting transitions involved in this marked change in lifestyle. Phylogenetically informed comparisons of the new taxon with other bats and non-flying mammals reveal that critical morphological and functional changes evolved incrementally. Forelimb anatomy indicates that the new bat was capable of powered flight like other Eocene bats, but ear morphology suggests that it lacked their echolocation abilities, supporting a ‘flight first’ hypothesis for chiropteran evolution. The shape of the wings suggests that an undulating gliding–fluttering flight style may be primitive for bats, and the presence of a long calcar indicates that a broad tail membrane evolved early in Chiroptera, probably functioning as an additional airfoil rather than as a prey-capture device. Limb proportions and retention of claws on all digits indicate that the new bat may have been an agile climber that employed quadrupedal locomotion and under-branch hanging behaviour.

Fluorescence using ultraviolet (UV) light has seen increased use as a tool in paleontology over the last decade. Laser-stimulated fluorescence (LSF) is a next generation technique that is emerging as a way to fluoresce paleontological specimens that remain dark under typical UV. A laser's ability to concentrate very high flux rates both at the macroscopic and microscopic levels results in specimens fluorescing in ways a standard UV bulb cannot induce. Presented here are five paleontological case histories that illustrate the technique across a broad range of specimens and scales. Novel uses such as back-lighting opaque specimens to reveal detail and detection of specimens completely obscured by matrix are highlighted in these examples. The recent cost reductions in medium-power short wavelength lasers and use of standard photographic filters has now made this technique widely accessible to researchers. This technology has the potential to automate multiple aspects of paleontology, including preparation and sorting of microfossils. This represents a highly cost-effective way to address paleontology's preparatory bottleneck.

Fluid injection-induced fracture slip during hydraulic stimulation of shales may be seismic or aseismic with the slip mode potentially influencing the evolution of permeability and subsequent shale gas production. We report a series of friction-permeability tests with constant and stepped velocities on planar saw-cut fractures of Longmaxi shale, Green River shale and Marcellus shale. In particular we explore the additive effect of stepped velocity on fracture permeability evolution relative to the background permeability driven at constant velocity. Fracture permeability decreases at larger slip displacement at constant velocity presumably due to asperity degradation and clay swelling. Sudden up-steps in slip velocity temporarily enhance fracture permeability as a result of shear dilation on hard minerals, but permeability net decreases with increasing slip displacement as wear products fill the pore space. Fracture surface roughness is the link between the fracture permeability and friction coefficient, which are both influenced by mineralogical composition. The fractures and sheared-off particles in the tectosilicate-rich and carbonate-rich shales dilate to increase fracture permeability, whereas asperity comminution readily occurs in the phyllosilicate-rich shale to reduce fracture permeability. The results potentially improve our ability to facilitate shale gas extraction and to mitigate the associated seismic risks.

Changes of morphological parameters of oil shale under thermal conditions are investigated. Analyses are based on 26 micro-computed tomography (micro-CT) images of Green River immature shale rock available under creative commons license. Several image processing and characterization algorithms are applied to sequential high-resolution micro-CT images of oil shale samples undergoing pyrolysis. Pore-scale morphology is extracted and quantified, providing results for pore size, throat size, grain size, specific surface, coordination number, and fracture aperture. The results demonstrate critical increases of porosity, coordination number and fracture aperture in the temperature range from 390 to 400  ∘ C , which translates into step change in the transport properties of the shale after pyrolysis. It is further observed that the coordination spectrum, the pore and throat size distributions, become smoother during the pyrolysis process. Finally, the absolute permeability of the samples is calculated at each step in three principal directions, and it is demonstrated that samples’ permeability is more correlated with the pore connectivity rather than the average pore size. The morphological characteristics presented here enable advanced microstructure-informed approaches to pore-scale modeling of transport for optimizing oil production.

As atmospheric carbon dioxide (CO2) and temperatures increase with modern climate change, ancient hothouse periods become a focal point for understanding ecosystem function under similar conditions. The early Eocene exhibited high temperatures, high CO2 levels, and similar tectonic plate configuration as today, so it has been invoked as an analog to modern climate change. During the early Eocene, the greater Green River Basin (GGRB) of southwestern Wyoming was covered by an ancient hypersaline lake (Lake Gosiute; Green River Formation) and associated fluvial and floodplain systems (Wasatch and Bridger formations). The volcaniclastic Bridger Formation was deposited by an inland delta that drained from the northwest into freshwater Lake Gosiute and is known for its vast paleontological assemblages. Using this well-preserved basin deposited during a period of tectonic and paleoclimatic interest, we employ multiple proxies to study trends in provenance, parent material, weathering, and climate throughout 1 million years. The Blue Rim escarpment exposes approximately 100 m of the lower Bridger Formation, which includes plant and mammal fossils, solitary paleosol profiles, and organic remains suitable for geochemical analyses, as well as ash beds and volcaniclastic sandstone beds suitable for radioisotopic dating. New 40Ar / 39Ar ages from the middle and top of the Blue Rim escarpment constrain the age of its strata to ∼ 49.5–48.5 Myr ago during the “falling limb” of the early Eocene Climatic Optimum. We used several geochemical tools to study provenance and parent material in both the paleosols and the associated sediments and found no change in sediment input source despite significant variation in sedimentary facies and organic carbon burial. We also reconstructed environmental conditions, including temperature, precipitation (both from paleosols), and the isotopic composition of atmospheric CO2 from plants found in the floral assemblages. Results from paleosol-based reconstructions were compared to semi-co-temporal reconstructions made using leaf physiognomic techniques and marine proxies. The paleosol-based reconstructions (near the base of the section) of precipitation (608–1167 mm yr−1) and temperature (10.4 to 12.0 ∘C) were within error of, although lower than, those based on floral assemblages, which were stratigraphically higher in the section and represented a highly preserved event later in time. Geochemistry and detrital feldspar geochronology indicate a consistent provenance for Blue Rim sediments, sourcing predominantly from the Idaho paleoriver, which drained the active Challis volcanic field. Thus, because there was neither significant climatic change nor significant provenance change, variation in sedimentary facies and organic carbon burial likely reflected localized geomorphic controls and the relative height of the water table. The ecosystem can be characterized as a wet, subtropical-like forest (i.e., paratropical) throughout the interval based upon the floral humidity province and Holdridge life zone schemes. Given the mid-paleolatitude position of the Blue Rim escarpment, those results are consistent with marine proxies that indicate that globally warm climatic conditions continued beyond the peak warm conditions of the early Eocene Climatic Optimum. The reconstructed atmospheric δ13C value (−5.3 ‰ to −5.8 ‰) closely matches the independently reconstructed value from marine microfossils (−5.4 ‰), which provides confidence in this reconstruction. Likewise, the isotopic composition reconstructed matches the mantle most closely (−5.4 ‰), agreeing with other postulations that warming was maintained by volcanic outgassing rather than a much more isotopically depleted source, such as methane hydrates.