The Late Triassic was a prolonged interval of elevated extinction rates and low origination rates that manifested themselves in a series of extinctions during Carnian, Norian and Rhaetian time. Most of these extinctions took place in the marine realm, particularly affecting radiolarians, conodonts, bivalves, ammonoids and reef-building organisms. On land, the case for a Late Triassic mass extinction is much more tenuous and has largely focused on tetrapod vertebrates (amphibians and reptiles), though some workers advocate a sudden end-Triassic (TJB) extinction of land plants. Nevertheless, an extensive literature does not identify a major extinction of land plants at the TJB, and a comprehensive review of palynological records concluded that TJB vegetation changes were non-uniform (different changes in different places), not synchronous and not indicative of a mass extinction of land plants. Claims of a substantial perturbation of plant ecology and diversity at the TJB in East Greenland are indicative of a local change in the paleoflora largely driven by lithofacies changes resulting in changing taphonomic filters. Plant extinctions at the TJB were palaeogeographically localized events, not global in extent. With new and more detailed stratigraphic data, the perceived TJB tetrapod extinction is mostly an artifact of coarse temporal resolution, the compiled correlation effect. The amphibian, archosaur and synapsid extinctions of the Late Triassic are not concentrated at the TJB, but instead occur stepwise, beginning in the Norian and extending into the Hettangian. There was a disruption of the terrestrial ecosystem across the TJB, but it was more modest than generally claimed. The ecological severity of the end-Triassic nonmarine biotic events are relatively low on the global scale. Biotic turnover at the end of the Triassic was likely driven by the CAMP (Central Atlantic Magmatic Province) eruptions, which caused significant environmental perturbations (cooling, warming, acidification) through outgassing, but the effects on the nonmarine biota appear to have been localized, transient and not catastrophic. Long-term changes in the terrestrial biota across the TJB are complex, diachronous and likely climate driven evolutionary changes in the context of fluctuating background extinction rates, not a single, sudden or mass extinction.
The distribution and abundance of Emiliania huxleyi (E. huxleyi) assemblages in the marine sediments of the Aravonitsa Plateau, Greece, and from the eastern Mediterranean are used (1) to evaluate the calcareous nannoplankton NN21a and NN21b biozones and the NN21a/NN21b boundary, and (2) to analyze the palaeoenvironmental and palaeoclimatic conditions prevailing in this interval. The sediment succession displays varied E. huxleyi assemblages and these are interpreted as reflecting climatic variability during marine isotope stages MIS 1-8.
The present paper addresses two tectonostratigraphic concerns on the Late Paleozoic Tianshan tectonic complex (TTC), Xinjiang, Northwest (NW) China: (1) stratigraphic succession and age constraint of the Bayingou ophiolite mélange, eastern Tianshan Mountains and (2) timing of closure of the southern Tianshan ocean and accretion of the Siberian craton recorded in the Aiweiergou (AWEG) area, eastern Tianshan Mountains by integrating stratigraphy, palaeontology, tectonopalaeogeography and palaeobiogeography. In the Bayingou area, the detailed palaeontological survey denies the presence of brachiopod Gigantoproductus fauna, typical of the Early Carboniferous faunas in central-south Tianshan complex, in the Anjihai Formation. In contrast, the Anjihai brachiopod assemblage, as a whole, appears to have a high affinity with the Late Devonian faunas of the eastern Junggar Basin, northern Xinjiang, suggesting a Late Devonian age for the Anjihai Formation. The overlying Shadawang Formation yields the Early Carboniferous radiolarians. These two units form the main part of the Bayingou ophiolite mélange, which therefore is likely Late Devonian to Early Carboniferous in age. The Bayingou area has been likely part of the northern Tianshan-Junggar block since the Late Devonian, although it may have been part of the Central Tianshan tectonostratigraphic province prior to the Late Devonian. The topmost strata of the Bayingou ophiolite mélange are characterized by alternation of volcanics, conglomerate and mudstone, and are better re-assigned to the Taoxigou Group rather than the Keguqingshan Formation. The Bayingou ophiolite mélange comprises the Late Devonian Anjihai Formation, the Carboniferous Bayingou and Shadawang Formations, and the Early Permian Taoxigou Group. In the AWEG area, the Permian and Triassic rocks were previously misinterpreted as the Late Permian turbidites and Late Triassic red beds, respectively. In fact, the Permian successions in AWEG consist of the Early Permian Taoxigou Group and early Middle Permian Lucaogou Formation. The former represents a foreland molasse succession, while the latter yields abundant non-marine fossils of plants, bivalves, and gastropods, and represents typical lacustrine facies deposits. The unconformity between the Permian and the Triassic rocks cannot represent the closure of the Tianshan Ocean, but indicates tectonic uplifts in the foreland basins. In contrast, the molasse-type sediments of the Lower Permian Taoxigou Group may have resulted from the post-orogenesis uplifting and mark the closure of the Tianshan Ocean prior to the Early Permian. Thus, the closure of the Tianshan Ocean and the final tectonic accretion of the South Tianshan block might have taken place over the Permo-Carboniferous transition, strengthened by faunal assemblages obtained from both southern and northern sides of the TTC.
We present coupled ocean-sea-ice simulations of the Middle Jurassic (~165 Ma) when Laurasia and Gondwana began drifting apart and gave rise to the formation of the Atlantic Ocean. Since the opening of the Proto-Caribbean is not well constrained by geological records, configurations with and without an open connection between the Proto-Caribbean and Panthalassa are examined. We use a sea-floor bathymetry obtained by a recently developed three-dimensional (3D) elevation model which compiles geological, palaeogeographical and geophysical data. Our original approach consists in coupling this elevation model, which is based on detailed reconstructions of oceanic realms, with a dynamical ocean circulation model. We find that the Middle Jurassic bathymetry of the Central Atlantic and Proto-Caribbean seaway only allows for a weak current of the order of 2 Sv in the upper 1000 m even if the system is open to the West. The effect of closing the western boundary of the Proto-Caribbean is to increase transport related to barotropic gyres in the southern hemisphere and to change water properties, such as salinity, in the Neo-Tethys. Weak upwelling rates are found in the nascent Atlantic Ocean in the presence of this superficial current and we discuss their compatibility with deep-sea sedimentological records in this region.
The Qinshui Basin in the southeastern Shanxi Province is an important area for coalbed methane (CBM) exploration and production in China, and recent exploration has revealed the presence of other unconventional types of gas such as shale gas and tight sandstone gas. The reservoirs for these unconventional types of gas in this basin are mainly the coals, mudstones, and sandstones of the Carboniferous and Permian; the reservoir thicknesses are controlled by the depositional environments and palaeogeography. This paper presents the results of sedimentological investigations based on data from outcrop and borehole sections, and basin-wide palaeogeographical maps of each formation were reconstructed on the basis of the contours of a variety of lithological parameters. The palaeogeographic units include the depositional environments of the fluvial channel, flood basin (lake), upper delta plain, lower delta plain, delta front, lagoon, tidal flat, barrier bar, and carbonate platform. The Benxi and Taiyuan Formations are composed mainly of limestones, bauxitic mudstones, siltstones, silty mudstones, sandstones, and economically exploitable coal seams, which were formed in delta, tidal flat, lagoon, and carbonate platform environments. The Shanxi Formation consists of sandstones, siltstones, mudstones, and coals; during the deposition of the formation, the northern part of the Qinshui Basin was occupied mainly by an upper delta plain environment, while the central and southern parts were mainly occupied by a lower delta plain environment and the southeastern part by a delta front environment. Thick coal zones occur in the central and southern parts, where the main depositional environment was a lower delta plain. The thick coal zones of the Taiyuan Formation evidently occur in the sandstone-rich belts, located mainly in the lower delta plain environment in the northern part of the basin and the barrier bar environments in the southeastern part of the basin. In contrast, the thick coal zones of the Shanxi Formation extend over the mudstone-rich belts, located in the areas of the lower delta plain environments of the central and southern parts of the Basin. The Xiashihezi, S hangshihezi, and Shiqianfeng Formations consist mainly of red mudstones with thick-interbedded sandstones. During the deposition of these formations, most areas of the basin were occupied by a fluvial channel, resulting in palaeogeographic units that include fluvial channel zones and flood basins. The fluvial channel deposits consist mainly of relatively-thick sandstones, which could have potential for exploration of tight sandstone gas.
Taking more than 1000 clastic hydrocarbon reservoirs of Bohai Bay Basin, Tarim Basin and Junggar Basin, China as examples, the paper has studied the main controlling factors of hydrocarbon reservoirs and their critical conditions to reveal the hydrocarbon distribution and to optimize the search for favorable targets. The results indicated that the various sedimentary facies and lithologic characters control the critical conditions of hydrocarbon accumulation, which shows that hydrocarbon is distributed mainly in sedimentary facies formed under conditions of a long lasting and relatively strong hydrodynamic environment; 95% of the hydrocarbon reservoirs and reserves in the three basins is distributed in siltstones, fine sandstones, conglomerates and pebble-bearing sandstones; moreover, the probability of discovering conventional hydrocarbon reservoirs decreases with the grain size of the clastic rocks. The main reason is that the low relative porosity and permeability of fine-grained reservoirs, lead to small differences in capillary force compared with surrounding rocks and insufficiency of dynamic force for hydrocarbon accumulation; the critical condition for hydrocarbon entering reservoir is that the interfacial potential in the surrounding rock () must be more than twice of that in the reservoir (); the probability of hydrocarbon reservoirs distribution decreases in cases where the hydrodynamic force is too high or too low and when the rocks have too coarse or too fine grains.