Triassic Sediments Research Articles

Triassic temporal and spatial migration of the provenance along the South Ordos Basin: Insights into the tectonic evolution of Eastern Palaeo‐Tethys Ocean

AbstractClarifying the role of mountain‐building processes in the filling history of large hinterland basins is an essential aspect of basin–mountain system research. We consider the case of the Triassic South Ordos Basin (SOB) to clarify these points. Located in the south‐western North China Block (NCB), the SOB which preserves the most complete Triassic deposition on the north of the Qinling Orogenic Belt (QB) is crucial for understanding the detailed tectonic processes of the QB. Sedimentological, petrological and zircon U–Pb geochronological signatures from the three parts (eastern, central and western) in the SOB indicate that the sediment source migrated both temporally and spatially. Stratigraphic correlation identified two fluvial progradational episodes from south to north in the fluvial–deltaic–lacustrine sedimentary system, one in the eastern SOB and the other in the central SOB. The Late Triassic detrital zircons in the central SOB with distinguishing Neoproterozoic ages were derived from the southern margin of the NCB and the QB. The western SOB exhibited the sediment source shifted from pre‐Triassic North Qilian Belt sedimentary cover to basement from the Middle‐to‐Late Triassic based on a zircon age transition from ca. 2000 to ca. 430 Ma. Late Triassic sediment sources also included the southern margin of the NCB and the QB. Differing provenances from east to west were also confirmed using thin section and heavy mineral analyses. Regional comparisons of zircon age distributions in the eastern SOB with published data indicate that detritus from the QB was first transported to the eastern SOB and then to the central and western SOB. Spatiotemporal changes in the sediment source and sedimentary filling transitions in the three parts of the SOB suggest that the QB underwent asynchronous uplift that began in the east during the Early Triassic and propagated westward, reaching its maximum extent in the early Late Triassic.

Devonian to Triassic paleobotanical record from Chile: An overview of the micro- and macrofossil record and fossil localities

Late Paleozoic to early Mesozoic floras are well represented in Chile by several continental fossiliferous outcrops across the country. The oldest floras are Late Devonian in age, and they are mostly located in northern Chile (e.g., El Toco, Arrayán, Las Placetas formations) and are dominated by herbaceous lycopsids. In turn, Middle to Late Triassic floras are widely distributed throughout Chile (e.g., Mamiña, La Ternera, San Felix, Las Breas, El Puquén, Santa Juana, and Panguipulli formations), and are characterized by typical Triassic Gondwanan taxa, such as the ferns Asterotheca, Cladophlebis and Dictyophyllum; the sphenophyte Neocalamites; the corystosperm Dicroidium; the cycadophytes Pterophyllum, and Pseudoctenis; the ginkgophytes Baiera, Sphenobaiera and Ginkgoites; the conifer Heidiphyllum, and gymnosperms of uncertain affinities (i.e., Linguifolium and Taeniopteris). Lycophytes are hitherto unknown in the Chilean Triassic macrofloras. A single fossil locality has been regarded tentatively as Early Triassic in age based on palynomorphs. Most of the Devonian to Triassic plants found in Chile are preserved as impressions, lacking organic matter. However, some adpression plant fossils and palynomorphs have also been found. Fossil woods have been reported from several Triassic sediments of Chile, especially in the northern part of the country. The plant fossil record from Chile is relevant for understanding the dynamics and evolution of the late Paleozoic to early Mesozoic vegetation in the southwestern edge of Gondwana. This contribution provides a general framework that will support future and more detailed paleobotanical studies in Chile. Lastly, this work intents to motivate new generations of paleobotanists in Chile.

Early Triassic (Griesbachian) Deposits of High-Energy Events at the Northwestern Upper Yangtze Region, China

Following the latest Permian mass extinction (LPME), the ocean experienced turbulent conditions due to elevated temperatures during the Griesbachian (Early Triassic). These adverse conditions resulted in a prolonged delay in biotic recovery. However, the current understanding of the sedimentological responses of the ocean at that time to these adverse conditions remains incomplete. The Griesbachian harsh ocean conditions led to the formation of abnormal carbonate rocks (known as anachronistic facies) all around the world. These facies were influenced by a combination of environmental conditions, biotic factors, and actualistic sedimentological processes (e.g., waves and currents, sedimentation). However, the role of actualistic sedimentological processes in forming anachronistic facies during the Griesbachian has been underemphasized in the existing studies. In this research, we examine calcirudite beds, such as flat-pebble conglomerates, from Member 1 of the Feixianguan Formation across multiple sections, including Shangsi, Yudongzi, Dagouli, and Jianfeng in the Upper Yangtze Region. Our analysis is grounded in field investigations, thin-section observations, and the study of triggering mechanisms and formation processes. We identified and described five calcirudite beds (S1–S5) in the Shangsi section, two beds (D1–D2) in the Dagouli section, one at Jianfeng (J1), and one (Y1) in the Yudongzi section. Bed S1 features matrix-supported flat pebbles with a normal grading, interpreted as the result of a debris flow mass-transport process. Beds S2, S3, D1, and J1 contain large mud rip-up clasts, ooids, and bioclasts, suggesting a potential link with tsunami backwash. Beds S4, D2, and Y1 display hummocky cross-stratification and ‘chrysanthemum-shaped’ flat pebbles, indicating storm influence. The presence of vermicular limestones in Bed S5 suggests harsh marine environmental conditions. Collectively, this evidence suggests that high-energy oceanic conditions, including tsunamis and frequent storms, potentially influenced Early Triassic biotic recovery.

Late Permian to early Middle Triassic palaeoenvironmental reconstructions of the High Atlas, Morocco: Geodynamic and climate implications in the intertropical western Peri-Tethyan domain

This study characterizes the depositional environment and climate evolution from the late Permian to the early Middle Triassic, based on detailed sedimentological and palaeosol analysis. Sequence stratigraphy and palaeoenvironmental reconstructions were used to define the Permian-Triassic (P-T) evolution of the High Atlas basins as well as to make a comparison with European basins.The late Permian in Morocco is dominated by distal fluvial fan environment, under arid to semi-arid paleoclimate conditions. Above the P-T unconformity (BS1), the Lower Triassic deposits, record a similar climate evolution from arid to subhumid conditions. In the Argana Basin, the Early Triassic starts by an aeolian deflation lag, followed by stacked debris flow lobes and sheetflood ephemeral alluvial fan deposits, showing immature to locally mature calcretes. The Marrakech High Atlas basins are further characterized by well-developed aeolian dunes in alluvial fan environment. These arid environments evolve through time from proximal to distal deposits, as a retrogradational trend, until well-developed floodplain or lacustrine deposits under semi-arid to subhumid climate (maximum flooding surface, MFS). From MFS, the evolution from distal to proximal environments, testified the progradational trend which is capped by a newly defined angular unconformity (BS2). Above this tectonically induced BS2, the sedimentary section, dated as Anisian is characterized by palaeoenvironments that include meandering river fluvial packages deposited in a semi-arid floodplain.Basin configuration, border fault direction, palaeoenvironments and palaeocurrents recorded in the Argana Basin confirm an independent system, separate from the Marrakech High Atlas (MHA) area during the Triassic. Above BS1, remnant topographies resulted in discrete catchment and discrete drainage systems are evidenced by palaeocurrent and palaeowind measurements controlled by border faults. Palaeoenvironment reconstructions show that the MHA was made up of numerous independent basins during the Early Triassic and the remnant topographies are progressively infilled until BS2. After the BS2, the palaeo-drainage became axial and basins were probably connected in the MHA. Above the P-T unconformity, a common climate evolution is observed in Morocco during the Lower Triassic until BS2, which could correspond to the European Hardegsen unconformity. The sedimentation record shows a similar change in climate and geodynamics to that recorded from both Europe and Morocco.

Andean-type orogenic plateau as a trigger for aridification in the arcs of northeast Pangaea

The interplay between continental motions during the assembly of Pangaea and late Palaeozoic climate change, including severe glaciation and global aridification, remains enigmatic. Here we identify the provenance of Permian–Early Triassic sediments that recorded climate change of North China and estimate palaeoelevation to constrain tectonic-climate interaction during the assembly of northeast Pangaea. Detrital zircon U-Pb-Hf analysis indicates the sediments were locally sourced from the ancient basement and associated with a late Palaeozoic (410–260 million years ago) continental arc, devoid of input from juvenile arcs of the Altaids. These sediments were interpreted as deposited in a retroarc foreland basin ascribed to subduction of the Palaeo-Asian Ocean. Crustal thickness estimated from whole-rock La/Yb yields an average value of 58 ± 11 km, which corresponds to a palaeoelevation of 3.8 ± 0.7 km. The results reveal the existence in North China of an orogenic plateau comparable to the Altiplano of the Andes that blocked moisture transport from the ocean and served as an important orographic barrier to trigger Permian aridification.

Floral and faunal biostratigraphy of the Middle–Upper Triassic Karamay and Huangshanjie formations from the southern Junggar Basin, China

Abstract In the Junggar Basin, northwestern China, the biostratigraphy and vegetation patterns of the Middle–Late Triassic sediments are comparatively poorly resolved. Here we investigate Middle–Late Triassic successions of the Dalongkou Section in the southern Junggar Basin for palynostratigraphy and vegetation patterns. Three palynological abundance zones are proposed here: the Aratrisporites Abundance Zone (Middle Triassic), the Dictyophyllidites – Aratrisporites Abundance Zone (latest Middle to early Late Triassic) and the Lycopodiacidites – Stereisporites informal abundance zone (Late Triassic). A review of previous records of the Fukangichthys Fauna indicates that this vertebrate fossil assemblage is stratigraphically located within the uppermost part of the Karamay Formation and is Middle Triassic in age. The revised dating of this and other faunas are further used to constrain the palynological zones in the Junggar Basin. Although the palynoflora is consistently dominated by non-striate bisaccate pollen (produced by seed ferns and/or conifers) in the studied section, spores record a distinctive abundance increase during the late Middle Triassic. Spore taxon abundance changes indicate a vegetational shift from a Middle Triassic–early Late Triassic community characterized by abundant lycophytes (likely Annalepis and Pleuromeia ) to a Late Triassic ecosystem with abundant dipteridaceous ferns (e.g. Dictyophyllum ) in the Junggar Basin and across North China. This study updates the Triassic biostratigraphy in the Junggar Basin, and sheds light on temporal floral changes in this basin and elsewhere in North China during the Middle to Late Triassic.

Vernaricum ‒ regional distribution, lithostratigraphy, tectonics and paleogeography

The Vernaricum is the highest partial unit belonging to the Hronic nappe system of the Internal Western Carpathians. The stratigraphic range of the Vernaricum sediments is from the Lower Triassic to the Lower Jurassic. The Permian rhyolites and volcaniclastics are tectonically incorporated into the Lower Triassic sediments. The Vernaricum overlies tectonic units of the Northern Veporicum, Fatricum, lower partial nappes of Hronicum and Southern Veporicum. The Gemeric, Meliatic and Silicic rock complexes are located in the tectonic overburden. The paleogeographic position of the Vernaricum is interpreted between the Veporic and Gemeric zones.

Triassic palynology of the Swiss Belchentunnel: a restudy of the Scheuring samples

Well-preserved Carnian (Late Triassic) palynomorphs are rare in Switzerland, despite sediments include one of the important plant fossil localities, Neue Welt near Basel. Modern detailed palynological studies on Triassic palynomorphs in general and especially in the Carnian are scarce, most palynological studies were carried out more than 50 years ago. Nevertheless (Late) Triassic sediments still yield surprises for palynological research. Here, we present the results of the re-study of the famous Belchentunnel samples that were studied and published by Bernhard Scheuring in 1970. The less cheerful result concerns the preservation of slides: more than 60% of the slides are degraded. On the other hand, the restudy of the well-preserved slides showed an unexpected number of algae, acritarchs, and spore taxa not described so far. Especially the spores facilitate the correlation with the well-known biostratigraphic schemes established for the Germanic Basin. The distribution of Porcellispora longdonensis throughout the Belchentunnel succession is especially striking. The acme just below the Schilfsandstein might suggest the presence of ephemeral ponds.

Phanerozoic Tectonic and Sedimentation History of the Arctic: Constraints From Deep‐Time Low‐Temperature Thermochronology Data of Ellesmere Island and Northwest Greenland

AbstractRocks exposed along both sides of the Smith Sound in Ellesmere Island and NW Greenland record the tectono‐sedimentary evolution of the whole Phanerozoic, including two periods of mountain building—the Palaeozoic Ellesmerian Orogeny and the Palaeogene Eurekan Orogeny—and the formation of two major sedimentary basins, the Franklinian and the Sverdrup Basins. We used geo‐ and thermochronology and apatite chemistry data to unravel this evolution. Apatite fission track and (U‐Th)/He dates vary strongly from >600 to <100 Ma. We present internally consistent thermal history models, which allow to explain the data variations by a unitized exhumation and burial history. Our models suggest that the cratonic areas were buried beneath a several km‐thick succession of Franklinian Basin deposits. During the Ellesmerian Orogeny, the craton acted as sediment source, as also suggested by the composition of apatite and by U‐Pb ages of zircon contained in Devonian foreland sediments. The Ellesmerian foreland was buried by up to 4–5 km thick strata on top of the preserved sedimentary rocks. During the Triassic, the Sverdrup Basin strongly widened and extended at least ∼370 km further toward the east, as compared with previous reconstructions of the basin based on the preservation of Triassic deposits. Thermal history modeling suggests Late Cretaceous to early Cenozoic reheating, which may be caused by deposition associated with the Eurekan Orogeny and/or enhanced heat flow associated with continental breakup. Our data also show that low‐temperature thermochronology is not suitable for resolving potential strike‐slip movements along the Wegener Fault.

Lithostratigraphy and geological evolution of Triassic rocks in the Palmyride Basin in Syria

The purpose of the research. This research aims to study the lithostratigraphy and geologic evolution of the Kurrachine Dolomite Formation in the middle Triassic along the Palmyrian Belt Zone in Syria. Studying this formation in its northern and southern parts has shown that it consists of two lithostratigraphic members, where each of them includes a series of lithological units. The petrographical study of the components of these units shows that they are composed of four distinguished components: dolomitic limestones, clayey limestones, clay and anhydrites, pure or mixed and deposited in repeated harmonic layers, gathered mostly in neutral sedimentary sequences. The relevance of the research. This scientific research can provide information about the sedimentary evolution and stratigraphic succession of the region and its historical development. In addition, it can provide insight into the relationships between different sedimentary layers, and mineral resources available in the basin and their potential for exploitation. This research can also lead to a better understanding of the ancient environment in the region. Research methodology. Data was collected from a range of sources, including geological maps and cross-sections, drill core log data from nine gas wells in the field, field observations, and published research. The study area was divided into different lithostratigraphic units, and the geology of each was studied in detail. Attention was paid to the lithology, hydrocarbon content, structural features and other features of each unit. The data collected was then used to construct a geological history of the region, including its tectonic, sedimentary, and paleogeographic evolution. This information was then used to make inferences about the regional stratigraphic framework, as well as to make predictions about future geological evolution. Results and conclusions. This article focuses on the lithostratigraphy, as well as the geological evolution, of Triassic rocks, specifically the Kurrachine Dolomite Formation in the Northeastern Palmyride Basin of Syria. Laboratory studies were conducted to explore the lithology and sedimentary facies of the formation. Results show that the Kurrachine Dolomite Formation is dominated by deposits of a limited lithological nature. It is limited to calcareous, limestone, dolomitic limestones, dolomite, shale, and clay rocks, with limited intrusions of anhydrite in the upper part. The sedimentary environment of the formation is interpreted as shallow-marine. All analysis reveals that the Kurrachine Dolomite Formation is mainly composed of Middle Triassic deposits. This indicates a change in the sedimentation dynamics in the Palmyride Basin during the Middle Triassic. The results of the study provide a better understanding of the geological evolution of the Palmyride Basin in Syria.

Understanding the provenance and depositional conditions of Triassic sedimentary rocks from the Spiti region, Tethys Himalaya, India

The Spiti region, renowned as the Museum of Indian Geology, is a world-famous sedimentary succession containing well-exposed sequences from Neoproterozoic to Cretaceous age. In this study, Triassic siliciclastic sedimentary rocks of the Lilang Supergroup were chosen to understand weathering history, provenance, paleoclimate, and depositional conditions using a geochemical and isotopic approach. Triassic shales show more or less similar compositions with substantial enrichment in CaO compared to PAAS (Post Archean shales from Australia), which may be attributed to the association with limestones in the region. However, the sandstones display significant depletion in the trace element concentrations signifying the effect of quartz dilution. The relative depletion of mobile elements (Rb, Ba) as against immobile elements (Zr, Nb, Hf) can be noticed in the trace element spider diagram of the shales. The Triassic sedimentary rocks are characterized by enriched LREE and depleted HREE patterns with pronounced negative Eu anomalies. The Chemical Index of Alteration (CIA; 56–86) indicates low to intense chemical weathering in the source area. The unusual decrease in CIA and other weathering indices in the stratigraphically up section is attributed to changes in climate and environmental conditions during the deposition of sediments in the Triassic period. Detangling the signatures is crucial to understanding the mass extinction crisis, particularly the role of anoxia in these events. Triassic black shales represent suboxic to anoxic depositional conditions in the redox-sensitive elemental binary diagrams. The carbon isotope data of the present study is very well supported by the Total Organic Carbon (TOC), which infers that the oceanic biological system tried to recover from the depletion of biological life. The εNd and 87Sr/86Sr systematics record a shift in source terrains from the Early to Late Triassic period. The Early Triassic samples show much older depleted mantle model ages (TDM = 1.94–1.98 Ga) compared to Late Triassic sediments (TDM = 1.76–1.91 Ga). Similar interpretations can be drawn from Th/Sc ratios (from ∼ 6 to ∼ 0.05) and (La/Yb) N ratios (from ∼ 32 to ∼ 5), which record an increase in these ratios from Early Triassic to Late Triassic formations of the Spiti sedimentary rocks. Overall, trace elemental ratios and radiogenic isotopic signatures of the Triassic rocks of the Spiti region point towards Pan African granitic origin with minor impressions from the juvenile mafic-rich sources, such as Panjal Traps, the African craton, and Arabian-Nubian shield.

Identification of intrusive objects from seismic data within the ledovoe field in the Barents Sea

The seismic field of the Triassic deposits of the sedimentary section of the Barents Sea is characterized by numerous reflections of increased intensity. These reflections are due to the Jurassic-Cretaceous basaltoid magmatism. On the case of the Ledovoe field, the features of the waves propagation associated with the intrusions – multi-tiered sills are shown. Regularities in the distribution of increased seismic time thicknesses of the mapped sills are revealed, and their relation to faults is established.

Towards an improved discrimination and correlation of Permian-Lower Triassic sediments in Central Europe: A chemostratigraphic approach

The stratigraphic classification and correlation of Permian-Lower Triassic clastic beds in the Central European Basin System traditionally rely on geophysical, bio-, and lithostratigraphic methods. However, in basin margin areas, the accuracy of these tools is diminished due to the heterogeneous distribution of stratigraphic markers, lack of index fossils, and greater climatic and tectonic disturbance. To overcome these limitations, this study introduces a more versatile, multifaceted and chemostratigraphy-based approach. By integrating results from bulk X-ray fluorescence analysis, sandstone petrography, Raman heavy mineral analysis, lithofacies characterisation and borehole gamma-ray logs, we produce robust multi-stratigraphic schemes for selected sequences in the Franconian Basin (SE Central European Basin System). Hierarchical chemostratigraphic zones, comprising five chemozones and sixteen subzones, were designed using key elemental ratios (Ga/Rb, Rb/K, Na/K, Ca/Mg, Cr/Ti, Th/Ti, Nb/Th, Ti/Nb, P/Ti, Zr/P, Zr/Y), whose changes through time reflect modifications in the mineralogical composition of sedimentary rocks. To ensure precise interpretations of geochemical data, we established links between mineralogical and chemical components through statistical processing and direct comparison with mineralogical assemblages. Our results demonstrate that chemostratigraphic boundaries can identify major changes in palaeo-depositional environments and sediment sources induced by eustatic, tectonic and climatic disturbances. For example, changes in the P/Ti and Zr/P ratios across the CP3-CT1 document the increased abundance in apatite-rich granitic detritus, resulting from the exposure of new source lithologies in the catchment area due to Early Triassic synsedimentary tectonism. Since these perturbations had a regional impact on sedimentation, their geochemical fingerprints are correlated across the basin, regardless of lithofacies variability or distance between sections. Moreover, integrating characteristic geochemical signals into multi-stratigraphic schemes enables more precise placement of stratigraphic boundaries, identification of locally deposited/preserved stratigraphic markers, and overall refinement of outdated classification schemes. The chemostratigraphic approach introduced in this study offers a solution to the limitations of conventional stratigraphic tools, allowing robust characterisations and correlations of Permian-Triassic sequences in the marginal regions of the Central European Basin System. In addition, the multi-analytical workflow for processing geochemical data, refining stratigraphic schemes and attributing geochemical anomalies to environmental perturbations represents a further step towards more precise applications of chemostratigraphy to the depositional record.

Triassic source rocks of the Eastern Ciscaucasia

Background. Triassic deposits of the Eastern Ciscaucasia belong to the upper part of the transient zone, which is considered promising for hydrocarbon exploration. The presence of numerous deposits, as well as non-commercial hydrocarbon flows in boreholes, indicate the existence of petroleum systems in this part of the section. However, issues related to the sources of hydrocarbons in the Triassic deposits still remain unresolved.Aim. To identify and study the possible source rocks for the Triassic deposits of the Eastern Ciscaucasia, as well as to assess their contribution to the hydrocarbon potential of the upper part of the transient zone.Materials and methods. Research materials involved all available geological, geophysical and geochemical data published on the section under study, as well as reports from the Russian Federation geological repository. The collected data were analyzed as part of the conducted basin analysis. Numerical basin modeling and paleogeographic reconstructions were performed.Results. The paleogeographic conditions of the Eastern Ciscaucasia and the adjacent areas of the Caspian Sea at the Triassic period were studied. The results of basin analysis were used to construct the distribution maps of Neftekumskaya, Kultaisko-Demyanovskaya and Kizlyarskaya source rocks and to assess their charging ability for Lower and Middle Triassic reservoirs.Conclusion. The conducted numerical modelling revealed several pods of still active source rocks in the Neftekumskaya, Kultaisko-Demyanovskaya and Kizlyarskaya sections. Lower Triassic reservoirs charged from both the Neftekumskaya and Kultaisko-Demyanovskaya source rocks, unlike Middle Triassic reservoirs that charged from the Kizlyarskaya source rocks. Thus, independent petroleum systems separated by the Anisian seal at the two stratigraphic levels in the Triassic part of the transitional complex of Eastern Ciscaucasia were identified.

First report of a Late Triassic dinosaur track from the Zigui Basin, Middle Yangtze region, China

Trace fossils offer a great potential to enhance our understanding of the rise of dinosaurs and their interactions with the environment. Here, we report a Rhaetian theropod footprint found in the Shazhenxi Formation of the Zigui Basin, representing the stratigraphically oldest dinosaur track recorded from the Middle Yangtze region and has great significance for understanding the Late Triassic theropods and their distribution across East Asia. The tridactyl track is assigned to cf. Eubrontes isp. and shows a similar morphology with some tracks from the Sichuan Basin, indicating that Eubrontes had a wider spatial distribution in the Upper Triassic than previously thought. This work highlights the great interest and importance of palaeoichnological prospecting in the Triassic deposits of the Zigui Basin.

Assessment of Hydrocarbon Potential Conversion in Source Rocks in the Southwestern Flank of the Korotaikha Depression, Timan–Pechora Basin

The 1-D burial and thermal history of the Korotaikha depression in the Timan–Pechora basin was numerically simulated for the sedimentary sequences of three wells: Korotaikhinskaya 1, Labogeyskaya 15, and Khavdeiskaya 1. This made it possible to numerically assess the conversion history of the hydrocarbon (HC) potential of source rocks in the southwestern flank of the Korotaikha depression in the northeastern Timan−Pechora basin. The modern modified kinetic spectrum of vitrinite maturation was used in calculations of the vitrinite reflectance to clarify the thermal history of the sedimentary cover of the study area. The occurrence of episodes of hydrothermal activity follows from comparison of the calculated and measured values of the vitrinite reflectance and explains the jumps in the maturity of organic matter at the boundaries of the unconformity of Quaternary and Triassic sediments, as well as the Permian and Carboniferous sediments. The simulations suggest a high conversion of the initial HC potential of the source rocks of the Silurian and Domanic horizons, Tournaisian, and Visean ages in the Korotaikhinskaya and Labogeiskaya areas and moderate generation in the Havdeyskaya area. The simulation shows that the high grades of the catagenesis (MC5 and higher) of the main source rocks and the significant role of secondary cracking of liquid HC fractions in the central part of the Korotaikha depression (wells Korotaikhinskaya 1 and Labogeyskaya 15) suggest that the possible HC accumulations should contain only gas. Accumulations in the southern part of the depression (Khavdeiskaya area), where secondary cracking was minimal and source rocks occur within the oil window, should contain both oil and gas (due to Permian rocks with terrigenous organic matter).

Prodigious shift in provenance across Permian-Triassic Boundary at Guryul Ravine Section, Kashmir, Tethys Himalaya, India: Evidences from Sr and Nd isotopes

The Permian-Triassic Boundary (PTB) section (Late Permian Zewan Formation and Early Triassic Khunamuh Formation) at Guryul Ravine (Kashmir, India) preserves potentially important information about the depositional conditions and provenance changes across the PTB. Several palaeobiological, sedimentological and geochemical studies have been conducted on this archetypal section to understand the causes of mass extinction at the PTB, however no integrated chemo-stratigraphic study focusing on provenance and geodynamics has been attempted. In the present study, samples from a 36 m thick interval across the PTB are analysed for major and trace element concentrations, Sr-, Nd- and Corg isotope geochemistry along with TOC (total organic carbon) contents to understand the contemporary environmental and provenance changes. The Late Permian Zewan Formation have relatively low chemical index of alteration (CIA) values (55–77) and low αAlCa (0.1–12.6), αAlNa (0.7–9.6), αAlMg (1.0–6.1) values, implying moderate weathering conditions; whereas the Early Triassic sediments of overlying Khunamuh Formation show higher CIA (69–79) and αAlCa (1.4–14.0), αAlNa (2.2–11.5), αAlMg (2.0–6.4) values indicating more intense chemical weathering conditions. The vertical profiles of δ13Corg, δ34Spyr and various redox-indicators suggest euxinic-anoxic condition during the latest Permian, and show a significant change in depositional conditions from anoxic to oxic across the PTB. The significant finding of the present study is the dramatic change of Sr- and Nd isotopic compositions across the PTB, indicating remarkable shift in provenance. The Late Permian samples show much less-radiogenic ɛNd(0) (avg. –15.27), radiogenic 87Sr/S6Sr(0) (avg. 0.72409) and older TDM ages (1.35–1.56 Ga) compared to the early Triassic samples (avg. εNd(0) = −9.49,87Sr/S6Sr(0) = 0.719282, TDM = 1.71–1.76 Ga). The εNd(0) and 87Sr/S6Sr(0) composition of Late Permian rocks overlap with the signatures of Tethyan Himalaya and Neoproterozoic-Cambrian Marwar Supergroup of NW India, indicating similar old cratonic sources. Higher εNd(0), younger TDM ages and lower 87Sr/86Sr(0) in Triassic samples suggest contribution from juvenile sources and Panjal volcanics, Cadimian arc of Cimmeria or African-Nubian shield could be the likely source terrains.

Petrography and geochemistry of siliciclastic sediments in Permo-Triassic transition from the southern Pranhita-Godavari Gondwana basin, India: Implications for paleoclimate

The Kamthi Formation, in the intracratonic Pranhita-Godavari Gondwana rift basin, bore signatures of climate change from a warm humid climate in Late Permian to hot arid during the Early Triassic. Sedimentation took place mainly under fluvial conditions. The Kamthi sediments were unaffected by burial diagenesis and the source remained the same, therefore this provides an excellent opportunity to study the climatic influence on petrogenesis in an intracratonic rift basin. Subsurface palynofacies data of Kamthi Formation from the southern part of the basin established the presence of Upper Permian rock units equivalent to the Raniganj Formation, which are overlain by Lower Triassic sediments equivalent to Panchet Formation of the Damodar valley Gondwana basins, and are separated by a gradational contact. QFL and trace element compositions reveal transitional continental to craton interior provenance with dominantly felsic source areas, along with some meta-sedimentary and mafic components. Dominance of kaolinite, coal, alteration of K-feldspar, and biotite in the Raniganj equivalent sandstones attests to a humid climate. The presence of mostly fresh K-feldspar, ferruginous matrices, Fe-carbonate nodules, cutans, and microcrystalline silica cement in the Panchet equivalent sandstones mark a shift from humid to arid/semi-arid. This climatic shift is not reflected in the uniform feldspatho-quartzose to quartzose sandstone compositions and mudstone major oxide compositions. The mudstones are depleted in mobile elements, have low K2O/Al2O3 (0.11–0.18), low ICV (0.35–0.72), high SiO2/Al2O3 (2.3–3.4), high K2O/Na2O and moderately high CIA (80.12–87.05) that collectively suggest moderately intense weathering. Despite the humid climate, the Raniganj Formation equivalent rock units did not attain the highest mineralogical maturity due to proximity to relatively high-relief source areas in a fluviolacustrine environment. This relationship resulted in a lack of short-term sediment storage that favoured rapid erosion and sedimentation.

Evaluation of Quantitative Criteria for Triassic Reservoirs in the South Mangyshlak Basin

Carbonate rocks of the Triassic deposits of the South Mangyshlak basin are investigated in this paper for their boundary values, which are important for interpretation of field geophysical data as well as perforation and blasting. Based on their lithological composition, Triassic deposits are classified as either terrigenous or carbonate reservoirs. Carbonate reservoirs are found in the Middle Triassic strata containing volcanogenic dolomite and volcanogenic limestone rocks. A complex type of reservoir characterizes these rocks: porous-fractured, porous-cavernous, and fractured. Upper Triassic sediments are formed by the intercalation of tuffaceous, siltstone-sandy, and mudstone rocks overlying Middle Triassic sedimentary rocks. Oil deposits are confined to polymictic sandstones, which are oil-saturated to varying degrees. In order to substantiate the quantitative criteria of the reservoir, experimental studies of the core samples were carried out in the laboratory. Fluid flow studies were performed where physical and hydrodynamic characteristics were determined when oil was displaced by displacing reagents. On the basis of the parameters obtained, correlations between reservoirs and non-reservoirs were constructed. Based on relationships between reservoir properties such as porosity and permeability versus residual water content, as well as effective porosity and permeability versus dynamic porosity, the boundary values were determined. Using these results, the porosity limit for the Middle and Upper Triassic strata has been determined to be 7%, the permeability limit for the Middle Triassic has been determined to be 0.02 X 10-3 μm2, and the permeability limit for the Upper Triassic has been determined to be 0.3 X 10-3 μm2.

Postsedimentary Transformations in the Lower Triassic Deposits in the North of Varandey-Adzva Zone (Pechora Oil and Gas-Bearing Basin)

New data on the mineral composition of Lower Triassic terrigenous deposits in the north of the Pechora oil and gas bearing basin are presented. The relevance of the study is due to the fact that terrigenous natural reservoirs confined to this part of the section have a heterogeneous structure both in area and in section. The purpose of the article was to identify the features of the formation and distribution of minerals that fill the void space of reservoirs. As a result of studying by the methods of optical microscopy, X-ray phase analysis, electron microscopy, signs of mineralogenesis processes, post-sedimentary transformations of sandy reservoirs were revealed. It is shown that the most widespread are quartz regeneration, transformation of minerals of the mica group, formation of calcite of various generations, formation of authigenic clay minerals, etc. Diagenetic changes in terrigenous rocks play a significant role in the formation of reservoir properties and lead to heterogeneity of reservoirs. It is shown that a large amount of calcite in sandstone cement leads to a significant decrease in porosity and permeability parameters. Pore cement of chlorite-smectite composition in fine-grained sandstones also leads to a decrease in the quality of reservoirs. Coarse and medium-grained sandstones with a low content of cement, predominantly of kaolinite or chlorite composition, are characterized by higher reservoir properties. Crustification cement of chlorite composition, pore-filling cement of kaolinite composition contribute to the formation of reservoirs with higher rates.