Jurassic-Lower Cretaceous Research Articles

Late Jurassic–Early Cretaceous dinosaur track assemblages from northwestern Hebei Province, China: Implications for paleoenvironment and paleoecology

The relationship between the Middle–Late Jurassic Yanliao Biota and the Early Cretaceous Jehol Biota has long been unresolved due to an approximately 20 Ma “vertebrate fossil gap”. However, a large number of dinosaur tracks have been reported from the Tuchengzi/Houcheng Formation in northern Hebei–western Liaoning, which occupies the stratigraphic position between the Yanliao Biota and the Jehol Biota. This paper presents new discoveries of diverse dinosaur track assemblages from the Upper Jurassic–Lower Cretaceous Houcheng Formation in the Shangyi Basin, northwestern Hebei Province, China. Based on the ichnological analyses, tracks are assigned to the sauropod Parabrontopodus, theropod Grallator, Anchisauripus, Eubrontes, and Therangospodus. The theropod tracks were likely produced by small-sized feathered theropod dinosaurs (Coelurosauria) that thrived in both the Yanliao Biota and the Jehol Biota. These findings imply that these two biotas evolved successively, without evidence of a complete turnover or extinction of biotas. Sedimentological studies of the tracksites reveal their occurrence in diverse sedimentary environments, including braided sandbar, floodplain, and deltaic plain. The coexistence of highly diverse dinosaur tracks with various preservation environments indicates that the living environment during that time was relatively comfortable. The increased diversity of dinosaur tracks in the upper part of the Houcheng Formation closely aligns with the intense volcanic activity of the Zhangjiakou Formation in northwestern Hebei Province. This suggests that volcanic activity likely served a crucial function in the proliferation of the dinosaur fauna in the Shangyi Basin and northern North China during the earliest Cretaceous.

Identification of new objects promising for porphyry molybdenum-copper mineralization when creating the State geological map 1000/3: Sheets O-55, O-56 (Northern Priokhotye, Magadan region) as an example

The Motykleisky, Chistoozerny, and Pavlovichsky new ore clusters promising for porphyry molybdenum-copper mineralization have been identified in the Magadan region due to results of creation of the State Geological Map 1000/3, sheets O-55, O-56. The porphyry-type mineralization is associated with the Priokhotsky plutonic belt of Albian-Cenomanian granitoids of the Magadan suite of the calcareous-alkaline series (K/Na <1). The granitoids are dominated by porphyritic tonalites and quartz diorites of type I magnetite series, often adakitic in composition. The mineralization is accommodated by the Jurassic-Lower Cretaceous island-arc sedimentary-volcanic formations. Relationship between the mineralization and granitoids is substantiated by the U-Pb SIMS SHRIMP and Re-Os TIMS dating. In potential ore clusters, the mineralization is manifested by extensive fi lds of hydrothermal-metasomatic alterations (propylites and quartz-sericite-pyrite metasomatites). Recommendations are given for follow-up large-scale geological survey and prospecting in the area of the potential ore clusters.

Dynamic subsidence in the Colorado basin, offshore Argentina, South Atlantic

The Colorado basin in the SW Atlantic is one of the key exploratory frontier basins along the Argentine shelf. The stratigraphy shows a typical rift basin, divided into two major seismic successions, a Jurassic-Lower Cretaceous synrift followed by an Upper Cretaceous to Cenozoic postrift. They represent, respectively, the breakup of Gondwana and passive margin evolution. While the synrift basin formation was associated with the development of structural grabens, the preservation of thick (thousands of meters) postrift sequences are still debated because they cannot be accounted for only by thermal subsidence. In this work, we conducted a multimethodological subsidence analysis across the Colorado basin, including part of the continental slope. We performed a 1D backstripping analysis on 10 hydrocarbon exploration wells and 32 pseudo-wells, covering the whole basin area and a uniform stretching model, which were supported using dynamic topography data from the study region. From the backstripping analyses, considering the six major postrift sedimentary successions described in the literature, we could recognize three subsidence stages. An initial rapid subsidence stage during the post-rift (125–83 Ma), which is restricted to the main depocenters, followed by a stage of generalized and low subsidence focused on the main axis of the basin (83–33 Ma), with an increase in the last 33 my (33–0 Ma). The stretching models exhibit a typical asymptotic curve, depicting significant subsidence at the onset of the postrift stage, gradually diminishing to minimal values within a few tens of millions of years. Upon comparing the backstripping curves with the stretching subsidence models, particularly during the final flat segments, a residual negative value emerges over time (locally exceeding −500 m), indicating considerable residual subsidence during the Cenozoic postrift evolution along the Colorado Basin. This could be interpreted as dynamic subsidence. This residual sinking in the Argentina shelf matches with dynamic topography numerical models in the study region as well as the occurrence of accumulated slabs in the mantle detected by seismic tomography studies. We propose that the accumulation of slabs along this segment of the South American subduction zone might be the drivers of dynamic subsidence, which assisted to the preservation of a large thickness of post-rift strata along the SW Atlantic margin.

Tectonostratigraphy of the Upper Jurassic-Lower Cretaceous siliciclastic (Shurijeh Formation) in the eastern Kopeh Dagh fold and thrust belt, Iran

During the Late Jurassic-Early Cretaceous, a significant gas-bearing siliciclastic succession was deposited in the Kopeh Dagh fold-thrust belt in northeastern Iran. Study of the regional evolution of depositional system and geodynamic setting of the red beds continental strata can help in a better understanding of the development of an intracontinental extension in this part of the Eurasia Plate. However, this evolution is driven by faulting events that are not fully understood. Facies analysis in wells and outcrops of the Upper Jurassic-Lower Cretaceous Mozduran and Shurijeh formations in the Saleh Abad area, the easternmost part of the Kopeh Dagh Basin, led to the identification of two fluvial braided river systems in the Shurijeh Formation. Provenance and sedimentological studies indicate that siliciclastic sediments were supplied from the south into the north during the Late Jurassic-Early Cretaceous in the Kopeh Dagh Basin. The higher compositional and textural maturity in the upper part of the Shurijeh Formation relative to the lower part indicate more recycling and more extensive transport of the sediments. Two stages of normal faulting can be identified based on the tectonostratigraphic evolution in this interval: The first phase was initiated with polymictic conglomerates during the Late Jurassic in the lower part of the Shurijeh Formation, while the basin-controlling fault was a buried structure. The second phase started with an influx of quartz conglomerates when the basin-controlling fault reached the surface in the middle part of the Shurijeh Formation. This study integrates new field observations and interpretations to enhance understanding of a complex history of multiphase deformation controlled facies patterns, structural geometries of the Late Jurassic-Early Cretaceous. Renewed Cretaceous extension generated accommodation space for the transgressive Shurijeh Formation.

Ilmenite Content of Different Genesis of Productive Sediments of the Trostyanytsky Deposit

The article presents information on the geological structure and ore content of the Trostyanytsky ilmenite deposit located in the northern part of the Volodarsk-Volynskyi massif of the Korostensky pluton bedrock. The deposit is localized in the weathering crust of the basement crystalline rocks and continental deluvial-alluvial and alluvial sediments of the Middle Jurassic-Lower Cretaceous, which were formed by erosion and redeposition of eluvium. Weathering crust together with deluvial-alluvial and alluvial sediments formed the productive deposits of the Trostyanytsky deposit. On the basis of the created target database containing conditional coordinates of wells, their description and testing results, mapping constructions (isohypses of the roof, sole, isopachites of the thickness of the weathering crust of crystalline rocks of the basement, alluvial sands and redeposited kaolins of the Middle Jurassic-Lower Cretaceous) were carried out; lateral distribution of the average ilmenite content in the weathering crust, in the Middle Jurassic-Lower Cretaceous fluvial deposits and in productive sediments, distribution of ilmenite content in the vertical section of wells). These mapping constructions were created based on the results of preliminary (1999) and detailed (2008) geological exploration. The direction and strength of correlations between the topography of the sole and the surface, topography of the sole and the thickness of ilmenite-bearing formations, sole relief and ilmenite content, sediment thickness and ilmenite content in the weathering crust, alluvial deposits of the Middle Jurassic-Lower Cretaceous and in productive deposits. The obtained results made it possible to clarify the structural and material parameters of the ore-bearing rocks, the lateral and vertical distribution of ore bearing in different genetic and different age's formations.

Special Aspects of the Application of Lithogeochemical Indicators for Reconstructing the Paleoclimate and Composition of Source Areas in the West Siberian Late Jurassic–Lower Cretaceous Sedimentary Basin

Special Aspects of the Application of Lithogeochemical Indicators for Reconstructing the Paleoclimate and Composition of Source Areas in the West Siberian Late Jurassic–Lower Cretaceous Sedimentary Basin

Features of Using the Lithogeochemical Indicators for the Reconstruction of Paleoclimate and Composition of Demolition Sources in the Late Jurassic-Lower Cretaceous West Siberian Sedimentary Basin

For the rocks of the Upper Jurassic-Lower Cretaceous Bazhenov formation, a significant positive linear dependence of the Th, Hf, Sc, La content on the Al2O3 content was revealed, and their terrigenous genesis was confirmed. It has been determined that the samples in which the distribution of the values of the Sc/Al2O3 and La/Al2O3 ratios does not satisfy the linear dependence are mixed clayey-siliceous rocks with a P2O5 content 1 mas. % or substantially pyritized (in which the content of pyrite exceeds the content of S and C/S ≤ 1), as well as siliceous mudstones with a SiO2 content 70 mas. % by weight. It is concluded that before analyzing geochemical indicators for reconstructing the conditions of formation of the Bazhenov formation, in addition to carbonated rocks, rocks of the above types, as well as rocks that have undergone late diagenetic kaolinization, should be excluded from the analysis. The conditions of formation of the studied deposits were reconstructed based on the analysis of the values of a number of geochemical modules and indicators. As a result of the study of CIA, CIW variations, it was confirmed that the climate in the Late Jurassic-Early Cretaceous period in the West Siberian sedimentary basin was warm, semiarid. It was revealed that during the entire period under review, it did not change significantly. For the deposits of the Bazhenov formation, a number of indicators such as (La/Yb)N, Eu/Eu*, as well as the distribution of trace element content values on the triangular diagram Th‒La‒Sc, suggest that in the central and southeastern regions of the formation distribution area, the sources of demolition of the mafic composition prevailed.

FIRST RESULTS OF STRATIGRAPHIC DRILLING IN THE EAST SIBERIAN SEA FOCUSED ON THE GEOLOGICAL STUDIES OF THE SUTURE ZONE OF THE CONTINENTAL SHELF’S MARGINAL STRUCTURES A ND DEEP-WATER AREAS OF THE ARCTIC OCEAN

At the initiative of the Federal Agency on Mineral Resources (Rosnedra), in August 2022, a shallow well was drilled in the East Siberian Sea for the first time with a purpose of geological studying the suture zone of deep waters of the Arctic Ocean and marginal structures of the continental shelf. The well was drilled by VSEGEI and Rosgeologia with the assistance of NK Rosneft and linked to the Rosneft’s long-term stratigraphic drilling program. Drilling was accompanied by continuous seismoacoustic profiling and well thermometry. The maximum well depth was 472 m from the bottom surface; in it, 147.5 m of core was taken to a depth of 268 m. Two sedimentary sequences were identified in the section: the lower Jurassic-Lower Cretaceous gently deformed sequence and the upper Neogene-Quaternary horizontally lying sequence. The sequences are separated by a thick unsampled interval with horizons of ascending thermal water. The Jurassic-Lower Cretaceous sequence occurs as a northwestern-dipping monocline, broken by faults and probably belongs to the complex filling the Zhokhov marginal trough of the Verkhoyansk -Chukotka orogen on the Eastern Arctic shelf.

Tectonic-geomorphological evolution and provenance-sedimentary response: Insights from the Middle Jurassic–Lower Cretaceous, Junggar Basin, China

Understanding the complex depositional systems within lake basins requires a comprehensive analysis of the interplay between tectonic-geomorphological evolution and climate change. Based on three-dimensional seismic data, outcrops, well logging, cores, thin sections, and heavy mineral data, this study reconstructed the tectonic-geomorphological evolution of the Middle Jurassic–Lower Cretaceous in the Junggar Basin and analysed the responses of sequence stratigraphy, sediment provenance, and depositional systems. The Jurassic Xishanyao and Cretaceous Qingshuihe Formations developed third-order sequences (SQ1 and SQ2, respectively), which both consisted of lake transgressive (TST) and regressive system tracts (RST). During the SQ1 period, the Chepaizi-Mosuowan palaeo-uplift underwent substantial erosion and supplied sediment to the surrounding sub-basins, where deposited braided-river deltas were formed. Middle Yanshanian tectonism resulted in rapid subsidence, and the Chepaizi-Mosuowan palaeo-uplift submerged. During the early TST stage of SQ2, sediment from the northeast and northwest formed shallow braided-river deltas in topographic lows surrounding the residual Chepaizi-Mosuowan palaeo-uplift and reduced topographic roughness, resulting in a gentle slope to the south. The rapid lacustrine transgression from southeast to north in the late TST stage of SQ2 formed local beach-bars at shallow depths. During the RST stage of SQ2, a climate transition occurred from arid to humid, resulting in depositional systems that evolved from braided to meandering river deltas. The sedimentary fillings of the SQ1 and SQ2 stages were mainly controlled by tectonic-geomorphology and climate change, respectively. Collectively, our results suggest that the tectonic-geomorphological evolution and climate change jointly controlled the sediment sources and determined the depositional features in the basin.

Upper Jurassic–Lower Cretaceous Deposits of the Eastern Part of the Oloy Zone: Stratigraphy, Geochemistry, Age, and Geodynamic Setting

Upper Jurassic–Lower Cretaceous Deposits of the Eastern Part of the Oloy Zone: Stratigraphy, Geochemistry, Age, and Geodynamic Setting

A comparative study of the paleoclimate, paleosalinity and paleoredox conditions of Lower Jurassic-Lower Cretaceous sediments in northeastern Iraq

The findings of this study are considered to be of great importance given their singularity in northeastern (NE) Iraq, as the first broader study that discusses various paleoenviromental proxies (i.e., paleoclimate, paleosalinity and paleoredox proxies) which were predominant during the Early Jurassic-Early Cretaceous period of NE Iraq. To this end, a comparative study of the mineralogical and geochemical features of the Sarki, Sehkanyian, Sargelu, Naokelekan, Barsarin and Chia Gara formations from the Early Jurassic-Early Cretaceous-age Ranya section, was carried out together with a study of the same formations from the Warte section (both sections are located in NE Iraq). Petrographic and microfacies analyses show that all six formations in both sections were deposited in tidal flat (supratidal), restricted lagoons and shallow marine to bathyal depositional environments. The paleoclimate proxies (Ca, Al, Sr/Ba, Rb/Sr and Sr/Cu) and paleosalinity proxies (Sr, Ca, Al and Sr/Ba) together with oxygen isotopes, suggest that the climate was predominantly hot and arid during the period of deposition, contrasting with periods of warm and humid climates during the deposition of the Late Jurassic-Early Cretaceous-age Chia Gara Formation. This climatic change was revealed by a shift in clay mineralogy, from a dominance of illite to increasing amounts (and even dominance) of kaolinite marking the change to more humid conditions within the Late Jurassic-Early Cretaceous period. Geochemical proxies for redox conditions (U/Th, V/Cr, Ni/Co, V/Sc and V/(V+Ni) indicate that deposition of the sediments in the examined areas occurred under anoxic (or reduced oxygen) conditions. This difference in paleoclimate, paleosalinity and paleoredox conditions is likely to be controlled by tectonic activity in the region of northern Iraq, with the development of small silled sub-basins within the broader Zagros Basin/Zagros Fold Belt.

Environmental controls on trace-fossil distribution in the Upper Jurassic-Lower Cretaceous Vaca Muerta Formation (Argentina): Implications for the analysis of fine-grained depositional systems

Over the past years, the interest in organic-rich, fine-grained depositional systems has been growing due to the increasing relevance of unconventional shale reservoirs and several breakthroughs in the study of mud. However, the paleoenvironmental application of ichnologic analyses of these systems is still hindered by the scarcity of discrete trace fossils, small burrow size, and difficulty in obtaining fresh rock samples. The Upper Jurassic-Lower Cretaceous, Vaca Muerta Formation is the most important fine-grained unconventional reservoir in South America, and hence, contains a large density of cores that provide fresh cross-section views with detailed information on mudstone. An ichnologic analysis was carried out on cores and outcrop to develop an integrated ichnologic-sedimentologic model and to understand environmental controls on trace-fossil distribution. The Vaca Muerta Formation shows indistinct bioturbation represented by biodeformational structures generating irregular-laminated and massive mudstone fabrics, and discrete bioturbation and biodeposition structures mostly associated with tuff and heterolithic successions. Trace fossils were grouped into nine ichnocoenoses that illustrate organism responses to environmental controls. Abundant biodeformational structures in mudstone are associated with soupy substrates, whereas a change to softgrounds or loosegrounds occurs during coarser-grained sedimentation (associated with contourite drift, fluid mud flow, slope hemipelagic, and volcanic ash sedimentation), enhancing preservation of discrete traces. Locally, higher-energy events associated with exhumation of consolidated sediment generated firmgrounds colonized by the producers of the Thalassinoides isp. ichnocoenosis. In terms of oxygen, increased bioturbation index, penetration depth, burrow size, and ichnodiversity record an increase in bottom and interstitial water oxygenation. Moreover, an overall food-rich environment precluded specialized feeding and the development of tiered communities. The present study provides a clear picture of the relationship between substrate and oxygen controls in trace-fossil composition and distribution, contributing to the understanding of taphonomic controls and paleoecologic dynamics in fine-grained depositional systems, and providing an additional tool to refine sedimentologic and sequence stratigraphic analyses in similar mudstone successions elsewhere.

Integration of petrophysical and geochemical approaches for lower Miocene Euphrates and Jeribe Formations in selected wells in Tawke Oil Field, Northwestern Iraq, Zagros-fold belt

The Lower Miocene Euphrates and Jeribe Formations are among Iraq's potential reservoirs with significant proven reserves. Petrophysical and geochemical techniques were used to investigate these Formations in the recently discovered Tawke Oil Field. Investigation consisted of acquiring a considerable amount of data from eight wells including conventional core analysis, wireline logging data, gas chromatography data and formation water analysis. The Euphrates and Jeribe Formations are considered to have low to moderate porosity (avg. 2.7–20.5%) and low matrix permeability (avg. 0.87–15mD). Secondary porosity is more prevalent than primary depositional porosity and is a significant factor in optimal reservoir properties with an average of 3.7–5.4% Secondary Porosity Index (SPI) for Jeribe and Euphrates Formations respectively. Meanwhile, fractures increased matrix permeability by up to 33mD and 56mD in the Euphrates and Jeribe Formations respectively. Lithology and core analysis revealed that the Dhiban Formation is a non-reservoir rock with maximum 2% He-Porosity and 0.069mD Klinkenberg permeability confirming that the formation is insufficient as a hydrocarbon reservoir, and that the rock properties are primarily controlled by the depositional environment. The Jeribe Formation contains crude oil of intermediate gravity and high sulfur content. According to gas chromatograph analysis the liquid and oil extracted from the Jeribe Formation originated from a matured marine setting that was possibly algae rich (Type-II kerogen) and has been deposited in a reductive environment. It is believed that these hydrocarbons were sourced from the Middle Jurassic Sargelu and Upper Jurassic-Lower Cretaceous Chia Gara Formations. The chloride-calcium water class is determined from the produced water in the Jeribe Formation and the concentration of elements with dissolved salts confirmed that the Jeribe Formation is in contact throughout eight Tawke wells studied.

Evidence of biotic interactions through shell repair on Early Cretaceous gastropods from west-central Argentina

Evidence of durophagous predatory behavior on benthic invertebrates in the Upper Jurassic–Lower Cretaceous of the Neuquén Basin is scarce, despite the abundant record of potential predators. Herein, we document shell repair in one gastropod from lower Barremian marginal-marine deposits in northern Neuquén Basin, Argentina. This is the first report of shell repair on Early Cretaceous gastropods from Argentina and of shell repair frequencies from the Lower Cretaceous. Paleoanculosa macrochilinoides shells from three sections of the La Tosca Member (Huitrín Formation) in Mendoza province were studied. We described and interpreted the repaired breakage, calculated repair frequencies which were compared among localities, tested for geographic differences in size distribution of total samples and of repaired vs. undamaged shells, and assessed whether this species reached a size refuge. Studied shell repair consists of fractures cutting through growth lines roughly diagonally, from suture to suture, and near the aperture, thus representing apertural damage. Given its stereotypical nature, the damage represents the record of a biotic interaction, likely sublethal predation, instead of diagenetic compaction or damage by physical disturbance. Repair frequencies are low, indicating that shell architecture made P. macrochilinoides susceptible to lethal predatory attacks, or else that there were few predator-prey encounters. There are no major geographic differences regarding repair frequency, size distribution, and preservation. Likely, P. macrochilinoides did not reach a size refuge. This study provides evidence from both a time slice and geographic area with scarce data on crushing predation and from an in-between phase within the Mesozoic Marine Revolution.

Shallow and deep subsurface sediment remobilization and intrusion in the Middle Jurassic to Lower Cretaceous Agardhfjellet Formation (Svalbard)

Abstract Sedimentary injectites are increasingly documented in many hydrocarbon plays at various scales, either interpreted as potential risks (e.g., topseal bypass, a drilling hazard) or benefits (e.g., reservoir interconnection, increased hydrocarbon volumes) for production operations. As such, they have potential critical implications for the assessment of suitability for CO2 injection and sequestration. Detailed characterization of such units, especially in terms of diagenesis and (paleo) fluid flow, is directly achievable at outcrop scale, overcoming dimensional and time constraints otherwise unresolvable at seismic scale. Two sedimentary injection complexes have been recognized in the succession of the Middle Jurassic–Lower Cretaceous Agardhfjellet Formation exposed at Deltaneset, central Spitsbergen, Norway, at different stratigraphic levels. The upper complex comprises two main clastic dikes characterized by different orientation and consolidation, tapering out vertically (upward and downward) within a stratigraphic thickness and lateral extent of more than 50 m and 200 m, respectively. The lower complex is coarser grained, made up by a network of interconnected dikes and sills, shooting off from isolated lenticular and morphologically articulated bodies, interpreted as sedimentary intrusions linked to seafloor extrusion (sand volcano). Petrographic and micromorphological analyses were used to identify the underlying lithologies of the Late Triassic to Middle Jurassic Wilhelmøya Subgroup as the possible source of this remobilized material for both the upper and lower complexes. This subsurface remobilization and consequent intrusion were first achieved in the lower complex during the Late Jurassic at shallow burial conditions, and then at higher confinement pressure for the upper complex, probably during the Late Cretaceous. These results highlight how field data can be used to constrain longlived spatiotemporal relationships of sedimentary intrusions, allowing a finely tuned upscaling of seismic data and interpretations.

Garau Formation as an unconventional hydrocarbon resource in southwestern Iran: a geochemical investigation

Due to the growing need for hydrocarbons and the limited conventional resources, paying attention to unconventional oil and gas resources is essential. The upper Jurassic-Lower Cretaceous in western and southwestern Iran contains the most crucial source rocks of the Zagros sedimentary basin. One of the richest source rocks is the shaly Garau Formation. Owing to geochemical and geological characteristics, the Garau Formation, with Neocomian to Coniacian age and periodicity of radiolore black limestones with black pyrite bituminous shales, ammonite, and chertite shale, is the suitable potential sweet spot as oil shale and gas shale. In this study, a comprehensive regional study was conducted on the entire Garau Formation basin using Rock–Eval parameters and organic matter maturity data. In addition to investigating the hydrocarbon generation potential of the Garau Formation as a source rock, the prospect of this Formation as oil and gas shales in the entire Garau basin was investigated. For this purpose, 31 fields in 5 important sub-basins of Zagros, including East Lorestan, West Lorestan, Izeh zone, Dezful Embayment, and Abadan plain were investigated. The study showed that total organic carbon varies between 0.17 and 24.6, and more than 75% of total organic carbon had values greater than 1. By examining the quantity, quality, and maturity parameters and considering the necessary thresholds, it was found that East Lorestan and West Lorestan have the conditions for oil and gas shales. The highest quantity and best quality of organic matter are related to Eastern Lorestan. By moving west and south of Garau Basin, the quantity and quality of organic matter decrease, and the hydrogen index proves the results. Vitrinite reflection studies indicated that the lowest and highest levels of organic matter maturity belong to East Lorestan and West Lorestan, respectively. Therefore, the northeast of Garau Basin (Eastern Lorestan) has the potential for oil shale, and the northwest of the Basin (Western Lorestan) has the potential for gas shale.

Тефростратиграфия пограничных отложений юры и мела Западной Сибири

The age of tuffaceous interlayers, represented by tuffs and tuffites, which are common in the Upper Jurassic-Lower Cretaceous deposits of Western Siberia (the Bazhenovo, Tutleim and Frolov Formations), is discussed. The nature of these interlayers is associated with the subglobal (transfer of more than 1--2 thousand km) spread of volcanic ash (0.001--0.1 mm) and its sedimentation and burial in a vast epicontinental marine basin during episodes of low sedimentation rates, weak hydrodynamic activity and in the absence of bioturbation. Despite the extremely low thickness of these pyroclastic layers (<1 mm -- first cm), they are systematically noted in the drill core at certain stratigraphic levels. Tuffs and tuffites are clearly recognized due to sharp boundaries and contrasting color and mineral composition comparing to the host rocks. Moreover, these layers often demonstrate exceptionally bright luminescence in yellow and orange tones in the ultraviolet. Some of these pyroclastic layers can be traced over a vast area (more than 700,000 sq km) and hence can be used as isochronous stratigraphic markers. Considering the importance of the information about the distal pyroclastics in sedimentary strata, we have summarized data on boreholes in Western Siberia, containing tuffs and tuffites in the Upper Jurassic - Lower Cretaceous. Detailed linking of interlayers by drilling depth and geophysical logging was performed. The findings of more than 370 tuff and tuffite interlayers in the core of 136 wells have been catalogued. The age of tuffaceous interlayers is justified by the combination of lithostratigraphic and biostratigraphic methods, and geophysical logging. The key ammonite taxa recovered from tuff-bearing boreholes are figured. A brief description of the zones of the Ryazanian stage of Western Siberia and the principles of their identification are given. We suggest to replace the type index of the Surites analogus zone with S. subanalogus. The described sequence of tuffaceous interlayers is combined into 8 sub-regional pyroclastic levels traced throughout the central part of Western Siberia in the Middle Volgian (4 pyroclastic levels), Ryazanian (3 levels) and Lower Valanginian (1 level) intervals. The trace elements content composition of tuffaceous layers is characterized. The enrichment of rare earth elements in the direction from the oldest to the youngest interlayers ones was revealed, and the ratios Gd/Yb, Ho/Yb, Yb/Lu, Zr/Hf, Nd/Sm determine the stratigraphic correspondence of the tuffaceous interlayer to the subregional pyroclastic level. Our results can be used as a tephrostratigraphic scale for the Jurassic-Cretaceous boundary beds. Catalog of finds of Upper Jurassic -- Lower Cretaceous tuffs and tuffites in the core of wells in Western Siberia [<a href="https://doi.org/10.2205/2022ES000817-data">https://doi.org/10.2205/2022ES000817-data</a>] in text format is available on the website of the Earth Sciences Database Repository (BDNS) [<a href="http://esdb.wdcb.ru/">http://esdb.wdcb.ru/</a>], located at the Geophysical Center of the Russian Academy of Sciences.

Basin circulation affecting sediment partitioning in a fine-grained carbonate–siliciclastic, subaqueous clinoform: the Upper Jurassic–Lower Cretaceous Vaca Muerta Formation, Neuquén Basin, Argentina

Fine-grained sediments deposited under oxygen-deficient conditions are enriched in organic matter and hold considerable economic interest as unconventional reservoirs. The present analysis integrates sedimentological, ichnological and geochemical datasets to understand depositional processes in the Upper Jurassic–Lower Cretaceous Vaca Muerta Formation (Argentina), the most important economic unconventional play outside North America. For this purpose, cores from eight wells and one outcrop were examined. The succession comprises 13 facies associations corresponding to marginal-marine, basin, drift and slope environments, deposited in a mixed carbonate–siliciclastic, shelf-margin, subaqueous clinoform system. Estuarine circulation during warm and humid climates produced a stable stratification. Sediment delivery was dominated by pelagic processes in the bottomset, and hemipelagic processes and fluid mud flows in the foreset. However, the typical estuarine circulation changed to weakened estuarine or anti-estuarine during cool and arid climates, triggering wind- and thermohaline-driven contour (bottom) currents that reworked and oxygenated the complete clinoform system. The analysis suggests that distal–proximal trends are of lesser importance for the delineation of sedimentary environments in settings with contrasting basin circulation regimes and provides several insights to understand sediment partitioning in fine-grained clinoform systems. Supplementary material : The stratigraphic context of the Vaca Muerta Formation, an example of facies distribution in a well, trace-fossil descriptions, and X-ray diffraction and total organic carbon geochemical data are available at https://doi.org/10.6084/m9.figshare.c.6294914

Using UAV-Based Photogrammetry Coupled with In Situ Fieldwork and U-Pb Geochronology to Decipher Multi-Phase Deformation Processes: A Case Study from Sarclet, Inner Moray Firth Basin, UK

Constraining the age of formation and repeated movements along fault arrays in superimposed rift basins helps us to better unravel the kinematic history as well as the role of inherited structures in basin evolution. The Inner Moray Firth Basin (IMFB, western North Sea) overlies rocks of the Caledonian basement, the pre-existing Devonian–Carboniferous Orcadian Basin, and a regionally developed Permo–Triassic North Sea basin system. IMFB rifting occurred mainly in the Upper Jurassic–Lower Cretaceous. The rift basin then experienced further regional tilting, uplift and fault reactivation during the Cenozoic. The Devonian successions exposed onshore along the northwestern coast of IMFB and the southeastern onshore exposures of the Orcadian Basin at Sarclet preserve a variety of fault orientations and structures. Their timing and relationship to the structural development of the wider Orcadian and IMFB are poorly understood. In this study, drone airborne optical images are used to create high-resolution 3D digital outcrops. Analyses of these images are then coupled with detailed field observations and U-Pb geochronology of syn-faulting mineralised veins in order to constrain the orientations and absolute timing of fault populations and decipher the kinematic history of the area. In addition, the findings help to better identify deformation structures associated with earlier basin-forming events. This holistic approach helped identify and characterise multiple deformation events, including the Late Carboniferous inversion of Devonian rifting structures, Permian minor fracturing, Late Jurassic–Early Cretaceous rifting and Cenozoic reactivation and local inversion. We were also able to isolate characteristic structures, fault kinematics, fault rock developments and associated mineralisation types related to these events

Type and evolution of the Middle Jurassic–Early Cretaceous basin at the northern margin of the Lhasa Block: constraints of sedimentary characteristics and provenance tracing based on zircon U-Pb ages

To identify its type and evolution features of the Middle Jurassic–Early Cretaceous basin at the northern margin of the Lhasa Block (NMLB) is of great significance for reconstructing its tectonic-paleogeography and assessing the petroliferous basins in the Bangong-Nujiang suture zone (BNSZ) and its adjacent area. This study conducted the sedimentary characteristic analyses and detrital zircon U-Pb dating of the Middle Jurassic–Lower Cretaceous strata exposed in the northern part of Nagqu County (NPNC), Tibet. The Middle–Upper Jurassic Lagongtang Formation was mainly deposited in a steep slope delta and its middle part is characterized by debris flows moving southeastward. The lower part of the Upper Jurassic–Lower Cretaceous Duoni Formation was characterized by molasses formation, and its middle and upper part were primarily deposited on a tidal flat-mixed shelf. The 384 detrital zircons from the debris-flow deposits of the Lagongtang Formation yielded ages of 2800∼210 Ma, except for one yielding an age of 174 Ma. The detrital zircons from the lower part of the Duoni Formation yielded ages of 2744∼152 Ma. Comprehensive research results show that the basin located at the NMLB is a peripheral foreland basin controlled by the BNSZ and had dual source supply, and around 152 Ma, the basin was accompanied by a stronger overthrust event and experienced the conversion from flysch basin to molasses one. Subsequently, a new foreland basin formed marked by the deposition of the Shamuluo Formation in the BNSZ.