Geological Events Research Articles

Long-Lasting Magmatic, Metamorphic Events in the Cathaysia Block: Insights from the Geochronology and Geochemistry of Inherited Zircons in Jurassic A-Type Granites

The Paleoproterozoic basement underlying the Cathaysia Block remains relatively understudied, and its contribution to the region’s tectonic evolution requires further investigation. In this study, we examined Jurassic Laiziling and Jianfengling A-type granites and identified a significant number of zircon grains exhibiting varied CL imaging characteristics. These zircons yielded four distinct age groups: <100 Ma, 200–100 Ma, 500–200 Ma, and >700 Ma. Detailed trace element analysis revealed that these age groups correspond to different zircon types: metamorphic recrystallized zircons (<100 Ma), primary magmatic zircons (200–100 Ma), and inherited zircons (500–200 Ma and >700 Ma). Through host rock and tectonic setting discrimination, we consider that the inherited zircons have host rocks of S-type granites and basic rocks, and these were formed in subduction-compression tectonic environments. In comparison to local significant geological events in history, we propose that these zircons record multiple tectonic events in the South China Block, including the amalgamation of the Yangtze and Cathaysia Blocks during the Neoproterozoic; an intracontinental orogenic event that occurred during the Middle Paleozoic; and subduction–exhumation processes related to the Paleo-Pacific slab; as well as extensional metamorphic events from the Cretaceous to Tertiary events. A comparison of Hf isotopic compositions revealed that zircons aged 500–200 Ma and >700 Ma share a 2.5–1.6 Ga crustal evolution zone, indicating that multiple re-melting events have occurred within the Paleoproterozoic basement of the Cathaysia Block.

The Inherited Crustal Structure and Lithospheric Thermal Field Beneath the Sea of Marmara (NW Türkiye): Observations From 3D Gravity Modeling and Seismic Tomography Analysis

AbstractThe North Anatolian Fault (NAF) extends for over 1,000 km across Türkiye and poses significant seismic hazard in the region. The Main Marmara Fault (MMF) segment of the NAF in the Sea of Marmara (NW Türkiye), exhibits along‐strike segmentation in its interseismic strain accumulation. Constraining the lithospheric configuration below the MMF is critical to understand its segmentation and assessing seismic hazard in the area. We present a new 3D lithospheric‐scale density of the Sea of Marmara, that combines gravity modeling and seismic tomography analysis. Using forward and inverse gravity modeling with free‐air gravity data and available constraints of geological units we derived the intra‐crustal density structure. Shear‐wave velocity tomography models provided insights into the temperature and density configuration of the uppermost mantle, and the geometry of the 1330°C isotherm. Our results highlight significant crustal density variations: lower‐density crust in the Sakarya Zone and Strandja Massif, and denser crust below the Istanbul Zone, which overlies a relatively hotter lithospheric mantle. This lithospheric configuration reflects both ongoing tectonic processes and inheritance from past geological events, including the drifting of the Istanbul Zone crustal block and the signature of past subduction events. The extent of the Istanbul Zone denser crust spatially correlates with the locked segment of the MMF. The bimaterial nature of the fault segment likely influences its interseismic and coseismic behavior. The denser, stiffer Istanbul Zone crust would promote interseismically locked conditions in contrast to the adjacent, more compliant crustal block and could result in asymmetric rupture with a preferred directivity.

The motion mechanism of a boulder transported by landslide

Various soil-rock mixed landslides occur in the natural environment. Carried along in the slide, boulders will eventually come to rest. The origin of boulder motion provides crucial constraints for inferring geological events. To overcome the challenges posed by the limited visibility within landslides and the subsequent difficulty in observing boulder motion, we propose a novel device to measure three-axis acceleration and angular velocity using Inertial Measurement Unit (IMU) technology. By comparing with the traditional high-speed camera, the efficacy of the IMU sphere is validated. In the study of boulder movements within landslides, we employ the IMU sphere to characterize boulders. Through experiments varying two key parameters—the initial position of the IMU sphere and the mass of fine particles—this study identifies three distinct final deposition states of the IMU sphere: separate, partially submerged, and completely submerged. By analyzing the potential and kinetic energy during the sliding process of the IMU sphere, we delve into the combined effects of motion enhancement due to landslide deformation and motion hindrance as the IMU sphere passes through fine particles, thereby revealing the underlying movement mechanisms of boulders within landslides. Analysis of leading wave heights indicates minimal sensitivity to the initial position of the IMU sphere, with the mass of fine particles exerting the primary influence. At last, through a comprehensive analysis of the IMU sphere's motion, a novel positional parameter is introduced, leading to the identification of motion mechanisms and distinct phase diagrams depicting deposition states.

Unveiling hidden diversity: Phylogenomics of neotomine rodents and taxonomic implications for the genus Peromyscus

Neotomine rodents (Cricetidae, Neotominae) represent one of the most commonly encountered and diverse group of rodents in North America, yet phylogenetic relationships within this group remain uncertain. This subfamily is known for its rapid evolution, adding more complexity to our efforts to unravel their evolutionary history. The main debate revolves around the recognition of the genus Peromyscus as monophyletic or paraphyletic due to its relationship with other genera such as Habromys, Megadontomys, Podomys, Neotomodon, and Osgoodomys. Here, we aim to resolve phylogenetic relationships within Neotominae, to further explore their evolutionary history and taxonomic boundaries. We used target capture and high-throughput sequencing of complete mitogenomes and thousands of genome-wide ultraconserved elements loci (UCEs). Our comprehensive analyses encompassed 53 species of Neotominae spanning 12 previously described genera, along with one yet-undescribed genus. We also investigated 12 out of the 13 species groups within Peromyscus. Our analyses, including Maximum Likelihood and Bayesian Inference with both mitogemomes and UCEs, as well as the coalescent species-tree-based approach with UCEs, consistently recovered concordant and well-resolved phylogenies with high levels of nodal support. We identified seven main clades within Neotominae that could potentially be recognized at the generic level, mostly to categorize the genus Peromyscus as a monophyletic group, including one species group within “Peromyscus”. Furthermore, our divergence dating estimates place the crown age of Neotominae to be around the late Miocene at ca. 7.9 – 10.7 mya. While generic level diversification continued through the Pliocene, species level diversification predominantly occurred during the late Pliocene, extending through the Pleistocene and Holocene. These epochs have been recognized as periods with significant changes in flora and fauna, driving ecological transformations on a global scale. We hypothesized that climatic and vegetation shifts during the Neogene and Quaternary, coupled with geological events, topographical features, and the presence of biogeographical corridors played a pivotal role in the speciation and diversification of Neotominae. Recognizing the importance of generating genomic-scale data coupled with a broad taxonomic sampling, our study, for the first time, offers resolution of the relationships among the main lineages of Neotominae. We expect that the phylogeny presented here will serve as a foundational resource for future systematic and evolutionary studies. This includes facilitating a proper comprehensive taxonomic revision of the group and the formal description and naming of new genera.

India–Eurasia convergence speed-up by passive-margin sediment subduction

The fast increase of convergence rate between India and Eurasia around 65 million years ago (Ma)—from approximately 8 cm yr−1 to a peak rate of approximately 18 cm yr−1—remains a complex geological event to explain1–8, given the inherent uncertainty surrounding the tectonic history and the intricate interplay of forces influencing plate speed9–11. Here we use a combination of geochemical analysis and geodynamic modelling to propose that this rapid convergence can be explained by sediment subduction derived from the northern Indian passive margin. Through isotope and trace element analysis, we find an enhanced contribution of terrigenous sediment melt to the mantle source of the Gangdese magmatic rocks around 65 Ma, concurrent with the acceleration of India–Eurasia convergence. Numerical experiments suggest that subduction of sediments more than 1 km thick covering an approximately 1,000-km-wide ocean basin abutting the northern Indian passive margin starting from 65 Ma could have spurred the increased convergence rate and further led to significant crustal extension, consistent with empirical observations. Our study implies that the acceleration of India–Eurasia convergence marks the arrival of passive-margin-derived sediments, constraining the initial India–Eurasia collision to be around 60 Ma. It further suggests that temporary accelerations in subduction rates might be a common feature at the final stage of continental assembly.

High-resolution sedimentary cyclostratigraphy and astronomical signals in the Upper Ordovician of Southwest China

During the Late Ordovician, a series of significant biotic and geological events occurred globally and more specifically in South China. The development of a high-resolution orbital cyclostratigraphic framework and a precise radioisotope dating has greatly enhanced our understanding of the factors controlling these events. In this study, quantitative proxies for palaeo-water depths, derived from sedimentological analyses, serve as indicators for orbital cyclostratigraphic assessment.Relatively shallow-marine carbonates with well-developed shallowing-upward cycles were deposited in the western Yangtze Platform during the Late Ordovician. High-resolution geochronological data were obtained from high-precision isotope dilution thermal ionization mass spectrometry (ID-TIMS) zircon dating of K-bentonite beds at the studied section. This facilitated sedimentary facies and environmental analyses, as well as the recognition of sedimentary cycles. Based on mud content, bioclastic content, and laminations, four sedimentary facies, twelve sedimentary microfacies, and forty-eight shallowing-upward sedimentary cycles were identified in the Daduhe Formation.Through comparative time series analysis of depth rank, lime mudstone-calcareous mudstone binary data, non-carbonate content, and anhysteretic remanent magnetization (ARM), astronomical cycles and trends in sedimentation rates have been identified. This study confirms the reliability of radioisotope dating, establishing a 0.46 Myr duration for the Dicellograptus complexus graptolite biozone and a 0.96 Myr duration for the Paraorthograptus pacificus graptolite biozone, both with an empirical uncertainty of 0.1 Myr. This research proposes a reliable method for identifying astronomical cycles through high-precision sedimentary microfacies and cyclostratigraphy, in comparison with rock magnetic cyclostratigraphy studies.

Cretaceous stratigraphy in the Songliao Basin, NE China

The Songliao Basin is one of the largest non-marine oil- and gas-bearing basins that developed during the Cretaceous period, recording an almost complete Cretaceous stratigraphy. With oil and gas exploration, as well as the Continental Scientific Drilling Project of Cretaceous Songliao Basin (CCSD-SK) (2006–21), significant progress has been made on the stratigraphy of the Songliao Basin. The Songliao Basin is therefore important for understanding the non-marine Cretaceous system. Based on lithostratigraphy, sequence stratigraphy, biostratigraphy, geochronology, magnetostratigraphy and cyclostratigraphy, a comprehensive stratigraphical framework of the Songliao Basin has been established in this study. The Lower Cretaceous strata (Hauterivian–Albian) of the basin are dominated by volcanic–sedimentary deposits, while the lower-middle Upper Cretaceous (Cenomanian mid-Campanian) strata are dominated by lacustrine deposits. The upper Upper Cretaceous strata (late Campanian–Maastrichtian) are dominated by fluvial–lacustrine deposits. Fossils are very abundant in the Songliao Basin, and three biotas – the Jehol Biota sensu lato , the Songhuajiang Biota and the Mingshui Biota – are recognized in the Songliao Basin. Furthermore, several important geological events, such as lake anoxic events, seawater incursion events and the K/Pg boundary extinction events are all recorded in the Songliao Basin.

Mitochondrial genome insights into the spatio-temporal distribution and genetic diversity of Dendrobium hancockii Rolfe (Orchidaceae).

With its distinctive evolutionary rate and inheritance patterns separate from the nuclear genome, mitochondrial genome analysis has become a prominent focus of current research. Dendrobium hancockii Rolfe, a species of orchid with both medicinal and horticultural value, will benefit from the application of the fully assembled and annotated mitochondrial genome. This will aid in elucidating its phylogenetic relationships, comparative genomics, and population genetic diversity. Based on sequencing results from Illumina combined with PacBio and Nanopore, the mitochondrial genome map of D. hancockii was constructed. Comparative analysis was conducted from the perspectives of phylogeny across multiple species, selection pressure on protein-coding genes, and homologous segments. The population diversity of D. hancockii was analyzed using single nucleotide polymorphism (SNP) data from the mitochondrial genome and single-copy nuclear genes. This research constructed a circular mitochondrial map for D. hancockii, spanning 523,952 bp, containing 40 unique protein-coding genes, 37 transfer RNA genes, and 4 ribosomal RNA genes. Comparative analysis of mitochondrial genes from 26 land plants revealed a conserved gene cluster, "rpl16-ccmFn-rps3-rps19," particularly within the Dendrobium genus. The mitochondrial genome of D. hancockii exhibits a lower point mutation rate but significant structural variation. Analysis of 103 resequencing samples identified 19,101 SNP sites, dividing D. hancockii into two major groups with limited gene flow between them, as supported by population diversity, genetic structure analysis, principal component analysis, and phylogenetic trees. The geographical distribution and genetic differentiation of D. hancockii into two major groups suggest a clear phytogeographical division, likely driven by ancient geological or climatic events. The close alignment of mitochondrial data with nuclear gene data highlights the potential of the mitochondrial genome for future studies on genetic evolution in this species.

AGE AND PETROGENESIS OF DOLERITES ON THE MARA RIVER (SAYAN MARGINAL UPLIFT OF THE BASEMENT, SOUTHERN PART OF THE SIBERIAN CRATON)

This work focuses on petrological-and-geochemical features, as well as age of dolerites widespread within the basins of the Mara, Kamenka and Uvat rivers. The isotope geochronological data acquired for baddeleyite allowed referring origination of these rocks to the time interval 1600–1620 Ma, interpreted as the time of their emplacement. It was ascertained, that the age of dolerites represents particular geological event proceeding independently of formation of Neoproterozoic Nersinsk gabbro-dolerite complex. The Sm-Nd isotope signature indicates that parent melt generated from the metasomatic lithosphere mantle.

Marine biofilms: cyanobacteria factories for the global oceans.

Cyanobacteria, highly diverse microbial organisms, play a crucial role in Earth's oxygenation and biogeochemical cycling. However, their connection to these processes remains unclear, partly due to incomplete surveys of oceanic niches. Our study uncovered significant cyanobacterial diversity in marine biofilms, showing distinct niche differentiation compared to seawater counterparts. These patterns reflect three key stages of marine cyanobacterial diversification, coinciding with major geological events in the Earth's history.

Mineralization processes in the Bainaimiao Cu-Au deposit in Inner Mongolia, China: Constraints from geology, geochronology, and mineralogy

The Central Asian Orogenic Belt underwent complex tectonic processes and is one of the most intensely accretionary areas globally. Porphyry copper deposits within the belt were likely subjected to deformation during tectonic processes. The Bainaimiao Cu-Au deposit is a typical example of a deformed porphyry deposit whose formation processes include a porphyry emplacement (Event I), a greenschist facies metamorphism (Event II), and a brittle deformation (Event III). Geochronology and trace element geochemistry of zircon, volatiles of magmatic apatite, along with the assemblages, textures, abundances, and compositions of phyllosilicates from these three events were investigated to unveil the physicochemical conditions under which the key geological events relevant to the deposit formation took place. LA-ICP-MS zircon U-Pb dating shows that the granodiorite porphyry in the northern and southern zones formed at 447.4 ± 1.6 to 445.8 ± 3.6 Ma and 436.1 ± 3.8 to 434.1 ± 3.3 Ma, respectively. The granodiorite porphyry in the northern zone has higher oxygen fugacity and Clmelt content but similar Smelt and Fmelt contents compared to the granodiorite porphyry in the southern zone. Microscopic and mineralogic observations point to Event I to be of high plagioclase (22–67 vol%) and quartz (6–40 vol%) content with a range of hydrothermal minerals related to potassic, phyllic, and propylitic alterations. Event II features high amphibole (38–83 vol%) or epidote-chlorite (up to 77 vol%) content with minerals precipitating along the schistosity planes. Event III is characterized by wide veins (3–80 cm) and the highest quartz (61–65 vol%) and calcite (12–19 vol%) content. Geothermometry results show the temperature of potassic and phyllic alterations of Event I to be ∼622 °C and ∼288 °C, respectively. Based on geothermometry and P-T pseudosections, the temperatures of metamorphism and metallic precipitation of Event II were ∼271–634 °C and 297–328 °C, respectively. Both mechanical and chemical mobilization of metallic elements results in Cu mineralization during Event II. The metallic precipitation temperatures of Event III spanned from 297 to 328 °C according to chlorite geothermometry. The ratios of Fe3+/Fetotal and Mg/(Mg + Fetotal) of biotite, chlorite Fe/(Fe + Mg), and white K-mica composition show the mineralizing fluid of Event III to be the most oxidized while that of Event II is the most reduced, F-rich and features the lowest water/rock ratio. This study suggests that deformation processes can increase the Cu mineralization grade of the deformed porphyry deposits through mobilization and re-precipitation of metallic elements.

The Mundeck Salt Unit: A Review of Aptian Depositional Context and Hydrocarbon Potential in the Kribi-Campo Sub-Basin (South Cameroon Atlantic Basin)

The Kribi-Campo sub-basin, located in the Gulf of Guinea, constitutes the southeastern segment of the Cameroon Atlantic Margin. Drilling in the Aptian salt unit revealed a sparse hydrocarbon presence, contrasting with modest finds in its counterparts like the Ezanga Salt in Gabon and the Rio Muni Salt in Equatorial Guinea. This discrepancy prompted a reassessment of the depositional context and hydrocarbon potential of the Mundeck salt unit. By integrating 2D seismic reflection and borehole data analysis, this study established the structural and stratigraphic framework of the area, emphasizing the salt unit’s significance. Borehole data indicate a localized salt unit offshore Kribi, with seismic reflection data revealing distinct forms of diapir and pillow. This salt unit displays a substantial lateral extent with thicknesses ranging from 4000 m to 6000 m. The depositional context is linked to the following two major geological events: a significant sea-level drop due to margin uplift during the Aptian and thermodynamic processes driven by transfer faults related to mid-oceanic ridge formation. These events were crucial in forming and evolving the Mundeck Salt. Regarding hydrocarbon prospects, this study identifies the unit as being associated with potential petroleum plays, supported by direct hydrocarbon indicators and fault-related structures. The findings suggest that untapped hydrocarbon resources may still exist, underscoring the need for further exploration and analysis.

Cicada minimum age tree: Cryptic speciation and exponentially increasing base substitution rates in recent geologic time.

We developed a new time-calibrated tree incorporating primarily endemic along with some cryptic Ryukyu islands cicada data, following the recent publication of global cicada data by Marshall et al. (2018), Łukasik et al. (2018), Simon et al. (2019), Price et al. (2019), and Hill et al. (2021). A total of 352 specimens were analyzed using BEAST v1. X software with a relaxed clock model. Fossil calibrations as old as Triassic were adopted largely following Johnson et al. (2018) and Moulds (2018), and a Quaternary geological event calibration was adopted following Osozawa et al. (2012, 2021b) and input into BEAST v1. X. Our timetree suggests that Tettigarctidae had a cicada basal lineage as old as 200.63 Ma, with Derotettiginae the next oldest lineage at 99.2 Ma. Tibicininae is a sister of the remaining subfamilies of Tettigomyiinae, Cicadettinae, and Cicadidae, and their species level differentiation and radiation began at 40.57 Ma. The Cicadinae clade consists of specific tribes with paraphyletic relationship, and the vicariance and adaptive radiation generated many cryptic species in each tribe. We estimated base substitution rate as a function of age, and the result strongly indicates an exponential increase of base substitution rate in recent geologic time. The consequent increase in cicada biodiversity, including generation of cryptic species in the Ryukyu Islands and surroundings, may have been driven by the generation and spreading of C4 grasses and coeval Quaternary climate change.

A time-calibrated phylogeny of the diversification of Holoadeninae frogs.

The phylogeny of the major lineages of Amphibia has received significant attention in recent years, although evolutionary relationships within families remain largely neglected. One such overlooked group is the subfamily Holoadeninae, comprising 73 species across nine genera and characterized by a disjunct geographical distribution. The lack of a fossil record for this subfamily hampers the formulation of a comprehensive evolutionary hypothesis for their diversification. Aiming to fill this gap, we inferred the phylogenetic relationships and divergence times for Holoadeninae using molecular data and calibration information derived from the fossil record of Neobatrachia. Our inferred phylogeny confirmed most genus-level associations, and molecular dating analysis placed the origin of Holoadeninae in the Eocene, with subsequent splits also occurring during this period. The climatic and geological events that occurred during the Oligocene-Miocene transition were crucial to the dynamic biogeographical history of the subfamily. However, the wide highest posterior density intervals in our divergence time estimates are primarily attributed to the absence of Holoadeninae fossil information and, secondarily, to the limited number of sampled nucleotide sites.

Impact of Tethyan domain evolution on the formation of petroleum systems in the Sichuan super basin, SW China

Based on the “unidirectional break-up and convergence” geodynamic model, this study investigates the impact of the evolution of the Tethyan domain on the formation of petroleum systems in the Sichuan super basin and explores the enrichment pattern of natural gas. The results show that, firstly, the Sichuan Basin and its surrounding areas have experienced two unidirectional rifting-aggregation cycles triggered by the Proto-Tethys Ocean and the Paleo-Tethys Ocean during the Neoproterozoic to Triassic. During Jurassic–Cenozoic, the Sichuan Basin is incorporated in the circum-Tibetan plateau basin-mountain coupled tectonic domain system. The episodic tectonic movements within the plate control the sedimentary infill styles. Second, the evolution of the Tethyan domain, paleoclimatic environment and major geological events controlled the formation and distribution of high-quality source rocks within the basin. The rift valley and intracratonic rift, passive continental margin slope, and intracratonic sags are favorable areas for the development of source rocks. Third, the evolution of the Tethyan domain, supercontinent cycles, global sea level changes, and tectono-climatic events controlled the distribution of carbonate platform and reservoir-caprock combinations. The cratonic platform margins and sub-platform internal high terrains are key areas for finding carbonate high-energy facies belts. Syndepositional paleo-uplifts and surrounding slopes, regional unconformities, and later faults zone are areas where large-scale carbonate reservoirs are distributed. The regional evaporite or shale caprock are beneficial for the large-scale preservation of oil and gas in the basin. Fourth, the spatio-temporal matching relationship of reservoir forming factors influenced by the early tectonic-sedimentary evolution pattern and the degree of later tectonic modification is the key to oil and gas enrichment. Future oil and gas exploration should focus on potential gas systems during the Sinian rift period, Cambrian pre-salt gas systems in the eastern and southern Sichuan, as well as whole oil and gas systems of Permian and Triassic.

Phylogeny and evolution of dissimilatory sulfite reduction in prokaryotes

Sulfate is the second most common nonmetallic ion in modern oceans, as its concentration dramatically increased alongside tectonic activity and atmospheric oxidation in the Proterozoic. Microbial sulfate/sulfite metabolism, involving organic carbon or hydrogen oxidation, is linked to sulfur and carbon biogeochemical cycles. However, the coevolution of microbial sulfate/sulfite metabolism and Earth’s history remains unclear. Here, we conducted a comprehensive phylogenetic analysis to explore the evolutionary history of the dissimilatory sulfite reduction (Dsr) pathway. The phylogenies of the Dsr-related genes presented similar branching patterns but also some incongruencies, indicating the complex origin and evolution of Dsr. Among these genes, dsrAB is the hallmark of sulfur-metabolizing prokaryotes. Our detailed analyses suggested that the evolution of dsrAB was shaped by vertical inheritance and multiple horizontal gene transfer events and that selection pressure varied across distinct lineages. Dated phylogenetic trees indicated that key evolutionary events of dissimilatory sulfur-metabolizing prokaryotes were related to the Great Oxygenation Event (2.4–2.0 Ga) and several geological events in the “Boring Billion” (1.8–0.8 Ga), including the fragmentation of the Columbia supercontinent (approximately 1.6 Ga), the rapid increase in marine sulfate (1.3–1.2 Ga), and the Neoproterozoic glaciation event (approximately 1.0 Ga). We also proposed that the voluminous iron formations (approximately 1.88 Ga) might have induced the metabolic innovation of iron reduction. In summary, our study provides new insights into Dsr evolution and a systematic view of the coevolution of dissimilatory sulfur-metabolizing prokaryotes and the Earth’s environment.

The Global Humanization Event (GHE)

The recent rejection of the “Anthropocene Series/Epoch,” as proposed by the Anthropocene Working Group (AWG), by the International Commission on Stratigraphy (ICS) and the International Union of Geological Sciences (IUGS), has reopened discussion about the Anthropocene as a geological event. This event has been referred to as the “Anthropocene Event” (AE) or the “Anthropogenic Modification Episode” (AME). This essay briefly discusses these terms and concepts, and proposed to use new terms such as “Earth System Humanization Event” (ESHE) or “Global Humanization Event” (GHE), which are more specific and terminologically more consistent with the already defined geological events.

Sedimentation-controlled double BSRs and implications for paleo hydrate dissociation in the Shenhu area, south China sea

Double/multiple bottom-simulating reflectors (BSRs) have been discovered worldwide, but their preservation and formation mechanism remain unclear because most studies are based on seismic data, lacking direct evidence like well logging data. This study introduces a novel well log-based interpretation of double BSR, suggesting that the secondary BSR (BSR2) is the interface between little residual gas and the overlying water-saturated sediment, and the free gas is trapped by capillary seals. The BSR2's amplitude is influenced by the nearby porosity, with lower porosity resulting in stronger reflections. Seismic attributes reveal a dynamic process of hydrate cycle that hydrate dissociation occurs above BSR2, followed by gas migrate to form a new BSR1. The upshift of BSR2 is mainly controlled by sedimentation rate, which varies across different regions, leading to larger upshifts in areas with higher sedimentation rates. Moreover, BSR2's upshift is negatively related to the reflection magnitude of BSR2, because rapidly depositing sediments with higher porosity and lower percolation threshold allow lesser gas sealed beneath the BSR2. Our findings suggest that double BSRs are predominantly formed in muddy sediments under rapid geological events like rapid sedimentation. However, each BSR can be preserved as well as observed to indicate that the BSR has existed for an extended period of time during which the geologic environment has been relatively stable, e.g., low sedimentation rates. This detailed sedimentation-controlled BSR adjustment provides new insights for the interpretation of double BSR and the paleo hydrate dissociation.

Paleoenvironmental Transition during the Rhuddanian–Aeronian and Its Implications for Lithofacies Evolution and Shale Gas Exploration: Insights from the Changning Area, Southern Sichuan Basin, South-West China

During the Rhuddanian–Aeronian interglacial period, global geological events such as glacial melting, synsedimentary volcanic activity, biological resurgence, and large-scale marine transgressions caused frequent fluctuations in paleoproductivity, climate changes, and sea level variations. These paleoenvironmental transitions directly influenced the development characteristics of shale lithofacies. This study investigates the Longmaxi Formation shale in the Changning area in the Southern Sichuan basin, focusing on 28 core samples from Well N1. Using scanning electron microscopy, QEMSCAN, TOC, XRD, and major and trace element analyses, we reconstructed the paleoenvironmental transitions of this period and explored their control over shale lithofacies types and mineral compositions. Four shale lithofacies were identified: carbonate rich lithofacies (CRF), biogenic quartz-rich lithofacies (BQRF), detrital clay-rich lithofacies (CRDF), and detrital quartz-rich lithofacies (DQRF). During the Rhuddanian period, rising global temperatures caused glacial melting and rapid marine transgressions. The low oxygen levels in bottom waters, combined with upwelling and abundant volcanic material, led to high paleoproductivity. This period primarily developed BQRF and CRF. Rich nutrients and abundant siliceous organisms, along with anoxic to anaerobic conditions, provided the material basis and preservation conditions for high biogenic quartz and organic matter content. High paleoproductivity and anoxic conditions also facilitated the precipitation of synsedimentary calcite and supplied Mg2+ and SO42− for the formation of iron-poor dolomite via sulfate reduction. From the Late Rhuddanian to the Mid-Aeronian, the Guangxi orogeny caused sea levels to fall, increasing water oxidation and reducing upwelling and volcanic activity, which lowered paleoproductivity. Rapid sedimentation rates, stepwise global temperature increases, and the intermittent intensification of weathering affected terrigenous clastic input, resulting in the alternating deposition of CRF, CRDF, and DQRF. Two favorable shale gas reservoirs were identified from the Rhuddanian–Aeronian period: Type I (BQRF) in the L1–L3 Layers, characterized by high TOC and brittleness, and Type II (DQRF) in the L4 Layer, with significant detrital quartz content. The Type I-favorable reservoir supports ongoing gas production, and the Type II-favorable reservoir offers potential as a future exploration target.

Study of thermoluminescence characteristics of quartz for high radiation doses (>1kGy): Implications for extending the luminescence dating range

Quartz is an omnipresent abundant natural mineral, used for luminescence dating. Lately, quartz optically stimulated luminescence (OSL) technique is widely used to estimate the equivalent doses (De) for dating geological events (up to 250 Gy, limited by saturation). Some works report thermoluminescence (TL) saturation around ∼ (10–40) kGy. Still dose estimates for such high radiation dose (HRD) range are not achieved. Significant research exists about luminescence response for low dose ranges (<250 Gy) but limited studies are done for HRDs (>1 kGy). This work characterizes the luminescence response of quartz for HRDs (1–21 kGy) to improve existing understanding of luminescence mechanism. Results show that the characteristics of the trap (<200 °C) differ significantly at HRDs than low doses. TL in multi-spectral detection (UV–Visible) band suggest an increase in 340–380 °C peak intensity up to 11 kGy dose. The measurements of saturation dose suggest that it depends on the trapping centres but is independent of recombination centres for the samples used for study. The traps are found bleachable by sunlight, reducing TL signal to residual levels in 1 h. Further, the bleachability is found to be anti-correlated with luminescence emission wavelength. At HRDs luminescence sensitivity is influenced by dose given in previous cycle which is difficult to correct by routine normalization procedures. The work also explores the various normalization methods to find appropriate method for HRD estimation and recommends the use of mass normalization as other normalization methods do not correct the sensitivity changes at HRDs adequately.