Zhiqiang Shi

Norian time interval is a crucial period in Earth’s evolutionary history, characterized by several organic carbon-isotope perturbations in the carbon cycle that are closely related to global environmental change and biotic turnover (Zaffani et al., 2017). Among them, the Norian “chaotic carbon episode” has been recently reported globally in North America, Italy, and Japan, from shallow to pelagic environments (Whiteside and Ward, 2011; Zaffani et al., 2017; Jin et al., 2022; Sato et al., 2023). However, the mechanisms and timing of these events are poorly understood, especially in the eastern Tethys. In this study, we have investigated the carbon isotope profiles and conodont assemblage changes from the middle to upper Norian bedded carbonate rock succession in the Sanhedong section, Southwest China, to provide new insights into the Norian carbon cycle perturbation and its impact on marine biodiversity. We thus collected several samples for conodont biostratigraphic investigations and organic and carbonate carbon isotope (δ13Corg, δ13Ccarb) and oxygen isotope data (δ18Ocarb) along the study section. We identified various conodont genera, including some typical Norian Arcyrogondolella, Norigondollela, Mockina, and Primatella, and established detailed conodont biostratigraphy that indicates a middle to upper Norian age for the Sanhedong section. Furthermore, we detected a significant negative carbon isotope excursion (NCIE) across the middle/upper Norian, which can be globally correlated with the NCIE events reported from North America, the central Panthalassa Ocean, and the Tethys Ocean. We have also observed changes in conodont diversity and abundance associated with the NCIE.Our study provides an accurate age and a high-resolution carbon isotope record for the Sanhedong section, revealing the global nature of the Norian carbon cycle perturbation and its impact on the biosphere in the eastern Tethys. Our preliminary results suggest that also the carbon isotope perturbation in Eastern Tethys may be associated to the middle-late Norian carbon-cycle perturbations, which were triggered by the emplacement of the Angayucham Large Igneous Province (Alaska). Further studies are needed to constrain the timing and magnitude of Norian volcanic activity.Keywords: Norian, conodont biostratigraphy, carbon isotope perturbation, Eastern Tethys Reference:Jin, X., Du, Y., Bertinelli, A., Shi, Z., Preto, N., Zou, H., Ogg, J.G., Han, L., Wu, Q. and Rigo, M., 2022. Carbon-isotope excursions in the Norian stage (Upper Triassic) of the Baoshan terrane, western Yunnan, China. Journal of Asian Earth Sciences, 230, p.105215.Sato, H., Nozaki, T., Onoue, T., Ishikawa, A., Soda, K., Yasukawa, K., Kimura, J.I., Chang, Q., Kato, Y. and Rigo, M., 2023. Rhenium-osmium isotope evidence for the onset of volcanism in the central Panthalassa Ocean during the Norian “chaotic carbon episode”. Global and Planetary Change, 229, p.104239.Whiteside, J.H. and Ward, P.D., 2011. Ammonoid diversity and disparity track episodes of chaotic carbon cycling during the early Mesozoic. Geology, 39(2), pp.99-102.Zaffani, M., Agnini, C., Concheri, G., Godfrey, L., Katz, M., Maron, M. and Rigo, M., 2017. The Norian “chaotic carbon interval”: new clues from the δ13Corg record of the Lagonegro Basin (southern Italy). Geosphere, 13(4), pp.1133-1148.

The Toarcian lacustrine deposits of the Sichuan Basin (China) are represented mainly by silty marlstones and bivalve rich limestones disposed in decametric-scale thickening upwards sequences. Dense accumulations of bivalve shells are related to episodes of mass mortality under oxygen depleted conditions in the bottom waters. The geochemical detrital proxies indicate a climatic turnover during the Toarcian. The lower part of the Toarcian succession is characterized by high values of Zr/Rb and Sr/Cu that point to warm and arid conditions, whereas the upper part is characterized by low values of Zr/Rb and Sr/Cu and enhanced C-value related to relatively more humid conditions.

Using thin-section images to estimate core permeability is an economical and less time-consuming method for reservoir evaluation, which is a goal that many petroleum developers aspire to achieve. Although three-dimensional (3D) pore volumes have been successfully applied to train permeability models, it is very expensive to carry out. In this regard, deriving permeability from two-dimensional (2D) images presents a novel approach in which data are fitted directly on the basis of pore-throat characteristics extracted from more cost-effective thin sections. This work proposes a Fluid–MLP workflow for estimating 3D permeability models. We employed DIA technology combined with artificial lithology and pore classification to calculate up to 110 characteristic parameters of the pore-throat structure on the basis of 2D rock cast thin sections. The MLP network was adopted to train the permeability prediction model, utilizing these 110 parameters as input. However, the accuracy of the conventional MLP network only reached 90%. We propose data preprocessing using fluid flow simulations to improve the training accuracy of the MLP network. The fluid flow simulations involve generating a pore network model based on the 2D pore size distribution, followed by employing the lattice Boltzmann method to estimate permeability. Subsequently, six key structural parameters, including permeability calculated by LBM, pore type, lithology, two-dimensional porosity, average pore–throat ratio, and average throat diameter, were fed into the MLP network for training to form a new Fluid–MLP workflow. Comparing the results predicted using this new Fluid–MLP workflow with those of the original MLP network, we found that the Fluid–MLP network exhibited superior predictive performance.

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.

Sea-level fall is considered one of the significant factors leading to the end-Permian mass extinction. Our study focused on the relative sea-level changes in Beifengjing section which deposited in shallow-water platform and Shangsi section which deposited in deep-water trough. The results indicated a sea-level fall during the Permian—Triassic transition in the Upper Yangtze region. Considering that there is no significant change in fossil abundance in the strata following the two sea-level falls observed in the Beifengjing section, we conclude that the reduction of shallow marine habitat caused by sea level fall alone was insufficient to cause the mass extinction. However, sea-level fall did exacerbate the input of terrestrial debris into the ocean, leading to the deterioration of the marine environment (e.g., soil-induced turbidity and eutrophication). Furthermore, the presence of multiple layers of volcanic tuff near the lithostratigraphic boundary between Permian and Triassic in both sections suggests frequent volcanic activity during sea-level fall. Therefore, we propose that the combined adverse effects of volcanic eruptions, sea-level falls, and other events exceeded the threshold for biological survival, ultimately resulting in the catastrophic end-Permian mass extinction.

During the Late Triassic, the southern margin of the Ordos Basin was influenced by the Indosinian Movement, in response to closure of the Paleo-Tethys Ocean. Thinly bedded tuff layers are exposed near the base of the Middle–Upper Triassic formations (Chang 8/7/6 members) in the Ordos Basin. Tuff samples from drilling core (well An-35) and outcrop (Motiangou section) samples in the Yanchang Formation were studied by the detailed field work. Igneous zircon crystals were picked and analyzed by the instruments of cathodoluminescence and laser ablation inductively coupled plasma mass spectrometery (LA-ICP-MS). The timing of volcanic activity was determined by means of high-precision zircon age. Combining tectonic setting and paleogeographic reconstruct, the ages of tuff layers indicate that volcanic activities occurred at three peaks (241.6 ± 1.1 Ma, 240.2 ± 1.1 Ma, and 233.5 ± 1.2 Ma) from the top of Chang 8 Member to the Chang 7 Member. The results implied that the volcanic activities lasted from Ladinian to Carnian, as well as define the sedimentary duration of the Chang 7 Member with a deposition rate of 1.34 cm/ka.

Miocene is an important period for the development of global stromatolites. The petrological and geochemical characteristics of stromatolite (dense and porous) laminae record the changes in paleo-environment, from a drilling hole, ZK-1 at Wudaoliang in the Hoh Xil Basin, Northern Tibetan Plateau. Based on the drilling core observations, these lacustrine stromatolites are hummocky, stratiform, or domelike in shape. The stromatolites consist of dense laminae (microspar-rich) and porous laminae (microcrystalline). The oxygen isotopes suggest that these stromatolites in the Wudaoliang Formation formed in a relatively warm environment which was suitable for stromatolite growth. The isotopic variation of lacustrine stromatolites indicates the periodic hydrological closure and opening of the Miocene Hoh Xil Basin. Most of the trace elements (Ba, Pb, Th, U, Hf, Y, V, Cr, Cu, Co, Ni, and Zn) are relatively depleted in the upper continental crust. And, the rare earth elements (REE) show a slight negative Eu anomaly. The Sr/Ba and B/Ga ratios are used as paleo-salinity proxy as well, together with the results of X-ray diffraction (XRD), showing that the stromatolites tended to exist in the condition of decreased salinity. Meanwhile, the arid-dominated climate of the Miocene is more suitable for stromatolite development during the Cenozoic.

The Bayingobi basin is the Mesozoic–Cenozoic basin in North China in which the Tamusu uranium deposit is located. The ore‐target layer of the deposit is the Lower Cretaceous Bayingobi Formation, which developed as a fan delta‐shallow lacustrine deposit. The distributary channel sand body of the fan delta plain and the underwater distributary channel sand body of the fan delta front formed a favorable uranium reservoir, so the study of sequence stratigraphy is extremely important to understanding the genesis of uranium deposits. On the basis of field investigation and a large number of borehole logs, the high resolution sequence stratigraphy of the Lower Cretaceous is divided and the system tracts of different periods are established. The relationship between deposition, interlayer oxidation and uranium enrichment is discussed. The Lower Cretaceous Bayingobi Formation can be divided into two fourth‐order sequences (Sq1 and Sq2). The lower member of the Bayingobi Formation is referred to as Sq1, which is composed of a falling‐stage system tract (FSST) on top. On the other hand, the upper member of the Bayingobi Formation is referred to as Sq2, which is composed of a lowstand system tract (LST), transgressive system tract (TST) and highstand system tract (HST). The lowstand system tract forms a favorable stratigraphic structure (mud‐sand‐mud formation) with the lacustrine mudstone of the overlying transgressive system tract, that is conducive for the migration of uranium‐bearing oxygen water. The organic matter and pyrite in the fan delta sand body, as well as the dark mudstone in the distributary bay, provided a reducing medium for uranium mineralization. The ore body mainly occurs in the distributary channel, underwater distributary channel or the mouth bar of the fan delta. As a result of the moderate thickness, high permeability, favorable barrier and rich reducing medium, the rich ore body mainly occurs in the underwater distributary channel and mouth bar sand body of the delta front. Based on study of the sequence stratigraphy, the model of the sequence, sedimentation and mineralization of the uranium deposit is established, which enriches uranium metallogenic theory and provides a reference for exploration of the same type of uranium deposits.