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Foreland thrust belts are globally significant areas for oil and gas exploration. These belts undergo unique tectonic activity, resulting in distinct variations in the accumulation of oil and gas. Studying the genetic evolution of deep oil and gas in these thrust belts is a crucial means of revealing the patterns of deep oil and gas accumulation. This study utilized a novel approach that combines reservoir geochemistry and basin simulation to determine the migration process of oil and gas in the foreland thrust fault belt of northwestern Sichuan Province. To achieve this goal, we established a thermal evolution model of lower Palaeozoic source rocks through organic chemical analysis. The balanced profile technique was used to determine the paleotectonic evolution pattern of the critical period in this area. Additionally, the mixed flow migration algorithm was employed to simulate the evolution of the Palaeozoic petroleum system. Through basin petroleum system modelling (BPSM), it was discovered that the bitumen found in the thrust nappe belt originated from the lower Cambrian strata. Furthermore, the gas reservoir in the hidden fault belt primarily migrated from the lower Cambrian strata and was also partially mixed with thermogenic gas from Permian source rocks. After establishing the genetic models of various tectonic belts in the study area, it became clear that there are notable differences in hydrocarbon accumulation within these belts. The BPSM results revealed that the oil present in the thrust nappe belt was generated in Lower Cambrian source rocks through early Indosinian hydrocarbon expulsion and continuous charging. The gas found in the thrust nappe belt was produced through the process of oil cracking in the deep reservoir located in the hidden front belt during the late Indosinian. The depth of the thrust nappe belt has helped to preserve hydrocarbon reservoirs. The natural gas present in the hidden fault belt primarily originates from lower Cambrian source rocks, which are combined with gas generated by oil cracking in lower Permian source rocks after the Yanshanian. Therefore, hydrocarbons accumulate deeply in the footwall of the thrust fault belt. The BPSM offers a fresh approach to hydrocarbon genetic models of thrust fault zones in the western Sichuan Basin, and it is beneficial for accurately evaluating the potential for deep hydrocarbon resources in comparable geological settings. [ABSTRACT FROM AUTHOR]

The geochemical properties of fracturing flowback fluids indirectly indicate the fracturing efficiency of the reservoir, the interaction between the reservoir and injected water, and the preservation of oil and gas, thereby offering robust data support for identifying fracturing flowback fluid sources, assessing fracturing effects, and proposing stimulation strategies. In this study, the ion characteristics, total salinity, and stable isotope ratio of fracturing flowback fluids of the Z202H1 and Z203 wells in Western Chongqing were measured. The findings suggest that with the extension of flowback time, the geochemical properties of fracturing flowback fluids evolve toward higher salinity and heavier stable isotope ratios, ultimately stabilizing. Upon comparing the water–rock reaction intensity and the rate of total salinity increase in the fracturing flowback fluids, it is concluded that fracturing flowback fluids contain a mixture of formation water. Because water–rock reactions elevate the total salinity of fracturing flowback fluids, we introduce the Water–Rock Reaction Intensity Coefficient (IR) to denote the intensity of these reactions. Based on the IR value, the binary mixture model for fracturing fluids in fracturing flowback fluids was adjusted. With the increase in flowback time, the content of fracturing fluids in fracturing flowback fluids of Z202H1 and Z203 stabilized at about 55% and 40% respectively. During the same flowback period, the fracturing flowback fluids of the Z203 well exhibit a higher total salinity, a heavier stable isotope ratio, a greater IR, and a lower fracturing fluid content in fracturing flowback fluids. This suggests that the fracturing effect of the Z203 well is superior to that of the Z202H1 well, leading to a higher production capacity of the Z203 well. [ABSTRACT FROM AUTHOR]

The comment by Yin (2024) referred to the systematic morphology and identification of the newly recovered in situ ammonite assemblage Tiltoniceras sp. and Hildoceratidae sp. from the Bilong Co section in the Qiangtang Basin. Yin (2024) suggests that Tiltoniceras sp. should be assigned to Oxycerites aspidoides. Upon re-examination of our paper and the reply to the released comment, it is demonstrated that the morphologic characteristics of the recovered ammonites are more consistent with Tiltoniceras rather than Oxycerites aspidoides. These ammonites, along with in situ calcite U–Pb age (ca. 181 Ma), carbon isotope stratigraphy, and age-diagnostic palynomorphs, constrain the age of the Bilong Co oil shale to the Lower Jurassic (Toarcian) with plausible credentials. [ABSTRACT FROM AUTHOR]

The Early Jurassic was primarily a greenhouse phase in Earth's history. Previous studies have predominantly focused on marine strata in the Tethyan Ocean, but continental records outside of Europe are still poorly understood, which has hindered a thorough understanding of its climate dynamics. To address this gap, organic, inorganic, and isotope geochemical analyses, along with mineralogical and sedimentological assessments, were conducted on samples from the Quemo Co Formation of well QZ-16 in the Qiangtang Basin (Eastern Tethys). This study aimed to investigate carbon cycle perturbations and consequences of redox conditions and paleosalinity within a lacustrine system during the Early Jurassic. The carbon isotope profile of well QZ-16 exhibited a long-term negative excursion of ca. −3.83‰ in lacustrine sediments, with relatively heavy δ13Corg values and small excursion magnitudes. Enhanced terrigenous input, as indicated by detrital proxies such as Si/Al, Ti/Al, and Zr/Al, was driven by accelerated continental weathering during the carbon isotope excursions. The presence of coarse-grained, pelitic siltstone deposits coincided with the onset of these negative carbon isotope excursions. Sr/Ba ratios (0.05–3.64, avg. 0.73) suggest a brackish to freshwater salinity regime within the third member, implying that the deposition of the Quemo Co Formation was influenced by both freshwater and seawater inputs. Most enrichment factors (VEF, ZnEF, NiEF) having a value below 1.0 and Corg/P ratios less than 50 indicate that the lacustrine environment was characterized by predominantly oxidizing conditions, particularly during the early Toarcian negative carbon isotope excursion (T-NCIE). Despite the record of the T-NCIE event, enhanced respiration in bottom and pore waters indicates that the Toarcian Oceanic Anoxic Event (T-OAE) was absent in this part of the eastern Tethys Ocean. The recorded Early Jurassic environmental settings in the Qiangtang Basin lacustrine system exhibit a close association with the T-CIE event (183 Ma), providing insights into the complex interplay between carbon cycle perturbation, climate, weathering, and biological processes during this greenhouse period. [ABSTRACT FROM AUTHOR]

The geochemistry of the clastic sedimentary units of the Suonahu Formation from the QD17 well in the northern Qiangtang basin, Tibet, was studied using various chemical analyses. Si[O.sub.2]/[Al.sub.2][O.sub.3] ratios indicated that compositional maturity and recycling of the sediments were low to moderate. The total rare earth element ([SIGMA]REE) contents of the clastic sediments ranged from 29.28 to 191.92 ppm. Element abundances suggest that the studied clastic sediments in the northern Qiangtang Basin were mainly sourced from felsic rocks mixed with small amounts of intermediate rocks, and that they were mostly developed in a continental setting. The REE geochemistry of the clastic sediments suggests that these different lithological samples were derived from a similar terrigenous source and that the Eu anomaly was inherited from the source rocks. The paleoclimate index (C-value) varied from 0.01 to 0.36, reflecting generally arid to semiarid conditions. In addition, Rb/Sr (about 0.41) and Sr/Cu (about 37.02) ratios support the idea that arid conditions prevailed during the deposition of the Suonahu Formation. Sr/Ba ratios (0.48-3.23) suggest a paleoenvironment with variable salinity. The covariation among this factor and paleoclimate indicators suggests that variations in climatic conditions exerted a primary control on salinity. The chemical index of alteration (CIA), A--CN--K ternary diagram, and low Th/U ratios indicate that the parent rocks of the clastic sediments experienced weak chemical weathering. Two multidimensional tectonic discrimination diagrams based on major elements show that the Suonahu Formation was deposited in a rift-related basin. The Ti[O.sub.2] versus Zr, La/Th versus Hf, and Co/Th versus La/Sc bivariate diagrams and multi-major elements discrimination diagram indicate that the detritus was primarily derived from felsic igneous rocks with less contribution from intermediate igneous rocks. Key words: clastic sediments, geochemistry, tectonic setting, paleoclimate, Suonahu Formation, northern Qiangtang basin. Diverses analyses chimiques ont ete utilisees pour etudier la geochimie des unites sedimentaires clastiques de la Formation de Suonahu du puits QD17 dans le nord du bassin de Qiangtang (Tibet). Les rapports Si[O.sub.2]/[Al.sub.2][O.sub.3] indiquent une maturite compositionnelle et un recyclage des sediments faibles a moderes. Les concentrations de terres rares totales ([SIGMA]ETR) des sediments clastiques vont de 29,28 ppm a 191,92 ppm. Les abondances d'elements donnent a penser que les sediments clastiques etudies du nord du bassin de Qiangtang proviennent principalement de roches felsiques melangees a de petites quantites de roches intermediaires, et qu'ils se sont principalement formes en milieu continental. La geochimie des terres rares de ces sediments indiquerait que les differents echantillons lithologiques sont derives d'une source terrigene semblable et que l'anomalie en Eu est heritee des roches meres. L'indice paleoclimatique (C) va de 0,01 a 0,36, temoignant de conditions generalement arides a semiarides. Les rapports Rb/Sr (environ 0,41) et Sr/Cu (environ 37,02) appuient en outre l'interpretation voulant que des conditions arides aient predomine durant le depot de la Formation de Suonahu. Les rapports Sr/Ba (0,48-3,23) indiqueraient un paleomilieu de salinite variable. La covariation de ce facteur et d'indicateurs paleoclimatiques donne a penser que des variations des conditions climatiques exercaient un controle de premier plan sur la salinite. L'indice d'alteration chimique (IAC), le diagramme ternaire A--CN--K et de faibles rapports Th/U indiquent que les roches meres des sediments clastiques ont subi une faible meteorisation chimique. Deux diagrammes de discrimination tectonique multidimensionnels bases sur les elements majeurs montrent que la Formation de Suonahu a ete deposee dans un bassin associe au rifting. Les diagrammes bivaries Ti[O.sub.2]-Zr, La/Th-Hf et Co/Th-La/Sc et le diagramme de discrimination de multiples elements majeurs indiquent que les detritus proviennent principalement de roches ignees felsiques et, dans une moindre mesure, de roches ignees intermediaries. [Traduit par la Redaction] Mots-cles : sediments clastiques, geochimie, milieu tectonique, paleoclimat, formation de Suonahu, bassin de Qiangtang septentrional., Introduction The chemical compositions of clastic sediments are useful for assessing paleoenvironmental conditions, material sources, and tectonic settings (Dickinson and Valloni 1980; Nesbitt et al. 1980, 1996; Dickinson et al. [...]

[Objective] The Lower Cambrian Shuijingtuo Formation black shale is an important source rock and shale gas exploration target in the Sichuan Basin. However, the enrichment mechanism of organic matter in this series of black shale is still unclear. [Methods] Here, we reported total organic carbon (TOC) contents, sedimentary microfacies, major and trace elements, and pyritic framboid size distributions in the lower part of Shuijingtuo Formation in the Chengkou area, northeastern Sichuan Basin on the Upper Yangtze Platform, providing new evidence for reconstructing the paleogeography, paleoenvironment, and main controlling factors of organic matter enrichment. The results show that the black shale succession in the Shuijingtuo Formation developed five sedimentary microfacies which related to the deep-water shelf slope environment. Productivity index (BaXS, P/Ti) and continental input index Ti, Al indicate that the sedimentary environment of black shale in the Shuijingtuo Formation is at a low level of paleoproductivity, and the continental input is relatively stable and has no obvious correlation with TOC. Therefore, paleoproductivity and continental input are not the main controlling factors of organic matter enrichment in the black shale of the Shuijingtuo Formation. The redox-sensitive element index (U/Th, UEF, MoEF ) and pyrite framboid size distributions show that the organic matter content is positively correlated with the redox index, indicating that the organic matter enrichment in Shuijingtuo Formation is mainly controlled by the change of redox conditions of the water column. [Conclusions] Based on the above understanding, it can be inferred that the organic matter enrichment of the black shale of the Shuijingtuo Formation was controlled by the fluctuation of redox conditions of the bottom water caused by the large-scale transgression event during the stage 2 to stage 3 Cambrian (529-514 Ma), and the organic matter enrichment model was proposed here. [ABSTRACT FROM AUTHOR]