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Palustrine‐lacustrine carbonates of the well‐dated Xichagou section (ca. 43 to ca. 13 Ma) next to the active Altyn Tagh Fault (ATF) are investigated in terms of abundance, lithofacies, strontium, carbon and oxygen isotopes, to differentiate tectonic and climatic controls on the evolution of intermontane lakes in the Tibetan Plateau. Volumetrically dominant siliciclastic strata document five depositional stages: mid‐Eocene alluvial fan (onshore), late Eocene fan delta (nearshore), Oligocene semi‐deep lake (offshore), early Miocene braided fluvial delta (nearshore) and mid‐Miocene fluvial plain (onshore). Carbonates are most abundant in the middle three lacustrine stages and contain various lithofacies, including calcretes, microbialites, grainstones and marlstones. Oxygen isotopes show two positive excursions (−1.17‰ and −2.59‰) at the first nearshore and late offshore stages, indicating two relatively saline stages linked to the Eocene and late Oligocene global warming climates. Carbon isotopes show a positive excursion (from −4.0‰ to +2.9‰) at the middle semi‐deep lake stage and meanwhile strontium isotopes of carbonates show a large negative excursion (from 0.7120‰ to 0.7113‰), both in response to the early Oligocene global humid and cooling climate and resultant lake expansion at the Qaidam Basin. Except for this lake expansion event, the first‐order lake transgressing, shallowing and regressing evolution at the Xichagou section were not consistent with Cenozoic global climatic change trends. Instead, the two‐stage strike‐slip faulting of the ATF probably induced the northeastward and eastward migration of basin depocenter and resulted in the lake transgression‐regression at the Xichagou section. The widespread presence and relatively minor variation in oxygen isotopes (from −7.5‰ to −7.0‰) of early Miocene microbialites in the northern Tibetan Plateau suggest a warm climate and a low relief before ca. 15 Ma. [ABSTRACT FROM AUTHOR]

Banded travertines are important parts of fissure ridge systems, but studies on geochemical characterization of banded travertines are limited. This study investigated the lithofacies and stable carbon and oxygen isotopic features of banded travertines from Xiagei (southwestern China) to examine their formation mechanisms. Petrographic analyses of the banded travertines revealed two lithotypes: thick-laminated palisade crystalline crust and thin-laminated composite crystalline crust. δ13C and δ18O of the Xiagei banded travertines range from 2.82‰ to 4.50‰ V-PDB, and from −25.86‰ to −20.90‰ V-PDB. Parent CO2 evaluation shows that the Xiagei banded travertines mainly received CO2 from the decarbonation of marine carbonates, but the contributions of magmatic CO2 and the dissolution of marine carbonates are also unneglectable. Significantly, the magmatic-derived CO2 might indicate that the delamination of the lithosphere along with the asthenosphere upwelling could be taking place in the eastern Tibetan plateau. Paleotemperature calculation shows that the Xiagei travertines were precipitated from moderate- to high-temperature hot springs (44.3 to 86.8 °C). Interestingly, the thick-laminated palisade crystalline crust and thin-laminated composite crystalline crust display calculated paleotemperature between 66.6 and 86.8 °C and between 56.6 and 77.7 °C, respectively, reflecting the great role of water temperature in controlling the lithofacies of banded travertines. A comparison between the banded travertines at Xiagei and other areas also shows temperature is a non-negligible factor controlling banded travertine precipitation. However, this does not mean that water temperature is the decisive controlling factor and more studies on banded travertines are still indispensable to disclose the potential factors controlling the factors/processes affecting banded travertine lithofacies. This study provides a good example for understanding the relationship between lithofacies and stable isotopic geochemical characteristics of travertine deposits. [ABSTRACT FROM AUTHOR]

The Archaeocyathid Extinction Carbon Isotope Excursion (AECE) and Mingxinsi Carbon Isotope Excursion (MICE) are major events in the Early Cambrian sedimentary records but controversially heterogeneous in their magnitudes, as well as local and global correlations. This paper presents a high-resolution δ13C carb profile from the Shiliu section in the western Yangtze Platform (China) that spans the lower part of the Lower Cambrian. The investigated Lower Tianheban interval (∼110 m) is dominated by marine carbonates (lime mudstones) alternating occasionally with thinly-bedded black shale and mudstone interbeds. The investigated micritic carbonates were examined through a multi-technique protocol, combining petrographic and geochemical assessments, to evaluate the degree of sample preservation. The δ13C carb values (−2.4‰–1.8‰) show an insignificant correlation with the δ18O carb values (−12.6‰ to −8.7‰, R2 = 0.012), the Mn/Sr ratios (R2 = 0.001), and Al concentrations (R2 = 0.041). This supports the preservation of predominantly at least near-primary δ13C carb signatures, which can be utilized to reconstruct a reliable, high-resolution δ13C carb profile for chemostratigraphic correlations in the area and beyond. The profile displays a lower positive excursion of ∼3‰ overlain immediately by a negative excursion of ∼2.3‰. The archaeocyath zonation scheme suggests that the lower excursion is correlated with the global MICE event and the upper excursion with the AECE event. The results provide an alternative option for interpreting the carbon isotope excursions in the Lower Cambrian within the Yangtze Platform as well as other equivalent sections at a global scale. • δ13C carb composition of the Lower Cambrian carbonates in northwestern Yangtze Platform. • Distinct δ13C carb excursions correlated with the MICE and AECE events. • Alternative interpretation of the MICE and AECE events in the Yangtze Platform. • A useful C-isotope profile for chemostratigraphic correlations in Yangtze Platform and beyond. [ABSTRACT FROM AUTHOR]

The Carnian Pluvial Event (CPE) is recorded widely across the Tethys region. Here we present high-resolution carbonate (δ13C carb) and organic (δ13C org) carbon-isotope records and mineral data from the Boli La to lower Bagong formations in the Quemo Co area of the Qiangtang Basin, Qinghai-Tibet Plateau. In this studied section, a calcareous fine-grained sandstone bed that yields a detrital zircon maximum depositional age of 232.5 ± 3.3 Ma, together with ammonoid species and bivalves, allows identification of the Carnian Stage. An intensification of siliciclastic supply and a large drop in calcite and illite is recorded in the Carnian section, suggesting a palaeoclimatic shift from arid to warm and humid during the CPE. A negative carbon-isotope excursion (CIE) in both δ13C org and δ13C carb is also reported, which could be explained by a global perturbation of the carbon cycle and the release of CO 2 enriched in 12C. The magnitude of the negative CIE in the Quemo Co area displays a significant shift towards lighter values compared to other reported carbonate carbon-isotope values across the onset of the CPE. A combination of both volcanic emissions from the synchronous Wrangellia large igneous province and release of methane clathrate hydrate is the most likely explanation for the significant negative excursion in δ13C. • The Carnian Pluvial Event (CPE) is investigated in Qinghai-Tibet Plateau. • Negative carbon isotope (organic, carbonate) excursion occurs across CPE. • Detrital zircon age indicate onset of CPE is 232.5 ± 3.3 Ma. • This age falls in the range of the ages of the Wrangellia LIP. • The CPE may be related to LIP and release of methane clathrate hydrate. [ABSTRACT FROM AUTHOR]

The Barremian and Aptian correspond to periods of marked changes in the atmosphere-ocean system, and offer valuable information about global tectonic events. Here, we present integrated high-resolution carbonate carbon-isotope (δ13C carb) and geochemical data that precede the Early Aptian oceanic anoxic event (OAE 1 a) in the Qiangtang Basin (Eastern Tethys). We identified a characteristic and well-correlatable Barremian-Lower Aptian carbon-isotope pattern that can be categorized into 10 Segments. The most notable features of the δ13C carb record are multiple negative carbon-isotope excursions in the Barremian-Aptian, and each is possibly linked to environmental changes. Two carbon isotopic plateaus are observed in the Upper Barremian, which are generally related to increased primary productivity, and to the concomitant development of dys-to anaerobic conditions. Our data indicate the development of anoxic conditions during shale deposition, which occurred under the conditions of a semi-enclosed lagoon environment. Such conditions, were likely localized, and not the primary mechanism responsible for the deposition of organic-rich sediments within the Shenglihe succession. The deposition of organic-rich shales was very likely due to global/regional warming. Rising temperatures and hydrological cycle strengthening during shale deposition are believed to have increased primary productivity, and thus resulted in the expansion of the local oxygen minimum zone within the water column. • Barremian was a time of marked changes in the atmosphere-ocean system. • δ13C record is subdivided into 10 δ13C segments prior to the OAE 1a. • Positive carbon isotope excursion is prominent in the Upper Barremian. • Global warming would raise surface productivity. [ABSTRACT FROM AUTHOR]