Paleoclimate during the Cenomanian-Turonian Oceanic Anoxic Event 2 (OAE 2, 94.5–93.9 Ma) was characterized by elevated atmospheric CO2 concentrations and peak global temperatures. In this study, we employ δ66Zn measured on samples spanning OAE 2 in an expanded hemipelagic section in Tibet to trace changes in the major fluxes that influence biogeochemical cycles. The prominent feature of the δ66Zn record in the studied section is a continuous decrease from ~1‰ at the onset of OAE 2 to a minimum of ~0.2‰ within the Plenus Cold Event (ca. 94.3 Ma), followed by a stepwise recovery through the upper part of OAE 2. The negative shift in δ66Zn corresponds with higher terrigenous inputs, as revealed by previously published detrital index and TOC/TN (total organic carbon to total nitrogen) ratio records, and covaries with a notable decreasing trend recorded in compiled pCO2 data of different basins. We propose that influx of isotopically light Zn from weathered volcanic rocks associated with submarine large igneous provinces and/or (sub)tropic Indian continental volcanics is likely responsible for the δ66Zn decrease. We infer that the recovery of δ66Zn was caused by continued high primary production and an inevitable decline in the flux of light Zn as volcanic terrains were progressively weathered. The ultimate cessation of OAE 2 may have been a consequence of the same effect, with the nutrient supply from weathering reaching a minimum threshold to maintain productivity-anoxia feedback.

A clastic dyke is a stratigraphically vertical, wall‐like body of clastic material that fills open fissures across strata, and may provide important information on regional depositional processes and tectonic activity. Clastic dyke swarms composed of greyish to brown, fine‐ to medium‐grained lithic‐rich volcaniclastic sandstone are widely exposed in the lower Aptian shales in the Gucuo and Wölong areas of the Tethyan Himalaya in southern Tibet, where they are distributed along a series of normal faults. The length and width of clastic dykes range from 5 to 50 m and from 20 to 150 cm, respectively. The U–Pb age spectra of zircon grains contained in clastic dykes are similar to those in Lower Cretaceous sandstones exposed in the studied areas (i.e., Wölong volcaniclastics) and display a youngest peak at 124.3± 2 Ma. Petrographic analyses show that the underlying strata and dykes contain more volcanic lithic fragments and less feldspar grains than the overlying strata, indicating that the dykes were derived from underlying strata and injected upward along faults. Their formation may be explained by a fault‐induced clastic‐dyke model: normal faults provided conduits for clastic material injected from the underlying unlithified sandstones which were undergoing refluidization owing to over‐pressure. We infer that the liquefaction of underlying strata was induced by earthquakes associated with the extensive magmatic activities and regional extension that affected the Indian passive margin of Neotethys during the Early Cretaceous.

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<p>The variations in carbon isotope (δ<sup>13</sup>C) values of the Aptian marine and terrestrial strata are globally comparable and regarded as an important tool for the stratigraphic correlation of the Aptian successions. The most remarkable feature of the δ<sup>13</sup>C curve of the Aptian is an abruptly negative excursion, which characterizes the onset of the early Aptian Oceanic Anoxic Event (OAE 1a, ~121 Ma). However, the identification of OAE 1a equivalent level in the Tibetan Himalaya remains debatable. Based on previously well-established foraminiferal biostratigraphy, we provide a lower Aptian high-resolution δ<sup>13</sup>C curve of bulk organic carbon from an expanded shale-dominated section, Chaqiela Section in the Tibetan Himalaya. The TOC/TN ratios of the studied section vary from 3 to 10, indicating that the organic matter is mainly sourced from marine plankton. Thus, we suggest that our results present the secular changes of δ<sup>13</sup>C in the dissolve carbon pool of the shallow sea on the south margin of eastern Tethys. The lower Aptian δ<sup>13</sup>C curve of the Chaqiela section is divided into eight segments, which can be well correlated to the representative sections in the western Tethys area.</p> <p>In the lower part of the section, an interval of sharp negative carbon isotope excursion (CIE) of ~1 ‰ is observed, which is followed by recovery of the δ<sup>13</sup>C values by a magnitude of ~2 ‰. This short-term carbon perturbation is superimposed on the long-term decrease in δ<sup>13</sup>C values of the early Aptian. The δ<sup>13</sup>C profile at this interval perfectly records the diagnostic characteristics of the OAE 1a: negative (C3), positive (C4), steady (C5), and positive (C6) segments. Lacking covariations of δ<sup>13</sup>C values with TOC/TN and TOC, and δ<sup>13</sup>C and Al in this interval indicate that the δ<sup>13</sup>C variations are not attributed to source changes of the organic matter. No obvious enrichments of the redox-sensitive major and trace elements indicate an oxic to sbuoxic condition during the sedimentation, it is in good agreement with the low C<sub>org</sub>:P<sub>tot</sub> ratios, but the slightly increase of C<sub>org</sub>:P<sub>tot</sub> ratios during the OAE 1a interval may imply a relatively oxygen-reducing trend and sustains till the end of OAE 1a. The paleoclimatic proxies imply a relatively warm and humid paleo-environment in mid-high latitudes (~50°S) of Tibetan Himalaya during this time interval, it is also testified by the moderate chemical weathering condition revealed by the A-CN-K ternary diagram.</p>

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