中国科学院南京地质古生物研究所机构知识库

Marine sedimentary intervals of the upper Barremian-upper Aptian record the profound changes in global plate configurations and the ocean-climate system. Black shale lithofacies of the Lower Cretaceous crop out extensively in the Tethyan Himalaya region of southern Tibet, and in the Gamba area they are assigned to the Gambadongshan Formation. By using 3-5% hydrofluoric acid, well-preserved planktic foraminiferal tests have been recovered for the first time from black shales in the Chaqiela section of the Gambadongshan Formation. The detailed foraminiferal biostratigraphic work allowed recognition of four upper Barremian to upper Aptian planktic biozones: Hedbergella excelsa Interval Zone, Globigerinelloides ferreolensis Taxon-Range Zone, Hedbergella infracretacea Partial-Range Zone, and the Paraticinella rohri Taxon-Range Zone. Total organic carbon (TOC) and organic carbon isotope (delta C-13(org)) records were generated for the Chaqiela section. The C-isotope profile and the planktic foraminiferal data enable the identification of Oceanic Anoxic Event 1a (OAE 1a) at the lower part of the Globigerinelloides ferreolensis Taxon-Range Zone. Diagenetic processes, lower sea surface temperature, and the regional hydrologic cycle were probably the main factors for the development of OAE 1a in the Chaqiela section. The rela-tively higher delta C-13(org) values and smaller size of carbon isotopic fluctuations in the Chaqiela section may represent the local expression of OAE 1a in the Gamba area. A long-term negative delta C-13(org) excursion and a decreased trend of planktic foraminiferal abundance relative to benthic foraminifera, in the upper part of the Gambadongshan Formation may suggest a lower sea-level during the late Aptian. (C) 2021 Elsevier Ltd. All rights reserved.