The Cenomanian–Turonian anoxic event in southern Tibet

• Published in: Cretaceous research Vol. 22; no. 4; pp. 481 - 490
• Main Authors: Wang, C.S., Hu, X.M., Jansa, L., Wan, X.Q., Tao, R.
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01-08-2001
• Subjects: Cenomanian/Turonian boundary; oceanic anoxic events; southern Tibet; southern Tibet; oceanic anoxic events; Cenomanian/Turonian boundary
• ISSN: 0195-6671; 1095-998X
• DOI: 10.1006/cres.2001.0271

The Cenomanian–Turonian black shales in southern Tibet record a global oceanic anoxic event (OAE). A combined sedimentological, geochemical and micropalaeontological study shows: (1) increased total organic carbon (TOC: 0.5–1.7%) with a peak accumulation across the Cenomanian/Turonian boundary (CTB); (2) sulfur/carbon ratios (S/C) and high degree of pyritization (DOP) indicating that the depositional environment in the Gyangze area was oxygen-depleted and H2S-rich, while synchronous, shallower deposits in the Gamba area accumulated in an oxic environment; (3) bulk-rock δ13C analyses of carbonates indicating a positive 2‰ excursion across the CTB, similar to that observed in the western Tethys and Pacific; and (4) an extinction rate of planktic foraminifera across the CTB reaching 50–70%, while the extinction of benthic foraminifera was as high as 90%. A major extinction of benthic foraminifera indicates the development of an inhospitable environment associated with the presence of poorly oxygenated bottom waters. The CTB OAE in Tibet documents a fundamental change in Late Cretaceous palaeoceanography associated with increased dispersal of the southern continents. As the Indian plate moved northward, there was a change in ocean circulation which may have led to the development of a layer of poorly oxygenated bottom and intermediate waters within both the western and eastern Tethys.