CRETACEOUS MID-CENOMANIAN EVENT FROM SOUTHERN HIGH LATITUDE OF INDIAN OCEAN, IODP SITE U1516

Mid-Cretaceous Cenomanian (100.5-93.9 Ma) is an age known for high-stand sea level and high average temperature. At the latest Cenomanian, Oceanic Anoxic Event 2 (OAE2) caused large perturbation of carbon cycle. The signal has been recorded as 2.5‰ positive δ¹³C excursion in the sedimentary rocks around the world. Two million years before this event, it is known that smaller event of carbon cycle perturbation called mid-Cenomanian Event (MCE) scored itself as ~1‰ positive δ¹³C excursion in the sediments mainly over Tethyan region. In the southern hemisphere, especially in higher latitude, reports of MCE were very limited. This study provides basic geochemical information across the MCE interval from IODP Exp. 369, Site U1516, southern high latitude of proto-Indian Ocean. Carbon isotope stratigraphy was constructed using bulk organic and carbonate carbon (δ¹³C_org, δ¹³C_carb respectively). Carbonate content (%CaCO₃), total organic carbon content (TOC), oxygen isotopes (δ¹⁸O) of bulk carbonate and selected biomarkers extracted from the sediments are reported from Site U1516C, cores 34R-36R.

Most remarkable result of this study is parallel carbon isotope fluctuation of δ¹³C_org and δ¹³C_carb. The carbon isotope stratigraphy with characteristic double peak clearly indicates exact horizon of MCE in the studied section correlative to other well studied sections in the world（Jarvis et al., 2006, Geol. Mag.）. δ¹⁸O showed periodicity comparable to ~100 kyr eccentricity orbital cycle. It recorded largest amplitude across the MCE interval and minimum value at the middle of the double peak. It may suggest amplification of SST fluctuation across the MCE interval and warming in the middle of MCE. Alkenones from haptophytes are detected through the section showing no significant change in its abundance across the MCE interval as same as that of %CaCO₃. They may indicate stable condition of the sea surface across the interval of MCE. Such stable sea surface condition may have allowed carbonate and organic carbon isotopes to have recorded their parallel fluctuation with minimum local noise.