Integrated Chronostratigraphy of the Oceanic Anoxic Event 2 (oae2) Interval at IODP Site U1516 in the Mentelle Basin, Se Indian Ocean

Oceanic anoxic event 2 (OAE2) occurring across the Cenomanian-Turonian boundary (CTB) at ~93.9 Ma represents an abrupt global climatic event in the mid-Cretaceous greenhouse world and is believed to hold clues to understanding future warming climate changes. Available OAE2 records are mainly from western Tethys, North Atlantic Ocean, Western Interior Seaway in North America and a few sites from eastern Tethys and the Pacific Ocean. IODP Expedition 369 retrieved the upper Cretaceous marine succession at site U1516 in the Mentelle Basin offshore SW Australia (SE Indian Ocean) and obtained an OAE2 record at the southern high-latitude. The Cenomanian-Turonian boundary (CTB) interval at site U1516 spans ~50 m and is dominated by rhythmic greenish and grey marly limestone interbedded with an ~3 m thick black shale unit. Since the black shale unit contains no carbonate, no δ13Ccarb data can be obtained, causing an ~3 m hiatus in the δ13Ccarb curve for the CTB interval at site U1516. The incomplete δ13Ccarb curve at site U1516 impedes detailed delineation of OAE2 evolution at site U1516 and inhibits reliable correlations of the southern high-latitude OAE2 record with the well-established OAE2 intervals in the northern hemisphere. Here we present an integrated chronostratigraphy for the CTB interval by performing an integrated analysis of magnetic susceptibility, foramnifera biostratigraphic data, and geochemical proxy data including carbon-, osmium, and strontium isotopes of the CTB intervals of site U1516. In addition, based on the integrated chronostratigraphy, we define a complete carbon-isotope excursion (CIE) over ~24 m thick strata, encompassing the build-up stage C3, plateau stage C4, and recovery stage C5, of the OAE2 interval at the southern high-latitude site. The OAE2 interval at site U1516 is further correlated with that in the Gongzha section of southern Tibet, China, an OAE2 record at southern middle-low latitudes, that has been correlated with other OAE2 records globally. The integrated chronostratigraphy provides an important basis for delineating detailed evolution of OAE2 at southern high-latitudes and for understanding its forcing mechanism.