MILANKOVITCH SCALE CYCLICITY DURING CRETACEOUS OCEANIC ANOXIC EVENT 2 AT DEMERARA RISE, WESTERN EQUATORIAL ATLANTIC OCEAN

Testing for Milankovitch cycles in stratigraphy allows for observations of astronomical forcing impacts on mineralogical cyclicity, carbon sequestration, and climatic effects on marine micro-organisms. Since Milankovitch cycles are global in nature, their recognition in stratigraphy also provides a means for high-resolution global correlation. Here this testing is applied to the organic black marine shales at Demerara Rise deposited during Oceanic Anoxic Event 2 (OAE2) delineating the Cenomanian-Turonian boundary in the Mid-Cretaceous period. Stratigraphic correlation of the Demerara Rise to OAE2-age sediment in the Western Interior Seaway and Tethys Ocean have relied largely on significant carbon isotope excursions (CIE’s) up to ~6 ‰. Here we present grayscale and X-Ray fluorescence data from ODP Leg 207 cores at Demerara Rise that depict millimeter scale mineralogical changes both during and around OAE2, and that can be correlated to the CIE’s. A superimposed meter-scale cyclicity in the grayscale data shows evidence for Milankovitch forcing, enabling new key refinements in the time scale and global correlation of OAE2. These innovations contribute to understanding the sequence of events that took place during the deposition of these organic-rich black shales, which are economically significant as source rocks for petroleum and natural gas.