Multi-Proxy Geochemical Characterization of Mid-Cretaceous Black Shales in the Newfoundland Basin

The primary objective of ODP Leg 210 was the investigation of the history of rifting and post-rift sedimentation in the Newfoundland-Iberia rift. During the Early Cretaceous sub-Arctic seas started to form in the North Atlantic when rifting began between Labrador and Greenland, and between Greenland and Eurasia. The establishment of anoxic and low-oxygen conditions in the main basin of the North Atlantic in Barremian to Cenomanian time, evidenced by black shales of the Hatteras Formation, therefore provides opportunities to examine whether this record of reduced ventilation extended northward into the developing sub-Arctic seas. To this purpose, we focused our geochemical investigation on the expanded sedimentary sequence of Cretaceous black shales recovered at Site 1276 in the Newfoundland Basin. This sequence extends from the lowermost Albian, or possibly uppermost Aptian, to the Cenomanian-Turonian boundary, and it is considered to be equivalent to the Hatteras Formation. Preliminary shipboard analyses indicated the presence of six sedimentary intervals characterized by high TOC contents, in several instances coupled with high HI (characteristic of marine derived organic matter) and high S2 that may record Oceanic Anoxic Events. These include the Cenomanian-Turonian boundary OAE 2 ("Bonarelli" Event), the "Mid-Cenomanian Event", and OAE 1b ("Paquier" Event), OAE 1c, and OAE 1d in the Albian. In addition another interval with geochemical characteristics similar to an OAE-type layer was recognized in the Albian, although it does not correspond to any of the known OAEs. Our shore-based multi-proxy geochemical survey of these OAE-related black shales is designed to confirm and complement preliminary shipboard data and to enable a comparison of the paleoceanographic conditions present in the Newfoundland Basin during OAEs with conditions elsewhere. We therefore identified past productivity rates, modes of productivity, and changes in type and origin of the organic matter through carbon and nitrogen isotopic analyses, biomarker compositions of the sedimentary organic matter, and Rock-Eval analyses. Additionally, redox conditions of the water column and sediment during deposition have been characterized by trace element analyses and nitrogen isotopic composition of the bulk organic matter. Preliminary results confirm the presence of elevated TOC contents within these sedimentary intervals, especially for OAE 2 and OAE 1b. The sequence is characterized by a prevalence of terrestrial organic matter with the exception of OAE 2 and 1b, which clearly have marine signatures. Finally, the low nitrogen isotopic composition of these layers confirms the presence of an altered nitrogen cycle found at other locations during OAEs.