Archaeal remains dominate marine organic matter from the early Albian oceanic anoxic event 1b

The sources for both soluble and insoluble organic matter of the early Albian (similar to 112 Myr) oceanic anoxic event (OAE) 1b black shales of the Ocean Drilling Program (ODP) site 1049C (North Atlantic Ocean off the coast of Florida) and the Ravel section of the Southeast France Basin (SEFB) were determined using optical, chemical, stable carbon and nitrogen isotopic analyses. Archaea-derived isoprenoidal tetraether membrane lipids and free and macromolecularly bound isoprenoid alkanes are abundant in these black shales. More specifically, the presence of certain ether lipids (bi/tricyclic biphytane tetraethers) indicates an important contribution of representatives of marine planktonic archaea. The large difference (up to 12 parts per thousand) in C-13/C-12 ratios between algal biomarkers and the much more abundant planktonic archaea-derived biomarkers indicates that the latter were living chemoautotrophically. This offset in C-13/C-12 ratios was used to estimate that up to similar to 40% of the organic matter of the SEFB and up to similar to 80% of the organic matter of ODP site 1049C preserved in the black shales is derived from archaea. Furthermore, it is shown that, even though there are apparent similarities (high organic carbon (OC) content, distinct lamination, C-13-enrichment of OC) between the black shales of OAE1b and the Cenomanian/Turonian (similar to 94 Myr) OAE, the origin of the organic matter (archaeal versus phytoplanktonic) and causes for C-13-enrichment of OC are completely different. (C) 2002 Elsevier Science B.V. All rights reserved.