Abstract:
The main goal of Ocean Drilling Program Leg 154 (Ceara Rise, western equatorial Atlantic; 5 degrees 58'N, 43 degrees 44'W, water depth 4356 m) was to study Neogene deep-water chemistry, but Hole 929E was drilled down into Paleocene-Eocene calcareous claystone to clayey nannofossil limestone. The PETM, however, was not identified. We used relatively fast core-logging methods to obtain continuous non-destructive chemical data (X-ray fluorescence [XRF] Core Scanner) at much finer spatial scales than is practical for individual sampling methods, identified the occurrence of the PETM, and studied its sedimentological, benthic foraminiferal and environmental changes. We obtained a high-resolution record of elemental concentrations in the deepest cores from Hole 929E (751 to 809 mbsf). Our XRF data documented a sharp Fe increase and Ca decrease (typical for the rapid environmental change at the PETM at other sites) in a prominent, 40 cm-thick, brown, calcareous claystone. Isotope analysis of bulk sediments at a sample resolution of 2 cm across this horizon showed the characteristic negative carbon isotope excursion (CIE). Benthic foraminifera were badly preserved, with many specimens crushed, but the benthic foraminiferal extinction occurred at the CIE: diverse faunas with common specimens of Stensioeina beccariiformis and other typical Paleocene species were replaced rapidly by low diversity faunas dominated by Nuttalides truempyi, abyssaminids, and agglutinated species such as Glomospira spp. In the interval of peak Fe-values, many specimens of N. truempyi are filled with pyrite. These faunas are thus dominated by species that may be opportunistic, but indicate a low food supply. Post-extinction faunas at Walvis Ridge Sites 525 and 527 are also dominated by such "low food supply faunas", whereas faunas at Weddell Sea Sites 689 and 690, and equatorial Pacific Site 865 indicate a high food supply. The Ca-values suggest that CaCO (sub 3) % did not drop as low as at the Walvis Ridge sites, but the post-extinction foraminiferal faunas at Site 929 contain a much higher percentage of agglutinants than the Walvis Ridge faunas. Our data demonstrate that we can locate PETM sediments at sites where they were not identified, so that we can document the spatial and bathyal variability of this event, which is important for its understanding.