During Ocean Drilling Program (ODP) Leg 207, expanded, shallowly buried Cretaceous and Paleogene sediments from Demerara Rise off Suriname, South America, were recovered. This period of the Earth's history involved episodes of ocean anoxia, rapid climate change, mass extinction, and opening of the Equatorial Atlantic Gateway. Therefore, the Demerara Rise provides ideal conditions for long-term paleoceanographic studies of the tropical Atlantic (Erbacher, Mosher, Malone, et al., 2004).
Our approach is to use bulk sediment geochemical data to analyze the sedimentation history of Demerara Rise. Major element composition provides insight into the relative proportions of major components in marine sediment: terrigenous detritus, biogenous material, and diagenetic products. Elements and element ratios related to terrigenous material also help to identify provenance characteristics and thus changes in climate and/or sediment supply. Cross-correlation analysis of elements gives information about different mineral phases suggesting different depositional environmental features. Changes in paleo-productivity are mirrored by elements related to biogenous processes, and the oxygenation state of the water column may be deduced from the abundance of redox-sensitive elements. Beside these paleoceanographic studies, element distribution patterns in pore water reveal information about postdepositional and ongoing diagenesis in the sediment. Study of the whole sediment column can therefore help to locate the depth of past and still-active biogeochemical processes.
The aim of this study is to provide a quantitative geochemical characterization of sediments representing the five lithologic units encountered during Leg 207. For this work, we used the cakes obtained from pore water squeezing. The advantage of this material is its suitability for later chemical analysis in onshore laboratories. Another advantage is its lower content of pore water. Because the effects of precipitated dissolved seawater salts are reduced, no otherwise essential salt correction is applied. We show that the material is useful for providing a first overview of the lithologic units by applying standard geochemical analytical methods.