Late Cretaceous black shales have been extensively studied because of their potential oceanographic implications for greenhouse oceans. Organic matter (OM) enrichment is often linked to anoxia associated with sluggish circulation. Recently a continental influence on marine OM enrichment in OAE intervals has also been reported in the form of preservational effects detrital clay minerals (soil derived) provide in marine sediments. A first order relationship between clay mineral controlled mineral surface area and TOC in black shales from West Africa (ODP 959) identifies a link with precessional scale climate influence on weathering and runoff on the African Continent. Here we show evidence for a similar clay mineral preservational effect on the South American margin during the interval associated with OM enrichment from OAE2. We present new data from the Late Cretaceous black shale intervals of ODP Leg 207 from the western Atlantic from three sites (1258, 1260 and 1261), and observe a strong relationship between MSA and TOC (R (super 2) = 0.92, 0.91 and 0.71 respectively). Since MSA is a function of continental hydrological conditions and provenance, this implies a dominant continental control on TOC enrichment traditionally considered the result of anoxia (OAE2). We also employ novel synchrotron-based spectroscopy to directly image the micro- to nano-scale distribution of organic matter and its association with mineral surfaces. Until recently, imaging of the spatial associations between clay minerals and various OM types has not been possible at the micro- to nano-scales required to provide direct mechanistic evidence of OM preservation by mineral surfaces.

West: -2.4408 East: -2.4408 North: 3.3740 South: 3.3740

Expedition: 159

Site: 159-959

Provider: SEDIS Publication Catalogue

Data set link: http://sedis.iodp.org/pub-catalogue/index.php?id=2013-031706 (c.f. for more detailed metadata)

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