Cretaceous Formations from the Lower Continental Rise off Cape Hatteras: Organic Geochemistry, Dinoflagellate Cysts, and the Cenomanian/Turonian Boundary Event at Sites 603 (Leg 93) and 105 (Leg 11)

Abstract

Geochemical characterizations of the Cretaceous formations at Site 603 are quite comparable with those at Site 105. In the Blake-Bahama and the Hatteras formations, the petroleum potential is medium (<5 kg HC/t of rock) to very low (<0.5 kg HC/t of rock), and the organic matter is mainly of type III origin, that is, terrestrial. At the top of the Hatteras Formation, there is a condensed series, which chiefly contains organic matter of type II origin, with up to 20 wt.% total organic carbon content in Core 603B-34 and 25 wt.% in Core 105-9. This accumulation corresponds to the Cenomanian/Turonian boundary event. An examination of dinoflagellates in the kerogen concentration assigns dates to the samples studied by organic geochemistry. The Cenomanian and Turonian age of the organic-matter-rich black claystones indicates a low rate of sedimentation, about 1 m/Ma. Furthermore, the occurrence of type II organic matter indicates an anoxic environment with insufficient oxygen renewal to oxidize the sinking hemipelagic organic matter. This organic enrichment is not related to local phenomena but to sedimentation over an extended area, because deposits are well known in various areas with different paleodepths in the North Atlantic.

Organic Geochemistry of Cretaceous Black Shales and Adjacent Strata from the Galicia Margin, North Atlantic Ocean

“…Because the concentrations of hydrocarbons are significantly higher for these samples (Table 2), the diminished proportions probably result from dilution by large amounts of the shorter chain-length components. Although land-derived n-alkanes are present in all of these Leg 103 distributions, their contributions are generally not as important as those reported from western North Atlantic Sites 391, 534, and 603 (Deroo et al, 1978;Erdman and Schorno, 1978;Stuermer and Simoneit, 1978;Herbin et al, 1983;Dunham et al, 1987;Herbin et al, 1987;Rullkotter et al, 1987;Joyce and Van Vleet, 1987), where downslope transport of sediments from shallower to deeper depositional areas is believed to have been important (Robertson and Bliefnick, 1983;Wise and van Hinte, 1987).…”

Changes in paleoenvironments in the Atlantic Ocean during Cretaceous times: results from black shales studies

“…Nevertheless, there is a strong similarity both in the bulk and molecular data of Core 17 (Senonian) and Cores 18/19 (Cenomanian/Turonian) samples at Site 367 (cf., e.g. KEN-DRICK et al, 1978;SIMONEIT, 1978;HERBIN et aS., 1986). In view of the high total organic carbon contents, the hydrogen indices of both Cenomanian/Turonian samples (and those of the related samples in the respective intervals) are suprisingly low.…”

“…The widespread occurrence of significant amounts of marine organic matter in sediments deposited over a wide range of water depths during Cenomanian/Turonian times has been interpreted by several authors to relate to an episode of ocean-wide ,,stagnation,, of deep water (e.g. DE GRACIANSKY et al, 1984;HERBIN et al, 1986). The distinct enrichment of heavy metals (such as Mo, Zn, and V) in these black shales is similar to that recorded in the modern Black Sea and thus is also interpreted as evidence for anoxic deep-water environments during times of Cenomanian/Turonian black shale deposition (BRUMSACK, 1980(BRUMSACK, , 1986.…”

Geochemical characterization of soil organic matter and variability of a postglacial detrital organic supply (chaillexon lake, france)

“…Following the description of OM in many marine basins (e.g. Crumière et al, 1990;Herbin et al, 1987), continental series, in spite of their scarcity (Reille and De Beaulieu, 1988) are also becoming attractive for palaeoclimatologists. High primary biological productivity (on the watershed and/or in the water column), high sedimentation rates and efficient preservation conditions make lake sedimentary infillings very good sinks and recorders of OM (Huc, 1988;Kelts, 1988;De Deckker, 1988).…”