Organic Geochemical Character and Hydrocarbon Source Potential of Selected Black Shales, Deep Sea Drilling Project Hole 603B

Abstract

LECO analysis, pyrolysis assay, and bitumen and elemental analysis were used to characterize the organic matter of 23 black shale samples from Deep Sea Drilling Project Leg 93, Hole 603B, located in the western North Atlantic. The organic matter is dominantly gas-prone and/or refractory. Two cores within the Turonian and Cenomanian, however, contained significant quantities of well-preserved, hydrogen-enriched, organic matter. This material is thermally immature and represents a potential oil-prone source rock. These sediments do not appear to have been deposited within a stagnant, euxinic ocean as would be consistent with an "oceanic anoxic event." Their organic geochemical and sedimentary character is more consistent with deposition by turbidity currents originating on the continental shelf and slope.

Late Cretaceous deep-water agglutinated foraminiferal assemblages from the North Atlantic and its marginal seas

“…In Hole 603B, a re-occurrence is also depicted in Cores 93-603B-26 and 25R (Lower to Middle Campanian biosiliceous event, ,,LMCE@ These assemblages are associated with grayish or greenish-gray claystones, which show slightly increased TOC-values in some cases KATZ, 1987;MEYERS, 1987;RULLKOTTER et al, 1987), thus indicating somewhat oxygen-depleted bottom and interstitial waters (Fig. 3).…”

“…TOC values (column 4) according to HERBIN et ai. (1987), KATZ (1987), MEYERS (1987) and RULLKOTTER et al (1987), specific diversity (number of specimens present in sample) is given in column 5. Thickness is not to scale (only recovered part of each core is taken into account).…”

Sources and deposition of organic matter in Cretaceous passive margin deep-sea sediments: a synthesis of organic geochemical studies from Deep Sea Drilling Project Site 603, outer Hatteras Rise

“…Concentrations of organic carbon are generally very low throughout this claystone unit, as shown in Figure 3 which summarizes data from Meyers (1987). Rock Eval analysis of claystones poor in organic carbon give low hydrogen index values, suggestive of microbially reworked, detrital continental organic matter (Herbin et al, 1987;Katz, 1987;Schaefer and Leythaeuser, 1987;Cunningham and Gilbert, unpublished data). Visual examinations of the organic matter content of these samples support this inference.…”

“…In these deposits, from cores 603B-33 and 34, hydrocarbon distributions indicate large proportions of marine lipid material (Herbin et al, 1987;Rullk6tter et al, 1987). Pristane/phytane ratios less than one in these Cenomanian/Turonian samples lead Herbin et al (1987) to suggest anoxic deposition, yet Dean and Arthur (1987) and Katz (1987) conclude that the sulphur contents of these samples are not high enough to indicate permanent bottom-water anoxia, and Bonnell and Anderson (1987) find that 634S values of disseminated pyrite are similar to those of modern oxic marine sediments. These findings do not, however, preclude short-lived periods of anoxia during the deposition of the Cenomanian/Turonian black shales.…”

“…Rock Eval data from Unit IV samples show a wide range of hydrogen index values (Figure 4). The Cenomanian black shale samples from the Hatteras Formation generally have high hydrogen indices and low oxygen indices (Dean and Arthur, 1987;Herbin et al, 1987;Katz, 1987;Meyers, 1987;Rullk6tter et al, 1987;Schaefer and Leythaeuser, 1987), representative of marine type II kerogen. Although most previous studies have concluded that the majority of the organic matter contained within western North Atlantic Cretaceous black shales is from continental sources, Summerhayes and Masran (1983) suggest that samples with higher organic carbon concentrations contain proportionately larger amounts of marine organic matter.…”