Analyses of Oil and Cap Rock from Challenger (Sigsbee) Knoll

Abstract

Analyses of Deep Sea Drilling Project Cores 5 and 6, Leg 1, Site 2 indicate that a bona fide crude oil exists in the Challenger Knoll in a normal cap rock environment. These conclusions are based upon oil composition, rock characteristics and isotopic data.The lithology of Core 5 is calcite at the top with calcite and sulfur at the base. Material recovered in Core 6 is gypsum. The calcite portion of Core 5 contains a low gravity, high sulfur oil which is highly aromatic and highly asphaltic-consistent with other low gravity petroleums. The known Gulf Coast Tertiary crude oils with high sulfur appear to be associated with salt dome cap rock. The Challenger Knoll oil has some unusual characteristics which, however, are shared by some known cap rock oils produced from the Gulf Coast Tertiary. Some unusual deficiencies in n-paraffins occur in the liquid petroleum gas and the virgin naphthas. The C 4 , C 5 , C 6 and C 7 hydrocarbons are deficient in nparaffins relative to the corresponding isomers. The profile of the C 7 hydrocarbons as a percentage of C 7 saturates in the Challenger Knoll oil is similar to that in known Tertiary cap rock oils from the Spindletop and Stratton Ridge fields produced from Gulf Coast Tertiary sediments.

Sites 535, 539, and 540

“…Oil-stained limestones were found adjacent to asphalt-filled fractures in the immature source-rock unit at Site 535 (lower Albian to Berriasian, Unit III-V). Oilstained carbonate was also encountered at DSDP, Site 2, Leg 1 (Challenger Knoll; Davis and Bray, 1969). The Challenger Knoll oil was extracted from the core and exhaustively analyzed.…”

Regional Aspects

“…Coupled with a strong evaporative climate, these conditions would have provided for the precipitation of evaporites throughout the Gulf basin, thereby providing, a possible source for the ubiquitous Louann Salt. This latter interpretation would fit if the Louann Salt is Jurrassic-Cretaceous, a prevalent view today (see, for example, Davis and Bray, 1969), and the crustal levels in the Florida Strait and the Yucatan Strait remained at essentially their present levels. Further investigation of the sediment that has accumulated in these channels and possible crustal movements will be required to properly evaluate this interpretation.…”

Geochemical Significance of Gas and Gasoline-Range Hydrocarbons and Other Organic Matter in a Miocene Sample from Site 134—Balearic Abyssal Plain

“…This extract, then, looks nothing like an accumulated oil such as the one found at Challenger Knoll (Davis and Bray, 1969). The asphaltene to heterocompound to aromatic hydrocarbon to saturated hydrocarbon percentages of this extract (92.6:6.0:1.0:0.4) are more heavily weighted toward the larger, more complex molecules than they are in the Challenger Knoll oils (for example, 14:19:37:30).…”

“…Hence, the occurrence must be considered a minor but significant seepage from below. While not as spectacular as the show at Challenger Knoll (Gealy and Davies, 1969;Davis and Bray, 1969), this "show" is another indication that petroleum has already begun to form and migrate in some shallowly-buried deep-sea sediments. …”

“…However, the gasoline is unusual when compared with either typical crudes or young, immature ones (Davis and Bray, 1969;Mommessin et al, 1969;Erdman et al, 1969;and Koons and Monaghan, 1969). In particular, the relatively few components, the equal quantities of iso-and normal pentane, the unusual abundance of methylcyclopentane, and the paucity of aromatics and dimethylpentanes make this sample atypical.…”