Abstract: Hydrocarbons in Surface Sediments of Mid-Atlantic Continental Shelf Region--Initial Survey

R. E. Miller, D. M. Schultz

One hundred-fifty surface-sediment samples consisting of composites from six separate grabs were analyzed for hydrocarbon content and concentration. These samples were collected from the Baltimore Canyon-Mid-Atlantic Continental Shelf where prospective petroleum exploration is considered to be imminent and where baseline levels of hydrocarbons must be established. Six cluster stations consisting of four substations were sampled according to biologic seasons. Three transects, involving six stations each, were sampled in the winter and summer.

Aliphatic hydrocarbons are generally in very low concentration (less than 5 ug/g sediment). Dominant among these hydrocarbons are: (1) series of partly identified, unsaturated, branched C₂₅ isomers appearing in the nC₂₀-nC₂₁ region (termed "triplet" in this discussion); and (2) long-chain, odd-carbon, wax-ester hydrocarbons, n-C₂₅, n-C₂₇, n-C₂₉, and n-C₃₁ (termed "wax esters"). These major component groups vary seasonally and spatially. The triplet increases in relative concentration from fall to spring and as distance from shore increases. The wax esters are of lower relative concentration in spring samples, corresponding to an increase in triplet concentration.

Wax esters are derived from decomposition of terrestrial and marsh plants; structure and source of the triplet are unproved. GC-MS data for the triplet suggest that these compounds are unsaturated branched C₂₅ homologs and indicate that one of the components may be a sterane isomer. Apparent seasonal variations in triplet concentrations suggest that these hydrocarbons are biologic in origin, possibly diagenetic products of phytoplankton and zooplankton metabolism.

Fatty-acid methyl esters, and only traces of aromatic hydrocarbons, were identified in benzene eluates from sediments extracts.

AAPG Search and Discovery Article #90968©1977 AAPG-SEPM Annual Convention and Exhibition, Washington, DC