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Hydrocarbon geochemical analyses of Mid-Atlantic Outer Continental Shelf sediments: an environmental assessment

January 1, 1979

Concentration levels of hydrocarbon in 122 composite mid-Atlantic shelf surface sediment samples have been examined during the second year (1976-1977) of the Bureau of Land Management environmental assessment program. The objective of this study was to establish baseline concentrations and provide data for the "natural variability" curve for the mid-Atlantic region.

Concentration levels (μg/g) have been determined for the total lipids recovered by liquid column chromatography, and hexane-soluble fraction (aliphatics) benzene fraction (aromatics) as resolved by gas chromatography for each composite sediment sample. Several geochemical parameter values were also determined among which were: 1) n-alkane odd-even ratio; 2) isoprenoid alkane/ n-alkane ratio; 3) pristine/phytane ratio; 4) pristane/n-C17 ratio; and 5) phytane/n-C18 ratio. Summary analyses of the concentrations and geochemical 18 parameters are included in this report.

Surface sediments examined from the mid-Atlantic shelf contained very low concentrations of resolved aliphatic hydrocarbons, less than 5.0 μg/gm sediment, and very low concentrations of resolved aromatic hydrocarbons, usually less than 1.0 μg/gm sediment. Mass spectral analyses of selected hexane eluates confirmed the presence of a series of normal aliphatic alkanes ranging from to n-C16 to n-C31 as well as the isoprenoids pristane and phytane. A series of three hydrocarbon peaks in the n-C20 to n-C21 range were tentatively identified as n-C25unsaturated, branched homologs, The aromatic fractions contained a number of polynuclear aromatics including phenanthrenes, methylphenanthrenes, fluoranthene and pyrcne, benzofluoranthene, and alkyl benzenes.

Data accumulated in the second year of the program, coupled with data from the first year's investigations (Miller et al., 1977), have provided the basis for establishing a preliminary natural. "variability curve" for the hydrocarbon concentration levels and distribution in these selected mid-Atlantic shelf samples. This curve shows the seasonal variability noted in both the aliphatic and aromatic hydrocarbons in these samples.

Publication Year 1979
Title Hydrocarbon geochemical analyses of Mid-Atlantic Outer Continental Shelf sediments: an environmental assessment
DOI 10.3133/ofr79363
Authors Raymond E. Miller, D.M. Schultz, H. Lerch, D. Ligon, D. Owings, C. Gary
Publication Type Report
Publication Subtype USGS Numbered Series
Series Title Open-File Report
Series Number 79-363
Index ID ofr79363
Record Source USGS Publications Warehouse