Biological markers in the Rhaetian black shales of South West Britain

• Published in: Organic geochemistry Vol. 10; no. 1; pp. 93 - 100
• Main Authors: Macquaker, J.H.S., Farrimond, P., Brassell, S.C.
• Format: Journal Article Conference Proceeding
• Language: English
• Published: Oxford Elsevier Ltd 1986; Elsevier Science
• Subjects: 4-mehtylsteroids; biomarkers; black shales; Earth sciences; Earth, ocean, space; Exact sciences and technology; Geochemistry; hopanes; Rhaetian; Soil and rock geochemistry; South West Britain; South West Britain; Rhaetian; 4-mehtylsteroids; biomarkers; black shales; hopanes; Mesozoic; Europe; England; Hydrocarbons; Great britain; United Kingdom; Aliphatic hydrocarbons; Black shale; Petroleum; Gas chromatography; Triassic; Sedimentary rocks; Organic residues; Clastic rocks
• ISSN: 0146-6380; 1873-5290
• DOI: 10.1016/0146-6380(86)90012-4

In the light of renewed interest in on-shore petroleum exploration within the United Kingdom we have investigated the aliphatic hydrocarbon distributions of contemporaneously deposited black shales from Rhaetian (upper Triassic, Westbury Formation) outcrops and subcrops in the Worcester Graben and Bristol Channel Trough. The aliphatic hydrocarbon compositions of six samples, three from each tectonic basin, are examined by gas chromatography—mass spectrometry. Although there are close similarities in the hydrocarbon content of the individual members of each sample suite, there are significant differences between the two suites. Most notably, the polycyclic components of the Worcester Graben samples are dominated by 4-methylsteroids thought to be products derived from dinoflagellate 4-methylsterols, and also hopanes. Indeed, polycyclic components are generally more abundant in the Worcester Graben. All the samples show evidence of minor terrigenous inputs (i.e. plant waxes) from the prominence of the odd numbered higher n-alkane components (in the range n-C 25- n-C 35). The distributions of biological marker compounds in the samples indicate that none is sufficiently mature to have generated oil. The shales from the Bristol Channel Trough are, however, more mature than those from the Worcester Graben.