Organic facies of the Asbian (early Carboniferous) Queensferry Beds, Lower Oil Shale Group, South Queensferry, Scotland, and a brief comparison with other Carboniferous North Atlantic oil shale deposits

• Published in: Organic geochemistry Vol. 29; no. 4; pp. 821 - 844
• Main Authors: Follows, B., Tyson, R.V.
• Format: Journal Article
• Language: English
• Published: Oxford Elsevier Ltd 1998; Elsevier Science
• Subjects: Asbian; Carboniferous; Earth sciences; Earth, ocean, space; Exact sciences and technology; Hydrocarbons; lacustrine; oil shale; Oil Shale Group; organic facies; palynofacies; Scotland; Sedimentary rocks; Stratigraphy; United Kingdom; Scotland; Great Britain; North Atlantic; Midland Valley Scotland; Western Europe; organic facies; palynofacies; Oil Shale Group; Carboniferous; Scotland; lacustrine; Asbian; oil shale; microfossils; carbonate rocks; Atlantic Ocean; algae; Lower Carboniferous; limestone; kerogen; Botryococcus; clastic rocks; Thallophyta; shale; mudstone; Europe; biomarkers; Plantae; steranes; Paleozoic; sedimentary rocks; palynomorphs; Chlorophyta; upper Paleozoic; lacustrine environment; Dinantian
• ISSN: 0146-6380; 1873-5290
• DOI: 10.1016/S0146-6380(98)00163-6

The 71 m foreshore exposure of the Queensferry Beds at South Queensferry is currently the best accessible section of the Oil Shale Group of the Midland Valley of Scotland. A combination of bulk organic geochemistry and kerogen microscopy (palynofacies, organic petrology) is used to define four organic facies and one variant. Organic facies 1 occurs in silty mudstones, has a mean TOC of only 2% and Type III–IV gas-prone or inert kerogen (HI<50). Organic facies 3 corresponds to true oil shales, has a mean TOC content of 12% and Type I, predominantly amorphous kerogen (mean HI>800); variant 3A is additionally characterised by an abundance of small (4 μm) spherical cells of possible cyanobacterial origin (occurring in one sample adjacent to a stromatolitic limestone). Organic facies 2 is transitional between 1 and 3. Organic facies 4 has atypically low C/S ratios and corresponds to the Pumpherston Marine Band. These organic facies can also be distinguished using biomarker parameters (Pr/Ph, OEP, C 25:C 15, predominant carbon number, etc.). The HI is very strongly correlated with the relative fluorescence of the organic matter, and strongly correlated with the AOM:phytoclast ratio, and the Botryococcus and total alginite contents; it is inversely correlated with the diameter of black equant phytoclasts. The organic-rich shales thus correspond to distal lower energy anoxic conditions during periods of meromixis (high preservation, low dilution). Similar Carboniferous lacustrine source rocks occur in eastern Canada and East Greenland; all are characterised by large lateral extents (500–2,000 km 2), a geographic and temporal association with strong syndepositional subsidence, generally low Botryococcus contents, and a dominance of amorphous Type II kerogen.