RE â OS AND PGE GEOCHEMISTRY OF ORGANIC-RICH
\nSEDIMENTARY ROCKS AND PETROLEUM

The research in this thesis is presented in paper format with each of four chapters
\nrepresenting one complete study. Chapter two presents Re–Os and geochemical
\nfingerprint data for UK Atlantic margin oils. organic and δ13C geochemical data
\ndemonstrate that the oil is sourced from Upper Jurassic marine shales and the Re–Os data
\nyields an age of 68 ± 13 Ma. Comparison of this date with published basin histories and
\nAr-Ar geochronology demonstrate that Re–Os ages correspond with the timing of oil
\ngeneration. Furthermore the similarities between oil and source rock 187Os/188Os at the
\ntime of oil generation (Osg) indicates that Osg can be used to identify oil source units.
\nChapter three demonstrates, through the analysis of Kimmeridge Clay Fm. core and
\nNorth Sea oil, that unradiogenic mantle like values within oils from wells in the Viking
\nGraben and East Shetland Basin cannot be inherited from source. It is hypothesised that
\nthey are caused by contamination by a hydrothermal fluid sourced from either Cenozoic
\nintrusive units or the mantle. Strain localisation is suggested to have caused the main
\nbasin bounding faults within the Viking Graben and East Shetland Basin to be of
\nsufficient depth to act as conduits for hydrothermal fluid to propagate through and
\ncontaminate oils within reservoirs.
\nChapter four investigates how Osi values across the Ordovician/Silurian boundary
\nGSSP at Dob’s Linn, Scotland, tracks the Hirnantian glaciation within a globally
\nimportant source unit: the Ordovician/Silurian “Hot” Shales. During the Late Katian, Osi
\nvalues increase from 0.28 – 1.08, providing evidence for increased silicate weathering of
\nradiogenic continental crust. A decrease to less radiogenic Osi (~0.60) occurs at the base
\nHirnantian and marks the onset of the Hirnantian Glaciation. This is ascribed to
\nHirnantian ice cover and reduced chemical weathering rates cutting the supply of
\nradiogenic material. In the Late Hirnantian an abrupt increase in Osi values to ~1.1 over
\n19 cm of stratigraphy, is attributed to the leaching of exposed radiogenic glacial deposits
\nand increased weathering of silicate terrane during deglaciation.
\nChapter five applies the Platinum Group Elements, specifically Pt/Pd ratios, to identify
\noil source units. It is demonstrated that asphaltenes from the well constrained UK Atlantic
\nmargin petroleum system contain similar Pt/Pd and Osg values to the known source unit.
\nA further study of the poorly constrained West Canadian Tar Sands demonstrates that
\nPt/Pd ratios in source rocks are not affected by hydrocarbon maturation and are distinct
\nbetween differing potential source units. Comparison of the Tar Sands with potential
\nsource units demonstrates that the Tar Sands are mainly sourced from the Lower Jurassic
\nGordondale Fm., with minor input from the Devonian/Mississippian Exshaw Fm.

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