RE – OS AND PGE GEOCHEMISTRY OF ORGANIC-RICH
SEDIMENTARY ROCKS AND PETROLEUM

Abstract

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