Re-Os geochronology and geochemistry of Proterozoic sedimentary successions

Abstract

Abstract
The Re-Os organic-rich sedimentary rocks (ORS) geochronometer has the potential to provide precise depositional ages and vital information on the Os isotope composition of palaeo-seawater. This thesis presents new geochronology data from Proterozoic sedimentary successions and insights into Re-Os systematics of organic-rich sedimentary rocks and petroleum products such as bitumen and oil.

New Re-Os ORS geochronology from two drill cores indicate that the Proterozoic Atar Group of the Taoudeni basin, Mauritania is ~200 Ma older than previous estimates (1107 ±
12 Ma, 1109 ± 22 Ma and 1105 ± 37 Ma). Furthermore, this data also provides precise Re-Os geochronology data from sedimentary rocks that have experienced flash pyrolysis and
demonstrate that the Re-Os systematics are not disturbed by the effects of very rapid heating. Coupled with palaeomagnetic data the Re-Os geochronology suggests that a
reassessment of the role of the West African craton during the assembly of Rodinia is required.

New Re-Os geochronology for the Ballachulish Slate Formation of the Dalradian Supergroup, Scotland yields a depositional age of 659.6 ± 9.6 Ma. The Re-Os age represents a maximum age for the glaciogenic Port Askaig Formation and represents the first successful application of the Re-Os geochronometer in sedimentary rocks with low Re
and Os abundances (<1 ppb and <50 ppt, respectively). This new age suggests that the Port Askaig Formation may be correlative with Sturtian glaciations rather than middle
Cryogenian events.

Laboratory-based hydrous pyrolysis experiments were employed to evaluate the complexation of Re and Os in ORS and their transfer behaviour into petroleum. The findings from these experiments demonstrate that the Re-Os geochronometer is not disturbed by thermal maturation of whole rocks. Furthermore, the data support the hypothesis that the isotope composition of oils and bitumens can be used to fingerprint petroleum to specific source rocks.