Stable Isotopes as New Correlation Tool for Clastic Rocks
Guasti, Elisa *1; Verreussel, Roel 1; Donders, Timme 1; van Hoof, Tom B.1
(1) TNO, Utrecht, Netherlands.
Stable isotope geochemistry is a rapidly evolving branch with a strong innovative application to E&P focuses on enhancing correlation at local, regional and global scale.
The combination of biostratigraphic data with the independent proxy from the stable isotope analyses provides excellent opportunities for chronostratigraphic calibration.
In our research we propose three case studies where this tool is proven to be extremely successful.
The Early Toarcian:
Biostratigraphic analysis on rock samples requires chemical treatment of the raw material. We are now developing novel techniques to utilize the biostratigraphic residues for stable isotope analysis.
A δ13C curve fn the Lower Jurassic Dunlin Group of the northern North Sea displayed a spectacular shift (~5 per mil) towards more negative values in the Cook Formation. In combination with the Early Toarcian age derived from palynology, a correlation with the Toarcian Carbon Isotope Event (CIE) could readily be made. The Toarcian CIE is associated with the organic rich source rocks known as Posidonia Shale or Jet Rock. Its presence is now confirmed in a completely different environmental setting and far away from geographic distribution of the Toarcian black shales. The chronostratigraphic resolution of the original biostratigraphic interpretation is enhanced accordingly to less than half of an ammonite Chronozone.
The Paleocene-Eocene transition:
The Paleocene-Eocene boundary from the Suriname Coastal plain is expected to occur in the high Gamma Ray interval in the top of the Upper Saramacca Member, based on the palynological results. The δ13C curve derived from the residues shows a significant shift towards lower values exactly where the PETM was predicted, and hence strongly supported the evidence from the palynological results. Since the P/E GSSP is in fact based on the δ13C signature this is a highly relevant result.
Permo-Carboniferous barren deposits:
For the first time, we apply stable isotope δ13C in combination to biogenic silica microfossils as stratigraphic tool in the Permo-Carboniferous sequences in the SNS (Rotliegend F.) and in the Middle East (Unayzah F.). Stratigraphic correlations in these deposits are notoriously difficult to determine due to a lack of effective correlation tools in the red bed deposits. The combination of the stable isotopic and biogenic silica improves existing regional geological correlations and the position regional unconformities.
AAPG Search and Discovery Article #90141©2012, GEO-2012, 10th Middle East Geosciences Conference and Exhibition, 4-7 March 2012, Manama, Bahrain