Stable Isotopes Stratigraphy (SIS)
Stable Isotopes Stratigraphy (SIS) uses changes in isotopic ratios to define stratigraphic correlations. At Chemostrat, we provide carbon oxygen stable isotope stratigraphy services that mostly relies on changes in the 13C/12C ratio (δ13C) through time.
SIS requires carbon in the sediment, limiting analysis to either carbonates (from which δ13Ccarb and δ18Ocarb are determined) or organic rich shales (from which (δ13Corg is determined). Chemostrat have successfully used shales with TOC of c. 0.3%, which means that almost any grey mudrock can be used for analysis. Isotope analysis uses an elemental analyser coupled to a Thermo continuous flow mass spectrometer (to measure δ13Corg) and a dual inlet mass spectrometer (to measure δ13Ccarb and δ18Ocarb).
The power of SIS lies in the chronostratigraphic correlations it supplies. Isotope curves are compared with the extensive published records publicly available, which allows the placement of sequences against the Geological Time Scale. By enabling absolute ages to be determined, SIS provides a means to determine sedimentation rates, which in turn can provide important input into sequence stratigraphic models.
SIS data from carbonates and mudrocks can be obtained from all sample types and as with elemental chemostratigraphy, it can be applied to sediments of any age, again making SIS a versatile stratigraphic tool.