CHEMOSTRATIGRAPHIC CALIBRATION OF TIME-ROCK CORRELATION: A NEW LEVEL OF ACCURACY FOR SEQUENCE STRATIGRAPHY

A robust time-rock (i.e., chronostratigraphic) framework is fundamental to accurate sequence stratigraphic interpretation, and to interpretation of a myriad of geological and paleobiological processes. Although there is an absence of high-quality 3D seismic data sets for most of the rock record, sequence stratigraphers today can draw from a rich arsenal of chemostratigraphic tools to reconstruct stratal geometries from scattered surface and subsurface localities. Determining the most effective tool(s) for a given basin can be difficult and much confusion persists about the accuracy and utility of some. Refinement of composite standards for carbon and other isotopic systems is providing a powerful chronostratigraphic baseline for many studies. Carbonates by their nature are buffered against alteration of their stable carbon isotopes, making them one of the most versatile chronostratigraphic tools.

We have generated an extensive data set of whole rock carbonate carbon isotope results (>15,000) for a variety of lithologies and geologic settings that provide the basis for the creation of a set of general principles for carbon isotope stratigraphy. Mapping of regional carbonate carbon isotope trends identifies isochroneity and diachroneity of unconformity-bound packages of strata and defines chronostratigraphic strike and dip. Moreover, these patterns yield insights into basin morphology and paleo-drainage patterns. Wholescale negative shifts in carbon isotope profiles can also indicate proximity to shorelines. Similarly negative offsets immediately below diastems may indicate subaerial exposure, while negative offsets above exposure surfaces reveal carbon cycle influence on sea level fluctuation.

New applications of chemostratigraphic tools provide significant new insights into sequence stratigraphic interpretations in most basins. Carbonate carbon isotope stratigraphy, one of the most versatile chronostratigraphic tools, provides significant new insights into sequence interpretation. Many questions fundamental to sequence stratigraphy, particularly position and relative importance of discontinuities, are now being robustly assessed.