STRATEGIES FOR THE INTEGRATION OF ASTROCHRONOLOGY AND CONSTRAINED OPTIMIZATION (CONOP) IN THE SOUTHERN OCEAN

The integration of deep-time stratigraphic records provides a crucial context for present and future environmental change. This is particularly true for the high southern latitudes, a lynch-pin of the global climate system. However, assembling and compositing a complete record in these regions is often difficult, owing to a range of logistical, environmental, and stratigraphic challenges. Many studies have leveraged the regional synthesis power of biostratigraphic constrained optimization (CONOP) to build composite histories. However, these results are principally ordinal, and interpretations about timing and rates must be conferred post hoc using dated horizons that have been incorporated into the composite section. This too can be challenging in the Southern Ocean, where radioisotopic dates are rare, and paleomagnetic data may be subject to re-interpretation.

This study explores methods of calibrating timescales built with CONOP using the geochronological information provided by Milankovitch Cycles identified in sedimentary sequences (i.e. astrochronology). Four approaches are described and tested here. These are 1) the “internal calibration”, whereby astrochronological information is coded directly into the CONOP database and used to constrain the composite, 2) the “external calibration”, where astrochronological interpretations are used to calibrate the CONOP composite using a line-of-correlation, 3) the “output calibration”, where astrochronological methods are applied to CONOP composite output files, and 4) the “ad-hoc calibration”, a range of approaches applied at different stages of the CONOP analysis to address specific uncertainties.

Each of these approaches has its own strength and weaknesses, but they are not mutually exclusive. We outline strategies for using these methods individually, or in concert, to investigate problems of Earth history. These approaches have the power to greatly increase the temporal resolution possible for composite geological histories, providing valuable insight to process operating at evolutionary and ecological timescales.