HIGH-RESOLUTION EARTH HISTORY: A SYNTHESIS OF ASTROCHRONOLOGY AND CONSTRAINED OPTIMIZATION (CONOP)

Accurate reconstruction of Earth history requires the integration of diverse datasets collected from disparate and far-flung localities. Geologic timescales provide an essential framework for the integration of such data, allowing calibration of the tempo of paleoceanographic/paleobiologic events and processes, testing of hypotheses, and evaluation of mechanisms. How can the voluminous body of biostratigraphic, magnetostratigraphic, chemostratigraphic, and radioisotopic data be managed and synthesized from many localities in an objective way, to provide the most reliable reconstruction of Earth history?

One technique that has been successfully applied is constrained optimization (CONOP), which generates an optimized sequence for stratigraphic events recorded at many localities, reconciling local contradictions in the most parsimonious way. Although this method has been used to generate highly resolved stratigraphic time-lines, the composite sequences produced by CONOP are primarily ordinal, and time significance must be inferred post hoc by interpolation between chronologically constrained horizons, such as radioisotopically-dated ash beds or magnetic polarity reversals. Such interpolation typically requires assumptions about sedimentation rate and biotic turnover that are known to be oversimplifications, especially on short timescales (e.g., <100,000 years).

We propose a new methodology to reconstruct Earth history by integrating CONOP with high-resolution astronomical timescales. As a test case, we have selected a large suite of data from deep sea sediment cores surrounding Antarctica (spanning the past 18 Ma) that has previously been evaluated with the conventional CONOP approach. Using this test dataset, we explore the best means to incorporate astrochronologic constraints into the CONOP framework. Initial simulations suggest an improved performance of the new approach, and ongoing work seeks to fully integrate CONOP and astrochronology into a streamlined methodology. Ultimately, application of the method to published and newly acquired Southern Ocean data should allow reconstruction of a detailed history of climate change, biotic response to shifting marine circulation patterns, and the growth of the Antarctic ice sheet through the Neogene.