Towards an Astronomically Calibrated Late Cretaceous to Early Paleocene Time Scale

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Gee 95064452 Recent 40Ar/39Ar dating has validated changes made to the Pliocene and Pleistocene portions of the Geomagnetic Polarity Time Scale (GPTS) by orbital tuning methods. Because orbital cycles mark off time in geologically short increments, they may be used to measure elapsed time between events such as magnetic reversals or biostratigraphic datums very precisely. We outline a work plan to improve and refine the Cretaceous and early Paleocene portion of the GPTS, an interval which is subject to errors from spreading rate changes in the South Atlantic sea-floor template by studying a number of DSDP/ODP drill sites of late Cretaceous to early Paleocene age that display precessionally (20 kyr repeat time) forced carbonate cycles. High resolution paleomagnetic sampling will be combined with gathering digital time series (color reflectance spectrometry) to produce a composite astronomical chronology for magnetochrons C33R through C27N (83 Ma to 62 Ma). The resulting improvement in the GPTS will be of use to geodynamicsts, biostratigraphers, and paleoceanographers.