143-13 Tracking Terrestrial Cyclostratigraphy Across the Cretaceous-Paleogene Boundary, Kiowa Core (Denver Basin, Colorado)

Abstract:

Milankovitch-forced cyclostratigraphy is an important geological tool for building timescales and correlating stratigraphic sections. Astrochronology is reconstructed from cyclostratigraphy by calibrating the latter to an astronomical model in numerical (absolute) time. However, there are two complicating factors: (1) sedimentary sections with both cyclostratigraphy and in situ geochronology or chronostratigraphy, the latter providing independent time constraints, are rare; and (2) planetary orbit dynamics has a “chaos horizon” at ~60 Ma, before which time astronomical models are inconsistent and not reliable for astrochronology.

Here we present a comparative analysis between portable gamma ray spectrometry and pXRF measurements from samples of a key terrestrial section, the Kiowa Core (Denver Basin, Colorado), which has well documented magnetic reversals and high-precision U-Pb TIMS ages. Lithologies alternate between fine and coarse-grained clastic facies. The goal of the analysis is to develop cyclostratigraphic proxies along the core section for astrochronological modeling of the K-Pg Boundary (KPB; ~66 Ma). 

Measurements of the Kiowa Core with a portable gamma ray spectrometer and pXRF provides a means to compare terrestrial elemental cyclostratigraphy from the late Cretaceous and early Paleogene. Results indicate good agreement between the portable gamma ray and pXRF data and differences in some of the elemental trends above and below the KPB. Research objectives of future analysis include: (1) development of an astrochronology for the Kiowa Core around the KPB; (2) correlation with ODP Site 1262, a KPB-bearing marine core with well documented cyclostratigraphy and magnetic reversals, and (3) comparison of KPB cyclostratigraphy with astronomical models to assess which model yields the best fit.

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