Astronomical climate control on paleosol stacking patterns in the upper Paleocene-lower Eocene Willwood Formation, Bighorn Basin, Wyoming

Details Astronomical climate control on paleosol stacking patterns in the upper Paleocene-lower Eocene Willwood Formation, Bighorn Basin, Wyoming Astronomical climate control on paleosol stacking patterns in the upper Paleocene-lower Eocene Willwood Formation, Bighorn Basin, Wyoming

Jul 2008

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008geo....36..531a&link_type=abstract

Geology, vol. 36, Issue 7, p.531-534

Physics

6

Scientific paper

The Willwood Formation of the Bighorn Basin (Wyoming, USA) isa thick succession of upper Paleocene and lower Eocene fluvial-floodplainsandstones and mudstones. Reddish paleosols, formed on the floodplainmudstones, alternate rhythmically on various scales with heterolithicintervals of small-channel sandstones and mudstones showingweak pedogenesis. Spectral analysis of redness in the Willwoodsuccessions at Polecat Bench and Red Butte reveals significantspectral peaks corresponding to cycle thicknesses of ~8 and~3 m. The ~8 m cycle reflects distinct clusters of 3-5paleosols. Age constraints show that the period of this cycleclosely matches the ~21 k.y. climatic precession cycle. The~3 m cycle corresponds to individual paleosols, with a periodof 7-8 k.y. This period is similar to millennial-scalesub-Milankovitch cycles found in marine and lacustrine successionsof Pliocene-Pleistocene age. Precession and millennial-scaleclimate variations probably affected paleosol development throughcyclic changes from predominantly overbank to predominantlychannel-avulsion deposition, with the latter periodically haltingsoil formation because of high sediment accumulation. A newage model was developed for the Paleocene-Eocene carbon isotopeexcursion (CIE) at Polecat Bench, based on the precessionalorigin of paleosol clusters. The main body of the CIE spans~5.5 precession cycles, or ~115 k.y., and the recovery tailof the CIE spans 2 precession cycles, or ~42 k.y. This outcomeis consistent with, and independently confirms, recent estimatesof CIE duration based on deep-sea cores.

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