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

Abstract

The Willwood Formation of the Bighorn Basin (Wyoming, USA) is a thick succession of upper Paleocene and lower Eocene fl uvial-fl oodplain sandstones and mudstones. Reddish paleosols, formed on the fl oodplain mudstones, alternate rhythmically on various scales with heterolithic intervals of small-channel sandstones and mudstones showing weak pedogenesis. Spectral analysis of redness in the Willwood successions at Polecat Bench and Red Butte reveals signifi cant spectral peaks corresponding to cycle thicknesses of ~8 and ~3 m. The ~8 m cycle refl ects distinct clusters of 3-5 paleosols. Age constraints show that the period of this cycle closely matches the ~21 k.y. climatic precession cycle. The ~3 m cycle corresponds to individual paleosols, with a period of 7-8 k.y. This period is similar to millennial-scale sub-Milankovitch cycles found in marine and lacustrine successions of Pliocene-Pleistocene age. Precession and millennial-scale climate variations probably affected paleosol development through cyclic changes from predominantly overbank to predominantly channel-avulsion deposition, with the latter periodically halting soil formation because of high sediment accumulation. A new age model was developed for the Paleocene-Eocene carbon isotope excursion (CIE) at Polecat Bench, based on the precessional origin of paleosol clusters. The main body of the CIE spans ~5.5 precession cycles, or ~115 k.y., and the recovery tail of the CIE spans 2 precession cycles, or ~42 k.y. This outcome is consistent with, and independently confi rms, recent estimates of CIE duration based on deep-sea cores.

Orbital forcing of terrestrial hydrology, weathering and carbon sequestration during the Palaeocene-Eocene Thermal Maximum

“…These are likely linked to catchment hydrology (e.g. Abdul Aziz et al, 2008), resulting from the interference of both northern and southern hemisphere precession signals within tropical 30 hydroclimates (Short et al, 1991). This is consistent with a strong hydroclimate control on sediment erosion and transport in the Tremp-Graus terrestrial basins during the PETM (Pujalte et al, 2015;Schmitz and Pujalte, 2007).…”

Eustatic variations during the Paleocene‐Eocene greenhouse world

“…[14] Using the stratigraphic thickness of the CIE and its estimated duration of $170 ka Sluijs et al, 2007a;Abdul Aziz et al, 2008], average sedimentation rates can be calculated for both New Jersey sites. At Bass River, the first $100 ka of the PETM (the upper part is truncated in the overlaying sequence boundary) is represented in $10 m of section between 357 and 347 m [Sluijs et al, 2007b], implying sedimentation rates of $10 cm/ka.…”

Drilling disturbance and constraints on the onset of the Paleocene–Eocene boundary carbon isotope excursion in New Jersey

“…Most stratigraphic records indicate a geologically rapid onset, but that definition could mean any duration between approx. 20 thousand years (Cui et al, 2011) and a few thousand years (e.g., Kennett and Stott, 1991;Thomas et al, 2002;Zachos et al, 2005Zachos et al, , 2007Aziz et al, 2008a) or just a few years, i.e., effectively instantaneous (Kent et al, 2003;Cramer and Kent, 2005). Resolution of this question will provide constraints on the likely source of the carbon and advance our understanding of disturbances of Earth's carbon cycle and their effect on ocean chemistry and life.…”