MARS ON EARTH: THE PERMIAN DUST BOWL OF THE WESTERN PANGAEAN TROPICS (Invited Presentation)

A persistent mystery of the Permian concerns the vast extent of redbeds. The Permian world must have looked like Mars— awash in iron-rich clastics. Much of this volume comprises very fine-grained material— siltstone and mudstone. In this talk, we review the evidence that the Permian was characterized by voluminous deposits of atmospheric dust (loess and reworked loess), even in tropical regions, and explore the sources and implications of this.

Many paleo-loess and dust deposits consist of red mud/siltstone in commonly structureless units, or are overprinted by pedogenic or sub-aqueous (e.g., lacustrine and marginal marine) processes, and also occur entrapped in epeiric carbonate systems formed isolated from fluvial input. The paleo-loess is characterized by an internally massive and laterally continuous character and fine grain size that reflect wind transport. Dust and loess deposits occur in the western-midcontinent US (western tropical Pangaea), as well as regions farther afield such as within carbonate systems of Bolivia (mid southern latitudes) and Japan (remote low-latitude Panthalassa). The thickest loess unit documented to date reaches nearly 1 km— the thickest anywhere on Earth, of any geologic age. Deposits of the Mid-continent may reach 2 km (largely subsurface). Moreover, sedimentologic, sequence stratigraphic, and geochronologic data indicate that loess deposition pulsed on a glacial-interglacial, Milankovitch timescale, recording a link between dust formation/deposition, and glacial expansion/contraction. Provenance data for Permo-Carboniferous paleo-loess in the western-midcontinent US indicate sourcing in the Central Pangaean Mountains (Ouachita-Appalachian) and Ancestral Rocky Mountains, including crystalline basement rocks.

The tropical setting for many of these units is remarkably unusual relative to loess distribution of the Cenozoic, and requires semi-arid to arid conditions at the source, and a glacial-interglacial modulation of the source processes. Climate modeling using the Community Climate System Model version 3 (CCSM3) suggests that cold tropical climate with upland glaciation represents one scenario capable of replicating the conditions necessary for dust generation and mobilization from the Central Pangaean Mountains.