Climatic and Biotic Consequences of Atmospheric Dust in the Late Paleozoic

Dust (including loess) deposits are well known as both an archive and agent of climate change for Earth’s late Cenozoic record. Loess deposits of pre-Cenozoic age are less known, but emerging evidence indicates widespread loess and dust in western tropical Pangaea during the Late Carboniferous-Permian. This interval (centered on ~300 Million years ago) is a well-known icehouse with widespread glaciation in the southern polar region, but little evidence for glaciation outside the southern high latitudes. Dust deposits in low-latitude continental settings reach and potentially exceed 1 km— the thickest known from any geologic interval— and abundant evidence indicates deposition in shallow epicontinental marine realms as well.  

Sedimentologic, sequence stratigraphic, and geochronologic data indicate that dust deposition pulsed on a glacial-interglacial, Milankovitch timescale. Provenance data indicate sourcing in the Central Pangaean Mountains (Ouachita-Appalachian system) and Ancestral Rocky Mountains of western equatorial Pangaea, with sources that included crystalline basement rocks.

The equatorial setting is remarkably unusual relative to the Cenozoic, signaling an oddly dusty tropical atmosphere, and requires semi-arid to arid conditions at the source, and a glacial-interglacial modulation of sourcing. Climate modeling (Community Climate System Model v.3) 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.

In our ongoing work, we are pursuing mid-latitude records of Late Paleozoic dust deposition to combine with mass accumulation rate estimates and constrain global model simulations of the dust cycle to further investigate the climatic effects, which may have included radiative cooling associated with volcanic dust additions. We are investigating the hypothesis that this unusual dust record may in part archive upland tropical glaciation, and that the voluminous atmospheric dust stimulated productivity in the marine and terrestrial biosphere, thus affecting biogeochemical cycling.