Dust and loess as archives and agents of climate and climate change in the late Paleozoic Earth system

AbstractPalaeo-loess and silty aeolian-marine strata are well recognized across the Carboniferous–Permian of equatorial Pangaea. Aeolian-transported dust and loess appear in the Late Devonian in the west, are common by the Late Carboniferous, and predominate across equatorial Pangaea by the Permian. The thickest loess deposits in Earth history – in excess of 1000 m – date from this time, and archive unusually dusty equatorial conditions, especially compared to the dearth of equatorial dust in the Cenozoic. Loess archives a confluence of silt generation, aeolian emission and transport, and ultimate accumulation in dust traps that included ephemerally wet surfaces and epeiric seas. Orogenic belts sourced the silt, and mountain glaciation may have exacerbated voluminous silt production, but remains controversial. In western Pangaea, large rivers transported silt westward, and floodplain deflation supplied silt for loess and dust. Expansion of dust deposition in Late Pennsylvanian time records aridification that progressed across Pangaea, from west to east. Contemporaneous volcanism may have created acidic atmospheric conditions to enhance nutrient reactivity of dusts, affecting Earth's carbon cycle. The late Paleozoic was Earth's largest and most long-lived dust bowl, and this dust represents both an archive and agent of climate and climate change.