| dc.description.abstract | This study documents the occurrence of atmospheric dust from Pennsylvanian carbonates of the Copacabana Formation, recovered in core (Mobil-Oxy Manuripi X-1) from the Madre de Dios basin (Bolivia), within southern mid-latitudes (~35˚S) of western Gondwana. The Copacabana Formation spans Late Carboniferous-Early Permian time, and thus formed coeval with and in relative proximity to ice centers and associated glacial deposits located at southern paleolatitudes in adjoining regions of Gondwana (e.g. the Paraná, Tarija, and Paganzo basins in Brazil, southeastern Bolivia, and Argentina, respectively). In Late Carboniferous time carbonate deposition of the Copacabana Formation occurred on a ramp isolated from fluvial-deltaic influx, and thus siliciclastic material in this system reflects atmospheric input. The study interval comprises a series of upwardly shallowing successions 1 – 3 m thick ranging from normal marine outer-mid ramp facies to more restricted inner-ramp facies, commonly capped by horizons of microkarsted and/or red mudstone reflecting subaerial exposure of the carbonate ramp. These surface mark abnormal exposure interpreted to record glacial lowstands.
Dust recovered from throughout the study section varies from ~1 – 43 wgt % in carbonate facies and is quartzo-feldspathic. Grain size modes range from <1 to 97 µm, with coarser intervals generally corresponding to peak dust content (wgt %), and high-frequency sequence (glacial-stage) boundaries. However, two discrete sources of atmospheric input occur–a western volcanic arc source and eastern continental source, recording both westerly (zonal) and easterly (katabatic) wind directions. The western (volcanic) source records zonal westerlies expected at this mid-latitude (~35˚S) locality. In contrast, easterly winds suggest the influence of katabatic winds associated with Gondwanan ice centers. The most likely dust-sourcing regions are the periglacial to proglacial regions of the Gondwanan ice sheets. Non-volcanic peaks occur most commonly associated with subaerial exposure surfaces suggesting peak dustiness that accompanied glacial stages. | en_US |
