ASSESSING AEOLIAN INPUTS TO A LATE PALEOZOIC SHALLOW MARINE SECTION
Here we present preliminary data from two time intervals (Moscovian or middle Pennsylvanian) from the Copacabana Formation, Madre de Dios Basin (Bolivia). Two sections of ~15 meters each representing carbonate inner platform environments were processed to isolate the fine-grained silicate mineral fraction (SMF). Given the proximity to arc volcanism there is potential for ash to disrupt the aeolian dust signal; initial work is aimed at assessing the volcanic versus continental inputs to the basin as well as addressing our primary goals. Visual inspection and initial physical - chemical measurements of the dust-loess size fractions indicate differences between the upper and lower sections, as well as between ash-rich and ash-poor intervals. The lower section has intervals with up to 72 weight-% suspected ash and SMF (non-ash) of 1-7%. The suspected ash layers in the lower section have larger grain sizes (20-40 μm) and distinct 143Nd/144Nd isotopic compositions (εNd = -3.5, -3.8) compared to the ash-poor intervals (~8 μm, εNd = -5.0 to -8.8). The upper section, free of visible ash layers, has high SMF (mean 4-7% up to 41%) with similar size distributions (6-11 μm) and εNd (-7.4 to -7.7) to the lower section, but more radiogenic 87Sr/86Sr compositions (0.797 versus 0.71 - 0.75). Qualitatively, the ash-influenced intervals exhibit abundant evidence for biological activity (bioturbation). The combination of distinct physical and isotopic characteristics of the ash and SMF in the sections and sub-intervals, and the correlation with biological productivity, suggests that (1) deconvolving ash and aeolian inputs to the marine biosphere is possible and (2) dust provenance may influence nutrient availability.