Atmospheric Dust Archived in Pennsylvanian Carbonates of the Midland Basin, West Texas

Sur, Sohini¹, Gerilyn S. Soreghan² (1) University of Oklahoma, Norman, Norman, OK (2) University of Oklahoma, Norman, OK

Detrital fraction varies through glacial-interglacial cycles in Upper Pennsylvanian carbonate mounds of the Horseshoe Atoll, Midland basin. We are testing the hypothesis that these variations reflect atmospheric dust flux and influenced shifts in productivity. The studied core spans 2 carbonate glacio-eustatic sequences that contain a small but measurable detrital (inferred eolian) fraction. We conducted high-resolution sampling (10 cm) to assess variation and grain size of the detrital fraction using low-field mass-specific magnetic susceptibility (MS), detrital residue (via various dissolution steps) volume and grain-size measurements. Our initial approach using MS to assess variations of the detrital fraction shows very high-frequency fluctuations within sequences and a general increase (~1.5 times) close to the sequence boundaries. These data track preliminary results of detrital residue volume and grain size in that concentration and grain size of the detrital fraction increase proximal to sequence boundaries, likely reflecting greater aridity and/or lowered sea level combined with higher wind strength during incipient glacials to incipient interglacials. Currently we are exploring the promising relationship between MS and the detrital residue volume and grain size. If these co-vary, then MS may be a proxy for detrital fraction/dust flux and/or the relative wind intensity. We are also assessing the hypothesis that high-frequency fluctuations in MS track high-frequency climate change and variations in detrital fraction might cause shifts in productivity via dust-induced nutrient seeding. The latter might also help explain development of classic “cyclothemic” black shales, alternatively explained as a product of upwelling-induced productivity, or anoxia resulting from salinity stratification.