Climatically Driven Shifts in Eolian (Dust) Flux to Upper Pennsylvanian Cycles of the Midland Basin, West Texas

Sohini Sur and Gerilyn S. Soreghan
University of Oklahoma, Norman, OK

Horseshoe Atoll is a complex of phylloid-algal buildups that formed in the interior Midland basin (Texas), far from basin-margin depositional systems.

We are studying detrital flux to upper Pennsylvanian cycles within one buildup (Reinecke Field) to examine relationships between glacioeustasy and glacio-climatic shifts in this tropical site. We hypothesize that the location, far removed from fluvio-deltaic feeders, indicates that detrital material present within these dominantly carbonate cycles reflects eolian influx, which forms a proxy for atmospheric dustiness (aridity and eolian supply). The sequence boundaries are marked by subaerial exposure (calcrete) and studied cycles are symmetrical, with grainstones proximal to sequence boundaries and wackstones/ packstones in mid-cycle position. We conducted high-resolution sampling (10 cm intervals from core) through one complete cycle and extracted the detrital residue fraction via a series of dissolution steps. Detrital fraction through carbonate facies ranges ~0.006- 3% with increased absolute amount and increased variability within ~5 m of sequence boundaries. Detrital fractions are highest (~65%) in the silty shale just above sequence boundaries. Furthermore, detrital fraction co-varies positively with pyrite content. Mid-cycle facies, recording greatest water depths, exhibit remarkably and uniformly low detrital flux. We suggest these data imply increased aridity during glacial to incipient interglacial phases. Reduced source distance during lowstands might have contributed to the high eolian flux near sequence boundaries. Stronger aridity during glacials and associated higher dust flux together could deliver more nutrients to the marine system and thus have influenced productivity and source-rock formation. The observed dust-pyrite relationship is consistent with this hypothesis.

AAPG Search and Discovery Article #90078©2008 AAPG Annual Convention, San Antonio, Texas