Systematic Fluctuations in Timing of Atmospheric Dust Flux through a Late Paleozoic Glacial- Interglacial Cycle of the Reinecke Field, Horseshoe Atoll, West Texas
Atmospheric dust is an important climatic agent as well as a valuable climatic archive. Recent studies have hypothesized ample dust deposits (loess) from late Paleozoic western equatorial Pangaea. However their relation with late Paleozoic climate change is understudied. We have developed a methodology for sequential extraction of the silicate mineral fraction (SMF) from lithified carbonates and have applied this to an upper Pennsylvanian glacio- eustatic sequence of Horseshoe Atoll, an isolated carbonate buildup of the Midland basin (west Texas).
The studied cycle (~ 30 m thick) consists almost entirely of carbonate with a thin interval of dark, pyritic mudrock at the sequence boundary. The SMF contains both detrital and authigenic silica and, using paleogeography, stratigraphy and petrographic constrains, we infer the origin for both components to be eolian. Accordingly, the SMF can be used as a proxy for atmospheric dust and attendant aridity. Dust varies over 2 orders of magnitude within the carbonate succession and is over 3 orders of magnitude higher in the mudrock. We interpret the mudrock as a loess deposit that was pedogenically modified and subsequently transgressed. The stratigraphic position of the the mudrock, juxtaposed between the sequence boundary and early transgressive carbonate facies, suggests maximum aridity during lowstand to early transgression (glacial to incipient interglacial). Time series analyses of the dust fraction within the carbonate reveals Milankovitch- and sub-Milankovitch-scale variations in atmospheric conditions through a single glacial cycle.
AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009