Examining the Effect of Glacial-Interglacial Climate Change from Atmospheric Dust Loading and Source Rock Deposition in the Upper Paleozoic Bird Spring Formation (Arrow Canyon, Nv)

Alice Stagner and Lynn Soreghan
Conoco Phillips School of Geology and Geophysics, University of Oklahoma, Norman, OK

The Bird Spring Formation formed in a west-facing, distally-steepened ramp of the Cordilleran Miogeocline. Though sedimentation in the region was dominantly carbonate, significant variation in siliciclastic silt occurs. The silt is inferred to be eolian in origin, owing to lack of a proximal siliciclastic source. We are investigating links among atmospheric circulation and the glacioeustatic-driven sedimentation and hypothesize that silt flux though glacioeustatic cycles might record systematic climate shifts.

Our study interval includes a Middle Pennsylvanian section of ~24m, and an Upper Pennsylvanian section of ~18m; both consist of shallowing-upward, up to 8-meter thick cycles of inferred glacioeustatic origin. Cycles tops typically have grainy facies—locally with exposure surfaces—overlain by siltstone or silty wackestone.

Six lithofacies occur: 1) photozoan (dominantly foram) mudstone; 2) bioclastic wacke- to packstone, with mixed heterozoan (crinoids, brachiopods, bryozoa) and photozoan (fusulinid, algaea) allochems; 3) pack-grainstone with variable, generally decreasing upwards photozoa; 4) coated-grainstone; tabulate coral Syringopora boundstone; and calcareous siltstone. Semi-quantitative petrographic analysis indicates a coarsening-upward trend in quartz-silt grain size and volume proximal to sequence boundaries, from <1% up to 30-40% in grainy facies.

Detrital residue extraction and quantitative grain-size analyses are being conducted to further assess intracyclic variation in silt volume and grain size, which we hypothesize might track aridity and wind strength. Sedimentologic and stratigraphic data will be integrated to evaluate links among atmospheric dust flux and glacioeustatic-driven sedimentation.

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