INVESTIGATING CHERTS OF UTAH AT THE LEADING EDGE OF THE PERMIAN SPICULITE BELT

Glass ramps are biosiliceous regimes that replaced coastal carbonate factories for multimillion-year intervals throughout Earth history, but are unknown to many geologists because the resulting cherts are difficult to distinguish from coincidental diagenesis. New field and microscopy analyses focus on cherts throughout Utah to shed light on glass ramp development during the Permian. Siliceous demosponges dominated benthic biosedimentation for perhaps tens of millions of years during the Permian, stretching from boreal to subtropical coasts of Pangea. The best-studied cases are exposed in Svalbard, in Arctic Canada, and scattered across the American West. Utah represents the southern-most extent of the sponge spiculite belt. This provides opportunities to examine initiation, persistence, and termination of the spiculite ecological regime. Bedded cherts of northern Utah reach 1000 m thickness and span the Middle Permian, whereas cherts are more nodular and intermittent in the limestones of southern Utah. We present initial field and laboratory observations of these cherts to frame questions of the sponge ecology and sedimentation through time and space. We characterize key chert facies from outcrop, hand sample, and microscopic scale, and present preliminary models to distinguish primary cherts of sponge accumulation, secondary cherts following macroscopic invertebrate trace fossils, and ambiguous or thoroughly diagenetic cherts. Further mapping and analyses of these facies throughout Utah will better illuminate the ecological processes that supported glass ramp establishment during the Permian.