A PALEOTROPICAL CARBONATE-DOMINATED ARCHIVE OF LATE PALEOZOIC ICEHOUSE DYNAMICS, BIRD SPRING FM., SOUTHERN GREAT BASIN, USA

Much of our far-field knowledge of glacial and climate dynamics during the late Paleozoic icehouse is built on decades of study of mixed carbonate-siliciclastic cyclothemic successions from paleotropical Euramerica. Far less has been inferred from carbonate-dominated successions despite their greater sensitivity to sea-level and climate changes. Here we present an across-platform reconstruction of sea-level changes through a 20 myr period of the Pennsylvanian recorded in the Permo-Carboniferous Bird Spring Fm., southern Great Basin. Correlation of five mountain-front successions (400 to 750 m thick) across a basin-slope to shelf-interior transect document changes in m-scale cycles, stacking patterns, and cycle bounding surfaces that support substantial variation in relative sea-level and climate during the Pennsylvanian. Ten genetic sequences are recognized and bounded by intervals dominated by restricted peritidal lithofacies, karst, terra rossa, rooted caliche or Protosols. Within sequences, 125 shallowing-upwards parasequences bounded by flooding surfaces stack into sets that in turn define lowstand, transgressive and highstand systems tracts. Large-scale trends in systems tracts and cycle stacking patterns define a latest Mississippian through latest Pennsylvanian relative sea-level history. The record suggests a lowstand across the mid-Carboniferous boundary followed by a short-term rise in relative sea-level during the early Pennsylvanian (Morrowan). Inferred amplitudes of glacioeustasy later increase during the early Pennsylvanian (Atokan), suggesting an interval of maximum southern Gondwanan ice sheet expansion. Much of the middle to late Pennsylvanian records progradation of the platform under an overall sea-level highstand punctuated by several short-lived (0.5 to ~2 myr) intervals of sea-level fall. Marked progradation of the platform under reduced short-term sea-level fluctuation magnitudes associated with the highstand coupled with possible tectonic reactivation of a margin edge fault system led to a shift from a distally steepened ramp to a steep-rimmed shelf. Inferred periods of relative sea-level maxima and minima correspond to far- and near-field records and contribute toward further constraining the dynamic glaciation history of the late Paleozoic.