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 ice age 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 high sensitivity to changes in accommodation space and environmental conditions. Here we present a relative sea-level history for a 20 m.y. period of the Pennsylvanian defined using an across-platform sequence stratigraphic analysis of the carbonate-dominated Bird Spring Fm., southern Great Basin. Correlation of five mountain-front successions (∼500 to 750 m thick) document changes in the lithofacies composition of m-scale cycles, their cycle stacking patterns, and cycle bounding surfaces that record 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 and/or Protosols. Within sequences, 128 shallowing-upwards parasequences, bounded by flooding surfaces, stack into parasequence sets that in turn define lowstand, transgressive and highstand systems tracts. The stratigraphic and acrossplatform patterns of systems tracts and cycle stacking patterns define a latest Mississippian through latest Pennsylvanian relative sea-level history (∼323 to 299 Ma) characterized by a lowstand across the mid-Carboniferous boundary followed by a gradual rise in relative sea-level throughout the Morrowan. The Atokan is characterized by stepped progradation of the platform during a gradual long-term fall in relative sea-level that culminated in the deposition of shallow water facies and exposure across the platform during the early Desmoinesian. Aggradation of shallow-water and peritidal carbonates across the Bird Spring platform during the Missourian through early Bursumian record a second protracted episode of relative sea-level rise in the late Pennsylvanian.;Inferred magnitudes of short-term (105 to 104 yr) sea-level fluctuations superimposed on the longer-term rises and falls range from 20 to ≥ 70 m during the early-mid Pennsylvanian and are substantially reduced (≤ 20 m) during the late Pennsylvanian. Inferred periods of sea-level maxima and minima correspond well to independent far- and near-field reconstructions of Pennsylvanian sea-level although regional variation in subsidence and post-Antler tectonism could have contributed to longer-term changes in relative sea-level.