THE DEVONIAN-MISSISSIPPIAN CLIMATE TRANSITION IN SOUTHEASTERN LAURENTIA (EASTERN USA): LATE FAMENNIAN GLACIATION, KINDERHOOKIAN COAL, OSAGEAN LOESS

Upper Famennian glacigenic deposits in the central Appalachian Basin, overlain by lower Tournaisian (Mississippian Sub-system; Kinderhookian Stage) chemically reduced siliciclastics, coal beds, and paleo-Spodosols are indicative of a cool-humid-climate mode that began in the Late Devonian and continued through the early Tournaisian. We suggest that a glacially induced stationary polar over southeastern Laurentia near 30°S likely controlled this cool-humid-climate rather than zonal atmospheric circulation. Stratigraphic evidence suggests an abrupt climate transition to zonal circulation and aridity occurred at or just above the Kinderhookian-Osagean Stage boundary in this region. This arid climate resulted in a siliceous facies tract consisting of continental loessite with Aridisols, marine loessite, evaporites, and cherty marine carbonates across southeastern Laurentia. The Osagean facies tract (from modern east to west) includes (but not limited to) the following formations or groups: 1) the continental Maccrady Formation (SW VA, and SE WV), 2) the marine Borden Formation (Group) and stratigraphic equivalents (informally, the Borden delta or Borden siltstone), and 3) the marine Fort Payne Formation (TN, KY), and Burlington and Keokuk Formations (undiff.) on the Burlington shelf, mid-continent (USA). We interpret the Maccrady Formation to be predominantly a continental loessite. We reinterpreted the Borden Formation to be the result of widespread loess deposition in proximal to medial marine environments. Equivalent distal siliceous silty and calcareous chert-bearing facies (Fort Payne and Burlington and Keokuk Formations) intertongue with the southern and western margins of the Borden siliciclastics respectively. Fine quartz-rich dust appears to have been the source of silica for these distal silty, cherty, carbonates. Detrital zircon dating suggests a common siliciclastic source of sediment for the Osagean facies tract. Conodont and palynomorph biostratigraphy constrain stratigraphic correlations within the facies tract. The Devonian-Carboniferous climate transitions are indicative of climatic controls on sediment supply and sedimentation in continental and marine environments, including dust as the source of silica for siltstones and sedimentary chert.