Paper No. 1
Presentation Time: 8:15 AM


CECIL, C. Blaine, USGS National Center (emeritus), Reston, VA 20192 and BREZINSKI, David K., Maryland Geological Survey, 2300 St. Paul Street, Baltimore, MD 21218,

Southern Euramerica experienced a succession of climate states (conditions) during the Late Paleozoic, each lasting millions of years (periods). From among the many climate transitions, the focus here is on changes that occurred from the Late Devonian through the Mississippian. Southern Euramerica was situated circa 30 degrees south during the Devonian-Mississippian transition (DMT), but drifted northward to within 10 degrees south by the beginning of the Pennsylvanian (Bashkirian). Strata that include glaciogenic diamictites, indicative of a cool humid climate state, succeeded Late Devonian strata indicative of a warm semiarid to dry-subhumid climate, which would be expected at 30 degrees south latitude. The DMT cool humid period lasted for ~ 10 myr, persisting well into the early Mississippian (late Tournaisian). In addition to evidence previously reported for Late Devonian ice in the Appalachian basin, early Mississippian glaciogenic strata have been reported in South America and North Africa suggesting that the DMT cool period was far more intense and extensive, temporally and spatially, than has been generally recognized.

There was a relatively abrupt switch from the cool humid state of the DMT to a warm arid state in the late Tournaisian. Aridity persisted through the Viséan as indicated by accumulation of evaporites and evaporite- and chert-bearing limestones and dolomites across the North American craton. The arid period persisted until near the beginning of the Serpukhovian (late Chesterian) when sea level began to fall and the climate became progressively more humid. By the end of the Serpukhovian sea level fall exposed much of southern Euramerica and led to the Mid-Carboniferous unconformity of near global scope. Sea level fall was accompanied by a relatively gradual development of a humid to perhumid climate state, which became the dominant paleoclimate state through the early and early middle Pennsylvanian (Bashkirian-Moscovian).

Abrupt shifts in climate were in response to changes in ice volume; humid states corresponded to cool periods and low sea level, whereas arid states corresponded to warm periods and high sea level. Change in Mississippian paleoclimate in response to the gradual northward drift of Euramerica tends to be masked by global climate change associated with changes in ice volume.