AN EMPIRICAL PALEOCLIMATE MODEL FOR THE ORIGIN OF CARBONIFEROUS STRATA IN NORTH AMERICA

Carboniferous strata in North America recorded paleoclimate periods (10Ma), epochs (1Ma), and stages (100 Ka). A Late Devonian to Tournaisian glacial period affected low latitudes. Coal, chemically reduced siliciclastic strata, and glaciogenic strata were deposited under cool-humid conditions controlled by a low pressure polar front at the distal edge of continental ice. Late Famennian ice reached the Appalachian basin at 30° south. Visean ice melting resulted in sea level rise and atmospheric high pressure. Evaporites and carbonates recorded Visean aridity in tropical latitudes of Pangea. The next glacial period began in the early Serpukhovian, culminated in the Bashkirian, deteriorated in the Moscovian, but lingered until the Kasimovian. Bashkirian subareal exposure was continental in scale when ice buildup was coincident with increasing rainfall that intensely weathered the craton surface. A Kasimovian interglacial Epoch created a dry-subhumid climate, recorded by eastern Pangean redbeds, petrocalcic paleosols, and a paucity of coal. The final Paleozoic glacial period led to a humid climate and Late Pennsylvanian coal deposits in the Appalachian basin. Climate stages resulted in cyclothems. Lowstand paleosols indicate an increase in rainfall coeval with ice buildup and sea level fall, culminating in humid to perhumid conditions during maximum lowstands so that water tables remained at the surface, resulting in vast peat swamps in eastern cratonic basins. Organic-rich strata were deposited when ice melted and sea level rise flooded cratonic basins. As peritidal depths were exceeded, bottom water mixing ceased. Atmospheric low pressure minimized surface winds, wind driven circulation and wave mixing, resulting in conditions favoring organic-rich mud deposition. High rainfall and run off in eastern equatorial Pangea delivered terrestrial organic matter and reduced salinity, perhaps resulting in a pycnocline. During interglacial stage highstands, seasonal hemispheric high pressure induced cross equatorial monsoonal flow, climate drying, wind driven circulation, elevated salinities and a switch from organic-rich mud to carbonate or sandy siliciclastic deposition in epeiric seas. Thus paleoclimate was a predominant control on Carboniferous stratigraphy at period, epoch, and stage scales.