The Euramerican Coal Province: controls on Late Paleozoic peat accumulation

Abstract

The ancestral, tropical peats and associated strata of the Euramerican Coal Province record the interwoven effects of climate, tectonism and eustasy during the Late Paleozoic. Many peats formed in foreland and intermontane basins associated with equatorial orogenic belts along the borderlands of Euramerica and Gondwana, while other peats formed in adjacent cratonic basins. The resolution of controls on Euramerican peat formation requires testing against a well-constrained temporal framework. The Late Paleozoic “coal age” followed the evolution of vascular plants in the late Silurian and was associated with assemblage of the Pangean supercontinent. Devonian and Early Carboniferous peats developed locally. The major phase of peat formation commenced in the Namurian A and persisted to the end of the Stephanian, spanning 10–30 Ma in different regions of Euramerica. It is ascribed in part to the residence of northward-drifting Euramerica within the equatorial rainy belt. Within individual depocenters, basin hydrology was suitable for peatland formation during a period (10 6–10 7 years) represented by the stratigraphic distribution of coal measures and termed here the basin-fill “coal window”. Repeated successions (cyclothems) of coal, siliciclastic and carbonate strata punctuate the coal window and typically represent 10 4–10 5 years. These stratal successions are widely ascribed to orbitally driven glacioeustasy, although cyclothems that lack marine strata may represent associated climatic shifts. Cyclothem groupings (mesothems) of 10 6 years duration are recognised locally, and may have eustatic or tectonic causes. Cyclothems produced by autocyclic events such as delta switching should have durations in the order of 10 3 years. The coal beds themselves represent autogenic processes of peat formation over periods of 10 3–10 4 years, constrained by longer term allogenic effects. Recorded in the coal bed are tolerable allogenic events such as fires and floods caused by short-term climatic excursions. The termination of most mires probably occurred when single or combined allogenic effects surpassed the inherent ability of the ecosystem to adapt.