Late Devonian–earliest Mississippian glaciation in Gondwanaland and its biogeographic consequences

Abstract

Late Devonian glaciation is well-documented in three Brazilian basins, and newer work has shown a wider extent for this event, reaching Bolivia, Peru, Central African Republic, Niger, and the USA. Physical evidence for this event includes glacial pavements and polymict striated, and faceted clasts as dropstones and within marine resedimented deposits. Late Devonian (Frasnian? and Famennian) onset of Gondwanaland's glaciations resulted in fundamental changes in coeval and later (Mississippian) depositional systems worldwide. Palynomorphs date the more widespread event within the Retispora lepidophyta (miospore) palynozone, which often occurs with the marine acritarch Umbellasphaeridium saharicum. This initial glaciation continued into earliest Carboniferous (Tournaisian) time. There were several consequences from the short-term glacioeustasy. In North America, central Europe and southern China there is a coeval sea-level fall that exhumed and eroded carbonate platforms, deposited siliciclastics, and generated lacunae in the Famennian record. The lowstand resulted in extensive carbonate breccias, shallow-water deposits and evaporites in western U.S.A. Lowstand clastic wedges were deposited in a regression (eastern U.S.A.) with widespread black shales. In Moravia, Famennian siliciclastic influx increased as a result of subaerial weathering in newly-emergent highs that resulted from sea-level drop. Partial sea-level drops were also manifested by ferruginous oolites, which developed in nearshore environments and were subsequently dispersed down adjacent slopes by storm resedimentation. In southern China, aggradation, siliciclastic influx, reflux-dolomitization from evaporation, and shallow-water carbonate resulted from Famennian sea-level fall. The coupling of glacial and lowstand events explains the sudden appearance of shallow-marine, as well as subaerially-affected features after the Frasnian transgression that breached the North American craton.