DEVONIAN GLACIATION IN GONDWANA: ESTABLISHING CARBONIFEROUS EUSTASY

In North America, central Europe and southern China there is a Late Devonian sealevel fall that exhumed, shut down, and eroded carbonate platforms, deposited siliciclastics, and generated lacunae in the Famennian record. The lowstand resulted in extensive carbonate breccias, shoal-deposits and evaporites in western U.S.A. Lowstand clastic-wedges were deposited in a major forced regression in black shales (eastern U.S.A.). The coeval Gondwana glaciation was apparently responsible for lacunae in the Famennian rock-record in many places. In Moravia, Famennian siliciclastic influx increased as a result of weathering in newly-emergent highs that resulted from sea-level drop. Partial sea level drops were manifested by ferruginous oolites, which developed in nearshore environments and were subsequently dispersed onto adjacent slopes by storm resedimentation The coupling of glacial and lowstand events explains the sudden appearance of shallow-marine, as well as subaerially-affected features within a generally transgressive sea that breached the North American craton during Late Devonian (Frasnian) time. It has been shown that Gondwana's well-known Carboniferous glaciations began in Late Devonian time. The Devonian glaciation event occurred over a broad area, including much of Brazil (Parnaíba, Amazonas, and Solimöes basins), Bolivia (Madre de Díos and Altiplano areas of the Paleozoic foreland basin), and sub-Saharan Africa. This initial glaciation continued into earliest Carboniferous (Tournaisian) time. It is dated within at least the LE, LN and VI palynozones. We estimate that with at least 16,000,000 square kms involved in the glaciation, sealevel fall was a minimum of 60m. Given the model of Buggisch (1991) we suggest that glaciation was involved with Devonian glaciations.