Abstract

The Meguma Zone is the second largest terrane in the Canadian Appalachians. Three thick sandstones (Cambrian, Upper Ordovician, and Lower Devonian) alternate with two thick shales (Lower Ordovician and Silurian). The succession is a marginal assemblage shoaling upward from deep-sea fan complexes to coastal facies. In terms of sequence stratigraphy, the succession consists of a basal type 1 sequence (the Meguma Supergroup) and three overlying type 2 sequences (collectively, the Annapolis Supergroup). Interpretations of sedimentary environments and stratigraphic relations agree with those of classical systems tracts.

The Meguma Zone is a sedimentary sink for an enormous amount of well-sorted fine-grained sand and silt. This quantity and its westward dispersal indicate a Gondwanan derivation. Stratigraphic units of the West African craton mimic those of the Meguma Zone in lithology, provenance, dispersal, succession, and age. During Neoproterozoic time, continental ice sheets, rivers, and wind moved sediment southeastward down a cratonic paleoslope from what is now Morocco through Mauritania and Mali. Remnants of widespread sand sheets extend across southern Mali. This sand reservoir became the source rock for the Meguma Zone. In the Early Cambrian the paleoslope reversed, perhaps due to birth of Iapetus. These same agents eroded the Malian sand sheets episodically during relative sea-level lows in Cambrian, Late Ordovician, and Early Devonian times. Remnants of the resulting northwestward-moving cratonic sands and silts occur today as mesas and buttes in northern Mali, Mauritania, southern Morocco, and Algeria. The ultimate destination of this detritus was the continental margin of North Gondwana. This sediment now forms the Meguma Zone and other terranes of southern Europe, northern Africa, and the Middle East.

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