Abstract

Deposits of nonterrigenous silica in the Ouachita orogen range in age from Middle Ordovician through Pennsylvanian with principal modes in Upper Ordovician and Devonian–Lower Mississippian strata. The coincidence of Paleozoic Taconic and Acadian orogenesis and Ouachita silica sedimentation is related to regional tectonic patterns and ocean surface-water circulation.

Throughout most of Paleozoic time, Ouachita sediments accumulated in the western part of a marginal sea between the southern edge of the North American craton and an orogenic zone marking the convergent junction between the North American and Gondwana plates. Westerly equatorial surface currents in the Paleozoic Atlantic Ocean were enriched in volcanic silica during orogenesis along the plate junction. Radiolaria flourishing in these currents were carried into the Ouachita basin and contributed significantly to formation of Upper Ordovician chert. Silica-rich waters also originated in areas of upwelling off the west coasts of North America and Gondwana during middle and late Paleozoic time. The eastward flow of this water across the Mexican peninsula and into the Ouachita basin was promoted by rises of sea level and by the disruption of westerly equatorial circulation. The accumulation of Radiolaria carried by these currents and indigenous silica-sponge remains along the northern and western margins of the Ouachita basin and on adjacent shelves led to the formation of Devonian–Lower Mississippian novaculite and correlative shelf chert and siliceous carbonate rock.

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