Abstract: Origin and Significance of Evaporites in Basins Around Atlantic Margin

Robert Evans

Immediately before the rifting and disruption of Pangaea, that great continent lay athwart the Triassic equator. The continental interior was arid, and isostatic adjustments following rifting produced drainage flowing away from the newly formed elongate troughs. These climatic and physiographic conditions led inevitably to the deposition of evaporites as the sea entered the rift zones whose margins now form the edges of the continents around the Atlantic. As a result, the sediment sequence in the Atlantic coastal basins shows a change from continental to evaporitic to normal-marine conditions, except where evaporites were deposited directly onto newly formed oceanic crust. The age of these evaporites gives a chronology for the establishment of a permanent body of water be ween the separating fragments of Pangaea. The North Atlantic appeared in the north in Late Triassic time and became established farther south by the Middle Jurassic. The South Atlantic became established during Aptian time. The Gulf of Mexico came into existence in Middle Jurassic time as a result of subsidence of continental material. The union of the two parts of the incipient ocean came about during or later than Albian time and the resulting free circulation of water in the Atlantic eliminated the restriction necessary for the continued accumulation of evaporite deposits. No such deposits are known, therefore, from the northern coast of Brazil or from the northern side of the Gulf of Guinea.

AAPG Search and Discovery Article #90968©1977 AAPG-SEPM Annual Convention and Exhibition, Washington, DC