Abstract

The late Jurassic to early Cretaceous Cumberland Bay and Sandebugten formations of South Georgia have different detrital petrography, although some of their detrital components are common to both units. Cumberland Bay strata become progressively more deformed with depth, and the more deformed portions strongly resemble Sandebugten rocks. Estimates of pressure and temperature of metamorphism suggest that Sandebugten rocks underwent pumpellyite-actinolite or greenschist facies metamorphism, at least 1 kbar and about 50°C higher than prehnite-pumpellyite facies metamorphism of the Cumberland Bay sediments. Both units are now separated by a low angle fault. Palaeocurrent data from Cumberland Bay strata show definite patterns, but data from Sandebugten Formation are equivocal. Variations in petrography are no more than occur in similar island arc-derived sediments from other areas around the Pacific margin. It is postulated that both units, and possibly other formations on South Georgia, may have been derived from one evolved volcanic arc with a sialic basement, rather than from two sides of a marginal basin, as has been previously suggested.

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