Geology of the passive margin off New England

Abstract

The results of a detailed geophysical investigation conducted by the Woods Hole Oceanographic Institution in 1975 have been used in conjunction with other available information to reconstruct the geologic history of the passive continental margin off New England. Rifting between northeastern North America and Morocco during the Middle-Late Triassic produced a complex series of horsts and grabens in Precambrian/Paleozoic crust. Intra-rift sediments consist of clastics, evaporites, and volcanics. Continental separation occurred and sea-floor spreading began 195-190 my B.P. The boundary between "normal" continental crust and crust radically altered by fracturing and intrusion may be represented by a pronounced basement "hinge zone". Prior to margin subsidence, extensive sub- aerial erosion carved a "break-up unconformity"-reflector "K" which truncated pre-existing rift structures and which must be approximately the same age as the oldest oceanic crust. Within the overlying "drift" sediments, six acoustic horizons have been regionally traced and correlated with strata sampled by a well drilled on the western Scotian Shelf. The total sediment thickness of both rift and drift sequences beneath Georges Bank may be 13 km, of which more than 80% is Jurassic in age. A Mesozoic reef/carbonate platform complex situated on the outer shelf-upper slope was an effective sediment barrier until the early Late Cretaceous, when prograding clastics buried the complex. This carbonate build-up and its basement foundation of altered continental or oceanic crust are responsible for the geographic position and steepness (5-8°) of the present continental slope south of Georges Bank.