Geology of Gulf of Maine and Adjacent Land Areas: ABSTRACT

Abstract

Seismic reflection, refraction, and magnetic measurements together with bedrock samples obtained with the submersible Alvin indicate that the Gulf of Maine has experienced a tectonic history similar to that of coastal New England. The major basement units include the late Precambrian Avalon platform, parts of the Appalachian eugeosyncline, Late Devonian to Middle Pennsylvanian basin and platform structures, and Early Triassic to Jurassic rift structures. The Avalon platform can be traced from the Canadian Maritime provinces to southeastern New England and may represent an ancient subduction zone formed during the early closing of the Atlantic in post-Grenville time. The Taconic and Acadian intrusive rocks of middle-late Paleozoic time also may have resulted from crustal c mpression during the final stages of closing. At that time the Avalon platform and Appalachian geosyncline were folded, faulted, and welded to the North American craton. Late Paleozoic rift structures apparently formed during the early phase of the opening of the present Atlantic or may have been the result of rotational compression between North America, Africa, and Europe during final closing of the proto-Atlantic. Tensional structures of Triassic age underlie a substantial part of the Gulf of Maine, most being beneath the gulf's many isolated basins. Similar tensional structures can be traced from Newfoundland to Florida and probably resulted from the separation of North America, Africa, and Europe, beginning in the Late Triassic. Mesozoic-Cenozoic igneous activity in northeastern Nor h America also appears to be related to the formation of the present Atlantic basin. The post-Triassic sedimentary framework of the Gulf of Maine consists of coastal-plain sediments of Late Cretaceous to early Pleistocene age which were deposited on a subsiding basement as the Atlantic widened and deepened with continued spreading. Coastal-plain deposits underlie Georges Bank and isolated topographic highs within the gulf which resisted subsequent removal by stream erosion and glacial activity. Well-defined unconformities beneath Georges Bank are inferred to separate the Upper Cretaceous sediments from the Tertiary and lower Pleistocene sediments and the Tertiary-lower Pleistocene strata from the Pleistocene glacial deposits. Moraine deposits of Pleistocene age mantle the northern slope of Georges Bank and much of the Gulf of Maine. Marine sediments of late Pleistocen to Holocene age are present in the gulf's basins. They are believed to be in part glacial rock flour carried into the basins by melt water and in part sediments winnowed from the moraine deposits on the nearby banks and ledges during the postglacial rise in sea level. The topography of the Gulf of Maine is believed to be the result of fluvial erosion during late Tertiary or early Pleistocene time. Pleistocene glaciation modified but did not alter significantly the preglacial drainage system. End_of_Article - Last_Page 2146------------