Late Triassic tectonic history of northeastern United States

• DOI: 10.2475/ajs.261.6.501
• Publication Date: 2010-09-01T01:41:09Z
• Authors: J. E. Sanders
• Keywords: Dike; Horst and graben; Imbrication; Sill

The Upper Triassic rocks of the New York-New Jersey-Pennsylvania and Connecticut Valley belts, generally considered to be deposits isolated basins, are inferred represent remnants filling an elongate rift valley that was 50 70 mi wide. In addition, stratigraphic thickness is hold approximately 30,000 ft. If these 2 conclusions correct, then Late tectonic history considerably more complex than previously thought can subdivided into 4 episodes. Episode 1: Initial graben subsidence without folds; deposition ft nonmarine sediments; extrusive intrusive igneous activity. 2: Longitudinal crustal arching in center initial graben; uplift, inversion topography, reversal drainage; erosion; central parts pre-Triassic floor ultimately elevated ft; no activity or transverse folds. 3: Second-generation subsidence, development folds NE. Hunterdon Plateau, Jersey, with maximum structural relief exceeding 4: Offsetting by faults, some strike-slip displacement up 12 mi; longitudinal Valley-and-Ridge type SW. Plateau during faulting; injection porphyritic dolerite dikes faults; formation mineral along faults. Extensive erosion took place after episode until transgressive Coastal Plain marine overlap Cretaceous, which buried rocks. structures have involved entire crust been controlled subcrustal processes, themselves merely reacting passively. magnitude complexity advocated here following regional geologic implications also suggested: 1) Much high position uncovering Precambrian basement medial Appalachians Triassic. 2) Large faults probably extend well beyond limits outcrop as, for example, straight western boundary Taconic allochthon Hudson Valley. 3) southward disappearance may due uplift on Danbury anticline subsequent erosion. 4) Many now at surface deeply buried. 5) were emplaced different ages bracket radiometric could detected between syndepositional late postdepositional rocks, estimate might made time required deformation. 6) Some Appalachian drainage originated flanks arch.