The Laurentian margin of northeastern North America

The eastern Laurentian margin in northeastern North America is marked by promontories and embayments that are defined by northeast-striking rift zones offset by northwest-striking transform faults. The complete history of the northeastern margin, from the initiation of continental rifting to the onset of passive-margin thermal subsidence, is preserved in a dynamic stratigraphic succession and in anorogenic magmatic suites. Late Neoproterozoic-Early Cambrian clastic and volcanic deposits overlie ca. 1.0 Ga and older Laurentian basement and define multiphase continental extension that rifted Laurentia out of Rodinia, opening the Iapetus Ocean as well as the more marginal Humber Seaway. Continental extension is also expressed in a set of basement fault systems that extend into the craton perpendicular to the northeastern Laurentian margin. Lower Cambrian sandstones at the base of a transgressive passive-margin succession overlie synrift rocks and basement, defining the time of transition for the eastern Laurentian margin from an active rift to a passive-margin environment. The passive margin is expressed as a broad late Early Cambrian through early Middle Ordovician carbonate bank and associated offshelf facies. Synthesis of the available data reveals significant along-strike variations in the thickness, composition, age, and facies of important synrift and postrift stratigraphic successions between the northern Appalachian rift zones. These variations are consistent with models for low-angle detachment rift systems and allow for the resolution of the underlying basement architecture of the eastern Laurentian margin specific to lowangle detachments, including upper-plate margins, lower-plate margins, and transform faults that bound zones of oppositely dipping low-angle detachments. © 2010 Geological Society of America.