EVIDENCE FOR A NEOGENE CONTRACTIONAL EVENT AFFECTING THE NEWARK SUPERGROUP

Contractional structures, including spaced cleavage and thrust faults, can be found affecting Neward Supergoup strata in several of the early Mesozoic basins of eastern North America. The amount of shortening represented by these contractional structures is much greater than can be reasonably attributed to post-breakup cooling and subsidence. In addition, apparently related structures outside of the basins can be observed locally cutting across the boundary between the older Paleozoic rocks and later Cenozoic sediments, emplacing Paleozoic rocks onto Cenozoic strata. It is proposed that these structures are all the result of a late-stage event, which I call the RGB event named for the redbeds of the Newark Supergroup in which the best evidence for contraction occurs, the Green Mountain front where the topographic and structural features constrain the timing of this event, and Blue Ridge where the topography is also indicative of a late stage contractional event

Timing of this event is difficult to constrain, except that it has to post-date the mid-Paleogene strata that are overridden by Paleozoic strata along the Green Mountain front and in southern North Carolina. Geomorphic evidence, however, suggests that much of the modern topography of the Green Mountains, Catskills-Alleghenies, and Blue Ridge system is the result of this event, and that this topography developed quite recently. Therefore, it is proposed that this event occurred in mid-Neogene time or later.