Faulting & Sedimentation/GSA Abstract

Timing of faulting and sedimentation in early Mesozoic rift basins, eastern North America

Abstract--Considerable controversy exists about the timing of faulting relative to sedimentation within the Mesozoic rift basins of eastern North America. It is a general feature of extensional basins that younger strata should progressively record a decrease in bedding when basin-boundary normal faulting and sedimentation are coeval. Based on the apparent lack of differences in bedding dip between the oldest and the youngest strata in some of the Newark Supergroup basins, some researchers have argued that basin-bounding faults were largely post-depositional structures. However, bedding dips are complicated by the effects of intrabasinal faulting as well as transverse folding adjacent to the border faults. Others have argued that border-fault fanglomerates indicate syndepositional border faulting. However, since the oldest strata are not generally exposed adjacent to the border faults and since these deposits--where exposed--are typically fine-grained, it is unknown if these deposits coarsen toward the boundary faults and if these faults were active during sedimentation.

Given often three-dimensional outcrop control of thicknesses of key stratigraphic intervals and well control in some basins, I will show that units of all ages generally thicken toward the border fault systems as well as toward the centers of the basins. This implies that the border fault systems were active during sedimentation and that displacement on these faults was maximized at the centers of the basins and decreased markedly toward the lateral edges. At least in reference to the major intrabasinal faults of the central Newark basin in New Jersey and Pennsylvania, faulting post-dated deposition of the preserved strata. [Note: this last statement has been contradicted by more recent work; see abstracts by Schlische et al., 1991; Jones and Schlische, 1993).]

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