Rift-basin development: lessons from the Triassic-Jurassic Newark Basin of eastern North America

We use seismic, field, core, borehole and vitrinite-reflectance data to constrain the development of the Newark Rift Basin, one of the largest and most thoroughly studied basins of the eastern North American rift system that formed during the break-up of Pangaea. These data provide critical information about the geometry of the preserved synrift section and the magnitude of post-rift erosion. We incorporate this information into a new structural restoration of the basin. Our work shows that the Newark Basin was initially narrow (,25 km) and markedly asymmetric; synrift strata show significant thickening towards the basin-bounding faults. Subsequently, the basin became wider (perhaps .100 km wide), deeper (up to 10 km) and less asymmetric; synrift strata exhibit subtle thickening towards the basin-bounding fault system. Several intrabasin faults dissected the Newark Basin after synrift deposition, and the basin fill was tilted (c. 108NW) and folded. Erosion (up to 6 km) accompanied the intrabasin faulting, NW tilting and folding, significantly reducing the basin size. Our work suggests that the eastern North American rift system is characterized by a very broad zone of upper-crustal extension in which a few, wide, deep, longlived, fault-bounded basins (like the Newark Basin) accommodated much of the extension. A massive rift zone developed within the Pangaean supercontinent during early Mesozoic time (Fig. 1, inset). The fragment of the rift zone now preserved on the margin of North America, the eastern North American rift system, consists of a series of exposed and buried rift basins extending from the SE United States to the Grand Banks of Canada (e.g. Manspeizer & Cousminer 1988; Olsen et al. 1989; Schlische 1993, 2003; Withjack et al. 1998, 2012; Withjack & Schlische 2005) (Fig. 1). Withjack & Schlische (2005) and Withjack et al. (2012) divided the eastern North American rift system into three segments based on tectonic history (Fig. 1). Rifting was underway in all three segments by Late Triassic time. The cessation of rifting (and, presumably, the onset of seafloor spreading) was diachronous, occurring first in the SE United States (latest Triassic), then in the NE United States and SE Canada (Early Jurassic), and, finally, in the Grand Banks (Early Cretaceous) – in agreement with the quantitative plate reconstructions of Schettino & Turco (2009). The exact timing of break-up and the early seafloor-spreading history, however, remain controversial (e.g. compare the plate reconstructions of Bird et al. 2007; Schettino & Turco 2009; Labails et al. 2010). Seismic-reflection, core and borehole data acquired by academia and industry, as well as abundant field exposures, make the eastern North American rift system a natural laboratory in which to study the tectonic processes associated with the rifting phase of passive-margin development. Despite this abundance of data, however, fundamental questions remain about the evolution of the eastern North American rift system. Some researchers have proposed that, during rifting, the basins were relatively long, narrow, isolated and asymmetric, bounded on one side by major faults, much as they are today (i.e. the local-basin hypothesis) (e.g. Barrell 1915; Ratcliffe et al. 1986; Manspeizer 1988; Schlische 1993, 2003) (Fig. 2a). Others have proposed that, during rifting, the basins were long, broad, interconnected and symmetric, with major faults on both sides (i.e. the broad-terrane hypothesis) (e.g. Russell 1878; Sanders 1963; McHone 1996) (Fig. 2b). Still others have proposed that the basins were originally broad sag basins that were later tilted and faulted (e.g. Faill 1973, 1988, 2003, 2005; de Boer & Clifton 1988; Root 1988) (Fig. 2d). The goal of this paper is to better define the evolution of the eastern North American rift system by analysing and synthesizing data from the Newark Rift Basin, one of the largest and most thoroughly studied basins of the rift system (Fig. 1). Using seismic, field, core, borehole and vitrinitereflectance data, we determine the geometry of the From: Mohriak, W. U., Danforth, A., Post, P. J., Brown, D. E., Tari, G. C., Nemcok, M. & Sinha, S. T. (eds) 2013. Conjugate Divergent Margins. Geological Society, London, Special Publications, 369, 301–321. First published online May 29, 2012, http://dx.doi.org/10.1144/SP369.13 # The Geological Society of London 2013. Publishing disclaimer: www.geolsoc.org.uk/pub_ethics by guest on July 26, 2013 http://sp.lyellcollection.org/ Downloaded from