The Geology of the Southeastern Margin of Canada

An investigation of salt tectonic structural styles in the Scotian Basin, offshore Atlantic Canada: 1. Comparison of observations with geometrically simple numerical models

“…[16] Applying these principles (i.e., the inference of stable versus unstable salt systems in the context of margin geometry and sedimentation regimes) to the Scotian Basin suggests that most of the salt associated with SSA was already expelled from its autochthonous basin by the end of the Jurassic, consistent with large differential loading, owing to Middle Jurassic deltaic sedimentation, that occurred early by comparison with SSB and SSC [Wade and MacLean, 1990;MacLean, 1991]. Given that large-scale listric normal faulting is observed in association with SSB (Figure 4), it is likely that an unstable configuration also existed in SPIII.…”

“…Evaporites of the Argo Formation range compositionally from finely crystalline dolomite and massive, white and purple, coarsely crystalline halite interbedded with shale in autochthonous domains [Wade and MacLean, 1990] to predominantly halite in allochthonous settings [Kidston et al, 2007]. Multiple wells encountered the Argo Formation but only two wells on the Scotian Shelf drilled into undeformed autochthonous salt.…”

“…[6] Sedimentation in the Scotian Basin started in the Middle Triassic during rifting of Pangea and the subsequent opening of the Atlantic Ocean [Wade and MacLean, 1990]. The earliest sediments comprise red continental clastics of the Eurydice Formation and evaporites of the Argo Formation (Figure 2).…”

“…These elements are consistent with an early mildly unstable period during which salt flowed seaward and thickened, but largely remained within its depositional limits. The subsequent seaward flow of the salt up and over older sediments requires sufficiently rapid evacuation of the salt basin, with more pronounced differential loading, suggestive of system driven by deltaic sedimentation (i.e., the Sable Delta [Wade and MacLean, 1990;MacLean, 1991]). In contrast, SSC formed in a largely stable setting because evidence for extension and contraction, and associated seaward motion of the overburden and/or salt is minor.…”

“…The Scotian Basin represents one of the deepest MesozoicCenozoic depocenters fringing the North American and African rifted margins systems [e.g., Wade and MacLean, 1990;Keen and Potter, 1995], and it contains multiple saltrelated structures that are classified by us into three principal structural styles (denoted SS) (Figures 1,3,4,and 5) : SSA, an open-ended roho system (listric, basinward dipping normal faults soling out onto allochthonous salt) with a synkinematic sediment wedge [Shimeld, 2004;Ings and Shimeld, 2006] (according to Schuster [1995], "the term roho was coined about 1970 at Shell Oil Co. from "C. C. Roripaugh's (a Shell geophysicist) Moho" to describe a high-velocity zone characterized by a thin band of high-amplitude discontinuous reflectors that form the base of most of the faults and allochthonous salt features in an area"); SSB, a linked salt tectonic system (landward extension and seaward contraction/salt sheet formation are dynamically linked) with listric normal faults, allochthonous canopies and roho systems [Jackson et al, 2003]; and SSC, salt diapirs and intervening minibasins. Despite recent improvements in seismic data and interpretations, the reasons for such contrasting structural styles, and the synrift basin-scale crustal configuration, are poorly understood.…”