A current debate concerns the timing and dynamics of marine ingression into the rift basins of the Central Atlantic Margin. Two scenarios of evolution are hypothesized for Late Norian to Rhaetian paleogeographic reconstructions: (i) marine ingression leading to salt generation through evaporation of seawater, or (ii) salt generation through groundwater evaporation within basins located far from marine influence. These hypotheses remain unproven.
Along the northern margin of the Central Atlantic Margin, the so-called eastern North American rift system, the dolostone-dominated Iroquois Formation is the first unequivocal evidence of marine-influenced sedimentation. Age of this unit is not consensual, but it is dated as Early to Middle Jurassic. Our investigation of two cores (assumed here to be of Rhaetian age) from the Eurydice Formation in the Scotian and Orpheus basins provides the first convincing sedimentological evidence of Late Triassic marine ingressions into the eastern North American rift system. This was likely contemporaneous with the main transgressive events recorded in Western Europe. Evidence suggests the studied interval of Eurydice Formation was deposited by tide-dominated processes, possibly in an estuarine or deltaic environment.
This work challenges the vison of a linear evolution of Central Atlantic Margin basins during the early stages of continental break-up and rifting; instead this story seems to be punctuated by marked and recurring changes in the depositional environments. Our findings have far reaching implications for the understanding of Triassic–Jurassic paleogeography and paleoclimates, biological evolution, and resources exploration. Additionally, these findings may have regional consideration for the development of major marine evaporite buildups and the timing of initial marine ingression during rift basin development.