Search

Interpretations of the Late Cretaceous to Quaternary geological history of the North American Basin rely on a seismic and lithostratigraphic framework developed predominantly from data along the northeastern United States margin. Prior to this study, attempts to extend this framework northward to the Nova Scotia margin were hindered by correlation issues across seamounts, limitations in data coverage, and significant complications caused by widespread canyon erosion and shallow salt structures. These challenges are overcome using modern seismic reflection data along the southwestern Nova Scotia margin, in the Shelburne sub-basin, where Upper Cretaceous through Quaternary sequences manifest four distinct phases in the interplay between down-slope and along-slope depositional and erosional processes. The first phase, spanning the Late Cretaceous to Late Eocene, is characterized by widespread periods of gully erosion interspersed with periods of pelagic and hemipelagic, carbonate-rich sedimentation. Extensive failure of upper slope regions related to the Montagnais meteorite impact also occurred during this time. The second phase, spanning the Oligocene to Late Miocene, is dominated by widespread erosion, deposition by gravity flow processes, and sediment re-working by bottom currents. Marked erosion and/or non-deposition along the mid-to lower slope is attributed both to down-slope and along-slope processes. The third phase, spanning the Late Miocene to Late Pliocene, is dominated by bottom current deposition including stacked sequences of giant sediment waves and large contourite drifts along the slope. The final phase, from the Late Pliocene to present, exhibits a return to predominance of down-slope gravity flows with deposition focused below the upper slope. This four phase history of depositional and erosional processes is similar to that documented south of the study area along the U.S. margin. [ABSTRACT FROM AUTHOR]

Two wide-angle seismic reflection/refraction profiles were acquired to determine the velocity characteristics of the Meguma terrane and adjacent Avalonia northeast of the Cobequid-Chedabucto Fault Zone (CCFZ) in eastern Canada. Line 99–1 is located along the Scotian margin whereas line 99–2 crosses the Scotian margin and onshore Nova Scotia and extends into the Gulf of St. Lawrence. Velocity models were derived by forward modelling of travel times. P-wave velocities of 5.5–6.0 km/s and 6.0–6.4 km/s are interpreted to be metasedimentary rocks of the Goldenville and Halifax groups and granitic rocks, respectively. This inference is based on comparison with laboratory velocities of a suite of rock samples, offshore sampling, links to onshore geology with multibeam bathymetry, and gravity modelling. On both lines a low velocity zone (LVZ) >350 km wide and up to 15 km thick is present at mid-crustal levels. The LVZ is not observed beneath onshore Nova Scotia or northeast of Orpheus Graben, the offshore extension of the CCFZ. The crustal thickness of the Meguma terrane varies between 31 and 38 km; in contrast, the Moho is at a depth of 41 km beneath Avalonia. The velocity of the lower crust on line 99–2 is 6.8–7.1 km/s beneath the LVZ and Avalonia, and 6.6 km/s beneath onshore Meguma terrane. Poisson's ratios calculated from P- and S-wave velocities are 0.19–0.23 in the Meguma terrane crust; in contrast, Poisson's ratios of 0.24–0.25 are indicated for Avalonian crust. • Seismic reflection/refraction, gravity, and rock density/velocity data were obtained. • Two velocity/depth models were generated onshore and offshore of Nova Scotia, Canada. • Both models show an extensive low-velocity zone in the offshore Meguma terrane. • Meguma terrane has crustal structure different from that of adjacent Avalonia. • Avalonia extends only 30 km under Meguma terrane in faulted contact. [ABSTRACT FROM AUTHOR]