Tectono-Stratigraphy of the Passive Margin Off Nova Scotia

Shallow crustal structure of the continental margin off Nova Scotia

Canadian Journal of Earth Sciences ◽

10.1139/e83-157 ◽

1983 ◽

Vol 20 (11) ◽

pp. 1657-1672 ◽

Cited By ~ 3

Author(s):

Thomas M. Brocher

Keyword(s):

Nova Scotia ◽

Velocity Structure ◽

Velocity Model ◽

Passive Margin ◽

Ocean Bottom ◽

Stoneley Waves ◽

Unconsolidated Sand ◽

Ocean Bottom Seismometers ◽

Well Data ◽

Sand And Gravel

The nature of the upper sediments of the shelf and slope on a passive margin was investigated by using high-quality refraction profiles recorded by ocean-bottom seismometers off Nova Scotia. In agreement with previously published reflection profiles, well data, and lithospheric models for the evolution of passive margins, we found little thickening of the post-Early Cretaceous section, implying an even sedimentation rate over the outer shelf for this time period. The velocity model determined from slant stacks agreed reasonably well with well-log data, but had velocities slightly lower than those found from a nearby refraction line using first-arrival travel-time methods. Starting at the sea floor the compressional velocity–depth model consists of a gradient of roughly 0.4 s−1 to a depth of about 1.25 km, followed by another gradient of roughly 1 s−1 to a depth of about 3.5 km. Beneath this depth the velocity gradient approaches zero and can be modelled as a constant velocity layer. Stoneley waves were used to investigate the velocity structure of the upper 260 m of the sediment column. These velocities cannot be measured in the oil wells located on the shelf by conventional 3.5 kHz echo sounders or by measuring the sonic velocities of sediments collected in piston cores. A thinning of the Pleistocene–Holocene Sable Island Sand and Gravel layer was documented by pronounced differences in the propagation of Stoneley waves across the shelf. Although the origin of the thinning is uncertain, the shear-wave velocity determined for this unit, 260 m/s, is appropriate for an unconsolidated sand.

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Depth-dependent inversion of normal faults: Structural analysis of the Penobscot 3D seismic volume, offshore Nova Scotia

10.5194/egusphere-egu21-150 ◽

2021 ◽

Author(s):

Alexander Peace ◽

Christian Schiffer ◽

Scott Jess ◽

Jordan Phethean

Keyword(s):

Nova Scotia ◽

Structural Evolution ◽

Passive Margin ◽

Normal Faults ◽

3D Seismic ◽

Petroleum Systems ◽

Passive Margins ◽

Kinematic Evolution ◽

Kinematic Modelling ◽

Kinematic Mechanisms

<p>The inversion of rift-related faults on passive margins through kinematic reactivation is documented globally. Such structures form an integral part in petroleum systems, provide essential constraints on the kinematic and structural evolution of rifts and passive margins, and can be used as global markers for far-field stresses. Despite the importance of inverted normal faults, the controls on their kinematic evolution, as well as existence and interactions within fault populations are often poorly constrained. Here, we present new structural interpretation and kinematic modelling of an inverted relay ramp structure located offshore Nova Scotia, Canada. This structure is imaged on the Penobscot 3D seismic reflection survey down to ~3.5 s TWTT, and is constrained by two exploration wells. We map two major normal faults that display evidence for inversion in their lower portions (reverse faulting and low-amplitude folding), below ~2.5 s TWTT, though retain a normal offset in upper sections. The wider fault population is dominated by ~ENE-WSW striking normal faults that dip both north and south, while both of the two major faults dip approximately south and are associated with antithetic and synthetic faults. This kinematic dichotomy along the major faults is important as inversion such as this may go unrecognised if seismic data does not image the full depth of a structure. To accommodate such depth-dependent inversion, if both horizons co-existed during inversion, a reduction in volume of the sedimentary package is required between the normal and reverse segments of the fault. In this study, we explore possible kinematic mechanisms to explain inversion structure and the mechanisms accommodating the volumetric changes/ or mass movements required using fault restoration and strain modelling. Our results favour a poly-phase deformation history that can be reconciled with other inversion structures on related passive-margin segments, suggesting these could be widespread processes.</p>

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