Deformation in the Maritimes Basin, Atlantic Canada

• Author / Creator

  Snyder, Morgan

• The Maritimes Basin is a sedimentary basin covering onshore and offshore Atlantic Canada with late Paleozoic strata. The basin comprises a series of partially-connected and isolated fault-bounded subbasins trending generally northeast. Two subbasins are chosen for detailed analysis: the Windsor-Kennetcook subbasin in Nova Scotia and the Bay St. George subbasin in Newfoundland. These two subbasins show complicated syndepositional and post-depositional structures. Many structures, including soft-sediment structures, folds, faults, and salt structures, crop out in the Upper Devonian to early Mississippian Horton/Anguille Group, and the Viséan Windsor/Codroy Group.In the Windsor-Kennetcook subbasin of Nova Scotia, soft-sediment deformation structures crop out along the macrotidal Bay of Fundy. Common features such as load structures, clastic dykes, and soft-sediment folds are accompanied by more unusual structures here termed bulb structures and microbasins. Many of these soft-sediment deformation structures are documented in correlative rocks in the Bay St. George subbasin. Two structure types exist in these two subbasins: those that form by liquidization of sediment soon after deposition, and those that form later during burial. Common triggers of soft-sediment deformation structure formation in the Maritimes Basin include seismicity and overpressured conditions.In the Bay St. George subbasin soft-sediment structure-bearing strata are overlain by an evaporite-bearing unit, the Codroy Road Formation. The Codroy Road Formation evaporites source many spectacular salt structures exposed along the coast. Remapping of key coastal outcrops led to the discovery of salt structures previously unrecognized. These structures include a primary salt weld in the northern subbasin, a secondary salt weld in the southern subbasin, and an abundance of siltstone breccia. The siltstone breccia, previously interpreted as a lithostratigraphic unit within the Codroy Road Formation, is reinterpreted as the remnants of salt-expulsion and dissolution at the surface. Offshore and in the subsurface, salt structures are imaged on bathymetric maps, aeromagnetic maps, and on seismic profiles. Salt structures offshore in Bay St. George include: salt-cored anticlines, salt-expulsion minibasins, and salt welds. Angular unconformities and drastic sediment thickness variation across the subbasin suggest that salt was moving early in the subbasin history.Large faults crosscut ductile structures onland and offshore in the Bay St. George subbasin. Normal and reverse faults striking NE–SW, parallel to subbasin boundaries, suggest that strike-slip deformation was the dominant tectonic style in the subbasin. The major brittle structure onshore, the Snakes Bight Fault, cuts across Anguille Group strata in the south central subbasin. In the hanging wall of the Snakes Bight Fault a thick package of Anguille Group strata is exposed at the surface. Inversion structures imaged offshore also bring older strata to the surface. Offshore, the relationship between salt movement and faulting is complicated. In the central offshore subbasin, a tectonic wedge inserted to the west cuts across suprasalt structures. Salt movement, however, could have continued during wedge insertion, as the shapes of minibasin trough surface traces, and variations in the locus of maximum accommodation through successive horizons show, that salt moved southeast northern and southern subbasin; in contrast, salt moved northwest in the central subbasin, where the tectonic wedge is present.Later deformation is recorded by fractures. Joints, veins, and faults are commonly exposed in outcrop and in well core from the Windsor-Kennetcook subbasin. Cross-cutting and abutting relationships between fractures indicate relative timing of fractures. A Markov chain analysis, a method previously used in sedimentology, is applied here for the statistical testing of fractures. The results are used to create a history of fracturing in the subbasin that can be related to the overall Maritimes Basin history. Early fractures are related to dextral strike slip along the Minas Fault Zone in the late Paleozoic, and later fractures are related to sinistral strike-slip reactivation of the same boundary in the Mesozoic.

• Subjects / Keywords

  • fracture analysis
  • soft-sediment deformation
  • salt tectonics
  • Maritimes Basin
  • deformation
  • strike-slip
  • Atlantic Canada

• Graduation date

  Spring 2019

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/r3-y2hc-5b61

• License

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