Transtensional deformation of the western Moncton Sub-basin, southern New Brunswick

  • Transtension - Moncton Sub-basin, N.B.

  • Author / Creator
    Kugler, Jared
  • The Maritimes Basin of Atlantic Canada contains deformed late Paleozoic sedimentary rocks. Major dextral strike-slip deformation produced complex structural geometries and stratigraphic relationships. Large strike-slip faults separate smaller sub-basins from basement uplifts; these sub-basins display similar stratigraphy and deformation histories. The Moncton Sub-basin in southern New Brunswick contains the unconformity-bounded, Late Devonian to Early Mississippian Horton Group. The Albert Formation within this group is host to the productive onshore McCully gas field, roughly 2.5 km below the surface. This member is up to 800 m thick and comprises interbedded sandstone, siltstone, and mudstone rocks. Wellbore and 2- and 3-dimensional seismic data from the McCully gas field was combined with outcrop data to investigate the 3D geometry of the Horton Group in the western Moncton Sub-basin. Kinematic parameters were calculated using the geometrical observations of faults and folds that deform the Frederick Brook and Hiram Brook members. At McCully, the subsurface data display large curved ESE-WNW-striking extensional faults within the upper Horton Group, with less common contractional faults and folds. Vertical seismic sections perpendicular to the normal faults show horizontal extension in the range of 12 to 16%, contrasted with vertical seismic sections parallel to the extensional faults that show smaller amounts of horizontal shortening. Analogous outcrop-scale structures are observed within the Albert Formation, 13 km from the seismic data location, along the general strike of the structural pattern. 3-dimensional outcrop mapping reveals a complex relationship of these structures. Relative orientations between extensional and contractional structures, as well as the orientations of the structures relative to the Kennebecasis Fault, indicates that major dextral strike-slip deformation has produced significant clockwise rotation of structures (upwards of 60° for extensional faults). Subsurface measurements, combined with outcrop observations, of the bulk strain suggest that the basin deformed in a transtensional setting with a large angle of divergence (59°) early in its history; however, variations in the apparent stretch and orientation of the faults across the shear zone indicate that the basin deformed heterogeneously in space and time, in addition to asynchronous development of structural features. Towards the SE, the apparent stretch decreases and the orientation of the faults relative to the shear zone boundary increases, resulting in a gradual decrease in α across the shear zone. It is possible to explain the SW-directed concave curvature of the extensional faults by using these variations in the kinematic parameters.

  • Subjects / Keywords
  • Graduation date
    Spring 2019
  • Type of Item
  • Degree
    Master of Science
  • DOI
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