Oruche, Dix and Kamo (2018)


Three stages of carbonate-platform development are preserved in the upper Turinian – lower Chatfieldian succession of the Ottawa Group in the Ottawa Embayment and represent deposition along the Late Ordovician Taconic foreland interior of paleo-southern Laurentia. Compared with contemporary stratigraphy in the adjacent northern Appalachian (southern Ontario, New York state) and western Quebec basins, the intermediate Stage 2 succession, which brackets the Turinian–Chatfieldian boundary, preserves embayment-specific stratigraphic patterns. These include: (i) dramatic west-to-east thickening of the upper Turinian Watertown Formation that defines differential subsidence along the present axis of the embayment, (ii) post- Watertown base-level fall defined by appearance of shoreface siliciclastics, (iii) early Chatfieldian marine transgression represented by the proposed L’Orignal Formation that is coeval with but lithologically distinct from the Selby Formation in the northern Appalachian Basin, and (iv) platform segmentation that resulted in a depositional mosaic of shallow banks (Rockland Formation) and equivalent deeper water micro-seaways (lower Hull Formation). The latter event immediately follows accumulation of the Millbrig bentonite, here dated at 453.36 ± 0.38 Ma. Bracketing these local stratigraphic patterns are the bounding stages (1 and 3) represented by the upper Turinian Lowville Formation and middle Chatfieldian Hull Formation, respectively, that contain facies attributes in common with the adjacent basins and characterize inter-regional depositional systems of first warm, then cooler oceanographic conditions. Stage 2 identifies a structurally controlled transition between these end-member stages: a far-field response in the foreland interior, localized along the axis of a late Precambrian fault system, to contemporary change in subsidence rates and tectonomagmatic events along the Laurentian margin.

Three stages of carbonate-platform development
Geological elements of the Ottawa Embayment (OE) and study localities. The embayment is bounded by Precambrian continental crust and is separated from the western Quebec Basin (nQB) by the Beauharnois–Oka arch, and northern limits of the Appalachian Basin (nAB) by the Frontenac Arch (FtA). Section locations are indicated (see Appendix A for coordinates). Other regional structures include the Adirondack and Laurentian highlands; the Grenville mafic dyke swarm (green); and Precambrian lithotectonic terrains: CMB, Central Metasedimentary Belt; FA, Frontenac–Adirondack lowland terrain; and MAH, Morin–Adirondack highland terrain. Possible subsurface extension and isolated blocks of the MAH terrain beneath the embayment are indicated by dashed grey lines. Paleozoic megasequences are indicated with (following Dix 2012), with the Tippecanoe I Megasquence divided into the initial foreland platform and subsequent foreland basin-fill succession. Fault pattern defines a prominent curvature of the Ottawa–Bonnechere graben extending northwest of the embayment, and the Gloucester and Rideau faults are highlighted. Map is based on Baer et al. (1977), Gupta (1991), Sanford and Arnott (2010), and Bleeker et al. (2011).


Search Carleton