Stratigraphy and sedimentology of the Upper Cambrian Strites Pond Formation, Philipsburg Group, southern Quebec, and implications for the Cambrian platform in eastern Canada

摘要

The Strites Pond Formation is part of the Philipsburg Group in the southern Quebec Appalachians. In this region, the Philipsburg Group forms the Philipsburg slice, the westernmost Taconian nappe. The Strites Pond Formation conformably overlies oolitic packstone and grainstone of the undated Rock River Formation, and is unconformably overlain by bioelastic lime packstone and wackestone, and shale of the late Tremadocian Wallace Creek Formation. The Strites Pond Formation consists of a lower member (69 m thick) dominated by coarse-crystalline dolostone, and an upper limestone-dominated member (154 m thick). Conodonts from the Strites Pond Formation indicate a Late Cambrian age, and we correlate the formation with the Cairnside Formation of the St. Lawrence Platform of southwestern Quebec. Sedimentologic attributes and lithostratigraphic framework of the Strites Pond Formation indicate a prograding lagoonal setting located between high-energy inner-shelf to littoral siliciclastics (Cairnside Formation) and platform-margin ooid shoals (Rock River Formation). The lower member of the Strites Pond Formation accumulated in a low-energy depositional environment situated along the leeward side of the ooid shoals whereas the upper member developed in a more protected lagoon. Stacking pattern of the lithofacies defines recurring metre scale, shallowing-upward parasequences. High frequency sea level fluctuations led to repeated subaerial exposure as documented by karstic cavities filled with coarsegrained sandstones and collapse breccias. These subaerial exposures were frequent during the later stage of basin fill. Stratigraphic analysis identifies formation progradation associated with third-order eustatic sea level fall, with superimposed higher order (fourth- and fifth-order) sea level fluctuations. This style is typical for Late Cambrian cyclic sedimentation in other parts of the Laurentian margin. The Strites Pond-Wallace Creek unconformity marks the maximum third-order sea level fall, and coeval hiatuses are recognized in shallow-marine strata in other basins of eastern North America. The late Tremadocian Wallace Creek Formation was deposited during a significant Early Ordovician sea level rise after the latest Cambrian sea level lowstand. Ubiquitous debris flow carbonate conglomerates and thick quartz arenites at the Cambrian-Ordovician boundary punctuate stratigraphy of the continental slope. These coarse-grained units are interpreted as the slope expression of the regional Cambrian-Ordovician unconformity.