Triassic Sedimentation, Maritime Provinces, Canada

Abstract

The Triassic rocks of the Canadian Maritime Provinces (Fundy Group) represent an inter-tonguing complex of continental red beds and tholeiitic basalts. Interbedded sharpstone conglomerates occur in the basin margins and are represented by the Gerrish Facies of the Wolfville Formation, Chedabucto Formation, Quaco Formation, Echo Cove Formation, and Lepreau Formation. An alternating flood-plain-alluvial-fan phase is represented by the Hants Facies of the Wolfville Formation; a lacustrine complex is represented by the Digby Facies of the Blomidon Formation (deposited within the active-wave zone) and the Del Haven Facies of the Blomidon Formation (deposited below wave base) and also by the Scots Bay Formation. Combinations of primary structures were most useful for recognition of different depositional environments. Alluvial-fan deposits contained crude cut-and-fill stratification and poorly sorted sharp-stone conglomerates and sandstones. Flood-plain-alluvial-fan intertongues were characterized by channel stratification, lenticular, wedge-shaped, and planar cross-stratification, current ripple marks, imbricate boulders, current lineation, and claystone breccia. Lacustrine deposits formed below wave base showed even, uniformly thick bedding, disturbed bedding, graded bedding, rhythmic lamination, and oscillation ripple marks, whereas lacustrine deposits formed in the active-wave zone showed these same primary structures in combination with channel stratification, lenticular cross-stratification, current ripple marks, flute casts, groove casts, oriented plant stems, rib-and-furrow structure, mud cracks, and raindrop imprints. Sandstones in the Fundy Group consist of low-and high-rank graywacke, arkose, impure arkose, and orthoquartzite. Their geographic distribution was found to be related to pre-Triassic geology, as Pre-Mississippian metamorphic and Mississippian sedimentary rocks generated low-rank graywacke, Paleozoic granites generated impure arkose, arkose and high-rank graywacke, and Pennsylvanian sedimentary rocks generated orthoquartzites. A provenance control of Fundy Group sandstone composition is suggested. Paleocurrent mapping confirmed the provenance inference. Comparison of Fundy Group sandstones with other ancient sandstones and modern sands demonstrates that provenance, rather than tectonics, controls sandstone composition.