麻豆传媒

The cliff section located on the northeast shore of Broad Cove, Cape Breton, contain fluvial strata of both the Canso and Riversdale Group. The Canso strata are composed of two facies assemblages. The Coarse Member facies assemblage consists of the sequence, massive conglomerate, planar laminated sandstone, massive sandstone, and rippled sandstone. This facies assemblage is restricted within the paleochannels of the Canso, and represents channel lag and fill units, deposited from waning flow. The Fine Member facies assemblage is composed of thickly bedded mudstone interbedded with the sheets of fining upward sandstone. These units represent overbank and splay deposits respectively. Width to depth ratios, and channel to overbank deposit ratios both suggest a moderate to high sinuoisity. Internal structure and the large vertical separation of the paleochannels indicates that the channels represent a single erosional event, followed by one or more infilling events. Petrographic data suggests a warm, arid climate. Thus the environment of deposition represents a periodically active, sinuous fluvial system traversing an arid alluvial plane. Other research indicates that the Canso strata at Broad Cove represent an arid fluvio-lacustrine system.

Two facies assemblages are present within the Riversdale strata of Broad Cove. The Gravel-Sand facies assemblage consists of a basalt matrix-supported conglomerate, overlain by trough cross-stratified sandstone, massive sandstone, rippled sandstone, with the sandstones often containing lenses of disturbed sandstone. This sequence represents a channel fill, consisting of a debris flow, overlain by a sequence of channel fill material deposited from waning flow and containing isolated pockets of bank collapse material. Lateral variations in structure suggest a complex and continually changing internal channel morphology. The second facies assemblage is composed of a massive mudstone which represents overbank flood material. The stacked, en echelon pattern of channel deposits is the result of channel aggradation followed by abrupt channels switching, and is typical of braided fluvial deposits. Longer term cyclic activation and abandonment of areas indicated at Broad Cove also suggests a braided system. Petrographic data indicates a warm, arid climate at the time of deposition. Thus, the environment of deposition represents a braided fluvial system, with cyclic depositional patterns over both the short and long term.

The lack if climatic change suggests the rejuvenation of the source area, which caused the change from the meandering to a braided system, was the result of tectonic activity during the time period represented by the unconformity between the Canso and Riversdale strata of Broad Cove.

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