The surficial sediments in an area of nearly equal 4000 km 2 in Hecate Strait, western Canada continental shelf, are composed predominantly of CaCO 3 . The deposit is Holocene and forms a discontinuous unit consisting of coarse shell debris, typically < 1 m thick, overlying Tertiary bedrock. Carbonate sediments are largely restricted to water depths of < 50 m and are closely associated with rock and gravel substrates. The faunas yielding these sediments are predominantly bivalves, barnacles, and bryozoans. Radiocarbon dates on surficial material range from modern to 1500 yr B.P. Vigorous water circulation through tidal and wave action, combined with rocky or coarse-grained substrates in some areas, favors suspension-feeding biogenic carbonate producers. The presence of carbonates in Hecate Strait results from the glacial and postglacial history of the region. Glaciation and subsequent subaerial erosion produced abundant rock and gravel substrates; subsequent transgression starved the region of terrigenous clastic sediments. Carbonate sedimentation on high-latitude continental shelves is restricted to areas where conditions favorable to production of biogenic carbonate coexist with low supply of terrigenous sediment. High-amplitude fluctuations of sea level, such as those produced during glaciations, may favor development of temperate carbonates during transgressive and highstand intervals.

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