The revised Lower Silurian (Rhuddanian) Becscie Formation, Anticosti Island, eastern Canada records the tropical marine faunal recovery from the end-Ordovician Mass Extinction
Copper, Paul; Jin, Jisuo
published: Apr 1, 2014
ArtNo. ESP026004701003, Price: 29.00 €
Inner to mid-shelf, shallow marine carbonates of the 80–85 m thick Becscie Formation conformably overlie the Ordovician/Silurian (Hirnantian/Rhuddanian) boundary. The carbonates were deposited on the eastern side of the Laurentia paleoplate, located at about 25° S latitude, within the tropical cyclone belt in the Early Silurian. The section is tectonically undeformed, largely retaining its original paleoslope depositional surface, and records marine carbonate sedimentation that apparently never reached intertidal or supratidal facies. The carbonates were commonly interrupted by shale partings, storm-disturbed shell beds, ripple-marked bedding planes, micritic hardgrounds and intraformational conglomerates of rip-up clasts. The Becscie Formation is marked by a clearly defined base and top, characterized by a distinct earliest Silurian (early Rhuddanian) brachiopod fauna similar to that of the Estonian Juuru regional substage. Beginning with a relatively low diversity, and generally small-sized shells, and a lack of colonial rugose corals and stromatoporoid sponges in the lower 35 m, the upper part of the formation begins to attain nearly standard marine tropical diversity in its shelly and coralline elements, with non-reefal coral patches and meadows near the top. The formation is herein formally divided into a lower Fox Point Member (spanning the Viridita lenticularis Biozone), and an upper Chabot Member (spanning the Virgiana barrandei Biozone). The Becscie Formation marks the initial stage of post-extinction Early Silurian faunal recovery, typified by the diversification of invaders from the east to form pentameride, rhynchonellide, atrypide and athyridide brachiopod assemblages, that came to dominate the shallow tropical Early Silurian seas.