Lime Peak--An Upper Triassic Reef Complex in Yukon: ABSTRACT

Abstract

End_Page 621------------------------------Upper Triassic carbonates in the Whitehorse trough, Yukon, are lenticular bodies surrounded by Triassic graywacke and volcanic-clast conglomerate derived from an arc to the west. The carbonates at Lime Peak are unusually well exposed. They show multiple stages of reef growth and a complete facies zonation from massive reefal limestone to offlapping slope and basin. The massive reefal limestones have variable lithology from peloidal mudstones to organic framestones containing spongiomorphs, tabulozoans, and calcareous sponges, with lesser contributions from corals, brachiopods, mollusks, algae, and echinoderms. Figure Slope deposits are alternations of thick beds of reef-derived debris with thinner beds containing attached spongiomorphs, thick-shelled pelecypods, large gastropods, and corals which colonized the debris beds. Basinal sediments include thin-bedded limestones and shales consisting of muddy layers rich in sponge spicules and organic matter and graded packstones containing thin-shelled bivalves and skeletal debris. The stages of growth were (1) initial development of lensoid masses each about 25 m thick (1 on sketch), (2) growth of a much larger reefal mass about 150 m thick (2 on sketch) which shed an apron of debris to the west (2a on sketch), and (3) development of a second thick buildup (3 on sketch) on the underlying forereef debris (2a) as the whole system prograded to the west. The Lime Peak reef complex is not typical of other Triassic buildups in North America which are generally low-relief, thin accumulations (less than 10 m thick) dominated by corals and spongiomorphs. The buildups at Lime Peak are much thicker, and tabuloazons and sponges are more important builders than corals. End_of_Article - Last_Page 622------------