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Adams, T.L., 2008

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Bibliographic Reference

Adams, T.L., 2008, Deposition and taphonomy of the Hound Island vertebrate fauna from the Late Triassic (middle Norian) of southeast Alaska: Dallas, Texas, Southern Methodist University, M.S. thesis, 99 p., illust., maps.

Abstract

Late Triassic marine vertebrates occur in the Hound Island Volcanics exposed on the eastern shore of Hound Island, southeastern Alaska. This fossil assemblage is derived from slope deposits in an intra-arc basin of a volcanic island arc complex associated with the allochthonous Alexander Terrane prior to its northern translation from sub-equatorial latitudes to its current latitude. Vertebrate remains consist of complete and fragmented cranial and post-cranial elements belonging to Eosauropterygia, Thalattosauria, and Ichthyosauria, including the genus Shonisaurus. Bones are frequently disassociated and show pre-depositional abrasion and breakage. Less common are several large associated elements, representing a single individual, found parallel to bedding and draped by shale. Rare Osteichthyes and Chondrichthyes teeth are also present. Bivalve and conodont fossils indicate a middle Norian age. Fossils occur in a 13-m-thick succession of interbedded calcareous shale and volcaniclastic-rich bioclastic limestone. The limestone layers are skeletal (vertebrate and invertebrate) packstones to wackestones containing volcanic grains, shale rip-up clasts, glauconite, and pyrite throughout. These limestone strata are episodic thin-bedded debris flow and turbidite deposits that resulted from slumping and redeposition of slope sediments.

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