TAPHONAMY AND DEPOSITION OF THE HOUND ISLAND VERETBRATE FAUNA FROM THE LATE TRIASSIC OF SOUTHEAST ALASKA

The Hound Island East (HIE) faunal assemblage occurs in the Hound Island Volcanics exposed within the intertidal zone on the eastern shore of Hound Island, southeastern Alaska. HIE is derived from slope deposits within 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 vertebrae, teeth, skull material, and rib fragments identified as Thalattosauria and Ichthyosauria. Bivalve and conodont fossils indicate a Late Triassic (middle Norian) age. Fossils occur within a 13 meter thick succession of interbedded calcareous shale and volcaniclastic-rich bioclastic limestone. Vertebrate remains are found in nineteen limestone layers. The limestone layers are skeletal (vertebrate and invertebrate) packstones to wackestones containing volcanic grains, shale rip-up clasts, glauconite, and pyrite throughout. Bones are frequently disassociated and show pre-depositional abrasion and breakage. These strata are interpreted as episodic thin-bedded debris flow deposits that resulted from slumping and redeposition of slope sediments. The original deposition of the limestone occurred on the upper slope before being transported an undetermined distance down slope by gravity flows. Vertebrate and invertebrate material was condensed in shallow-water carbonate zones through redistribution and winnowing of sediments by storms and currents, and reduced net rates of deposition prior to becoming incorporated in debris flows.