BENTHIC FOSSILS FROM PROBABLE UPPER TRIASSIC ARGILLITE, ADMIRALTY ISLAND, ALASKA

The objective of this study was to confirm the probable Upper Triassic age of a 15 m core of metamorphosed and structurally-complex grey argillite from the Greens Creek Mine, Admiralty Island, Alaska. Transmitted light microscopy of 4 m-thick fossil-rich interval reveal numerous but indeterminate fragments of brachiopods, echinoderms, gastropods, corals, spongiomorphs in the argillite matrix. Most shells are recrystallized, replaced, and/or deformed. Attempts to recover conodonts via acid-dissolution and SEM analysis failed. One 1.5cm-long siliceous sponge spicule was found in the residue.

The presence of fragmented, shallow marine fossils in the deep-water argillite suggests transport of a benthic assemblage from a shelf to a basin environment. The assemblage, particularly the constituent spongiomorphs, resembles faunas of Upper Triassic age reported from the southern part of the island.