Stratigraphy, Paleontology, and Paleogeography of the Middle Pleistocene Tugidak Formation, Trinity Island, Alsaka

Tugidak Island, the northenunost of the Trinity Islands off the S W coast of
Kodiak Island is the stratotype of the Tugidak Formation. The continuous section ofthe
Tugidak Formation crops out in the sea cliffs along the northern and southwestern parts
of the island and is the most complete section in the Trinity Islands. The exposed section
of the Tugidak Formation is composed of 1395 m of glacial marine diamictite containing
abundant molluscan fossils. Seismic profiles and well data indicate a regionally
extensive deposition of the Tugidak Formation across the Kodiak Shelf. Paleomagnetic
sampling and diatom analysis in this work has further refined the age of the Tugidak
Formation as early-middle Pleistocene. By attempting a reconstruction of the tectonic
evolution and through faunal identification, inferences are made about the
paleobiogeography, paleoclimate and timing of sedimentary depositional cycles, around
Tugidak Island.