Upper Triassic rocks in the Keku Strait area of southeast Alaska record a variety of facies in an intra-arc setting. The Hyd Group consists of the Burnt Island Conglomerate, Keku sedimentary strata, Cornwallis Limestone, Hamilton Island Limestone, and the Hound Island Volcanics. The Burnt Island Conglomerate represents initial infill of the basin and underlies the Hamilton Island Limestone, which is coeval with the Cornwallis Limestone and Keku sedimentary strata. Volcanic and sedimentary rocks of the Hound Island Volcanics overlie the entire area.

An improved biostratigraphic framework indicates deposition from early Carnian through late Norian time. Conodonts originating in the late...