Exposed in eastern Alaska, unit is divided into two informal members: an upper member of dominantly thin-bedded, very fine-grained spiculite, impure chert, impure limestone, and shale; and a lower member that is characteristically thin-bedded impure limestone, calcareous carbonaceous shale, and impure, locally spiculitic chert (MacKevett, 1978). Fossils in upper member indicate an Early Jurassic age, from Hettangian to Pliensbachian, and Monotis subcircularis, M. alaskana, and M. jakutica (Silberling and others, 1997) from the lower part of the lower member indicate a Late Triassic, mainly late Norian, age. Unit as a whole is deep marine and the depositional character indicates a restricted environment, possibly a starved basin. Unit also includes some rocks in west-central Alaska that are similar to the lower part of the McCarthy Formation (unit Trsl)