Weyla santuccii n. sp. (Bivalvia, Pectinidae) from the Pogibshi Formation, south-central Alaska, the oldest species known of the genus in western North America

Abstract

Species of the pectinid genus Weyla s.l. were previously reported from several localities in Alaska, where they have a wide age range within the Early Jurassic. This paper provides a full description and discussion of the new species Weyla santuccii, believed to be the oldest of the group. It occurs in Early Jurassic marine sedimentary and volcanic deposits in the July member of the informally named Pogibshi formation on the Kenai Peninsula southwest of Seldovia, Alaska. The Pogibshi formation is assigned to the accreted Peninsular terrane of southern Alaska, and the middle July member is an understudied fossiliferous unit, perhaps encompassing the Triassic-Jurassic boundary (TJB). A paleontological and geochronological search for the TJB has resulted in the new record of the Early Jurassic (Hettangian) pectinid bivalve Weyla, as well as other marine invertebrates, including solitary stylophyllid scleractinian corals, and the gastropod Pleurotomaria. These fossils are significant because they are among the oldest known Jurassic megafossil occurrences in Alaska. Biochronology of ammonites and isotopic dating of detrital zircons confirm the middle Hettangian age of the Weyla, with a maximum depositional age of 200.5 ±2.5 ±1.8 Ma.