BELEMNITES OF THE NOOKSACK FORMATION (WASHINGTON, USA) AND PALEOGEOGRAPHIC IMPLICATIONS

This study describes two belemnite taxa found in Valanginian (Early Cretaceous) strata of the Nooksack Formation in northern Washington state, USA, and discusses their significance for reconstructing the paleogeographic origins of the Nooksack and related geologic units within the Northwest Cascades System (NWCS). Fossils were collected from three localities in Mt. Baker-Snoqualmie National Forest, and belemnite specimens were taxonomically identified using morphometric measurements and other diagnostic traits. The fossils’ age was constrained to the Valanginian on the basis of bivalve biostratigraphy, the belemnites occurring in association with Buchia crassicollis and B. pacifica. Belemnite specimens included both calcite rostra and external casts of dissolved rostra. Two belemnite taxa were identified, Arctoteuthis ex gr. baculus (Crickmay) and Duvalia sp. Belemnite taxa tend to be strongly provincial in distribution and could therefore yield insights as to whether the Nooksack was translated northward or southward of its original geographic location. Arctoteuthis is associated primarily with the Boreal realm, whereas Duvalia is typically Tethyan. The cooccurrence of these two belemnite genera in Early Cretaceous rocks has not previously been described for the Pacific Coast region of North America, and the data do not clearly favor either hypothesis for the Nooksack’s geographic provenance. Further description of belemnites and other fossils from the Nooksack, as well as oxygen isotope analysis of belemnite rostra to recover water temperatures, is recommended to constrain the latitudinal range at which they could have been deposited. By formally describing Nooksack belemnite taxa for the first time, this study provides a foundation for future research. Its findings improve current understanding of the belemnite fossil record in North America and highlight the potential value of fossil assemblages for reconstructing the tectonic history of the NWCS.