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Understanding A Critical Basinal Link In Cretaceous Cordilleran Paleogeography: Detailed Provenance Of The Hornbrook Formation, Oregon And California, Kathleen Surpless, Emily Beverly

Kathleen D. Surpless

The Hornbrook Formation is a Cretaceous overlap assemblage that rests unconformably on accreted terranes and plutons of the Klamath Mountains in southern Oregon and northern California. The combined results of sandstone petrography, detrital zircon U-Pb age and Hf isotopic systematics, and whole-rock Nd analysis document an abrupt change in sediment sources for the Hornbrook Formation during the Late Cretaceous. The lower members of the Hornbrook Formation record provenance in the Klamath Mountains and the Sierran Foothills belt that is characterized by detrital zircon age distributions with large Jurassic and Early Cretaceous peaks (170-130 Ma) and positive zircon Hf and whole-rock …