Palynology and plate tectonics — a case study on cretaceous terrestrial sediments in the eastern Klamath mountains of northern California, U.S.A.

Abstract

The western part of the North American Cordillera is thought to be made up of a collage of allochthonous crustal fragments formed in a variety of tectonic settings at some distance west of their present location. Paleontological and radiometric age dating of the rocks associated with these terranes is critical in understanding their geological history. The basal conglomeratic unit of the Hornbrook Formation (Klamath River Conglomerate) and isolated exposures of some unnamed, undated conglomerates at the Pythian Cave locality, 40 km northwest of Mt. Shasta and south of the town of Yreka, California, both lie nonconformably over the basement rocks that form the Yreka‐Trinity composite microplate in Hornbrook Basin. Palynological data indicate that the geologic age of the unnamed conglomerates at Pythian Cave is middle Albian, and that of the Klamath River Conglomerate is middle Cenomanian. This study also shows that the Pythian Cave conglomerates have a different source, and have formed in a different environment of deposition. The Pythian Cave conglomerates seem to be the oldest preserved sedimentary blanket deposits over the Yreka‐Trinity composite terrane in Hornbrook Basin. Radiometric data indicate that the Yreka‐Trinity composite terrane accreted to the North American continent no later than Hauterivian‐Barremian time.

Notes

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