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Date Permissions Signed
Date of Award
Master of Science (MS)
Suczek, Christopher A., 1942-2014
Engebretson, David C.
Babcock, R. Scott (Randall Scott)
The Flattery breccia, an informally designated unit within the middle Eocene Lyre Formation, consists of sedimentary breccia and conglomerate exposed at Cape Flattery, located at the northwestern point of the Olympic Peninsula, Washington. The Flattery breccia was deposited during the late Narizian, approximately 44 to 42 Ma.
The boulder- through sand-size detritus of the Flattery breccia and western Lyre Formation, which changes in texture along strike, were deposited by sediment- gravity flows, such as surging high-density turbidity currents and sandy debris flows. Interfingering alluvial fan-deltas, interfingering lobes of coarse detritus on a submarine fan, or resedimented wedges of coarse-grained detritus deposited on slope or base of slope settings can be considered possible depositional environments for the Flattery breccia and western Lyre Formation.
The sandstones within the Flattery breccia are lithic arenites or lithic wackes, coarse-grained, angular to subangular, poorly sorted, with long and concavo-convex contacts, all of which indicate rapid sedimentation and burial from a nearby source. Petrologic trends along strike support the interfingering of two sources of detritus; petrologic data remain consistent, however, going up section into the overlying Hoko River Formation.
Vancouver Island is regarded as the major source of detritus to the Flattery breccia and western Lyre Formation due to matching lithologies, its close proximity, and its agreement with paleocurrent directions observed of flow to the south-southeast. Wrangellia, the Crescent terrane, and the Leech River Complex appear to comprise variable portions of detritus to both the Flattery breccia and western Lyre Formation, while the Pacific Rim Complex and/or the Pandora Peak unit may be exclusive to the Flattery breccia source.
The Flattery breccia was deposited during the time of a major plate reorganization, which involved the demise of the Kula plate at 42 Ma. This plate reorganization probably caused regional uplift, perhaps including the Eocene rift basin basalts, as well as the initiation of Cascade arc volcanism and the metamorphism of the Leech River Complex. The Flattery breccia records evidence of regional uplift, such as the rapid unroofing of the Leech River Complex, as well as the existence of a dissected source teirane with a steep, rocky shoreline. Finally, the presence of an "exotic" source terrane to the west, possible based on the paleocurrent data observed, is not a necessity, because all clasts found in the Flattery breccia can be accounted for by lithologic units exposed on Vancouver Island.
Flattery breccia, Sedimentary breccia, Eocene Lyre Formation
Western Washington University
Flattery, Cape (Wash.)
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Shilhanek, Alice Benkovich, "The Sedimentology, Petrology, and Tectonic Significance of the Middle Eocene Flattery Breccia, Lyre Formation, Northwestern Olympic Peninsula, Washington" (1992). WWU Graduate School Collection. 673.