Quaternary geology and stratigraphy of Kitsap County, Washington

New radiocarbon dates and stratigraphic evidence indicate correlations between stratigraphic units on Whidbey Island and in Kitsap County. Eight new C14 dates and five previous dates, together with the stratigraphic position of units and similarities in their composition, support the concept that the Double Bluff Drift, Whidbey Formation, and possibly Possession Drift, extend south of Whidbey Island into Kitsap County. In Kitsap County, fine-grained floodplain deposits of the Whidbey Formation, with radiocarbon dates beyond the limits of conventional laboratory methods, are located at higher elevations than adjacent floodplain deposits of the Olympia nonglacial interval. This stratigraphic relationship suggest that the Whidbey floodplain was extensively eroded prior to deposition of the Olympia floodplain sediments which are unconformable upon this irregular surface. Thus, Molenaar’s belief that the Kitsap Formation was deposited during the Olympia nonglacial interval and his useage of the term Kitsap Formation for these stratified fine-grained sediments of various ages, is incorrect. The type locality of the Kitsap Formation, near Maplewood in southeast Kitsap County, includes a silt and two thin peat units lying between oxidized gravel of a pre-Vashon glaciation that is overlain by fine-grained Olympia sediments. Molenaar interpreted this sequence as a transition from glacial to nonglacial deposition and included the silt, peat, and oxidized gravel in the Kitsap Formation. However, a recent C14 date obtained from the peat was \u3e40,000 yrs B.P. (WW ), whereas the oldest C14 date obtained by the author from Olympia sediments elsewhere in Kitsap County is 36,235 yrs B.P. (U.W. 446). In addition, the arbitrary contact chosen by Molenaar between glacial and nonglacial sediments at Maplewood is not representative of the contact elsewhere in Kitsap County, and by including the oxidized gravel as part of the Kitsap Formation, he has deviated from the fine-grained nonglacial description originally used in the defining the Formation