A TURBIDITE SERIES IN THE CRESCENT FORMATION, OLYMPIC PENINSULA, WA

A series of turbidites composed of alternating fine sand and silt layers are present in an 84 m section on the Olympic Peninsula, WA. The sedimentary sequence is interbedded within the predominantly basaltic 15-km thick Crescent formation. Lab analyses with pretrographic thin sections and the SEM reveal fine, angular to sub-angular constituent grains of clinopyroxene, plagioclase, porphyritic basalt and chlorite. The absence of quartz and micas, which would otherwise indicate a continental source for the sediment, suggests deposition as a submarine fan from an offshore volcaniclastic origin isolated from continents. The alternating strata, with an average of 2 cm a bed, can be classified as facies c and facies d (Mutti & Ricchi Lucchi, 1971). The facies classification is probable representation of the middle to outer fan. This turbidite sequence is on strike with a similar deposit located 11 km away and may be part of the same submarine source.