Abstract

Sediments of the Scotts Mills Formation exposed on the flanks of Oregon's central Western Cascade Range accumulated along a storm-dominated rocky coastline during the Oligocene-Miocene transition. During this time, the development of depositional facies was controlled by the physiography of the underlying erosional surface. Lithofacies include a cross-stratified barnacle limestone (headland) facies; a fossiliferous, graded conglomerate (wave-cut platform/sea stack) facies; a burrowed claystone (tidal flat) facies; an amalgamated sandstone (coastal sand tongue) facies; and a graded mudstone (proximal tempestite) facies. The transgressive sedimentary deposits described here are characterized by 1) oligomictic intrabasinal detritus, 2) epilithic invertebrate faunas, 3) mass transport deposits, and 4) abrupt basinward gradation of conglomeratic nearshore sediments to offshore muds. The development of these depositional environments and their relationship to the physiography of the underlying unconformity has been translated here into a rocky coast facies model.

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