Fluvial, coastal, nearshore, and shelf deposition in the Upper Proterozoic (?) to Lower Cambrian Addy Quartzite, northeastern Washington

Abstract

Quartzose and lesser argillaceous strata of the approximately 1300 m thick Upper Proterozoic (?) to Lower Cambrian Addy Quartzite of northeastern Washington record shelf, coastal, and continental sedimentation on an actively subsiding, relatively young passive margin. The lower 400 to 500 m of the Addy Quartzite was deposited immediately following the initiation of subsidence in a wave-dominated coastal and eventually storm-dominated shelf environment. This sequence records relative sea level rise that culminated in high-stand conditions. These sediments grade upwards into approximately 150 m of fluvial strata that record progradation of terrestrial environments during a period of relative sea level fall and a regional low-stand. The upper 700 m of the Addy Quartzite fines upwards from nearshore- to shallow-marine-dominated sediments into shelf-dominated deposits. This sequence marks the reestablishment of net sea level rise. The overall fining-upwards trend displayed by the Addy Quartzite indicates that regional subsidence of the newly formed passive margin was one of the most important factors controlling Addy sedimentation. However, variation seen in this trend throughout the Addy Quartzite indicates that rates of sea level rise associated with subsidence fluctuated and occasionally even reversed. Causes for the variation are inferred to be related to variations in subsidence rates and sediment supply. Textural and compositional data suggest Addy detritus was derived from relatively proximal recycled sedimentary source terranes and more distal continental crystalline terranes.