Sedimentary architecture and radar facies of a fan delta, Cypress Creek, West Vancouver, British Columbia

Abstract

AbstractFan deltas are common depositional features along the macro-tidal, fjorded coast of southern British Columbia. To determine the sedimentary architecture of the Cypress Creek fan delta, West Vancouver, British Columbia, a combined ground penetrating radar and geomorphological study was carried out. Five radar facies were identified and their associated geomorphic environments were established: oblique clinoform radar facies (delta front); mounded radar facies (debris-flow deposits); undulating subhorizontal radar facies (beach zone); concave radar facies (river channels) and horizontal radar facies (salt-water intrusion). The delta plain was formed primarily by debris flows, some of which reached the delta front to form prograding foreset beds. Radar facies analysis established the occurrence of arcuate scars and masses of slumped material, signifying mass movement on the delta front. Wave action, working over a 4.9 m tidal range, has reworked the distal delta-plain debris-flow sediments into an armoured gravel beach. A depositional model is proposed for a fan delta in a macro-tidal fjord setting.