The modern coarse-grained fan deltas of south-western British Columbia, Canada: a geomorphologic study

The geomorphology, sedimentology, and depositional architecture of six modern coarse-grained fan deltas in south-western British Columbia, Canada are examined. Methods included geomorphologic mapping, morphometric analyses, section logging, sedimentary facies mapping, and ground-penetrating radar (GPR) surveying. The fan deltas exhibit Gilbert-type depositional architectures; major depositional sub-environments include: (i) subaerial fan-delta plains formed by alluvial processes and mass-wasting processes (debris flows and sheetfloods); (ii) beach environments that exhibit complex geomorphologic and sedimentologic characteristics, having been supplied sediments by terrestrial processes and being (re-)shaped by coastal sediment-reworking processes; and (iii) steep-gradient (≤~35º) fan-delta front environments that are characterized by decameter-scale foreset beds. Depositional models and a suite of diagnostic geophysical characteristics are proposed for the fan deltas and the fan-delta beach environments.