Effects of relative sea level change on the depositional character of an embayed beach, Bay of Fundy, Canada

Sedimentological mapping and interpretation of shallow-seismic profiles collected at Waterside Beach, Bay of Fundy, Canada reveal a varied post-glacial depositional history for the shore and near-shore system. Four sedimentologically and seismically distinct units are identified: 1) rounded pebbles and cobbles; 2) laminated silty sand; 3) rooted, laminated silt and clayey silt; and 4) mixed sand and gravel. These four units were deposited at different stages of relative sea level (RSL) fall and rise and under significantly diverse hydraulic conditions. The rounded pebbles and cobbles unit is glacial outwash deposited into a marine setting during rapidly falling RSL. This was followed by a seaward shift of the shoreline and development of intertidal and subtidal mud flats (laminated silty sand unit) during continued sea level fall. Salt marshes (rooted laminated silt and clayey silt unit) developed landward of the mud flats upon subsequent sea level rise, and finally the beach (mixed sand and gravel) developed as sea level rise exposed the rounded pebble and cobble unit to wave reworking and erosion. The relatively complex nature of the deposits and depositional processes, and the significant changes in the sedimentological and geomorphological character of the Waterside coastline during RSL fall, lowstand, and rise elucidates the variability that may be observed in sediments over relatively short time frames (< 15 000 yr) — particularly for sediments deposited in embayments. Within embayed settings, relative sea level change does not only imply a shift of the shoreline, but may also result in significant changes in depositional environments, basin configuration, and/or hydraulic conditions. This is the case for Waterside Beach, where the post-glacial depositional character of the coastline developed in response to three main factors: 1) notable increase in tidal range; 2) large-scale changes in the configuration of the upper Bay of Fundy; and, 3) availability of coarse-grained sediment and a mechanism to deliver that sediment to the coastline.