Slave River delta: geomorphology, sedimentology, and Holocene reconstruction

Abstract

The Holocene Slave River delta (8300 km2) is a long (170 km), narrow (42 km average width) alluvial sand body, which extends north from the Slave River rapids at Fort Smith to Great Slave Lake, Northwest Territories. The delta is flanked by the Talston and Tethul rivers and Canadian Shield to the east and by the Little Buffalo River to the west. Wave-associated sedimentary structures in lithostratigraphic logs from river cutbanks indicate that the sandy delta was wave influenced. Most of the logs (34) consist of three facies: basal laminated mud (unknown thickness), interbedded mud and sand (2.5 m), and planar-tabular ripple sets interbedded with cross-laminated to flat-bedded sand (3.0–14.5 m).Eleven radiocarbon-dated wood samples from river cutbanks were used to reconstruct the delta paleoshoreface and to calculate the rate of progradation, which averaged 20.7 m/year from 8070 BP to the present. In the same period isostatic rebound of the delta region relative to the Liard River delta averaged 12 cm/km (a total rebound of 48 m). The data were calculated normal to the retreating Laurentide ice front.From the surface to depths of 59 m, the subaerial and subaqueous delta front exhibits barrier islands, lagoons, offshore bars or sand waves, tensional cracks, slumps and pressure ridges. The barriers and offshore bars consist of medium grain-sized sand, whereas the slumps and pressure ridges are interpreted as mud.