HALFWAY POINT

The HY transect is located west of a relatively narrow, long promontory that jets out for several kilometers into the shallow James Bay and intercepts the anticlockwise marine current and longshore drift (Figs. JBS 3, 4; HY 1). Consequently, the area experiences a relatively high rate of sedimentation in the lower part of the intertidal area. The transect is characterized by inland freshwater marsh/fen complex, shoreline complexes consisting of beach ridges/salt marsh, a narrow high tidal flats intermixed with patches of salt marsh, and an intertidal sand flat (Figs. HY 2, 3).

The freshwater marsh lies in the back of the beach ridges and grades imperceptibly into costal fens inland (Fig. HY 6) and salt marsh seaward (Figs. HY 7, 8). It is drained by few creeks, and shows a marked regular landward increase in silt and organic matter and a progressive disruption of laminations (Figs HY 3, 5, 9, 10). The saltwater marshes occur in swales and in front of near-shore beach ridges (Figs. HY 3, 11).

Multiple ridges form a beach ridge/salt marsh complex at the shoreline (Figs. HY 3, 11, 12). These beach ridges are relatively flat, discontinuous, and occur in an en echelon pattern. They are composed of sand and gravel, and show landward dipping cross-beds capped by thin inclined laminations formed by washover materials (Figs. HY 5, 13, 14).

The intertidal area is separated into two parts by a shore-parallel swale (Fig. HY 3 station 5). A high tidal flat with some sand-cover stabilized by algal mat occurs landward from the swale (Figs. HY 15, 16). Parts of the surface is eroded during storms and deflated by wind at low tide. The resultant sediment profiles are characterized by structureless lag deposits of silt and sand mixed with pebbles (Figs HY 4, 17). The coarse sand and fine pebbles eroded from the high tidal flat constitute the source material for the small bar type beach ridges.

The intertidal sand flat occurs seaward from the coastal swale. They are characterized by sand waves (Figs HY 2, 18, 19) that become progressively lower in elevation and less well defined in the lower parts of the flat. The sand waves are distributed in an approximate en echelon pattern. The sand-wave swales have lag deposits of coarser materials reworked by channeled tidal flat flow. In general the sand flats are covered by ripple marked sand, fossiliferous including Macoma balthica shells and Arenicola burrows; locally cross-beds develop (Figs. HY 4, 20, 21, 23). Toward the lowermost part of the sand flat, some ripples have a coating of silt in their troughs (Fig. HY 22).