The Ontario coasts of Hudson Bay and James Bay delimit a major physiographic unit of Canada, the Hudson Bay Lowland (HBL) that is the second largest unconfined peatland of the world after the West Siberia Plain (Fig. HBL 1, CIS 2). The Hudson Bay Lowland is bounded by Precambrian rocks of the Canadian Shield and is underlain by flat lying to slightly dipping Paleozoic carbonates and sandstones and, in the southernmost part, Mesozoic clastic rocks, except for the area of the Cape Henrietta Maria Arch (CHN) where Precambrian meta-sedimentary and meta-volcanic rocks are exposed (Figs. HBL 1, 2, 3; Sanford and Norris, 1975). Since early Precambrian times the arch has subdivided the HBL into two basins, the Hudson Basin to the north and the Moose River Basin to the south (Figs. HBL 2, 4; Sanford et al., 1968; Sanford and Norris, 1975). It has influenced the distribution of ancient sediments and the trend of reefs on its flank. Normal faults locally separate the Paleozoic每Mesozoic rocks from the Precambrian terrain (Fig. HBL 4; Sanford and Norris, 1975). Evidence indicates that during Paleozoic times the Hudson and Moose River basins were connected with those of the Great Lakes (GL) area to the south, whereas Mesozoic sedimentation occurred mainly to the north (Fig. HBL 1; Sanford et al., 1968). However, a long erosional period, up to and including the Pleistocene, removed much of the Phanerozoic sedimentary cover and exposed Precambrian rocks in part of the Canadian Shield.
Pleistocene the area was repeatedly glaciated (Figs. CIS 3,
HBL 5). Because of cannibalization by subsequent glaciers, a good
stratigraphic record is present only for the uppermost Pleistocene glaciation in
the form of till and glacial landforms (Figs. HBL 5,
6). Each time, including Holocene last
deglaciation, the glaciers melted away and retreated northward in a semi-regular
fashion (Fig. HBL 7).
During deglaciation, large lakes developed in front of the ice, and when
an opening allowed intercommunication with the open sea to the east through Hudson
Strait salt waters suddenly replaced the lacustrine waters. This abrupt
lake每sea transition is marked by a intraformational ＆clay-pebble gravel＊
in the stratigraphic record (Fig. HBL
6). This occurred about 7500
years when a late-glacial sea (Tyrrell Sea) formed also covering land subdued by the
isostatic load of the ice sheets (Fig. CIS 4; Lee,
Since that time the HBL has undergone a continuous post-glacial isostatic uplift
developing into an extensive (order of thousands of square kilometers), emerged
costal plain that has been progressively paludified (covered by peatlands) as
the poorly drained land rises (Fig. HBL
8). The present coasts of the Hudson Bay and James Bay represent the
modern stage of such an emersion. The modern coast is still rising at approximately
70每100 cm/century (Barnett, 1966).
Emersion and paludification generated a characteristic uppermost Pleistocene每Holocene regressive sequence (Fig. HBL 9). Sparsely fossiliferous, blue-gray argillaceous silts (referred to as ＆clay＊ in the local geologic literature) characterize the deeper marine deposits of the Tyrrell Sea. They overly till. cover much of the lowland, and are particularly thick (order of several tens of meters) in subdue valleys. They are absent from local substrate highs. The clays or, locally, tills and occasionally bedrock subcrops are overlain by thin (order of meters) sand and gravel costal deposits, bouldery on substrate highs. In the proximity of rivers, thin (order of meters) fluvial deposits (gravel and sand in channels, sand and silt with disseminated ice-rafted coarser clasts on levees) form relatively narrow strings crossing the HBL. As the land rose, the coastal deposits and landforms and part of the fluvial systems become paludified and covered by peat that may be as thick as 5 to 6 m in the inland part of the extensive, unconfined peatlands. Remnant stratigraphic sections indicate that similar sequences developed during the earlier Paleocene times upon retreat of older ice sheets (Fig. HBL 6).
The western coasts of James Bay and southwestern Hudson Bay are characterized by a uniform, gentle offshore slope of approximately 0.5 m/km. James Bay is a shallow brackish inland sea that is covered by ice for approximately six months of the year (Figs. JBC 5 right, JB 9). Wide bays, particularly in the southern part of James Bay, receive large amounts of fresh water from rivers (Fig. JBC 5 left). Freshwater to brackish water marshes develop at river mouths and to the south and east of them because of redistribution of freshwater plumes by the marine, anticlockwise, geostrophic current.
Some wide, low promontories expose Paleozoic carbonate bedrock, tills, or accumulations of erratic or ice rafted boulders (Sanford et al., 1968). Other narrow promontories protrude for several kilometers into the shallow James Bay and act as natural large groins for the marine geostrophic currents. Thus, wide sandy tidal flats develop in their northern updrift sides backed by large well developed salt marshes, and erosional (half-heart bays) and some depositional (spits) landforms develop on their southern downdrift sides (Martini and Protz, 1978). Wide sand flats also develop in other sheltered areas.
Successions of multiple beach ridges and spits develop parallel to the main coast open to sea waves. They contain sandy fine gravels (Martini and Protz, 1978).
As coastal features are isostatically uplifted, they become vegetated and become incorporated into wide peatlands. Some original coastal features remain recognizable because of major difference between the vegetation growing in the wetter swales and the one (coniferous forest) growing on to the ridges themselves. Chevron ridges are one of the most characteristic features. They are a landform characterized by a combination of transverse and longitudinal ridges (Fig. JBS 6; King, 1972; Martini and Protz, 1978; Martini et al., 1981a).
The coastal environments and sediments are acted upon by the following principal processes.
rebound of the land that began approximately 7500每8000 years ago at about 3
m/century and still continues at a rate of approximately 70-100 cm/century
2) Marine semi-diurnal tides that generally have a low range (0.7每1.5 m), reaching a maximum of 3 m at some localities. The tidal waters carry much silt and clay in suspension (Martini et al., 1979).
3) In steeper shores, large waves generated in the open sea during storms can sweep tidal flats and rework sand and pebbles onto beach ridges. On the whole, though, this coast is considered a low energy shore, because of the dampening open sea waves on the wide, shallow shore areas.
4) A slow (0.8 m/sec maximum) anticlockwise, marine current redistributes fluvial and wave reworked sediment along the coast (Martini et al., 1979). In straits and bays, gyres develop, re-distribute, and trap fine sediments.
5) Sea ice covers and protects the coast for approximately six months of the year. During spring每early summer breakup, ice floes raft much material along tidal flats and push and scour sediments (Martini, 1981b).
6) Wind may locally rework sediments of the upper parts of tidal flats and beach ridges. Blowouts and sand dunes are not frequent and most occur in the northern part of James Bay and along the Hudson Bay coasts.
7) Cold climate (Dfe in the Koppen system in the southern part) sustains intense freeze-thaw processes comminuting thinly bedded rocks such as limestone and dolostone in the northern part of the coast. No permafrost and permafrost features are recognizable near the coast except some frost mounds on the marshes in the northernmost part of the studied coast. Permafrost is fully developed inland, ranging form sporadic in the south to continuous in the north. This permafrost has formed during the Holocene as the land was emerging from the early postglacial Tyrrell Sea.
8) The physical and biochemical action of organisms in tidal flats and inland areas, combined with chemical weathering, modify the primary characteristics of upper parts of the deposits and a variety of soils develop, from gleysols in the paludified lowland and podzols in the drier forested beach ridges (Figs. HBL 10, 11; Protz, 1982a , b; Protz et al., 1984). The gleysols of coastal marshes retain primary sedimentary laminations, but also develop ferrans around plant roots (Fig. HBL 10). Podzols develop inland on beach ridges (Fig. HBL 11). Montmori1lonite clays form in their Ae horizons, and develop cemented Bh horizons that contain abundant cutans of organic matter around grains.
9) The coastal sedimentary deposits vary from thick (up to 2每3 m) primarily sandy in wide tidal flats backed by extensive sandy to muddy marshes, to bouldery, pebbly, sandy accumulations up to 5 m thick in beach ridges near promontories, to thick silty pebbly accumulations that develop in poorly drained tidal flats and marshes associated with large rivers. These sediments are the major topic of this Website (see ＆transects＊ of the various coasts).
10) From the coast inland there is a general rapid depletion of sodium and other marine salts. Salt marshes develop near the shoreline grading into brackish, then freshwater marshes and fens inland. Locally, however, reversals may occur where brackish water marshes develop near the shore and saltwater ones farther inland also above the reach of storm surges, such as in southmost James Bay. There they inland salt marshes receive salt from groundwater desalinating buried, older, marine silty clays.
11) The distribution of the coastal vegetation of Hudson Bay and James Bay is similar to that of northern boreal, subarctic, and arctic ones of Alaska, the Canadian Arctic, Greenland, Scandinavia, and Russia (Chapman, 1960). Well best developed the costal systems are characterized by shallow subtidal areas that may be colonized by Zostera marina, a primarily unvegetated tidal flat, grading landward into a high tidal flat characterized primarily by a blue-green algal mat, finally grading into costal marshes.
The lower part of the salt marsh is characterized everywhere by the Puccinellia phryganodes, the principal colonizing pant, and contains minor others such as Potentilla egedii, the grass Puccinellia lucida and the sedge Carex subspathacea. The latter forms more extensive turfs in the lower salt marsh zones of more northerly James Bay localities. Shallow brackish ponds may occur as well partly colonized by the sedge Scirpus maritimus associated with the grass Puccinelia lucida. In a few coasts a lower salt-marsh pan zone develops with slightly higher salinity and significant Salicornia europaea growths (Fig. HBL 12).
The upper part of the marsh experiences less frequent inundations by seawater and is less saline. The Pucinellia phryganoides is greatly reduced or disappears and new plants occur, such as Senecio congestus, Ranunculus cymbalaria, and Hordeum jubatum. Farther inshore, better drained areas may be slightly more saline and are characterized by the two dominant species are the rush Juncus balticus and the leguminous forb Lathyrus palustris, associated with several other forbs. Less well drained, brackish areas are characterized primarily by sedges such as Carex paleacea and Eleocharis palustris, and the forb Hippurus vulgaris may be present.
The salt marsh is bounded landward by a willow (Salix spp.) thicket每freshwater marsh/fen. The freshwater marsh/fen is characterized by Potentilla palustris, Menyanthes trifoliata, Myrica gale, several sedges of the genus Carex, and the typical marsh cattail, Typha latifolia. Significant amount of organic matter is generated and preserved to form peat. The fens are the first peatlands formed which eventually develops into the thick inlad fens and ombrotrophic bogs of the inner part of HBL.
Organisms that live along these coasts include Macoma balthica an Hydrobia minuta in the intertidal areas, with minor and local Littorina (L. obtusata and L. saxatilis) (occasionally up to 3,700 individuals/ m2), mussels (Mytilus sp.), limpets, several round worms (nematodes), oligochaetes (Paranais sp.) and polychaetes, a variety of foramanifera, copepods, ostracods, amphipods, cladocerans, ectoprocta and barnacles. In In the lower Puccinellia phryganodes salt marsh, principal components of the infauna are dipteran larvae and oligochaete worms; with at some southern localities numerical densities up to 530/m2 and 3300/m2, respectively. Pitfall traps set in different vegetation zones of the marsh have revealed a diverse insect fauna, whose members show great variations in seasonal abundance. 318 species of invertebrates, from 105 families and 14 orders, were identified, including at least eight new species (Kakonge et al., 1979). Mosquitoes and biting flies are a prominent component of the invertebrate fauna: the former have been estimated to occur at some 5,000,000 per acre on parts of the Hudson Bay coast (West, 1951) (Martini et al., 1980).
These coasts support an extensive migratory avifuana. The two most important groups utilizing coastal flats and marshes are shorebirds and waterfowls (Figs. HBL 13, 14). In general, shorebirds undertake long migrations to wintering grounds ranging from the Atlantic and Gulf coasts of the United States of America to the southern parts of South America (Fig. HBL 15). The most prominent species are the Hudsonian Godwit (Limosa haemastica), Red Knot (Calidris canutus), and Semipalmated Sandpipers (Calidris pusilla) which occur along coasts characterized by wide, well developed marshes with extensive short grass (Puccinellia phryganodes) zone (Fig. HBL 16). Both Greater Yellowlegs (Tringa melanoleucus) and Lesser Yellowlegs (Tringa favipes) occur in large numbers. Other prominent species on the coast include the Black-bellied Plover (Pluvialis squatarola) , Golden Plover (Pluvialis dominica) , Semipalmated Plover (Charadrius semipalmatus) , White-rumped Sand Piper (Calidris fuscicollis) , Least Sandpiper (Calidris minutilla) , Dunlin (Calidris alpina) , Sanderling (Calidris alba), Pectoral Sandpiper (Calidris melanotos), Whimbrel (Numenius phaeopus), Marbled Godwit (Limosa fedoa) and the Common Snipe (Gallinago gallinago) (Martini et al., 1980).
Geese and ducks make heavy use of the coastal marshes. Canada Geese (Branta canadensis) breed in large numbers, though at low densities in inland marshy areas and are numerous on the coast on migration. Lesser Snow Geese (Chen caerulescens) are very abundant on migration and there are extensive colonies of some in excess of 50-60,000 pairs in several areas along from Akimiski Island northwards. Brants (Branta bernicla) concentrate in areas of the coast where eelgrass (Zostera marina) is abundant in the low intertidal zone.
Many species of ducks breed in inland areas and occur in large numbers on the coast on migration. Prominent species include Pintail (Anas acuta), Black Ducks (Anas rubripes), Green-winged Teal (Anas carolinensis) , Mallard (Anas platyrhynchos) , Widgeon (Mareca americana) , and Scaup (Aythya sp.). Large rafts of Scoters (mostly Black Scoters Melanitta vigra) in flocks of several hundred to several thousand totaling up to about 40,000 birds, are found in the northern part of James Bay. Mergansers (Mergus sp.) and loons (Gavia sp.) utilize coastal waters for feeding and inland lakes and ponds for breeding (Martini et al., 1980).
Polar bears use the coastal zone during the summer from a far south as Akimiski Island, but more commonly from the northeasternmost part of James Bay and along the Hudson Bay coast. Part of that area is now protected under a large national park, the Polar Bear Park. Some caribou herds visit the shore of Hudson Bay during the summer near northern end of the Ontario coast.
Tables reporting measured sediments and soils properties are available in yearly reports by Martini and Protz (1978, 1980, 1981, 1983), Martini et al. (1979, 1982, 1983), Salvadori et al. (1983).