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Considerations on the sub-arctic coastal environments of the Akimiski island area, N.W.T. and Ontario, Canada
Sedimentary Geology, 37 (1983/1984) 225-228
225
Elsevier Science Publishers B.V., Amsterdam - Printed in The Netherlands
C O N S I D E R A T I O N S ON T H E SUB-ARCTIC COASTAL E N V I R O N M E N T S OF T H E AKIMISKI ISLAND AREA, N.W.T. AND ONTARIO, CANADA
I.P. MARTINI
Department of Land Resource Sctence, Unit,ersitv of Guelph, Guelph, Ont. NI G 214"1 (Canada) (Accepted for publication August 19, 1983)
The area around Akimiski Island has been widely publicized by a false-color print of an outstanding Landsat satellite image which shows a complex pattern of sediment plumes around the island (Fig. 1). Except for this view and some information about the bedrock geology, some general information about the wetlands, the wildlife and the sparse Indian population, little else was known (SjOrs, 1959: Haworth et al., 1978). This area is of particular interest, however, to geologists and geomorphologists for several reasons. The most outstanding feature of the bedrock geology is the Silurian reefal tract of the Attawapiskat Formation which rims the northern side of the Paleozoic cratonic Moose River Basin. The reefal tract forms the backbone of Akimiski Island, and particularly in the upstream reaches of the Attawapiskat River, it evolves into numerous karstic features (Sanford et al., 1968). The area is close to the Pleistocene centers of glaciations. The glaciers have left typical erosional scars and relatively thin bouldery sandy tills and local deposits of water-sorted sand and gravel. However, the most outstanding feature related to glaciations is the strong isostatic rebound that the land has sustained in Holocene times (Hood, 1968). Akimiski Island is a microcosm displaying most of the coastal emergent features observable along the Ontario coast of the Hudson and James bays, although some are not well developed because of sand-starved conditions. Nevertheless, sandy and gravelly beach ridges are present, as well as transverse ridges, patterned (jig-saw)marshes, wave-cut bedrock benches, and boulder pavements (Martini et al., 1980a; Martini, 1981a,b). Among other characteristic features is the progressive paludification (formation of wetlands and peats) the area has undergone while being uplifted (Sj6rs, 1959). The paralic and inland freshwater sequences provide instantaneous views to be used for studying analogue ancient deposits of boreal forests and peatlands, such as interglacial and interstadial Pleistocene sequences that are buried and preserved under the Hudson Bay Lowland itself, or some cold Carboniferous to Permian coal measures such as some of those of the Sydney and Bowen Basins of Australia (Herbert and Heiby, 1980). Environments of sedimentation that can serve for similar comparative sedimento003%0738/84/$03.00
'g:' 1984 Elsevier Science Publishers B.V.
226
Fig. 1. Turbidity plumes around Akimiski Island and in Akimiski Strait. (Landsat image 1447-15534, October 13, 1973; a color composite of bands 5, 6, 7 is available as well.) A T = Attawap~skat: Ekwan River is just south of SUT. The southermost large anastomosing river is the Albany River.
logical analysis include the wide mudflats that have developed under mesotidal, cold, brackish sea conditions. They generally support a restricted infauna dominated by Macoma balthica and by ttydrobia minuta. They are skirted by wide marshes characterized by an association of either Puccinellia phrvganodes or Htppuris tetrapkilla in the lower marsh, depending on the freshness of the environment, and a Care.,: subspathacea association in the upper marshes (Martini et al., 1980a). In any one of these environments, particular care must be taken to understand the effect of the ice both as a direct agent in erosion and rafting, and as an indirect agent in changing the boundary conditions of the environment. For instance, in winter the
227
ground freezes, 8eneratin~ lenses and other structural features in the sedimentary sequence. Such a frozen state, together with the ice cover developed on the sea and rivers, protects the sedimentary sequence from erosion during a period when the most severe storms would otherwise develop. Furthermore, in the case of the Akimiski Strait, partial melting of the ice in spring changes the tidal strait into an ice-walled bay closed to the north. This enhances the tidal range and the rate of sedimentation of fine materials in the northwestern parts of the strait during a critical period of the year when the rivers flood and carry in a considerable amount of sediments (Martini, 1981b). Finally, the mainland coast of the Akimiski Strait is influenced by two major rivers: the shallower and steeper Ekwan River and the Attawapiskat River. Both display typical, for this northern region, anastomosing lower reaches, although the Attawapiskat River has a dominant channel reaching the sea. It is this dominant channel that drains out and captures the flow of the secondary canals as the land rises. These streams carry considerable amounts of organic-rich water throughout the year. However, the great majority of the sediment is carried to the sea during brief periods at break-up times. The sediments are derived from river bank erosion where sequences of tills are superimposed by Holocene marine deposits, ranging from subtidal fossiliferous silty clay and coastal sand and gravels, to a cap of marshy organic-rich silty sands which, in turn, are capped by fluvial levee deposits and thin woody peats. No substantial amount of material is eroded from the floor of the channel as the river entrenches quickly through the overburden to the more resistant carbonate bedrock. The fluvial accumulations consist primarily of thin channel bars, mostly formed in the downstream parts of islands in the anastomosing reaches, of thin fine materials deposited primarily in semi-abandoned side channels, and of suspended and ice-rafted sediment on narrow levees. The rivers do not shift course frequently, although switching of the whole system may occasionally occur. The abandoned channels are later filled with organic matter. In general, these streams form relatively narrow ribbons of thin fluvial sediments across the wide wetlands. They would be indeed difficult to recognize in ancient sequences. The collection of papers in this issue of Sedimentary Geology contributes to the understanding of sedimentary sequences (mineral and organic ones) deposited in cold, subarctic, coastal and fluvial environments within a cratonic basin. Such an understanding may be put to a fruitful, comparative use in trying to decipher analogue ancient geological deposits. REFERENCES Haworth, S.E., Lowell, D.W. and Sims, R.A., 1978. Bibliography of published and unpubhshed literature on the Hudson Bay Lowland. Report 0-X-273, Can. Forestry Service, Dept. on the Environ.. S. Ste. Marie, Ont.. 270 pp. Herbert, C. and Helby, R., 1980. A guide to the Sydney Basin. Geol. Survey at New South Wales, Bull., 26, 603 pp.
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Hood, P.J., 1968. Earth Science Symposium on Hudson Bay. Geol. Surv. Can,, Pap. 58-53, 386 pp. Martim, I.P,, 1981a. Morphology and sediments of the emergent Ontario coast of James Bay, Canada. Geogr. Annal., Ser. A., 63: 81-94. Martini, I.P., 1981b. Ice effect on erosion and sedimentation on the Ontario shores of James Bay, Canada. Z. Geomorphol., 25: 1-15. Martini, I.P., Cowell, D.W. and Wickware, G.M., 1980a. Geomorphology of Southern James Bay: a low energy, emergent coast. In: S.B. McCann (Editor), Coastline of Canada. Geol. Surv. Can. Pap. 80-10, pp, 293 301. Martini, I.P., Morrison, R.I.G., Glooschenko, W.A. and Protz, R., 1980b. Coastal studies m James Bay, Ontario. Geosci. Can., 7:11 21. Sanford, B.V., Norris, A.W. and Bostock, H.H., 1968. Geology of the Hudson Bay Lowlands, IOperation Winisk). Geol. Surv. Can., Pap. 67-60, 118 pp. Sjors, H., 1959. Bogs and fens in the Hudson Bay Lowlands. Arctic, 12: 2-19.
225
Elsevier Science Publishers B.V., Amsterdam - Printed in The Netherlands
C O N S I D E R A T I O N S ON T H E SUB-ARCTIC COASTAL E N V I R O N M E N T S OF T H E AKIMISKI ISLAND AREA, N.W.T. AND ONTARIO, CANADA
I.P. MARTINI
Department of Land Resource Sctence, Unit,ersitv of Guelph, Guelph, Ont. NI G 214"1 (Canada) (Accepted for publication August 19, 1983)
The area around Akimiski Island has been widely publicized by a false-color print of an outstanding Landsat satellite image which shows a complex pattern of sediment plumes around the island (Fig. 1). Except for this view and some information about the bedrock geology, some general information about the wetlands, the wildlife and the sparse Indian population, little else was known (SjOrs, 1959: Haworth et al., 1978). This area is of particular interest, however, to geologists and geomorphologists for several reasons. The most outstanding feature of the bedrock geology is the Silurian reefal tract of the Attawapiskat Formation which rims the northern side of the Paleozoic cratonic Moose River Basin. The reefal tract forms the backbone of Akimiski Island, and particularly in the upstream reaches of the Attawapiskat River, it evolves into numerous karstic features (Sanford et al., 1968). The area is close to the Pleistocene centers of glaciations. The glaciers have left typical erosional scars and relatively thin bouldery sandy tills and local deposits of water-sorted sand and gravel. However, the most outstanding feature related to glaciations is the strong isostatic rebound that the land has sustained in Holocene times (Hood, 1968). Akimiski Island is a microcosm displaying most of the coastal emergent features observable along the Ontario coast of the Hudson and James bays, although some are not well developed because of sand-starved conditions. Nevertheless, sandy and gravelly beach ridges are present, as well as transverse ridges, patterned (jig-saw)marshes, wave-cut bedrock benches, and boulder pavements (Martini et al., 1980a; Martini, 1981a,b). Among other characteristic features is the progressive paludification (formation of wetlands and peats) the area has undergone while being uplifted (Sj6rs, 1959). The paralic and inland freshwater sequences provide instantaneous views to be used for studying analogue ancient deposits of boreal forests and peatlands, such as interglacial and interstadial Pleistocene sequences that are buried and preserved under the Hudson Bay Lowland itself, or some cold Carboniferous to Permian coal measures such as some of those of the Sydney and Bowen Basins of Australia (Herbert and Heiby, 1980). Environments of sedimentation that can serve for similar comparative sedimento003%0738/84/$03.00
'g:' 1984 Elsevier Science Publishers B.V.
226
Fig. 1. Turbidity plumes around Akimiski Island and in Akimiski Strait. (Landsat image 1447-15534, October 13, 1973; a color composite of bands 5, 6, 7 is available as well.) A T = Attawap~skat: Ekwan River is just south of SUT. The southermost large anastomosing river is the Albany River.
logical analysis include the wide mudflats that have developed under mesotidal, cold, brackish sea conditions. They generally support a restricted infauna dominated by Macoma balthica and by ttydrobia minuta. They are skirted by wide marshes characterized by an association of either Puccinellia phrvganodes or Htppuris tetrapkilla in the lower marsh, depending on the freshness of the environment, and a Care.,: subspathacea association in the upper marshes (Martini et al., 1980a). In any one of these environments, particular care must be taken to understand the effect of the ice both as a direct agent in erosion and rafting, and as an indirect agent in changing the boundary conditions of the environment. For instance, in winter the
227
ground freezes, 8eneratin~ lenses and other structural features in the sedimentary sequence. Such a frozen state, together with the ice cover developed on the sea and rivers, protects the sedimentary sequence from erosion during a period when the most severe storms would otherwise develop. Furthermore, in the case of the Akimiski Strait, partial melting of the ice in spring changes the tidal strait into an ice-walled bay closed to the north. This enhances the tidal range and the rate of sedimentation of fine materials in the northwestern parts of the strait during a critical period of the year when the rivers flood and carry in a considerable amount of sediments (Martini, 1981b). Finally, the mainland coast of the Akimiski Strait is influenced by two major rivers: the shallower and steeper Ekwan River and the Attawapiskat River. Both display typical, for this northern region, anastomosing lower reaches, although the Attawapiskat River has a dominant channel reaching the sea. It is this dominant channel that drains out and captures the flow of the secondary canals as the land rises. These streams carry considerable amounts of organic-rich water throughout the year. However, the great majority of the sediment is carried to the sea during brief periods at break-up times. The sediments are derived from river bank erosion where sequences of tills are superimposed by Holocene marine deposits, ranging from subtidal fossiliferous silty clay and coastal sand and gravels, to a cap of marshy organic-rich silty sands which, in turn, are capped by fluvial levee deposits and thin woody peats. No substantial amount of material is eroded from the floor of the channel as the river entrenches quickly through the overburden to the more resistant carbonate bedrock. The fluvial accumulations consist primarily of thin channel bars, mostly formed in the downstream parts of islands in the anastomosing reaches, of thin fine materials deposited primarily in semi-abandoned side channels, and of suspended and ice-rafted sediment on narrow levees. The rivers do not shift course frequently, although switching of the whole system may occasionally occur. The abandoned channels are later filled with organic matter. In general, these streams form relatively narrow ribbons of thin fluvial sediments across the wide wetlands. They would be indeed difficult to recognize in ancient sequences. The collection of papers in this issue of Sedimentary Geology contributes to the understanding of sedimentary sequences (mineral and organic ones) deposited in cold, subarctic, coastal and fluvial environments within a cratonic basin. Such an understanding may be put to a fruitful, comparative use in trying to decipher analogue ancient geological deposits. REFERENCES Haworth, S.E., Lowell, D.W. and Sims, R.A., 1978. Bibliography of published and unpubhshed literature on the Hudson Bay Lowland. Report 0-X-273, Can. Forestry Service, Dept. on the Environ.. S. Ste. Marie, Ont.. 270 pp. Herbert, C. and Helby, R., 1980. A guide to the Sydney Basin. Geol. Survey at New South Wales, Bull., 26, 603 pp.
228
Hood, P.J., 1968. Earth Science Symposium on Hudson Bay. Geol. Surv. Can,, Pap. 58-53, 386 pp. Martim, I.P,, 1981a. Morphology and sediments of the emergent Ontario coast of James Bay, Canada. Geogr. Annal., Ser. A., 63: 81-94. Martini, I.P., 1981b. Ice effect on erosion and sedimentation on the Ontario shores of James Bay, Canada. Z. Geomorphol., 25: 1-15. Martini, I.P., Cowell, D.W. and Wickware, G.M., 1980a. Geomorphology of Southern James Bay: a low energy, emergent coast. In: S.B. McCann (Editor), Coastline of Canada. Geol. Surv. Can. Pap. 80-10, pp, 293 301. Martini, I.P., Morrison, R.I.G., Glooschenko, W.A. and Protz, R., 1980b. Coastal studies m James Bay, Ontario. Geosci. Can., 7:11 21. Sanford, B.V., Norris, A.W. and Bostock, H.H., 1968. Geology of the Hudson Bay Lowlands, IOperation Winisk). Geol. Surv. Can., Pap. 67-60, 118 pp. Sjors, H., 1959. Bogs and fens in the Hudson Bay Lowlands. Arctic, 12: 2-19.