Once upon a river: archaeology and geology of the Bow River Valley at Calgary, Alberta, Canada
LccFC 3697.56 W54 1981 Fiche
LcshGeology, Stratigraphic - Quaternary
Geology - Alberta - Bow River Valley
Glacial landforms - Alberta - Bow River Valley
Bow River Valley - Antiquities
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AbstractLate Quaternary geology and archaeology of the Bow River valley at Calgary, Alberta, Canada are considered in terms of archaeological visibility, defined as recognizability of any archaeological manifestations or patterns, in the field or laboratory. Geological factors selectively obscured portions of the record in the west Calgary study area (Bow Valley, Happy Valley Park to Elbow River mouth). Multiple tills suggest at least an interglacial age for the valley. Wisconsin Laurentide ice dammed glacial Lake Calgary, which left silts over ~0 m deep. With ice retreat, escaping waters cut spillways across south Calgary and incised the inner Bow Valley through lake deposits, leaving Late Wisconsin or older high terraces. Valley-bottom gravel fill (Bighill Creek Formation) 10,000 to 11,500 yr old was deposited after the valley was scoured through till to bedrock. Mammuthus sp., Equus conversidens, Camelops cf. hesternus, and Bison bison antiquus were recovered from these gravels at Calgary. Dated Holocene fills record deposition from about 9500- 9000 B.P., 8300-5000 B.P., 4700-?3000 B.P., and ?2000-150 B.P. Deposition through the Hypsithermal contrasts with erosion in the southern Plains and shows the danger of extrapolating that sequence too far north. Hypsithermal fill (to T3 filltop) is largely in areas where chutes had been cut into the Bighill Creek Formation T~ fillstrath, away from the Bow channel. The Bow armored its channel and has not cut far enough laterally to reveal many such deposits in cutbanks. The chutes, perhaps with fringing vegetation, were arenas for bison kills; components 8200, 6700, 5400, and 5100 yr old were revealed at the Mona Lisa site (EgPm-3, south city core). Mummy Cave complex projectile points from the two upper kills resemble later point types, indicating a problem of typological visibility added to that of burial away from river cutbanks. These factors account for at least part of the 11Altithermal hiatus n in the archaeological record. A black paleosol is pre-Hypsithermal (ea. 9000-8300 B.P.) and other Alberta nAltithermal1 soils are possibly of similar age. Mazama ash in alluvial (overbank) and slopewash fan settings is an early Hypsithermal marker; later ashes are obscure, if present. At EgPm-127 (Point Mackay, N.W. Calgary) sedimentary structures (transverse ribs) indicate overbank flow strong enough to have removed all bones. Stone features were partially displaced, flake clusters were apparently not displaced, and bones were removed, reflecting differential entrainment and hence an important visibility constraint. Holocene landscape changes were significant and modern topography is at best a crude guide in site reconstruction. Because cities provide excavated profiles in areas not exposed by natural processes, selective river erosion, mass-wasting, and other taphonomically significant processes are partly countered, aiding archaeological visibility. Cities therefore have potential for vigorous prehistoric archaeological programs.
Bibliography: p. 422-464.