Holocene Stratigraphy and Geomorphology of Flintstone Hill, Lauder Sandhills, Glacial Lake Hind Basin, Southwestern Manitoba

Abstract

Sediments exposed at Flintstone Hill in a Souris River cutbank provide the most complete postglacial stratigraphic section in the Glacial Lake Hind Basin (GLHB), southwestern Manitoba. Four lithologic units, A-D, are observed: A1 (~2 m thick), glaciolacustrine silts and clays that grade upward to peat and record final regression of Glacial Lake Hind (~10 500-9300 BP); A2 (~1.5 m thick), low energy fluvial marl and silts grading to O-horizon(s) (by 6700 BP); B (1.5 m thick), dune sands that migrated from the southwest, contrary to the modern wind regime (after ~6700 BP); C (1.0 m thick), thin fluvial deposit between eolian sand sheets (~5500-3200 BP); D (up to 7 m thick), parabolic dune on the modern landscape oriented consistent with the modern wind regime, blowouts suggest episodic dune reactivation (~3200 BP to present). Overall, Flintstone Hill deposits record draining of Glacial Lake Hind, establishment of the Souris River channel through the GLHB, mid-Holocene eolian activity / landscape instability greater than present, and a return to nearly modern conditions by ~5400 BP. Native inhabitants in the GLHB focused on exploiting wetlands and wet meadows before 9300 BP and a landscape similar to the present thereafter.Les sédiments à découvert de la Flintstone Hill, sur la berge escarpée de la rivière Souris, offrent la séquence stratigraphique postglaciaire la plus complète du bassin du Lac glaciaire Hind. Quatre unités lithologiques, de A à D, y sont observées : A1 (~2 m d’épaisseur), silts et argiles glaciolacustres au granoclassement vertical progressif jusqu’à la tourbe témoignent de la dernière régression du Lac glaciaire Hind (~10 500-9300 BP) ; A2 (~1,5 m d’épaisseur), marnes fluviatiles de faible énergie et silts jusqu’à un horizon O (vers 6700 BP) ; B (1,5 m d’épaisseur), sables dunaires en provenance du sud-ouest, contrairement au régime des vents actuel (après ~6700 BP) ; C (1,0 m d’épaisseur), dépôt fluviatile mince entre des couches de sable (~5500-3200 BP) ; D (jusqu’à 7 m d’épaisseur), dune parabolique faisant partie du paysage moderne et orientée selon le régime des vents actuel, avec des creux de déflation témoignant de réactivations dunaires épisodiques (~3200 BP à aujourd’hui). En résumé, les dépôts de la Flintsone Hill attestent d’abord de la vidange du Lac glaciaire Hind, puis de l’établissement du chenal de la rivière Souris à travers le bassin, d’une activité éolienne et d’une instabilité des paysages à l’Holocène moyen plus grande que maintenant et de l’établissement de conditions quasi contemporaines vers 5400 BP. Les premiers habitants du bassin ont d’abord exploité les terres humides et les prés humides avant 9300 BP, puis un paysage semblable à celui d’aujourd’hui par la suite.Los sedimentos expuestos en la zona de Flinstone Hills en la ribera del Souris River proporcionan el registro estratigráfico post-glaciar más completo de la cuenca del Lake Hind, al sudoeste de Manitoba. Se distinguen cuatro unidades litológicas: A-D. La unidad A1, de unos 2 m de grosor, está compuesta por limo...

Paleoecology of an Early Holocene Wetland on the Canadian Prairies

“…This record has recently been used to address the nature of early Paleoindian landuse in the glacial Lake Hind basin (Boyd et al, 2003). For a detailed discussion of the entire FSH lithostratigraphic sequence, see Boyd (2000) and Running et al (2002).…”

“…Unit A2 is composed of interbedded fine sand, silt, clay and marl, with an overall higher carbonate content than Unit A1, and abundant gastropod and bivalve shells (Running et al, 2002); pollen and plant macrofossils are rare. This unit coarsens upward to a thinner, discontinuous, organic deposit up to 15 cm thick in a fine sand matrix.…”

“…Although river cutbanks are unconventional sites for paleoecological analysis, Flintstone Hill exposes a >2 km long lithostratigraphic sequence spanning the terminal Late Pleistocene to the present (Boyd, 2000(Boyd, , 2002Running et al, 2002;Boyd et al, 2003). The basal unit (A1), the focus of this paper, contains a laminated organic deposit with diverse and well-preserved macrofossils constrained by 14 C dates to the interval between >10.6 and 9.1 ka BP.…”

“…The modern landscape of the Hind basin is dominated bỹ 18 discontinuous dune fields ("Oak Lake dunes" of David, 1977) mostly of late Holocene age (Boyd, 2000;Running et al, 2002;Wallace, 2002). Near Flintstone Hill, the dominant eolian landforms are large parabolic dunes with arms (<10 m high, 500-2 000 m long) that are oriented WNW-ENE.…”

“…A conventional radiocarbon age on wood from this organic deposit places it at 6700 ± 70 BP (Beta-111142; 7667-7462 cal BP) (Boyd, 2000). Unit A2 represents the early Souris River prior to incision that established its present channel through the glacial Lake Hind basin (see Running et al, 2002). The observed distribution of marl, grain sizes and bedding that generally coarsen upward, and greater carbonate content compared to Unit A1, are consistent with low-energy accretion in a position away from the thalweg of the channel (Running et al, 2002).…”