Tertiary gravels and sands in the Canadian great plains
Vonhof, Jan Albert
Remnant fluvial sand and gravel deposits comprise the uppermost beds of the Tertiary stratigraphic sequence in the Swan Hills, Hand Hills, Wintering Hills, an area northeast of Handhills, Lake, the Del Bonita area, Cypress Hills, Swift current Upland, and the Wood Mountain and Willow Bunch Lake areas, all in the Canadian Great Plains. Except for the Swift Current area, where the Cypress Hills Formation occurs as a bedrock valley fill, all other dposits are true upland deposits whose lower contacts with older formations lie several hundred feet above the elevation of the surrounding plains. Except for the Swift Current area, where the Cypress Hills Formation occurs as a bed rock valley fill, all other deposits are true upland deposits whose lower contacts with older formations lie several hundred feet above the elevation of the surrounding plains. The deposits reveal in in their feet above the elevation of the surrounding plains. The deposits reveals in their primary directional structures, their stream gradients, and their source areas a northeasterly direction of stream flow for the ancient streams that transported and deposited the sediments. The source areas for the sediments are the Rocky Mountains east of the Rocky Mountain Trench, the Foothills, and the Interior Plains. It becomes evident from detailed lithologic studies that the deposits in the various areas can be grouped into four lithologic provinces which reflect differences in the gross ,lithology of the Rocky Mountain region. These provinces are the Swan Hills (quartzite), the Hand Hills (quartzite, chert, and limestone), the Del bonita area (quartzite, argillite, and basic intrusive and extrusive rocks), and the Cypress Hills (quarttzite, chert, and acidic intrusive and extrusive rocks). Within each lithologic province there is uniformity of the gross lithologty. However, the separate deposits within ta province can be distinguised on the basis of minor but consistent diffferences in the heavy mineral assemblages and the gravel lithology. Study of the size-frequency distribution of the grafel in the various areas revealed that the number of granules and condquently the total weight of the granules in the smaller size classes varies considerably with the lithologic composition of the gravel. The major Teritiary drainage systems originated during the culmination of the Laramide orogeny in the Eocene Epoch. Subsequent intermittent (?) regional uplift and tilting (?) resulted in the deposition of progressively younger sediments at successively lower elevations, a significant shift of the major streams toward the south, reworking of older Teritiary fluvial deposits, and general denudation. The position of the major Quaternary preglacial valleys, compared to the older Tertiary fluvial deposits, indicates that little or no change has taken place in the position of the headwater regions since Eocene - Oligocene time. Althought he position of the present major valley (Athabaska, Bow - Saskatchewan, Missouri) in western Canada and northwestern Montana has change considerable since ealy Pleistocene time, their headwaters were established during early Tertiary time in approximately the smae areas as they are today.