ABSTRACT: Quaternary Stratigraphy and Surficial Geology of the Sand River Area 73L

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Abstract

This document describes the Quaternary stratigraphy, surficial geology, and Quaternary history of the area covered by the Sand River map sheet NTS 73L, east-central Alberta. Eight glacial and nonglacial formations are defined for the Quaternary sequence in the Sand River area. The thick drift cover, combined with a paucity of exposures, necessitates reliance on test hole data for the differentiation and correlation of these units. The stratigraphy of the upper 50 m is defined primarily from sediment grain size and carbonate content, and from very- coarse-sand composition data derived from dry auger samples at 1 m intervals. Rotary drill samples and electric log responses are essential to define the deeper stratigraphy. The relative abundance of four rock groups (igneous and metamorphic rock, quartz, carbonates and local bedrock) within the 1- to 2-mm sand fraction are me most useful criteria in differentiating the tills. The standardization of electric-log responses with the analytical values enables correlations of the units beyond areas where samples were collected. Textural and lithologic variations allow the division of some formations into units or members. The formations are named and type sections designated. The Empress Formation is the oldest, and is divided into three units on the basis of Ethology: unit 1, preglacial sand and gravel; unit 2, silt and clay; and unit 3, glacial sand and gravel. The Bronson Lake Formation overlies the Empress Formation. It consists of clayey till and clay deposited by the first glacier in the area, the Cherry Grove Glacier. Glaciofluvial sand and gravel of the Muriel Lake Formation were deposited on top of the Bronson Lake Formation, both during the retreat of the Cherry Grove Glacier and during the advance of the Fort Kent Glacier. Till of the Bonnyville Formation overlies me Muriel Lake Formation. It was deposited by the Fort Kent Glacier, and is characterized by a relative abundance of quartz and a paucity of carbonate in the silt-clay and very-coarse-sand fractions. Glaciolacustrine silt and clay of the Ethel Lake Formation were deposited in proglacial lakes during the advance of the Ardmore Glacier. To of the Marie Creek Formation was de- posited during later stages of that advance. The till is characterized by a relative abundance of carbonate rocks, mainly dolostone, in the silt-clay and very-coarse-sand fractions. Glaciofluvial sand of the Sand River Formation was deposited during the retreat of the Ardmore Glacier as well as during the advance phase of the subsequent Cold Lake Glacier. The Grand Centre Formation consists of till and glacially displaced sediment deposited by the last glacier in the area the Cold Lake Glacier. The till is characterized by an abun- dance of igneous and metamorphic rock fragments in the very-coarSe-Sand fraction. Four members, defined mainly by grain size, are recognized within the formation. The presence of oxidized profiles on the surfaces of the W formations suggests that lengthy periods of weathering followed each major glacial episode. The surficial geology is mapped according to a classification based on genesis, composition, and morphology and relief, with each category indicated on the map by a symbol. The genetic categories, the first heel of subdivision, are designated organic, colluvium, fluvial, eolian, lacustrine, moraine, and bedrock. The composition categories indicate the dominant grain size of the sediment (silt and clay for example), and for some of the moraine units, the presence of significant quantities of recognizable bedrock inclusions. A combination of letters and numbers is used to designate each map unit, for example ctMSDh2. The lowercase letters (where present) preceding the capitals indicate the composition of the unit. The first uppercase letter indicates the genetic class. The following uppercase letter(s) indicate the genetic modifier and provide additional information about the genetic unit. The lowercase letters following these indicate the morphology type and the amount of local relief. The absence of the compositional, genetic, or morphologic modifier for a particular unit indicates that the data are insufficient to determine that property. The Sand River area includes some types of glaciotectonic landforms not previously described. Three broad types recognized in the study area are the hill-hole pair, hills with a fault-bounded depression, and rubble terrain. Hill-hole pairs form a major portion of the thrust moraine, and consist of a hill and an associated up-glacier depression that is commonly water-filled to form a lake. Hills with fault-bounded depressions consist of a hill-hole pair in which the up-glacier depression is bounded on at least one side by a linear margin believed to represent the trace of a tear fault created during the glacial excavation of the sediment Rubble terrain consists of a group or series of hills composed of a mixture of syngenetic till and distinct blocks of preexisting sediment. Typically the hills decrease in size down-glacier from the source depression. The Late Wisconsinan history began with the advance of the Cold Lake Glacier over the area. This glacier advanced in the form of three independent lobes, each of which flowed beyond the limits of the area. The southwestward-flowing lobe, the Primrose Lobe, deposited the Hilda Lake and Reita Lake members of the Grand Centre Formation in the eastern half of the area. The southward-flowing lobe, the Seibert Lobe, deposited the Kehiwin Lake Member of the Grand Centre Formation in the western half of the area. The youngest lobe, the Lac La Biche Lobe, flowed southeastward and deposited the Vilna Member of the Grand Centre Formation over part of the western half of the area. During the late stage of the Cold Lake Glaciation the Sand River developed as an ice-walled channel along the north-south trending margin of the Primrose and Seibert lobes. The Sand River first flowed along the north-south portion of the present Sand River channel into the Truman and Minnie Lake segments, and later into the Kehiwin Channel. Fluctuations in the Primrose Lobe margin resulted in the eventual infixing and abandonment of the Truman and Minnie Lake segments, and the formation of the Moose Lake River and Moose Lake. Later, drainage within the southern few kilometres of the Sand River was diverted southeastward into the Moose Lake River. The present-day Beaver River channel developed west of the Sand River at this time, subsequent to the stagnation of the Seibert Lobe. East of the Sand River the subsequent stagnation of the Primrose Lobe resulted in a northward shift of the active Me margin to a position north of the present-day Beaver River channel. This allowed the development of the eastern segment of the Beaver River and the subsequent abandonment of the Moose Lake River-Kehiwin Channel drainageway. A minor glacial readvance southwestward out of Cold Lake temporarily blocked the eastern half of the Beaver River and likely resulted in a short-lived rejuvenation of the Kehiwin Channel drainageway. Following this, drainage along the eastern channel of the Beaver River was reestablished and the present-day drainage patters developed.

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