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The AAPG/Datapages Combined Publications Database

AAPG Bulletin

Abstract


Volume: 55 (1971)

Issue: 3. (March)

First Page: 541

Last Page: 542

Title: Sequence Elements in Stratigraphic Analysis of Lower Colorado (Cretaceous) Strata, West-Central Saskatchewan: ABSTRACT

Author(s): Frank Simpson

Article Type: Meeting abstract

Abstract:

Sedimentary rocks referable to the Lower Colorado subgroup are fairly well defined in the subsurface as that predominantly argillaceous sequence delimited by the base of the Speckled Shale Formation (Turonian) and the top of the Mannville-Blairmore succession (middle Albian). The sequence exhibits pronounced lateral variation and locally discernible diachronism of sandstone bodies; both the lowermost Joli Fou Formation and the uppermost Big River Formation display a northerly increase in sand content, whereas the lenticular sandstone bodies of the Viking Formation, which separates them over most of the study area, become progressively finer grained on the north, so that the formation may no longer be differentiated.

The Lower Colorado succession may be described in terms of repetition of 5 principal sequence elements, each characterized by the predominance of particular gross lithologies and associated internal sedimentary structures: (1) a mudstone element, including structureless mudstones and mudstones containing lenses and intermittent layers of siltstone; (2) a siltstone element, in which lenticular and wavy-layered siltstones and fine-grained sandstones alternate with structureless mudstones; (3) a silty sandstone element, consisting of sandstones with varying proportions of silt-grade material and thin, discontinuous mudstone interlayers, displaying disruption of flaser layering, due to burrowing activities of organisms, as well as loading and injection phenomena; (4) a sandstone element, hich may exhibit dune-scale, inclined laminae, horizontal laminae, ripple cross-laminae, and trough cross-laminae; and (5) a conglomeratic element, with pebbly sandstones, conglomerates, and pebbly mudstones. Subordinate lithologies, such as coquinoidal limestones, sideritic oolites, concentrations of iron sulfides, and accumulations of phosphatic bodies, also are present.

The use of sequence elements in stratigraphic analysis provides a systematic approach to description of

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lithologic variation, an aid to local correlation of sequences, and a basis for environmental interpretation. Type (3) elements are of particular economic importance as the main reservoir rock of the hydrocarbon-bearing Viking Formation.

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