Stratification Produced by Migrating Bed Forms
Published:January 01, 1975
1975. "Stratification Produced by Migrating Bed Forms", Depositional Environments as Interpreted from Primary Sedimentary Structures and Stratification Sequences, J. C. Harms, J. B. Southard, D. R. Spearing, R. G. Walker
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Sedimentary structures have been observed and described by geologists for many decades. Because there are many varieties of primary sedimentary structures and an abundant literature of diverse authorship, terminology and classification are confusing. We hope to be clear in our descriptions within the following text, but we do not propose to provide a thorough review of classification or a complete classification scheme of our own. For those interested in classification, the following references offer a fairly complete spectrum of views: Blatt, Middleton and Murray (1972, p. 111 to 118), Pettijohn, Potter and Siever (1973, p. 102 to 127), McKee and Weir (1953), Allen (1963), Campbell (1967), and Conybeare and Crook (1968).
We shall adopt the following general approach to description for the purposes of this course:
Description should aim at defining the original bed configuration because this emphasis provides the most logical link to interpretation of flow conditions. Some primary sedimentary structures represent the original complete bed form, as do ripples or flute casts. However, most structures are incomplete remnants of an original form, for example, sets of cross strata bounded by erosional surfaces. Then careful observation must be used to infer the complete form.
Descriptive terms are a shorthand to convey an image either to yourself or another geologist. In most cases, the terminology best suited to this purpose is descriptive and emphasizes principal shape characteristics with simple adjectives. But many descriptions begin to include
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Depositional Environments as Interpreted from Primary Sedimentary Structures and Stratification Sequences
The focus of these notes is on the use of primary sedimentary structures and stratification sequence as tools for interpretation of depositional environment of clastic sediments, emphasizing advances in understanding that the authors judge to be important. To accomplish the primary objective, several topics have been selected. Experimental flume studies are summarized with emphasis on work which extends the understanding of distribution of bed forms over increased ranges of grain size, flow depths, or velocity. Studies of modern and ancient sedimentary sequences are used to illustrate and interpret environments of deposition. Fluvial sediments are reviewed to show how experimentally derived generalizations are applied or qualified to interpret natural environments.