Conglomerate: Sedimentary Structures and Facies Models
Published:January 01, 1975
1975. "Conglomerate: Sedimentary Structures and Facies Models", 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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In Chapters 5 and 6 of these notes, we have emphasized the increasing difficulty of direct interpretation of facies in environments where unidirectional flow of water over a sandy bed (Chapter 2) becomes less and less important. In this chapter, we will focus on a little studied lithology--conglomerate--and attempt to establish facies models for three different types. We can no longer refer either to the experimental results of Chapter 2, or to the individual sedimentary structures discussed in Chapter 3. To begin, we will therefore examine the possible descriptive features of conglomerate that could be used in a facies analysis, and make some interpretations of those features. We use the term conglomerate to include consolidated and semiconsolidated deposits with mean sizes in the granule, pebble, cobble, and boulder range, although our emphasis will be on the coarser (cobble and boulder) deposits.
There are relatively few modern environments in which conglomerate is accumulating, and where there is some chance of preservation. The main environments are: (1) alluvial fans, (2) braided rivers, (3) shorelines, (4) deep sea submarine fans, and (5) glacially-influenced environments (marine and nonmarine) where till is deposited. Facies models for environments of conglomerate deposition are poorly developed, mainly because of the general absence of a descriptive framework--that is, there is little agreement as to the features that must be observed and recorded in outcrops of conglomerate. This is highlighted when one considers the comparative abundance of descriptive features in
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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.