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GEOREF RECORD

The effect of synsedimentary substrate modification on the composition of paleocommunities; paleoecologic succession revisited

Kenneth R. Walker and Wesley W. Diehl
The effect of synsedimentary substrate modification on the composition of paleocommunities; paleoecologic succession revisited
Palaios (February 1986) 1 (1): 65-74

Abstract

Three kinds of paleoecological succession have been recognized: 1) long-term (through a considerable stratigraphic interval), 2) reef succession, and 3) short-tern (usually recorded in a single bed). The third kind must have occurred under more or less constant conditions of external environment, and over a short time interval. It is, then, the only type of fossil succession which is directly comparable to modern ecological successions. The nature and causes of short-term succession are the subject of this study. We believe short-term paleoecological successions were often controlled by gradual change in the nature of the substratum during or shortly after deposition. We call these processes of substratum change synsedimentary modification; three kinds of processes are recognized. First, water loss from the substratum produces gradual change in its consistency from fluid to soft, and ultimately to firm. The nature and relative timing of these consistency changes can be discerned by observing burrow/sediment interrelationships. Fossil assemblages commonly reflect these changes by containing a mix of morphotypes, each of which was adapted to a different substratum consistency. The second modification process involves the changing mix of substratum niches as successive taxa colonize the environment. The most common example is the paving of initially "soupy" substrata by sediment "floaters", and the subsequent use of the skeletons of the pavers as settlement sites for later population. Finally, sediment may undergo substantial change early in its history by marine cementation. The process is patchy in three-dimensional distribution, so at any given time the substratum consists of scattered areas of hardground interspersed with areas of loose sediment. Again the ultimate result is the mixing in one bed of morphotypes adapted to these divergent substratum types. Subsequent lithification may encrypt the relative timing of various cements, but petrographic analysis allows its resolution. The examples given here are drawn from the Middle Oradovician. The acquisition of the kind of data required for discernment of these processes and resultant assemblages requires more careful sedimentologic analysis than is common in paleoecological studies.


ISSN: 0883-1351
Serial Title: Palaios
Serial Volume: 1
Serial Issue: 1
Title: The effect of synsedimentary substrate modification on the composition of paleocommunities; paleoecologic succession revisited
Affiliation: Univ. Tenn., Dep. Geol. Sci., Knoxsville, TN, United States
Pages: 65-74
Published: 198602
Text Language: English
Publisher: Society of Economic Paleontologists and Mineralogists, Tulsa, OK, United States
References: 38
Accession Number: 1986-035937
Categories: Stratigraphy
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. strat. col., sketch map
N35°00'00" - N36°45'00", W90°15'00" - W81°40'00"
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Reference includes data supplied by SEPM (Society for Sedimentary Geology), Tulsa, OK, United States
Update Code: 1986
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