Fluvial and Lacustrine Environments
Published:January 01, 1984
Aquatic nonmarine (i.e., fresh water) deposits can be conveniently subdivided into lotic (running water) and lentic (standing water) environments. Rivers, streams and wave-swept beaches of lakes are mostly lotie; while ponds, lakes and pools are lentic. Such environments often are characterized mistakenly as being devoid of trace-making organisms, and, in many cases, this trait has been utilized to distinguish fresh water from marine deposits in the rock record. However, contrary to this popular belief, modern fluvial and lacustrine environments commonly are inhabited by a diverse assemblage of infaunal and epifaunal organisms, which can and do create preservable biogenic structures.
Little ichnologic work has been done in modern aquatic nonmarine deposits. Recently, however, significant strides have been made to better understand the animal-sediment relationships of such environments (e.g., see Chamberlain, 1975a; Meichior and Ericson, 1979; Fisher, Lick, McCall and Robbins, 1980; Ratcliffe and Fagerstrom, 1980; McCall and Tevesz, 1982; Fisher, 1982; Cohen, 1984).
The physical characteristics of freshwater environments are fairly well known. Fluvial deposits have received in-depth study, and a number of facies models, including characteristic vertical sequences, have been erected (e.g., see Collinson, 1978; Cant, 1982). Lacustrine environments, on the other hand, are much more enigmatic; however, criteria for their recognition have been summarized by several workers (e.g., see Picard and High, 1972; Collinson, 1978b; Pouch and Dean, 1982.
As is the case with marine environments, ichnologic investigations of fresh water deposits have proceeded from two main directions: (1) study of Holocene traces, the organisms that produce them, and
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Ichnology: The Use of Trace Fossils in Sedimentology and Stratigraphy
Ichnology is a fascinating field of endeavor. As with science in general, it is a process of solving mysteries–in this case, mysteries of fossil behavior. In a very real sense the ichnologist is Sam Spade or Sherlock Holmes–following footprints, searching for traces of dastardly deeds, studying artifacts, attempting to reconstruct a sequence of events from subtle clues, pursuing the identity of someone (or something) long dead. Who was the culprit? What was he/she doing? Where was he/she living, working or going? Not only intellectually intriguing, ichnology also has practical application and economic importance. In today’s frenzied quest for energy and mineral resources, exploration geologists value every tool that aids their search. Ichnologic observations and analyses can help the sedimentologist reconstruct ancient depositional environments, help the stratigrapher correlate sedimentary strata, help the paleontologist determine the nature of fossil communities, and help the geochemist determine the effect of organisms on sediment composition. This publication was written to serve as a comprehensive and intelligible introduction to ichnology for anyone with even rudimentary geologic training, whether or not that person enrolls in a formal course on the subject. The book emphasizes sedimentologic, stratigraphic and paleoecologic al aspects of ichnology.