Marginal Marine and Intertidal Environments
Published:January 01, 1984
Marginal marine zones comprise a multitude of depositional environments, including salt marshes, tidal flats, washover fans, lagoons, bays, estuaries, tidal deltas and tidal inlets and channels. The facies of many of these environments are intimately related and may differ from one another only in subtle ways. Considerable work has been accomplished on the physical and biogenic characteristics of such facies along modern coastlines, particularly the coasts of Georgia (Howard and Frey, 1980a, 1980b, 1980c; Frey and Howard, 1980, California (Warme, 1967,1971; Ronan, Miller and Farmer, 1981 and Germany (Schafer, 1962; Reineck and Singh, 1973.
From a biological standpoint marginal marine zones are environmentally very stressful, because they are subject to extreme short-term variations in temperature, salinity, subaerial exposure, energy level and food supply. For these reasons they are inhabited only by organisms that are well-suited to withstand such rigors. Trace-making organisms constitute an integral part of the assemblage, and the distribution of their traces aids in recognizing marginal marine environments in the rock record.
Washover fans are formed from wind-generated storm surges that cross over or cut through barrier islands. Such deposits generally range in thickness from a few centimeters to several meters, and they consist of lobate to sheet-like sand bodies, which extend into the marsh or back-barrier lagoon (Andrews, 1970; Schwartz, 1975). Under transgressive conditions, the development of washover fans constitutes an important mechanism for the landward migration of barrier island complexes (Reinson, 1979). Their recognition in the rock record, therefore, may be critical in interpreting marginal marine
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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.