Shallow Marine Carbonate Environments
Published:January 01, 1984
Justification for a separate chapter on the subject of ichnology of marine carbonate - as opposed to terrigeneous - sediments lies in the nature of carbonate grains and the environments in which they are produced, cemented and destroyed. The special properties of carbonate substrates and carbonate depositional environments are reflected by the characteristic trace fossils in several ways. In most respects, however, the ichnology of the shallow marine carbonate environments resembles that of their physical equivalents for terrigeneous sediments (see Chapter 15). The emphasis of this chapter is on carbonate systems of the warmer seas; those of temperate regions are more elastic in nature than their warm-water equivalents, and their ichnology has received little attention.
Aspects of ichnology that are peculiar to carbonate environments belong in three general categories: (i) bioturbation and burrows; (2) pellet formation; (3) bioerosion of carbonate grains (including miente envelope formation), of beachrock and coasts, and of hardgrounds and reefs.
Unbioturbated sediments of beach and restricted subtidal environments tend to be strongly laminated. Thus, the presence of any burrows within the fabric is conspicuous, as also is the complete destruction of the lamination by total bioturbation when it occurs. Absence of bioturbation is much more common, as it is in the same environments in the terrigeneous realm, and usually this may be accounted for by either physical reworking of the sediments or lack of benthos.
In high-energy settings, physical reworking of sediment and the concomitant deposition of thick, single-event units, are frequent and tend to obliterate
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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.