Ichnologic Controls on Early Diagenesis and Secondary Mineralization
Published:January 01, 1984
1984. "Ichnologic Controls on Early Diagenesis and Secondary Mineralization", Ichnology: The Use of Trace Fossils in Sedimentology and Stratigraphy, A. A. Ekdale, R. G. Bromley, S. G. Pemberton
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Organisms that produce traces occupy such a wide range of substrates that it can be said that as long as a sediment is exposed, it may be occupied. This is especially the case in marine settings, where a succession of infaunal communities may inhabit a deposit as it progresses through the successive stages of soupground, softground, firmground and hardground/rockground. The transition of soupy sediment to indurated rock occurs by compaction and diagenesis and thus accompanies the succession of ichnocoenoses in the same deposit. Complex ichnofabrics result from the juxtaposition of trace fossils produced in an ever-lithifying substrate. For example, borings of the Trypanites ichnofacies (i.e., in a rockground) may be superimposed on burrows of the Glossifungites ichnofacies (i.e., in a firmground), which in turn may be juxtaposed upon burrows of the Skolithos ichnofacies (i.e., in a softground), which themselves may have been emplaced in an already thoroughly bioturbated sediment (i.e., in a soupground).
An excellent example of this parallel succession of diagenetic and ichnologic events affecting a sediment can be seen in the Upper Cretaceous chalk of northern Europe. Compaction deformation of trace fossils and sharpness of burrow margins provide information about the character of the original chalk substrate. Zoophycos and Chondrites, for example, occur only in situations where the sediment was firm but uncemented, even though they commonly are overprinted on a background ichnofabric containing indistinct, highly compacted and deformed burrows. Thalassinoides, on the other hand, apparently was produced in a variety of substrate conditions, including soupgrounds, softground, firmgrounds
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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.