Sedimentologic and Stratigraphie Applications
Published:January 01, 1984
Trace fossils typically are good facies indicators, and for that very reason they typically are poor index fossils for biostratigraphy. That is, trace fossils generally are characterized by long time ranges and restriction to particular benthic habitats. Body fossils of rapidly evolving, universally distributed taxa are much more useful for stratigraphie correlation and age-dating. When such body fossils are not present, however, trace fossils may prove helpful in accomplishing gross stratigraphy. In some lithologies, such as coarse siliciclastics, or in some environments where the inhabitants are mainly soft-bodied, such as lakes or deep-sea basins, trace fossils often are the only game in town. The following examples demonstrate the utility of traces in solving stratigraphie problems.
In most parts of the world, the Precambrian-Cambrian boundary is defined at the horizon where the first fossils of shelled organisms appear, and almost invariably these are trilobites. The question arises, should be boundary be picked at the lowest trilobite fossils (i.e., either body fossils or trace fossils), or must one find actual body fossils of the animals? We suggest that the latter is an incomplete approach to biostratigraphy; if trace fossils testify that trilobites were present earlier than the body fossil record along would indicate, that important paleontologic evidence should be considered in constructing evolutionary chronologies and establishing stratigraphie boundaries.
In many places (e.g., northern Norway, central Sweden, Greenland, northern Spain, southern Australia, southwestern Canada and eastern California), tracks which may have been made by trilobites occur in rocks that lie stratigraphically below the
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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.