EXERCISE 13 (Palynology & Trace Fossils) (2).docx -...

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EXERCISE 13 Trace Fossils and Palynology 13.1. Introduction to trace fossils Trace fossils are remnants of the activities of live organisms, but do not include the body or body parts of the organisms themselves (Fig. 13.1). Trace fossils (also referred to as Lebensspuren or ichnofossils ) include such phenomena as tracks, burrows, coprolites (fossil dung), and scratches in sand made by live seagrasses waving on a beach. They do not include shells, molds of dead organisms, the track of a carcass washed across a sand flat, nor scratches in sand made by dead seagrasses waving on a beach. Sedimentary structures that were not produced by organisms, but that look superficially as if they were, are called pseudofossils . With a little experience, body fossils, trace fossils, and pseudofossils can be distinguished in most instances. However, occasionally a structure may be difficult or impossible to assign to one of these three categories. For example, the traces of dead and live grass tips are impossible to distinguish. Trace fossils were almost always formed in the place where they are found and were not transported. Trace fossils are the only type of fossils preserved within some sedimentary units, so provide a local record of organisms that would not otherwise be preserved. Trace fossils are given latinized generic and species names in the same manner as body fossils. The purposes of this exercise are: 1. To examine a variety of traces that represent different behavioral categories; and 2. To use traces as a key to environments in which the enclosing rocks were deposited. 13.2. Categories of trace fossils Several different bases have been used for classification of trace fossils. Descriptive-genetic classifications are based on recognition of such categories as tracks, trails, burrows, etc. Some classifications are based on preservation, while others are based on behavior. Classification by behavioral category is widely used, relatively straight-forward, and useful in interpretations of paleoenvironments. Therefore, behavioral category is used here as a means of organizing and interpreting trace fossils. Seven behavioral categories exist to which trace fossils are assigned: resting or hiding, locomotion, dwelling, deposit feeding, surface grazing, escape following burial or exposure, and highly patterned structures that suggest some sort of farming or husbanding of environmental resources (Fig. 13.2, Table 13.1). Traces were originally made by organisms moving across, burrowing within, or stopping on or within the substrate. Traces within substrates may collapse if not back-filled with processed sediment or fecal pellets, or infiltrated by sediment from the substrate surface. Some grazing, feeding, and dwelling behaviors involve repetitious activities within a small area so that each excursion of the animal from a starting point partially overlaps and is parallel or subparallel with the previous excursion. These structures that are referred to as spreite (plural, spreiten ). See examples in Fig. 13.1 (g and h).
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  • Fall '19
  • Trace fossil

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