The study of trace fossils is a useful and necessary part of any core study and should be joined with other paleontologic, petrologic and sedimentologic data to give the most plausible geological interpretation. For the petroleum industry, cores, in many instances, are the best or only source of data for determining the paleogeography and paleoenvironment of subsurface deposits. Consequently, the study of trace fossils in cores becomes especially important in order to acquire the maximum information from costly samples. Such studies can be applied either to single facies or to a more general basin analysis.
In the course of an ichnological study, sedimentologic, stratigraphic, structural, paleontologic, paleoecologic, paleogeographic and paleoenviron-mental data may be included. Sedimentologic events that are influenced by biologic activity include: 1) alteration of grains by ingestion; 2) disruption of fabric and creation of new fabric, which may reduce or increase permeability and porosity within beds or transmissibility between beds; 3) production of sediments by organisms, and 4) trapping of sediment by organisms (e.g., stromatolites, sabellarid worms; see Chapter 2). Some sedimentologic interpretations that can be made by investigation of certain traces include: 1) initial history of lithification; 2) rates of deposition; 3) current energy levels (Howard, 1964; Spencer, 1976); 4) relative amounts of erosion and deposition; 5) coherency (stability) of the medium burrowed; and 6) relative degrees of compaction (see Chapters 2 and 6).
Where the rocks are otherwise “unfossiliferous”, trace fossils may provide biostratigraphic information (Seilacher, 1970)
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Trace Fossil Concepts
The advancement of ichnological research has left in its wake a considerable volume of literature that contains many important concepts and the results of some excellent field studies. These notes try to consolidate the most salient topics of the discipline and emphasize the application of ichnological concepts and data to geological problems. In many respects, a detailed knowledge of trace fossil concepts is a matter of experience rather than education. Trace fossils, unlike other fossils, are part of the rock and, thus, they are difficult to collect and curate. As a result, interested geologists must go to the field and see a lot of trace fossils in a variety of different views, preserved under a variety of different conditions, to build a working expertise on such structures. This short course is designed to suit the needs of a diversified audience, which is made up of geologists from both academic and industrial institutions. Although the primary concern is to introduce the subject to those having little background in ichnology, the hope is to also update those geologists who already use trace fossil information in their investigations.