Published:January 01, 1984
Bioerosion of carbonate substrates by microorganisms more or less constitutes a subdiscipline of its own. This distinction from macroscopic bioerosion is due to the fact that the organisms involved are dominantly plants, fungi and prokaryotes. Because the borings themselves are so small, they demand special techniques for their study. Consequently, microscopic bioerosion is a field for specialists that is rarely entered by workers in related fields.
Several animal groups bioerode on a microscopic scale. Radula traces produced by chitons and snails can barely be seen with the naked eye. The borings produced by phoronids and bryozoans also are so small that they can only be studied using the same casting techniques that are used for microscopic bioerosion.
This chapter deals with endolithic plants, fungi and prokaryotes, which, although taxonomically diverse, form an ecologically homogeneous group. The organisms involved are listed in Table XI-1.
The chiorophytes comprise a number of genera and species that actively bore in carbonate substrates. They produce branching networks of tunnels varying greatly in size. Some may be as little as 2μ m in diameter. In some species such fine filaments may collect together in main canals as wide as 25 μ m, but including sack-like chambers of greater size (Golubic, Perkins and Lukas, 1975, p. 243). A shell or light-colored rock that has been thoroughly bored by green algae takes on a pale green color.
Two genera of rhodophytes, Porphyra and Bangia, are endolithic in early stages of their life cycle, after which they become epilithic.
Figures & Tables
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.