|Exploring for Oil and Gas Traps|
|Series||Treatise in Petroleum Geology|
|Part||Predicting the occurrence of oil and gas traps|
|Author||Robert L. Fleisher, H. Richard Lane|
Phosphatic microfossils, notably conodonts, are composed of crystallites of calcium phosphate (apatite) embedded in an organic matrix. There is one type of stratigraphically significant phosphatic microfossils (conodonts); but fish teeth, of less practical utility, are found in some marine strata.
Conodonts are extinct toothlike microfossils composed of calcium phosphate whose biological affinities, while poorly understood, lie with chordates. Conodonts are widely distributed in marine rocks of Cambrian through Triassic age. They are excellent indicators of time and thermal maturity—especially in carbonates, where other methods of evaluating organic thermal maturity are less successful. Conodonts are commonly used as zonal indices for the latest Cambrian through Triassic because they were abundant, evolved rapidly, and were widespread geographically. Although found in most marine rocks, conodonts are most efficiently recovered from the insoluble residues of carbonates dissolved in weak acids or from easily disaggregated shales.
Individual conodonts vary greatly in morphology, and taxonomy was originally based on the morphology of these individual specimens. While conodonts are common, the preserved remains of the soft-bodied animal that bore them are extremely rare. Based on a few preserved whole-animal specimens discovered recently (e.g.,  conodonts appear to have been located in the cephalic area and may have functioned as teeth. However, the conodont animal apparently bore many conodonts of differing shapes and morphologies, based on the study of the very rare whole-animal specimens and rare bedding-plane groupings of conodonts representing individual animals. This recent information has led to more accurate multielement species concepts.
Figure 1 shows some typical conodonts.
- Microfossils in exploration
- Calcareous microfossils
- Agglutinated microfossils
- Siliceous microfossils
- Palynomorphs (organic-walled microfossils)
- Sweet, W. C., 1988, The Conodonta: morphology, taxonomy, paleoecology, and evolutionary history of a long-extinct animal phylum: Oxford University Press Monographs on Geology and Geophysics 10, 212 p.
- Gabbott, S. E., R. J. Aldridge, and J. N. Theron, 1995, A giant conodont with preserved muscle-tissue from the Upper Ordovician of South Africa: Nature, vol. 374, p. 800–803., 10., 1038/374800a0
- Purnell, M. A., 1995, Microwear on conodont elements and macrophagy in the first vertebrates: Nature, vol. 374, p. 798–800., 10., 1038/374798a0