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Abstract

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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