LOWER TO MIDDLE ORDOVICIAN BIOSTRATIGRAPHY OF THE APPALACHIANS: IS THERE ANY NEED FOR IMPROVEMENTS?

Fossils can be used to infer ages of lithological units, understand facies differentiations, structural complexities and paleogeographic relationships in the Early Paleozoic of eastern North America. In this respect, graptolites are more commonly used than any other fossil groups, even though diverse macro- and microfossil assemblages are also available for study. Unfortunately, graptolites are lacking in certain lithologies due to their organic composition, and are replaced as biostratigraphically important elements by conodonts and other microfossils, which are often less precise and more long-ranging. Exact dating of lithostratigraphical units, therefore, is often impossible, leaving wide spaces for improvement.

Graptolites are the most commonly used macrofossils to identify ages of Lower and Middle Ordovician rocks in the New York, Quebec and Newfoundland Appalachians and provide the data for a precise correlation of lithostratigraphical units along the length of the orogen. Especially the succession of the continental slope and rise, preserved in the allochthonous slices of the Humber tectono-stratigraphic zone in western Newfoundland and Quebec, and the overlying foreland basin of the Table Head Group of the Port-au-Port Peninsula are an excellent study region to understand Ordovician biostratigraphy and application of paleontological data. The intercalation of various lithologies and their individual preservational potential for macro- and microfossils provide the opportunity to study, correlate and integrate biostratigraphies of various fossil groups, including graptolites, trilobites, phosphatic and calcareous brachiopods, conodonts, chitinozoans and radiolarians, and, thus, improve their usefulness for dating and other purposes considerably. As the various groups of fossil organisms occur in different lithologies and facies relationships, the biostratigraphic correlation of their occurrences is often hampered with difficulties. Miscorrelations are common and may be of immense impact for the timing of events and the understanding of tectonic structures.