COLLABORATIVE RESEARCH: The Biostratigraphic Effects of Facies Control, Depositional Sequences, and Sampling Intensity: An Interactive Modeling and Field Approach

9705829 Patzkowsky The principal problem facing all biostratigraphic correlation methods is that first and last occurrences in local sections do not always reflect the true times of origination and extinction. Sampling, facies control, and sequence stratigraphic architecture all impose biases on local stratigraphic ranges. Many methods claim to account for these biases, but this claim has rarely been tested and the relative accuracy of different methods is poorly known. We propose to test three poplar biostratigraphic methods (traditional zonal biostratigraphy, dual biostratigraphy, and graphic correlation) to determine which is the most effective at dealing with the biased fossil record and to identify those factors that exert the strongest control on the accuracy of biostratigraphic correlation. We will approach this problem through a combined modeling and field study. Modeling will be used to test the relative accuracy of these three methods under a variety of sampling densities, levels of facies control, and sequence stratigraphic architectures. The advantage of modeling is that we will ultimately know the correct correlation, so we can objectively and quantitatively measure the accuracy of the various methods under different conditions. The techniques we develop here will allow many other types of biostratigraphic methods to be tested in the future. Armed with the knowledge gained from the modeling studies, we will evaluate a classic correlation problem with brachiopods in the Middle Ordovician of eastern Tennessee and southwestern Virginia. We will apply these same three biostratigraphic methods to the field data and compare the resulting correlations to the existing conodont-based stratigraphic framework. This study will lead not only to a general evaluation of the effects of sampling, facies control, and sequence stratigraphic architecture on three common biostratigraphic methods, but will also apply these results to develop a combined brachiopod-biozone and sequence strati graphic correlation framework to supplement existing conodont-based correlations in the Middle Ordovician of the Southern Appalachians. Because biostratigraphy is the principal means by which events are ordered throughout much of the stratigraphic record, the results of this study have broad implications for how Earth's history is reconstructed.