Biostratigraphy type relative dating technique

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The following material focuses on key fossil taxa present in the Trenton Limestone, their distribution or occurrence within the overall succession of Upper Ordovician strata, and their role in the establishment of the Upper Ordovician time scale.The goal of biostratigraphy is to use fossil occurrences within the rock record to establish correlations between time-equivalent rock strata as determined by the presence of a particular fossil species.New York localities are world famous for Cambrian through Devonian strata and fossils, but of particular importance to this website discussion is the contribution of the Ordovician rocks of central New York State to the establishment of a North American focused biochronology.The rocks found in the central New York Mohawk River Region, by definition of their fossil content, are now established as belonging to the Mohawkian Series of the Upper Ordovician Period.In addition to biostratigraphic and sequence stratigraphic zonation, also diagramed is the relative scale provided by the composite standard section (CSS).This represents a composite stratigraphic section for all of the Middle to Upper Ordovician rocks of central and eastern North America based on graphic correlations techniques (see Sweet, 1984 for more information).Biostratigraphy is a sub-discipline of sedimentary geology that relies on the physical zonation of biota, both in time and space, in order to establish the relative stratigraphic position (i.e.older, younger, same age) of sedimentary rocks between different geographic localities.

The roll-over diagram above highlights key taxa useful for biostratigraphic studies of the Upper Mohawkian Series.Although the diagram above shows all the chronostratigraphic information for the Middle to Upper Ordovician of central to eastern North America, the key interval of importance to the discussion of the Trenton Group here is that of the upper Mohawkian Series (roughly equivalent to the middle Caradocian Series of the European System).The Trenton Limestone represents a single lithostratigraphic group, but it is clearly composed of a variety of carbonate rock types, and lithostratigraphic sub-units deposited during a relatively long period of time (estimated at approximately 4-5 million years).These surveys focused not only on New York's geological resources, but also emphasized the establishment of spatial and temporal relationships of stratigraphic units based on both lithologic and paleontologic composition.By the mid-1800's the New York Surveys had resulted in the development of a relative stratigraphic zonation based primarily on fossil distribution.

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