Studies on a roughly five million year long Middle Ordovician sequence in the Taconic Foreland Basin, New York are addressed to these questions: How did water temperature and oxygen content vary with depth in going from a continental carbonate platform down the outer slope of a subduction trench? Was oceanic deep circulation driven by sinking of warm, saline water from low-latitude platforms, as has been suggested for this and other times of highest sea stand? Twelve years' background work on the stratigraphy and paleontology of the sequence, including an ongoing two-year feasibility study, has made a unique opportunity for answering these and related questions from carbon and oxygen isotopic studies on shells of bathymetrically wide-ranging benthic invertebrates, and from carbon analyses of sediments. Relative water depth is measured in terms of position on downslope transects along individual volcanic ash layers and, over time, through gradient analysis of fossil assemblages. Relative water temperature will be determined from oxygen isotopic composition in one articulate brachiopod (low-Mg calcite), two inarticulate brachiopods (calcium phosphate), and other taxa selected for comparison. Evidently, texturally and chemically well-preserved calcareous brachiopods are isotopically little-altered: specimens from the same sampling station yield tightly clustered 18 values similar to those of the best-preserved Middle and Late Ordovician material. The density of puncta on the articulate brachiopod's shell (proportional to temperature in modern forms) is proportional to relative depth, and may provide a check on 28 as a temperature measure. Research will aid in paleoceanographic reconstruction and in identification of possible areas for resource exploration.
