ZOOPHYCOS SIZE AS A KEY TO PALEOENVIRONMENT IN THE LOWER DEVONIAN CARLISLE CENTER FORMATION OF NEW YORK STATE
The trace fossil Zoophycos has long been used to estimate water depth, although throughout much of its history, Zoophycos has ranged from subtidal to basinal environments. Their size may be used to determine their preferred environmental range. The larger the trace maker, the more suitable the environment likely was in that location. In less favorable environments, the trace makers will be smaller and therefore make smaller feeding structures.
The Carlisle Center Formation (Lower Devonian) of New York State is characterized by the ubiquitous presence of Zoophycos. Zoophycos is so pervasive that all primary sedimentary structures have been destroyed by bioturbation. This quartz siltstone also shows a distinct lack of shelly fauna except in unbioturbated lenses, which contain ostracodes, tentaculitids, holothurian plates, conodonts, rare conulariids and small brachiopods.
Zoophycos sizes were measured and compared to data from a similar study by Marintsch and Finks of the Lower Devonian Esopus and Pine Hill Formations near Highland Mills, New York. The menisci height and the web diameter of the Zoophycos traces were measured. Measurements were taken at several localities along the Lower Devonian outcrop belt in the Mohawk and Hudson Valleys. The Zoophycos diameters in the Carlisle Center Formation are on average 10 centimeters larger than the Zoophycos from Highland Mills. Therefore, the Carlisle Centers paleoenvironment appears to have been much more suitable for the Zoophycos trace maker. The paleoenvironment for the Carlisle Center Formation appears to be below storm wave base, based on the absence of any tempestites, while the Esopus and Pine Hill Formations near Highland Mills contain tempestites with brachiopod dominated shell lags, and beach sands. Lack of a benthic macrofaunal community in the Carlisle Center Formation suggests dysoxic conditions prevailed during deposition. Sedimentation was likely low and episodic, given the relative thinness of discrete Zoophycosed packages and the presence of abundant glauconite. These lines of evidence would suggest that the Carlisle Center Formation was an outer shelf environment. The size of Zoophycos has long been overlooked as an indicator of environmental quality. This study, however, supports its use as a larger paleoecological research project.