STRATIGRAPHIC, FACIES, ETHOLOGIC, AND PRESERVATIONAL SIGNIFICANCE OF ICHNOSPECIES PTERIDICHNITES BISERIATUS , UPPER DEVONIAN, CATSKILL SEQUENCE

A synthesis of previous studies, including unpublished detailed ichnospecies analysis and new stratigraphic documentation within the Upper Devonian of New York fully describes the ethology, preservation, and facies significance of Pteridichnites biseriatus and suggests limits to its use as an index fossil.

This unique ichnofossil is a straight to gently curving repichnia, 2 to 5 mm wide, 2 to 8 cm long, containing two rows of nearly equidimensional roughly circular imprints that alternate along a central axis. It is preserved as convex hyporelief on siltstones less than 2 cm thick and as concave epichnia. Rare hypichnial imprints contain transverse scratch marks. Detailed analyses of hypichnial morphology and curvature indicate production by a shallow burrowing arthropod.

Studies of New York exposures indicate a Frasnian to earliest Famennian stratigraphic range of P. biseriatus. It occurs from Tully clastic correlatives upward through the Genessee, Sonyea, and West Falls Groups. To the south is has been recognized in the Braillier and Foreknobs Formations of West Virginia and Maryland. P. biseriatus is confined to turbidite slope facies associations including silt-and sandstone bundles, channelized turbidites, interlobe slope, and proximal areas of transgressional shales. It is absent from basinal black shale. Within the slope environment the trace-making organism tolerated differing paleoenvironmental parameters as evidenced by association with ichnoassemblages consisting of Paleodictyon/Megagrapton; Paleophycus/Chondrites/Rhizocorallium; and Diplocrateron/Arenicolites groupings.

Size frequency and curvature analyses indicate that Fucoides graphica is a preservational counterpart of P. biseriatus,. The former occurs as hyporelief on relatively thick turbidite sandstones that exhibit linear sole marks. Their stratigraphic range is identical.

The ubiquitous distribution of P. biseriatus and F. graphica within the slope facies and their Frasnian to early Famennian stratigraphic range limit their use as index fossils to generalized paleogeographic and stratigraphic problems.