TAPHONOMY AND PALEOECOLOGY OF ORDOVICIAN PYRITIZED DEEP-WATER TRILOBITE FAUNAS FROM UPSTATE NEW YORK

Beecher's Trilobite Bed (BTB), from the Late Ordovician Frankfort Formation near Rome, NY, is a classic locality for the preservation of trilobite appendages. In particular, it is the source of our knowledge of the limbs of the olenid trilobite Triarthrus. Olenid trilobites have been interpreted as having a symbiotic relationship with sulfur bacteria (Fortey 2000) allowing them to live in environments that would prove very demanding or toxic to most invertebrates. Previous studies at the BTB site concentrated almost entirely on the 4 cm-thick 'Trilobite Bed' and neglected the rest of the sequence, which is essential for understanding the environment in which the trilobites lived. Here we report a second locality yielding exceptionally-preserved olenids, which was discovered recently in the Ordovician Whetstone Gulf Formation near Lowville, NY.  The assemblages at Lowville are more diverse and may yield previously unknown examples of soft-tissue preservation.

Field-work has revealed that conditions suitable for pyritization were not confined to the historic "Trilobite Bed" but occur in more than one horizon both at the BTB locality and at Lowville. Geochemical analyses (iron systematics, sulfur isotopes) show that soft-tissue pyritization occurs in beds with a high 'reactive' iron content and high d³⁴S values.

Preliminary geochemical, sedimentological and paleontological results suggest that conditions in the basin fluctuated, possibly with periods of bottom-water anoxia. The low diversity and high abundance of the olenid trilobites, coupled with the geochemical signature, implies an unusual mode of life in this inhospitable basin.