PYRITIZED SPINOSE MICROSPHERES FROM THE MIDDLE DEVONIAN TULLY FORMATION OF PENNSYLVANIA: THE FIRST RECORD OF MUELLERISPHAERIDA FROM THE UNITED STATES

Spinose spherical microfossils occur in the lower part of the Middle Devonian (Givetian) Tully Formation near Lock Haven, PA. The microspheres occur in a single 20 cm thick bed of hard, dark-colored, fine-grained limestone, and so far are unknown from other beds in the exposure or equivalent beds elsewhere. The microspheres are about 100 µm in diameter and possess spines that are up to 20 µm in length. The spines expand toward the base, are circular in cross-section, and are broken at the tips. Spines are spaced about 40 µm apart and are arranged in a regular pattern over the surface of a microsphere. The microspheres are composed of a mosaic of authigenic pyrite crystals about 5-10 µm in length. The microspheres occur with microscopic (larval?) bivalves, gastropods and other organisms, all of which are preserved as pyrite steinkerns lacking original carbonate. Macrofossils do not occur in the microsphere horizon. The size and shape of these microspheres and the presence of spines indicates that they are representatives of an enigmatic group of microfossils known as Muellerisphaerida (incertae sedis). Although muellerisphaerids are generally phosphatic in composition, pyritic examples are known from the United Kingdom. The Lock Haven specimens are the first muellerisphaerids reported from the United States.