Paper No. 32
Presentation Time: 8:00 AM-12:00 PM
WHOLE-COLONY BRYOZOAN GROWTH MORPHOLOGY: AN UNDERUTILIZED TOOL IN UNDERSTANDING TYPE-CINCINNATIAN PALEOECOLOGY
Bryozoans are a prevalent and underutilized source of paleoecologic data in the type Cincinnatian. We report the morphology, taphonomy, and paleoecology of a nearly complete colony of the trepostome bryozoan Heterotrypa sp. collected from the Clarksville Member of the Waynesville Formation, near Oxford, Ohio. This reassembled colony adds to an emerging understanding of Ordovician growth forms, which we believe to be the first step toward a more complete understanding of bryozoan paleoecology. This will help resolve outstanding questions concerning type-Cincinnatian deposystems. The colony (30 cm in diameter, 11cm high) was recovered from a mudrock interval in life position. The top of the colony was embedded in a 6 cm rudstone. The colony has been injected into the overlying limestone during compaction, a process that also resulted in crushing of colony branches. The unattached base of the colony was found overlying a nodular limestone interval. No encrusting base that might represent the ancestrula was found. The present bottom of the colony appears to have been insufficient to support a colony of this size, especially in the presence of bottom currents. We suggest that the colony was not transported, but lived at least partially buried in the mud, though the extent of burial during life is unknown. Three types of breaks appear. Clean breaks are thought to have formed during weathering of the outcrop, corroded breaks are thought to have formed during life, shortly after burial, or during compaction. Breaks with a deteriorated endozone are common to the upper surface of the colony, but absent on the lateral margins. These are interpreted as growth tips, where the thin, new, exozone had been dissolved. Unlike the colony of H. frondosa described by Waugh and Erickson, (2002), this colony has thinner fronds, lacks the well-developed chambers and walled-off lateral margins. Bryozoans, especially if observed from unassembled fragments, appear to belong to only a few growth form types. However, when colonies are reassembled, subtler morphologies are realized and taphonomic histories can be recognized. Continued recognition of Cincinnatian growth forms and their comparisons are needed to develop the bryozoan paleoecology that we feel should be reconstructed and applied to deposystems of the Type-Cincinnatian.