Interactions of bryozoans and microbes in a chemosynthetic hydrothermal vent system: Big Cove Formation (Lower Codroy Group, Lower Carboniferous, Middle Viséan/Arundian), Port au Port Peninsula, Western Newfoundland, Canada

In the lower Carboniferous (330 Ma), a hydrothermal vent system developed within an extensive fault setting over a fractured Ordovician limestone basement in western Newfoundland. The vent system supported a complex biological community, which ultimately accumulated to form carbonate mounds. The most likely source of energy for the mounds was chemosynthesis. These mounds are unique because they contain the first recorded fossil bryozoan remains associated with a vent community, and possibly the only fossilized record of the interactions of bryozoans with abundant microbial activity, probably promoted by sulfides emitted by the vent system. The microbial deposits and, to a lesser extent, the sulfides, coated the invertebrate population of monospecific trepostomatous bryozoans, brachiopods, and probable vestimentiferan tubeworms. Various extant sessile invertebrates, including bryozoans, secrete antimicrobial substances that prevent excessive microbial growth. Based on evidence from the fossil record, i.e., the general absence of excessive microbes in association with bryozoans, it appears that the same was probably true in the past. High abundances of materials of probable microbial origin associated with the Carboniferous bryozoans in western Newfoundland are enigmatic.