BRYOZOAN SPECIES IN UNUSUAL GREEN-SHALE MOUNDS, LOWER MISSISSIPPIAN, MIDDLE TENNESSEE

Waulsortian-type carbonate-mud mounds containing scattered fenestrate bryozoans and flanked by crinoids are well known from Lower Mississippian strata. Similar mounds, except composed of siliciclastic clay-mineral green-shale mud, occur in northern middle Tennessee, sandwiched between the underlying thin Maury green shale and the overlying Fort Payne siliceous limestone (Stapor & Knox '95). Our purpose is to document the bryozoan species and constructional roles in these mounds, previously dated as late Osagean, and denoted as New Providence or Ridgetop Shales. Mounds were sampled 11.8 and 10.5 mi (18.9, 16.8 km) N60ºW of Cookeville, 1.4 mi (2.2 km) S45ºE of Gainesboro, 1.0 mi (1.6 km) due S of Celina, and 7.9 mi (12.7 km) N30ºE of Livingston.

The green-shale mounds yielded 19 bryozoan species (from 107 zoaria), of which 2 (*) also occur rarely in the overlying limestone caps developed above some mounds. Two were abundant (30-16 specimens), bifoliate fistuliporoid Cystodictya lineata and delicate fenestrate "Fenestella" regalis. Two were common (15-10 specimens): "Fenestella" filistriata (*) and rhabdomesid Rhombopora bedfordensis. Three were uncommon (9-5 specimens), Cystodictya pustulosa, "Fenestella" compressa, and trepostome Proutella discoidea. The rest were rare (4 or fewer specimens): fenestrates Exfenestella exigua, "Fenestella" triserialis, Hemitrypa pateriformis, Rectifenestella tenax (*), Polypora cestriensis; pinnates Penniretepora flexuosa, vinei; rhabdomesids Saffordotaxis angustata, incrassata, ohioensis; Streblotrypa major; trepostome Lioclema gracillimum.

These species' proportions (few important, many sparse) suggest preservation in place with little taphonomic alteration. Their distributions indicate that the bryozoans functioned in the green-shale mounds as mud-sediment trappers/bafflers to some extent, possibly also as sediment stabilizers/fixers, but did not form any rigid skeletal framework nor contribute much bioclastic sediment.