BRYOZOAN SPECIES IN THE PLEASANT HILL "WAULSORTIAN" BIOHERM (MISSISSIPPIAN, KENTUCKY)

Unusual bryozoan-crinoid mud-mound bioherms ("Waulsortian" facies) in the Mississippian of southeastern Kentucky are not entirely carbonate, but instead consist of a limestone cap draped over a green-shale core, all embedded within the background siltstone facies of the Fort Payne Formation (late Osagean), deposited on the slope down into the cratonic basin to the west. One such bioherm, at Pleasant Hill (Ausich & Meyer '90), was examined for its bryozoan content, identified from roughly 150 colonies.

      This bioherm is exposed on the west bank of Caney Creek (arm of Lake Cumberland), 0.3 mi (0.5 km) north of the Pleasant Hill boat ramp at the end of Ky. Hwy. 1680, 5 mi (8 km) SE of Jamestown (Carter coordinates 1600' WEL, 1800' NSL, section 11, grid F-54, Jamestown 7.5' quadrangle, Russell County).

      The limestone cap yielded few identifiable bryozoan fragments, although finely comminuted fenestrate debris is common enough in thin sections for the rock mostly to be classified as wackestone rather than micstone. (Crinoid-rich pockets are packstones). The cap overlies the mudstone core sharply, with no intergradational marlstones at the contact.

      In sharp contrast, the green shale or mudstone core yields many fallen broken bryozoans, presumably contributors to trapping and stabilizing the accumulating clay muds, although adding little volumetrically as skeletal sediment and none as framework. Virtually the same assemblage of species is found in the core and in the shales outside the flank (and also in the cap). One species is abundant: Fenestella regalis, a delicate fenestrate. Two are common: Cystodictya lineata, C. ocellata, both thin narrow bifoliates. Two more are uncommon: Laxifenestella maculasimilis, Minilya sivonella, both delicate fenestrates. Twenty-two additional species were quite rare: 10 delicate fenestrates, 4 robust fenestrates, 2 delicate pinnates, 4 rhabdomesids, and 2 fistuliporoids. These numbers are consistent with preservation of this bryozoan assemblage in situ, with no taphonomic alteration.