BRYOZOAN SPECIES OF SMALL MICRITE MOUNDS (WAULSORTIAN) IN THE BURLINGTON LIMESTONE (MISSISSIPPIAN) OF CENTRAL MISSOURI

Mississippian lime-mud mounds sparsely inhabited by fenestrate bryozoans and crinoids, the Waulsortian facies, range greatly in size. Smallest are low limestone mounds like those dotting the slope from the shallow Burlington Shelf of central Missouri down into the intracratonic Illinois Basin, during mid-Osagean time. That shelf is known for its well-washed crinoidal grainstones (classic Burlington Limestone), but its foreslope deposits include considerable micstone-wackestone as well (King '86 JSP).

      To determine bryozoan species composition and paleoecologic constructional roles in these small buildups, samples were collected from two adjacent Burlington mounds on the west side of U.S. Hwy. 63 18 mi (29 km) S of Columbia, and 1.6 mi (2.6 km) S of the exit to Hartsburg (Co. Rd. A), on E edge NE¼ SE¼ sec. 3, T.45 N., R.12 W., Boone Co.

      The southern mound is 10 ft (3 m) thick, light-gray micstone, with pockets of abundant fenestrates, rare bifoliates, and uncommon crinoid ossicles. The northern mound, 2 ft (0.6 m) thick, is tan dolomicrite, with few fenestrates and crinoids. Both mounds are flanked by crystalline grainstones with abundant crinoid columnals.

      Most of the bryozoans are broken, horizontally-lying fronds, but a very few are preserved erect, upright, in original growth position. In some parts of the mounds, the bryozoans were numerous enough to have been mud trappers/bafflers and stabilizers, in other places so sparse as to have probably made no sedimentologic contribution. Overall, they also added minor comminuted skeletal sediment.

      Out of 35 colonies identifiable to species, the delicate fenestrate Fenestella regalis is common, the robust fenestrate Polypora cestriensis and bifoliate fistuliporoid Cystodictya lineata are uncommon, and 10 other species are each rare (5 delicate and 2 robust fenestrates, 2 bifoliates, and 1 rhabdomesid/rhomboporoid). Such faunal proportions suggest preservation in place, with minimal taphonomic alteration.