BRYOZOAN SPECIES IN THE CHICKASAW BRYOZOAN REEF (ORDOVICIAN, OKLAHOMA)

For the first time, bryozoan species composition of a mid-Ordovician bryozoan reef far outside the Appalachians has been analyzed, thereby permitting informative comparisons with other such structures of comparable age. We identified 120 colonies from different ecozones in the Chickasaw bryoherm (Cuffey & Cuffey '95), of basal Blackriveran age (low in Mountain Lake Member of Bromide Formation), on U.S. Hwy. 177 1.4 mi (2.3 km) SE of the center of Sulphur in south-central Oklahoma.

      The micritic cruststone core of the Chickasaw bryozoan reef contains all the species identified in and around this small bioherm. Crustose to massive Batostoma chazyensis (incl. campensis) and Dianulites fastigiatus are abundant, Lunaferamita (Fistulipora) bassleri common, and Tarphophragma (Hallopora) multitabulata and bifoliate Escharopora recta sparse. Broken fragments of these also occur scattered through the calcarenitic packstone flank beds.

      Seventeen additional species are rare in the core (some also rare in the crinoidal grainstones underlying [*] or overlying [**] the reef). Many are similar trepostomes: Batostoma ramosa, sheldonensis, Dianulites petropolitana*, Diplotrypa bassleri, Homotrypa dickeyvillensis*, tuberculata, Mesotrypa angularis, Nicholsonella acanthobscura, Orbignyella sublamellosa; a few, cystoporates: Ceramoporella ingenua, Lunaferamita virginiensis. Some are thin-branching trepostomes: Champlainopora (Atactotoechus) chazyensis*, **, and Batostomella (Bythopora) subgracilis; or bifoliates: Graptodictya (Stictopora) elegantula, Graptodictya (Arthropora) simplex, Pachydictya (Athrophragma) sheldonensis*, Stictopora (Rhinidictya) fenestrata.

      Most of these species functioned as encrusting frame-builders, sometimes eroded off the reef to form skeletal grains. The more delicate trepostomes and bifoliates grew like sparse grass across the mound surface.

      The Chickasaw reef contains the greatest concentration of bryozoan species (21) identified in the immediate area. This bryodiversity is noticeably higher than the somewhat older Vermont Chazyan bryoherms (particularly the earliest one, at Garden Island), but is comparable to other crust-mounds of similar Blackriveran age (Tennessee, Virginia). Moreover, the proportion of abundant to rare species suggests fossilization in place with little if any taphonomic alteration.