The Rockhampton Group represents a sequence of over 2000 m of marine siltstones and sandstones that contain scattered, thin carbonate intervals and spans Late Tournaisian to Late Visean time. The group crops out in a large area, mostly west of Rockhampton, central-eastern Queensland. The purpose of this project is to describe the coral fauna of the Rockhampton Group, evaluate its potential for biostratigraphic correlation in eastern Australia, and investigate the environments of deposition of the limestones in which the corals occur.
Rockhampton Group limestones were deposited on a broad, gently sloping shelf with the western-most exposures very near the shoreline. The limestones are predominantly oolitic and represent two basic types of deposits. The thickest limestone intervals mostly represent autochthonous accumulations of oolitic and, less commonly, bioclastic sands that were deposited in shallow-water, high-energy conditions. These limestones contain a variety of coral-algal-cryptalgal bioherms and biostromes. The remaining limestone intervals mostly represent allochthonous accumulations of oolitic sands that have been transported from shallower shoaling areas. Many of these limestones contain calclithites derived from previously eroded oolitic and/or biohermal lithologies.
Six coral biofacies are recognized in the Rockhampton Group. These are the: 1) biohermal; 2) biostromal; 3) forebank slope; 4) shallow shelf mobile sand; 5) near shore mobile sand; and 6) offshore silt biofacies. All biofacies represent very shallow water, high energy conditions with the exception of the forebank slope biofacies, which is characterized by lower energy conditions and periodic sedimentation, and the offshore silt biofacies, which represents relatively stable, low energy conditions. The majority of Rockhampton Group coral species are restricted to bioherms and biostromes, or calclithites derived from them. In all, 84 species are described of which 68 have not been described previously. Included are 3 new genera with the following type species: Stereodepasophyllum amplexum n. gen. et sp., Alinkioduncanella crassa n. gen. et sp., and Dinostrophinx hadros n. gen. et sp. The following 22 new species are also described: Amplexocarinia pumila n. sp., Kabakovitchiella? hardingsae n. sp., Amygdalophyllum archeri n. sp., A. minimum n. sp., Aphrophyllum edgari n. sp., A. julli n. sp., Merlewoodia abnormalis n. sp., Symplectophyllum densum n. sp., S. rosewoodensis n. sp., 'Siphonodendron' fasciculiseptatum n. sp., Schoenophyllum dalmaensis n. sp., 'Orionastraea' flemingi n. sp., Michelinia crassaspina n. sp., Turnacipora? hillae n. sp., Acaciapora jelli n. sp., Multithecopora minor n. sp., Pseudoroemeripora queenslandica n. sp., Palaeacis cuneiformis australis n. subsp., P. cuneiformis granvillensis n. subsp., P. grandis n. sp., P. robusta, n. sp., and P. serrata n. sp.
Rockhampton Group corals are very useful for biostratigraphic correlation in eastern Australia and can be grouped into 4 successive assemblages. The lowest assemblage, assemblage A, occurs in the Gudman Formation and is Late Tournaisian in age (Spirifer sol brachiopod zone). The assemblage consists of a variety of small solitary corals and abundant Turnacipora? with rare colonial rugose corals. It is not recognized elsewhere in Queensland, but is similar to the coral fauna of the Rangari Limestone of New South Wales. Assemblage B is middle to Late Visean in age (Orthotetes australis, Delepinia aspinosa brachiopod zones) and occurs in the Cargoogie Oolite Member of the Malchi Formation. It consists of a large and varied fauna of lithostrotionids, aphrophyllids, and the syringoporoid Syringopora. It is also recognized in the lower part of the Cannindah Limestone and in the Washpool Creek Formation of Queensland. Assemblage C is Late Visean in age (Rhipidomella fortimuscula brachiopod zone) and occurs in the Lion Creek Limestone. It consists of a large and varied fauna of lithostrotionids, aphrophyllids, and the syringoporoids Multithecopora and Pseudoroemeripora and has no species common with assemblage B. It is also recognized in the upper part of the Cannindah Limestone, the Riverleigh Limestone, Splinter Creek Formation, O'Bil Bil Road Conglomerate, and the Mundubbera Sandstone. Assemblage D is Late Visean in age (Marginirugus barringtonesis brachiopod zone) and occurs in unnamed limestones on the eastern flank of the Craigilee Anticline. It consists largely of aphrophyllids and species of Palaeacis. It is also recognized in the Baywulla and Dakiel Formations and Killala Creek Limestone of Queensland.