Brachiopods and the Main Classification of the Carboniferous

ABSTRACT: As a contribution to the discussion on the proposals for an international chronostratigraphic subdivision of the Carboniferous, the brachiopod distribution is reviewed, especially with regard to the major boundaries. Obviously not all groups prove to be equally important: the Inarticulata, Orthida, Orthotetidina, Rhynchonellida, and Terebratulida are of little value, because they are rare, show little evolutionary development, or have not been monographically treated recently. The Chonetidina and Isogrammatidae are of some interest. The most important groups are undoubtedly the Productidina and Spiriferida, both being very abundant and highly varied and showing rapid evolution. Although the evolution of the brachiopods during the Carboniferous was gradual, there were times when important changes took place. By far the most important change within the Carboniferous occurred at the Serpukhovian-Bashkirian boundary, thus supporting the proposal to use this level as the boundary of two subsystems, the Mississippian and Pennsylvanian. Another important boundary, though definitely less so, is the Middle-Upper Carboniferous boundary, which is in accordance with their proposed status as separate series within the Pennsylvanian Subsystem. A problem that arises here is that there are three levels which could be used for this boundary, as far as hrachiopods are concerned: a horizon in the upper Myachkovian (within the uppermost Westphalian D), the Myachkovian-Kasimovian boundary (within the middle Cantabrian), and a horizon within the Lower Kasimovian (near the top of the Cantabrian). The Visean-Namurian boundary, like the Bashkirian-Moscovian boundary, is far less important, though still recognizable, and it merits stage recognition.