Expanded reef-rock textural classification and the geologic history of bryozoan reefs

The wide range of colony forms assumed by bryozoans results in a greater variety of bryozoan-reef-carbonate-rock types than can be accommodated within present classifications. Consequently, the currently used textural classification is expanded to include several new reef-rock categories (branchstone, cruststone, globstone, lettucestone, shellstone) immediately applicable to bryozoan reefs. Those in the early Paleozoic were small mounds, largely cruststones and bindstones, accompanied later by globstones and lettucestones; a very few similar mounds live today. Others, many larger, in the mid-and late Paleozoic, were branchstones and bafflestones, in some cases so sediment-rich as to appear mostly as floatstones with interspersed rudstones to micstones.