Benthic, or sea floor, communities gave rise to the Cincinnatian Series limestone through a process called lithification. These communities were diverse and underwent frequent dramatic changes, which contributed to sediment formation. Such changes were often precipitated by events that wiped out most life in a given local community.Characteristics of a Benthic Community
Benthic communities were home to a wide array of organisms, both plants and animals. For the most part, fossil evidence of the shelled, invertebrate animals, is all that survives. However, worm burrows and other "trace fossils" preserve evidence of shell-less creatures. Trilobites, corals, echinoderms, bryozoa, brachiopods, mollusks, gastropods, and algae were all present on the sea floor. In addition, cephalopods, an ancestor of octopi and squid, would have visited frequently, looking for food, as shown in the picture shown below.
The Rise and Fall of a Benthic Community
The cyclic nature of a Cincinnatian Series benthic community during the Late Ordovician Period was likely caused by the periodic influx of muddy sediments from a volcanic mountain chain located where the Appalachians are today.
According to this interpretation, these muddy sediments and the storms that accompanied them would often damage or destroy local invertebrate communities. Over time, however, the communities would re-establish themselves. The figure below summarizes the destruction of benthic community life.
Once a benthic community has been wiped out by excessive sediment, the resulting subtidal, terrigenous mud substrate was usually colonized by either bryozoans or by thin, flat brachiopods such as Onniella, or both. The accumulation of brachiopod valves provided a pavement upon which erect bryozoans could grow.
The images below show some assorted brachiopods and a couple bryozoa.
Further stabilization of the substrate allowed other organisms to become established as well (Harris and Martin, 1979). The figure below summarizes the process of accumulation of the carbonate sediments following large storm events. This accumulation undergoes lithification and eventually becomes limestone.