PALEOZOIC CARBONATE MUD-MOUND EVOLUTION & GLOBAL PALEOGEOGRAPHY

With the exception of South America, mud-mounds have been identified in all other present day continents. The geologic record of mud-mounds spans at least one billion years, as they are known to range from the Proterozoic to the present. Nonetheless, the greatest number of carbonate mud-mound occurrences reported to date is from the Paleozoic. In this time interval they are known from every Period and from every Epoch. Global paleogeographic reconstructions illustrate that mud-mounds were latitudinally widespread, extending from tropical to temperate to polar belts. If their preserved geologic record reflects their original distribution, then carbonate mud-mounds would appear to have been most common during a span that encompasses the Middle Devonian to the Early Carboniferous. In the history of the Earth this Late Paleozoic interval is characterized by ice-house conditions. The circumstances outlined may be interpreted to indicate that carbonate mud-mound proliferation occurs when cool and cold marine waters encroach the seafloor. These conditions are common at depth, with upwelling and during sea-level rises as these waters flood continental shelves.

While the community structure of Paleozoic carbonate mud-mounds appears to have evolved throughout the Paleozoic, an important and puzzling building block embodied in stromatactis and zebra structures remained constant. These structures clearly represent early cavities and were stabilized by early submarine cementation. While the cavities vary morphologically, they may be relics of former gas clathrate hydrate deposits (gas charged ice). Significantly, present day, oceanic gas clathrate hydrate occurrences are associated with cool and cold waters and with abundant carbonate spar and micrite cements. Nevertheless early submarine cementation of mud-mounds, a widely recognized phenomenon, would have resulted in the development of stable substrates that depending on near seafloor ecological conditions would have been colonized by phototrophic, heterotrophic and lithotrophic organisms.