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The AAPG/Datapages Combined Publications Database

AAPG Bulletin


Volume: 63 (1979)

Issue: 3. (March)

First Page: 421

Last Page: 421

Title: Developmental Phases in Lagoonal Patch Reefs--Implications for Paleozoic Bioherms, or New Models for Reefs: ABSTRACT

Author(s): Rena M. Bonem

Article Type: Meeting abstract


Observation of modern reefs indicates that lagoonal patch reefs may provide a more useful model for Paleozoic bioherms than conventional fringing or barrier-reef models.

Most Paleozoic bioherms develop within inland basins or seaways surrounded by continental masses. Adjacent lands contribute varying quantities of fine clastic material to "reef"-derived carbonate rocks. Thus, bioherms are commonly associated with micrite or calcareous shales and mudstones. Few Paleozoic bioherms occur on coarse-grained carbonate substrates similar to those of modern fringing or barrier reefs. Rather, the bioherms generally appear to have had a mud substrate like that common in modern lagoonal settings.

Similar development of modern lagoonal reefs and Paleozoic bioherms further strengthens the proposed model. Development of many Paleozoic bioherms progresses from an initiation phase of substrate stabilization, to a diversification phase, and finally to a termination phase dominated by a single group of organisms. Modern lagoonal patch reefs have been observed to develop in an identical manner in response to rapid fluctuation in sedimentation, a common condition in the lagoonal environment.

In addition to substrate and developmental phases, there are other implications of a lagoonal model for Paleozoic bioherms. Reduced light penetration causes modern lagoonal coral and algal associations to occur in shallower water than predicted. Also, increased suspended matter results in dominance of sponges over corals in the lagoon.

Recognition that lagoonal patch reefs exhibit developmental phases and substrate characteristics similar to those described for many Paleozoic bioherms demonstrates the potential importance of replacing conventional models with lagoonal patch reefs when examining Paleozoic bioherms.

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Copyright 1997 American Association of Petroleum Geologists