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The AAPG/Datapages Combined Publications Database

AAPG Bulletin


Volume: 65 (1981)

Issue: 5. (May)

First Page: 923

Last Page: 923

Title: Field and Experimental Studies of Biogeochemical Processes Governing Diagenesis in and near Reefs, Gulf of Elat, Red Sea: ABSTRACT

Author(s): Samuel A. Epstein, Gerald M. Friedman

Article Type: Meeting abstract


Carbonate cementation in the surface layer of reefs and beachrock eliminates porosity and partly replaces detrital quartz grains. The uptake and release of CO2 by photosynthesis and respiration in reef communities cause a shift in the carbonate buffer system of seawater. Field studies and experimentation show minimum values of CO2 (1.9 mmol/l) and HCO-3 (2.4 Meg/l) in association with maximum values of pH (10) and O2 (> 100% saturation) in waters covering corals and alga prior to sunset. The converse is true for these variables prior to sunrise, when minimum values of pH (7.6) and O2 (< 66% saturation) occur with maximum values of CO2 (2.7 mmol/l) and HCO-3 (2.8 Meg/l) Experimental tanks containing plain seawater showed almost no diurnal variability in pH (a constant 8.0) or O2 (~ 58% saturation) measurements. Seawater adjacent to reef biomass with elevated pH and supersaturated with calcium carbonate is pumped into the underlying reef rock and beach rock where carbonate precipitation and quartz dissolution occurs. As the system equilibrates, pH values progressively decrease.

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Copyright 1997 American Association of Petroleum Geologists