Reefs cementation

Pedley, H.M. (1992) Freshwater (Phytoherm) reefs the role of biofilms and their bearing on marine reef cementation. Sedimentary Geology 79, 255-274. 

Human activities have resulted in exposure of Antarctic fishes to petroleum-derived PAHs (McDonald et al. 1992). Fish captured near Palmer station on the Antarctic peninsula had induced EROD activities and elevated concentrations of biliary PAH metabolites of phenanthrene and naphthalene when compared to conspecifics from reference sites (McDonald et al. 1995). Artificial reefs consisting of oil and coal flyash stabilized with cement and lime in Florida waters near Vero Beach contained elevated PAH levels ranging from as high as 1.2 mg fluoranthene/kg and 0.25 mg naphthalene/kg. But there is negligible leaching because seawater is not an effective medium for removing PAHs from reef bricks or the ash (Frease and Windsor 1991). 

Although coral looks like a plant, actually it is mainly comprised of (10) the limestone skeleton of a tiny animal called a coral polyp. While corals are the main components of reef structure, they are not the only living participants. Coralline algae cement the myriad corals, and other miniature organisms such as tube worms and mollusks contribute skeletons to this dense and diverse structure. Together, these (15) living creatures construct many different types of tropical reefs. 

Clastic sedimentary rock A sedimentary rock largely consisting of cemented particles from preexisting rocks rather than chemical precipitates or materials excreted by organisms (e.g. coral reef deposits). Sandstones are examples of clastic sedimentary rocks. 

Waite, J.H., Jensen, R.A., and Morse, D.E., Cement precursor proteins of the reef-building polychaete Phragmatopoma califomica (Fewkes), Biochem., 31, 5733, 1992. 

Figure 6.5. Examples of reef barrier cementation. Void filling cements are believed to be formed by direct chemical precipitation, while renalcis filling is assumed to be produced by organisms. (After Harris et al., 1985.)...

Figure 6.8. Schematic representation of energy environments and cements in a reef. (After Lighty, 1985.)...

The net of reaction (6.13) and (6.14) can result in addition of some dissolved calcium to Checker Reef interstitial water, and possible deposition of cement in the pores of the reef structure. 

An important conclusion of Sansone s studies was that thermodynamic disequilibrium, among dissolved species like CH4 and SC>42% implies microzonation of chemical reactions. This microzonation resulting in slight differences in reef interstitial water compositions, as well as temporal changes in water composition, induced by a variety of factors including seasonal variables, may account for the coexistence of different cement mineralogies in reef structures, as well as the zonation... 

Early carbonate diagenesis and cementation of reefs need to be quantitatively and mechanistically examined. 

Lighty R.G. (1985) Preservation of internal reef porosity and diagenetic sealing of submerged ealy holocene Barrier Reef, southeast Florida Shelf. In Carbonate Cements (ed. O.P. Bricker), pp. 123-151. John Hopkins Press, Baltimore, MD. 

Mitchell J.T., Land L.S. and Miser D.E. (1987) Modem marine dolomite cement in a north Jamaican fringing reef. Geology 15, 557-560. 

Pigott J.D. and Land L.S. (1986) Interstitial water chemistry of Jamaican Reef sediment sulfate reduction and submarine cementation. Mar. Chem. 19, 355-378. 

Dando, P.P., O Hara, S.C.M., Schuster, U., Yaylor, L., Clayton, C.J., Bayliss, S. and Laier, T., 1994. Gas seepage from a carbonate-cemented sandstone reef on the Kattegat coast of Demnark. Marine Pet. Geol., II 182-189. 

Schroeder, J.H., 1972. Fabrics and sequences of submarine carbonate cements in Holocene Bermuda cup reefs. Geol. Rundsch., 61 708—730. 

Ginsberg, R.N., Marszalek, D.S. and Schneidermann, N., 1971. Ultrastructure of carbonate cements in a Holocene algal reef of Bermuda. J. Sediment. Petrol, 41 472—482. 

Pierson, B.J. Shinn, E.A. (1985) Cement distribution and carbonate mineral stabilization in Pleistocene limestones of Hogsty reef, Bahamas. In Schneidermann, N. Harris, P.M. (Eds) Carbonate Cements. Special Publication 36. Tulsa, OK Society of Economic Paleontologists and Mineralogists, pp. 153-168. 

Beachrock is a friable to well-cemented sedimentary rock that results from rapid lithification of sand and/or gravel by calcium carbonate cement precipitation in the intertidal zone. It occurs predominantly on tropical ocean coasts, but is also found in temperate realms that extend up to 60° latitude. In contrast to the implications of the name, beachrock precipitation phenomena are not restricted to beaches but also occur on reef ridges, tidal flats and in tidal channels. Intertidal beachrock may be confused with other sediments lithified in the intertidal and subtidal zones, such as hardened crusts or certain reef limestones. 

Figure 11.1 Photographs of beachrock outcrops. (A) Seaward dipping layers of beachrock on the northwest coast of Basse Terre, Guadeloupe, West Indies. This is the area that Charles Lyell (1832) mentioned in his Principles of Geolog/. Beachrock consists largely of quartz and volcanic sand cemented by calcium carbonate. (B) Extensive outcrop of beachrock, which also exhibits significant erosion. Windward side of Halfmoon Cay, Lighthouse Reef, Belize. (C) Beachrock ridge on southern shore of Kuramathi island, Rasdu Atoll, Maldives. Note flat and karstified top of outcrop, which resulted from meteoric dissolution.

Figure 11.3 Outcrop and hand specimens of beachrock. (A) Freshly broken piece of beachrock with mostly sand-sized constituent particles. Kuramathi island, Rasdu Atoll, Maldives. Height of picture is 5 cm. (B) Beachrock with mostly cobble-sized fragments of coral. Long Cay, Glovers Reef, Belize. (C) Close-up of fossil beachrock outcrop from Ras Al-Julayah, southern Kuwait. Note how fine-grained layers are better cemented than coarse-grained ones. (For overview of outcrop see Figure 11.9A.)...

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