Reef limestones

Mangrove Forest ecosystems occur on the surface of compact cavernous reef limestone or on carbonate sands, aleuritic and clayey silts in lagoons and shallow... 

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. 

Reef limestones are mounds and units of organically produced debris, cemented in situ and often consisting of complete fossils. 

FIGURE 8 Block diagram to illustrate the diflierent types of stratigraphic traps. (A) Fossil reef limestone. (B) Coastal barrier-bar sand. (C) Sandstone infilled channel. (D) Onlap of sand above unconformity. (E) Truncation of limestone beneath unconformity. 

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. 

Eggshells are mostly calcium carbonate. Seashells, pearls, limestone, and chalk are also made of calcium carbonate. So are some of the most beautiful and complex places on earth—coral reefs. 

Reactive metal that easily forms many compounds found in limestone, lime, marble, and gypsum important component of bones and coral reefs. 

Reef-Type Traps. These have accounted for some of the most important production in recent years. The reef is generally considered a type of stratigraphic trap. The reef was formed under the right combination of conditions by the remains of millions of small underwater animals. Building their limestone residences on top of those built by their ancestors, the tiny... 

Matthews R.K. (1974) A process approach to diagenesis of reefs and reef associated limestones. In Reefs in Time and Space (ed. L.F. Laporte), pp. 234-256. SEPM Spec. Pub. No. 18, Tulsa, OK. 

The most actively cycled reservoir of carbon is atmospheric C02 (it constitutes 0.034% of the atmosphere). Carbon dioxide dissolves readily in water and is in direct equilibrium with dissolved inorganic forms of carbon (H2C03, HCO, and CO7-, see Section 6.2.1.3). Once there, it may precipitate as solid calcium carbonate (limestone). Corals and algae encourage this reaction and build up limestone reefs in the process, but a much larger portion in the deep sea equilibrates only at the slow rate of... 

Calcium Calcium is an essential element for humans, especially in maintaining healthy bones and teeth. Calcium is found widely in nature, mainly combined with carbon and oxygen in calcium carbonate. This compound is the main ingredient in rocks such as limestone, chalk, and marble. Coral reefs build up from calcium carbonate exoskeletons that are created by marine animals called corals. Calcium carbonate is used in antacid tablets and as an abrasive in toothpaste. An abrasive is a hard material used to polish, smooth, or grind a softer material. Emery boards and sandpaper are examples of abrasive materials. 

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. 

Scoffin, T.P. McLean, R.F. (1978) Exposed limestones of the northern province of the Great Barrier Reef. Philosophical Transactions of the Royal Society of London A291, 119-138. 

Fig. 7. Schematic north—south cross-section through San Antonio and the Muil Field (see Fig. 1). Jurassic and Lower Cretaceous sediments (the aquifer ) are shown by the limestone Pattern since most are carbonates. They are overlain by Upper Cretaceous clay and chalk. The northern-most outcrops are associated with the Balcones Fault zone near San Antonio. The shallow part of the section is underlain by Paleozoic basement , or by Triassic rocks further south. Jurassic salt is shown by solid hatchures. Darkened areas at A, B and C depict the three producing zones, the Stuart City Reef Trend (the carbonate platform margin), the Karnes Trough and the Atascosa Trough, respectively. Note the faulting associated with them. The temperature axis is speculative below 5 km.

Calcium carbonate is currently more actively studied in aqueous solution. Earth s oceans are saturated with Ca2+ ions, especially near the surface. The calcium is delivered to the oceans mostly by rivers and streams. (As rocks weather, calcium ions are released and attracted to water molecules.) Because there is such a high concentration of calcium ions in the oceans, it easily precipitates out as calcium carbonate or, less commonly, as calcium sulfate. The precipitate contributes to the formation of coral reefs in warm lagoons and shallow tropical seas. Inland salt seas and lakes, such as the Dead Sea in Israel, the Great Salt Lake in Utah, and Mono Lake in eastern California, often have whitish limestone deposits around their shores. (All of these bodies of water are saltier than the oceans.) Softer deposits tend to be called chalk. In locations where spring water bubbles up through the floor of a salty lake, mounds of limestone, called tufas,... 

Calcite is also crucial to aquatic organisms like oysters, claims, snails, corals, and sea urchins that use it to build their shells. As these shellfish die, their shells add to the coral reefs and to the layers of limestone already building up on the ocean floor. Eons later, the sea floor rises and the limestone layers become geological features of valleys, canyons, and mountains. Because CaC03 is an important component of corals and shells, these sedimentary materials often contain the fossil remains of once-living organism. 

Traps associated with salt intrusions are of many types (example Fig. 1.2 -1.3) limestone reefs (Fig. 1.4) can also serve as reservoir rocks and give rise to overlying traps of anticlinal form as a result of different compaction. Examples are also known in which the reservoir rock extends to the surface of the earth but oil and gas are sealed in it by clogging of the pores by bitumen or by natural cements [3], Many reservoirs can display more than one of the factors that contribute to the entrapment of hydrocarbons. 

Consider just a few cases of aqueous equilibria. The magnificent formations i n limestone caves and the vast expanses of oceanic coral reefs result from subtle shifts in carbonate solubility equilibria. Carbonates also influence soil pH and prevent acidification of lakes by acid rain. Equilibria involving carbon dioxide and phosphates help organisms maintain cellular pH within narrow limits. Equilibria involving clays in soils control the availability of ionic nutrients for plants. The principles of ionic equilibrium also govern how water is softened, how substances are purified by precipitation of unwanted ions, and even how the weak acids in wine and vinegar influence the delicate taste of a fine French sauce. In this chapter, we explore three aqueous ionic equilibrium systems acid-base buffers, slightly soluble salts, and complex ions. 

At limestone dolomitization porosity increases by 12-13% (Domenico and Schwartz, 1997), which promotes increase in rock porosity and permeability. Dolomitized reefs in Western Canada have average porosity by 1%, and permeability by the factor of 10 higher than non-dolomitized ones. 

The principal carbonate minerals are calcite (CaC03), magnesite (MgC03), dolomite [MgCa(C03)2], and siderite (FeC03). Calcite is the principal mineral in limestone and the main constituent of marble, chalk, pearls, coral reefs, and the shells of marine animals such as clams and oysters. Although CaC03 has low solubility in pure water, it dissolves readily in acidic solutions with evolution of CO2 ... 

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