Oolitic sand

A) Horizontal beds forming a transition from floodplain deposits to a palustro-lacustrine environment and lacustrine limestones. (B) Lacustrine deposits with stromatolitic bioherms (C) Palustrine limestone with abundant root traces. (D) Lacustrine bottom-set sediments enriched in organic matter and showing thin turbiditic layers. (E) Palustrine limestone with a well developed palaeosol at the top. (F) Various types of crushed shell fragments in a lacustrine mud. (G) Lacustrine bioclastic and oolitic sand deposited near a shore. 

Nonskeletal carbonates Oolite sand (Ot) Aragonite needles (At)... 

Eisen-reihe, /. iron aeries, -refin, -resinit, m. (Min.) humboldtine. -rhodanid, n. ferric thiocyanate, iron(III) thiocyanate, -rho-daniir, n. ferrous thiocyanate. iron(II) thiocyanate. -rogenstein, m. oolitic iron ore. -rohr, n., -rohre, /. iron pipe or tube, -rost, m. iron rust, -rostwasser, n. iron liquor, iron mordant, -rot, n. colcothar. -safraQt m. saffron (or crocus) of Mars, -salmiak, m. (Pharm.) ammoniated iron, iron and ammonium chloride, -salz, n. iron salt, -sand, m. ferruginous sand, -sau, /. iron sow. 

Bedded Ores. These often are composed of oolites of hematite, sidcrite. iron silicate, or less commonly, limonitc in a matrix of sideriie. calcite. nr silicate. They have a wide geographic distribution associated with cither sedimentary rocks. They sometimes contain fossils and line grains of sand. They nften have a fairly high phosphorus content and may he self-fluxing. 

In nature, a series of minerals are known to interact with organic substances, notably carbohydrates and amino compounds103-108. In the context of this discussion the dominance of acidic amino acids in oolites is significant109-111. Oolites are spherical bodies up to 1—2 mm in diameter which are chemically precipitated in tropical lagoons, e.g. Bahamas, Bermudas and Red Sea in the form of aragonite and accumulate as fine sand. The process of precipitation is a slow one and may proceed over a period of a few hundred years. 

Figure 8.33. Porosity-age relationships for odlitic grainstones. Notice that although the average porosity of these calcareous sands does not change significantly for a million years, the older oolites exhibit a spread in porosity because of dissolution-precipitation events. (After Scholle and Halley, 1985.)...

Bathurst R.G.C. (1967) Oolitic films on low energy carbonate sand grains, Bimini Lagoon, Bahamas. Mar. Geol. 5, 89-109. 

Fig. 4 Scheme of the bottom sediments of the Aral Sea [10]. (1) Sand (2) oolitic-calcareous sand (3) coarse silt (4) fine silt (5) clayey-calcareous mud (6) deltaic clayey mud of the northern bays and small Sea... 

Bottom sediments in the depressions of the Aral Sea are clayey-calcareous mud - a homogeneous mineral mass enriched with diatoms fmstules, with inclusions of hydrotroilite and pyrite. There are areas of oolitic calcareous sands along the eastern sea coast. 

Chemical sediments are created by a precipitation of low temperature/pressure minerals from water solution onto a depositional surface or within sediment pores. Depending on the acidity, oxidation, temperature, or salinity, a variety of chanical sedimentary rock may result. Examples of chemical sediments include carbonates, evaporites, opal, chert (may form in other ways too), iron oxides, and aluminum oxides. Chanical textures are usually o-ystaUine with some special terms, such as oolitic or pisolitic. Sandstone is a clastic sedimentary rock made up mainly of sand-size (1/16 to 2 mm diameter) weathering debris. 

A fairly common variety of limestones in this category are the oolitic limestones, which are composed of so-called ooliths, i. e., more or less spherical rock particles grown by accretion around a nucleus and of the order of 1 mm in diameter. These calcareous ooliths are formed in shallow water (less than about 2 m depth) subject to considerable motion. When a certain amount of lime has been deposited around the nucleus (which may be a grain of sand or a shell fragment), the oolith sinks to the bottom by gravity. Portland limestone belongs to this type. 

Particle shape grains of bioclastic carbonate sand may be curved (shells), platy, thin-walled, flaky and hollow or porous (intra-particle porosity) and often have a high angularity, while oolites generally are rounded and massive (see Figure 9.21). 

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