Sparit

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A biopel parit, d. H. a sparitic limestone with bioclasts and peloids as main components, in thin section . While the micritic peloids appear dark, the sparitic cement is translucent and correspondingly light.
Concentric Sparitic cavity fillings (white, gray) in a polished section of a Devonian carbonate rock from the Massif Central (France)

Sparit (from English: sparry calcite 'late calcite') is fine to small crystalline calcitic cement which , as a result of precipitation from a pore solution, fills the gaps between the coarse-grained constituents (components) of a limestone . Often the cleavage surfaces of the sparit crystals cause a glitter on fresh fracture surfaces in the corresponding rocks.

General

The minimum size of sparite crystals is set at 4 µm, since below this size a clear distinction between diagenetic formations and the finest among the primary carbonate sediment particles of the so-called matrix (see →  Micrite ) is difficult. Together with all the particles in the matrix (<63 µm), sparit forms the basic mass of a limestone. However, whether sparite is actually present in the base mass depends on the ratio of the matrix to the coarser primary constituents, the components (> 63 mm), because this has an influence on the size of the pore space. A high proportion of components and a low proportion of matrix result in a large pore volume. On the one hand, a high pore volume enables the free circulation of solutions in the sediment, from which sparitic cement can precipitate, and on the other hand it offers space for cement to precipitate. Limestone with a high proportion of a particularly fine-grained matrix and a low proportion of components therefore usually has no or only a small proportion of sparitic cement.

However, sparit does not necessarily have to have failed as the primary cement. Particularly in the case of geologically older and heavily diagenetically overprinted limestones, sparit is not infrequently the result of recrystallization of the originally micritic matrix. In these cases one also speaks of pseudosparite .

Folk carbonate classification

Limestones, the basic mass consists mainly of sparite crystals are (1962) in the Karbonatklassifikation by Folk Sparite mentioned. The further naming depends on the type of coarser constituents (components) of the rock: intrasparites consist largely of clasts , oosparites of ooids , biosparites of biogenic components such as brachiopod or mussel shells . Pelparites and oncosparites primarily contain peloids or oncoids as components. If the rock has two types of main components, combinations such as intrabiosparite are also possible.

literature

  • Roland Vinx: Rock determination in the field. Elsevier, Munich 2005, ISBN 3-8274-1513-6
  • Hans Füchtbauer: Sediments and sedimentary rocks . 4th edition. Schweizerbart'sche Verlagbuchhandlung, Stuttgart 1988, ISBN 3-510-65138-3 .

Web links