a. A foraminifera biomicrite ( eocene ) italy. Diam 3 mm. Abundant foraminifera in a matrix of microcristalin calcite ( stiipled ) orbitoids predominate but a variety of outher form is included.

b. Gastropoda biomicrite Ulm, germany diam 3mm. Fresh – water limestone containing abundant whole and broken planorbis shell. Matrix is turbid microcrystalin calcite ( dark stippling ) containing patches of clear coarser calcite. Larger shells were partly filled with carbonate mud at time of deposition. Voids remaining within shells and also cavites under shell fragments were later filled with coarser spar as a result of authigenic preciptation. The filling within several shells is a example of gropelal structor. Contact between microcystalin calcite and sparry calcite within shells is the beedding surface and is shown right side up.

c. trilobite sparite ( sillurian ) norway diam 3 mm. Very abudant carapaces of the trilobite olenus enclosed in sparry calcite cement in which crudely collumnar cristal stand apporoximetely normal to the shell surfaces.

Biolithite or bounds tone even though other organism and fragmental material may predomite. These names are proper however, only if the reef – forming skeletal structure is intact in growth position the names should not be used for broken chunks of reef rock, however large that occur as fragments in many calcirudites.

Laminated boundstones or biolithites, produced by filamentous algae are called stromalites. They retain no recognizable organic skeleton and are characteristic instead by millimeters – thin carbonate laminae some of which clearly formed at angles that would be impossible under the influence of gravity alone. Algal stromatolites have a variety of configuration. And they have been classified by the geometry of the laminated structure. Which is a probably related to the particular condition under they were formed. Some are crinkled matlike layers or lenses of laminated micrite. Others consits of cabbagelike neads or stack of laminated micrite more or less linked together, some are discrete laminated spheroids called oncolites or algal pisolites. These deposits are presumed to be analogous to modern deposits formed by filamentous green and blue green algae, which produce stick organic maats that as they continue to grow trap successive films of line sediments and thus produce a succestion of very thin laminae. At the time of deposition the sediment is bound bay the algal filaments but when the organic material has decomposed only laminated sediments remains. Algae deposits of this tipe form today in a wide range of enviroments and are particullary characterictic on tidal flats and on very shallow bottoms near shore.

Microcristalin limestones

Most exccedingly fine – grained limestone originated as carbonate mud ooze and have since been firmly lithified in hand spesiment they are dull and opaq, in they section they are subtransculent. And dark ussually brownish. Limestone of the kind are called micrite. Carbonate mudstone or calcilutite. Those of ultrafine grain and very uniform texture because of their use the thecnology of printmaking are called lithograpich limestone.

Carbonate muds consists of particles that originate both by inorganic and organic precipitation and also by physical disintegration and abrasion of skeletal material. In the marine enviroments, they appear to the largelly of biogenic origin. Regardless of how they were produced in great abudance in warm seas and many lakes and they have accumulated on the bottom wherever turbulence was insufficient to put them in suspension and currents were too weak to carry them away. Areas of this kind incluted much of the open sea floor as well as low – energy areas in shallows shelf seas, but there accumulate in these two.