#Geology #Petrology #Sedimentary #Limestone #CarbonatePetrology #Biochemicalrocks #Sedimentology
Origin:
precipitation of minerals from water through various chemical or biochemical processes.

Five Fundamental types:
(1) Carbonates,
(2) Evaporites,
(3) Siliceous sedimentary rocks (cherts),
(4) Iron-rich sedimentary rocks,
(5) Phosphorites.
(6)Coal and Oil Shales
Oil shale, like all shales, contains not only clay, but also
between 25% and 75% organic material in a form called Kerogen.
Most Abundant : Carbonate Rocks
1. Precambrian and Paleozoic-dolomite,
2. Mesozoic and Cenozoic carbonates-limestone.

Importance :
1. Limestones contain richly varied textures, structures, and fossils that yield important information about ancient marine environments, paleoecological conditions, and the evolution of life forms, particularly marine organisms, through time.

2. Carbonate sedimentary rocks are also an economically important group of rocks because limestones and dolomites are useful for agricultural and industrial purposes, they make good building stones and, most importantly, they act as reservoir rocks for more than one-third of the world’s petroleum reserves.

3. The elemental chemistry of carbonate rocks is dominated by calcium (Ca2+), magnesium (Mg2+), and carbonate (CO3 2-)ions. Calcium and magnesium are present in both limestones and dolomites; magnesium is a particularly important constituent of dolomites.

Components and Classification:

1. Allochemical : any grains of calcium carbonate that, after formation, are transported and deposited as clasts. e.g. Ooids and Bioclasts

2. Orthochemical: These are not transported and deposited as clasts. Orthochems are found precisely where they formed or have been moved only a short distance.

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