Sedimentary rock cementing process

Stratigraphic traps are formed by depositional and sedimentary factors. In such traps the depositional process and the follow-on cementing process, which changes the sediment bed into a rock, create porosity and permeability alterations in geometric forms that provide traps. 

Diagenesis is the set of processes by which sediments evolve after they are deposited and begin to be buried. Diagenesis includes physical effects such as compaction and the deformation of grains in the sediment (or sedimentary rock), as well as chemical reactions such as the dissolution of grains and the precipitation of minerals to form cements in the sediment s pore space. The chemical aspects of diagenesis are of special interest here. 

Diagenesis—Compaction, cementation, and other processes that transform sediments into sedimentary rock at low temperatures. 

Sedimentary rock—Rock formed by deposition, compaction, and cementation of weathered rock or organic material, or by chemical precipitation. Salt and gypsum form from evaporation and precipitation processes. 

Cementation The diagenetic process whereby clastic sedimentary grains are lithified or consolidated into sedimentary rocks, often by mineral deposition or precipitation on the grain surfaces or in the interstitial spaces. 

Sediments on the surface of the Earth may form in several ways (1) by mere mechanical accumulation (via wind or water), such as gravel and sand deposits in a river or sand dunes in a desert (2) by chemical precipitation, such as salt and calcite precipitation in shallow seas and lakes and (3) by activity of organisms, such as carbonate accumulation in coral reefs or the accumulation of organic matter in swamps (coal precursor). Sediments are typically deposited in layers or beds called strata. When sediments become compacted and cemented together (a process known as lithification), they form sedimentary rocks. This compaction or lithification of sedimentary materials into stratified layers is probably the most significant feature of sedimentary rocks. 

The most common nonphosphalic accessory minerals associated with sedimentary phosphate rocks are quaife— clays, and two carbonates dolomite (CaMg(C03)2) and calcite (CaCOs). Carbonate-cemented phosphate rocks are particularly noteworthy because of their abundance. McClellan and Gremillion [14[ estimated that there are 3 tonnes of carbonate-cemented phosphate rock for every tonne of ore that could be handled by conventional milling and flotation processes (quartz- and clay-containing phosphate rocks). 

---