Introduction to Sedimentary Rocks:
About 70 percent of rocks in earth surface have sedimentary origin and usually these rocks are formed from sandstones, limestones, shales and a few amounts of saline deposits, ironstones, coal and chert.
Sediments after precipitation are under effect of diagenesis process, and this process is in three physical, chemical and biological forms and cause compaction, cementation, recrystallization and other changes in primary sediments. There are many reasons for sedimentary rocks study, since economical value of minerals and available materials is not too much.
Many factors control sedimentation, effect on them and determine kind of produced sedimentary rock and facies. In total scale, important factors of controlling include:
A) Sedimentary Process B) Sedimentary Environment C) Tectonic Position D) weather
Water depth, amount of turbulence and salinity are important physical factors in subaqueous environment and these factors have effect on creatures life in or on the sediment or those form Eh potential of sediments. Chemical factors such as acidity- alkalinity of surface water and intravesicular water have influence on oxidation- reduction, PH and living organism, and also control minerals precipitation. Supplying sediment with low rate, is important and suitable for producing limestones, evaporate rocks, phosphates and ironstones, and high amounts of producing organic materials is important in forming limestones, phosphates, cherts, coal and oil shale. Another factor that is effective in sedimentary facies is world position of sea level and its relative changes.