Useful notes on Inorganic precipitates as Source of Marine Deposits
According to Sverdrup, inorganic precipitates are not found in large quantity in marine sediments, even then they may form conspicuous and diagnostically important components.
The inorganic precipitates comprise phosphorite, glauconite, carbonates, dolomite, amorphous silica, manganese iron oxide and barite nodules. It is to be remembered that inorganic precipitates are formed when, according to Sverdrup, the solubility product of some substance is exceeded.
The temperature changes in the sea water bring about certain chemical changes in it as a result of which various types of inorganic substances such as minerals are deposited on the floor. The precipitation of inorganic substances may also be the result of the removal of carbon dioxide where photosynthesis occurs.
It may also be caused by the changes in hydrogen-ion concentration or oxidation-reduction potential caused by the marine animals. These precipitates may also result from evaporation in shallow waters of the lagoons and seas.
Many deposits of amorphous silica found in the sedimentary rocks are thought to have an inorganic marine origin. It is because of the chemical precipitation that iron and manganese oxides in the form of concretions are formed.
Similarly, phosphatic and barite nodules are the result of chemical precipitation in sea water. However, it is rather difficult to draw boundaries between inorganic precipitates and those that are formed as a result of the biological activity.
Some of the substances found in the marine deposits are the products of chemical transformation. Examples of those substances resulting from such chemical changes are glauconite, feldspar, phillipsite, clay minerals, and phosphorite, etc.