Sedimentology Lecture Series - Residual deposits

 Residual deposits

What is it?

The residual deposits are the insoluble products of rock weathering which have escaped transportation. They are found over the rocks from which they have been formed. The rocks belonging to this class are made up of two components.

• Unaltered minerals from the original rock

• The insoluble products of chemical weathering.

Its texture?

The residual sediments are composed of unsorted and angular materials as they have not suffered transportation. The grain size of the deposits are determined by the nature and grain size of the weathered rock. 

Some of its types:

(a) Terra Rossa:

This deposit is found in limestone countries in arid regions. Terra rossa is a reddish clayey soil covering the limestone country rock. constituting the insoluble residue of clay and other mineral matter after removal of the limestone by solution. In areas of comparatively high rainfall, the terra rossa is washed into depression, swallow holes and caves soon after its formation. The bones of Pleistocene animals and relics of primitive man are often found buried in this deosits.

(b) Laterite and Bauxite:

Laterite is a reddish brown porous concretionary deposit made up of chiefly a mixture of hydrated ferric oxide with hydrated alumina in various proportions. It also contains in small quantities manganese chloride, titanium dioxide and free silica (quartz). The deposit covers vast areas in tropical and subtropical regions i.e. the formation of laterite is favoured by warm and humid climate. When the alumina content increases the red colour disappers and it becomes yellowish or whitish with earthy or clay like appearance. This rock is called Bauxite (Beaux, in the south of France).

Want to know more check out this video.

• References:
• Sengupta S M., Introduction to sedimentology (Second edition)
• Pettijohn, F.J. – 1967 – Sedimentary Rocks, Harpers and Bros
• Gary Nichols, 2009 – Sedimentology and Stratigraphy, John Wiley and Sons
• Sam Boggs, 2006 – Principles of sedimentology and stratigraphy, Pearson Prentice Hall