structure of sedimentary rocks

Structures of Sedimentary rocks:

·        Shallow water deposit structures 200 meter depth in sea.

A.    Bedding or Stratification Structure:

Sediments are deposited layer upon layer when two successive layers differ from each other in grain size, color, texture.

• Each layer is called bed, or stratum and structure is called bedding.

Sedimentary rocks are stratified rock. The bed may be few mm to many meter in thickness. If thickness is less than 1 cm are called laminae and lamination Structure.It shows by shale. Contact of two beds is called as bedding plane or junction.

B.  Gradded bedding:

Regular stratification according to size from bottom to top is called gradded bedding.

C.  Concordant bedding :

If layers approx. Parallel to one another is called concordant bedding.

D.  Discordant/current/false/cross/torrential bedding

Bedding plane which are inclined to the major lines of bedding is called discordant bedding. Due to rapid change in direction, velocity of stream which carrying sediments

E.   Ripple marks :

They are well known wavy pattern seen on sandy beaches and under special conditions may be preserved in the sediment. Ripple produced by current of action of water.

F.   Rain Prinks :

G.  Tracks and Trails :

Welding and cementation:

     When first formed sediment are loss, soft and unconsolidated but in course of time, they become firm, hard, compact this is due to chiefly two processes.

A.  Welding or compaction or indurations :

In welding the material is consolidated by pressure which may be due to either load of above laying rocks or to earth movement. All water squeezed out by pressure and grains strongly together as they are brought within the limit of molecules concentration. It is effective in fine grained as compared with coarse grain.

B.  Cementation :

In cementation water circulating in rocks deposit in the empty spaces between grains. The dissolved substance carried in a solution.

These act as cement and held together the loose grains so that hard compact rocks are formed. Common cement is silica, calcium, magnesium, carbonates and iron oxides. The degree of cementation depends on age. The older the sediment the higher the degree of cementation. Cement is responsible for porosity and permeability of rocks.