Sedimentary Structures in Petroleum Geology

Sedimentary structures

These are formed by mechanical and physicals process. It includes -

1.  Bedding 
2. Cross Bedding (Current Bedding)
3. Ripple Marks
4. Graded Bedding
5. Mud Cracks
6. Cruscentic marks
7. Rain Drops
8. Convolute Bedding
9. Scour Marks

1. Bedding

It is the arrangement of the rock mass, into distinguish layer, these are 3 types of bedding. 1. Lamination bedding - whose thickness is less than 1 cm. , 2. Stratum - whose thickness greater than 1 cm and 3. Massive Beddive :- Which is apparently structure less.

2. Cross Bedding / Current Bedding  

It is the sedimentary structures, the various layer line one or another are not parallel, but bear an irregular relationship to each other. This structure indicates rapid changes - Velocity and direction of the wind caring the sediment. In cross bedding the minor beds are inclined and stacked up in the direction of the prevailing wind. 

3. Ripple Marks

These are wavy undulations seen on the surface of the bedding plains. These structures may be form on the surface of the deposit formed by wind. Ripple marks are two types -

• Symmetrical RM 
• Asymmetrical RM

4. Graded Bedding

Here each bed shows of, variation ingrain size, from coarse below to fine above  -- When the sequences of rock is made up of such graded layer. This structure is known as graded bedding. Normally such perfectly graded beds are the result of the sedimentation, In bodies of standing water, where the factor of gravitative settling from a mixed sediments loud is the predominant process. This structure is generally found in Graywacks ( Gray-wacks )

5. Mud Cracks 

The structure consist of polygonal or irregular cracks which straight along the surface of an exposed sedimentary layer mud cracks are developed due to dissication ( state of extreme dryness ) at close and compact of water saturated body sediment. The size of the polygon varry in with  from a few mm to over 30 cm, they make penetrate to a depth of 1 to 2 cm of several tons of metre.

6. Rain Drops Imprints

Rain drops falling on soft sediment surface makes small impact craters, which is circular If the rain falls vertically downward & slightly elliptical if the path is obliged to the surface.

This may get dried up and subsequently preserved, this imprints became a part of deposition.

7. Crescentric Marks 

These are produced on the consolidated sediment surface around obstacles such as peddles, shells, or wood fragments. In the path of water flow the obstacle line on the way of the current tend to deflect the flow-line, which results either a erosion or deposition or both below the obstacle.

8. Scour Marks 

These are produced as a result of erosion of sediment surface by the current flowing over it. The soft but cohesive type sediment generally mud, id sculptured by the scouring action of current.

9. Convolute Bedding

Con volute bedding shows crumbling or complicated folding layer. Con volute bedding shows more or less sharp crest, alternating with bladder  trough.

It is generally develop fine grain non cohesive sediment.

Notes:- Data is collected from different university class notes . Main purpose to write this articles is to help peoples.

Article Written by-

Ritu Raj Medhi

Founder & President

Chief technical & editorial officers 

Petroleumbuddy websites and initiatives

 

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