Primary sedimentary structures

helpfull for Geology student

1. Topic Primary sedimentary structures Prepared by Azhar Mahmood

2. Primary sedimentary structures Structures acquired during deposition of sedimentary rock unit are called as primary sedimentary structures.

3. Uses of primary sedimentary structures. These are useful for maping purpose. These are useful to mark paleocurrent direction. These are also use for marking of top and bottom of strata. Environment of deposition can also have been marked by primary sedimentary structures. Relative age is also marked by them.

4. Primary Sedimentary Structures Stratification - horizontal bedding is most common structure in sedimentary rocks

5. Primary Sedimentary Structures Cross-bedding - inclined stratification recording migration of sand ripples or dunes

6. Primary Sedimentary Structures Ripples - undulating bedforms produced by unidirectional or oscillating (wave) currents

7. Ripple marks

8. Uses Asymmetrical ripple marks describe the past flow direction Symmetrical marks top and bottum

9. Primary Sedimentary Structures Graded bedding - progressive decrease in grain size upward in bed • indicator of upwards direction in deposit • common feature of turbidites

10. uses It,s useful for maping purpose. These are also use for marking of top and bottom of strata.

11. Primary Sedimentary Structures Sole marks - erosional grooves and marks formed by scouring of bed by unidirectional flows • good indicators of current flow direction

12. Primary Sedimentary Structures Fossils – preserved remains of organisms, casts or moulds • good strain indicators • determine strain from change in shape of fossil • relative change in length of lines/angle between lines

13. Rip-ups  are pieces of   shale  or  mudstone  created when an erosive current containing suspended sediment flows over a shale bed, tears up pieces of it, and carries these "rip ups" some distance

14. uses Use for top and bottum Use for determine relative age

15. Rain-pits  are a geological feature characterized by small craterlike pits with slightly raised edges that are the result of the impact of rain on soft sediment surfaces

16. Mud Cracks are polygonal cracks that form when mud shrinks as it dries. They indicate that the mud accumulated in shallow water that periodically dried up.

17. uses It,s tell us Top and bottum Environment [Arid,Semi Arid] Condition

18. Pebble Imbrication Imbrication is the orderly, overlapping arrangement of flattened or sub-spheroidal grains in the direction of flow. Flow in this case is usually water flow, but it can be other types of fluid flow

19. Uses To determine paleo-path of rivers and channel Current direction {which is always opposite to dip direction}

20. Flute Cast When a river flow in the center of river V type structure formed by loose material are called flute cast

21. Soft Sediment Deformation In it deformation as well as sedimentation carried out side by side S.S.D = Deformation + Sedimentation Types 1: Slump fold 2: Flame structures 3: Clastic Dikes

22. a. Slump Fold A  slump  is a form of  mass wasting  that occurs when a coherent mass of loosely consolidated materials or rock layers moves a short distance down a slope Movement is characterized by sliding along a concave-upward or planar surface. Causes of slumping include earthquake shocks, thorough wetting, freezing and thawing, undercutting, and loading of a slope

23. b. Flame structures A term introduced by Walton (1956, p. 267) for a sedimentary structure consisting of sharp-crested wave- or flame-shaped plumes of mud that have risen irregularly upward into an overlying layer, generally a rapidly deposited sand

24. c.Clastic Dikes A  clastic dike  is a seam of  sedimentary  material that fills an open  fracture  in and cuts across  sedimentary rock   strata  or layering in other rock types. Clastic dikes form rapidly by fluidized injection (mobilization of pressurized pore fluids) or passively by water, wind, and gravity 

25. d. Contour Bedding

26. e. Growth Fault  They extend parallel to  passive margins  that have high  sediment  supply. Their fault plane dips mostly toward the basin and has long-term continuous displacement