Process of Transport and Generation of Sedimentary Structures

sedimentary structures ,sedimentary rocks ,weathering and erosion ,sediment transport mechanism ,hjulstrom curve ,types of flow of sediments ,reynold number ,froude number ,laminations ,bedding plane ,cross bedding ,herringbone structure ,ripple marks ,graded bedding ,sole marks ,mud cracks ,ball and pillow structures ,stylolites ,concretion ,nodules

1. PROCESS OF TRANSPORT AND GENERATION OF SEDIMENTARY STRUCTURES AKSHAY D. RAUT M.Sc. SEM- 3, K.S.K.V. KACHCHH UNIVERSITY

2. SEDIMENT Sediment is solid material that is moved and deposited in a new location Sediment can consist of rocks and minerals, as well as remains of plants and animals. It can be as small as a grain of sand or as large as a boulder. Sediment is produced by the weathering and erosion of preexisting rock bodies. Once formed, sediment is transported to a new area where it is deposited as layers that are subsequently lithified to form sedimentary rocks.

3. GENERATION OF SEDIMENTARY ROCKS

4. WEATHERING Weathering is the breakdown or decomposition of preexisting rock body. Three types of Weathering 1) Physical Weathering 2) Chemical Weathering 3) Biological Weathering

5. PHYSICAL WEATHERING

6. CHEMICAL WEATHERING

7. BIOLOGICAL WEATHERING

8. EROSION Erosion  happens when rocks and sediments are picked up and moved to another place by different transporting agents. Transporting Agents involved in the process are- Wind Water Ice, etc.

9. TRANSPORT Once sediment has been eroded, it is moved to a new location by water , wind, ice, or mass movement. Sediment Transport Media 1 . Water- Overland flow, channel flow Waves, tides, ocean currents 2. Air ( small particles) 3. Ice 4. Gravity- Rock Falls Debris flows

10. Sediment Transport Mechanism Fluid Flow 1) Traction - Rolling over the bed surface 2) Saltation- Jumping over the bed surface 3) Suspension – Permanent transport within the fluid 4) Solution- Chemical Transport

11. Gravity Flow Grain Flow - Cohesionless Sediment movement Debris Flow - Viscous sediment Movement Liquefied Flow - over-pressured interstitial fluid movement Density/turbidity Flow : slurry movement driven by differential density

12. Hjulstrom curve Hjulstrom curve used to determine the Erosion, Transportation and Deposition of sediments .

13. TYPES OF FLOW OF SEDIMENTS 1. Laminar Flow 2. Turbulent Flow 3. Transition Flow

14. Laminar Flow- Sediment followed a straight path that was parallel to the boundaries. Transitional Flow- Sediment followed wavy but parallel path that was not parallel to boundary path. Turbulent Flow- Sediment followed very complex path

15. Reynolds Number Reynolds number is used to check whether flow is laminar or turbulent using following formula Where, Ρ is the density of the fluid, V is the velocity of the fluid, Μ is the viscosity of fluid, L is length of the fluid The Kind of flow depends on value of R e If Re < 2000 the flow is Laminar If Re > 4000 the flow is turbulent If 2000 < Re < 4000 it is called transition flow.

16. FROUDE NUMBER Froude number describes different flow speed and can be find by using following formula Where: V =  Water velocity D = Hydraulic depth (cross sectional area of flow / top width) g = Gravity When: Fr = 1,     critical flow, Fr > 1,     supsercritical flow (fast rapid flow), Fr < 1,     subcritical flow ( slow flow )

17. Primary Sedimentary Structures Formed at time of sedimentation. These can be classified on the basis of following criteria- Bedding Geometry Bedding of internal Structure Bedding Plane Markings Deformed Structures

18. Bedding Geometry 1. Lamination : Beds with thickness less than 1cm is called laminae. They are characterised by fine grained sediments. 2. Wavy Bedding : Wavy bedding occurs when mud is deposited over the whole area of a bed of rippled and/or cross stratified sand.

19. TERMINOLOGY OF BED THICKNESS

20. DIFFERENT TYPES OF BEDDING OR LAMINATIONS

21. Flaser bedding is where cross-laminated sand contains mud streaks, usually in the ripple troughs. These are commonly forms in relatively high energy environments Wavy bedding is where thin-ripple cross-laminated sandstones alternate with Mudrock are commonly forms in environments that alternate frequently from higher to lower energies Lenticular bedding is where mud dominates and the cross-laminated sand occurs in lenses. They are commonly forms in relatively low energy environments.

22. B. Bedding of internal structures : Cross Bedding : When the flow has changed the direction, the structure is known as Cross Bedding. Cross bedding forms on a sloping surface such as  ripple marks  and  dunes, and allows us to interpret that the  depositing agents were water or wind.

23. Basically , two main types of cross-bedding can be defined by the geometry and their bounding surfaces: i. Planar or Tabular planar cross-bedding, and ii. Trough cross-bedding.

24. Herringbone cross-bedding – Herringbone cross-bedding is produced by reversals of the current, causing dunes and sand-waves to change their direction of migration. C ross-bed dips of adjacent sets are oriented in opposite directions

25. RIPPLE MARKS Ripple marks are small marine, lake or riverine topographic features, consisting of repeating wavelike forms with symmetrical slopes, sharp peaks and rounded troughs. There are mainly two types of ripples 1. Symmetrical Ripple Marks 2. Asymmetrical Ripple Marks

26. Graded Bedding : In Graded bedding the gran size within a bed decreases upward. Coarse material deposited first and finer material deposited later. There must be repeated depositional events with changes in precipitation of materials over time

27. C. BEDDING PLANE MARKINGS When beds separate along bedding planes, the surfaces produced commonly display various markings and structures . Sole Marks – These are markings found on the lower side of the beds . Types of Sole Marks- Scour Marks Tool Marks

28. Scour Marks- They mainly form due to current action. They are produced by cutting action of a current of water flowing over the bottom. E.g.. Flute Marks Tool Marks- They are produced by object carried by the flow interacting with the bed rather the flow itself. E.g. Grooves Scour Marks Tool Marks

29. Surface Marks : Markings present on the surface of beds. Mud Cracks : This sedimentary structure forms as muddy sediments dries and contracts. Crack formation occurs due to reduction in water content. Some irregular polygonal fractures are present on the surface of beds.

30. D. Deformation Structures – Gravitational displacement may occur during sedimentation or shortly there after, which deform the depositional structure. 1. Load Cast – These are the structures produced by sinking of heavier into lighter sediments.

31. 2. Ball and Pillow Structures – Ball-and-pillow  deformations are a result of a physical shock that has been applied to unconsolidated sediment. This shock causes rupturing to occur in the sedimentary rock layer, which induces instability. Individual lobes caused by break off move downward, settling into the underlying layers . These are characterized by hemispherical or kidney shaped masses resembling balls and pillows.

32. CHEMICAL SEDIMENTARY STRUCTURES The Structures formed by chemical processes such as oxidation, reduction, precipitation and evaporation, etc. 1. Stylolites- These are surfaces within a rock mass at which mineral material has been removed by pressure dissolution, in a process that decreases the total volume of rock.

33. Nodules- A nodule is generally spherical or irregularly rounded in shape. These are typically solid replacement bodies of chert or iron oxide. Concretion- A concretion is a hard, compact mass of matter formed by the precipitation of mineral cement within the spaces between particles

34. THANK YOU !!