BSc 4 th Semester Open Elective Other than Geology main students Dr Abdullah Khan Associate Professor Department of Geology AMU Sedimentary structures Sedimentary structures are generally threedimensional physical features of sedimentary rocks they are best seen in outcrop or in larg ID: 1021347
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1. Primary and Secondary Sedimentary StructuresBSc 4th Semester (Open Elective)Other than Geology main students Dr Abdullah KhanAssociate ProfessorDepartment of Geology, AMU
2. Sedimentary structuresSedimentary structures are generally three-dimensional physical features of sedimentary rocks; they are best seen in outcrop or in large hand specimens rather than through a microscope. Sedimentary structures include features like bedding, ripple marks, fossil tracks and trails, and mud cracks.Sedimentary structures are those structures formed during or just after sediment deposition.
3. TYPES SEDIMENTARY STRUCTUREPRIMARY SEDIMENTARY STRUCTURESECONDARY SEDIMENTARY STRUCTURE
4. PRIMARY SEDIMENTARY STRUCTUREStructures that are produced during formation of sedimentary rock in which they occur are called as primary sedimentary structures.Examples include bedding or stratification, graded bedding, cross-bedding, Ripple marks etc.Sedimentary structures that are produced shortly after deposition and as a result of compaction and desiccation are called penecontemporaneous sedimentary structures. Example mud cracks
5. Still other sedimentary structures like concretions, stylolites which form well after deposition and penecontemporaneous modification; these are known as secondary structures.
6. Stratification (or bedding)Stratification (or bedding) is expressed by rock layers (units) of a general tabular or lenticular form that differ in rock type or other characteristics from the material with which they are interstratified
7. Graded beddingGraded bedding simply identifies strata that grade upward in term of clast size.
8. Cross Bedding Cross Bedding: These are stratification which lie at certain angle from main bedding plane.Types (Planar and Trough Cross Bedding)
9. Ripple Marks Ripple marks are the wavy undulationsThey are formed under shallow environment Types (Symmetrical and Asymmetrical Ripple marks)
10. Mudcracks (Pn. Str.)Mudcracks are sedimentary structures formed as muddy sediment dries and contracts. Crack formation also occurs in clayey soils as a result of a reduction in water content.
11. Concretions (Sec. Str.)They are formed by chemical precipitation of mineral around a centre, forming a globular mass. On cutting a slice concentric bands can be observed.
12. StylolitesStylolites are stylus-like, as seen in cross-section, it seams result from the irregular, interlocking penetration of rock on each side of the suture.They form as a result of pressure solution.