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Lecture 2: Stratigraphic data

Lecture 2: Stratigraphic data. Boris Natalin. Stratigrapher uses - Data from surface outcrops - Subsurface data such as cores, well logs, and seismic data Today’s topics are sedimentary rocks and their structures

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Lecture 2: Stratigraphic data

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  1. Lecture 2: Stratigraphic data Boris Natalin

  2. Stratigrapher uses - Data from surface outcrops - Subsurface data such as cores, well logs, and seismic data Today’s topics are sedimentary rocks and their structures Classification of sedimentary rocks:- Clastic (Siliciclastic)- Biogenic- Chemical Sedimentary structures

  3. Sandstone • Clastic sedimentary rocks consist of rock and mineral grains derived from the chemical and mechanical breakdown (weathering) of pre-existing rock. They contain rock fragments and more commonly, particles of quartz and feldspar. Clastic rocks are further classified on  the basis of grain size.

  4. Classification Phi(φ) scale φ= -log2 diameter (in millimeters) 0.0625 mm

  5. Classification • Conglomerates (> 2mm) is consolidated gravel • Boulder (>256mm) • Cobble (65-256 mm) • Pebble (4-64 mm) • Granule (2-4 mm) • Sandstones (0.062-2 mm) consolidated sand • Very coarse (1.0 - 2.0 mm) • Coarse (0.5 - 1 mm) • Medium (0.25 - 0.5 mm) • Fine (0.125 - 0.25 mm) • Very fine (0.0625 - 0.125 mm) • Shales (<0.0062 mm) is consolidated mud, rich in organic matter. • Silt (0.0039 - 0.0625 mm) • Clay (0.0002 - 0.0039 mm)

  6. Conglomerate

  7. Breccia

  8. Shape and Roundness • The degree of abrasion of sedimentary particles

  9. Sorting

  10. Mudrocks or mudstone (<0.06 mm) • Silt • Shale (lithified clay) • Bedded silt or bedded shale (>10 mm) • Laminated silt or laminated shale (<10 mm)

  11. Carbonates • Chemical/Biochemical • Limestone • Dolomite

  12. Chemical sedimentary rocks • Evaporates • Siliceous sedimentary rocks (cherts) • Phosphorites

  13. Sedimentary structures • A geologic structure is a geometric feature in rock whose shape, form, and distribution can be described • Large scale feature of sedimentary rocks • Information on origin of rocks • Information on younging direction • Information on paleocurrent direction

  14. Beds, or strata are tabular or lenticular layers of sedimentary rock that have lithologic, textural, or structural unity that clear distinguishes them from layers above and bellow

  15. Description of bedding

  16. Bedding planes • Groups of similar beds or cross beds are called bedsets • Bed termination may occur: - merging of bedding planes (pinch-out)- lateral gradation of composition (die out)- meeting of crosscutting features such as channel or unconformity

  17. Bedding

  18. Three mechanisms are responsible for the formation of bedding planes 1) Sedimentation from suspension 2) Horizontal accretion from a moving bed load 3) Encroachment into the lee of an obstacle • Bed load is a part of the stream load that moves on or immediately above the stream bed • Streamload is all material that is transported by a stream

  19. Lack of bedding means:(1) bioturbation(2) deposition from highly concentrated stream load(3) rapid deposition from suspension.

  20. Graded bedding • Commonly produced by turbidity currents • Turbidity current is poorly sorted material suspended in water. When flow begins to slow down, material settles according to the grain size.

  21. Younging direction Younging direction Graded bedding

  22. Inverse grading

  23. Bed and bedforms • Bed – the smallest lithostratigraphic unit, commonly ranging in thickness from a centimeter to a meter or two and distinguishable from beds above and below (3D) • Bed (in sedimentology) – the floor of a body of water (2D) • Bed form or bedform – any deviation from a flat bed, generated by stream flow on the bed of a channel (2D)

  24. Bedforms: Ripples

  25. Bedforms: Ripples (ancient; 570 Ma)

  26. Bedforms: Dunes

  27. Ripple marks

  28. Bedforms

  29. Erosion of topset Cross beds in fluvial deposits of the Manzurka Formation, Baikal Lake

  30. Cross stratification • Cross stratification from Jurassic age Navajo sandstones. Wind direction is from left to right

  31. Convolute folds

  32. Convolute lamination

  33. Load casts Flame structures Extend downward from a sand layer into an underlying mud or very fine sand layerYounging direction

  34. Photo Andrew Alden

  35. Bedding plane structures • Groove cast; striations, bounce, brush, prod, and roll mark • Flute cast • Parting lineation • Track, trails burrows • Mudcracks and syneresis cracks

  36. Bedding plane structures

  37. Grooves (Oluk yapıları) Striations (Buzul kertikleri)

  38. Kaval yapıları (flute casts). Akıntı yönü yukardan aşağıya.

  39. Flute marks Load casts Groove casts

  40. Biogenic sedimentary structures

  41. Biogenic structures

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