1. Sedimentary Analysis

2. Types of Sedimentary Material Terrigenous Clastics (TC) –Detrital Particles –Derived from pre-existing rocks –Derived external to the depositional basin –Transported by surface processes to the site of deposition Particulate Residues: quartz, feldspar, rock fragments, etc (unaltered rock forming mineral/rock grains) Secondary Minerals: minerals new-formed in the surface weathering environment: clay minerals, oxides, amorphous silica, etc

3. Types of Sedimentary Material Allochemical Particles formed in situ at the site of deposition; of chemical/ biochemical origin –Carbonates: ooids, fossil fragments, pellets, lithoclasts –Glauconite, phosphate :in situ authigenic/particulate minerals –Biogenic sediments: pelagic tests, siliceous and calcareous

4. Types of Sedimentary Material Orthochemical Components –Chemical Precipitates Secondary cement Primary chemical sediments: halite, etc Organic Particulate Material (detrital organic matter ) –terrestrial and particulate –marine pelagic –95% found in mudrocks and indicative of low Eh and low current strength Laminated Castile Formation basinal evaporites. Dark laminae are calcite plus organic matter; light laminae are gypsum (Peter Scholle) Coal

5. Types of Sedimentary Material Pyroclasts – particles fragmented and transported by volcanic processes Tephra: tuff deposits Volcanic mudflows: lahar and volcanic breccia deposits Tephra Volcanic Ash

6. Terrigenous Sediment

7. Sedimentary Analysis Requires description (qualitative, quantitative) Analysis (graphical, statistical) interpretation

8. Describing Siliciclastics Description –Size –Texture –Fabric Analysis Maturity –Textural –Compositional

9. Describing Siliciclastics-Size Size Gravel and larger (> 2 mm) Sand (1/16 - 2 mm) Mud(< 63  m = < 1/16 mm) Silt4  m>x<63  m Clay<4  m

10. Gravel-Size (Pebbles & Cobbles) (> 2 mm)

11. Sand (1/16 - 2 mm)

12. (< 63  m = < 1/16 mm) Mud

13. Describing Siliciclastics- Size Wentworth scale Udden- Wentworth size scale Udden, 1914; Wentworth, 1922 Resolves problems with size classification Cumbersome to discuss size Limiting to restrict to 3 classes Four basic groups + modifiers make more Clay (< 4  m) Silt (4  m - 63  m) Sand (63  m - 2 mm) Gravel (> 2 mm)

14. Siliciclastic Rock Classification:Texture Descriptive Textural Classification –Grain Size Uden-Wentworth grain size scale Phi (  )=-log 2 (grain diameter in mm) naturally occurring groups; Gravel ~ rock fragments, Sand ~ individual mineral grains (particulate residues) Clay ~ chemical weathering products (clay minerals, etc.) Mud ~ particulate residues +/- chemical weathering products

15. Describing Siliciclastics- Size Wentworth scale (cont’) –Subdivided scale by factor of 2.0039 mm clay.0078 mm very fine silt 128 mm = cobbles 256 mm = boulders Logarithmic (base 2) progression!  = -log 2 (grain diameter in mm) As grain size increases, phi size decreases

16. Describing Siliciclastics- Sedimentary Texture Aspects of texture –Shape –Degree of sorting –Surface texture Result of – Parent rock type (shape) – Weathering – Transport history (sorting, shape) Generally for siliciclastics but can be useful for other types

17. Describing Siliciclastics Roundness Degree of angularity Function of transport history Edges chip off as clasts knock into one another (progressive) Estimate visually or calculate from cross- section Sphericity How closely clast approximates a sphere (equant) Inherited feature! (function of shape formed in weathering) slab may become discoidal but stays flat with time Form/Shape Zingg indices spherical (equant), oblate (disk or tabular), bladed, prolate (roller )

18. ZINGG DIAGRAM Where: d i = intermediate diameter d l = long diameter d s = short diameter

20. Texture: Sorting & Shape Sorting: measure of the diversity of grain size A function of grain origin and transport history Clast Rounding: surface irregularity –Due to prolonged agitation during transport and reworking

21. Describing Siliciclastics Degree of sorting Measure of distribution of clast sizes Well sorted most clasts fall into one class on the Wentworth scale Poorly sorted wide range of clast sizes Due to origin and transport history Greater distance (or repeated agitation of sediment), better separation of sizes Qualitative (visual) and quantitative methods

23. Statistical/Graphic Presentation of Texture: Grain Size/Sorting Quantitative assessment of the % of different grain sizes in a clastics –Mean: average particle size –Mode: most abundant class size –Median: 50 th percentile

24. Describing Siliciclastics Grain size analysis Quantitative analysis –(granulometric analysis) Quantitative assessment of % of different grain sizes in clastic sediments –Useful in interpretting depositional history of clasts, especially in modern environments Technique used varies with grain size –Direct –Indirect

25. Describing Siliciclastics Grain size analysis- techniques Gravel direct measurement in the field measure all within a quadrant meter is used for pebbles, cobbles Sand pass through a stack of sieves with mesh keyed to  weigh contents of each sieve, get distribution by wt.

26. Describing Siliciclastics Grain size analysis- graphic analysis Plots –Histogram of weight percentage of size fractions –Frequency curve –Cumulative frequency curve When plotted, grain size increases from right to left, f ines to right, coarse to left Graphically represent grain size distribution –mean grain size –standard deviation from a normal distribution (sorting) –symmetry (skewness) –flatness of curve (kurtosis)

27. Describing Siliciclastics Grain size analysis- graphic analysis Different depositional environments exhibit different grain size distributions Glacial sediments poorly sorted River sediments moderately sorted Beach sediments well sorted

28. Statistical/Graphic Presentation of Texture; Granulometry

30. Refraction Index: immersion oils of known refractive index and comparing the unknown mineral to the oil