2 Preview of Lab 2 Classification in general Classification of sedimentary rocksClastic sedimentary rocksChemical and biochemical sedimentary rocksFundamental constituents of sedimentary rocks
3 Objectives of Lab 3 Textures of sedimentary rocks Grain size Roundness and sortingMaturityColorCohesiveness (firmness)Mineral composition and sedimentary structuresFramework and matrixCements in sedimentary rocks
4 Textures of Sedimentary Rocks Sedimentary rocks may have1. Clastic (fragmental) textureGrains are stuck together.Characteristic of clastic sedimentary rocks.Examples: sandstone and conglomerate.2. Non-clastic (crystalline) textureInterlocking crystals.Characteristic of chemical sedimentary rocks.Examples: limestone, dolomite, and chert.
6 Non-clastic (crystalline) Texture From eos.ubc.ca
7 Grain Size (1) Grain sizes can be determined by: Direct measurement with calipers or meter sticks.For particles larger than several centimeters.Screening and petrographic microscope.For particles from 2 mm to about 1/16 mm.Pipette or hydrometer (settling rates in water)For particles less than 1/16 mm.
8 Grain Size (2)Results of grain-size analysis can be demonstrated as histograms, cumulative curves, or frequency curves.Many statistical parameters can be calculated (e.g., median, mean, skewness, kurtosis, etc.).Used to characterize depositional processes and depositional environments.Udden-Wentworth grain-size scale is the most widely used.
13 Roundness and Sorting Roundness (angularity) Sorting Indicates how smooth or sharp the edges and corners of particles are.Usually measured with reference to a comparative chart (the commonest is Powers’ , 1953).SortingThe degree of uniformity of grain sizes.
15 Degrees of sortingFrom Compton (1962)* Note the standard deviation values between classes
16 Visual estimation of sorting From Tucker (2001)
17 MaturityDepends on how many cycles of erosion and redeposition the components of a rock have undergone.There are two types of maturity:1. Compositional maturityCompositional maturity = quartz + chert / feldspars + rock fragments.2. Textural maturityTextural (structural) maturity = sorting and roundness of sand-sized grains.
19 ColorOrganic matter, sulfides, and some iron oxides give rocks a dark color.Indicating deposition in a reducing environment.Some iron oxides give rocks red or yellowish color.Indicating deposition in an oxidizing environment.
20 Color Indications Black - organic matter FeS Yellowish - pyrite, markasite FeS2Yellowish or bluish - sulphates, carbonates, and chloridesYellowish to brownish - limonite, goethite FeO(OH)Reddish - iron oxides FeO
26 Framework and MatrixThe grains in a sand-sized or coarser grained sedimentary rock are known as the framework.These grains are either:In contact with each otherSurrounded by empty spaces (pore spaces)Surrounded by finer grained sediment (matrix)Cemented together by a bonding material (cement)
28 Cements in Sedimentary Rocks The most common cements in sedimentary rocks are:Silica (quartz, opal, or chalcedony)Carbonates (calcite, dolomite, or siderite)Iron oxides (hematite)Recognition of matrix and cement is not always possible in hand specimens.
30 References Compton, 1962. Manual of field geology. Folk, Petrology of sedimentary rocks.Folk, Stages of textural maturity in sedimentary rocks: Journal of Sedimentary Petrology, v. 21.Immenhauser, Sedimentology for master students.Tucker, Sedimentary petrology: an introduction to the origin of sedimentary rocks. Blackwell Science, London, UK.eos.ubc.ca