Relative susceptibility To weathering
Products of Weathering
Factors influencing Weathering Rates Rock structures – chemical/mineral composition, physical features Topography Climate Vegetation Time
Sediments and Sedimentary Rocks
Sediments - unconsolidated particles created by 1. The weathering of rock 2. The secretions of organisms or decomposition of organic matter 3. Chemical precipitation
Sedimentary Rock Formation Weathering – breakdown both physically (clasts) or chemically Erosion – loosening of weathered products (clasts) and initial transport Transportation – movement of materials via wind, water, or ice; sorting and rounding can occur Deposition – material settles out of the transporting medium Lithification – process of either cementation or compaction of the material
W. W. Norton
Sedimentary Rocks Composed of lithified sediments by compaction – weight of overlying sediment compresses sediment, important in fine-grained sediments by cementation – materials carried in solution precipitates minerals - iron oxides, carbonates, silica Two Classifications - clastic -nonclastic
Fig. 7.16 W. W. Norton
Sedimentary Rocks Clastic Rock – composed of fragments of preexisting rocks. Nonclastic Rock – composed of chemical precipitates or biochemical matter.
Daily Question Use a Venn diagram to compare and contrast clastic, chemical nonclastic, and biochemical nonclastic sedimentary rocks. Identify at least five characteristics. Clastic Chemical Biochemical
Types of Sediments - Clastic Broken fragments of rock produced by weathering. Classified according to size. Range in size from largest boulder to smallest clay particle.
Clastic Texture Increasing distance from source The size, shape, and distribution of particles that collectively make up a rock Increasing distance from source
Which sample is closer to the source of sediment?
Sorting - a function of transport mechanism 1. Water 2. Wind 3. Glaciers
Sorting by Wind
Fig. 7.26a Stephen Marshak
Graded Beds Fining up
Texture and Transport Distance In general, as transport distance increases, rounding and sorting increase. Examples: Breccia – cemented close to source Conglomerate – transported then cemented
Types of Sediments - Biogenic Terrestrial sediments - mainly plant matter ex. Coal Marine sediments - mainly carbonates Corals - large components of reefs. Bivalves, gastropods, foraminifers - whole or partial skeletons form sand and gravels. Algae, crinoids, echinoderms, bryozoans - disintegrate to form some sand particles and lime mud. Diatoms, Radiolaria – bedded chert sio2
Coral (carbonate)
Foramanifera
Diatoms
Types of Sediments - Chemical Inorganic process, no biological activity involved. Formed by minerals precipitating from solution. i.e. – Ca2+ + CO32- = CaCO3 Na+ + Cl- = NaCl
Chemical Sediments Terrestrial - Evaporites: Gypsum - CaSO4 . H2O Anhydrite -CaSO4 Halite - NaCl
Chemical Sediments 2. Marine Carbonates - CaCO3 (limestone) Chert (Quartz) – SiO2
Bedding – Layering or stratification in sedimentary rock
Fig. 7.25abc W. W. Norton
Cross Bedding – water or wind
Ripple Marks
Sedimentary Environments
Sedimentary Systems and Plate Tectonics