Relative susceptibility To weathering
Dec 16, 2015
Relative susceptibilityTo weathering
Mineral Residual Products Material in Solution
Quartz quartz grains silica
Feldspar clay minerals silica, K+, Na+, Ca2+
Amphibole (hornblende)clay minerals, limonite,
hematite silica, Mg2+, Ca2+
Olivine limonite, hematite silica, Mg2+
Products of Weathering
Factors influencing Weathering Rates
1. Rock structures – chemical/mineral composition, physical features
2. Topography
3. Climate
4. Vegetation5. 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
1. Weathering – breakdown both physically (clasts) or chemically
2. Erosion – loosening of weathered products (clasts) and initial transport
3. Transportation – movement of materials via wind, water, or ice; sorting and rounding can occur
4. Deposition – material settles out of the transporting medium
5. Lithification – process of either cementation or compaction of the material
W. W. Norton
Sedimentary RocksComposed 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 QuestionUse 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.
The size, shape, and distribution of particles that collectively make up a rock
Clastic Texture
Increasing distance from source
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
Fining up
Graded Beds
Texture and Transport Distance
In general, as transport distance increases, rounding and sorting increase.
Examples: Breccia – cemented close to sourceConglomerate – transported thencemented
Types of Sediments - BiogenicTerrestrial 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
1. 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