relative susceptibility to weathering. products of weathering

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