Sedimentation & Stratigraphy (89.352)

http://faculty.uml.edu/lweeden/SedStrat.htm

Kinds of Sedimentary Rocks

Siliciclastic: sedimentary rocks that are composed of dominantly silicate materials, such as quartz, feldspar, and rock fragments. (i.e.: Conglomerates, sandstones & shales.) Volcaniclastic: Siliciclastic sedimentary rocks that are formed mainly from the products of explosive volcanism. (i.e.: conglomerate composed primarily of fragment of volcanic glass and rocks – Breccia & Tuff.) Chemical/Biological: sedimentary rocks that are composed of minerals precipitated mainly from ocean or lake water by inorganic and or organic processes. (i.e.: limestone, chert, gypsum and iron-rich sedimentary rocks.) Carbonaceous: sedimentary rocks that contain (>~15%) highly altered remains of the soft tissue of plants and/or animals. (i.e.: coal & oil shale.)

Sedimentology: The scientific study of the classification, origin and interpretation of sediments and sedimentary rocks. Stratigraphy: The science of rock strata. It is concerned more with processes and establishment. Diagenesis: Any chemical, physical, or biological change undergone by a sediment after its initial deposition and during and after its lithification, exclusive of surface alteration (weathering) and metamorphism. These changes happen at relatively low temperatures and pressures and result in changes to the rock's original mineralogy and/or texture. Weathering: Physical disintegration and chemical decomposition of older rock to produce solid particulate residues.

Brief History of Sedimentation and Stratigraphy

Nicolas Steno (1638 – 1686) Principles of Superposition and Original Horizontality.

James Hutton (1727 – 1797) Principle of Uniformitarianism (aka. Actualism)

William “Strata” Smith (1769 – 1839) Law of Faunal Succession.

Johannes Walther (1860 – 1937) Walther’s Law of succession of facies

Chapter 1: Weathering and Soils

I. Physical Weathering

A. Freeze – Thaw (Frost Wedging)

B. Insolation Weathering

C. Salt Weathering

D. Wetting & Drying Weathering

E. Stress Release Weathering

F. Other Physical Process

How does surface area contribute to weathering processes?

Frost Wedging

Insolation Weathering (Spalling)

Salt Weathering

Wetting and Drying Weathering

Stress – Release Weathering

II. Chemical Weathering (Table 1.1)

A. Simple Solution

B. Hydrolysis

C. Oxidation / Reduction

D. Hydration / Dehydration

E. Ion Exchange

F. Chelation

III. Weathering Rates

There is no mathematical solution to precise weathering rates. It is all relative….

A. Climate (physical - cold and dry; chemical – hot and wet.)

B. Stability of Minerals “Happiness Principle” Table 1.2

C. Subaerial Weathering (Table 1.3)

D. Submarine Weathering

1.Halmyrolysis

2.Magnitude of Circulation and effects.

Physical weathering dominates in cold and dry climates.

Chemical weathering dominates in warm and wet climates.

Stability of Minerals and “The Happiness Principle”

Order of increasing “weatherability”

Sand and Silt-size minerals Clay-size minerals

Mafic Minerals Felsic Minerals 1. Gypsum, halite Olivine 2. Calcite, dolomite, apatite Ca plagioclase 3. Olivine, amphiboles, pyroxenes Pyroxene 4. Biotite

Amphibole Ca-Na plagioclase 5. Na plagioclase, Ca plagioclase, K-feldspar, volcanic glass

Na-Ca plagioclase 6. Quartz Na plagioclase 7. Muscovite 8. Vermiculite (clay mineral) Biotite 9. Smectite (clay mineral) K-feldspar 10.Pedogenic (soil) chlorite Muscovite,quartz 11.Allophane (clay mineral) 12.Kaolinite, halloysite (clay mineral) 13.Gibbsite, boehmite (clay mineral) 14.Hematite, goethite, magnetite (increasing stability)

15.Anatase, titanite, rutile, ilmenite (all titanium-bearing minerals), zircon

Table 1.2

Subaerial Weathering (Table 1.3)

Weathering process Type of Example Ultimate Weathering product depositional product Physical weathering Chemical weathering Hydrolysis Simple solution Oxidation

Particulate residues Soluble constituents Secondary minerals Soluble constituents Secondary minerals Soluble constituents

Silicate minerals such as quartz and feldspar; all types of rock fragments Silicic acid (H4SiO4); K

+, Na+, Mg2+, Ca2+, etc. Clay minerals Silicic acid; K+, Na+, Mg2+, Ca2+, HCO3

-, SO4

2-, etc. Ferric oxides (Fe2OOH); manganese oxides (MnO2) Silicic acid; SO4

2-

Sandstones, conglomerates, mudrocks Cherts, limestones, etc. Mudrocks (shales) Limestones, evaporites, chert, etc. Minor constituent in Siliciclastic rocks Chert, evaporites, etc.

Submarine Weathering and Halmyrolysis

IV. Soils

A. Soil is a product of bedrock weathering.

B. The thickness and characteristics of a soil is a function of:

1. Bedrock lithology

2. Slope of bedrock surface

3. Climate

4. Biological activity

5. Additions to ground surface

C. Transformation

D. Transfers

E. Removals

F. Bioturbation of Soils

Soil-Forming Processes

1. Additions to the ground surface—Precipitation of dissolved ions in rainwater; influx of solid particles (dust, etc.); addition of organic matter from surface vegetation (leaf litter, etc .)

2. Transformations

a. Decomposition of organic matter with soils to produce organic compounds.

b. Weathering of primary minerals; formation of secondary minerals, including iron oxides.

3. Transfers

a. Movement of solid or suspended material downward from one soil horizon to a lower horizon by groundwater percolation (eluviation)

b. Accumulation of soluble or suspended material in a lower horizon (illuviation)

c. Transfer of ions upward by capillary movement of water and precipitation of ions in the soil profile

Soil forming processes continued…

4. Removals—Removal of substances still in solution to become part of the dissolved constituents in groundwater or surface water

5. Bioturbation of soil—Soil disrupted by animals (i.e. ants and termites) and plants.

G. Soil Profile

Bedrock

Water enters system

Minerals leached

Altered minerals accumulated with different chemistry than original material

H. Soil Classification (Taxonomy)

1. Gelisols

2. Histosols

3. Spodosols

4. Andisols

5. Oxisols

6. Vertisols

7. Aridisols

8. Ultisols

9. Mollisols

10.Alfisols

11. Inceptisols

12.Entisols

Review climatic effects of soil formation.

I. Paleosols—ancient soils, fossil soils or soils that escaped the effects of erosion to become part of the sedimentary record.

Recognition of Paleosoils –Glaebules, Mottles & Burrows…Oh my!

See Figure 1.6 of Text