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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 ironrich 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”
Table 1.2
Sand and Silt-size minerals
Mafic Minerals
Olivine
Felsic Minerals
Ca plagioclase
Pyroxene
Amphibole
Ca-Na plagioclase
Na-Ca plagioclase
Na plagioclase
Biotite
K-feldspar
Muscovite,quartz
(increasing
stability)
Clay-size minerals
1. Gypsum, halite
2. Calcite, dolomite, apatite
3. Olivine, amphiboles, pyroxenes
4. Biotite
5. Na plagioclase, Ca plagioclase, Kfeldspar, volcanic glass
6. Quartz
7. Muscovite
8. Vermiculite (clay mineral)
9. Smectite (clay mineral)
10.Pedogenic (soil) chlorite
11.Allophane (clay mineral)
12.Kaolinite, halloysite (clay mineral)
13.Gibbsite, boehmite (clay mineral)
14.Hematite, goethite, magnetite
15.Anatase, titanite, rutile, ilmenite
(all titanium-bearing minerals), zircon
Subaerial Weathering (Table 1.3)
Weathering process
Type of
Weathering product
Physical weathering
Particulate residues
Example
Ultimate
depositional product
Silicate minerals such as
quartz and feldspar; all
types of rock fragments
Sandstones,
conglomerates, mudrocks
Chemical weathering
Hydrolysis
Soluble constituents
Secondary minerals
Simple solution
Oxidation
Soluble constituents
Secondary minerals
Soluble constituents
+
Silicic acid (H4SiO4); K ,
+
2+
2+
Na , Mg , Ca , etc.
Clay minerals
+
+
Silicic acid; K , Na ,
2+
2+
Mg , Ca , HCO3 ,
2SO4 , etc.
Ferric oxides (Fe2OOH);
manganese oxides
(MnO2)
2Silicic acid; SO4
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.
2.
3.
4.
5.
6.
Gelisols
Histosols
Spodosols
Andisols
Oxisols
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