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Intro to Weathering, Texture and Maturity Study Notes

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LECTURE 1: INTRO TO WEATHERING, TEXTURE AND MATURITY
SEDIMENTARY ROCKS why study them?
• cover about 3/4 of the Earth’s surface!
• provide essential information to understand many Earth processes:
paleoclimate
paleoecosystems
paleogeography
environments of deposition
They host hydrocarbons and minerals:
almost all oil, gas, coal; as well as phosphorites, gypsum.
most industrial minerals and aggregate resources, many gemstones
Mississippi Valley-type Pb-Zn, sediment-hosted base metals
majority of uranium deposits
majority of mined Gold
An estimated 50% of all gold mined on Earth came from 3 GA alluvial deposits at Witwatersrand, WA
containing 1.5 billion ounces of gold
Sedimentology: the study of the origin, classification, and interpretation of sediments and
sedimentary rocks.
• concerned with the physical (texture, primary structure and mineralogy), chemical, and the
biological (fossils) properties of sedimentary rocks.
Stratigraphy: the study of rock strata
• the age relationships with other strata, successions of beds, local and world-wide correlation,
stratigraphic order, depositional architecture and chronological management of beds in the
geological column.
Huge overlap between sedimentology & stratigraphy intimately associated
Sedimentary Rock Classification, Weathering and Textures
To understand how sedimentary rocks form:
• Need to understand
processes
by which sediment forms
how particles are weathered, eroded, transported and ultimately deposited
1) Weathering
2) Erosion
3) Transportation via waters, glaciers, and wind
4) Deposition
5) Burial and compaction
6) Diagenesis
Weathering
• All sedimentary rock comes from the weathering
of pre-existing material.
• Two main types of weathering:
Physical or Mechanical Weathering: physical break-up of rock into smaller pieces.
Chemical Weathering: chemical decomposition of unstable minerals to form more stable minerals

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and compounds like clays, iron oxides, as well as dissolved chemicals held in suspension (e.g., Ca, Mg,
Si).
Bowen’s Reaction Series (High Temp and Pressure to Low Temp and Pressure)
is the Reverse of Mineral Stability at the Earth’s surface.
Olivine, Pyroxene, Amphibole, Mica, Plagioclase, Oligoclase and Quartz
Quartz is most stable at the Earth’s surface; other minerals progressively less stable moving towards
olivine.
Other mineral groups tend to weather mainly to clays (small, hydrated platy minerals) and calcium
carbonate (held in solution).
• During weathering, Solid Particles may:
accumulate in situ to form soils
• be removed by erosion and transported to depositional basins.
transported solids are the source materials for conglomerate, sandstone and mudstone
(shale), and are referred to as: Clastic Grains (fragments of pre-existing rocks).
• if derived from the land = Terrigenous Clastics.
• typically dominated by quartz and other silicate minerals, thus Siliciclastic”
Dissolved Chemical Products
• typically Ca, Mg, Si, Na, K, Cl, etc.
easily removed from the weathering site by surface flow and groundwater, and transported to
lakes or ocean basins
• When concentrations become sufficiently high:
precipitated by Chemical means, or by organisms to make their skeletons (Biochemical) to
form Chemical or Biochemical rocks
• limestones, dolostones, chert, and salts.
Chemical Weathering Products
Organic Matter
• an important constituent of many rocks
• results from the degradation of plant and animal products
• if mixed with high concentrations of sediment = Carbonaceous Rocks
• if rock is almost entirely plant material = Coal
Biochemical Weathering
Textures of Siliciclastics are produced mainly by physical transport and depositional processes.
• main textural elements are:
Grain Size (maximum Grain Diameter and Sorting)

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LECTURE 1: INTRO TO WEATHERING, TEXTURE AND MATURITY SEDIMENTARY ROCKS – why study them? • cover about 3/4 of the Earth’s surface! • provide essential information to understand many Earth processes: • paleoclimate • paleoecosystems • paleogeography • environments of deposition • They host hydrocarbons and minerals: – almost all oil, gas, coal; as well as phosphorites, gypsum. – most industrial minerals and aggregate resources, many gemstones – Mississippi Valley-type Pb-Zn, sediment-hosted base metals – majority of uranium deposits – majority of mined Gold An estimated 50% of all gold mined on Earth came from 3 GA alluvial deposits at Witwatersrand, WA containing 1.5 billion ounces of gold Sedimentology: the study of the origin, classification, and interpretation of sediments and sedimentary rocks. • concerned with the physical (texture, primary structure and mineralogy), chemical, and the biological (fossils) properties of sedimentary rocks. Stratigraphy: the study of rock strata • the age relationships with other strata, successions of beds, local and world-wide correlation, stratigraphic order, depositional architecture and chronological management of beds in the geological column. Huge overlap between sedimentology & stratigraphy – intimately associated Sedimentary Rock Classification, Weathering and Textures To understand how sedimentary rocks form: • Need to understand processes by which sediment forms – how particles are weathe ...
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