Understanding Sedimentary Rock Characteristics: Provenance and Weathering

Explore the significance of provenance analysis in interpreting the origin of sedimentary rocks based on lithological characteristics. Learn about mechanical and chemical weathering processes, compositional and textural maturity, mineral stability during weathering, and how rock particles indicate tectonic settings through QFL diagrams and ternary plots.

• Sedimentary Rocks
• Provenance Analysis
• Weathering Processes
• Mineral Stability
• Tectonic Settings

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1. Provenance Analysis

2. Provenance: Provenance: the lithological (and chemical, isotopic, age) characteristics of the source region for a sedimentary rock Composition of sediments (mostly sandstones) can tell you about the location, tectonic setting, climate, etc. of the source area and the transport mechanism and pathway

3. Mechanical weathering Mechanical weathering No changes to mineralogical composition of sediment produced from rock Chemical weathering Chemical weathering Mineralogical composition of sediment differs from parent rock

4. Chemical weathering dominates in warm, wet climates

5. Mineral stability during weathering follows Bowens reaction series

6. Compositional Maturity: Compositional Maturity: degree to which sediment contains only resistant grains (quartz and stable heavy minerals like magnetite, apatite, rutile, zircon)

7. Textural Maturity: Textural Maturity: based on presence of clay, sorting, and rounding More transport leads to greater textural maturity

8. Rock particles can indicate the tectonic setting of the source QFL diagram plots relative percentages of quartz, feldspar, and lithics If chert or quartzite are abundant, treat them as lithics and plot monocrystalline quartz (Qm)

9. Other ternary plots (QpLvmLsm and LmLvLs) subdivide and plot just the lithic components for discrimination of tectonic settings Lm = metamorphic lithics Qp = polycrystalline quartz (chert, quartzite) Lv = volcanic lithics Lvm = volcanic and metavolcanic lithics Ls = sedimentary lithics Lsm = sedimentary and metased lithics

10. Sm Sm/ /Nd Nd isotopes isotopes Negative Nd values found in continental crust (Nd system has been separated from Sm enriched mantle for long time) Positive Nd values are commonly found in mantle derived melts

11. Strontium isotopes Strontium isotopes ( (87 87Sr/ Sr/86 86Sr) Sr) Rubidium (87Rb) strongly partitions into continental magmas and decays to 87Sr Continental crust is enriched in 87Sr/86Sr Primitive mantle and magma have low 87Sr/86Sr Ratio tracks continental influence on source rocks

12. Detrital zircon U Detrital zircon U- -Pb Pb Single-crystal age dates give age of rocks in source region