Sedimentary Rocks Lecture 9

Sedimentary Rocks Overview

• Types:

  • Clastic (e.g., sandstone, shale)

  • Chemical (e.g., limestone, rock salt)

  • Biochemical (e.g., coal)

Formation of Clastic Sedimentary Rocks

• Process:

  • Clasts eroded & transported by water/wind/ice/gravity.

  • Deposited in water/basins; gain texture reflecting deposition energy.

  • Lithified through compaction and cementation over time.

Compaction and Cementation

• Mechanism:

  • Water deposits chemicals in clast pores, cementing them over time.

  • Common cements:

  • Chalcedony (SiO2)

  • Calcite (CaCO3)

Chemical Sedimentary Rocks Formation

• Process:

  • Water evaporation/oversaturation leads to mineral precipitation.

Common Chemical Sedimentary Rocks

• Halides and Carbonates:

  • Halite = NaCl (Rock Salt)

  • Calcite = CaCO3 (Limestone)

  • Dolomite = CaMg(CO3)2 (Dolostone)

• Silica:

  • Chalcedony = SiO2 (Chert)

Weathering and Erosion

• Weathering:

  • Breakdown of rock with no transport.

• Erosion:

  • Transport of weathered rock by processes (wind, water, ice).

Physical Weathering Types

• Examples:

  • Frost wedging

  • Abrasion

  • Root wedging

  • Thermal expansion/contraction

Chemical Weathering Types

• Processes:

  • Oxidation: Alters minerals by oxygen exposure.

  • Dissolution: Soluble minerals dissolve in water.

  • Hydrolysis: Silicate minerals partially dissolve, forming clay minerals.

Bowen's Reaction Series

• Composition of Continental Crust:

  • Mostly felsic & intermediate igneous rocks.

  • Commonly transforms to clay minerals from silicate minerals (excluding quartz).