Lecture 10: Sedimentary Rocks

Sedimentary Rocks Overview

• Lecture 10 focused on sedimentary rocks classification, particularly clastic sedimentary rocks.

Key Factors in Classification

• Texture: Includes grain/clast size, angularity, and sorting.

• Mineral Composition: Important for identifying types of sedimentary rocks.

• Environments: Context in which sediments are deposited.

Texture of Clastic Sedimentary Rocks

• Grain Size:

  • Clay: Cannot see with naked eye.

  • Silt: Head of a pin to head of a pen/pencil.

  • Sand: Size of a pea to palm.

  • Gravel: Coarse, larger grains.

• Angularity: Influences clast shape during transport (e.g., angular, sub-angular, rounded).

• Sorting: Range of sizes in a rock; influenced by depositional environment.

Sediment Transport Processes

• Higher elevations (highlands) provide more surface area for erosion and sediment production.

• Different environments play roles in sediment transport: e.g., glacial, fluvial, eolian, deltaic.

Sediment Maturity

• Maturity reflects sediment texture evolution:

  • Average grain size decreases, roundness/sorting increases.

  • More quartz and clay content in mature sediments.

  • Most mature rocks: Quartz sandstone and shale.

Mineral Composition

• Continental crust is principal source of sediment; primarily composed of igneous minerals.

• Common minerals include quartz and various clays.

Chemical Sedimentary Rocks

• Types:

  • Halides (e.g., Rock Salt): Source from evaporating salt water.

  • Carbonates (e.g., Limestone): Form in warm seawater or shells.

  • Silica (e.g., Chert): From spongy sea animals.

Identification Tests

• Hardness is key for differentiating minerals.

  • Harder than glass: igneous minerals.

  • Reactivity with acid (calcite) helps identify certain rocks.