Sedimentary Processes and Sedimentary Rocks

Key Ideas

• Sedimentary Process: Formation of sediments involves multiple processes.

• Sedimentary Rock Formation: Sediments convert into rock through lithification and diagenesis.

Major Processes to Form Sediments

• Weathering: Breakdown of rocks into smaller particles.

  • Mechanical Weathering: Physical fragmentation without chemical composition change (Ex. freeze-thaw cycles, exfoliation).

  • Chemical Weathering: Changes in chemical composition (e.g., dissolution, hydrolysis).

• Erosion: Dislodging and movement of weathered particles via water, ice, air, and gravity.

Types of Environments Producing Sediments

• Fluvial: River systems leading to sorted sediments.

• Marine: Oceanic environments producing chemical and biogenic sediments.

• Aeolian: Wind-driven environments creating fine textural sediments.

Soil Definitions

• Soil: Weathered material containing organic matter and supporting plant life.

• Regolith: Unconsolidated material covering Earth's surface.

Processes Converting Sediments into Rock

• Diagenesis: Physical and chemical changes after deposition; includes compaction and cementation.

• Lithification: Turning loose sediments into solid rock through compaction and mineral binding.

Main Types of Sedimentary Rocks

• Clastic Sedimentary Rocks: Formed from mechanical weathering debris.

  • Examples: Sandstone, Shale, Conglomerate.

• Chemical Sedimentary Rocks: Formed by precipitation from solution.

  • Examples: Limestone, Gypsum.

• Biogenic Rocks: Formed from organic material or biogenic processes.

  • Example: Coal, Fossiliferous Limestone.

Sedimentary Structures

Characteristics

• Bedding: Presents stratification and thickness variability in sediments.

• Types of Structures:

  • Cross-bedding

  • Graded bedding: Changes in grain size from bottom to top within a single bed.

  • Bioturbation: Mixing of sediments caused by organisms.

Burial and Lithification Processes

• Burial: Accumulation of sediments leading to increased pressure and temperature.

• Compaction: Reduction in volume from overlying sediment weight.

• Cementation: Minerals crystallizing in pores bind sediment particles together.

Sedimentary Environments

Environment Classifications

• Clastic: Involves particles from weathering processes.

• Chemical and Biological: Includes evaporite environments and biogenic processes.

• Carbonate: Features limestone and dolostone.

Principles of Metamorphism

Metamorphic Processes

• Factors Influencing Metamorphism:

  • Temperature: Typically increases by 30°C per km depth.

  • Pressure: Increases at a rate of 0.23 kbar per km depth.

  • Fluid Chemistry & Time: Fluids can catalyze reactions; processes can require extensive time.

Types of Pressure in Metamorphism

• Confining Pressure: Equal force application in all directions.

• Directed Pressure: Specific directional stress causing deformation.

Types of Metamorphic Rocks

• Foliated: Rocky structures displaying mineral alignment.

• Non-Foliated: Crystallized rocks that do not show preferred orientation.

• Examples:

  • Foliated: Schist, Gneiss

  • Non-foliated: Marble, Quartzite

Rock Cycle Review

Overall Cycle Components

1. Sedimentation

2. Erosion

3. Weathering

4. Melting & Crystallization

5. Metamorphism

• Three Rock Types: Igneous, Sedimentary, Metamorphic based on formation processes.