Coal Formation Stages

• The 'raw material' for coal is large amounts of plant matter which accumulate in low-oxygen environments, allowing for partial decomposition.

Stages of Coal Formation

• Swamp/Peat: Initial stage where plant matter accumulates in a swamp environment.
• Low-oxygen environment prevents full decomposition, leading to peat formation.
• Burial/Compaction: Peat is buried under sediment layers.
• Overlying sediment compacts the peat, removing water and volatile substances.
• Lignite: Peat transforms into lignite, a soft brown coal with low carbon content, due to increased burial and compaction.
• Bituminous Coal: Further burial and compaction increase pressure and temperature, changing the coal to bituminous coal.
• Bituminous coal is denser, black coal with a higher carbon content than lignite.
• Anthracite: Under high temperature and pressure (metamorphism and stress), bituminous coal transforms into anthracite.
• Anthracite is a hard, black coal with the highest carbon content.

Key Concepts

• Coal originates from organic plant material.
• Decomposition is the process of breaking down organic matter.
• Low-oxygen environments are crucial for coal formation, preventing complete decomposition.
• Compaction is the process of sediments being squeezed together, reducing pore space
• Metamorphism is the transformation of rocks due to heat and pressure.
• Coal formation is a gradual process with distinct stages.
• Diagenesis: Loose sediment transforms into solid sedimentary rock.
• Compaction is the most important lithification process for fine-grained sediment.
• Sedimentary rock cements include calcite, silica, and iron oxide.
• Calcite identification: Reaction with hydrochloric acid causes fizzing.
• Silica: The hardest cement.
• Iron oxide is typically orange or dark red in color.
• Chemical sedimentary rocks are distinguished by mineral composition.
• Detrital rocks are named based on particle size.
• Clastic rocks are made of broken mineral or rock fragments.
• Nonclastic rocks are made of crystals formed from chemical processes.
• Detrital rocks have a clastic texture.
• Sedimentary environments are categorized as continental, marine, and transitional.
• Continental environments are on land.
• Marine environments are in the ocean.
• Transitional environments are where land meets water.
• A sedimentary rock layer can exhibit different types of sedimentary rocks due to variations in the depositional environment over time, called facies.

Sedimentary Rock Features

• Stratification is the layering of rocks.
• Cross-bedding: Inclined sediment layers occur.
• Graded bedding: A gradual change in particle size within a single layer is seen.

Mud Cracks

• Mud cracks form when wet mud dries and contracts, creating polygonal cracks.
• Mud cracks indicate past wet/dry conditions.
• Mud cracks indicate sediment exposure to air.

Ripple Marks

• Ripple marks are small ridges formed on sediment surfaces by water or wind movement.
• Ripple mark shapes and orientations can indicate current direction.
• Ripple mark size and spacing can provide clues about the strength and type of current.
• Some ripple marks form in shallow water, while others form in deeper water.
• Sedimentary structures serve as records of past environments.
• Climate (wet or dry) can be determined by patterns in the rock.
• Water flow direction and strength can be found.
• Environmental changes over time can be tracked.

Significance

• Understanding these features is crucial in sedimentary geology and paleogeography.
• They aid our understanding of sedimentary rock layer formation and depositional environment.
• They are important tools used to understand the geologic past.