Sedimentary Rocks

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Sediment

Loose, solid particles of mineral originating from weathering, erosion, or precipitation

Detrital Sedimentary Rocks

Rocks composed of material transported as solid fragments known as clasts

Chemical Sedimentary Rocks

Rocks composed of material transported as ions in solution and precipitated

Organic Sedimentary Rocks

Rocks formed from the consolidation of organic plant remains like coal

Lithification

The process of converting loose sediment into solid rock through compaction and cementation

Compaction

The packing of loose grains tightly together, reducing pore space during burial

Cementation

The precipitation of minerals around grains that binds them into a firm rock

Weathering and Erosion

The first step in transforming existing rocks into sediment

Transportation

Movement of sediment by wind, flowing water, glacial ice, or gravity

Deposition

Occurs when transporting agents lose energy and can no longer move the sediment

Burial

Occurs as new sediment layers are piled onto existing layers, causing compaction

Rounding

The grinding away of sharp edges on rock fragments during transportation

Sorting

The process by which transport agents select grains based on size, shape, or density

Clastic Texture

A rock consisting of grains bound by cement in a rigid framework

Crystalline Texture

A rock formed by the growth of crystals precipitated from a solution

Breccia

A coarse-grained rock with angular fragments; indicates very short transport distance

Conglomerate

A coarse-grained rock with rounded gravel; indicates significant transport

Sandstone

A medium-grained rock formed by the cementation of sand grains

Arkose

A sandstone containing at least 25% feldspar, indicating short travel and mechanical weathering

Shale

A fine-grained rock (silt and clay) that splits into layers, known as fissility

Limestone

A carbonate rock formed either biochemically (shells) or inorganically

Chert

A hard, fine-grained rock composed of silica (SiO2)

Coal

An organic rock formed from partially decomposed plant matter in oxygen-poor environments

Evaporites

Rocks like rock salt and gypsum that form as water evaporates

Bedding Planes

The visible boundaries between different layers of sedimentary rock

Cross-Bedding

Inclined layers formed by currents of wind or water

Graded Bedding

A layer with a vertical change in particle size, from coarse at the bottom to fine at the top

Mud Cracks

Polygonal cracks formed in fine sediment as it dries, indicating exposure to air

Turbidity Current

An underwater avalanche of sediment-laden water that creates graded beds

Principle of Original Horizontality

The concept that sediments are deposited in flat, horizontal layers

Principle of Superposition

The rule that in an undisturbed sequence, the oldest layers are at the bottom

Alluvial Fan

A fan-shaped deposit of cross-bedded sandstone and conglomerate at the base of mountains

Delta

A body of sediment deposited where a river flows into standing water, often containing coal or shale

Shallow Marine Environment

Characterized by sandstone, siltstone, and fossils like clams or snails

Deep Marine Environment

Characterized by shale, chert, and graywacke sandstone from turbidity currents