Stratum

Layer of sedimentary rock or soil with internally consistent characteristics

Stratum in Quebrada de Cafayate, Salta, Argentina

A stratum (plural: strata) is a layer of sedimentary rock or soil with internally consistent characteristics that distinguish it from other layers. Each stratum is typically one of a number of parallel layers that lie one upon another, laid down by natural processes. Strata are used in the study of stratigraphy, which is the branch of geology concerned with the order and relative position of strata and their relationship to the geological time scale.

Formation

Strata are formed by the deposition of sediment in a variety of environments, including rivers, lakes, oceans, and deserts. Over time, these sediments are compacted and cemented to form sedimentary rock. The process of sedimentation is influenced by factors such as climate, tectonic activity, and sea level changes.

Characteristics

Strata are characterized by their composition, texture, and color. The composition of a stratum can include minerals, fossils, and organic material. The texture refers to the size, shape, and arrangement of the particles within the stratum. Color can vary widely and is often influenced by the mineral content and the conditions under which the stratum was formed.

Example of stratum in a rock formation

Types of Strata

Strata can be classified based on their composition and the environment in which they were deposited. Common types include:

• Clastic strata: Composed of fragments of pre-existing rocks, such as sandstone and shale.
• Chemical strata: Formed from the precipitation of minerals from solution, such as limestone and evaporites.
• Organic strata: Consist of accumulated organic material, such as coal and oil shale.

Stratigraphic Principles

The study of strata is governed by several key principles:

• Law of Superposition: In an undeformed sequence of sedimentary rocks, each layer is older than the one above it and younger than the one below it.
• Principle of Original Horizontality: Layers of sediment are originally deposited horizontally under the action of gravity.
• Principle of Lateral Continuity: Layers of sediment initially extend laterally in all directions; in other words, they are laterally continuous.

Strata in Southeastern Utah

Applications

Strata are crucial in the fields of geology, archaeology, and paleontology. They provide valuable information about the Earth's history, including past climates, environments, and life forms. In archaeology, strata are used to date artifacts and understand human activity over time.

Related pages

• Sedimentary rock
• Stratigraphy
• Geological time scale
• Fossil

Strata in the French Alps