lowerstratum

Lowerstratum, commonly written as lower stratum, refers to the bottom layer in a stratified sequence of rocks, sediments, or other layered materials. In geology and stratigraphy, the lower stratum lies beneath all younger layers and typically records the earliest phase of deposition at a site. The term is used to describe the foundational layer from which a stratigraphic column is built.

In geology and stratigraphy, the lower stratum is a key reference point for interpreting the history of a rock sequence. Its lithology, grain size, mineral composition, and fossil content help identify the depositional environment and can reveal long-term changes in climate, sea level, or sediment supply. The lower stratum is usually separated from overlying strata by a contact that may be conformable, indicating continuous deposition, or unconformable, indicating erosion or a hiatus in deposition.

Identification and analysis rely on stratigraphic logging and mapping, correlation across regions, and dating techniques. Biostratigraphy using index fossils, radiometric dating, magnetostratigraphy, and chemostratigraphy are common tools to constrain the age of the lower stratum and to place it within a broader geologic framework.

In social science, the term lower stratum is sometimes used to denote the lowest tier of social stratification, typically associated with lower income, education, occupation, and access to resources. Discussions about the lower stratum address issues of inequality, social mobility, health outcomes, and policy implications.

Note that the term lowerstratum is less commonly used as a single word; most references spell it as two words, lower stratum. The concept, whether in geology or sociology, denotes foundational or baseline layers within a hierarchical structure.