Stratigrafiaa

Stratigrafiaa, commonly spelled stratigraphy, is a branch of geology concerned with the study of rock layers and their arrangement in time. It describes the distribution, lithology, and fossil content of sedimentary sequences and aims to establish their relative order and, where possible, absolute ages. Stratigraphy provides the framework for understanding Earth's history as recorded in rocks.

Stratigraphic work relies on units and principles. The main stratigraphic units include formations, members, and beds. Core principles such as superposition (younger layers over older), original horizontality, lateral continuity, cross-cutting relationships, and the principle of faunal succession underlie age dating and correlation. In practice, stratigraphers separate rock types (lithostratigraphy), fossils (biostratigraphy), and time (chronostratigraphy), and increasingly use sequence stratigraphy to interpret changes in relative sea level.

Methods include field mapping and description, construction of stratigraphic columns, correlation of distant sections, and fossil analysis using index fossils. Dating combines relative frameworks with absolute techniques such as radiometric dating, magnetostratigraphy, and chemostratigraphy, as well as luminescence dating in appropriate contexts.

Applications span petroleum geology, mineral resources, hydrogeology, environmental and paleoenvironmental reconstructions, archaeology, and stratigraphic dating of geological events. The discipline evolved from foundational ideas of early geologists and anatomists to modern, multidisciplinary approaches that integrate sedimentology, paleontology, and geochronology.