stratigrafi

Stratigraphy, sometimes referred to as stratigrafi in some languages, is the science concerned with the layering of rocks (strata), their succession, and the relationships among them. It aims to reconstruct the geological history of an area by describing the lithology, thickness, fossil content, and geochemical characteristics of rock sequences, and by correlating these sequences across regions.

Core principles of stratigraphy include the law of superposition (older layers are buried beneath younger ones in undisturbed sequences), the principle of original horizontality (deposits form nearly horizontal layers), and the principle of faunal succession (distinct fossil assemblages indicate relative ages). Additional concepts such as cross-cutting relationships and lateral continuity help determine the relative timing of events like tilting, faulting, or erosion.

Stratigraphy encompasses several subfields. Lithostratigraphy groups rocks by lithology; biostratigraphy uses fossils to establish relative ages; chronostratigraphy links rock layers to absolute geological time units; sequence stratigraphy analyzes depositional sequences and their bounding surfaces; magnetostratigraphy uses changes in Earth's magnetic field; and chemostratigraphy relies on chemical signatures to correlate strata.

Dating and correlation methods combine relative dating with absolute dating techniques, including radiometric methods (for example, U-Pb, K-Ar, C-14) and the geomagnetic polarity timescale. Stratigraphy has wide applications in oil and gas exploration, archaeology, paleoclimatology, and groundwater studies, where understanding the arrangement of rocks and their ages informs reconstruction of environments, resources, and histories.

Historically, stratigraphy developed from Nicolas Steno’s principles in the 17th century and flourished with William Smith’s principles of faunal succession, evolving into a foundational framework for interpreting Earth’s past.