Lithostratigrafi

Lithostratigraphy is the branch of stratigraphy that classifies and correlates rock sequences primarily on lithology and stratigraphic relationships rather than on absolute age. It focuses on the physical characteristics of rocks—rock type, mineral content, grain size, color, and sedimentary structures—to define units that are mappable in the field and in subsurface data.

The basic lithostratigraphic units are formations, members, beds, and groups. A formation is a mappable body of rock with a distinctive lithology that separates it from neighboring units. Formations may be subdivided into members, and members into beds, each defined by consistent lithologic traits. Names are typically derived from a geographic locality where the unit is well exposed, and a formal description and type section establish its defining characteristics.

Boundaries between lithostratigraphic units are defined by contacts where rock types change, which can be abrupt or gradational. These boundaries are based on rock properties and are not inherently tied to specific time intervals, since lithostratigraphy emphasizes lithology over age. Consequently, correlating units across regions often requires supplementary methods.

To relate lithostratigraphic units regionally or globally, geologists use additional stratigraphic tools such as biostratigraphy (fossil content), chemostratigraphy (chemistry), magnetostratigraphy, and sequence stratigraphy. Lithostratigraphy remains fundamental for geological mapping, resource exploration (hydrocarbons, groundwater, minerals), and reconstructing depositional environments and tectonic history. Formal lithostratigraphic practice is guided by regional conventions and international standards, with units named and described in the published geological literature.