Lithostratigraphy: Formation of the Formation

Lithostratigraphy has traditionally dealt with the nomenclature of well-preserved and weakly metamorphosed sedimentary rocks. Lithodemic stratigraphy has been established for igneous plutonic and more strongly metamorphosed rocks. Allostratigraphy is based on unconformity-bounded stratigraphic units. All three have formally defined classification schemes with the fundamental units being Formation, Lithodeme and Alloformation, respectively. Definition, formal requirements and procedures for establishing units are described here. Although lithostratigraphy is the most descriptive and objective branch in stratigraphy, various phenomena may cause difficulties in description and reconstruction and selected case studies are described. They include 'layer-cake' geology, lateral facies changes and complex geometries, spatially widely distributed units and different national approaches, mappable bodies due to alteration, imbricate thrust sheets, plutonic igneous rocks, igneous and metamorphic rocks, high metamorphic grade terrane, and an allostratigraphic example from the Cretaceous. Different approaches for non-marine Quaternary sediment bodies are noted.