Stratigraphy - Lithologic Stratigraphy

Lithologic Stratigraphy

Lithostratigraphy, or lithologic stratigraphy, is the most obvious. It deals with the physical lithologic, or rock type, change, which is both vertical in layering or bedding of varying rock type and lateral, reflecting changing environments of deposition, known as facies change. Key elements of stratigraphy involve understanding how certain geometric relationships between rock layers arise and what these geometries mean in terms of the depositional environment. One of stratigraphy's basic concepts is codified in the Law of Superposition, which simply states that, in an undeformed stratigraphic sequence, the oldest strata occur at the base of the sequence.

Chemostratigraphy is based on the changes in the relative proportions of trace elements and isotopes within and between lithologic units. Carbon and oxygen isotope ratios vary with time and are used to map subtle changes in the paleoenvironment. This has led to the specialized field of isotopic stratigraphy.

Cyclostratigraphy documents the often cyclic changes in the relative proportions of minerals, particularly carbonates and of fossil diversity with time, related to changes in palaeoclimates.