A fundamental lithostratigraphic unit of intermediate
rank, characterized by similar lithologic units or rock
types, or other distinguishing features. They may range in
thickness from about a meter to several thousands of meters.
Formations are the only formal lithostratigraphic units
defined on the basis of lithology. They must be mappable,
distinguishable from other formations, have defined boundaries
and relationships to other formations, and be the product
of similar conditions. Some formations are made of a
singular lithological type, whereas others may be made of a
repetition of several different types, such as cyclic alternations
between sandstone, shale, and limestone. Formations
may represent short or long intervals of geologic time. They
may be subdivided into members or grouped into groups and
are named after prominent geographic features in the area in
which they are defined.
See also STRATIGRAPHY.
Tidak ada komentar:
Posting Komentar
Catatan: Hanya anggota dari blog ini yang dapat mengirim komentar.