What is a formation?
Q: What is a formation?
A: A formation, or rock formation, is the fundamental unit of lithostratigraphy. It consists of a certain number of rock strata that have similar lithology (rocks), sedimentary facies (appearance) or other properties.
Q: How are formations defined?
A: Formations are not defined on the thickness of the rock strata, and the thickness of different formations can therefore vary widely. The concept of formally defined layers or strata is central to stratigraphy.
Q: What are members and groups in relation to formations?
A: A formation can be divided into 'members' and are themselves packed together in 'groups'.
Q: How were formations initially described?
A: Formations were initially described as time markers, based on relative dating and the law of superposition. The divisions of the history of the Earth were the formations described and put in chronological order by geologists and stratigraphers during the 18th and 19th centuries.
Q: How long do environments persist for where sedimentary deposition occurs to form rock formations?
A: Environments where sedimentary deposition occurs to form rock formations may persist for hundreds of millions of years. For example, up to 1200 million years worth sedimentation has been preserved intact in Pilbara's Hammersley Basin in Western Australia. Here, up to 300 million years is represented by a single unit consisting banded iron formation and shale.
Q: Who first studied geological stratigraphy?
A: Geologists and stratigraphers during the 18th and 19th centuries first studied geological stratigraphy by describing various rock formations as time markers based on relative dating principles such as law superposition.
