Stratotype

In <a href="/facts/Geology/WGvVRIYF">geology</a>, a stratotype or type section is the <a href="/facts/Location_(geography)/fXux5RaJ">physical location</a> or <a href="/facts/Outcrop/3MC1NG4y">outcrop</a> of a particular reference exposure of a <a href="/facts/Stratigraphy/o3J6Ij3R">stratigraphic sequence</a> or stratigraphic boundary. If the stratigraphic unit is layered, it is called a stratotype, whereas the standard of reference for unlayered rocks is the <a href="/facts/Type_locality_(geology)/ky6QjASt">type locality</a>. 
Also it can be defined as "The particular sequence of strata chosen as standard of reference of a layered stratigraphic unit."[This quote needs a citation] 
When a stratigraphic unit is nowhere fully exposed, the original type section may be supplemented with reference sections covering the full thickness of the unit. A reference section may also be defined when the original type section is poorly exposed, or for historical units which were designated without specifying a type section according to more modern standards.

Stratotype open-in-new

Stratotype