key bed; marker bed
Geological term for a distinctive, widespread rock layer used as a reference for stratigraphic correlation. Also known as 鍵層 (かぎそう) in Japanese.
See also: 鍵層
The key bed in this area is a volcanic ash layer that can be traced over a wide area.
Variant spelling with a middle dot; less common but still used.
Loanword from English 'key bed', a geological term.