ANISIAN STAGE

the lower of two subdivisions in the Middle Triassic Series, representing all those rocks deposited worldwide during the Anisian Age (240 to 235 million years ago). The stage's name is derived from an area along the Anisus River at Grossreifling in the Austrian Alps, where a thick sequence of rocks was deposited in a marine environment. The limestone strata there contain four ammonite biozones (shorter spans of time characterized by a particular type of fossil mollusk), beginning with Lenotropites caurus and ending with Frechites chischa. No global stratotype section and point (GSSP) for the base of the Anisian Stage has been approved by the International Commission on Stratigraphy. Rocks of the Anisian Stage underlie those of the Ladinian Stage and overlie rocks of the Spathian Stage.