Hauterivian

The base of the Hauterivian is defined as the place in the stratigraphic column where the ammonite genus Acanthodiscus first appears.

A reference profile for the base (a GSSP) was officially ratified by the International Union of Geological Sciences in December of 2019, and is placed in La Charce, France.

[2] The top of the Hauterivian (the base of the Barremian) is at the first appearance of ammonite species Spitidiscus hugii.

The Hauterivian cold snap appears to be associated with permafrost at high elevations and large ice sheets that potentially stretched as far south as the modern Iberian Peninsula, based on the existence of Hauterivian ice-rafted dropstones in Iberia.

Cold conditions are also known to have existed in the Southern Hemisphere during the same time period, based on records from Australia.