CONIACIAN STAGE

the third of six divisions in the Upper Cretaceous Series, representing rocks deposited on a global basis during the Coniacian Age (88.5 to 87.5 million years ago). The vicinity of the town of Cognac (from which the name Coniacian was derived) in western France serves as the classic type district for rocks of this age. However, no global stratotype section and point (GSSP) for the base of the Coniacian Stagei.e., worldwide standard for defining the stratigraphic boundaryhas been approved. Conventionally, the base of the stage is defined by the first appearance of the ammonite biozone Barroisiceras haberfellneri. Also diagnostic is the planktonic foraminifera biozone Whiteinella inornata. The Coniacian Stage is represented in England by part of the Upper Chalk and in the United States by part of the Niobrara Limestone (q.v.). Rocks of the Coniacian Stage overlie those of the Turonian Stage and underlie rocks of the Santonian Stage. Many conflicting names have been proposed for this and other stages of the Cretaceous System, but the present scheme follows closely the order imposed by Alcide Dessalines d'Orbigny in the mid-19th century.