About This Item
Share This Item
The lower 1,000 feet of the Horquilla limestone of southeast Arizona contain abundant early and middle Pennsylvanian fusulinids. Unconformities lie at the base of the Horquilla and at the top of the zone of Fusulina about 1,000 feet above the base of the formation. The lowest fusulinid zones, the zones of Millerella and Profusulinella, are relatively thin and in combined thickness make up about 100 feet of strata. The overlying zone of Fusulinella varies from about 100 to nearly 400 feet thick and has a diverse fusulinid fauna which is divisible into three subzones. The evolution of species of Fusulinella from early into later fusulinid groups is remarkably complete. Above this the zone of Fusulina reaching 600 feet in thickness is divisible into four subzones.
End_of_Article - Last_Page 544------------