ABSTRACT

Miocene and younger sediments of the Gulf Coast locally contain large numbers of arenaceous Foraminifera. Certain genera and species are particularly useful in subsurface stratigraphy. Arenaceous forms present difficult problems in identification. These problems are compounded by the fragmentary condition of specimens present in the washed residues usually available to industrial paleontologists. Special care in washing is required if arenaceous forms are to reach the paleontologist in identifiable condition.

Bigenerina, Clavulina, and Martinottiella can frequently be identified when only uniserial fragments are available. These three genera are valuable guides in the recognition of depositional energy regimes. Bigenerina is typically found in high-energy lithotopes. Specimens are often encountered in beach and offshore-bar deposits. Clavulina requires a lower energy regime. It can be found in protected bays, or seaward from the surf zone on the open marine shelf. Martinottiella is restricted to low-energy environments. It is a minor component of middle Miocene and younger outer-neritic faunas. Whereas all three genera are locally useful as stratigraphic horizon markers, they have a broader utility in suggesting probable sand conditions. The higher the energy level of the depositional environment, the more abundant and coarser the sand (under most conditions).

Several species of arenaceous Foraminifera used by oil industry paleontogists for subsurface correlations on the Gulf Coast are found in the same relative stratigraphic positions at least as far as the Caribbean Basin. Textularia crassisepta, which marks the Plio-Pleistocene contact (Valvulina "H" datum) in offshore Louisiana, seems to hold a similar level in Jamaica. Textularia subplana is typical of middle Pliocene (Buliminella "1") deposits in Louisiana. Specimens from samples of the same (?) age were found in northern Columbia and in Jamaica. Bigenerina humblei is one of the middle Miocene index species in Texas and Louisiana. The name may be a junior synonym for Textularia falconensis Cushman and Renz, a Venezuelan stratigraphic horizon marker. Dr. Renz believed the latter to be useful in the Caribbean region.