Recent studies of sediments and faunas on the present continental shelves and slopes of the world have afforded paleoecologists many valuable data for interpreting the depositional history of older rocks. The thick subsurface wedges of marine and shore-line sediments in the Gulf Coast Tertiary, and their contained faunas, lend themselves ideally to paleoecologic interpretations using principles developed from studies of modern distributions.

Characteristics of modern faunas, principally the Foraminifera, have been most useful in Tertiary sediments. Specific and generic distributions where applicable are most diagnostic. Non-specific characteristics such as gross population characteristics, generic dominance, faunal diversity, and morphology become more useful in older Tertiary rocks.

The application of these characteristics in the Texas Gulf Coast Oligocene allows the construction of essentially time-stratigraphic paleogeographic maps and interpretation of the depositional history of Oligocene sediments. Such interpretations are essential to a valid understanding of subsurface stratigraphy.

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