Simple planktonic/benthonic foraminiferal ratios, when contoured, outline parameters of ancient environments of deposition. Ratio maps of four successive subunits of Upper Cretaceous strata in east Texas, southern Arkansas, and northern Louisiana show the evolution and changes in paleocurrent systems, and when and where contemporaneous structural or topographic features of the sea floor acted as effective barriers to oceanic circulation. High-value planktonic ratios, characteristic of deep-water open-ocean environments, were also found in paleocurrent systems developed in shallow water.

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