The Glen Rose Formation (Lower Cretaceous) contains a microfossil flora which is useful as a paleoecologic tool. Examination of measured sections and three mapped terrigenous-clastic units shows that gymnosperm pollen and dinoflagellate hystrichospheres are useful in diagnosis of subtidal and supratidal conditions if coupled with lithologic evidence. Fern spores and angiosperm pollen were of limited use in paleoenvironmental interpretations.

Percentage-distribution maps of gymnosperm pollen and hystrichospheres for three units in a terrigenous clastic sequence in the Glen Rose of Somervell County show an increase of hystrichospheres and a decrease in gymnosperms toward probable open-water sediments. This suggests that palynomorph number is influenced by distance from source area.

Hystrichosphere morphologic types were found to change with depositional environment. Barb-spined forms commonly were associated with shallow-water open-marine sediments. Straight-spined forms commonly were associated with sediments deposited in shallow brackish-water.

Angiosperms, fern spores, and certain hystrichospheres were not related clearly to depositional environments inferred from lithologic evidence and other palynomorphs. Distribution of these microfossils may be explained by wind- and water-current fluctuations during deposition. Particle characteristics, such as settling velocity and size sorting, also may have influenced their distribution.

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