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Abstract: Classification and Analysis of Palynomorphs of the Aguja Formation (Campanian), Big Bend National Park, Brewster County, Texas

Nina Lucille Baghai

Exposures of the Aguja Formation (84-74.5 m.y.) at Big Bend National Park contain deltaic sequences deposited on the southwestern margin of the Western Interior seaway. Nearshore marine shelf sandstones interfinger with floodplain mudstones as a result of multiple regressive-transgressive cycles. Palynomorph plant microfossils record regressive depositional phases. The Aguja microfossil flora, previously undescribed, is preserved in brown to black organic-rich, dinosaur-bearing shales or lignite beds within sandstone horizons.

Palynomorph samples collected and processed from five stratigraphic sections from the western part of Big Bend National Park include vitrinite, wood fragments, tree resin, dispersed leaf cuticle, petrolitic filaments, pollen/spores, fungal hyphae, and dinoflagellates. Numerous and varied pollen/spore grains, ranging from 10 to 90 µm, suggest that the region supported a rich and diverse tropical to subtropical flora. Dry seasons are suggested by abundant thin (2-5 µm) dispersed cuticles. Quantitative counts and analysis of 65 samples reveal 35 genera of angiosperms, 9 genera of gymnosperms, 32 genera of ferns, 8 genera of algae and/or dinoflagellates, and 2 genera of fungi. Common genera are Aercipites, Liliacidites, and Palmaepollenites (monocotyledons); Momipites, Plicapollis, Vitipites (dicotyledons); Cycadopites, and Inaperturopollenites (gymnosperms); and Cyathidites, Granulatisporites, and Gleicheniidites (ferns). Coastal marsh deposits possess the richest assortment of fungi, ferns, gymnosperms, and tricolpate and triporate angiosperms; intertidal nearshore deposits contain dinoflagellates; and fluvial deltaic deposits contain a major component of dispersed leaf cuticles and a minor component of dicotyledon pollen.

AAPG Search and Discovery Article #90983©1994 GCAGS and Gulf Coast SEPM 44th Annual Meeting, Austin, Texas, October 6-7, 1994