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Changes in benthic foraminiferal assemblages accompany changes in total sediment texture and mineralogy (primarily percent phosphatic grains) throughout the Pungo River Formation in Onslow Bay, North Carolina. Only Burdigalian (late-early Miocene) deposits have been cored in southern Onslow Bay. Basal phosphorite sands (30% phosphate) are overlain by phosphatic (8%) muds and slightly phosphatic (4%) quartz sands. Elongate buliminaceans (Bolivina, Bulimina, Buliminella, Uvigerina) comprise over 50% of the benthic assemblage in phosphorites. They also predominate (43%) in phosphatic muds where Siphogenerina and Florilus become conspicuous faunal elements. Diverse trochospirally coiled forms (mainly Hanzawaia, also Valvulineria and Cibicides) become predominant in quartz san s; buliminaceans decline to 30% of the fauna. Pungo River deposits in northern Onslow Bay are Burdigalian, Langhian (early-middle Miocene), and Serravallian (middle Miocene) in age. Burdigalian deposits are nonphosphatic, muddy quartz sands in which Hanzawaia predominates and buliminaceans comprise only 22% of the fauna; Florilus accounts for 5%. Hanzawaia remains the dominant genus in the slightly phosphatic (4%) quartz sands of the Langhian and the phosphatic (10%) sands of the Serravallian; buliminaceans increase to 29% of the fauna, but Florilus nearly disappears. Both vertically and laterally through the Miocene of Onslow Bay, nutrient-loving buliminaceans thrive where phosphate content increases. Florilus and Siphogenerina are associated with the influx of fine-grained terrigenous ediments. The Hanzawaia-dominated assemblage thrives in clean,
coarser-grained substrates. Regional trends in the distributional patterns of these taxa may aid in locating additional phosphate deposits.
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