Biofacies Analysis of Zanclean Sediments in Virginia: Unraveling the Past Through Benthic Foraminifera
2025
Whittney Spivey
Early Pliocene sedimentary deposits are exposed at the surface along the James and York Rivers, across southeastern Virginia. The Zanclean age (5.33&ndash:3.60 Ma) Sunken Meadow Member of the Yorktown Formation records a relatively large-scale marine transgression in the Salisbury Embayment. A total of 15 samples were collected from an outcrop near Spring Grove, VA, for grain-size analysis and to document benthic and planktic foraminiferal assemblages. The sediments are generally moderately well-sorted, shelly fine sands. A total of 48 benthic taxa were recorded from the Sunken Meadow Member, though only 14 taxa occurred in proportions high enough to be included in the Q-mode cluster analysis (>:3% of the total assemblage). Low numbers of planktic foraminifera indicate relatively shallow water deposition. Biofacies analysis shows three distinct biofacies groups in the Sunken Meadow Member and the benthic foraminiferal community shifts throughout the unit are indicative of changes in nutrient availability, surface productivity, and bottom water oxygenation. The results indicate a middle to outer neritic depositional environment similar to modern conditions found south of Cape Hatteras, NC.
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