BENTHIC FORAMINIFER ANALYSIS OF PLIOCENE SEA LEVEL, SOUTHEASTERN VIRGINIA

Sea level rise, caused by melting of polar ice and the thermal expansion of warming oceans threatens coastal areas worldwide. Sea level, in a particular coastal area, is a balance of local influences including vertical movements of the Earth’s crust, and the deposition or removal of material by sedimentary processes.

History of sea level for a particular area is captured in sedimentary sequences. Cores drilled in the Coastal Plain by the USGS and cooperators expose a timeline of past deepening and shoaling.A single core can inform the history of a single location. A collection of cores from an area can inform a regional model of change.

One way to interpret sea level change is to examine fossil remains of microorganisms included in sedimentary layers.One group of organisms, benthic foraminifera, are somewhat ubiquitous in coastal sediments.The constituent species of a foraminifer assemblage representing a place and time is highly dependent on environmental conditions such as temperature, seasonal temperature flux, salinity, and local conditions associated with water depth. The assemblages associated with various environmental conditions are known, so shifts in the composition of assemblages through the core reveal a record of sea level change over time.

Pliocene sediments from three cores taken at varied distances from the shore line were sampled and analyzed.While the Smithfield Core, Smithfield, VA and the Holland Core, City of Suffolk, yield rich assemblages for analysis, even the most distal core, Dory, drilled approximately 25 miles inland, yields an assemblage of foraminifers indicating a marine past.

The coast of Southeastern Virginia hosts military bases, shipbuilding, commercial shipping and recreation industries so the investment in facilities and infrastructure there is large. While models can predict the magnitude of sea level rise and predict potential inundation, decision making can also be informed by the local history of coastal dynamics associated with past climates. While this study encompasses a small slice of time in three places, it can be expanded temporally by more extensive sampling and analysis of these cores, or can be expanded geographically by sampling material from a wealth of existing cores drilled by the USGS or in cooperation with Virginia Department of Environmental Quality.