2015 GSA Annual Meeting in Baltimore, Maryland, USA (1-4 November 2015)

Paper No. 134-10
Presentation Time: 9:00 AM-6:30 PM


SHMORHUN, Nina, Geology, Bryn Mawr College, 101 N Merion Avenue, Bryn Mawr, PA 19010, BARBER, Donald C., Geology, Bryn Mawr College, 101 N. Merion Ave, Bryn Mawr, PA 19010 and KEGEL, Jessica, Geological Sciences, East Carolina University, Greenville, NC 27858, nshmorhun@brynmawr.edu

Late Holocene relative sea-level records show differing submergence rates along the North Carolina coast. Differential glacial isostatic adjustment explains some of the observed pattern, but other spatial or temporal effects could also be important, e.g., uplift near the Cape Fear Arch or variable dynamic sea-surface heights along the coast. High-resolution sea-level reconstructions exist for three locations (Croatan Sound, southern Pamlico Sound and Wrightsville Beach), but additional records are needed to quantify and model regional sea level rise. We are working toward development of a new continuous sea level record from saltmarsh peat cores in Smyrna Creek, a small tributary of Jarrett Bay approximately 20 km north of Cape Lookout. The local mean and spring tidal ranges are 33 and 41 cm, respectively, and salinity ranges from 18 to 36 ppt. Juncus romerianus is the dominant vegetation over most of the study area. Leveling to a nearby geodetic benchmark places most of the marsh surface 20 – 25 cm above local MSL (LMSL), at or near the local MHHW elevation. Short-form Spartina alterniflora forms a narrow band at lower elevations along the creek, whereas higher elevations (>30 cm above LMSL) exhibit Spartina patens and Distichlis spicata; Spartina cynosuroides occurs close to the upland boundary at elevations >40 cm above LMSL. Surface samples from the Juncus high marsh near Smyrna Creek contain an agglutinated foraminiferal assemblage dominated by Trochammina inflata, with decreasing abundance of Arenoparella mexicana, Miliammina fusca, Tipotrocha comprimata and Siphotrochammina lobata, respectively. More landward assemblages also contain Ammoastuta inepta. A foraminiferal assemblage similar to that found in the surface sample transect occurs in down-core peat samples to a depth of 2.65 m below the present marsh surface (2.37 m below LMSL, or -2.45 m NAVD88). Cores contain mostly Juncus material with organic matter content ranging from 15-65%. Comparisons with the stratigraphy of Sand Hill Point (Cedar Island, southern Pamlico Sound) indicate Smyrna Creek could provide a sea-level record that extends >2,500 years BP. This would help elucidate regional sea-level variations and resolve uncertainties in the early parts of existing Late Holocene sea-level reconstructions.