STRATIGRAPHY AND LATE QUATERNARY GEOLOGIC HISTORY OF BUCKRIDGE COASTAL RESERVE, TYRRELL COUNTY, NORTH CAROLINA: INTERESTING IMPLICATIONS CONCERNING HOLOCENE SEA LEVEL

Buckridge Coastal Reserve is a low lying, wetland-dominated area surrounded on three sides by the Alligator River estuarine system. Eighteen Geoprobe and vibra-cores, penetrating up to 20 m below mean sea level, were taken to determine the late Quaternary stratigraphy of the area. Stratigraphic patterns between cores were determined by a series of peat-probe and ground penetrating radar surveys. Chronology was established using radiocarbon and amino-acid racemization (AAR) age estimates and was correlated with regional age data.

The reserve is situated on a paleo-topographic high comprised of at least two Pleistocene sequences. The lowermost sequence (BDS-3) is a succession of estuarine to shelly marine deposits with an AAR age between 90 and 70 ka. Overlying BDS-2 is ~6 m of non-marine sand and mud which extends to the land surface on uplands and which underlies organic-rich mud and peat (BDS-1) within paleo-valleys. BDS-1 was deposited as valleys formed by tributary networks of the Alligator River drainage system during the last glacial stage were subsequently filled with peat in response to rising Holocene sea level.

Detrital peat accumulation began in paleo-channels ~10 ka and fluvial processes dominated until at least 5.8 ka. Estuarine conditions followed from 5.5 to 3.8 ka. The peat record suggests that bay ravinement during the middle Holocene (~ 5 ka) removed much of the earlier Holocene landscape. The organic remains of this older landscape were deposited as detrital peat in deeper channels. Between 3.8 and 3.0 ka, a stillstand or fall in sea level allowed for the expansion of fresh to low-brackish cattail marsh upon the bay ravinement surface. Marsh dominated the area from around 2.9 to at least 1.4 ka with peat accretion in response to sea-level rise. Marsh peat is overlain by woody peat in the upper ~2 m of the section. It is hypothesized that the replacement of marsh peat by forested wetland and woody peat was a response to either slowed sea-level rise or falling sea level during the Little Ice Age (~600 to 100 BP).