Stratigraphy of Tidal Sequences
Previous lithostratigraphic studies of incised, valley-fill systems on the mid-Atlantic coast of the United States indicate a continuous Holocene sea-level rise. Likewise, the lithostratigraphic evaluation of vibracores from Albemarle Sound, North Carolina, can be interpreted as a simple infill history resulting from a continuous Holocene transgression. However, an integrated litho-, high-resolution seismic-, and chronostratigraphic approach suggests that the infill record of Albemarle Sound may be the result of several relative sea-level oscillations during the Holocene.
The Holocene section of Albemarle Sound contains at least three depositional sequences (ASDS-1 to ASDS-3), each consisting of lithologically similar successions of depositional environments. Basal sediments from ASDS-1 were deposited in a restricted-estuarine environment behind a continuous barrier island system between 8.1 ka and 5.9 ka. For some interval between 5.9 ka and 5.5 ka sea level dropped (<6 m), producing an extensive erosional surface throughout the middle- and outer-estuarine zone. Deposition resumed as sea level rose to form ASDS-2. Basal sediments of ASDS-2 were deposited in an open-estuarine system between 5.5 ka and 2.9 ka, suggesting that the previous barrier island complex was extensively breached. ASDS-2 is capped with closed-estuarine sediments that date from 2.9 ka to 1.5 ka, suggesting the reformation of a continuous barrier island complex. Another small drop of sea level occurred for some interval between 1.6 ka and 0.4 ka, which truncated ASDS-1 and ASDS-2. This drop was only between 1–2 m based on the absence of basal open-estuarine sediments in the overlying depositional sequence (ASDS-3), suggesting that the barrier island system was preserved and active during this interval. ASDS-3 consists of closed-estuarine sediments that are being deposited during the ongoing sea-level transgression and behind the modern, well developed barrier island system.