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.
Figures & Tables
Tidalites: Processes and Products - Tidal processes are important agents of sediment transport and deposition in most marine coastal zones. Recent development of better tools for recognizing tidal deposits (e.g., tidal bundles and tidal rhythmites) has also revealed that such deposits are much more common and extensive than previously thought. This volume presents the latest ideas on tidal sedimentation, including exciting new work concerning the tidal flats of the Wadden Sea, the area where modern-day studies of tidal sedimentation began; the origin, interpretation, and uses of tidal rhythmites; and the sequencestratigraphic context of tidal sediments.