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The AAPG/Datapages Combined Publications Database
Kiawah Island is an anomaly among barriers along the United States East Coast. Whereas most barriers today are actively eroding and transgressing landward, Kiawah displays a history of seaward progradation. The island is composed of a series of parallel beach ridges, which are morphologic evidence of a period of long-term accretion.
To examine the Holocene stratigraphy of Kiawah Island, 35 core holes were drilled to an average depth of 12.9 m into underlying compact Pleistocene clays of the Talbot Formation. The Holocene stratigraphy is a regressive sequence of environments with fine-grained, rooted, trough and planar cross-bedded beach-ridge, berm, and washover sands overlying burrowed, laminated, interbedded silts and clays. Faunal analysis suggests a shoreface to continental-shelf depositional environment for the Mulinia-rich silts and clays that comprise the lower half of the Holocene section. Carbon-14 dates of shell, wood, and peat material indicate a history of seaward progradation and beach-ridge development over at least the past 2,500 to 3,000 years. In contrast, the most landward beach ridge consists o a very thin (3.0 to 4.5 m) Holocene section of leached, poorly sorted, fine to coarse-grained sands capped by a poorly developed soil profile suggesting that this beach ridge represents the initial or primary barrier deposited during an earlier transgressive phase of history for Kiawah Island prior to 3,000 years B.P.
Understanding the unique depositional history of regressive barrier islands is especially significant in that these barriers have the highest potential for preservation in the rock record.
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