HOLOCENE GEOLOGIC AND CLIMATE HISTORY OF ONSHORE AND OFFSHORE DELMARVA PENINSULA

The Delmarva Peninsula is in a unique location, bordered by two major estuaries and the Atlantic Ocean, to preserve a geologic record of Holocene climate and sea-level rise. Newly-accepted subdivisions (Early, Middle, and Late) of the Holocene (Walker, 2019) provide a chronologic framework based on global climate signals for the Holocene of the Delmarva Region. Onshore and offshore geologic mapping were combined with 634 radiocarbon dates to develop a Holocene geologic and climate history. The Early Holocene (11.7 ka to 8.2 ka) experienced relatively low rates of sea-level rise with tidal deposition limited to MIS-2 paleovalleys and Carolina Bays on the uplands. The Middle Holocene (8.2 to 4.25 ka), in contrast, was a time of rapid sea-level rise and migration of the shoreline, transgressing up to 4 km over 250 years in some locations. Organic deposition on the uplands all but ceased indicating arid conditions. A correlative condensed section in deep Chesapeake Bay cores, which implies low sediment supply, also indicates an arid period. By the beginning of the Late Holocene (4.25 to 8.2 ka) the Atlantic shoreline was nearing its present position and shoals were deposited across the inner shelf. The modern configuration of the Atlantic barrier island-lagoon system developed during this period. The rate of sea-level rise slowed and tidal deposition in expansive marshes occurred adjacent to the estuaries. Organic deposition on the uplands became widespread in Carolina Bays and in the development of Cypress Swamp, indicating a return to wetter conditions.