Paleo-environmental changes and sea level history of the Leipsic River, Delaware

Detailed stratigraphy, paleoenvironmental interpretation of tidal wetland facies, radiocarbon dating, paleogeographic reconstructions, and modern marsh accretion rates are used to reconstruct the late Holocene sea level history of the Leipsic River valley.; In the early Holocene the Leipsic River was a tributary to the ancestral Delaware River. The Holocene transgression reached the geomorphic setting of the Leipsic River around 5,000 BP, when brackish tidal wetlands began to develop in the area. Around 3,000 BP, the Leipsic River valley was flooded and turned into an open water environment. Deceleration of the sea level rise resulted in the expansion of the brackish marshes in the valley. Tidal creeks migrating on the marsh paleosurface were eroding brown peat and depositing mud units at different depths. Brackish wetland environments persisted in the Leipsic River valley till about 1,000 BP, when salt marsh began to replace the brackish wetlands. By 300 BP, the study area was occupied with modern salt marsh.; Salt marshes developed in the valley during the last 100 years with a vertical accretion rate of 0.29 cm/yr. Twenty years ago, the marsh vertical accretion rate increased to 0.46 cm/yr.; Radiocarbon dates of twelve basal peats from the Leipsic River valley, and ten previously unpublished basal peat dates from the Delaware coast were used to revise the Delaware sea-level curve. A review of published and unpublished 137Cs and 210Pb analyses, and tidal gauge data provide the basis for evaluating shorter-term (102 yr) sea-level trends.; The updated curve is similar to Belknap and Kraft's (1977) original sea-level curve from 12,000 to about 2,000 years BP. The updated curve documents a rate of sea-level rise of 0.9 mm/yr from 1,250 years BP to present. This relatively low rate is in good agreement with other sea-level curves from the northern and central U.S. Atlantic coast, while the previous curve documents rates of about 1.3 mm/yr.; A review of 210Pb and 137Cs analyses from Delaware salt marshes indicates average vertical marsh accretion rates of 3 mm/yr. for the last 100 years, in good agreement with shorter-term estimates of sea-level rise from tidal gauge records.