This data set includes a variety of bulk organic carbon, lignin-phenol biomarker, and sedimentation rate data from a set of sites in the Blackwater Marsh in Chesapeake Bay. At each site, a short core was taken, and all data is organized according to depth below the marsh surface. Data includes: • Bulk %OC, bulk %N, atomic carbon:nitrogen ratios, stable carbon isotopes (d13C) • Lignin-phenol biomarker parameters, including 8, Ad:Alv, C:V, S:V, and the individual concentrations of each lignin-phenol (in lambda units, or mg per 100 mg OC). • Pb-210 and Cs-137 activities • Sediment bulk densities In addition to the sediment core data, we are also including d13C values from vegetation samples collected from each of the marsh sites. These values are reported for each species, with some broken down between belowground and aboveground biomass.