LATE HOLOCENE STRATIGRAPHY OF FINE-SEDIMENT DEPOCENTERS WITHIN THE PLEASANT BAY AND NAUSET MARSH BACK BARRIER SYSTEMS, CAPE COD

Analysis of organic rich sediment cores within back barrier marine environments allows for reconstruction of recent environmental conditions, including Holocene sedimentation patterns, anthropogenic forcings, and sea level changes. In the ecologically and economically important areas of Nauset Marsh and Pleasant Bay, adjacent to the outer edge of the Cape Cod National Seashore, composite sediment cores were taken from three depocenters. Locations for Kullenberg and Livingstone coring include Meetinghouse Pond (MHP) and Frostfish Cove (FFC) within Pleasant Bay, and Orleans Town Cove (OTC) in Nauset Marsh. All Livingstone cores reached refusal, likely at the ravinement surface, at depths of 343 cm, 285 cm, and 103 cm, for OTC, FFC, and MHP, respectively. Black muds exhibiting sulfuric odor present in the upper 130 cm of the Nauset Marsh core may represent anoxic conditions, with intermittently laminated light brown, sandy mud deposited below. Sediments in Pleasant Bay cores are a uniform light brown, sandy, fine grained mud containing abundant bivalve and periwinkle shells throughout. Volume magnetic susceptibility values are low for all cores, averaging 2.7*10^‑5 SI in Pleasant Bay and 0.79*10^‑5 SI in Nauset Marsh. Low susceptibility values are due to an abundance of diamagnetic material, likely due to high organic content and lack of clastic fluvial deposits. In the upper 90 cm, 65 cm, and 35 cm of the OTC, FFC, and MHP records, respectively, a significant rise in susceptibility (T-tests: P<0.0001 for Pleasant Bay, P=0.0007 for Nauset Marsh) indicates the effect of burning fossil fuel associated with industrialization. The correlative rise suggests the cause was regional, and we date this depth in the record as the onset of the Industrial Revolution, ca. 1880. From this proxy date to present, sedimentation rates for OTC, FFC, and MHP are 0.67 cm/ yr, 0.48 cm/yr, and 0.26 cm/yr, respectively. Ongoing analyses, including radiocarbon dating and CNS isotope analyses will allow for a more thorough time-constrained environmental history of the region.