Abstract: Sedimentation Rates in Hudson River Estuary

C. R. Olsen, H. J. Simpson, S. C. Williams

Geochemical and sedimentologic studies have been conducted on one 6-m core and on a series of 1 to 3-m cores taken over a range of approximately 100 km in the Hudson River estuary. Much of the recent sediment accumulation is occurring in New York Harbor and in protected areas along the sides of the estuary upstream from New York City. The vertical distribution of fallout and reactor-produced radionuclides indicate sedimentation rates on the order of 20 cm/year in some areas of the harbor. The top 10 cm of this sediment is highly liquefied and the top meter is extensively turbated showing only hints of lamination. The turbation may be not only a result of mechanical mixing by organisms but also of the release or entrapment of biochemically formed gases.

The fine-grained sediments of the natural channel and subtidal bank, upstream from the harbor, are characterized by alternating layers of fine sandy silts and clay-rich silts, on a millimeter to centimeter scale. Coarse sand-shell layers (channel) from 1 to 20 cm thick and turbate zones (subtidal bank) from 1 to 10 cm thick are present at the surface and are interlayered with zones of laminated fine-grained sediment at greater depths. Radiocarbon dating of subsurface shell layers in the channel 18 to 24 mi (29 to 38 km) upstream of the southern tip of Manhattan indicate net sedimentation rates on the order of 2 to 3 mm/year. Reactor- and bomb-produced radionuclides as well as human detritus, such as coal, fly ash, and metalliferous slags, appear to be confined to the surface turbate z ne (subtidal bank) or to the coarse surface-channel lag in this area of the Hudson.

It is proposed that the laminated fine-grained sediments are deposited rapidly when the Hudson transports relatively high concentrations of sediment; the turbate zones represent periods of slower or nondeposition during normal-flow conditions, and the coarse sand-shell layers result from intense scour by tidal currents or increased sand transport during high-energy conditions.

AAPG Search and Discovery Article #90972©1976 AAPG-SEPM Annual Convention and Exhibition, New Orleans, LA