Late-stage estuary infilling controlled by limited accommodation space in the Hudson River

High-resolution seismic data and sediment cores reveal the late Holocene subsurface stratigraphy of the broad Tappan Zee–Piermont region of the Hudson River Estuary. We identify a series of distinct, extensive horizons beneath the marginal flats, channel banks, and main channel in this area. Physical properties and lithology from sediment cores suggest that these horizons are surfaces of erosion or nondeposition. Radiocarbon dates indicate that they correspond with three distinct time horizons, with maximum ages of 3400, 2200, and 1600 yr BP. We also distinguish two sedimentary facies that occupy the marginal flats and channel banks. The deeper facies forms a deposit 2 km wide and 7 km long that accumulated at rates of 2–4 mm/yr in the vicinity of the Sparkill Creek prior to ∼ 1700 yr BP, overlying and onlapping the 2200 yr BP seismic surface. Based on its internal geometry, morphology, and proximity to a tributary, we interpret this facies as a delta deposit. The shallower facies accumulated more slowly (1–2 mm/yr), overlying the delta deposit to the south and dominating the marginal flats to the north. Surface sediment samples and geophysical data reveal that the modern marginal flats are no longer actively depositional, but dominated by nondeposition or erosion. Limited accommodation space in the Hudson River Estuary may be the critical factor contributing to the observed sedimentary pattern, characterized by intervals of deposition punctuated by episodes of erosion. An estuarine system that has reached a state of morphological equilibrium will be sensitive to even small fluctuations in sea-level and climate conditions, which may account for the intervals of deposition and erosion we observe. Limited accommodation space and intermittent sediment deposition in the Hudson River Estuary may be due to its evolution from a fjord filled with glacial lake sediments, which distinguishes its infilling behavior from the classic drowned river valley estuary.