Channel bank deposit

The eastern and western banks of the channel are markedly different in morphology, surficial sediments, and subsurface structure. For much of the survey area, the eastern channel bank is narrow and steep whereas the western bank is broad and gently sloping. A field of irregular sediment waves covers much of the western channel bank, whereas sediment waves are found within only a narrow strip along the eastern channel bank in the southern half of the area. Elsewhere the eastern channel margin deposits are comprised of sandy silt with no discernable bedforms and moderate to

Figure 5.12. Sun-illuminated image of the hull of a sunken ship (probably a Hudson River Sloop) found in the Hudson River during this study. Scale bar is 25 m long, and the small-scale pattern to the lower left of the hull outline is an artifact. A number of shipwrecks and other items of possible historical significance have been discovered as part of this mapping program, and suitable steps need to be taken to inventory, identify, and preserve these features.

Figure 5.12. Sun-illuminated image of the hull of a sunken ship (probably a Hudson River Sloop) found in the Hudson River during this study. Scale bar is 25 m long, and the small-scale pattern to the lower left of the hull outline is an artifact. A number of shipwrecks and other items of possible historical significance have been discovered as part of this mapping program, and suitable steps need to be taken to inventory, identify, and preserve these features.

low backscatter. Adjacent to Croton Point, a field of irregular pinnacles is found with prominent channel-parallel sediment wave trains developed on their southern side. These pinnacles appear to be erosional remnants of the eastern marginal flat deposits, or they may be built of debris of anthropogenic origin.

The sub-bottom data reveal a distinct sediment package associated with each channel bank. Beneath the east channel bank, sediment layers typically are parallel to the riverbed, dipping west into the channel. In places, east bank sediments overlay channel deposits, possibly due to slumping along this channel wall. North of the channel bend, sediment layers can be traced uninterrupted from the western channel bank to beneath the axial deposits to form a nearly continuous depositional unit. South of the channelbend, these dipping sediment layers are truncated at the riverbed. At the channelbend a series of dipping layers, bounded by unconformities, document a history of prograding depositional layers terminated by erosional events. Channel bank deposits on both margins uncon-formably overlay the marginal flats deposits, indicating that the entire package of channel axis and channel bank sediments are younger than the marginal flats deposits.

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