Analysis of high-resolution seismic reflection and sonar data from the East China Sea (ECS) continental shelf reveals the presence of an extremely broad (Ͼ 330 km) and deep (maximum incision of 72 m) incised-valley complex whose development and subsequent fill is constrained to the end of the last glacial cycle (ϳ 20,000 yr BP to present).Results from this study indicate that sea-level change, climate-controlled discharge and sediment supply, and shelf physiography were important factors in the development and subsequent fill of the ECS incised-valley complex. For example, wet climatic conditions during the initial Marine Oxygen Isotope Stage (MIS) 2 fall of sea level promoted fluvial erosion of the exposed shelf. However, the trend toward drier conditions during the MIS 2 fall of sea level slowed the overall development of the incised-valley complex to the point where only minor incision occurred during the maximum lowstand. Furthermore, the low-gradient morphology of the exposed outer shelf diminished the ability of fluvial systems to incise. Instead, fluvial systems migrated laterally, creating a shallow (Ͻ 30 m) but wide (Ͼ 300 km) incisedvalley system on the outer shelf.During the late MIS 2 rise of sea level, accommodation was generated within the flooded reaches of the valley complex. However, arid climatic conditions that prevailed at this time resulted in minor sediment delivery to the transgressive shoreline via the incised-valley complex. Thus, the upper part of the drowned lowstand fluvial deposits were exposed at the sea floor and reworked into a valley-wide tidalbar and tidal sheet complex. Wetter climatic conditions during middle to late MIS 1 resulted in abundant sediment delivery to the drowned parts of the valley complex (estuary) and buried lowstand fluvial deposits below the depth of tidal ravinement, where they remained undisturbed.Current sequence stratigraphic models can be applied to the late Quaternary stratigraphic secession of the ECS. However, these models are too simplistic because they rely largely on rates and directions of sea-level change to explain stratal architectures. Although the extent and rate of sea-level change is extremely important, this study shows that high-frequency climate change and shelf physiography also play important roles in the development of stratigraphic architectures. These factors are particularly important for the development of incised valleys, where they directly influence incised-valley morphology and facies distributions.
Seismic reflection surveys of 8 of the 11 Finger Lakes of central New York Statehave documented the deep (as much as 306 m below sea level) glacial scour of these lake basins and their subsequent infill by thick (up to 270 m) unconsolidated sediment. Drill data indicate that sediment infill occurred rapidly during a short interval between ~14,400 and 13,900 14C yr ago, coeval with Heinrich event H-1 when large volumes of icebergs and meltwater were discharged into the North Atlantic during an unstable phase of the Laurentide ice sheet.Six acoustically defined depositional sequences beneath the lakes, correlated with drillcore and piston core samples, record the infill history of the Finger Lakes during the late Wisconsin. Depositional sequence I is equivalent to thick, water-laid sands and gravels of the Valley Heads moraine deposited ~14.4 ka. During retreat of the ice margin from its Valley Heads position, subglacial meltwaters transported large volumes of fine-grained sediment into the Finger Lake basins (sequences II and III). Sequence IV records a phase of high-level proglacial lakes when ice blocked northern outlets of the Finger Lakes and fine-grained sediments continued to be transported into the basins from the north. An abrupt drop of proglacial lake levels and a drainage reversal is recorded by sequence V when sediments first began to enter the Finger Lakes from the south following retreat of the ice margin past the northern outlets of the lakes. The well-known modern glens and waterfalls of the Finger Lakes region formed at this time when lateral streams adjusted to dramatically lowered
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