Investigation of a Decapitated Paleo-River System on the Mid-Atlantic Continental Shelf Grant uri icon

abstract

  • Today, many rivers drain the East Coast of the United States. These same rivers would have extended across the continental shelf during low stands of sea level (e.g., the Last Glacial Maximum (LGM)). The LGM pathways of most paleo-rivers are not known and may have been impacted by a pronounced forebulge in areas near ice-sheet loading. During Late Pleistocene and Holocene sea-level rise, the morphology and strata of these systems likely were modified by coastal processes and decapitated during shoreline transgression (Fig. 1). Because of their incised nature, the basal portions of river systems are thought to be best sites of coastal- zone-strata preservation (Belknap and Kraft, 1981). Several sea-level curves indicate that rise since the LGM was not steady. Rather, it was punctuated by several pronounced flooding pulses (Fairbanks, 1989; Bard et al., 1990; Liu and Milliman, 2004). Varying rates of sea-level rise may have had a profound impact on the preservation (i.e., the extent of decapitation) of paleo-river and coastal systems on the modem shelf. The sedimentary record preserved within paleo-river systems may be the key to refining existing sea-level curves. Additionally, the heterolithic fill of these features may cause them to function as modem groundwater conduits, with significant impact on continental shelf ecosystems. We propose to study the Decapitated Albemarle-Roanoke River System (DARRS) on the modem continental shelf with the following objectives and hypotheses: 1) Determine the LGM fluvial pathway of the DARRS. We hypothesize data will help support the case for a pronounced forebulge during the LGM by providing evidence of southward deflection of the fluvial channel. 2) Assess cross-shelf variation in DARRS morphology and strata, including any paleo-shorelines. Morphological and stratal characteristics across the shelf are anticipated to show notable variability related to sea-level rise rates (and extent of stratigraphic decapitation). 3) Evaluate if the D ARRS is a conduit for modem groundwater flow. The general nature of D ARRS fill (fluvial sands underlYing muddy estuarine sediments) is hypothesized to allow significant groundwater flow to discrete areas on the continental shelf. Variability identified in objective #2 will likely relate to groundwater flow areas.

date/time interval

  • April 2005 - April 2006