--> Abstract: Controls from Late Quaternary Valley Incision: A Look from Coastal-Plain Systems from the Mid-Atlantic and Northern Gulf of Mexico Margins, by Christopher R. Mattheus and Antonio B. Rodriguez; #90078 (2008)

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Controls from Late Quaternary Valley Incision: A Look from Coastal-Plain Systems from the Mid-Atlantic and Northern Gulf of Mexico Margins

Christopher R. Mattheus and Antonio B. Rodriguez
Institute of Marine Sciences, University of North Carolina, Morehead City, NC

Previous research indicates that late Pleistocene paleovalleys are equilibrated to their fluvial drainage basins at the Stage 5e highstand shoreline along the northern Gulf of Mexico. Their river systems are situated along a margin characterized by little along-strike variability in gradient and coastal-plain geology. It is necessary to study time-equivalent valleys from morphologically different margins to determine a broader applicability of this trend. A solid relationship between paleovalley size and drainage-basin dimension could provide a useful tool for studying the ancient rock record.

Quaternary coastal-plain valleys from the North Carolina Atlantic margin are compared to the existing Gulf database to outline effects of varying subsurface geology on large-scale fluvial incision. Newly studied basins do not exceed 1,500 km2 in size, are characterized by river gradients that are an order of magnitude less than those of size-equivalent Gulf systems (0.34-0.60 m/km versus 1.5-1.6 m/km for dominant river channels), and drain a margin defined by a much thinner veneer of unconsolidated Quaternary sediments.

Incision depths are similar among size-equivalent valleys, suggesting little geologic control on their vertical profile. Several Atlantic margin paleovalleys meander more than their straight, steep-flanked Gulf counterparts. Asymmetrical, terraced morphologies vary significantly along dip, making an unbiased assessment of their dimension difficult. North Carolina valleys that are not constrained by bedrock are morphologically similar to the Gulf systems and conform to established regression models. Relationships between incised-valley size and width and drainage-basin dimension are not functions of gradient and hold true only for systems incised into unconsolidated sediments.

 

AAPG Search and Discovery Article #90078©2008 AAPG Annual Convention, San Antonio, Texas