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Paleobasin Mapping using Lunette Morphology

Maria Brunhart-Lupo

Lunette deposit morphologies are related directly to the amount of water that they are exposed to over time. In a recent study at the Great Sand Dunes National Park and Preserve, Colorado, three distinctive morphological expressions were recognized in lunettes; the single discrete lunette; the merged lunette; and the modified lunette (fluvially modified within the GRSA) in order of increasing complexity of morphology. In the current depositional regime, the largest and most morphologically complex lunette deposit is located in the depocenter of the current sub-basin within the San Luis Basin system. Surrounding that deposit, is a 'ring' of merged lunettes, followed by the single, discrete lunette furthest from the depocenter. The lunettes do not extend to the edge of the basin itself, but instead are present within the central region only. The pattern indicates the current depocenter margins and dating indicates that this has been the case for at least the past 10,000 years. Using the premise that the most heavily modified lunette is at the center of the basin, and the lunettes become less complex from the center towards the margins of the basin, paleobasinal depocenters can be mapped by use of lunette morphology, giving a surficial methodology for establishing the movement of the deepest location of the depocenter over time. This is an important method for use in areas that are protected and preserved as it is non-invasive and requires only minimal sampling to establish the relative ages of the deposits.

 

AAPG Search and Discovery Article #90156©2012 AAPG Rocky Mountain Section Meeting, Grand Junction, Colorado, 9-12 September 2012