Abstract: A Quantitative 3-D Model from Superimposed Meander Belts: Method, Geometric Exploration And Application

Margarita Diaz-Molina, Felix Miguez Marin

The studied fluvial sediments are a part of the Tortola fluvial fan, filling the Loranca basin (central Spain) from late Oligocene to early Miocene. Stair-like topography with/or transverse valleys, helped 3-D observation of sedimentary bodies along two exposures 1300 and 500 m long, covering a stratigraphic interval of 50 m. Meander belt reconstructions were obtained on the basis of mapping, stratigraphic correlations, facies analysis and geomorphological concepts. From the detailed reconstruction of superimposed meander belts, a file of geometric data was recorded, containing coordinates and thickness of meander loop bodies. With the help of a CAD program, 3-D views and calculations of areas and volumes are possible, and the internal architecture can be explored.

Since these ancient meander loop deposits were left by very small channels (the biggest meander loop can be represented by a prism with a total volume of 8 × 10⁵ m³), the 3-D model does not exemplify a true economic reservoir analog; however, some of its characteristics can be considered as a norm for the internal architecture in this type of deposit: puzzling style, and low ratio between meander loop basal surfaces/interconnection areas in spite of a proportion of connected meander belts of 1.

The parameters obtained from the 3-D model, along with the estimations of mean rate of recorded sediments, basin section, meander-belt aggradation and avulsion periodicity, allow the simulation of the alluvial stratigraphy. From this approach, the 3-D model can be used as a predictor by comparison of the Loranca basin parameters and climate (during late Oligocene to early Miocene) with those of other basins to be evaluated.

AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994