Sedimentology of braided alluvial interval of Dakota Sandstone, northeastern New Mexico
Abstract
The Dakota Sandstone (Cretaceous) in northeastern New Mexico is subdivided i to 3 intervals (Jacka and Brand, 1973). The lower interval is a braided al luvial sheet composed of fine- to medium-grained, cross-stratified sandstone with conglomerate lenses. The middle interval represents a meander -belt environment and contains fine- to ery fine grained, lenticular sandstone with interbedded carbonaceous shal e and coal. The upper interval represents a transgressive marine succession containing fine - to very fine grained, horizontally stratified sandstone with burrow casts of Ophiomorpha. Paleocurrent analysis of the braided alluvial interval indicates a domina nt southeasterly transport direction. This conclusion is supported by a decrease in mean grain size and thickness to the east and southeast. Analysis of the stratification ratio indicates that proximal braided -stream facies are predominant in the west and northwest parts of the study area, and that distal braided -stream facies are predominant to the east and southeast. The sediment dispersal pattern and the presence of proximal braided stream facies indicate that the source areas were the San Luis and Apish apa uplifts of Colorado and N w Mexico.
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