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Median-porosity contour maps of the J Sandstone, Dakota Group, in the Denver Basin, Colorado, Nebraska, and Wyoming Median-porosity contour maps of the J Sandstone, Dakota Group, in the Denver Basin, Colorado, Nebraska, and Wyoming

The Lower Cretaceous J sandstone of the Dakota Group is present in the Denver basin in eastern Colorado, southeastern Wyoming, and southwestern Nebraska. Deposited during a regression of the Cretaceous epicontinental sea, this informally named unit is composed primarily of sandstone and shale of deltaic and near shore-marine origin. The J sandstone can be divided into an upper...
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