All the fundamental rock properties (composition, texture, and sedimentary structure) are required to determine the depositional environments of sandstone bodies. Once depositional environments have been established, however, petrography alone can be a significant factor in identifying environments. Petrography is particularly useful if only small samples are available, such as core chips or side-wall cores. Thin-section analysis of such samples yields compositional and textural data which can be environmentally sensitive.

This is confirmed by a study of the Muddy Sandstone in the subsurface of the eastern Powder River basin. In this area, barrier bars are characterized by high quartz content (> 90%) and low matrix (< 10%); delta destructional bars by moderately high quartz (60-90%) and matrix (10-40%); and fluvio-deltaic sediments by low quartz (45%) and relatively high matrix (35%) and rock fragments (20%). The vertical sequence of mean grain-size change in each environment is significant, but maximum grain size is also a key value and is generally a grade coarser in fluvio-deltaic than barrier or delta-destructional sandstones. Plots of quartz mean size versus quartz content are environmentally sensitive, and from only a few thin sections an estimate may be made of depositional environment when other data are not available.

Indirect tools, such as electric logs, appear unreliable for identification of environment, unless the environment is established first on the basis of fundamental rock properties.

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