Eolian Environments | Eolian Environment in Petroleum Geology?
Paleontology Eolian Environments
Desert dune formations composed almost exclusively of quartz sand are, to a large extent, predictably barren of fossil remains. Root let horizons, animal tracks, mudcracks, and raindrop impressions are all evident in present-day wet interdune areas, and are occasionally seen in outcrop. They are, however, inevitably rare in core samples. Reptile bones, freshwater mollusks, crustaceans, and arthropods have been reported from the major Late Paleozoic Early Mesozoic eolianite formations of the western United States, for example:
- Navajo sandstone (Triassic-Jurassic)
- Coconino sandstone(Permian)
- DeChelley sandstone(Permian)
- Lyons formation(Permian)
- Weber-Tensleep sandstone(Pennsylvanian-Permian)
In general, the difficulty of distinguishing eolian complexes points out the importance of outcrop study for the geologist. Examining rocks in their most exposed state is, of course, an idea circumstance for most petroleum geologists who must often remain satisfied with the more-or-less isolated and, at times, random sampling in the form of cores. Let it be said, then, that where outcrops exist, they should never be passed over in favor of borehole data. Cores are, in a sense, artificial exposures; the second most direct form of evidence for analysis.
Geometry Eolian Environments
There is no distinctive shape to eolian formations. The original dune morphology of a sand sea is generally reworked and planed out by transgressing waters before another facies is deposited. Basically, the final shape is a blanket. Thicknesses may be 300 m or more (Navajo sandstone), but are commonly less. Aerial distribution of both ancient-and modern examples is highly variable, ranging from tens to hundreds of thousands of square kilometers.
