Arkansas, Louisiana, Mississippian and Alabama stratigraphic column

The Wilcox Group is an important

geologic group Geology () is a branch of natural science concerned with Earth and other astronomical objects, the features or rocks of which it is composed, and the processes by which they change over time. Modern geology significantly overlaps all other Eart ...

in the

Gulf of Mexico Basin The formation of the Gulf of Mexico, an oceanic rift basin located between North America and the Yucatan Block, was preceded by the breakup of the Supercontinent Pangaea in the Late-Triassic, weakening the lithosphere. Rifting between the North ...

and surrounding onshore areas from Mexico and Texas to Louisiana and Alabama. The group ranges in age from Paleocene to Eocene and is in Texas subdivided into the Calvert Bluff, Simsboro and Hooper Formations, and in Alabama into the Nanafalia and Hatchetigbee Formations. Other subdivisions are the Lower,

Middle Middle or The Middle may refer to: * Centre (geometry), the point equally distant from the outer limits. Places * Middle (sheading), a subdivision of the Isle of Man * Middle Bay (disambiguation) * Middle Brook (disambiguation) * Middle Creek (d ...

and Upper Wilcox Subgroups, and the Carrizo and

Indio Formation The Indio Formation is a geologic formation of the Wilcox Group in Mexico. The sandstones, shales, conglomerates and claystones preserve fossils dating back to the Ypresian age ( Wasatchian to Bridgerian in the NALMA classification) of the ...

Lithologies

The group comprises mostly

mudstone Mudstone, a type of mudrock, is a fine-grained sedimentary rock whose original constituents were clays or muds. Mudstone is distinguished from '' shale'' by its lack of fissility (parallel layering).Blatt, H., and R.J. Tracy, 1996, ''Petrology. ...

with secondary sandstone and

lignite Lignite, often referred to as brown coal, is a soft, brown, combustible, sedimentary rock formed from naturally compressed peat. It has a carbon content around 25–35%, and is considered the lowest rank of coal due to its relatively low heat ...

beds, ironstone concretions, as well as

siltstone Siltstone, also known as aleurolite, is a clastic sedimentary rock that is composed mostly of silt. It is a form of mudrock with a low clay mineral content, which can be distinguished from shale by its lack of fissility.Blatt ''et al.'' 1980, p ...

s, conglomerates and limestones. The total thickness is about .Wilcox Group, Texas
- USGS

Provenance of sandstones

Sandstone modal compositions and detrital zircon U‐Pb analyses of the Wilcox Group indicate long‐distance sediment transport from primarily volcanic and basement sources to the west, northwest, and southwest. The Wilcox Group represents the earliest series of major post‐Cretaceous pulses of sand deposition along the western margin of the Gulf of Mexico. Laramide

basement A basement or cellar is one or more floors of a building that are completely or partly below the ground floor. It generally is used as a utility space for a building, where such items as the furnace, water heater, breaker panel or fuse box, ...

uplifts have long been held to be the source of Wilcox sediments, implying that initiation of basement uplift was the driving factor for the transition from carbonate sedimentation to clastic deposition. Zircon age‐spectra for the sandstones of the Wilcox Group reveal a complex grain assemblage derived from Laramide uplifted crystalline blocks of the central and southern Rocky Mountains, the Cordilleran arc of western North America, and arc‐related extrusive and intrusive igneous rocks of northern Mexico. Zircon ages also suggest possible recycling of older sediment through uplift related to accretion of arc terranes along the westernmost North America, but that recycling of Cordilleran foreland basin sediments was not a major contributor. Comparison of Upper and Lower Wilcox zircon age-spectra indicate that Lower Wilcox sediments are richer in arc and volcanic material, whereas Upper Wilcox sediments are richer in basement material. Regional trends in detrital zircon age‐spectra indicate that Upper Wilcox sediments are moderately homogeneous over the region studied, whereas the Lower Wilcox shows significant heterogeneity. The drainage area for the Gulf of Mexico during the Paleocene and Eocene was larger than previously thought, encompassing not only the Laramide basement uplifts, but the volcanic province of northern Mexico and possibly Cordilleran tectonic regions along the westernmost North America.

Petroleum geology

The Wilcox Group comprises important source and reservoir rocks in the

. Structural and geochemical evidence indicates that hydrocarbons found in Wilcox reservoirs such as the Wilds sandstones were emplaced by vertical migration along

wrench fault In geology, a fault is a planar fracture or discontinuity in a volume of rock across which there has been significant displacement as a result of rock-mass movements. Large faults within Earth's crust result from the action of plate tectonic ...

s and associated fracture zones from underlying Cretaceous and Jurassic source rocks.2007 - Goddard - Petroleum Geology: Middle Wilcox Reservoirs, East Central Louisiana
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Lithologies

Provenance of sandstones

Petroleum geology

See also

References

Further reading