Wilcox Group
| Wilcox Group Stratigraphic range: Selandian-Bartonian ~ | |
|---|---|
| Type | Geologic group |
| Unit of | |
| Sub-units | , & (Texas) Nanafalia, (Alabama) |
| Underlies | |
| Overlies | Midway Group |
| Thickness | up to 1,800 ft (550 m) |
| Lithology | |
| Primary | Mudstone, sandstone |
| Other | Siltstone, conglomerate, limestone, lignite |
| Location | |
| Location | Gulf Coast |
| Coordinates | 30°25′N 96°24′W / 30.417°N 96.400°WCoordinates: 30°25′N 96°24′W / 30.417°N 96.400°W |
| Region | Alabama, Georgia, Louisiana, Maryland, Mississippi, North & South Carolina, Texas Nuevo León, Tamaulipas |
| Country | United States Mexico |
| Extent | Maryland to Tamaulipas |
| Type section | |
| Named for | |
The Wilcox Group is an important geologic group in the 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 , and ,[1] and in Alabama into the Nanafalia and .[2][3] Other subdivisions are the , and , and the and Indio Formations.[4]
Lithologies[]
The group comprises mostly mudstone with secondary sandstone and lignite beds, ironstone concretions,[1] as well as siltstones, conglomerates and limestones.[5] The total thickness is about 1,400 to 1,800 feet (430 to 550 m).[1]
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 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.[6]
Petroleum geology[]
The Wilcox Group comprises important source and reservoir rocks in the .[7] Structural and geochemical evidence indicates that hydrocarbons found in Wilcox reservoirs such as the Wilds sandstones were emplaced by vertical migration along wrench faults and associated fracture zones from underlying Cretaceous and Jurassic source rocks.[8]
See also[]
- List of fossiliferous stratigraphic units in Alabama
- List of fossiliferous stratigraphic units in Louisiana
- List of fossiliferous stratigraphic units in Mexico
- List of fossiliferous stratigraphic units in Texas
- Paleontology in Alabama
- Paleontology in Louisiana
- Paleontology in Texas
- Wilcox Formation
References[]
- ^ a b c Wilcox Group, Texas - USGS
- ^ Wilcox Group; Nanafalia Formation, Alabama
- ^ Wilcox Group; Hatchetigbee Formation, Alabama
- ^ 1986 - Hargis - Proposed Stratigraphic Classification of the Wilcox of South Texas
- ^ Wilcox Group at Fossilworks.org
- ^ 2010 - Mackey et al. - Provenance of the South Texas Paleocene-Eocene Wilcox Group, Western Gulf of Mexico Basin: Insights from Sandstone Modal Compositions and Detrital Zircon Geochronology
- ^ 2012 - Hackley - Geologic Assessment of Undiscovered Conventional Oil and Gas Resources—Middle Eocene Claiborne Group, United States Part of the Gulf of Mexico Basin
- ^ 2007 - Goddard - Petroleum Geology: Middle Wilcox Reservoirs, East Central Louisiana
Further reading[]
- . 1979. Stratigraphy of the Simsboro Formation, East-Central Texas, 1–43. . Accessed 2018-06-14.
- . 1988. Stratigraphic Framework and Sedimentary Facies of a Clastic Shelf-Margin: Wilcox Group (Paleocene-Eocene), Central Louisiana, . Louisiana State University. Accessed 2018-06-14.
- . 1968. Environments of Deposition Wilcox Group, 1–43. Houston Geological Society. Accessed 2018-06-14.
- Geologic groups of Alabama
- Geologic groups of Georgia (U.S. state)
- Geologic groups of Louisiana
- Geologic groups of Maryland
- Geologic groups of Mississippi
- Geologic groups of North Carolina
- Geologic groups of South Carolina
- Geologic groups of Texas
- Geologic groups of North America
- Paleogene United States
- Geologic formations of Mexico
- Paleogene Mexico
- Selandian Stage
- Thanetian Stage
- Ypresian Stage
- Bartonian Stage
- Mudstone formations
- Reservoir rock formations
- Source rock formations
- Gulf of Mexico
- Geography of Nuevo León
- Geography of Tamaulipas