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Mississippi Interior Salt Basin
The Mississippi Interior Salt Basin is an extensional rift basin located primarily in the southern/southern central region of Mississippi with parts of the basin also reaching into northeastern Louisiana and southwestern Alabama.

The basin has an elongate shape and was formed during the late Jurassic and early Cretaceous. It has salt diapirs and pillow structures throughout from the underlying Jurassic Louann salt, and its average width is about 125 miles.

Although it is not a massive basin by any means, it is a popular source of hydrocarbon exploration because of the presence of salt domes with thick anhydrite sections that act as great seals for hydrocarbon systems.

Geologic Setting/Tectonics
The Mississippi Interior Salt Basin is situated between the Monroe Uplift in the northwest, the Pickens-Gilbertown Fault Zone in the north, and the Wiggins Arch in the southeast. It is larger than both the East Texas Salt Basin and North Louisiana Salt Basin. Translateral movement along the original pangean rift margin that occurred in the late Triassic and early Jurassic caused the initial rift configuration of alternating crustal highs and lows that formed the Mississippi Interior Salt Basin.

The early Cretaceous did not experience too much tectonically, but a stable platform formed from south Texas to Florida, and over 10,000ft (>3000m) of carbonate and evaporite deposition occurred. The carbonate system was weakened by an inflow of sediment in Mississippi, and nearby clastic rocks grade downdip basinward into carbonates on the outer shelf.

The rifting in the late Triassic and early Jurassic allowed the deposition to occur in the early Cretaceous despite its relative tectonic stability.

Stratigraphy/Sedimentology
The majority of information regarding the stratigraphy and sedimentology of the Mississippi Interior Salt Basin is focused on the Cretaceous aged sections of the basin. This is because the Mississippi Interior Salt Basin is known to be exploited for hydrocarbon exploration, and exploration primarily occurs in formations of the basin that are Cretaceous in age.

In the Lower Cretaceous strata of the basin, there are eleven formations that are primarily discussed. From oldest to youngest, the formations are the Cotton Valley Formation, Hosston Formation, Sligo Formation, Pine Island Shale, James Limestone, Rodessa Formation, Ferry Lake Anhydrite, Mooringsport Formation, Paluxy Formation, Dantzler Formation, and the Tuscaloosa Formation. The Pine Island Shale and James Limestone are commonly present within the Rodessa Formation but are sometimes not seen in Mississippi. The Bexar Formation is also sometimes discussed and described as the area between the base of the Rodessa and top of the James Limestone.

Thermal Maturation
Solid bitumen reflectance values found in the Mississippi Interior Salt Basin Increase southeast to northwest across the basin, and the eastern portion of the basin has thermal maturity that shows a gradual increase with respect to depth.

The cross section and map included here show that the thermal gradients are lower in the northwest section of the basin and in the southeast section of the basin.

The western margin of the Mississippi Interior Salt Basin has shallower depths and higher peak temperatures, and it is suggested that this is due to either greater present-day and paleoheat flux or deeper burial and differential uplift and erosion.

Hydrocarbon Exploration in the Citronelle Oil Field
The Mississippi Interior Salt Basin is mostly known for its source of hydrocarbons. Although hydrocarbon exploration occurs in nearly all of its lower Cretaceous formations, a large majority takes place in the Rodessa Formation of the basin. One of the most prolific oil fields in the Rodessa Formation is the Citronelle Oil Field.

The Citronelle Oil Field is located approximately 50km (30mi) north of Mobile, Alabama and has produced over 169 million bbl of oil since its discovery. The Citronelle Dome is a salt-cored anticline with its crest being the drilling site for over 600 wells. Shale and anhydrite from the Ferry Lake and Mooringsport Formations acts as the top seal for the Citronelle Dome. It is estimated that primary and secondary methods of exploration have found 31-34% of the original oil, but CO2 enhanced oil recovery could possibly increase reserves by 20%.

The Rodessa Formation in which the Citronelle Dome is located consists of approximately 244m (800ft) of interbedded shale and sandstone, with the sandstone beds forming fining-upwards successions between 2.4-12.2 m (8-40ft) thick and maintaining a porosity of about 13%.