The Michoud fault is a

geological fault Geology (). is a branch of natural science concerned with the Earth and other astronomical objects, the rocks of which they are composed, and the processes by which they change over time. Modern geology significantly overlaps all other Earth ...

that runs through eastern

New Orleans New Orleans (commonly known as NOLA or The Big Easy among other nicknames) is a Consolidated city-county, consolidated city-parish located along the Mississippi River in the U.S. state of Louisiana. With a population of 383,997 at the 2020 ...

. The Michoud fault is the subject of extensive scientific inquiry into why

Louisiana Louisiana ( ; ; ) is a state in the Deep South and South Central regions of the United States. It borders Texas to the west, Arkansas to the north, and Mississippi to the east. Of the 50 U.S. states, it ranks 31st in area and 25 ...

is losing vast tracts of land. Subsurface mapping identified the Michoud fault, on the basis of well cutoffs and seismic surveys. Sedimentary growth implies that movement along the Michoud fault has been intermittent since

Oligocene The Oligocene ( ) is a geologic epoch (geology), epoch of the Paleogene Geologic time scale, Period that extends from about 33.9 million to 23 million years before the present ( to ). As with other older geologic periods, the rock beds that defin ...

time (Bebout and Gutierrez, 1983). A cross section in McBride (1998) shows a high-angle normal fault that was correlated by Dokka (2006) with the Michoud fault. This fault merges with a low-angle

detachment fault A detachment fault is a gently dipping normal fault associated with large-scale extensional tectonics. Detachment faults often have very large displacements (tens of km) and juxtapose unmetamorphosed hanging walls against medium to high-grade me ...

at –7 km deep that developed along the top of a slightly south-dipping zone of weak

salt In common usage, salt is a mineral composed primarily of sodium chloride (NaCl). When used in food, especially in granulated form, it is more formally called table salt. In the form of a natural crystalline mineral, salt is also known as r ...

and

shale Shale is a fine-grained, clastic sedimentary rock formed from mud that is a mix of flakes of Clay mineral, clay minerals (hydrous aluminium phyllosilicates, e.g., Kaolinite, kaolin, aluminium, Al2Silicon, Si2Oxygen, O5(hydroxide, OH)4) and tiny f ...

. These structures are considered to be related to a regional south-vergent extensional-contractional complex described by Peel et al. (1995; Fig. 1). Movement of the complex and thus on the Michaud fault reflects gravitational instabilities and down-dip motion during times of high sedimentation (Peel et al., 1995). The Michoud fault belongs to a class of geologic structures known as

growth fault Growth faults are syndepositional or syn-sedimentary extensional faults that initiate and evolve at the margins of continental plates. They extend parallel to passive margins that have high sediment supply. Their fault plane dips mostly toward th ...

s (Mauduit, T., Brun, J. P. 1998). Growth faults are common geologic structures of regions undergoing high sedimentation rates, such as

river delta A river delta is a landform, archetypically triangular, created by the deposition of the sediments that are carried by the waters of a river, where the river merges with a body of slow-moving water or with a body of stagnant water. The creat ...

s and

passive margin A passive margin is the transition between Lithosphere#Oceanic lithosphere, oceanic and Lithosphere#Continental lithosphere, continental lithosphere that is not an active plate continental margin, margin. A passive margin forms by sedimentatio ...

s. They often develop where weak rock layers (detachments) such as

anhydrite Anhydrite, or anhydrous calcium sulfate, is a mineral with the chemical formula CaSO4. It is in the orthorhombic crystal system, with three directions of perfect cleavage parallel to the three planes of symmetry. It is not isomorphous with the ...

, or

underlie regions of rapid sedimentation. These weak zones allow the growing mass of material above them to slide downhill, either continuously or episodically. These downslope movements will be correspondingly experienced in the headwall region (such as that occupied by the Michoud fault) either as slow (barely perceptible) or rapid (catastrophic) subsidence. Growth faults are also sometimes called "listric faults", implying that the fault is a concave-upward surface that transforms nearly vertical displacements at the surface into nearly horizontal ones at depth. The Michoud fault is not unexpected or unusual as a geologic feature of the Mississippi River Delta.

Holocene The Holocene () is the current geologic time scale, geological epoch, beginning approximately 11,700 years ago. It follows the Last Glacial Period, which concluded with the Holocene glacial retreat. The Holocene and the preceding Pleistocene to ...

faulting and tilting is widely recognized in many world deltas, such as the

Nile The Nile (also known as the Nile River or River Nile) is a major north-flowing river in northeastern Africa. It flows into the Mediterranean Sea. The Nile is the longest river in Africa. It has historically been considered the List of river sy ...

, the

Ganges The Ganges ( ; in India: Ganga, ; in Bangladesh: Padma, ). "The Ganges Basin, known in India as the Ganga and in Bangladesh as the Padma, is an international which goes through India, Bangladesh, Nepal and China." is a trans-boundary rive ...

Brahmaputra The Brahmaputra is a trans-boundary river which flows through Southwestern China, Northeastern India, and Bangladesh. It is known as Brahmaputra or Luit in Assamese, Yarlung Tsangpo in Tibetan, the Siang/Dihang River in Arunachali, and ...

, the

Yangtze The Yangtze or Yangzi ( or ) is the longest river in Eurasia and the third-longest in the world. It rises at Jari Hill in the Tanggula Mountains of the Tibetan Plateau and flows including Dam Qu River the longest source of the Yangtze, i ...

, the

Po River The Po ( , ) is the longest river in Italy. It flows eastward across northern Italy, starting from the Cottian Alps. The river's length is , or if the Maira (river), Maira, a right bank tributary, is included. The headwaters of the Po are forme ...

, and the

Rhine The Rhine ( ) is one of the List of rivers of Europe, major rivers in Europe. The river begins in the Swiss canton of Graubünden in the southeastern Swiss Alps. It forms part of the Swiss-Liechtenstein border, then part of the Austria–Swit ...

.(Törnqvist et al., 2006)

References

*Bebout, D.G., and Gutiérrez, D.R., 1983, Regional cross sections, Louisiana Gulf Coast: Baton Rouge, Louisiana Geological Survey Folio Series 6, 10 p. *Dokka R.K., 2006. Modern-day tectonic subsidence in coastal Louisiana. Geology vol. 34, p. 281-28

*Hickey, M., and Sabate, R., eds.,1972, Tectonic map of Gulf coast region, U.S.A.: Tulsa, Oklahoma, Gulf Coast Association of Geological Societies and American Association of Petroleum Geologists, Scale 1:1,000,000 *Peel, F.J., Travis, C.J., and Hossack, J.R., 1995, Genetic structural provinces and salt tectonics of the Cenozoic offshore U.S. Gulf of Mexico: A preliminary analysis, in Jackson, M.P.A., et al., eds., Salt tectonics: A global perspective: American Association of Petroleum Geologists Memoir 65, p. 153–175. *Törnqvist, T.E., Bick, S.J., van der Borg, K., and de Jong, A.F.M., 2006. How stable is the Mississippi Delta? Geology vol. 34, p. 697-70

*Mauduit, T., Brun, J. P. 1998. Growth fault/rollover systems: Birth, growth, and decay. J. Geophys. Res. Vol. 103, No. B8, p. 18,119-18,136.

References

External links

Fault Motion Animation

Tectonic control of subsidence and southward displacement of southeast Louisiana with respect to stable North America

{{coord missing, Louisiana Structural geology Geographic areas of seismological interest Seismic faults of the United States Geology of Louisiana