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Sonnier Banks

2000 Office of Public Affairs at The University of Texas at Austin
From: Rezak et al., 1985; Britton and Morton, 1989

Sonnier Banks are located at 28.3°N latitude and 92.45°W longitude on the Texas-Louisiana Shelf. It is a mid-shelf bank composed of tertiary limestones, sandstones, claystones and siltstones. It appears to tolerate conditions of low light intensity and moderate turbidity better than other types of reef building corals in the northwestern Gulf. Marine life incident at the banks include fishes, sponges, molluscs and other mobile invertebrates.

Sonnier Banks

Location on Continental Shelf:   Mid-Shelf Bank
Coordinates:   28.30° N   92.45° W
Nearest Largest City:   New Orleans, Louisiana, USA

Selected Characteristics:
Minimum Depth:   18 m
Maximum Depth:   60 m
Minimum Temperature:   13oC
Maximum Temperature:   30oC
Minimum Salinity:   28 ppt
Maximum Salinity:   36 ppt

Community Structure:
Biotic communities on Sonnier are typically the same as at Stetson Bank, but Sonnier populations are somewhat more abundant. The crest of Sonnier is almost entirely encrusted with fire coral (Millepora alcicornis) and the sponges (Neofibularia nolitangere and Ircina sp). The fire coral population extends downward to 40 m depth but is severely diminished below the bank's crest. Dead branches and broken pieces of fire coral occur abundantly in the unconsolidated sediment at the bases of the shallower outcrops, along with siltstone chips and fine silt and clay-sized particles. A stony coral, the saucer-shaped agariciid, occurs at a depth of 52 m. Populations of fishes and conspicuous mobile invertebrates at Sonnier Banks are diverse and abundant. Among the more numerous reef fishes are several species of large angelfishes and butterfly fishes and others typical of submerged reefs and banks in the northwestern Gulf.

Geological Characterization:
Sonnier Banks are a surface expression of salt diapers and are outcrops of relatively bare, bedded tertiary limestones, sandstones, claystones and siltstones. Several peaks arranged in an arcuate pattern from a depth of about 60 m to crest at about 20 to 58 m. The peaks and surrounding areas are composed of steeply dipping bedded rocks. The individual peaks are apparent fault blocks that have been created by the collapse of the crest of the salt diaper. Two high peaks, the northern "twin" peaks, occur in the bank. They consist of steeply dipping tertiary sandstones, siltstones and claystones. The central area of Sonnier banks consists of steep dips. At approximately 52 m depth, the bank transitions to soft bottom and the outcrops become smaller and give way to a mud bottom with loose boulders and cobbles of sandstone and siltstone, all covered with veneers of sediment.

Britton, J.C. and B. Morton. 1989. Shore Ecology of the Gulf of Mexico. University of Texas Press, Austin.

Rezak, R., T.J. Bright and D.W. McGrail. 1985. Reefs and Banks of the Northwestern Gulf of Mexico: Their geological, biological, and physical dynamics. Wiley, New York, NY, USA, 259 p.

Keywords:   Bank, Salt diaper, Fire coral, Sponge

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