Established Series


The Gentilly series consists of very deep, very poorly drained, very slowly permeable slightly to moderately saline soils. These soils formed in thin accumulations of herbaceous plant remains and semifluid clayey alluvium over consolidated clayey deposits. Slopes are less than 1 percent.

TAXONOMIC CLASS: Fine, smectitic, nonacid, hyperthermic Typic Hydraquents

TYPICAL PEDON: Gentilly muck--slightly saline marsh.
(Colors are for moist soil unless otherwise stated.)

Oa1--0 to 4 inches; dark gray (10YR 4/1) muck; massive; nonsticky, very fluid, flows easily between fingers when squeezed leaving small residue; about 18 percent fiber, 8 percent rubbed; about 70 percent mineral; slightly acid; abrupt smooth boundary. (4 to 16 inches thick)

Oa2--4 to 10 inches; very dark gray (10YR 3/1) muck; massive; nonsticky, very fluid, flows easily between fingers when squeezed leaving small residue; about 12 percent fiber, 5 percent rubbed; about 65 percent mineral; many coarse yellowish brown herbaceous plant stems and roots; slightly acid; abrupt smooth boundary. (0 to 12 inches thick)

Cg1--10 to 20 inches; gray (5Y 5/1) clay; very fluid, flows with slight difficulty between fingers when squeezed leaving small residue; common medium prominent dark yellowish brown (10YR 3/4) iron concentrations; neutral.

Cg2--20 to 40 inches; gray (5Y 5/1) clay; very fluid, flows easily between fingers when squeezed leaving small residue; common medium prominent dark brown (7.5YR 4/4) and yellowish brown (10YR 5/6) iron concentrations; neutral.

Cg3--40 to 80 inches; greenish gray (5GY 5/1) clay; massive; very sticky, very plastic, (will not flow between fingers when squeezed); common medium distinct olive (5Y 4/4) iron concentrations; slightly alkaline.

TYPE LOCATION: Orleans Parish, Louisiana; about 14 miles northeast of New Orleans; 1 mile north of U. S. Highway 90; 270 feet west of U. S. Highway 11. Spanish Land Grant 1, T 11S, R.13E.

RANGE IN CHARACTERISTICS: Soil salinity (EC) ranges from 4 to 16 dS/m. COLE is estimated to be more than 0.09 in mineral horizons, but because the soil is continuously saturated it does not crack to a depth of 20 inches. All layers at depths of 8 to 20 inches below the mineral surface have an n-value of more than 0.7. The mineral layer within the 10- to 40-inch control section has 35 to 60 percent clay content.

The Oa horizon is 4 to 16 inches thick and consists of muck, mucky peat, peaty muck, or peat. Color is in hue of 7,5YR or 10YR, value of 2 to 4, and chroma of 1 to 3. Reaction ranges from moderately acid to slightly alkaline, but it becomes strongly acid or very strongly acid after drainage.

The Cg horizon has hue of 10YR, 5Y, or 5GY, value of 4 or 5, and chroma of 1 or it is neutral with value of 4 or 5. Texture is clay or silty clay. Iron concentrations are brownish and/or olive in color. Reaction is neutral or slightly alkaline, but it becomes moderately acid to very strongly acid in the upper part after drainage. Depth to underlying layers with n-values of 0.7 or less ranges from 20 to 40 inches below the mineral surface.

COMPETING SERIES: These are the Caplen, Creole, Leerco, Mckee, and Riomar series. Caplen and Creole soils have n-value of more than 1.0 throughout. Leerco soils have EC of less than 4 dS/m. Mckee and Riomar soils have EC more than 16dS/m in the upper 60 inches.

GEOGRAPHIC SETTING: Gentilly soils are in marshlands in the lower Mississippi River delta and coastal areas that are dominantly slightly to moderately saline. Typically they occur on subsiding distributaries of the Mississippi River. The underlying firm clays probably consolidated before subsidence. Mean annual precipitation is about 65 inches and the mean annual temperature is about 68 degrees F. near the type location. Slope is less than 1 percent.

GEOGRAPHICALLY ASSOCIATED SOILS: These are the Allemands, Barbary, Fausse, Lafitte, Maurepas, and Sharkey soils. Allemands, Lafitte, and Maurepas soils have organic layers more than 16 inches thick. Fausse soils have n-value of less than 0.7 in th e 8 to 20 inch section. Sharkey soils are Vertisols.

DRAINAGE AND PERMEABILITY: Gentilly soils are very poorly drained. The water table is at the surface most of the time. Internal drainage is very slow to none. Permeability is very slow.

USE AND VEGETATION: The main use of these soils is wildlife habitat. Some areas have been diked and drained for development to urban uses. The dominant native vegetation is cattail, cutgrass, marshay cordgrass, big cordgrass, and seashore saltgrass.

DISTRIBUTION AND EXTENT: Gulf Coast Marshes (MLRA 151) of Louisiana Texas. Extent is moderate.


SERIES ESTABLISHED: Orleans Parish, Louisiana; 1972.


Diagnostic horizons and features

Histic epipedon - 0 to 10 inches

High n-values. n-values are greater than 0.7 10 to 40 inches

National Cooperative Soil Survey