Foraminiferal faunas in cores offshore from the Mississippi Delta 47 



Table I— Locations and depths of cores 



The topographic charts of the northwestern Gulf of Mexico, constructed by Gealy 

 (1955), end at the approximate position of the Mississippi Delta, and all of the present 

 core stations are off her chart except cores 7-12 (Fig. 2). Core 18 was taken at a 

 depth of 88 m on the lower part of the narrow continental shelf Most of the other 

 cores came from the continental slope, except those at the outer end of the traverse 

 which are in or on the edge of the Gulf of Mexico basin. The continental slope in 

 this area appears to be quite rugged, and is cut by the Mississippi Canyon. The Sigsbee 

 Deep Scarp described by Gealy may not be present in the area traversed by the cores. 



This is an area of high runoff from the Mississippi River and is presumed to have a 

 rather high rate of sedimentation. It has been shown by Scruton (MS.) that the 

 highest sedimentation rate is close to the delta distributaries and decreases rapidly 

 offshore. There appears to be rather rapid sedimentation for approximately 60 miles 

 offshore, according to analyses by Phleger (MS.). It seems likely that sedimentation 

 is more rapid farther offshore in this area than in any other part of the northern Gulf 

 of Mexico. 



The physical oceanography of the area is not well-known. Offshore surface 

 temperatures vary from a mean minimum of 20° C in February to a mean maximum 

 of 29° C in August, according to Fuglister (1947). It thus has the surface-water 

 temperatures of North Atlantic mid-latitudes in winter and of low latitudes in summer. 

 A considerable amount of low-latitude water enters the Strait of Yucatan, and while 

 much or most of this flows out the Florida Strait, its effect may be pronounced in the 

 area of the outer part of the present traverse. Offshore salinities in the Gulf of 

 Mexico are approximately 36"/^ 3. A near-shore wedge of lower-salinity water is 

 expected in this high runoff area. Parr (1935) shows salinities of approximately 

 24°/^^ in the upper 50 m a few miles to the east of the present traverse. 



METHOD OF STUDY 



The cores were collected with a coring tube described by Hvorslev and Stetson (1946). The 

 samples used in the present study were one-fourth of each core cut into sections approximately 

 5 cm in length, so that the entire core was sampled. Each sample was trimmed oi approximately I 8 

 inch of sediment to prevent contamination between samples and was washed free of tine sediment 

 over a brass sieve having an average opening of 074 mm. 



