GULF OF MEXICO FORAMINIFERA 



By Fred B. Phleger and Frances L. Parker,' The Scripps Institution of Oceanography, University of California 



Foraminifera are relatively large, marine Pro- 

 tozoa having either a calcareous or an arenaceous 

 test; they are both benthonic and planktonic in 

 habitat. Their tests contribute a large percentage 

 of the material in marine sediments. Study of 

 Foraminifera has been mostly confined to the 

 occvu-rencc of empty tests m marine sediments, 

 and all identifications are based upon test 

 morphology. 



Little is known of Gulf of Mexico Foraminifera 

 except from the Dry Tortugas and from the north- 

 west area. Phleger (1951) and Phleger and Parker 

 (1951) have studied living and dead assemblages 

 from plankton tows and cores taken off shore 

 between Point Isabel and Atchafalaya Bay, and 

 the present report is largely a summary of the per- 

 tinent features of that work. These samples were 

 collected from 551 stations spaced in 12 traverses 

 extending fi-om the 10-fathom curve to the center 

 of the Sigsbee Deep. Flint (1899) and Cushman 

 (1918-31) have described material collected by the 

 United States Bureau of Fisheries ship. Albatross, 

 from the northern part of the Gulf of Mexico east 

 of the Mississippi Delta. Kornfeld (1931) de- 

 scribed some shallow-water and littoral Fora- 

 minifera from a few stations between the Missis- 

 sippi Delta and the International Boundary. 

 Cushman and Bermudez (1945) reported a new 

 species of Rotalia from the mouth of the Rio 

 Grande. Cushman (1922) has described numer- 

 ous species from the shallow-water areas of the 

 Tortugas. 



BENTHONIC FORAMINIFERA 



The area investigated in the northwest Gulf of 

 Mexico between the Mississippi Delta and the 

 International Boundary is one of clastic sediments. 

 Clastic sediments also occur east of the delta as 

 far as Mobile Bay and along the coast of Mexico. 



' Contribution from the Seripps Institution of Oceanography, New Series 

 No. 660, Contribution No. 16, Marine Foraminifera Laboratory. Work 

 done on Office of Naval Research Project NR 081 060. 



The continental shelf bordering Louisiana and 

 Texas has numerous isolated calcareous reefs. 

 The principal calcareous areas in the region are 

 along the coasts of Florida and Yucatan. The 

 Foraminifera assemblages in these two sedi- 

 mentary environments are quite distinctive and 

 are treated separately in the following summary. 

 The most extensive sampling and study has been 

 done in the clastic sediments. 



Clastic areas. — Figures 55 through 58 list the 

 principal benthonic species found in the northwest 

 Gulf of Mexico; this figure is reproduced from 

 Phleger (1951). The depth range shown for each 

 species is a generalization based upon distributions 

 from samples in all 12 traverses taken. This 

 assemblage is related to the Atlantic assemblage 

 but contains some elements reported only from 

 the Gulf of Mexico. 



The benthonic faunas in the northwest Gulf 

 may be grouped into six depth biofacies with 

 boundaries at the following approximate depths: 

 100 m., 200 m., 600 m., 1,000 m., and 2,000 m. In 

 addition, there are three subfacies in the upper 100 

 m. of water depth. The boundaries between these 

 biofacies are not sharp but vary through about 

 10-20 percent of the depth involved. Figure 59 

 summarizes the depth of biofacies and gives depth 

 ranges of representative species as an illustration 

 of the basis for distinguishing the facies. 



The most striking depth biofacies boundary in 

 this area is at about 100 m. This coincides with 

 the depth of the water layer which is affected by 

 changing seasons and therefore shows seasonal 

 temperature ranges, in which the greatest organic 

 production occurs, and which is turbulent, at 

 least in part. Deeper biofacies boundaries may 

 be correlated with the temperature ranges if they 

 occur in the permanent thermocline. The bound- 

 ary at about 2,000 m. is believed to be due to some 

 environmental factor other than temperature, 

 since there is no significant temperature change 



235 



