Distribution of Planktonic Foraminifera in Surface Sediments of the Gulf of Mexico

Abstract

Distributional patterns of 40 individual species and subspecies of planktonic Foraminifera are plotted on the basis of relative abundance at each of 90 stations located throughout the Gulf of Mexico. All species are illustrated with scanning electron photomicrographs. There is only a poor relationship between the areal distribution of most species and the distribution of temperature and salinity values in the overlying water mass. Only nine species exhibit moderate correlation to trends of temperature and salinity in near surface waters. This results from factors that obscure such relationships during the process of incorporation into the sediments. Important factors in the Gulf of Mexico include the effects of surface currents and the absolute abundance of the particular species in question. Differential resistance to solution and downslope displacement are of lesser importance. The concept of using "ideal" or key species as paleoecological indicators is rejected because no single species fulfills all of the requirements: sensitivity to temperature and salinity changes, high resistance to solution, and great absolute abundance. Plotting ratios between species indicative of different ecological conditions only compounds the problem. Dealing with larger faunal elements, such as tropical vs. non-tropical species, produces the most accurate reflection of conditions in the overlying water mass. The relative ages of sediments exposed on the floor of the Gulf of Mexico were determined through the use of commonly accepted planktonic foraminiferal criteria. Except for the extreme southwestern portions of the study area, micropaleontological interpretations agree closely with those from the seismic profiler studies used to compile the preliminary map of the Gulf.