Foraminifera populations have been analyzed from 550 bottom samples, 65 submarine cores, and 27 serial plankton tows from the northwestern Gulf of Mexico. Twenty-five complete hydrographic stations and 473 bathythermograms give data on the temperature and salinity conditions. Field and laboratory methods are described.
Six benthonic Foraminifera depth facies are recognized, with boundaries at the following approximate depths: 80–120 m., 180–220 m., 500–750 m., 1000–1300 m., and 1800–2000 m. Subfacies are recognized in some traverses, especially in depths shallower than 100 m. Determination of facies and subfacies is based largely on overlap ranges of species. Temperature range is suggested as a key factor affecting facies distribution. The most marked facies boundary is at 80–120 m., the depth of the top of the main thermocline. Above this depth oceanographic conditions are strikingly different from those at greater depths.
Living specimens of 78 benthonic species have been collected. There is good correlation between abundance of living specimens and empty tests for each species. Average production of living benthonic Foraminifera is approximately 10 times as great above 100 m. as at greater depths. Production rates and population census give a possible method for determining relative rates of sedimentation.
Planktonic Foraminifera in abundance are characteristic of offshore water masses. Living planktonic specimens are found at all depths of water sampled down to 1400 m., the deepest plankton tow taken. At most stations there is a larger population of planktonic specimens in the upper 50 m. than at other depths; at a few stations there is a larger population at greater depths.
Most of the submarine cores contain a fauna below the surface which is characteristic of areas having lower surface-water temperatures than the present Gulf of Mexico. This lower fauna is interpreted as late glacial in age. Faunas in a few cores suggest rise of sea level since late glacial time.