NATIONAL OCEANOGRAPHIC PROGRAM—1965 93 
075/0* analyses of the shell material have given isotopic of plus 1.5 percent with 
respect to the Chicago standard PDB-1. This would indicate a bottom tempera- 
ture only slightly higher than existing today (about 7° C.). 
APPENDIX 
For those not familiar with biological terminology, a few pertinent comments 
are given in the following: 
(a) Foraminifera: An order of marine protozoans. Single-celled animals, 
most of which deposit CaCO: shells. Dimensions of the shells: 200p to 1,000z. 
Foraminifera may be benthonic (living on the bottom, from the shoreline to the 
greatest oceanic depths) or planktonic (freely floating at, or near the ocean 
surface). The shelis of planktonic Foraminifera fall to the bottom when the 
animal reproduces. Most of the foraminiferal shells in Globigerina ooze sedi- 
ments are planktonic, the bethonic ones amounting to only 1 to 2 percent. 
Planktonie Foraminifera evolved about 150 million years ago, and have been 
very abundant since. Planktonic foraminiferal species number about 2,000 
living and 100,000 fossil. 
(b) Coccolithophoridae: Planktonic marine protophyta. Single-celled plants 
depositing C,.COs; platelets all around their bodies. Diameter of the platelets: 
about 5u to 10pz. Coccolithophoridae evolved about 150 million years ago and pro- 
vide an important food source for planktonic Foraminifera. 
(c) Diatoms: Planktonic and benthonic, marine and fresh water protophyta. 
Single-celled plants depositing two valves consisting of hydrated 8:02 Maxi- 
mum diameter of the valves: about 50z. 
(d@) Radiolaria: Planktonic marine protozoa. Single-celled animals depositing 
shells consisting of hydrated SiOs. Diameter of shell: about 250u. One family 
deposits S,SO¢ shells. 
The taxonomy of Foraminifera has been studied in detail during the past 
100 years. Although much remains to be done, a fairly satisfactory stratigraphy 
for the Cretaceous-Cenozoic (the past 100 million years) of the Tethys (the 
ancient sea stretching from the Caribbean through the Mediterranean to In- 
donesia) and adjacent regions has been established on the basis of Foramini- 
fera. Planktonic Foraminifera, in particular, are useful for correlations of 
marine deposits in distant regions. 
The taxonomy of Coccolithophoridae, Diatoms, and Radiolara has been studied 
much less than that of Foraminifera. Therefore, these organisms are less useful 
than Foraminifera for stratigraphic purposes. 
[From Science magazine, June 1964] 
GEOCHRONOLOGY OF MARINE AND FLUVIAL SEDIMENTS 
For more than 100 years, scientists have been trying to develop methods to 
determine the onset and duration of the Pleistocene epoch. Analysis of con- 
tinental deposits is not reliable for this purpose because such disturbances as 
faulting, erosion, and glaciation leave only discontinuous records. Deep sea 
sediments, however, offer a possibility of determining sedimentation rates and 
absolute ages of recent geological periods. The extremely slow deposition of 
minerals under the protective layer of thousands of meters of sea water makes 
these sediments suitable material for dating. Included in the techniques for 
dating marine sediments are the micropaleontological method (Science 139, 728 
(1963) ), and a method based on the radioactive decay of members of the two 
uranium families in the sea. The former method depends upon the characteriza- 
tion and distribution of Foraminifera as a function of depth within the sedi- 
ments. The appearances of Foraminifera are related to the temperature of 
their environment and are correlated stratigraphically. The latter method is 
based on the concept that uranium is soluble in sea water; the daughters Th” 
and Pa™ are insoluble and are concentrated in the sediments in a distribution 
which is not in equilibrium with their respective parents, U™ and U*. Still 
another method, which is sometimes useful for obtaining sedimentation rates, is 
the ratio of Th to Th™’. Here, Th*’ decays very slightly during the Pleistocene 
epoch, while Th*’ decays with a 76,000-year half-life. After deposition this ratio 
is assumed to vary only because of the shorter half-life of Th”. 
Although these methods are used in many laboratories in the United States 
and abroad, many controversial issues exist, such as problems of sample col- 
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