Mineralogical and Chemical Composition of the Tests of Certain Pelagic Foraminifera
1955; Micropaleontology Press; Volume: 1; Issue: 4 Linguagem: Inglês
10.2307/1484483
ISSN1937-2795
Autores Tópico(s)Geology and Paleoclimatology Research
ResumoX-ray and spectrographic analyses of a number of species of Recent and Pleistocene pelagic foraminifera from Caribbean, Atlantic and Pacific deep-sea cores indicate that the tests are made of virtually pure calcite, with only about 0.11% of strontium. Mineralogical and chemical composition of the tests of certain pelagic foraminifera CESARE EMILIANI Institute for Nuclear Studies University of Chicago Chicago, Illinois Very little work has been done on the mineralogical and chemical composition of the tests of pelagic foraminifera. To the knowledge of the writer, only three X-ray analyses have been published. These show a calcitic structure for Globorotalia menardii (Mayer, 1932) and for Globigerinoides rubra and Globorotalia tumida (Switzer and Boucot, 1955). The few chemical analyses which have been published (Clarke and Wheeler, 1922; Revelle, 1944) show small amounts of Si, Al, Fe and Mg. Only the latter two may actually be contained in the calcite structure. The others may indicate sedimentary contamination, as it is impossible to wash specimens absolutely clean in preparation for analysis. At the suggestion of the writer, X-ray and spectrographic analyses were made on a number of species of pelagic foraminifera by Dr. J. R. Goldsmith and Mr. 0. Joensuu, respectively, of the Department of Geology, University of Chicago. The X-ray analyses followed a method for determining Mg in Ca positions in the calcite structure. Powder diffraction pictures were taken with North American Philips 114.19 mm. cameras using Fe radiation, as described by Goldsmith, Graf and Joensuu (1955). Back-reflections, highly sensitive to Mg content, were compared with a pure calcite standard. The spectrographic analyses were made with a 21-foot grating spectrograph (Jarrell-Ash Co.), using a technique which will be described elsewhere by Joensuu. These analyses are accurate to within ?+10% of the determined values. The foraminifera were obtained from deep-sea cores from the Caribbean Sea, the equatorial and North Atlantic Ocean, and the Pacific Ocean, kindly furnished by Professor H. Pettersson of the Oceanographic Institute of G6teborg, D. B. Ericson of the Lamont Geological Observatory, and Dr. G. Arrhenius of the Scripps Institution of Oceanography. The locations and depths of cores are given in Table 1. The pr fix A identifies the Lamont cores. Cores distinguished by A or B following the core number are short pilot cores intended to sample superficial sediments. The cores have been described by Arrhenius (1952), Ericson (1953), and Phleger, Parker and Peirson (1953). TABLE 1 LOCATIONS AND DEPTHS OF CORES Core No. A179-4 234A, 234 246A, 246 280A 58B, 58 Location 13036' N. 74048' W. 5045' N. 21043' W. 0?48' N. 31?28' W. 34057' N. 44016' W. 6?44' N. 129028' W. Depth (meters) 2965 3577 3210 4256 4440 Samples from the uppermost portions of the pilot cores and of core A179-4 are thought to represent essentially modern sediments, while the deeper samples represent Pleistocene sediments. Foraminifera belonging to different species were separated from each sample and crushed between glass slides, washed in distilled water in an agitator for one hour, and dried in an oven at 95? C. The results are listed in Table 2. Results of the X-ray analyses all indicate that the cell spacings are the same as those of virtually pure calcite. The presence of substituting cations was always beyond detectability ( <1%). micropaleontology, vol. 1, no. 4, pp. 377-380, text-figs. 1-3, tables 1-4, october, 1955 377 This content downloaded from 157.55.39.18 on Sat, 06 Aug 2016 04:15:53 UTC All use subject to http://about.jstor.org/terms
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