Fossil "Microforaminifera" in Various Sediments and Their Reaction to Acid Treatment

Abstract

Grayson (1956) believes that artificial conversion of calcite to fluorite explains presence of microforaminifera in standard acid preparations. In reality, natural resistance of many minute structures in samples of various sediments is very great. Microforaminifera are recognizable even after natural decalcification, when they possess membranous linings or when their chamber walls have been replaced with resistant mineral matter at an early stage of sedimentation. In addition, microfossils commonly associated with them are not polospores (Grayson, 1956), but variousflagellate Protista, preserved because of characteristic organic material of which their tests are composed. Fossil microforaminifera in various sediments and their reaction to acid treatment OTTO WETZEL Flintelklause Mikropaldontologisches Laboratorium Eutin, Holstein, Germany present note is a reponse to article by Grayson (1956) entitled The conversion of calcite to fluorite. In that article, Grayson states that shells and tests of calcite-producing organisms were not destroyed by the standard hydrofluoric acid treatment for removal of siliceous matter, and also that no reaction occurred when remains were subsequently treated with hydrochloric acid. X-ray analysis showed that shellfragm ents were no longer composed of calcium carbonate, but were now composed of calcium fluoride. Grayson presents figures illustrating excellent preservation of various shells examined to confirm first results in residues from standard successful application of his method to tests of foraminifera such as Globigerina sp., and knowledge that hydrochloric acid used alone and applied directly to normal shells of foraminifera dissolves calcite completely, caused Grayson to criticize strongly interpretations proposed by Wilson and Hoffmeister (1952) and by Hoffmeister (1955) to explain presence of microforaminifera in hydrochloric and hydrofluoric acid preparations. Grayson considers most of specimens of foraminifera from Tertiary shales illustrated by Wilson and Hoffmeister (1952, text-figs. 1-20 or 21) as products of conversion of calcite to fluorite during the standard hydrofluoric acid treatment. Two of their microfossils (Wilson and Hoffmeister, 1952, text-figs. 22 and 23), however, are believed by Grayson to be fungal in origin rather than 'microforaminifera,' and similar to some microfossils extracted by Grayson from Cretaceous sediments (Grayson, 1956, p. 72, text-fig. 1, consisting of three figures). Both sets of figures, Wilson and Hoffmeister's textfigures 22 and 23 (1952) perhaps more clearly than some parts of Grayson's text-figure 1 (1956), show small round bodies arranged according to size in a short and sometimes incomplete spiral series. This structure is similar to that of first-formed chambers of a number of foraminiferal species (Rotaliidae and others). resistance of such membranous forms, which can be isolated from enclosing sediments by acid treatment, is natural and requires no artificial conversion; it is a result of fact that inner coats of individual chambers are composed of an organic chitin-like material. occurrence ofthese spiral foraminiferal linings and of similar rectilinear chains of linings is not rare; they have been observed in various sediments and their residues by various authors since days of Ehrenberg (1838, 1854). Eisenack (1954) recently published a brief bibliography of these microfossils. In present note, I have assembled a few examples illustrating them (see also Wetzel, 1933a, b; 1948; 1951a, b). In addition to membranous linings, there are other factors that may explain why these small chambers are recognizable in samples of sediments or their residues in spite of natural (not always complete) decalcification. One factor is pseudomorphous transformation of microfossils, whose micropaleontology, vol. 3, no. 1, pp. 61-64, pl. 1, january, 1957 61 This content downloaded from 207.46.13.120 on Wed, 14 Sep 2016 05:50:12 UTC All use subject to http://about.jstor.org/terms