Recently, “Naphtha method” by using naphtha and sodium hexametaphosphate was introduced for treatment of rocks for microfossils analysis (Maiya and Inoue, 1973). However, calcareous microfossils were found to be soluble in sodium hexametaphosphate solution in the course of disintegration. The authors investigated the dissolution effect of sodium hexametaphosphate solution on planktonic foraminifera. The experimental solution was divided into the following concentration (1.0, 0.4, 0.2, 0.1, 0.01, 0.001%). Under these experimental concentrations, binocular microscopical observations were made on the dissolution effect on planktonic foraminiferal tests at the following periods (0.5, 1.2, 4, 6, 12, 24, 48, 72 hrs). The results obtained are as follows: 1. The dissolution of planktonic foraminifera increases in accordance with concentration of the solution as well as time within the limits of this experiment. The same result was obtained in dissolution experiment of inorganic calcium carbonate. 2. Planktonic foraminifera used in this experiment can be divided into two groups, that is, one is species to be susceptible to dissolved and the other those resistant to dissolution. Resistant species to dissolution in this experiment agree approximately with the dissolution ranking of planktonic foraminifera suggested by Parker and Berger (1971). On the other hand, susceptible species to dissolution do not always agree with that of Parker and Berger (op. cit.). Especially, Globigerinita is most susceptible to dissolution among species tested in this experiment. 3. It is concluded that, in “Naphtha method”, the use of sodium hexametaphosphate above the concentration of 0.01% is not suitable for treatment of rocks for microfossils analysis.
Recently, the theory of late diagenetic origin of petroleum, which admits that most commercial oils originated by thermal transformation of insoluble organic matter (kerogen) and water required for primary migration could he supplied by dehydration of expandable clays during burial of source sediments, has recieved much support from many workers. In this paper, a general review and the author's coments for the basic problems on this theory are presented. The important points among those are as follows. In the Japanese Tertiary oil fields, it seems that water released by such dehydration of expandable clays as suggested by Powers (1967) have not been effective for the primary migration of oil based on the depth-pattern investigation of clays and hydrocarbons. Accordingly the alternative explanation will be needed for the primary migration of the Japanese Tertiary oils. Commercial oils have not been found so much in areas consisting of oil shales principally, despite of the result that oil shales contain predominantly lipid-rich kerogen which has higher potential for oil generation by the advocators of “late diagenetic thory.” Although Powers (1967) has given only a simple explanation for this problem from the view of clay components of oil rhales, more thorough research on this problem will be required. At present, most of the studies favoured to “late diagenetic theory” are essentially carried out on the basis of “fossil” kerogen and the problems on transformation mechanism and process of “young” to “fossil” kerogen are left unsolved. However, for the formation of commercial oils, hydrocarbons generated during transformation of “young” to “fossil” kerogen seem to be much more important based on various geological and geochemical data. Further study on this problem is required.