Direction and intensity of residual magnetism of rocks measured by Astatic magnetometer, are analyzed with vector analysis method or Fourier series analysis. The former is more popular, however the vector analysis is effective only in the case that curve of residual magnetism is typical sine curve. In another case this method is unsuitable, if the sample has not ideal shape or has magnetic anisotropy. Such samples can be analyzed only approximately by Fourier series expansion. In both cases, it is necessary to measure the curve of residual magnetism as precisely as possible. The relationship between the results of analysis and precision of the measurement is studied in this paper. The authors also studied the cause of magnetic anisotropy of rock samples whose curve of residual magnetism are not sine curves by microscopic observation. The authors used computers for Fourier series analysis and for the correction of results of residual magnetic declination by a successive approximation.
The analysis of the composition and relative stratigraphic occurrences of radiolarian assemblages in the Neogene formations of the Niigata sedimentary basin has been carried out by the writers, after a total about 4500 samples collected from main sections and 12 wells was under examination. In this area there are seven characteristic radiolarian assemblages, namely Lp, Ta-Ar, CtLt, Ln, Tj, Tj-Ar and Form B types. While, the radiolarian zones, namely, Cyrtocapsella tetrapera, Lychnocanium nipponicum and Thecosphaera japonica zones were proposed by the writers. In this paper, some problems concerning the stratigraphic and geographic occurrences of these radiolarian assemblages, and the relation between radiolarian and planktonic foraminiferal zones were discussed. These results are shown in figure 14.
Vitric tuff is the most common reservoir rock in Akita. Fujioka and Yoshikawa recently suggested that the permeability of vitric tuff decreased when the tuff reacted with high alkali drilling mud under well conditions. They also said that oil wells producing oil from such a reservoir were required to be stimulated by acidizing treatment. Our purpose here is to investigate the reactions of hydrochloric acid on vitric tuff. The vitric tuffs used in these experiments were from 10 per cent to 20 per cent soluble when the pulverized samples were immersed in HCL at 30°C for 24 hours. The permeability of the vitric tuffs was measured with the apparatus shown in Fig. 4. Hydrochrolic acid and 1.5 per cent NaCl solution were used in the flow tests. The results are shown in Fig. 6 and Fig. 7.