Experimental Studies on Diagenesis under Hydrothermal Conditions

The submarine topolography and subsurface sediments were studied off Aino-Shima island，north of Fukuoka day.Mechanical grain analysis was made，and the contents of calcareous sediments，mainly shell fragements，and magnetic mineral were measured。Medium sand is distributed at the southwestern part，and course one occupies the other area。Calcareous bioclastic sediment attains more than 60%，and magnetic content is 0.3 to 0.1%，and also 34 species of the molluscan shells are identified.Hydrothermal changes from amorphous silica gel into-cristobalite with additions of cobalt compounds，such as Co，CoO，Co(OH)_2，and CoCl_2·6H_2O，for 24-240hours，were examined at the reaction temperatures of 350°C，300℃，and 250℃Consequiir&gt；CoCl_2·6H_2O Hydrothermal changes from amorphous silica gel are studied under the conditions at 250-350°C for 96-384hours with addition of CaCO_3.SiO_2and CaCO_3are effective mutually to dissolve，and they progress crystallization each other.Then this can well explain that limestone and chart in fields occur frequently with close relationship.Shell powder as starting material was treated for dolomite synthesis under hydrothermal conditions at 250-350°C in mixed solutions of CaCl_2 and MgCl_2 with various Mg/Ca molar ratio。Dolomite phase was obtained at above 250°C.The time，elaspsed until the first appearance of crystals of dolomite，was increased with temperature.Thus，the activation energy for dolomite formation was found to be24kcal/mol。Dolomite crystals were formed in mixed solutions with Mg/Ca molar ratio in the range of 0.2 and 0.7。Above this range，only magnesite crystals were finally formed。It is very interesting for the consideration of diadenesis of dolomite formation that LMC and HMC were necessarily formed as intermediate phases.

The submarine topolography and subsurface sediments were studied off Aino-Shima island, north of Fukuoka day. Mechanical grain analysis was made, and the contents of calcareous sediments, mainly shell fragements, and magnetic mineral were measured. Medium sand is distributed at the southwestern part, and course one occupies the other area. Calcareous bioclastic sediment attains more than 60%, and magnetic content is 0.3 to 0.1%, and also 34 species of the molluscan shells are identified.Hydrothermal changes from amorphous silica gel into -cristobalite with additions of cobalt compounds, such as Co, CoO, Co(OH)_2, and CoCl_2・ 6H_2O, for 24-240 hours, were examined at the reaction temperatures of 350゜C, 300゜C, and 250゜C. Consequently, their crystallizing order is such as follows;Co(OH)_2 > CoO > Co > CoCl_2 ・ 6H_2OHydrothermal changes from amorphous silica gel are studied under the conditions at 250-350゜C for 96-384 hours with addition of CaCO_3. SiO_2 and CaCO_3 are effective mutually to dissolve, and they progress crystallization each other. Then this can well explain that limestone and chart in fields occur frequently with close relationship.Shell powder as starting material was treated for dolomite synthesis under hydrothermal conditions at 250-350゜C in mixed solutions of CaCl_2 and MgCl_2 with various Mg/Ca molar ratio. Dolomite phase was obtained at above 250゜C. The time, elaspsed until the first appearance of crystals of dolomite, was increased with temperature. Thus, the activation energy for dolomite formation was found to be 24 kcal/mol. Dolomite crystals were formed in mixed solutions with Mg/Ca molar ratio in the range of0.2 and 0.7. Above this range, only magnesite crystals were finally formed. It is very interesting for the consideration of diadenesis of dolomite formation that LMC and HMC were necessarily formed as intermediate phases.