Saburo Aoki

Sedimentary history and chemical characteristics of clay minerals in cores from the distal part of the Bengal Fan (ODP 116)

Abstract The purpose of this study is to clarify the sedimentary history and chemical characteristics of clay minerals found in sediments deposited in the distal part of the Bengal Fan since the Himalayas were uplifted 17 m.y. ago. A total of seventy-eight samples were collected from three drilled cores which were to be used for the clay mineral analyses by means of XRD and ATEM. The results obtained from the analyses show that individual clay mineral species in the sediment samples at each site have similar features when the samples are of the same age, whereas these species have different features in samples of differing geological ages. Detrital clay minerals such as illite and chlorite were deposited in greater amounts than kaolinite and smectite during the Early to Middle Miocene. This means that the Himalayan uplift was vigorous at least until the Middle Miocene. In the Pliocene chemical weathering was more prevalent so that instead, in the distal part of the Bengal Fan, kaolinite shows the highest concentrations. This would accord with weaker uplift in the Himalayas. In the Pleistocene period, vigorous Himalayan uplift is characterized by illite-rich sediment in place of kaolinite. In the Holocene, smectite shows the highest concentration in place of the illite and kaolinite which were the predominant clay minerals of the earlier periods. Increasing smectite concentration suggests the Himalayan uplift to have been stable after the Pleistocene period. The smectite analyzed here is found to be dioctahedral Fe-beidellite, and it originated largely from the augite-basalt on the Indian Deccan Traps. The tri-octahedral chlorite is subdivided into three sub-species, an Fe-type, a Mg-type and an intermediate type. The mica clay mineral can be identified as di-octahedral illite which is rich in potassium. The chemical composition and morphology of each clay mineral appears to exhibit no change with burial depth in the sedimentary columns. This implies that there was no systematic transformation of clay minerals with time.

Cenozoic sedimentation and clay mineralogy in the northern part of the Magellan Trough, Central Pacific Basin

Abstract Assemblages of clay-sized minerals in twelve deep-sea cores from the northern part of the Magellan Trough in the Central Pacific Basin clearly show that authigenic smectite together with clinoptilolite formed subsea in situ and predominated throughout Palaeogene time. Clastic clay minerals such as chlorite, illite and kaolinite increased at the expense of smectite in sediments deposited since the Pliocene. Most of the authigenic smectites are of the di-octahedral, iron-rich type. The most probable origin of the authigenic smectites is formation from precursors such as volcanic glass. As part of this process biogenic silica evidently contributed to the formation of smectite and zeolites as clinoptilolite. The presence of a tri-octahedral saponite and the TEM morphology of some smectites, on the other hand, suggests that not all of the smectite studied was formed subsea in situ but that some had an allogenic origin. Systematic vertical changes in the assemblage of clay-sized minerals suggest that the authigenesis of submarine smectite and clinoptilolite prevailed in conditions of reduced aridity and weak wind activity throughout the Palaeogene in the study area. However, allogenic clay minerals such as chlorite and illite increased since the Olduvai event under conditions of severe aridity and strong wind activity caused by global climatic change. The west-northwest movement of the Pacific plate must have partly played a role in deposition of the clastic clay-sized minerals from the Asian continent by westerlies in the study area. The widespread occurrence of Cenozoic hiatuses in the study area is attributed to the influence of Antarctic Bottom Water (AABW). The latter must have influenced non-deposition of the clay-sized minerals at times during the Cenozoic.

The vertical change in clay mineral composition and chemical characteristics of smectite in sediment cores from the southern part of the Central Pacific Basin

Abstract Clay mineral composition and chemical characteristics of smectite in five piston core samples collected from different sedimentary provinces in the Central Pacific Basin were studied using XRD and ATEM. The results show that submarine authigenic smectite occurs as the most abundant constituent in four clay mineral assemblages throughout the Neogene, whereas it was diluted by continental clastic clay minerals, such as illite, chlorite and kaolinite, which were transported to the ocean in Quaternary time. The submarine authigenic smectite is characterized as di-octahedral iron-rich beidellite, its morphology comprising the fleecy or lath forms which are considered to have been formed by submarine volcanism or hydrothermal reactions.

Clay mineral distribution in sediments of the Gulf of Thailand and the South China Sea

The 25 sediment samples collected from the Gulf of Thailand and the South China Sea were analyzed for clay mineral investigation. Results showed the presence of 35% montmorillonite, 13% chlorite, 30% illite, and 22% kaolinite in sediments of the Gulf and also 16% montmorillonite, 21% chlorite, 41% illite, and 22% kaolinite in sediments of the South China Sea. The relatively high concentration of montmorillonite in sediments of the Gulf as compared with that in sediments of the South China Sea may suggest that montmorillonite in these area has been largely derived from soil formation of the bordering land areas of the Gulf, particularly from the northern part of Malay Peninsula. On the contrary, the content of illite in sediments of the South China Sea is higher than that in the Gulf. This mineral appears to have been supplied from Borneo as well as the Mekong Delta. However, chlorite which shows a similar distribution to that of illite in sediments of the Gulf and the South China Sea has not indicated Borneo Isl. as a principal source area for chlorite. Greater resemblance in amount of kaolinite in both sediments of the Gulf and the South China Sea is due to the prevailing distribution of kaolinite as “low latitude clay mineral” on the bordering land areas. The distribution of clay minerals in sediments of the study area appears to be closely related to the soil formation and geology of the adjacent land areas.

Hydrothermal clay minerals found in sediment containing yellowish-brown material from the Japan Basin

Abstract In a previous report, we suggested that the Fe-P mineral discovered in the yellowish-brown material from the deepsea bottom in the eastern part of the Japan Basin could have been formed in situ under hydrothermal conditions. The present study of clay minerals in the muddy sediment containing the yellowish-brown material confirms the possibility of a submarine hydrothermal origin of these clay minerals, along with the Fe-P mineral. Fe-smectites such as nontronite and ion-rich saponite and Fe-Mg chlorite indicated that Fe types rather than Mg type can be formed by slow alteration under submarine hydrothermal conditions at relatively lower temperatures.

Mineralogical and chemical properties of smectites in a sediment core from the southeastern Pacific

Abstract A sediment core section nearly 80 cm long (50 to 125 cm below the sea bottom) from the southeastern Pacific is largely composed of smectites. X-ray, thermal, infrared, and chemical analyses indicate the smectites to be iron-rich montmorillonite (SiO 2 , 50.17%; TiO 2 , 0.77%; Al 2 O 3 , 7.11%; Fe 2 O 3 , 11.46%; FeO, 0.25%; MnO, 0.09%; MgO, 5.41%; CaO, 0.30%; Na 2 O, 2.86%; K 2 O, 0.57%; H 2 O + , 8.02%; H 2 O − , 12.03%; total, 99.04%) and aluminous montmorillonite (SiO 2 , 49.39%; TiO 2 , 1.18%; Al 2 O 3 , 14.39%; Fe 2 O 3 , 4.73%; FeO,—; MnO,—; MgO, 3.61%; CaO, 0.23%; Na 2 O, 2.12%; K 2 O, 0.34%; H 2 O + , 6.86%; H 2 O − , 15.20%; total, 98.05%). The iron-rich montmorillonite is rare and similar mineralogically and chemically to that of the northeastern Pacific previously reported by the authors. The aluminous montmorillonite is similar to the common type on land. The hypothesis that the iron-rich montmorillonite could have been formed by the interaction of hydrothermal solutions and seawater is supported by circumstantial evidence, whereas the aluminous montmorillonite was probably altered from volcanic ash transported from some other place.

Mineralogical study of the core samples from the Indian Ocean, with special reference to the vertical distribution of clay minerals

The clay minerals in the 18 core samples collected from the northern, equatorial and southeastern Indian Ocean are illite, chlorite, montmorillonite and kaolinite. In the fraction finer than 2Μ in the surface layer (top to 5 cm deep) of each core, the relative abundance of clay minerals varies widely from area to area. Kaolinite possesses the maximum proportion of the clay mineral composition and chlorite has the minimum proportion.Kaolinite is particularly dominant in sediments near off the northwestern coast of Australia. In the factions finer and coarser than 2Μ of the surface layer, montmorillonite and kaolinite tend to be abundant in the fraction finer than 2Μ, and chlorite and illite tend to be abundant in the fraction coarser than 2Μ. In some cores, kaolinite-rich layers in sediments which are considered to have been transported by turbidity currents from the Bay of Bengal are found. Turbidity currents appear partly a role in transport of sediments to the equatorial Indian Ocean.As to the relation between the vertical change of clay mineral composition and geochronological data, montmorillonite and kaolinite tend to be more abundant in interglacial ages than in glacial ages, while illite and chlorite tend to exhibit opposite trend.Muscovite and biotite highly concentrated in the cores Ka-9′ and Ka-15 collected from the equatorial Indian Ocean seem to originate from granite or gneiss of Ceylon and/or India.

The distribution of clay minerals in recent sediments of the Okhotsk Sea

Abstract The clay fractions of surface sediments from the Okhotsk Sea contain montmorillonite, chlorite, illite, and small amounts of kaolinite. The concentrations of these minerals differ from place to place, but they are not determined by submarine topography such as basins and rises. The distribution seems to be influenced mainly by the supply of clay minerals from volcanic materials, various rocks, and soils in the bordering lands.

Modern sedimentation in the Japan Trench: implications of the mineralogy and chemistry of clays sampled from sediment traps

Abstract To determine the mineralogical and chemical characteristics of clay minerals, the composition of the clay-sized fraction and the sedimentological processes which affect these clay particles, two sediment traps were moored at depths of 8700 and 4000 m at the triple junction of the Japan Trench. Six types of clay minerals and nine types of non-clay minerals were identified by transmission electron microscopy. Smectite and illite were the most important clay minerals whereas quartz and plagioclase were the major non-clay minerals. Chemical analyses of the clay minerals showed that the smectite was an Fe–Al beidellite, illite a di-octahedral type rich in potassium and chlorite an Fe–Mg type. Two major mechanisms govern the transportation of the lithogenic mineral particles in the Japan Trench: (1) transportation by the turbidity currents in the neighbouring trough and canyon and (2) wind-borne transport of loess from mainland China. The settling time of clay-sized minerals to the bottom of the Japan Trench was roughly estimated to be 1 year.

Clay minerals in the deep-sea cores from the North Pacific

Clay minerals in the <2μ fraction of the four deep-sea cores collected from the northeast and central North Pacific are studied. In the surface layers of the cores, illite is more dominant in the pelagic samples than in the near-shore ones, and montmorillonite is vice versa. Chlorite in the near-shore sample is relatively abundant in the areas of higher latitude than in those of lower latitude. Kaolinite content is less than 10 percent in all samples. The presence of particles of amphibole in the clay-size was confirmed by X-ray analysis in the whole of the core-st. 18 taken from the northeastern portion of the area. This fact suggests that, for a long time probably since the Tertiary age, particles of amphibole have been supplied from source areas. In the three cores except the core-st. 18 it is shown that montmorillonite clearly increases downward. It is suggested that montmorillonite has been derived from volcanic glassy material by a diagenetic change. Montmorillonite in the bottom layer (400–405 cm) of the core-st. 9 is particularly rich in iron.