Clay Mineralogy of Deep-Sea Sediments in the Northwestern Pacific, DSDP, Leg 20

Abstract

INTRODUCTIONClay mineral study of samples collected during Leg 20 of the Deep Sea Drilling Project in the western north Pacific was carried out mainly by means of X-ray diffraction analyses. Emphasis was placed on determining vertical changes in mineral composition of sediments at each site.Results of the semiquantitative and quantitative determinations of mineral compositions of analyzed samples are shown in Tables 1, 2, 3, 5, and 7. The mineral suites presented here show some unusual characters as discussed below. The influence of burial diagenesis is also evidenced in the vertical distribution of some authigenic minerals.These results may contribute to a better understanding of deep-sea sedimentation on the northwestern Pacific plate. ANALYTICAL PROCEDURESEach sample was dried in air, and X-ray diffraction patterns were obtained using aggregates on glass slides. The clay minerals were identified as follows:1) X-ray analysis: (a) untreated, (b) treated with ethylene glycol, and (c) heated for 1 hour at each of the following temperatures: 300°C, 500°C, and 600°C. In each case X-ray examination was performed at room temperature immediately upon cooling.2) Differential thermal analysis for selected samples.3) Electron microprobe X-ray analyses by the Shimadzu-ARL Electron Microprobe X-Ray Analyzer EMX-SM for selected samples. Intensity Ratios of Basal Reflections of Clay MineralsIn the case where principal basal reflections of clay minerals do not overlap with one another, it is easy to obtain the intensity ratio of reflections. When a specimen has a complex clay-mineral composition, the reflections of respective clay minerals sometimes overlap. In such cases, the specimen must be treated either thermally or chemically to eliminate or move X-ray reflections of certain minerals, so that the reflection intensity of individual minerals can be obtained.When montmorillonite and chlorite coexist in one specimen and the (001) reflections of both minerals overlap with each other, the reflection intensity of each mineral cannot be obtained without any treatment. In this case, by heating the specimen at 300°C, the 15 Å reflection of montmorillonite is moved to 9 to 10 Å, and the intensity of the (001) reflection of chlorite is obtained. Treatment with ethylene glycol or glycerol usually shifts the reflection of montmorillonite from 15 Å to 17 Å. The (001) reflection intensity of montmorillonite can be obtained by subtracting the (001) reflection intensity of chlorite from the preheating or pretreating reflection intensity at 15 Å.In a specimen with coexisting kaolinite and chlorite, their overlapping reflections make it difficult to determine quantitatively these mineral compositions. For such specimens Wada's method (Wada, 1961) and heat treatment were adopted.The following shows examples of the determination of some intensity ratios of reflections of clay minerals.Case 1 Montmorillonite (two layers of water molecules between silicate layers)-kaolinite mixture. This is the situation in which samples contain both montmoril...

Clay-Sized Minerals from Cores of the Southeast Pacific Ocean, Deep Sea Drilling Project, Leg 35

“…Similar trends of increasing montmorillonite and decreasing chlorite and illite contents with depth have been noted previously in DSDP sites in various areas of the Pacific Ocean-in the northeastern marginal zone (Hayes, 1973), in the Tasman Sea (Matti et al, 1973), and in the northwestern part of the Pacific Ocean (Okada and Tamuda, 1973). Hayes suggested that these trends are the result of the in- fluence of many factors on the formation of clay such as, currents, turbidites, fluctuation of volcanic activity, glaciation, lowering of sea level, degree of erosion and weathering, mechanism of transport, etc.…”

“…In his opinion, montmorillonite alters to mica in the deeper layers of the sediment. In the western part of the Pacific Ocean, Okada and Tamuda (1973) noted changes in the interlayered water content in montmorillonites: one layer occurred in shallow sediments and two layers occurred in the deeper ones.…”

Western North Atlantic: Sedimentary Evolution and Aspects of Tectonic History

“…According to this view the extinc¬ tions were caused in some way by (a) global cooling resulting from volcanic ash emission, (b) toxic traceelement contamination of the atmosphere and oceans, (c) other geochemical and climatological effects, for ex¬ ample SO 2 and CO 2 emission, or (d) some combination of the above. At Site 384, increasing montmorillonite and clinoptilolite concentrations are observed across the Cretaceous/Tertiary boundary (Koch and Rothe, this volume), and these components commonly are pro¬ duced by the devitrification of volcanic ash (Okada and Tomita, 1973). However, because no ash layers were observed in the Site 384 calcareous oozes, any volcanic activity could not have been nearby.…”

Clinoptilolite, paragenesis and stratigraphy

“…This coexisting suite of minerals can be correlated to the chert occurrences in the Deep Sea Drilling Project which show occurrence peaks in the Cretaceous and Eocene (Davies & Supko, 1973;Hurd & Theyer, 1975, Kolodny, 1976. Calvert (1971) has pointed out that many of the porcelanites (opal C-T) in the North Atlantic occur in sequences of zeolitic (clinoptilolite) and montmorillonitic clays and they also occur in sediments containing abundant sepiolite and palygorskite (Peterson et al, 1970). Trauth (1974) Okada & Tamita (1973) have also observed 'a negative correlation between clinoptilolite and cristobalite' (opal C-T).…”