Nagayoshi Katsuta

Climate system transition from glacial to interglacial state around the beginning of the last termination: Evidence from a centennial‐ to millennial‐scale climate rhythm

A periodic variation on a centennial to millennial scale was observed in the manganese and iron contents of Lake Suigetsu sediments in Japan, dating from 19.0 to 5.7 cal. kyr B.P. (calibrated thousand years before present). The increased manganese and iron contents, which mainly indicate the relative abundance of siderite, result from a greater vertical circulation in the lake during a cold period, with a higher mass of manganese and iron oxide being precipitated. The cold periods inferred from the increased manganese and iron contents coincide with the timing of ice-rafting debris (IRD) events in the North Atlantic, which span from the last termination to the Holocene, suggesting that the climate shift was hemispheric or probably global in nature. The manganese variation resembles the residual atmospheric 14C production (Δ14C) data of the Holocene that reflect variation in solar activity, and its periodicities correspond with those of solar-related climate changes from paleoproxy records in the North Atlantic and East Asia from the last cold stage to the Holocene. In particular, the Mn variation was larger in amplitude and shorter in timescale during the last cold stage when compared with those during the last termination and the Holocene, thereby possibly showing a significant difference in climate response to solar irradiance. The transition of the climate system from a glacial to an interglacial state corresponds to the beginning of the last termination.

Calcite–dolomite cycles in the Neoproterozoic Cap carbonates, Otavi Group, Namibia

Abstract The lower cap carbonate (Rasthof Formation) overlies Neoproterozoic glacial deposits (Chuos Formation) and is exposed in the Khowarib-Warmquelle area in Northern Namibia. The basal 14.2 m part of the Rasthof Formation (total about 220 m) consists of the carbonate rhythmite. The rhythmite part of the Rasthof Formation contains 1 m cycles of dark- and light-coloured rhythmites. Alizarin-red staining of thin sections and elemental mapping of polished samples indicate that the dark-coloured parts are rich in calcite, whereas the light-coloured parts are dolomite-rich. On a 1 cm scale, a reddish clay layer is intercalated in each calcite rich dark-coloured rhythmite part. These cycles of reddish clays as well as some associated major turbidites can be well correlated between columns up to about 20 km distance. Furthermore, at one locality (K4), rip-up clasts occur in a turbidite bed. Their lithology consists of dark- and light-coloured rhythmite and a reddish clay layer and can be judged to have been derived from underlying horizons. Because the clasts are elastically deformed, it is strongly suggested that the difference in lithology observed within the basal part of the Rasthof Formation existed when clasts were ripped-up shortly after sedimentation. This suggests that the cycle involving dolomite is synsedimentary, and not a diagenetic feature. Direct precipitation of dolomite does not occur in present day open marine seawater. Hurtgen et al. (2002) suggest that seawater was depleted in sulphate after Neoproterozoic glaciation. It is proposed here that some possible depositional models of cycles that consist of calcite-rich and dolomite-rich parts as well as reddish clay beds in rhythmites of the Rasthof cap carbonate.

Early post-mortem formation of carbonate concretions around tusk-shells over week-month timescales.

Carbonate concretions occur in sedimentary rocks of widely varying geological ages throughout the world. Many of these concretions are isolated spheres, centered on fossils. The formation of such concretions has been variously explained by diffusion of inorganic carbon and organic matter in buried marine sediments. However, details of the syn-depositional chemical processes by which the isolated spherical shape developed and the associated carbon sources are little known. Here we present evidence that spherical carbonate concretions (diameters φ : 14 ~ 37 mm) around tusk-shells (Fissidentalium spp.) were formed within weeks or months following death of the organism by the seepage of fatty acid from decaying soft body tissues. Characteristic concentrations of carbonate around the mouth of a tusk-shell reveal very rapid formation during the decay of organic matter from the tusk-shell. Available observations and geochemical evidence have enabled us to construct a ‘Diffusion-growth rate cross-plot’ that can be used to estimate the growth rate of all kinds of isolated spherical carbonate concretions identified in marine formations. Results shown here suggest that isolated spherical concretions that are not associated with fossils might also be formed from carbon sourced in the decaying soft body tissues of non-skeletal organisms with otherwise low preservation potential.

Possible Age Models for Lake Onuma Lacustrine Sediments Based on Tuffs Recovered in Three Cores

Lake Onuma, Hokkaido, Japan, is located south of Hokkaido-Komagatake volcano. The present Lake Onuma was formed by an intensive eruption and partial collapse of the volcanic cone in 1640 AD, which caused a debris flow that dammed the drainage. Three cores (ON12A, C, and D) were recovered from Lake Onuma to examine the environmental change in the region. These three cores are correlated based on lithological descriptions and water content fluctuation. Volcanic deposits Ko-a (1929 AD), Ko-c1 (1856 AD), Ko-d (1640 AD), and possibly Ko-c2 (1694 AD) were successfully identified with the help of radiocarbon age dating, 137Cs radioactivity measurement, and chemical analyses, to construct an age model of these cores.

Non-destructive method to detect the cycle of lamination in sedimentary rocks: rhythmite sequence in Neoproterozoic Cap carbonates

Abstract Environmental changes were flagged by lamination within Precambrian sedimentary rocks sequences using a high-resolution method. A continuous sample was collected and embedded in epoxy resin to form sample plates in order to investigate 2D laminations on sample surfaces. Elemental distributions in laminated samples were determined and recorded as XRF profiles, using the scanning X-ray analytical microscope (SXAM) and an image processing lamination tracer. These methods were used to study a rhythmite sequence at the base of a Neoproterozoic cap carbonates, which immediately overlies glacial deposits in Namibia, to determine profiles of Si, Ca, Mn, Ti, Fe, and Sr. At the base and top of each interval, the concentrations of six elements were relatively constant. In the middle of the interval, Ca–Sr and Mn, which reflect presence of calcite and dolomite respectively, fluctuated. This reflects seventeen cycles. The cyclic fluctuations of Ca–Sr and Mn were interpreted as calcite–dolomite cycles. Strontium also recorded two cycles. Furthermore, the fluctuations of Ca–Sr and Mn in calcite–dolomite cycles were laterally traceable. Possibly, these calcite–dolomite cycles were deposited synchronously and regionally. New methods allow the extraction of data that record cyclic- and event-phenomena from long sequences of laminated sedimentary rocks; this is not isolated to the Neoproterozoic but also throughout Earths history.

Generalized conditions of spherical carbonate concretion formation around decaying organic matter in early diagenesis

Isolated spherical carbonate concretions observed in marine sediments are fascinating natural objet trouve because of their rounded shapes and distinct sharp boundaries. They occur in varied matrices and often contain well preserved fossils. The formation process of such concretions has been explained by diffusion and rapid syn-depositional reactions with organic solutes and other pore water constituents. However, the rates, conditions and formation process of syngenetic spherical concretions are still not fully clear. Based on the examination of different kinds of spherical concretions from several locations in Japan, a diffusion based growth diagram was applied to define the generalized growth conditions of spherical concretions formed around decaying organic matter. All analytical data imply that the spherical concretions formed very rapidly, at least three to four orders of magnitude faster than previously estimated timescales. The values indicate that spherical concretions are preferentially grown within clay- to silt-grade marine sediments deposited in relatively deep (a few tens of metres) environments dominated by diffusive solute transport, very early in diagenesis.

Response of Biogenic Silica Production in Lake Baikal and Uranium Weathering Intensity in the Catchment Area to Global Climate Changes

Takuma Murakami1,6, Nagayoshi Katsuta2, Takejiro Takamatsu3, Masao Takano1, Koshi Yamamoto1, Toshio Nakamura4 and Takayoshi Kawai5 1Graduate School of Environmental Studies, Nagoya University, 2Faculty of Education, Gifu University, 3National Institute for Environmental Studies, 4Center for Chronological Research, Nagoya University, 5Association of International Research Initiative for Environmental Studies, 6Low Level Radioactivity Laboratory, Institute of Nature, Environmental Technology, Kanazawa University, Japan

Centennial-Scale Environmental Changes in Terhiin Tsagaan Lake, Mongolia Inferred from Lacustrine Sediment: Preliminary Results

Terhiin Tsagaan Lake in central Mongolia is a dammed lake formed by the eruption of a volcano at ca 7,000 year BP. Eight short sediment cores, lake water samples and inlet and outlet samples were collected. The concentrations of major dissolved species in the samples revealed that the lake water is Ca2+-HCO3 − type, but that the Ca2+ and HCO3 − levels are relatively low. The water has high dissolved SiO2 concentrations, which suggests favorable conditions for formation of biogenic silica depending on the surrounding environment. Analyses of the X-ray CT images of the cores showed that the average brightness over the horizontal direction, which represents averaged density of each layer, exhibited pulsed-like peaks as well as gradual fluctuations. The pulsed-like peaks in the pattern were probably resulted from the density currents including clasitic materials from the catchment area, therefore, can be used for the indicator for some hydro-climatic events and/or lake level changes. The gradual fluctuation of the averaged brightness was well correlated with the contents of biogenic silica plus organic matter. The profiles of the brightness can provide high resolution information regarding the biological activities in lake. The patterns of averaged brightness of five cores, obtained from deeper parts of the lake, exhibited similar patterns, with a positive peak in upper part of the sediments, and the minimum brightness just below the positive peak. The comparison of the core obtained from the previous study (Sevastyanov et al. 1989) showed that the short cores obtained from the deeper parts of the lake in present study can provide a record back to 1,000 year B.P. The minimum brightness indicates that the higher biogenic response at 200 years ago. The presence of a positive peak above the minima indicates that the condition became lower biogenic response at 100 years ago and then gradual increase in response as time progressed toward the present.

Fractal Nature of the Band-Thickness in the Archean Banded Iron Formation in the Yellowknife Greenstone Belt, Northwest Territories, Canada

Banded iron formations (BIFs) are chemically precipitated deposits on the Precambrian sea floor and are characterised by alternations of repeat Fe-rich and Si-rich layers [1]. Temporal varia‐ tions in the volumes of BIFs are considered to be related to early evolution of the atmosphere, oceans, life and the Earth’s interior [2, 3]. In general, BIFs contain various scales of banding. Bands with a thickness of several tens of meters to meters, a thickness of centimetres and a thickness of submillimetre to millimetres are named macrobands, mesobands and microbands, respective‐ ly [4]. Some depositions are related to periodic phenomena, such as annual cycles [4], tidal and solar cycles [5–7], and Milankovitch cycles [8, 9] in the Precambrian. On the other hand, quanti‐ tative analysis of the banding is limited to Paleoproterozoic Hamersley (Superior-type) BIFs, although BIFs occur within an age range from 3.8 Ga to about 0.7 Ga [10]. Therefore, it is necessa‐ ry to investigate different BIFs, in terms of both their age and type, clarified by size and litholog‐ ical facies (i.e., Superiorand Algoma-types) to understand the nature of their banded structures.

Continental Erosion/Weathering Changes in Central Asia Recorded in the Holocene Sediment from Lake Hovsgol, Northwest Mongolia, by Synchrotron μ-XRF Mapping Analyses

Nagayoshi Katsuta1, Takuma Murakami2,3, Yuko Wada2, Masao Takano2, Masayuki Kunugi4 and Takayoshi Kawai2,5 1Faculty of Education, Gifu University 2Graduate School of Environmental Studies, Nagoya University 3Low Level Radioactivity Laboratory, Kanazawa University 4Environment Safety Center, Tokyo University of Science 5Association of International Research Initiatives for Environmental Studies Japan