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Research Interests: Geology, Oceanography, East Asia, China, Quaternary, and 3 moreMonsoon, East Asian Monsoon, and China Sea
The Tarim Basin is the major source of aeolian dust in the northern hemisphere. Glacial activity in the mountains, transportation by rivers and homogenization by wind are believed to be responsible for dust production within the basin.... more
The Tarim Basin is the major source of aeolian dust in the northern hemisphere. Glacial activity in the mountains, transportation by rivers and homogenization by wind are believed to be responsible for dust production within the basin. However, the major source(s) and homogenization process(es) are not clear. Moreover, provenance studies on fine fractions have never been conducted. Here, we measured electron spin resonance (ESR) signal intensity and the crystallinity index of quartz in fine (< 16 μm) and coarse (> 64 μm) fractions of river sediments, dry lake sediments and mountain loess to examine the process(es) that produce aeolian dust. The result suggests that the coarse fraction of the river sediment was derived from the bedrock in the drainage area. The ESR signal intensity and crystallinity index of the fine fraction of river sediments from the Tian Shan Mountains and mountainous rivers in the westernmost Kunlun and Pamir mountains are also similar to the coarse fracti...
Research Interests: Geology, Provenance, China, Weathering, Mountains, and 8 moreQuartz, Asia, Loess, Sediments, Tarim Basin, Uplift, Aeolian Dust, and Crystallinity Index
The inner shelf sediments of the East China Sea (ECS) preserve valuable information regarding climatic changes on land through detrital material discharged from large rivers, particularly the Yangtze River. In this paper, we examine the... more
The inner shelf sediments of the East China Sea (ECS) preserve valuable information regarding climatic changes on land through detrital material discharged from large rivers, particularly the Yangtze River. In this paper, we examine the provenance changes of fine-grained detrital quartz preserved in the sediment of the MD06-3040 core retrieved from the mud belt on the inner shelf of the ECS during the last 6 kyrs. The provenance of the fine silt fraction (4–16 μm) of the sediments, which is considered to represent the suspended particulate matter (SPM) from the Yangtze River, is estimated based on the electron spin resonance (ESR) signal intensity and crystallinity index (CI) of quartz. By comparing the ESR signal intensity and CI of quartz in the fine silt fraction of sediments to those from different parts of tributaries in the modern Yangtze River drainage, we can discriminate the SPM sourced from the northwestern and southeastern tributaries of the Yangtze River. Shifts in the E...
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Research Interests: Geology and Geochemistry
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Seven different labs XRF scanned the same seven marine sediment sections. Additionally, four labs XRF scanned pellets that had known compositions determined by ICP-ES and ICP-MS. These datasets contain the XRF scanning results of the... more
Seven different labs XRF scanned the same seven marine sediment sections. Additionally, four labs XRF scanned pellets that had known compositions determined by ICP-ES and ICP-MS. These datasets contain the XRF scanning results of the seven sediment section and four pellets.The seven 1.5 m core sections of marine sediment core used in this study were drilled during Integrated Ocean Drilling Program (IODP) Expedition 346 at Site U1424 in the Japan Basin (40°11.39'N, 138°13.90'E, 2808 m water depth) and Site U1425 on the Yamato Rise (39°29.43' N, 134°26.55' E, 1909 m water depth). The sections selected (Hole U1424C Sections 1H4, 2H5, 3H5 and Hole U1425C Sections 2H3, 2H4, and 2H6, and 3H6) cover a range of sediment compositions. U-channels extracted continuous marine sediment approximately 1 cm thick from the center of each split core section. One lab scanned sections from different holes at the same sites (U1424A, U1425B, and U1425D) that were stratigraphically aligned...
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Lake Suigetsu is known for its highly precise age-depth model based on numerous C dating combined with varve counting and wiggle matching with Chinese stalagmite record. For this reason, the sediments are capable of providing extremely... more
Lake Suigetsu is known for its highly precise age-depth model based on numerous C dating combined with varve counting and wiggle matching with Chinese stalagmite record. For this reason, the sediments are capable of providing extremely precise and high resolution records of past climatic changes. Several paleo-climate reconstruction studies have been conducted based on pollen and diatom analyses of the Lake Suigetsu sediments. However, studies focusing on its detrital material were rare because its detrital component is expected to be a mixture of eolian dust, detrital material derived from surrounding slope of the lake, and suspended material derived from Hasu River that flew into Lake Mikata and came into Lake Suigetsu through a narrow and shallow channel, and it is difficult to separately evaluate materials from these different sources. However, our recent study revealed that it is possible to evaluate the contribution of the detrital material derived from Hasu River through Lake...
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The Tsushima Warm Current (TWC), which is only source of oceanic water in the Japan Sea during Holocene, transports heart, salt and nutrients from the East China Sea via the Tsushima Strait, and plays important roles of climate and... more
The Tsushima Warm Current (TWC), which is only source of oceanic water in the Japan Sea during Holocene, transports heart, salt and nutrients from the East China Sea via the Tsushima Strait, and plays important roles of climate and ecosystem of the Japan Sea. In this study, we reconstructed Holocene changes of sea surface temperature (SST) based on radiolarian fossil records from more than 20 cores. In south of the polar front, the SST increased significantly through 12.5 ka to 8 ka, and showed millennial scale oscillations after that. On the other hand, low SST conditions have continued at north of the polar front due to weak influence of the TWC.
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Abstract Climate and vegetation in Japan are strongly influenced by the East Asian Monsoon (EAM) and the ocean environment of the Japan Sea. This study discusses the findings from a new pollen record from Integrated Ocean Drilling Program... more
Abstract Climate and vegetation in Japan are strongly influenced by the East Asian Monsoon (EAM) and the ocean environment of the Japan Sea. This study discusses the findings from a new pollen record from Integrated Ocean Drilling Program Site U1427, situated off the northern coast of the Honshu Island in western Japan, which allows for direct comparisons with other oceanographic proxies from this area. Our findings demonstrate the orbital-scale vegetation changes in this area and their land-ocean-atmosphere linkages during the last 550 ka. During surface-water freshening events in the Japan Sea, likely associated with colder water temperatures caused by the very low eustatic sea levels and the consequent isolation from the surrounding seas during the full-glacial periods, cold-cool conifer forests became dominant under the extremely dry pseudo-continental conditions in the Japanese islands. In contrast, temperate broadleaf forests increased rapidly when the surface-freshening events ended and a weak inflow of warm water began at the onset of deglaciation, in addition to the rapid atmospheric climate warming during termination periods. During the intermediate periods between the full interglacial to the full-glacial, the Tp ratio (pollen temperature index) increased in association with the summer insolation maxima caused by the Earth's precession cycle that coincide with Chinese stalagmite negative δ18O peaks, whereas Cryptomeria pollen abundance (high-precipitation index) increased in association with the winter insolation maxima. Those orbital-scale vegetation fluctuations were attributed to the changes in seasonal temperature and precipitation patterns, where were influenced by the EAM changes that were associated with seasonal insolation changes around the Japanese archipelago. Cryptomeria forests likely developed under cool and wet conditions throughout a year with low seasonal contrasts, whereas deciduous broadleaf forests increased under condition of high seasonality with cool summers and colder, drier winters. Alternating fluctuations between the Tp ratio and Cryptomeria pollen abundance following the insolation changes were typically observed after MIS 9 and are thought to have been affected by the periodicity shift in the EAM fluctuations across the Mid-Brunhes Event.
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There are several reports of Australasian tektites found within a stratum called “laterite” layer widely distributed in Indochina. However, it has been debated whether these tektites are in situ or reworked. This uncertainty is because a... more
There are several reports of Australasian tektites found within a stratum called “laterite” layer widely distributed in Indochina. However, it has been debated whether these tektites are in situ or reworked. This uncertainty is because a detailed description of their field occurrence is lacking. Here, we describe the detailed occurrence of a cluster of tektite fragments recovered from the “laterite” layer near Huai Om, northeastern Thailand, and demonstrate the evidence of in situ occurrence of the tektites. At least 331 tektite fragments with a total weight of 713 g were found from a 40 × 30 cm area with 10 cm thickness in the uppermost part of the “laterite” layer. The very angular shapes and very poorly sorted nature of the fragments, restoration of larger tektite fragments into one ellipsoidal Muong Nong-type (MN) tektite mass, and the similar chemical composition of the fragments suggest that these MN tektite fragments represent a tektite mass that fragmented in situ. The fact ...
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ABSTRACT
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Abstract The biogenic chert-shale sequences in the Upper Paleozoic and Lower Mesozoic Inner Chichibu terrain and in the Tertiary Setogawa terrain formed on a bank or in the central part of a marginal sea adjacent to a nearby land. The... more
Abstract The biogenic chert-shale sequences in the Upper Paleozoic and Lower Mesozoic Inner Chichibu terrain and in the Tertiary Setogawa terrain formed on a bank or in the central part of a marginal sea adjacent to a nearby land. The rhythmic layering results from periodic turbidity currents. In spicule-radiolarian bedded cherts of the Inner Chichibu terrain, most chert beds are of symmetrical triple-layered type composed of a middle siliceous layer and upper and lower argillaceous layers. The amounts of hydrogenous base metals, such as Fe, Mn, Cu, Ni, V and Zn, are higher in chert than in shale partings. The MnO/Al 2 O 3 ratio and sedimentation rate diagram in Fig. 4 shows that the average sedimentation rate is 7.1 m m.y. −1 for chert and 45 m m.y. −1 for shale partings. These lines of evidence suggest that the shale partings formed from distal turbidity currents and are interbedded with hemipelagic biogenic chert. On the other hand, in the Tertiary diatomaceous bedded cherts of the Setogawa terrain, most sets of chert beds and overlying shale partings were deposited as siliceous turbidites, like in many bedded cherts in other orogenic belts of the world. The frequency of occurrence of such periodic turbidity currents is calculated as one per 11,200-17,700 yrs in the Inner Chichibu terrain and one per 2600-10,000 yrs in the Setogawa terrain.
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After the most severe mass extinction event in the Phanerozoic at the Permian/Triassic (P/T) boundary, biotic recovery from the extinction required about 5 Myr that corresponds to the entire Early Triassic. The absence of radiolarian... more
After the most severe mass extinction event in the Phanerozoic at the Permian/Triassic (P/T) boundary, biotic recovery from the extinction required about 5 Myr that corresponds to the entire Early Triassic. The absence of radiolarian bedded chert across the P/T boundary is widely recognized in the pelagic sequence of Japan and considered as resulted from prevalence of anoxic deep water.
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Phosphorite deposits in Egypt, known as the Duwi Formation, are a part of the Middle East to North Africa phosphogenic province of Late Cretaceous to Paleogene age. Phosphatic grains in these deposites are classified into phosphatic... more
Phosphorite deposits in Egypt, known as the Duwi Formation, are a part of the Middle East to North Africa phosphogenic province of Late Cretaceous to Paleogene age. Phosphatic grains in these deposites are classified into phosphatic mudclasts and phosphatic bioclasts. Phosphatic bioclasts are subdivided into fish bone fragments and shark tooth fragments. All phosphatic grains are composed of francolite.Chemical mapping
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Research Interests: Geology, Geochemistry, Oceanography, Ecology, Quartz, and 3 moreContinental shelf, Bering Sea, and Yukon River
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ABSTRACT
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The Santa Ynez Mountains and the adjacent offshore areas are situated on the northwest edge of the western Transverse Range province. Oligocene-lower Miocene strata in this province record complex interactions among local and regional... more
The Santa Ynez Mountains and the adjacent offshore areas are situated on the northwest edge of the western Transverse Range province. Oligocene-lower Miocene strata in this province record complex interactions among local and regional eustatics and local and regional tectonics and shed light on the sedimentary and tectonic history of this poorly understood region. Correlation of lithofacies units in Oligocene-lower Miocene Vaqueros Formation outcrops the Santa Ynez Mountains with Vaqueros cores from the Hondo and Capital fields leads to the delineation of three major facies tracts within the offshore and coastal areas: fan-delta conglomerates, shoreline sandstones and conglomerates, and inner shelf sandstones. Vaqueros strata at both Hondo and Capital fields are part of the inner shelf sandstone facies tract. Outcrops of the inner shelf facies typically consist of amalgamated packets of locally burrowed, cross-bedded, gravelly sandstones. In outcrop, bioturbation is most common near the tops of the cross-bed sets. In Hondo field a thinner, more basinward portion of this facies is characterized by bioturbated medium- to coarse-grained sandstones. Both in outcrops and at Hondo the base of the Vaqueros is marked by a sharp grain-size change and by a change from interbedded fluvial/deltaic strata below (the Alegria/Sespe formations) to innermore » shelf strata above (the Vaqueros Formation). The inner shelf facies tract represented by these three localities, fines, thins, and becomes more pervasively bioturbated in the present-day offshore direction suggesting a similar shoreline polarity however, the Oligocene-early Miocene paleogeography is more complex. Facies tracts present in outcrop in the western Santa Ynez Mountains become thinner and coarser in the present-day westerly direction and record deposition on a topographically and geomorphically complex shoreline.« less
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Research Interests: Geology, Quaternary, High Resolution, IODP, Expedition, and 3 moreU, Quaternary Sediments, and Japan Sea
List of the analyzed riverbed sediments collected from the Yangtze drainage basin. (XLS 39Â kb)
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East Asian Summer Monsoon (EASM) drives the hydrological cycle in East Asia, and its intensity and spatial pattern strongly affect lives of billions of people living there. Thus, it is important to investigate the behavior and controlling... more
East Asian Summer Monsoon (EASM) drives the hydrological cycle in East Asia, and its intensity and spatial pattern strongly affect lives of billions of people living there. Thus, it is important to investigate the behavior and controlling factors of EASM by reconstructing the spatiotemporal distribution of EASM precipitation in past. Climate in the drainage of Yangtze River is under the influence of EASM. It is known that there are positive correlation among precipitation, water discharge, and sediment yield (>90% is in the form of suspended particulate matter) in Yangtze drainage. Thus the provenance of the sediments discharged from the river mouth is thought to reflect the spatial distribution of EASM precipitation within the drainage. To reconstruct the behavior of EASM during the late Holocene, the sediment cores covering the past 6000 years were recovered from the rivermouth area of Yangtze in 2013 (YD13). However, based on the analysis of Cs isotope, the uppermost part of t...
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Elemental carbon (EC) is a combustion product which is composed of rich C and depleted O, H, S, and N. Biomass burning is major source of Pre-industrial EC, while fossil fuel burning is the most important source since the 18th. EC... more
Elemental carbon (EC) is a combustion product which is composed of rich C and depleted O, H, S, and N. Biomass burning is major source of Pre-industrial EC, while fossil fuel burning is the most important source since the 18th. EC transferred in the atmosphere as aerosols, and aerosols including EC have a great impact on the climate, where EC is the second strongest contribution to global warming and changing albedo by darkening of snow and ice surface. On the other hand, aerosols including EC have also negative effect on radiative forcing. Although it is difficult to evaluate net EC effect on climate, evaluation of temporal variability of atmospheric EC is necessary to understand the relationship between biomass burning and climate.
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We reconstruct the provenance of aluminosilicate sediment deposited in Ulleung Basin, Japan Sea, over the last 12 Ma at Site U1430 drilled during Integrated Ocean Drilling Program Expedition 346. Using multivariate partitioning techniques... more
We reconstruct the provenance of aluminosilicate sediment deposited in Ulleung Basin, Japan Sea, over the last 12 Ma at Site U1430 drilled during Integrated Ocean Drilling Program Expedition 346. Using multivariate partitioning techniques (Q-mode factor analysis, multiple linear regressions) applied to the major, trace and rare earth element composition of the bulk sediment, we identify and quantify four aluminosilicate components (Taklimakan, Gobi, Chinese Loess and Korean Peninsula), and model their mass accumulation rates. Each of these end-members, or materials from these regions, were present in the top-performing models in all tests. Material from the Taklimakan Desert (50–60 % of aluminosilicate contribution) is the most abundant end-member through time, while Chinese Loess and Gobi Desert components increase in contribution and flux in the Plio-Pleistocene. A Korean Peninsula component is lowest in abundance when present, and its occurrence reflects the opening of the Tsushima Strait at c. 3 Ma. Variation in dust source regions appears to track step-wise Asian aridification influenced by Cenozoic global cooling and periods of uplift of the Tibetan Plateau. During early stages of the evolution of the East Asian Monsoon, the Taklimakan Desert was the major source of dust to the Pacific. Continued uplift of the Tibetan Plateau may have influenced the increase in aeolian supply from the Gobi Desert and Chinese Loess Plateau into the Pleistocene. Consistent with existing records from the Pacific Ocean, these observations of aeolian fluxes provide more detail and specificity regarding the evolution of different Asian source regions through the latest Cenozoic.
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Although there is increasing evidence for wet, monsoonal conditions in Southeast Asia during the late Eocene, it has not been clear when this environment became established. Cenozoic sedimentary sequences constrained by radiometrically... more
Although there is increasing evidence for wet, monsoonal conditions in Southeast Asia during the late Eocene, it has not been clear when this environment became established. Cenozoic sedimentary sequences constrained by radiometrically dated igneous rocks from the Jianchuan Basin in the southeast flank of Tibetan Plateau now provide a section whose facies and climatic proxies determine this evolution. Semi-arid conditions had dominated the region since Paleocene controlled by the northern subtropical high pressure system, culminating in mid Eocene when desert dunes developed. From 36 Ma, the basin began to accumulate swamp sediments with coals, together with synchronous braided river deposits and diversified pollen assemblages, indicating significant increase in precipitation. This remarkable transition from dry to wet conditions precedes the Eocene/Oligocene boundary at 34 Ma, thus excluding general global cooling as the prime driver. We propose that uplift of Tibetan Plateau might have reached a threshold elevation by that time, operating through thermal and dynamic forcing, causing the inception or significant intensification of monsoonal rains to penetrate into this downwind locality.