Mean Grain Size Research Articles

Environmental changes during the past 13500 cal. a BP deduced from lacustrine sediment records of Lake Qinghai, China

A 475-cm long sediment core (QH-2005) from Lake Qinghai was used to carry out multi-proxy analysis of δ18O and body length of ostracod valves and redness and grain size of sediments, in order to reconstruct environmental changes during the past 13500 cal. a BP. The age model was based on 6 14C dates for bulk orgnic carbon (BOC) and 2 14C dates for lignin. The lignin 14C dates are apparently younger than the corresponding layers’ BOC 14C dates, indicating that the reservoir age varied from 728 to 1222 a since the Late Glacial and from 2390 to 2490 a immediately before the pre-bomb era. Hence, the 14C age model for Core QH-2005 was corrected by the changing reservoir age. Ostracod δ18O values were primarily related to dilution and evaporative enrichment of the lake water. The reconstructed salinity based on ostracod body length coincides well with ostracod δ18O values. High redness and mean grain size (MZ) values indicate increased riverine supply to Lake Qinghai associated with increasing monsoon rainfall. Multi-proxy results show that climate during 13500–10900 cal. a BP was relatively cold and dry with frequent short-term fluctuations; a warm and wet climate began at about 10900 cal. a BP and culminated around 6500 cal. a BP as a result of monsoon strengthening; the climate became cold and dry afterwards and has remained relatively stable since 3400 cal. a BP. Our data also reveal short-term (millennial/centennial timescales) climatic fluctuations including: Younger Dryas events, ice-rafting events 8 and 1 (by ∼11000 cal. a BP and ∼1600 cal. a BP respectively), 8200 cal. a BP cold event, Little Ice Age and the Medieval Warm Period.

Late Holocene terrestrial tephra record at western Anatolia, Turkey: Possible evidence of an explosive eruption outside Santorini in the eastern Mediterranean

A 27 cm thick, loose tephra deposits has been observed within coarse-grained colluvium at Çardak area of Denizli on the northern apron of the Acıgöl graben in western Anatolia, Turkey. It is a biotite-rich tephra with mean grain-size of coarse silt. Chemically it is dacite and rhyolite with average of 66.35% SiO 2 and 4.70% alcalia (Na 2O + K 2O) in bulk analyses. It was deposited a time between 5380 ± 90 and 2395 ± 65 yrs cal. BP, possibly between 4750 and 3385 yrs cal. BP according to 14C dating of two palaeosol layers within the colluvium. This is only and the thickest Holocene air-fall tuff layer found in terrestrial sediments in this region so far, and according to present knowledge there is no young volcanic source for such a formation in western Turkey. Analyses and comparisons of the analytic results with those of various young volcanic rocks suggest that the Çardak tephra originated from a volcanic source in the Aegean Sea. Besides, its geochemical composition, formation time and significant thickness represent probably a separate late Holocene explosive eruption in the eastern Mediterranean, apart from the Santorini event.

Patterns of grain-size temporal variation of sediment transported by overland flow associated with moving storms: interpreting soil flume experiments

Abstract. This study describes and interprets the evolution of grain-size distribution of sediment yields generated in an experimental soil flume subjected to downstream and upstream moving rain storms. Results of laboratory experiments show that downstream moving storms cause more soil loss than do upstream moving storms. The pattern of sediment grain-size evolution in time during a runoff event exhibits a clear dependence on the direction of storm movement. A strong relationship between overland flow discharge and mean sediment size is found. Nevertheless, the mean grain-size of sediments transported during the rising limb of the hydrograph is coarser than during the recession limb of the hydrograph. This is more marked for downstream moving storms.

Relation between radiocarbon, archaeological dating and sediment properties on the example of colluvial deposits (NE Poland)

This study focuses on the analysis of the structural and textural features of the colluvial (deluvial) deposits in the Suwałki Lake District (NE Poland) and their absolute age. The colluvium has a thickness of up to 150 cm. The dates of the peat under colluvium or lowermost fossil humus-rich horizons point to the ages from 5405±80 BP to 480 BP. Deposition of material at the footslope is a result of a denudation triggered by human action (surface water erosion and tillage erosion) and usually corresponds with the settlement stages. The 14C dating of deposited sediment sometimes indicated to older dates of colluvium then the archaeological evidence available for examined sites. Locally, the overlying fossil humic horizon was older then the lowermost one. The textural features of the colluvial deposits such as: the content of fine fraction, weak sorting and relationship between the mean grain-size (Mz) and the sorting index (σ1) were used to recognize sediment redeposited from the upper part of the slope. Basing on the mineral composition and electrical conductivity of fossil humus horizon it is possible to say whether the soil was degraded or aggraded. These features of the humus-rich horizons occurring between colluvial sediments can be used to explain discrepancy between the radiocarbon dating and archaeological evidence.

Mesoscale simulation of discontinuous dynamic recrystallization using the cellular automaton method

A dynamic recrystallization (DRX) cellular automaton (CA) model that can mark the microstructure with DRX circle was developed. The efiects of initial grain size on the stress-strain curve, mean grain size and DRX fraction were mainly investigated, and the simulated results were compared with those obtained from previous researches. The results show that the shape of the stress-strain curve is sensitive, while the stress and mean grain size at the steady state are insensitive to the initial grain size. The transition from a multiple-peak stress-strain curve to a single-peak one can be explained by variations in DRX circle fraction, and the initial grain size to make this transition is between 70 and 80 „m.

Evolution of Microstructure and Texture during Annealing of Aluminum AA1050 Cold Rolled to High and Ultrahigh Strains

The microstructure and texture of commercial purity aluminum (AA1050) have been investigated after cold rolling to von Mises strains of 3.6 to 6.4 followed by recovery and recrystallization during annealing. The evolution of structural parameters of the deformed microstructure, such as boundary spacing and fraction of high-angle boundaries (HABs), did not reach saturation in the given strain range. Recovery was accompanied by structural coarsening and by a decrease in the fraction of HABs. The coarsening rate increased with increasing strain prior to annealing. Recrystallization nuclei were found to form both in deformation zones around coarse particles and in recovered lamellar structures. The process of recrystallization in the present material can thus be characterized as discontinuous recrystallization. In recrystallized conditions, the average grain size was related to the grain orientation: the mean size of grains having orientations of the rolling texture was smaller than the size of grains with other orientations. The orientation dependence of the recrystallized grain size was more pronounced in the samples rolled to ultrahigh strains.

Tsunami Sediment Characteristics at the Thai Andaman Coast

This paper describes and summarizes the 2004 Indian Ocean tsunami sediment characteristics at the Thai Andaman coast. Field investigations have been made approximately 3 years after the 2004 Indian Ocean tsunami event. Seven transects have been examined at five locations. Sediment samples have been collected for grain-size analyses by wet-sieve method. Tsunami sediments are compared to three deposits from coastal sub-environments. The mean grain-size and standard deviation of deposits show that shoreface deposits are fine to very fine sand, poorly to moderately well sorted; swash zone deposits are coarse to fine sand, poorly to well sorted; berm/dune deposits are medium to fine sand, poorly to well sorted; and tsunami deposits are coarse to very fine sand, poorly to moderately well sorted. A plot of deposit mean grain-size versus sorting indicates that tsunami deposits are composed of shoreface deposits, swash zone deposits and berm/dune deposits as well. The tsunami sediment is a gray sand layer deposited with an erosional base on a pre-existing soil (rooted soil). The thickness of the tsunami sediment layer is variable. The best location for observation of the recent tsunami sediment is at about 50–200 m inland from the coastline. In most cases, the sediment layer is normally graded. In some cases, the sediment contains rip-up clasts of muddy soils and/or organic matter. The vertical variation of tsunami sediment texture shows that the mean grain-size is fining upward and landward. Break points of slope in a plot of standard deviation versus depth mark a break in turbulence associated with a transition to a lower or higher Reynolds number runup. This can be used to evaluate tsunami sediment main layer and tsunami sediment sub layers. The skewness of tsunami sediment indicates a grain size distribution with prominent finer-grain or coarse-grain particles. The kurtosis of tsunami sediment indicates grain-size distributions which are flat to peak distribution (or multi-modal to uni-modal distribution) upward. Generally, the major origins of tsunami sediment are swash zone and berm/dune zone sands where coarse to medium sands are the significant material at these locations. The minor origin of tsunami sediment is the shoreface where the significant materials are fine to very fine sands. However, for a coastal area where the shoreface slope is mild, the major origin of tsunami sediment is the shoreface. The interpretation of runup number from tsunami sediment characteristics gets three runups for the 2004 Indian Ocean tsunami at the Thai Andaman coast. It corresponds to field observations from local eyewitnesses. The 1st runup transported and deposited more coarse particles than the following runups. Overall, the pattern of onshore tsunami sediment transportation indicates erosion at swash zone and berm/dune zone, followed by dynamic equilibrium at an area behind the berm/dune zone and after that deposition at inland zone until the limit of sediment inundation. The total deposition is a major pattern in onshore tsunami sediment transportation at the deposition zone which the sediment must find in the direction of transport.

Microstructural Evolution and Mechanical Properties of Powder Hot Extruded Al-Zn-Mg-Cu Alloy

In this study, an ultrastrength Al-10Zn-3.2Mg-2.3Cu alloy was fabricated by powder hot extrusion technique. The microstructures of powder, extruded and subsequently heat treated rods were investigated by means of X-ray diffractometer (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM) with energy dispersive spectrometry (EDS) for compositional analysis. During extrusion, more MgZn2 compounds were precipitated from the supersaturated Al matrix and observed on the grain boundaries and in the grain interiors. The microstructure of as-extruded alloy is composed of Al matrix and MgZn2 phases in different shapes. After solution treating, the MgZn2 phases were mostly dissolved into matrix and the major constituent are Al7Cu2Fe phase as well as oxides. The mean size of grains was controlled to 2.5μm, and the major precipitates were GP zones and/or η’(MgZn2) phases in the Al matrix after peak-aging (T6) treatment (120°C for 20h). The ultimate tensile strength (σb), yield strength (σ0.2) and elongation (δ) are 745Mpa, 690MPa and 9.0%, respectively.

A 60-year record of rainfall from the sediments of Jinheung Pond, Jeongeup, Korea

This paper describes mean grain-size data from the 137 Cs- and 210 Pb-dated sediment core BS-3 (33-cm long) recovered from Jinheung Pond, located in the southwestern part of the Korean Peninsula. Grain-size analysis of the Jinheung Pond sediments shows a clear signal for changes in annual precipi- tation over the past 60 years. Instrumental records of annual precipitation (AP) and the annual summation of the precipitation of (50 mm per day (AP50), which reflects the energy available for sediment transport, correlate well with the mean grain-size distributions measured in the core. The most plausi- ble mechanism for this response in mean grain size is variations in the annual amount and intensity of precipitation. Heavy precipitation enhances soil erosion over the catchment area and increases the transport capacity of streams and rivers. Thus, coarser mean grain size should reflect higher precipitation, and smaller mean grain size should reflect lower rainfall. In the data from core BS-3, however, grain- size peaks attributed to increased annual precipitation are not prominent. This is because a dam prevents removal of fine particles from the pond via the outflow. Therefore, the mean grain-size value repre- sents somewhat larger sediments together with fine clays. The results of this study show that sediments of dammed lakes and ponds are well suited for high- resolution environmental investigations, especially for records of changes in precipitation over time.

AFM surface analysis of ZnO layers prepared by pulsed laser deposition at different oxygen pressures

Polycrystalline thin films of zinc oxide were deposited by pulsed laser deposition onto silicon substrates at different oxygen partial pressures in the range of 1–35 Pa. For ablation of the sintered zinc oxide target a pulsed Nd:YAG laser was used. Other processing parameters such as laser pulse energy, pulse repetition rate, substrate temperature and deposition pressure were identical. The effect of oxygen pressure on the structural properties of the films was systematically studied by using atomic force microscopy. The surface morphology, average roughness S a, root mean square S q, and mean size of grains on selected places with 2 × 2 μm 2 area of prepared samples were evaluated. Detailed structural analysis confirmed that partial oxygen pressure leads to the modification of surface morphology. Mean grain size in height and lateral direction decreases with raising oxygen pressure from 1 to 5 Pa while the further increase of oxygen pressure from 5 to 35 Pa results in grain size enlargement. The zinc oxide film formed at oxygen partial pressure 5 Pa shows smallest values of evaluated parameters ( S a = 0.6 nm, S q = 0.7 nm and mean size of grains 50 nm).

Structural evolution of nanocrystalline silicon thin films synthesized in high-density,low-temperature reactive plasmas

Silicon thin films with a variable content of nanocrystalline phase weredeposited on single-crystal silicon and glass substrates by inductively coupledplasma-assisted chemical vapor deposition using a silane precursor withoutany hydrogen dilution in the low substrate temperature range from 100 to300 °C. The structural and optical properties of the deposited films are systematicallyinvestigated by Raman spectroscopy, x-ray diffraction, Fourier transform infraredabsorption spectroscopy, UV/vis spectroscopy, scanning electron microscopyand high-resolution transmission electron microscopy. It is shown that thestructure of the silicon thin films evolves from the purely amorphous phase to thenanocrystalline phase when the substrate temperature is increased from 100 to150 °C. It is found that the variations of the crystalline fractionfc, bonded hydrogencontent CH, optical bandgapETauc, film microstructureand growth rate Rd are closely related to the substrate temperature. In particular, at a substrate temperature of300 °C, the nanocrystalline Si thin films of our interest feature a high growth rate of1.63 nm s−1, a low hydrogen content of 4.0 at.%, a high crystalline fraction of 69.1%, a low opticalbandgap of 1.55 eV and an almost vertically aligned columnar structure with a mean grainsize of approximately 10 nm. It is also shown that the low-temperature synthesis ofnanocrystalline Si thin films without any hydrogen dilution is attributed to the outstandingdissociation ability of the high-density inductively coupled plasmas and effectiveplasma–surface interactions during the growth process. Our results offer a highlyeffective yet simple and environmentally friendly technique to synthesize high-qualitynanocrystalline Si films, vitally needed for the development of new-generation solar cellsand other emerging nanotechnologies.

Climate instability during the last glaciation recorded in the Yuanbu loess section

Abrupt events within the Linxia Yuanbu loess section in the western Loess Plateau in China were investigated. The climatic proxy index of the content of mean grain-size and >4 μm grain-size fraction of the section was used as a climatic indicator, and a moving average method was applied in the statistical analysis to extract the abrupt events recorded in the section. It was found that the loess of the last glaciation recorded not only the abrupt events teleconnected with the high-latitude North Atlantic and Greenland regions but also as many as 15 abrupt events in addition to the Heinrich (H) and Younger Dryas (YD) events. This indicates that abrupt climate changes were typical of the climate changes occurring in the Loess Plateau during the last glaciation. The widely recognized mechanisms of the abrupt climate changes, including the heat transfer theory of the North Atlantic Ocean, the atmospheric circulation theory, and the theory of the interaction between low-latitude ocean and the atmosphere remains to be discussed. Perhaps this problem could be resolved by revealing the relation between the evolution of the features of the East Asian monsoon climate and the climate in the surrounding areas. Through a detailed study of the features of the Heinrich and YD events, criteria on which the abrupt events recorded in the loess could be distinguished were tentatively defined. The events were associated with a large grain size, high carbonate content, high lightness, low susceptibility, low redness and low yellowness. In addition, the variation amplitude of the adjacent peak and valley on the curve of the content of the mean grain-size and >40 μm grain-size fraction was larger than 3.4 μm and the content of >40 μm grain-size fraction was larger than 2.0 μm. Lastly, the length of the variation time was less than 500 years. If all these criteria were met, the event was viewed as an abrupt event.

The three-dimensional distribution of sedimentary facies and characteristics of sediment grain-size distribution in a sandy tidal flat along the Kushida River estuary, Ise Bay, central Japan

Comprehending the temporal and spatial transitions of depositional processes in intertidal environments is of major importance to understanding sediment transport and the development of geomorphology in such environments. In this study, subsurface sediments were cored from the sandy tidal flat in the Kushida River estuary, Ise Bay, central Japan, and we investigated the three-dimensional distribution of sedimentary facies. In addition, we analyzed grain-size distribution using a settling tube method and determined the distribution characteristics for each sedimentary facies. As a result, three sedimentary units (Facies A–C) were recognized. Facies A, a wave-influenced deposit formed by the migration of sand bars, is characterized by a fine- to medium-grained sand layer showing weak coarsening upward or no grading with faint parallel lamination tendencies. Facies B; a channel-fill deposit influenced by fluvial forcing, consists of poorly sorted coarse- to medium-grained sand with a fining-upward trend. Facies C is a river flood deposit composed of mud or muddy sand, including a large amount of organic matter such as terrigenous plant debris. Grain-size analysis showed that Facies A and B are best discriminated by coefficient of variance (CV), a dimensionless value equal to a facies' sorting (standard deviation) divided by the mean grain-size of their respective grain-size distributions. Facies A has a low CV, indicating relatively well sorted sediments. Facies B has a higher CV, indicating relatively poor sorting. The CV value is thus expected to be an indicator of the degree of wave winnowing. Furthermore, the three-dimensional spatial distribution of sedimentary facies in subsurface sand was revealed using the CV values of facies' grain-size distributions as a proxy. We illustrate the temporal and spatial transitions of two main depositional processes, waves and fluvial currents, which control sediment transport and the development of geomorphology on the tidal flat. The CV may be an important proxy in facies analysis.

Experimental and simulation studies of resistivity in nanoscale copper films

The effect of film thickness on the resistivity of thin, evaporated copper films (approximately 10–150 nm thick) was determined from sheet resistance, film thickness, and mean grain-size measurements by using four-point probe, profilometer, and electron backscatter diffraction (EBSD) and X-ray diffraction (XRD) methods, respectively. The resistivity of these films increased with decreasing film thickness in a manner that agreed well with the dependence given by a versatile simulation program, published earlier, using the measured values for the mean grain size and fitting parameters for surface and grain boundary scattering. Measurements of the change in sheet resistance with temperature of these films and the known change in resistivity with temperature for pure, bulk copper were used to calculate the thickness of these films electrically by using Matthiessen’s rule (this is often referred to as an “electrical thickness”). These values agreed to within 3 nm of those obtained physically with the profilometer. Hence, Matthiessen’s rule can continue to be used to measure the thickness of a copper film and, by inference, the cross-sectional area of a copper line for dimensions well below the mean free path of electrons in copper at room temperature (39 nm).

Variations in sediment provenance during the past 3000 years off the Tagus River, Portugal

Marine sediments from the Portuguese shelf are influenced by environmental changes in the surrounding continental and marine environment. These are largely controlled by the North Atlantic Oscillation, but additional impacts may arise from episodic tsunamis. In order to investigate these influences, a high resolution multi-proxy study has been carried out on a 5.4 m long gravity core and five box cores from the Tagus prodelta on the western Portuguese margin, incorporating geochemical (C org/N total ratios, δ 13C org, δ 15N, δ 18O, C org and CaCO 3 content) and physical sediment properties (magnetic susceptibility, grain-size). Subsurface data of the five box cores indicate no major effect of early postdepositional alteration. Surface data show a higher fraction of terrigenous organic material close to the river mouth and in the southern prodelta. Gravity core GeoB 8903 covers the last 3.2 kyrs with a temporal resolution of at least 0.1 cm/yr. Very high sedimentation rates between 69 and 140 cm core depth indicate a possible disturbance of the record by the AD1755 tsunami, although no evidence for a disturbance is observed in the data. Sea surface temperature and salinity on the prodelta, the local budget of marine NO 3 − as well as the provenance of organic matter remained virtually constant during the past 3.2 kyrs. A positive correlation between magnetic susceptibility (MS) and North Atlantic Oscillation (NAO) is evident for the past 250 years, coinciding with a negative correlation between mean grain-size and NAO. This is assigned to a constant riverine supply of fine material with high MS, which is diluted by the riverine input of a coarser, low-MS component during NAO negative, high-precipitation phases. End-member modelling of the lithic grain-size spectrum supports this, revealing a third, coarse lithic component. The high abundance of this coarse end-member prior to 2 kyr BP is interpreted as the result of stronger bottom currents, concentrating the coarse sediment fraction by winnowing. As continental climate was more arid prior to 2 kyr BP (Subboreal), the coarse end-member may also consist of dust from local sources. A decrease in grain-size and CaCO 3 content after 2 kyr BP is interpreted as a result of decreasing wind strength. The onset of a fining trend and a further decrease in CaCO 3 around AD900 occurs simultaneous to climatic variations, reconstructed from eastern North Atlantic records. A strong increase in MS between AD1400 and AD1500 indicates higher lithic terrigenous input, caused by deforestation in the hinterland.

Modern benthic foraminifera on Banco Chinchorro, Quintana Roo, Mexico

Benthic foraminiferal assemblages may be used as environmental indicators on Banco Chinchorro, an isolated carbonate platform off the eastern coast of the Yucatan Peninsula. Seventy-seven species from 44 genera were identified in 14 surface sediment samples, which were collected along an E–W windward-to-leeward transect across the platform. A total of 15,493 foraminiferal tests (max. 1,200 tests per sample) were investigated and served as the basis of this study. As many taxa range throughout several platform zones, assemblages are better environmental indicators as compared to individual species. Four foraminiferal assemblages were identified using statistical methods including (1) a Homotrema assemblage, which occurs at the windward platform margin, (2) an Archaias-Homotrema assemblage which is found on the leeward margin and on platform interior coral patch reefs, (3) a Quinqueloculininae-Archaias-Rosalina assemblage of the western platform, and (4) an Archaias-Quinqueloculininae assemblage characteristic of the eastern platform interior. Environmental factors which influence variation in foraminiferal distribution and diversity on Banco Chinchorro include exposure to waves and currents and substrate (plant and algal growth). Sediment transport does not play a major role in Banco Chinchorro based on the observation that there are only limited amounts of taxa found outside their typical habitats, and, that mean grain-size and sorting of foraminiferal tests do not exhibit clear patterns.

Structure and Fatigue Properties of the Mg Alloy AM60 Processed by ECAP

This paper reports on the microstructures and fatigue properties of ultrafine-grained (UFG) AM60 magnesium alloy processed by equal channel angular pressing (ECAP) at various temperatures. After ECAP processing, samples exhibited an increase in fatigue endurance limit, which correlates well with a decrease in grain size. In case of lowest ECAP temperature, the mean grain size is as small as 1 2m which leads to an increase in fatigue endurance limit by 70 % in comparison to coarse-grained alloy. The temperature of ECAP not only governs the grain size and misorientation angles of grain boundaries but also the volume fraction of precipitates, thus affecting the probability of twinning and grain growth after fatigue treatment.

Paleoenvironmental changes during the last 8400 years in the southern Yellow Sea: Benthic foraminiferal and stable isotopic evidence

We used benthic foraminiferal, stable isotopic and grain-size data from an AMS 14C dated core from the southern Yellow Sea to decipher Holocene paleoenvironmental changes. Large-amplitude changes in δ 18O, δ 13C and benthic foraminiferal assemblage composition indicate that major environmental changes occurred during the last 8400 years in the southern Yellow Sea. We recognize 3 stages of environmental development: 1. A low salinity estuarine environment stage, at 8.4–6.9 cal. kyr BP, 2. A low salinity shallow sea environment stage at 6.9 to about 6–5 cal. kyr BP and 3. A modern marine shelf environment stage after about 6–5 cal. kyr BP The δ 18O and δ 13C values of Ammonia aomoriensis (Asano), combined with benthic foraminiferal assemblage data indicate a low bottom-water salinity (< 15‰) during stage 1, suggesting a large amount of river runoff. Abrupt increases in δ 18O and δ 13C around 6.9 cal. kyr BP were accompanied by a decrease in mean grain-size and in abundance of benthic foraminifera, possibly caused by a North-ward shift of the Yellow River's outlet. During subsequent stage 2 the southern Yellow Sea was still characterized by a low salinity (< 28‰) even though sea-level was high, possibly due to the continued strong influence of river input, and/or limited exchange between the southern Yellow Sea and the open ocean. At about 6–5 cal. kyr BP, an A. aomoriensis dominated benthic foraminiferal assemblage was replaced by an Ammonia ketienziensis (Ishizaki) dominated assemblage, indicating an increase in bottom-water salinity. Grain-size and stable isotope data, suggest that the modern circulation was probably established at that time. We speculate that the combined impacts of reduced river runoff, enhanced East Asia Winter Monsoon, and increased influence of southern, warm ocean currents caused this transition.

Algorithm of determining the ratio between cobalt interlayer and carbide grain size from the results of measurements in the thin section plane

ular, mean size of carbide grains and the mean thickness of a cobalt interlayer are defined by this method. Though in most cases these parameters are employed to describe the dependence of physico mechanical properties of a hard alloy on its microstructure, the problem of the reconstruction of a hard alloy three dimensional structure remains important [1]. In particular, characteristics of the three dimensional structure are required in using the self consistency method known in the composite material mechanics. The essence of the method is that a grain of the strengthening phase covered with an intermediate layer having properties of a binder is placed into an unbounded medium, whose properties are taken equal to macroscopic properties of the composite under study [2]. In this case the stressed strained state of phases depend, in par ticular on the ratio of carbide grain radius a to external radius b (b – a being the thickness of a cobalt inter layer).

Development of the East Asian monsoon: Mineralogical and sedimentologic records in the northern South China Sea since 20 Ma

We here reconstruct the past change of the East Asian monsoon since 20 Ma using samples from Ocean Drilling Program (ODP) Site 1146 in the northern South China Sea based on a multi-proxy approach including a monomineralic quartz isolation procedure, identification of clay minerals by X-ray Diffraction (XRD) and grain-size analysis of isolated terrigenous materials. Terrigenous supply to ODP Site 1146 was dominated by changes in the strength of multiple sources and transport processes. Grain-size data modeled by an end-member modeling algorithm indicate that eolian dust from the arid Asian inland and fluvial input have contributed on average 20% and 80% of total terrigenous material to ODP Site 1146, respectively. Specifically, about 40–53% of the total (quartz + feldspar) and only 6–11% of the total clay is related to eolian supply at the study site. Detailed analysis of the sedimentary environment, and clay minerals combined with previous studies shows that smectite originates mainly from Luzon, kaolinite from the Pearl River and illite and chlorite from the Pearl River, Taiwan and/or the Yangtze River. The proportion and mass accumulation rate (MAR) of the coarsest end-member EM1 (interpreted as eolian dust), ratios of (illite + chlorite)/smectite, (quartz + feldspar)% and mean grain-size of terrigenous materials at ODP Site 1146 were adopted as proxies for East Asian monsoon evolution. The consistent variation of these independent proxies since 20 Ma shows three profound shifts in the intensity of East Asian winter monsoon relative to summer monsoon, as well as aridity of the Asian continent, occurred at ∼ 15 Ma, ∼ 8 Ma and the youngest at about 3 Ma. In comparison, the summer monsoon intensified contemporaneously with the winter monsoon at 3 Ma. The phased uplift of the Himalaya–Tibetan plateau may have played a significant role in strengthening the Asian monsoon at ∼ 15 Ma, 8 Ma and 3 Ma.