Middle and Late Quaternary depositional sequences and cycles in the eastern Mediterranean

Although most of the Quaternary sediments of the eastern Mediterranean appear reworked, extensive areas of hemipelagic sediments occur, mainly in the central part of the basin (Mediterranean Ridge). The most obvious character of these muddy sediments is the numerous changes in colour. They result from the organic carbon content as well as from concentration and chemical form of metallic elements (Mn, Fe, Cu, Zn). The succession of coloured layers is arranged into sequences developed between two sharp contacts; a complete sequence involves five lithofacies, from an oxidized layer at the base to a reduced sapropel at the top, and displays progressive internal changes of colour from ochre, beige, greyish-beige, grey and black layers: several sequence-variants (top-truncated, base-truncated, recurrent) are identified. These sequences are a consequence of changes in oceanographic conditions, i.e. from oxidizing to reduced environments, resulting in different organic and mineral contents. Based on detailed studies of Quaternary sediments collected by coring, a synthesized standard succession representative of the ordered sequences in the eastern Mediterranean is proposed, from about 650 000 yr as deduced from the calculated rate of sedimentation of 1·7 mm 1000yr^?1. This succession appears modulated by cyclic events: large-scale periods (200 000 yr) of reduced and oxidized sequences correlate with major alternate phases of flooding and reduced flow of the Nile River during the Quaternary. Subsequent sequences of shorter time-scale (20 000–50 000 yr) results from two factors: heaviest monsoons leading to an increase of the influx of the Nile River and global climatic changes (Eurasian ice sheet meltwater); these two factors act synchronously or independently along the studied time-span. These interplaying factors result in periodic stages of increasingly restricted conditions in the basin and explain the complexity of the eastern Mediterranean succession, at least since 650 000 yr ago.     

Akaganéite (β-FeOOH) precipitation in inland acid sulfate soils of south-western New South Wales (NSW), Australia

The prevalence of sulphidic sediments in inland wetlands has been only recently recognized in many parts of the world, including Australia. The exposure of sulphidic sediments in these wetlands due to natural and human induced drying events has resulted in the oxidation of iron sulfide minerals, the formation of secondary iron minerals characteristic of acid sulfate soils and the release of highly acidic solutions. The objective of this study was to determine the mineralogy and morphology of sediments collected from the oxidized surface horizon (0-5 cm) of an inland acid sulfate soil located in south-western New South Wales (NSW), Australia. Random powder X-ray diffraction (XRD), transmission electron microscopy (TEM) and scanning transmission electron microscopy combined with energy dispersive X-ray spectroscopy (STEM-EDS) techniques were used to characterize the minerals present in these sediments. Akaganéite was identified as the major mineral phase in the sediments; K-jarosite was also determined in small amounts in some sediments. The XRD patterns of sequentially washed (E-pure® water-0.01 M HCl-0.01 M EDTA) sediment samples showed all akaganéite peaks; the Rietveld refinement of these patterns also revealed a predominance of akaganéite. The chemical analyses of the original and washed sediments using STEM-EDS clearly showed the presence of akaganéite as a pure mineral phase with an average Fe/Cl mole ratio of 6.7 and a structural formula of Fe₈O₈(OH)_6.8(Cl)_1.2. These findings show that the extreme saline-acidic solutions (pH ∼ 2, EC = 216 dS/m) at the Bottle Bend lagoon provide ideal conditions for the crystallization of this rarely forming mineral.     

黄河上游全新世特大洪水及其沉积特征

黄河上游官亭盆地的黄河二级阶地面上沉积了厚约2m左右的平流沉积物,每次洪水形成1个由红色粘 土水平层和黑灰色粘土水平层组成的洪水单元。对研究剖面洪水沉积层的磁化率测量区分出了14个洪水单元, 代表了14次特大洪水的发生;利用盆地内的考古资料,将古洪水频繁发生的时期定为3700～2800aB.P.。粒度分 析表明官亭盆地平流沉积的沉积物几乎全部由粒径小于4φ的悬移物质组成,其分选系数>2,偏度<0,峰态中等。 与黄河中游进行比较,官亭盆地的平流沉积粒级更小,偏度更小且呈负偏。     

Influence of Climate Changes in the Late Pleistocene–Holocene on Composition of Bottom Sediments of the Selenga–Buguldeika Saddle,Lake Baikal

The study of bottom sediments of Lake Baikal recovered by submarine drilling at the Selenga–Buguldeika saddle (core VER93-2 st. 24GC) allowed us to reconstruct the climatic events in the Baikal region in the last 20–25 k.y. On the basis of the data on distribution of chemical elements in the core section, the mineral composition of sediments was calculated by the physicochemical modeling method. A study of how ratios of clay minerals changed in the section allowed us to identify the Pleistocene–Holocene boundary, Bølling–Allerød postglacial warming, and Late Dryas cooling. The calculated data on mineral composition of bottom sediments from the core VER93-2 demonstrate a good fit to the X-ray diffraction analysis results. The proposed approach can be used in calculation of mineral compositions of other sedimentary sequences with known chemical composition.     

The relationship of sediment texture with coastal environments along the Kuala Terengganu Coast, Malaysia

The subtidal sediments of four coastal environments (beach, berm, surf zone and nearshore sea floor) of Kuala Terengganu have been studied in terms of their textural characteristics and depositional process. Sampling and statistical analyses of the grain size distributions of beach, surf zone and shallow sea-floor sediments at various locations along the coastline show that they varied in their mean grain size as well as values of sorting and skewness. The statistical parameters of grain size distributions thus allowed recognition of distinct sub-environments. The size distribution of such sediments suggests that the various processes that are responsible for their transportation and deposition are wave, current and wind action. The different energy conditions and the morphology of each coastal environment seem to be reflected in the characteristics of the sediments in each environment.     

Swell impact on reef sedimentary processes: A case study of the La Reunion fringing reef

Two surface‐sediment sampling campaigns were carried out in November and December 2003, before and after a strong swell event, in the back‐reef area of a microtidal fringing reef on the western coast of La Reunion, Indian Ocean. The spatial distributions of the mean grain size, sorting and skewness parameters are determined, and grain‐size trend analysis is performed to estimate the main sediment transport pathways in the reef. The results of this analysis are compared with hydrodynamic records obtained in the same reef area during fair weather conditions and during swell events. Sediment dynamics inferred from the hydrodynamic records show that significant sediment erosion and transport occur only during swell events and under strongly agitated sea states. Under normal wave conditions, there is a potential for onshore sediment transport from the reef‐flat to the back‐reef, but this transport is episodic and occurs principally during high‐tide stages. Sediment transport trends revealed by the grain‐size trend analysis method show onshore and alongshore low‐energy transport processes that are in agreement with the hydrodynamic records. The grain‐size trend analysis method also provides evidence of an offshore high‐energy transport trend that could be interpreted as a real physical process associated with return flow from the shore to the reef. The impact of swell on the reef sediment dynamics is clearly demonstrated by onshore and alongshore transport. Considering different combinations of the vector transport trends computed through the grain‐size trend analysis approach, more realistic and pertinent results can be obtained by applying an exclusive OR operation (XOR case) on the vectors. The main results presented here highlight a trend towards the accumulation of carbonate sands in the back‐reef area of the fringing reef. These sediments can only be resuspended during extreme events such as storms or tropical cyclones.     

Application of CCSEM to heavy mineral deposits: Source of high-Ti ilmenite sand deposits of South Kerala beaches, SW India

For the characterization of sediments, Computer Controlled Scanning Electron Microscopy (CCSEM) is a powerful method in obtaining chemical data on individual mineral grains and modal analysis of the heavy mineral fraction of sediment samples. Here we show how the CCSEM method can be used to evaluate ilmenite ore grade as well as a tool to investigate the source of heavy mineral deposits.The heavy mineral rich deposits in beach sands around the town of Chavara in SW India are characterized by ilmenite with elevated TiO₂ contents, often exceeding 60 wt.%. In order to determine the origin of these high-TiO₂ ilmenite deposits, we collected a series of beach sediment samples (22) from a c. 800 km long stretch of coastline from northern Kerala state to well within the Tamil Nadu state. A set (7) of river sediments was also taken, roughly covering the catchment area to the beach samples. The data show that the sediments in the Chavara high-Ti ilmenite deposit are distinguished by minor elements in ilmenite, garnet chemistry and heavy mineral assemblage: Chavara ilmenite has high MgO and low MnO contents; garnets have low grossular components and the heavy mineral assemblage is dominated by sillimanite–kyanite in addition to ilmenite. These features correlate with basement geology in the hinterland, and with sediments from rivers, draining the basement. Based on these observations we conclude that high-Ti ilmenite from Chavara beaches originates in the khondalite belt of high-grade metasediments. Our study demonstrates rapid mineral analyses in sediments by CCSEM to be efficient in the characterization of mineral compositions and assemblages in sediments, in the identification of possible source regions and thus ultimately in exploration for industrial mineral resources.     

GPR studies over the tsunami affected Karaikal beach,Tamil Nadu,south India

In this study, results of GPR profiling related to mapping of subsurface sedimentary layers at tsunami affected Karaikal beach are presented . A 400 MHz antenna was used for profiling along 262 m stretch of transect from beach to backshore areas with penetration of about 2.0 m depth (50 ns two-way travel time). The velocity analysis was carried out to estimate the depth information along the GPR profile. Based on the significant changes in the reflection amplitude, three different zones are marked and the upper zone is noticed with less moisture compared to other two (saturated) zones. The water table is noticed to vary from 0.5 to 0.75 m depth (12–15 ns) as moving away from the coastline. Buried erosional surface is observed at 1.5 m depth (40–42 ns), which represents the limit up to which the extreme event acted upon. In other words, it is the depth to which the tsunami sediments have been piled up to about 1.5 m thickness. Three field test pits were made along the transect and sedimentary sequences were recorded. The sand layers, especially, heavy mineral layers, recorded in the test pits indicate a positive correlation with the amplitude and velocity changes in the GPR profile. Such interpretation seems to be difficult in the middle zone due to its water saturation condition. But it is fairly clear in the lower zone located just below the erosional surface where the strata is comparatively more compact. The inferences from the GPR profile thus provide a lucid insight to the subsurface sediment sequences of the tsunami sediments in the Karaikal beach.     

堰塞湖沉积物粒度特征分析——以岷江上游叠溪古堰塞湖为例

对叠溪149个古堰塞湖沉积物样品作了物质组成分析、粒度参数计算和概率累积曲线的统计,结合有关资料对比分析了不同沉积环境中沉积物的粒度特征。结果显示湖相沉积上游段的沉积物主要是粉砂质砂和砂质粉砂,中游和下游段的沉积物较细,主要是黏土质粉砂和粉砂。受河流扰动的影响,湖相沉积上游段沉积物的粒径较粗,平均粒径在4～6φ之间,多为负偏度,峰态宽平,分选性差;中游和下游段的平均粒径在6～8φ之间,均为正偏度,峰态中等,沉积物的分选比上游段好。堰塞湖沉积物是由三个或四个粒度次总体组成,其中上游段沉积物含有4个次总体,中游和下游段含有3个次总体,受物源区的控制,上游段中推移总体的含量远大于中、下游段。这些特征均表明堰塞湖上游段沉积物的搬运方式和沉积环境与中、下游段明显不同。与其他环境中的沉积物相比,堰塞湖沉积物的截点偏细,跃移组分分选性最差。     

长江、汉江沉积物磁学特征比较研究

长江和汉江现代沉积物的磁学特征分析研究结果表明：  1）长江和汉江现代沉积物中铁磁性矿物均以亚铁磁性矿物为主,它们主导了样品的磁性特征。但长江沉积物比汉江沉积物亚铁磁性矿物含量要高;  2)长江和汉江沉积物的亚铁磁性矿物晶粒都以假单畴~多畴为主。相对汉江沉积物,长江沉积物磁性颗粒总体上要比汉江的粗;   3）长江沉积物中的不完全反铁磁性矿物含量比汉江高,但不完全反铁磁性矿物对沉积物磁性参数和SIRM的贡献却比汉江的小;   4）长江上游金沙江段比长江中游（宜昌-武汉）江段沉积物中亚铁磁性矿物含量要高,且长江中游沉积物样品磁性颗粒要比长江上游的偏细,这可能与搬运距离有关;   5）长江样品的磁性参数的变化区间比汉江大,数据间的相关性也比汉江差。这可能与长江较汉江流域范围广、支流多、物源复杂有密切的关系。     

Interpretation of moment measures derived from water-lain sediments

ABSTRACT Although mean size provides a useful value for characterizing sediments, it is an inadequate expression of the interaction between sediments and hydraulic regimes and many authors have explored the significance of other statistical moment measures in different parts of the particle size spectrum. Few publications, however, have described such relationships over a very wide range of particle sizes. Using a combined data base (of marine and lacustrine sediments) we have been able to demonstrate the following: The distributions of standard deviation (and entropy) values are repeated in similar form on either side of the sand size class, describing mixtures between sands and gravel and sands and clay. Skewness is modified by the hydraulic response of the sediment and a skewness divide is present at about 2.7 φ, where it coincides with the minimum shear velocity required to initiate particle motion. This divide may be used to distinguish between high and low energy regimes. Kurtosis, like standard deviation, is a measure of the mixing of end member populations but it is more sensitive to changes in the tails of distribution curves. The maximum positive peak of kurtosis, at about 2.5 φ, lies close to the skewness divide (in our data). By using skewness/kurtosis plots it is possible to define separate field distribution for sediments which, to a greater or lesser degree, appear to conform to hydraulic equilibrium. By using sediments which are close to equilibrium (and lie at or close to our skewness/kurtosis boundary curves, it should be possible to define hydraulic shear velocities, at the time of formation. Values may be established by empirical relationships or by defining the break-point (traction and intermittent suspension) between linear components of individual sample φ size/probability distribution plots. Such relationships should be enhanced by using hydraulic equivalent diameters instead of sieve diameters. In fine sediments, the use of fractional (silt: clay) ratios offers sensitivity at a level comparable to that of skewness/kurtosis plots and may be more easily computed.     

The Stream Sediment Geochemistry of the Walawe Ganga Basin of Sri Lanka - Implications for Gondwana Mineralization

A regional geochemical and mineralogical study aimed at investigating the mineralization in the western-part of the Walawe Ganga (river) Basin in Sri Lanka is represented in this paper. The river basin is the 3^rd largest in the country and has within it a boundary zone between two geologically different crustal blocks, which are marked by granulitic grade rocks and amphibolite grade rocks. Size fractions of stream sediments (< 63 μm; 63–125 μm; 125–177 μm and 177–250 μm) developed on the granulite-grade metamorphic terrain have been analysed at their source for their mineralogical and selected element compositions. Thirty-eight (38) sediment samples and 15 representative probable parent rock samples were chemically analysed giving special emphasis to the High Field Strength trace Elements (HFSE) including the Rare Earth Elements (REE). The granulite grade rocks in the study area is geochemically similar to that of post Archean upper crust. However the stream sediments developed from the high-grade rocks during the intense weathering, are markedly enriched with HFSE and REE. The enrichment of HFSE and LREE is accounted for by the presence of HFSE- and REE- rich accessory mineral phases such as zircon, monazite, apatite, garnet and rutile in the sediments. In some samples, the content of heavy minerals contributes as much as 50 wt. %. These minerals act as a source of elements in the sediments. However, extreme hydraulic sorting of HFSE- and REE-bearing minerals during the sediment deposition cannot be expected within a short distance from near the sources except from a mineralized occurrence. Therefore, the higher enrichment of these elements presumably indicates occurrences of scattered mineral sources such as highly differentiated granites and associated pegmatites within the Walawe Ganga drainage basin. These granitic pegmatites are probably intruded during or soon after the main granulite-facies metamorphic event and similar events are seen in other terrains of East-Gondwana.     

东天山喀尔里克山北坡淖毛湖盆地土壤粒度分布特征及成因

对东天山喀尔里克山北坡-淖毛湖盆地不同类型土壤的粒度进行分析.结果表明:研究区土壤主要由粉粒和砂粒组成,从喀尔里克山北坡、中部地区到淖毛湖盆地,土壤粒度平均值逐渐变大,颗粒分选性差,偏度多属极正偏或正偏,峰态集中在宽、中等和窄3个等级,表明其成土母质较粗、来源相对复杂.土壤的粒度参数Mz、σ、SK和KG值很好地表征了不同土地类型和植被类型及盖度对土壤粒度特征的影响.土壤粒度分维值呈现出随海拔降低逐渐减小的趋势,并且分维值与粘粒含量呈正相关关系.喀尔里克山北坡土壤中粘粒的含量高于中部地区和淖毛湖盆地的土壤,反映出不同地区土壤母质来源和沉积环境的差异.不同地带土壤概率累积曲线的空间变化及综合参数特征表现出地形和气候对颗粒运动形式有一定影响,并且不同地区土壤在成因上既有区别又有联系.     

Characteristics of clay minerals in sediments of Hemudu area,Zhejiang, China in Holocene and their environmental significance

The Ningshao Plain experienced sea-level fluctuation and climate change in the Holocene and gave birth to a Neolithic Civilization, the Hemudu Culture (about 5000 BC). Using XRD method, this paper studied the clay mineralogy of sediments in core HMD-1301 from Hemudu Site area in Ningshao Plain. Results show that the clay mineral assemblages in all samples are quite consistent. They are dominated by illite (about 57%) and smectite (about 26%), and a small amount of kaolinite (about 6%) and chlorite (about 9%). In addition, illite, chlorite, and kaolinite are originated mainly from eolian loesses. Smectite is resulted mainly from chemical weathering of local volcanic rocks outcropped. Illite crystallinity indicates the climatic characteristics of the source region, and illite chemistry index reflects the climate nature of the sedimentary area. It is our understanding that water medium properties in a sedimentary environment affect clay mineral assemblage and the distribution, based on which were cognized the Holocene transgression-regression events in the Hemudu Site area. These mineral indices are well comparable with geochemical indicators in identifying the transgression-regression events. We believe that these events affected the ancient civilization of the ancient residential communities at the time.©2019 China Geology Editorial Office.     

Some effects of compaction and geological time on the pore parameters of argillaceous rocks

Graphical statistics have been applied to the pore-size distribution curves of argillaceous rocks to characterize the changes in pore parameters that result from compaction and geological time. The most striking characteristic of recently deposited sediment is the high variability in mean pore size and in the sorting and skewness of the pore system. The mean pore size ranges from 15 to 980 nm, sorting ranges from very well sorted to poorly sorted, and skewness varies from systems in which small pores predominate over large ones to systems in which large pores predominate. This high variability in pore structure represents the many environmental and mineral-related variables that affect the pore system of newly deposited sediment. The mean pore size of shales decreases with increasing compaction and approaches a limiting value of about 3·5 nm at depth. Within a geological time span of 50 m.y. and/or depth of burial of about 1200 m, most sediments have reached an irreversible, well sorted pore-size distribution. Early diagenetic processes apparently affect the skewness of pore systems more than compaction, such that within about 50 m.y. the pore system is negatively skewed, with small pores predominating over large. Sediments buried to a depth of 500 m or less exhibit a porosity range of 40--85%; below 500 m, porosity decreases linearly with burial depth. No correlation exists between the surface area of shale pore systems and depth of burial, geological age, and the pore parameters mean pore size, sorting, and skewness.     

Paragenesis of mineralization within fractured pebbles in Witwatersrand conglomerates

Mineralized conglomerates in the Witwatersrand goldfields consistently exhibit intense fracturing of quartz pebbles. The fractures are coated with quartz, phyllosilicates, organic matter, uraninite, gold, and base metal sulfide minerals, showing that all of these phases were at least partially epigenetic. Samples from five goldfields (Evander, West Rand, Carletonville, Klerksdorp, Welkom) across the Witwatersrand Basin show comparable paragenetic sequences of fracture-fillings. This implies that fracturing and several episodes of mineral deposition were basinwide events, rather than the result of local processes. Fluid inclusion data for the quartz indicates precipitation from these basinwide fluids at relatively low temperatures (<250 °C), which may be consistent with other evidence for mineralization following the Vredefort Event at 2025 Ma.     

Large-scale rhomboid bed forms and sedimentary structures associated with hurricane washover*

Hurricane washover fans from the Texas Gulf Coast exhibit large-scale rhomboid bed forms developed on washover deposits of fine sand with varying shell content. Washover processes inferred from aerial photographs, storm characteristics, and physical settings suggest that these bed forms are the product of (1) storm surge flooding or (2) high wind shear stress. Multiple bed forms, including large-scale rhombs, are responsible for sedimentary structures preserved in washover deposits. Proximal channels exhibit scour and fill sequences capped by mud drapes. Mid-channel fan deposits also have scour bases marked by shell lags which are overlain by horizontal laminations and foreset and backset laminae. Distal fan sediments are relatively shell free and are interbedded with tidal flat deposits characterized by bioturbated, alternating sand and mud laminae. Rhomboidal patterns can form on the free surface of water in response to five processes: (1) wave interference from two externally independent sources, (2) wave interference from refraction of a single set of wave fronts, (3) standing oblique waves caused by bed roughness elements, (4) standing oblique waves formed at channel boundaries and channel transitions, and (5) wind stress. Geologically, standing oblique waves from unidirectional nearly supercritical flow is probably the most important process in rhomboid bed form development.     

Iron mineralisation in Mio-Pliocene sediments of the Tamra iron mine (Nefza mining district, Tunisia): Mixed influence of pedogenesis and hydrothermal alteration

The Tamra iron mine (Nefza mining district, N. Tunisia) has been exploited for about one century. There are, however, very few publications modelling the mineralisation within this 50 m-thick Messinian–Zanclean sedimentary series. We present the result of a detailed sedimentological, mineralogical and geochemical study on the siliciclastic sediments heavily mineralised in iron. In their present state of preservation, these are rather unusual sediments, wherein most of sedimentological information is obliterated by iron impregnation. The whole series consists of a succession of fining-upward sequences (a few meters in thickness) that are capped by clay-bearing variegated and mottled horizons, each sequence being interpreted as a shallowing-upward sequence topped by an emersive horizon corresponding to a paleosoil. We propose that alteration and/or pedogenesis by the downward percolation of meteoric fluids accounts for most of the initial iron concentration, while a hydrothermal overprint, linked to the neighbouring Miocene magmatic rocks and associated mineral deposits (Sidi Driss Fe–Pb–Zn mine), accounts for the existing extreme iron enrichment. The proposed model is likely to apply to several other iron mines linked to the Miocene magmatic activity in the whole Maghreb area, and especially along the Apenninic thrust front (locally known as Tell-Rif front).     

OSL signal resetting in young deposits determined with a pulsed photon‐stimulated luminescence (PPSL) unit

Optical Stimulated Luminescence (OSL) is a technique that can be used for dating geological materials deposited within the last half‐million years, including sediments transported by air, water or gravity, as well as rocks heated at high temperatures. Recently, several studies have shown that OSL can also provide information on sediment transport. The pulsed photon‐stimulated luminescence (PPSL) unit (also known as a portable OSL reader) developed by the Scottish Universities Environmental Research Centre is an instrument designed to read luminescence signals from bulk (untreated) sediment samples comprising poly‐mineral and poly‐grain fractions. In this contribution, we evaluate the potential of the PPSL unit to assess the degree of OSL signal resetting in 27 young deposits (<2 ka) transported by different geomorphic agents in volcanic, coastal and fluvial depositional settings located in Mexico. Our results are in agreement with previous findings that used the Risø TL/OSL reader, confirming that sediments transported by debrisflows contain the highest inherited luminesce signals. Infrared stimulation (IRSL) values in volcanic ash, lavas, and sand beach and dune deposits exhibit low scatter. However, with blue stimulation (BLSL) these samples reveal a large degree of scattering, attributed to charge transfer in the case of the coastal deposits and to the low sensitivity of quartz in the case of volcanic material. The luminescence signals of fluvial sediments exhibit a highly scattered distribution in both IRSL and BLSL. We conclude that the use of a PPSL unit is a simple approach to assess the degree of OSL signal resetting in deposits sourced from different geological environments. This research contributes to previous studies that have investigated new applications of the PPSL unit to assist in OSL dating of geological materials.