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Heyvaert V.M.A.,Geological Survey of Belgium | Walstra J.,Ghent University | Verkinderen P.,Ghent University | Verkinderen P.,The Netherlands Flemish Institute in Cairo | And 2 more authors.
Quaternary International | Year: 2012

This study is concerned with the Late Holocene floodplain history of the Karkheh River in Lower Khuzestan, and in particular with the role of human action upon its channel shifts. The research was conducted in a multidisciplinary way, in which resources and approaches from different research fields were combined: (1) geomorphological mapping based on the interpretation of Landsat and CORONA satellite imagery, (2) analyses of geological sequences, including the identification of sedimentary facies and radiocarbon dating of organic material, (3) an archaeological field survey of ancient settlements, and (4) consultation of historical documents, mainly Arabic texts from the 9th-14th century and European travel literature from the 16th-early 20th century. Three main channel belts of the Karkheh were identified (labelled Kh1, Kh2 and Kh3), corresponding to successive stages in the evolution of the floodplain. Two river shifts are documented in the datasets, both taking place within the last 2000 years. The first avulsion regards a shift from channel belt Kh1, once a tributary of the Karun, to the straight river bed of Kh2, taking place at least after 1240-1310cal BP/710-640 AD. The second avulsion, from Kh2 to Kh3, is clearly documented in historical sources and happened in a single night event in the year 1837/113cal BP. Reactivation of the Kh2 river bed and its irrigation canals can be attributed to the recent construction of an artificial canal bypassing the second avulsion point. Both river shifts were strongly influenced by human interference, whereby an artificial irrigation canal took over the entire river flow from the main channel belt. Most likely, a combination of human-induced factors, such as weakening of the river levees, high sedimentation rates and disadvantageous channel gradients, led to a situation prone to avulsion. © 2011 Elsevier Ltd and INQUA. Source

Baeteman C.,Geological Survey of Belgium | Baeteman C.,Vrije Universiteit Brussel | Waller M.,Kingston University | Kiden P.,TNO
Boreas | Year: 2011

A number of disciplines are involved in the collection and interpretation of Holocene palaeoenvironmental data from coastal lowlands. For stratigraphic frameworks and the assessment of relative sea-level (RSL) change, many non-specialists rely on existing regional models. It is, however, important that they are aware of major developments in our understanding of the factors controlling coastal change and of the potential sources of error in sea-level reconstructions. These issues are explored through a critical evaluation of a new sea-level curve presented by Behre (2003, 2007) for the southern North Sea. In contrast to most sea-level curves published from this region over the last 20 years, the curve shows strong fluctuations that are interpreted as representing vertical movements of sea level. We present a detailed examination of the data used by Behre. From this analysis it is clear that many of the data points used are unsuitable for high-resolution (centimetre or decimetre) sea-level reconstruction. This paper also gives an overview of possible sources of error with respect to the age and altitude of sea-level index points and of changes in our understanding of the processes that underpin the interpretation of the organic and occupation levels used as index points. The constraints on the spatial scale over which sea-level reconstructions can be applied (changes in palaeotidal range and crustal movements) are also considered. Finally, we discuss whether the large-amplitude centennial-scale sea-level fluctuations proposed by Behre can be reconciled with the known mechanisms of sea-level change and other recent high-resolution studies from this region. We conclude that such fluctuations are highly unlikely to be real features of the sea-level history of the southern North Sea. © 2011 The Authors. Boreas © 2011 The Boreas Collegium. Source

Bao H.-Y.,Tongji University | Han G.-M.,Geological Survey of Belgium | Yang F.-L.,Tongji University | Zhu J.-C.,Tongji University | Zhou Z.-Y.,Tongji University
Jilin Daxue Xuebao (Diqiu Kexue Ban)/Journal of Jilin University (Earth Science Edition) | Year: 2010

Based on sampling analysis of clay minerals on Early Triassic storm deposits outcroped in Jingxian, Ningguo and Yixing in the Lower Yangtze region and integrated sedimentological and paleontologyic studies, it is confirmed that when Kübler index (KI) increase the content of smectite decrease and smectite illitization would be restrained. In addition, the clay mineral associations are distinctly different. Therefore, it is concluded that provenance is the main factor that affects smectite illitization and the difference of clay mineral combination. The sources can be divided into two sequences according to the sedimentological characteristics and the content of smectite and illite in clay mineral combination. The results show that the provenance of storm deposits from profiles of Ningguo and Yixing (sequence I) are of proximal type, while that of Jingxian profile (sequence II) demonstrates a combination of proximal and distal type, which means that the location of Jingxian profile is closer to the transitional zone. Source

Wang D.-P.,Tongji University | Zhou Z.-Y.,Tongji University | Han G.-M.,Geological Survey of Belgium | Trentesaux A.,Liue University
Jilin Daxue Xuebao (Diqiu Kexue Ban)/Journal of Jilin University (Earth Science Edition) | Year: 2011

Clay mineral study and illite crystallinity determination are performed mainly on Cambrian to lo-wer Triassic marine sedimentary rocks, dominated by carbonates, in north Chaohu region, Anhui Province. The results show that illite, which accounts for 73%, is the forming clay mineral of marine strata in this region. Clay minerals diagenesis is characterized by smectite to illite. According to the diagenesis-very low-grade metamorphism classification, based on illite Kübler index, the strata studied have reached the highest diagenetic stage. The vertical changes of illite crystallinity can be generally divided into the lower part and the upper part. The crystallinity values of the lower part from Cambrian to Silurian vary from 0.41 to 0.60°Δ2θ, which are related with depth. So diagenesis is the controlling factor of the clay mineralogy of the lower part. While the crystallinity values of the upper part from Devonian to Lower Triassic are scattered between 0.45 and 0.77°Δ2θ. Smectite is present in the upper part, implying that the upper part from Devonian to Lower Triassic has not been deeply buried with sedimentation as its controlling factor. The distribution of smectite in Lower Triassic of north Chaohu region as well as the widespread enrichment of kaolinite at the top of Wutong Formation of Upper Devonian is of important significance for the paleoclimate study of this region. Source

Mauz B.,University of Liverpool | Baeteman C.,Geological Survey of Belgium | Bungenstock F.,Lower Saxony Institute for Historical Coastal Research | Plater A.J.,University of Liverpool
Quaternary Geochronology | Year: 2010

The accuracy of optical ages derived from tidal sediments depends largely upon the transport processes. These processes constrain the degree of bleaching by the time of deposition and the choice of grain size for dating. This study looks at flow regime, sediment bedding, particle size and suspended sediment concentration (SSC) over tidal flats in order to identify the tidal sub-environment from which reliable multigrain optical ages are most likely to be achieved. The resulting conceptual model is then compared with empirical OSL data obtained from Holocene sediments of the southern North Sea tidal coastal plain of continental Europe. Optical dating of the tidal sediments included single-aliquot-regenerative dose protocol applied to multigrain aliquots of fine sand and fine silt, statistical analysis using weighted skewness, standardised kurtosis and over-dispersion. It is inferred from the model that smaller grains should be better bleached than larger grains. However, because transport and deposition processes are extremely variable in both space and time, unequivocal "bleaching rules" could not be assigned to a particular tidal sub-environment. In this context more than 85% of our samples return accurate ages and around 13% of our optical ages are overestimated when compared with ages from established well-constrained stratigraphic frameworks. The empirical study confirms the concept of "variable bleaching rules": both accurate and inaccurate ages are obtained from silty and sandy OSL samples regardless of the sub-environment and well-bleached samples may be obtained from all tidal sub-environments. Although our study is based on multiple-grain aliquots it also shows that an independent statistical treatment of equivalent dose data is an indispensable procedure to detect and correct for insufficient bleaching. © 2010 Elsevier B.V. Source

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