Reconstructing landscape evolution in the Lower Khuzestan plain (SW Iran): integrating imagery, historical and sedimentary archives

During the late Holocene, an avulsion-controlled Karun megafan developed in the Lower Khuzestan plain. Based on the interpretation of satellite data, at least three different Karun channels were detected. A chronological framework is provided by archaeological sites and textual sources. The presence of extensive irrigation systems highlights the important role of human activity in the development of the plain. In addition, there is clear evidence of human actions (construction and destruction of dams) which caused repeated avulsions in the lower reaches of the present-day Karun. Similar impacts may have contributed to other channel shifts in historical times

Characteristics of direct human impacts on the rivers Karun and Dez in lowland south-west Iran and their interactions with earth surface movements

Two of the primary external factors influencing the variability of major river systems, over river reach scales, are human activities and tectonics. Based on the rivers Karun and Dez in south-west Iran, this paper presents an analysis of the geomorphological responses of these major rivers to ancient human modifications and tectonics. Direct human modifications can be distinguished by both modern constructions and ancient remnants of former constructions that can leave a subtle legacy in a suite of river characteristics. For example, the ruins of major dams are characterised by a legacy of channel widening to 100's up to c. 1000 m within upstream zones that can stretch to channel distances of many kilometres upstream of former dam sites, whilst the legacy of major, ancient, anthropogenic river channel straightening can also be distinguished by very low channel sinuosities over long lengths of the river course. Tectonic movements in the region are mainly associated with young and emerging folds with NW–SE and N–S trends and with a long structural lineament oriented E–W. These earth surface movements can be shown to interact with both modern and ancient human impacts over similar timescales, with the types of modification and earth surface motion being distinguishable. This paper examines the geomorphological evidence and outlines the processes involved in the evolution of these interactions through time. The analysis shows how interactions between earth surface movements and major dams are slight, especially after ancient dam collapse. By contrast, interactions between earth surface movements and major anthropogenic river channel straightening are shown to be a key factor in the persistence of long, near-straight river courses. Additionally, it is suggested that artificial river development, with very limited river channel lateral migration, may promote incision across an active fold at unusually long distances from the fold “core” and may promote markedly increased sinuosity across a structural lineament

Revising the Gent Formation : a new lithostratigraphy for Quaternary wind-dominated sand deposits in Belgium

In Belgian lithostratigraphy, the Gent Formation was previously introduced to encompass all Quaternary sandy aeolian sediments. It has been difficult to apply, however, as it was incomplete, regionally biased, and not based on sediment properties alone. To solve this problem the Gent Formation is revised both in terms of definition and subdivision. Morphological and chronological criteria were omitted to allow ranking strata on the basis of visible lithological properties. The Belgian sand belt is newly introduced to designate the area where these sediments were deposited. The Gent Formation is subdivided into five members based on distinct lithological properties, and as a consequence reflecting different palaeoenvironmental conditions during deposition. Whenever feasible, each member is put in a chronostratigraphical and geomorphical context. The new subdivision is discussed and compared with earlier Belgian lithostratigraphical frameworks, as well as to the most recent one for comparable deposits in the Netherlands

Sedimentary evidence of the Late Holocene tsunami in the Shetland Islands (UK) at Loch Flugarth, northern Mainland

Tsunami deposits around the North Sea basin are needed to assess the long-term hazard of tsunamis. Here, we present sedimentary evidence of the youngest tsunami on the Shetland Islands from Loch Flugarth, a coastal lake on northern Mainland. Three gravity cores show organic-rich background sedimentation with many sub-centimetre-scale sand layers, reflecting recurring storm overwash and a sediment source limited to the active beach and uppermost subtidal zone. A basal 13-cm-thick sand layer, dated to 426–787 cal. a CE based on 14C, 137Cs and Bayesian age–depth modelling, was found in all cores. High-resolution grain-size analysis identified four normally graded or massive sublayers with inversely graded traction carpets at the base of two sublayers. A thin organic-rich ‘mud’ drape and a ‘mud’ cap cover the two uppermost sublayers, which also contain small rip-up clasts. Grain-size distributions show a difference between the basal sand layer and the coarser and better sorted storm layers above. Multivariate statistical analysis of X-ray fluorescence core scanning data also distinguishes both sand units: Zr, Fe and Ti dominate the thick basal sand, while the thin storm layers are high in K and Si. Enriched Zr and Ti in the basal sand layer, in combination with increased magnetic susceptibility, may be related to higher heavy mineral content reflecting an additional marine sediment source below the storm-wave base that is activated by a tsunami. Based on reinterpretation of chronological data from two different published sites and the chronostratigraphy of the present study, the tsunami seems to date to c. 1400 cal. a BP. Although the source of the tsunami remains unclear, the lack of evidence for this event outside of the Shetland Islands suggests that it had a local source and was smaller than the older Storegga tsunami (8.15 cal. ka BP), which affected most of the North Sea basin.</p

A 1500‐year record of North Atlantic storm flooding from lacustrine sediments, Shetland Islands (UK)

Severe storm flooding poses a major hazard to the coasts of north‐western Europe. However, the long‐term recurrence patterns of extreme coastal flooding and their governing factors are poorly understood. Therefore, high‐resolution sedimentary records of past North Atlantic storm flooding are required. This multi‐proxy study reconstructs storm‐induced overwash processes from coastal lake sediments on the Shetland Islands using grain‐size and geochemical data, and the re‐analysis of historical data. The chronostratigraphy is based on Bayesian age–depth modelling using accelerator mass spectrometry 14 C and 137 Cs data. A high XRF‐based Si/Ti ratio and the unimodal grain‐size distribution link the sand layers to the beach and thus storm‐induced overwash events. Periods with more frequent storm flooding occurred 980–1050, 1150–1300, 1450–1550, 1820–1900 and 1950–2000 ce, which is largely consistent with a positive North Atlantic Oscillation mode. The Little Ice Age (1400–1850 ce ) shows a gap of major sand layers suggesting a southward shift of storm tracks and a seasonal variance with more storm floods in spring and autumn. Warmer phases shifted winter storm tracks towards the north‐east Atlantic, indicating a possible trend for future storm‐track changes and increased storm flooding in the northern North Sea region

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A middle to late holocene avulsion history of the Euphrates river : a case study from Tell ed-Der Iraq, Lower Mesopotamia

Geoarchaeological research was performed to reconstruct the floodplain history in the surroundings of two ancient Mesopotamian cities: Tell ed-Der and Sippar. The mapping of the floodplain is based on facies analyses of the sedimentary succession of 225 hand-operated boreholes. The archaeological sites Tell ed-Der and Sippar are closely linked to a palaeochannelbelt of the Euphrates, located in the western part of the study area. Channel activity started at least in ca 3100 BC/5050 cal BP, until ca 1400-1000 BC/3350-2950 call 13P. The channel belt was part of an avulsion driven multiple Euphrates channel network that gradually became abandoned from the second half of the 2nd millennium BC. A second mapped Euphrates, Tigris or joint Euphrates -Tigris palaeochannel belt became abandoned well before 3100 BC, Examples of natural processes as well as human interactions triggering avulsion are given. Moreover, textual, archaeological and geological data show clearly that flood-control techniques and the construction of large-scale dikes seemed to be a common practice. (C) 2008 Elsevier Ltd. All rights reserved