No description available.

The Bermuda islands are constructed predominantly of aeolian dunes, termed eolianites, whose episodic accumulation has been correlated with Pleistocene sea-level oscillations. Despite a long-standing, now disputed, notion of Bermuda as a “tide-gauge” for Pleistocene glacio-eustacy there has never been a consensus on Bermuda’s palaeo-sea-level history. Most recently there has been disagreement over the interpretation of littoral deposits of the Belmont Formation. Based on U-series ages from coral fragments and analyses of sedimentary lithofacies, it is contended here that a sea level of ≥4.5m above present mean sea level at the penultimate interglacial is represented by these Belmont deposits. It is inferred from the anomalously high elevation of this sea-level imprint relative to the estimated global eustatic sea level of the time that glacio-hydro isostatic and possibly, to a lesser extent, tectonic influences have contributed to a composite RSL (relative sea level) signal at Bermuda. This and other interglacial highstands at Bermuda left their imprint in the form of exceptionally well exposed emergent coastal facies assemblages. The most complete assemblages are shown to have developed in two stages, S1 and S2, respectively during a rising RSL and a falling RSL. S1 records beach progradation, barrier construction and back-barrier inundation. S2 begins with emergence of an ultimately wooded backshore, and ends with its burial by advancing dunes sourced on expanding beaches at a highstand termination. Past hypotheses that Bermuda’s dunes were static aggradational structures which accumulated rapidly in storms are tested by analyses of eolianite stratification, wind data and drift potential. It is demonstrated that the eolianites are the remnants of mobile landward-advancing bedforms constructed predominantly when winds above the threshold velocity were directed onshore across source beaches. The model developed for the evolution of beach-dune systems on Pleistocene Bermuda is applicable to present-day clastic coasts which are vulnerable to RSL rise.

No description available.

The predominantly dryland climate of interior South Africa precludes the widespread preservation of organic proxy records. Various potential geoproxy records exist, but their exploitation requires accurately constrained chronologies. This study investigates the development of two luminescence chronometers, quartz OSL and K-feldspar post-IR IRSL. At four sites across the eastern interior (Moopetsi, Voordrag, St Paul's and Goedgedacht), these chronometers are used to constrain the timing of: (i) the late Quaternary initiation of deposition; (ii) intervening phases of erosion, deposition andpedogenesis; and (iii) the current deep erosional phase. The value of using paired ages (i.e. determining quartz and K-feldspar ages from the same sample) becomes apparent, particularly at Voordrag where quartz OSL reaches saturation within the limit of radiocarbon dating. Paired chronologies show good agreement for younger samples (<24 ka) but systematic underestimation of quartz ages for older samples. Investigation of the post-IR IRSL protocol showed that signal transfer between the Lx and Tx measurements caused systematic underestimation of older feldspar ages. Dose recovery tests showed that it was not possible to recover a large given dose (400 Gy) when using a small (5 Gy) test dose. Two solutions were investigated, specifically increasing the size of the test dose to ~30 % of the De value and increasing the IR stimulation time. This led to the development of a `modified' post-IR IRSL protocol. The derived quartz and K-feldspar single grain chronologies show that the initiation of deposition was not synchronous at the four study sites, and ranges from ~153 { 65 ka. Intervening phases of erosion, deposition and pedogenesis remain difficult to constrain but broad inferences regarding climatic and geomorphic drivers can be made. The current phase of deep erosion appears to be linked to two periods of abrupt climate change, the 3.8 { 4.2 ka arid event and the Little Ice Age.

No description available.

Explosive eruptions occurred throughout the Ethiopian Rift Valley during the Quaternary, depositing tephras that have provided crucial chronology for archaeological sites in eastern Africa. However, Holocene tephras are largely unstudied and the recent volcanic history of Ethiopia remains poorly constrained. The first < 17 ka regional tephrostratigraphy is presented here, constructed using sediments from seven Ethiopian lakes: Ashenge and Hayk (Ethiopian Highlands), Dendi and Hora (Yerer-Tullu Wellel Volcano Tectonic Lineament, YTVL) and Awassa, Tilo and Chamo (central Main Ethiopian Rift, CMER). A database of 2100 major and trace element single grain glass analyses will aid the future identification of these tephras at proximal and distal locations. Peralkaline rhyolitic tephras are dominant throughout the Ethiopian Rift. Tephras are more differentiated in the central Main Ethiopian Rift than those deposited in northern Ethiopia. The uniquely phonolitic-trachytic Dendi tephras are derived from volcanoes on the rift shoulders, where magma evolved under high pressure. Archives from the Ethiopian Highlands record < 17 ka distal volcanism from seven unknown volcanic centres in the Afar Rift. Eruptions occurred every <1000 years between 15:3􀀀1:6 cal. ka BP. Different tephras were deposited in lakes Ashenge and Hayk, and they were not dispersed towards lakes further south. Tephras erupted from centres in the CMER are recorded in the Awassa, Tilo and Chamo archives. Glass compositions are indistinguishable from recent Corbetti eruptives. During < 10 ka, eruptions from Corbetti occurred every < 800 years and 6 eruptions were highly explosive. Two tephras are correlated between Tilo and Chamo (170 km SW of Tilo). However, eruptions from Corbetti are not recorded in archives from Ashenge, Hayk and Dendi. These findings demonstrate the potential for further study to construct a comprehensive tephra framework, enabling assessment of regional volcanic hazards. Further geochemical characterisation of regional volcanoes will constrain the sources of these tephras and their petrogenesis.

The stratigraphy of the Ordovician and Silurian rocks of Eastern Murrisk, Co. Mayo, Eire, is described and the facies changes in relation to the rocks of neighbouring areas interpreted, During Ordovician times the South Mayo trough, initially deep, became steadily infilled with sediments, principally derived from the rising Connemara Cordillera to the south-east. These sediments are described, and variation in the principal constituents analysed. The Silurian rocks of shelf facies occurring in the Croagh Patrick Syncline are described, and the effect of two phases of post-Wenlockian deformation and the resultant structures discussed. Two phases of injection have been recognised in the serpentine intrusi671 along the Highland Boundary Fault, the latter being post-Wenlockian. Pre-Carboniferous peneplanation was followed by submergence and deposition of shallow water sediments during the Lower Carboniferous. Tertiary faulting led to a renewal of movement along older faults, and produced fault blocks which control the present day topography. The whole area was subsequently modified during the Pleistocene glaciation.

No description available.

As part of the INTAS funded CLIMAN project into Holocene climatic variability and the evolution of human settlement in the Aral Sea basin, fossil diatoms obtained from Chernyshov Bay in the Aral Sea have been examined in order to reconstruct conductivity and lake level change since ca. 400 AD. In an effort to establish whether fluctuations in lake level are a result of natural climatic variation or human activity across the region, the values of 613C of organic material (8I3Corg) have also been determined. The extent of anthropogenic impact on the lake has also been assessed by ascertaining the history of trace metal (Cd, Pb and Hg) contamination. Palaeoconductivity has been derived using the EDDI diatom-conductivity transfer function. Results indicate a waterbody that fluctuates between fresh and oligosaline conditions which is punctuated by three phases of elevated conductivity, all within the mesosaline range and corresponding low lake levels at ca. 400 AD, ca. 1195 - 1355 AD and ca. 1780 AD to the present day. These regressions are confirmed by diatom habitat requirements, where, due to the morphology of the lake, planktonic species are indicative of regressive phases. The C/N ratio of organic material (< 10) throughout the core indicates that 8,3Corg provides a record of within lake productivity rather than switches of vegetation in the lake's catchment. The highest values are seen to correspond with high diatom inferred conductivity and low lake levels, due to increased salinity, residence time and algai productivity. This suggests that the severity of the observed lake level changes were a result of the natural diversion of the principal source of the lake's hydrological inputs, the Amu Darya river and anthropogenic activity in the form of irrigation, social upheaval and military conflict. Since 400 AD, the trace metal record from Chernyshov Bay indicates no local or long range anthropogenic contamination of Pb and Hg. Increases of Cd over the last ca. 100 years may be related to increased fertilizer application in tandem with increased cultivation in the region.

No description available.