Water-lain Sediments Research Articles

Landscape evolution and hydrology at the Late Pleistocene archaeological site of Narabeb in the Namib Sand Sea, Namibia

The Namib Sand Sea (NSS) in Namibia is known to preserve a wide variety of Pleistocene-age archaeological sites. However, few Middle Stone Age (MSA) sites in this region have been systematically investigated and basic questions around chronology and technological organization remain open. Here we examine Narabeb, an open air MSA surface site exposed in an interdune pan, ∼30 km into the northern NSS. Narabeb was first documented in the 1970s, and then re-examined in 2021 and 2022 by members of this team. Lithic technological analysis combined with a geomorphological description of the site, palaeoenvironmental interpretation of fine-grain water-lain sediments, and luminescence ages from northern and southern locations on the Narabeb pan provide some of the first understanding of human-environmental interactions and estimates of chronology from the later-Middle and Late Pleistocene in the NSS. In addition, we apply a quantitative approach to aeolian linear dune accumulation and extension to explore possible scenarios for landscape development at this site, in order to better understand the former water course(s) affecting the area. The new chronology suggests this site contained standing water at, or just after, the MIS 7/6 transition, and again at, or just after, the end of MIS 6 into early MIS 5. The timing of greater phases of water availability have some overlap with the speleothem growth record at Rössing Cave, situated ∼90 km north of the NSS (and ∼135 km north of Narabeb). Our results provide the foundation for larger, regional-scale analyses of early human adaptive strategies in this unique environment within Southern Africa.

Single-grain K-feldspar luminescence dating of the late Quaternary rapid decline in the largest Lake over the Tibetan Plateau

Well-preserved shorelines, situated at elevations ranging from tens to hundreds of meters above the current lake levels, are commonly found in the lake basins across the Tibetan Plateau (TP). These shorelines offer a valuable opportunity to reconstruct past hydroclimate changes, contingent upon precise age determination of palaeoshorelines. While single-aliquot luminescence methods have been extensively employed for dating palaeoshoreline sediments, both quartz and K-feldspar fractions, the application of single-grain (SG) dating techniques has been relatively limited, particularly in the case of water-lain sediments where partial bleaching must be taken into account. In this study, we applied the single-grain K-feldspar dating technique using the post-IR IRSL (pIRIR) protocol to a selection of palaeoshorelines from Qinghai Lake, the largest lake on the TP. Our primary objectives were to investigate the behavior of single-grain K-feldspar pIRIR signals and to establish precise timing for late Quaternary lake level fluctuations based on SG data. Our findings reveal a clear correlation between the De (equivalent dose) values of single grains and their fading rates. The higher fading rates observed in dim grains constitute the primary reason for the underestimation of De values. However, it appears that the internal K content of the grains cannot explain the relationship between fading rates and grain brightness. Finally, we utilized the 30% brightest grains for SG pIRIR De determinations, allowing us to reconstruct the historical water level fluctuations of Qinghai Lake. Our results indicate a pronounced decline in lake levels during the last interglacial-glacial transition, approximately 90,000 to 75,000 years ago. This decline can be attributed to the response of regional hydroclimate patterns to global environmental changes.

Sedimentary facies and chronological study for a Late Pleistocene sand layer with swash cross bedding within a sand hill at north of Poyang Lake, as inferred from sedimentary structure and optical dating of K-feldspar and quartz grains

Poyang Lake is the largest freshwater lake in China. Currently, there are several sand hills around Poyang Lake and they were mainly interpreted to be formed by aeolian process. However, by field investigation, it is found that several sand/silt layers with parallel bedding, horizontal bedding and swash cross bedding were preserved within sand hills around Poyang Lake. Compared with recent highest water level in Poyang Lake since 1949, the sand/silt layers with parallel bedding, horizontal bedding and swash cross bedding are higher than 22.63m from several meters to more than 10 m. From the view of sedimentary structure, the sand/silt layers mentioned above should be treated as water-lain sediments. In this study, one sand layer with swash cross bedding at elevation of ∼47.5m within a sand hill at north of Poyang Lake was targeted. The bleaching of K-feldspar IRSL signals and quartz OSL signals during their deposition were further investigated by using optical dating techniques. It is found that both K-feldspar IRSL signals and quartz OSL signals were partially bleached and such phenomenon is very different from typical aeolian sediments. The partially bleaching of both K-feldspar IRSL signals and quartz OSL signals is consistent with interpretations by sedimentary structure of the targeted sand layer, i.e. the sand layer with the swash cross bedding within the sand hill should be interpreted as hydraulic sediments and they were not formed by aeolian process. The OSL ages of targeted sand layer were then analyzed by three different methods, i.e. single aliquot MET-pIRIR dating of K-feldspar, single aliquot OSL dating of quartz as well as single grain OSL dating of quartz. The OSL ages of three methods were all consistent with each other and the age results show that the targeted sand layer was formed during MIS 3a. Although previous studies suggested that previous Poyang Lake (Pengli Ze) was initially formed during mid-Holocene, our study indicates that previous Poyang Lake (Pengli Ze) already existed during MIS 3a and it might experience extremely high water level phase at that time.

The geoarchaeological investigation on the defunctionalisation of an Assyrian canals system reveals Late-Holocene land use transitions in Northern Mesopotamia

During the Assyrian rule over Northern Mesopotamia (present-day northern Iraq), complex systems of canals were built to increase the surface of cultivable land and improve the movement of people and goods across the irrigated waterscape of the hinterland of Nineveh and other major urban centres, with the aim of granting socio-economic prosperity to the empire. Nevertheless, supra-regional political instability eventually led to the rapid downfall of the Assyrian state during the late seventh century BCE, causing the swift abandonment of the canal systems. In this study, we examine the post-abandonment formation processes of the natural and anthropogenic infillings of three portions of King Sennacherib’s Khinis canal system (705–681 BCE, northwestern Kurdistan Region of Iraq) through means of archaeological, sedimentological and micromorphological analyses. We identify water lain sediments, desiccation features, colluvial gravel intake and pastoral occupation layers, anchoring the deposit to radiometric dating and contextualising it against the known regional climatic history. The interpretation of pedostratigraphic evidence highlights subsequent phases of use, abandonment, and repurposing of the canals, reflecting shifts in land-use from agriculture to pastoralism and dynamic adaptation and resilience of the local ancient communities in response to Late-Holocene climate changes and geopolitical events.

Multi-method pIRIR dating of sedimentary sequences at the southern edge of the Gurbantunggut Desert, NW China and its palaeoenvironmental implications

The Gurbantunggut Desert is the second-largest desert in China, located in the westerly-dominated region of north-western China. Previous understanding of palaeoclimate of this desert was mostly based on lake and loess records from the Junggar Basin and Tian Shan Mountains, whilst direct dating of sedimentary records from the desert was very limited. This study applies high-resolution post-infrared infrared stimulated luminescence (pIRIR) dating to three sedimentary profiles at the southern edge of the Gurbantunggut Desert, which contain aeolian sand and water-lain sediments, recording palaeoenvironmental changes at the desert margin since the Last Glacial Maximum (LGM). Different pIRIR dating procedures were applied for samples with different ages. For Holocene-aged samples, a single-aliquot regenerative-dose (SAR) pIRIR procedure based on a three-stepped pIRIR measurement at 110 °C, 140 °C and 170 °C was used, and a standard growth curve (SGC) procedure yields an equivalent dose (De) similar to that of the full-SAR procedure; thus, is applicable for accelerating De measurement. For samples much older than the Holocene, a multi-aliquot regenerative-dose (MAR) pIRIR procedure based on a three-stepped pIRIR measurement at 150 °C, 200 °C and 250 °C was found to be the optimal dating procedure, because a SAR procedure would yield underestimated ages due to uncorrected initial sensitivity change. pIRIR dating results of the investigated profiles reveal a substantial sand accumulation during the LGM, an intensification of aeolian deposition at ∼12 ka and a wetter depositional environment at ∼10–8 ka. A rapid fluvial deposition is dated at ∼20–19 ka, corresponding to the deglaciation period. The sedimentary records from the desert margin show some correlation with lake and loess records in the same region and suggest a complex response of the desert environment to different climatic factors.

The geology of the late-Cretaceous Salpeterkop volcano near Sutherland: A geomorphologic benchmark

The Salpeterkop volcano is spatially part of the Sutherland Suite of alkaline rocks in the Northern Cape. It is one of the best preserved volcanoes in South Africa with part of the tuff ring still intact, remnants of the ejecta mantle outside the crater still preserved, and is host to epiclastic rocks, including ash and lapillistone and water lain sediments, inside the crater. New dates from apatites and phlogopites from Salpeterkop suggest an age close to 70 Ma. This Upper Cretaceous age is supported by the silicified wood found within the epiclastic sediments. Its relationship to the alkaline rocks in this cluster is not entirely clear but field evidence suggests that initial olivine melilitites and ultramafic bodies were followed by the main eruption that produced Salpeterkop. Clear igneous components in the associated breccias and pyroclastics are rare but indicate that this volcano was linked to an alkaline (trachytic) intrusion driven by phreatic magmatism. This is further highlighted by the presence of (nepheline?) syenite xenoliths in some carbonatite breccias and dykes that are part of the later carbonatites with its associated hydrothermal alteration products. Although the carbonatites are largely late-stage, there is evidence of earlier carbonatite activity from a precursor carbonatite dyke that has off-set an olivine melilitite dyke. Relatively unaltered pyroclastics, associated with two vents, northeast and northwest of the crater respectively, represent the final phase of this volcanic centre. Finally, the preservation of the Salpeterkop crater and its associated volcaniclastics highlights the change of intense landscape denudation, that ensued from Gondwana break-up to the end of the Cretaceous, to a period of drastically reduced erosion rates during the Cenozoic Era.

Dryland dunes and other dryland environmental archives as proxies for Late Quaternary stratigraphy and environmental and climate change in southern Africa

AbstractThe Namib Desert and the Kalahari constitute the drylands of southern Africa, with the current relatively humid portions of the latter having experienced periodically drier conditions during the Late Quaternary. This study explores the range of dryland archives and proxies available for the past ~190 ka. These include classic dryland geomorphological proxies, such as sand dunes, as well as water-lain sediments within former lakes and ephemeral fluvial systems, lake shorelines, sand ramps, water-lain calcrete and tufa sediments at the interface of surface hydrological and hydrogeological, speleothems and groundwater hydrogeological records, and hyrax middens. Palaeoenvironmental evidence can also be contained within geoarchaeological archives in caves, overhangs and rockshelters. This integration of records is undertaken with the aim of identifying a (or a number of) terrestrial regional chronostratigraphic framework(s) for this time period within southern Africa, because this is missing from the Quaternary stratigraphy lexicon. Owing to a lack of long, near-continuous terrestrial sequences in these drylands, the correspondence between nearby terrestrial records are explored as a basis for parasequences to build this chronostratigraphy. Recognising the modern climatological diversity across the subcontinent, four broad spatial subdivisions are used to explore potential sub-regional parasequences, which capture current climatic gradients, including the hyper-arid west coast and the decrease in aridity from the southwest Kalahari toward the north and east. These are the Namib Desert, the northern Kalahari, the southern Kalahari and the eastern fringes of the southern Kalahari. Terrestrial chronostratigraphies must start from premise that climate-driven environmental shifts may have occurred independently to those in other terrestrial locations and may be diachronous compared to the marine oxygen isotope stratigraphy (MIS), which serves as a global-scale master climatostratigraphy relating to global ice volume. The fragmented nature of preserved evidence means that we are still some way from producing unambiguous parasequences. There is however, a rich record to consider, compile and compare, within which seven broad wetter intervals are identified, with breaks between these inferred to be relatively drier, and some also have proxy evidence for drying. The onset and cessation of these wetter intervals does not align with MIS: they occur with greater frequency, but not with regular periodicity. Precession-paced insolation forcing is often invoked as a key control on southern African climate, but this does not explain the pacing of all of the identified events. Overall, the pattern is complex with some corresponding wetter intervals across space and others with opposing west-east trends. The evidence for drying over the past 10 ka is pronounced in the west (Namib Desert), with ephemerally wet conditions in the south (southern Kalahari). The patterns identified here provide a framework to be scrutinised and to inspire refinements to proposed terrestrial chronostratigraphies for southern Africa. Considering changes across this large geographic area also highlights the complexity in environmental responses across space as we continue to test a range of hypotheses about the nature of climatic forcing in this region.

How much of the sediment in Gale crater's central mound was fluvially transported?

The origin of the sedimentary mound within Gale crater, the landing site for the Mars Science Laboratory rover Curiosity, remains enigmatic. Here we examine the total potential contribution of fluvial material by conducting a volume-based analysis. On the basis of these results, the mound can be divided into three zones: a lower, intermediate, and upper zone. The top boundary of the lowermost zone is defined by maximal contribution of water-lain sediments, which are ~13 to 20% of the total mound volume. The upper zone is defined by the elevation of the unbreached rim to the north (-2.46 km); sediments above this elevation cannot have been emplaced by flowing water. These volume balance calculations indicate that mechanisms other than flowing water are required to account for the overwhelming majority of the sediments transported into Gale crater. The most likely candidate process is settling from eolian suspension.

Chapter 6 Material properties and geohazards

Abstract In engineering terms, all materials deposited as a result of glacial and periglacial processes are transported soils. Many of these deposits have engineering characteristics that differ from those of water-lain sediments. In the UK, the most extensive glacial and periglacial deposits are tills. Previously, engineering geologists have classified them geotechnically as lodgement, melt-out, flow and deformation tills, or as variants of these. However, in this book tills have been reclassified as: subglacial traction till, glaciotectonite and supraglacial mass-flow diamicton/glaciogenic debris-flow deposits (see Chapter 4, Sections 4.1–4.3). Because this classification is new, it is not possible to relate geotechnical properties and characteristics to the subdivisions of the new classification. Consequently, the domain/stratigraphic classification, recently developed by the British Geological Survey and others, has been used and their geotechnical properties and characteristics are discussed on this basis. The geotechnical properties and characteristics of the other main glacial and periglacial deposits are also discussed. For some of these (e.g. glaciolacustrine deposits, quick clays and loess), geohazards relating to the lithology and/or fabric of the deposit are discussed along with their properties. Other geohazards that do not relate to lithology and/or fabric are discussed separately as either local or regional geohazards. In some cases (e.g. glaciofluvial sands and gravels), the geotechnical properties and behaviour are similar to sediments deposited under different climatic conditions; these deposits are therefore not discussed at length. Similarly, some of the local geohazards that are found associated with glacial and periglacial deposits relate to current climatic conditions and are not discussed here. Examples include landsliding and highly compressible organic soils (peats).

Provenance of clay used in Garamantian ceramics from Jarma, Fazzan region (south-west Libya): A combined geochemical and microfossil analysis

Geochemical (XRF) and microfossil analyses were applied to a sample of 1st millennium BCE and 1st millennium CE handmade pottery from Jarma, Fazzan region, Libya. The provenance of a particular group of painted ware has important implications for the production and distribution of this material. A parallel geochemical analysis of selected water-lain sediments in the region suggests a Saharan clay source for the material used in the pottery. Geochemical analysis identifies halite, gypsum and dolomite as components of the clay source, and this is consistent with the mineralogical content of local palaeolake sediments. Illite/kaolinite clay signatures are also consistent with a Saharan, as opposed to sub-Saharan, origin for the clay. Microfossil assemblages within some of the pottery comprise of thin-shelled, apparently monospecific ostracod assemblages together with possible fragments of gastropods, and are consistent with faunas of intra-continental Saharan lakes. Our analysis builds on previous assessments of the clay sources of Garamantian pottery that suggest that materials were sourced in palaeolake sediments fairly locally. The red on white painted ware with ostracods stands out from other material at Jarma and this suggests that the ware was the object of localised trade in the Sahara. The production of some versions of the painted ware in fabrics lacking ostracods also seems to indicate some local imitations at Jarma.

Ductile and brittle styles of subglacial sediment deformation: An example from western Ireland

In western Ireland, within a drumlin formed inside the margin of the late Pleistocene ice sheet, a range of different styles of ductile and brittle sediment deformation is observed within subglacial diamicton (till) and associated subglacial waterlain sediments. At Roonah Point, County Mayo, the structures associated with these different deformation styles include gravel clusters that have loaded subjacent sediments, glacitectonic shears, water escape structures, and clastic dikes. These structures are found for tens of metres laterally within the same diamicton units and the structures may cross-cut or be superimposed upon one another. Based on these properties and geometric relationships, the relative chronology and processes and patterns of subglacial deformation can be reconstructed, including an evaluation of subglacial conditions and pore water pressure regimes. This illustrates the relationship between glacitectonic forcing by ice–bed coupling, and the structural response within subglacial sediments to changing pore water pressure gradients.

Does a Heavy Fe-Isotope Composition of Akilia Quartz-Amphibole-Pyroxene Rocks Necessitate a BIF Origin?

The age and origin of the quartz-amphibole-pyroxene (qap) gneiss from the island of Akilia, southern West Greenland, have been the subject of intense debate since the light C-isotope composition of graphite inclusions in apatite was interpreted to indicate the presence of Earth's earliest biological activity. Although this claim for biogenic relicts has been vigorously challenged, the possibility that the rocks might represent some of Earth's earliest water-lain sediments and, hence, a suitable repository for life remains an open question. While some workers have suggested that the entire sequence represents an originally mafic-ultramafic igneous precursor subsequently modified by metasomatism, quartz injection, high-grade metamorphism, and extreme ductile deformation, others maintain that at least a small part of the sequence retains geochemical characteristics indicative of a chemical sedimentary origin. Fractionated Fe isotopes with δ(56)Fe values similar to those observed in Isua BIF have been reported from high-SiO2 units of qap and used to support a chemical sedimentary protolith for the qap unit. Here, we present new Fe isotope data from all lithologic variants in the qap gneiss on Akilia, including layers of undisputed ultramafic igneous origin. Since the latter require introduction of fractionated Fe into at least part of the qap unit, we argue that Fe isotopes must therefore be treated with considerable caution when used to infer BIF for part or all of the qap protolith.

Subglacial sediment, proglacial lake-level and topographic controls on ice extent and lobe geometries during the Last Glacial Maximum in NW Russia

Investigations in sections along the rivers Severnaya Dvina and Vaga, and morphological mapping based on a new digital elevation model and Landsat imagery, allow for a reinterpretation of the extent of the Scandinavian Ice Sheet during the Last Glacial Maximum (LGM). The reconstruction provides a much better link between stratigraphical and morphological expression of glaciation than previous proposals. Most striking is the configuration of long, low-gradient ice-lobes (ice-streams) extending for some 300–400 km up the wide and smooth river valleys. Their extremely low surface gradients are evidenced by glacial trimlines that formed along the sides of the ice-lobes in contact with the gentle valley slopes. In the main valleys, end moraines marking terminal positions are present, whereas drumlins are rare in the peripheral areas of the ice sheet but found in some tributary valleys at somewhat higher elevations. Large drumlin fields, however, are found farther up-ice. The glacial sediment succession is composed of waterlain sediments and tills. The sediments provide evidence of distal ice damming, glacier overriding and retreat, and finally distally glaciolacustrine sedimentation and lake drainage. The diamicton unit associated with the LGM shows evidence of basal coupling, although more striking is the abundant evidence for ice–bed decoupling. These include in situ waterlain sediments within tills, and clastic sills running along the till/substrate contact showing lift-off. These features indicate that the weight of the glacier lobes was, to a large extent, carried by pore-water pressure in subglacial sediments, and that subglacial shear and erosion were moderate. Thus, fast ice flow in the lobes is envisaged. The balance between glacier weight and pore-water pressure was probably maintained over time by the buoyancy effect of glaciers advancing into proglacial lakes. Subglacial lakes may have formed by capture of proglacial lakes during glacial advance. The combination of low-gradient ice and decoupled beds indicate that glacier advance and extent was largely controlled by lake levels and topographic thresholds. This is taken to indicate that steeper-gradient ice much farther upstream was providing the gravitational push. A presumably abrupt change in ice-surface profile is supported by the mapped distribution of glacial bedforms. The model presented herein potentially has wide applicability for large parts of northern Russia as the topographic setting and glacier advance in lakes across fine-grained low-permeable sediments provide very similar conditions.

Testing the application of an elevated temperature post IR-IRSL protocol for the dating of Pleistocene waterlain sediments from the northern Alpine foreland

Testing the application of an elevated temperature post IR-IRSL protocol for the dating of Pleistocene waterlain sediments from the northern Alpine foreland

Testing the application of post IR-IRSL dating to fine grain waterlain sediments

The polymineral fine grain fraction of a set of ten known age samples were used to test the suitability of elevated temperature post-IR infrared stimulated luminescence (pIRIR) to date waterlain sediments in Switzerland. Equivalent Dose (De) values were obtained using elevated temperatures of 225 °C (pIRIR225) and 290 °C (pIRIR290) and IRSL50/225 (preceding measurement of pIRIR225), and these displayed a systematic increase with increasing stimulation temperature, which brought those derived from the pIRIR protocols into saturation for the older half of the samples (>100 ka). Significant residuals were recorded for the pIRIR signals, and these were found to further increase following attenuation of the bleaching source confirming that these signals are harder to bleach than the IRSL measured at 50 °C. Fading tests recorded g-values of between 1 and 4%, and displayed no obvious decrease with increasing stimulation temperature. For the younger half of the samples, fading corrected ages for all protocols resulted in overestimation compared to robust independent dating for all samples, and draw into question the relationship of fading measured in a laboratory generated signal to that which is naturally generated. Uncorrected IRSL50/225 ages for all samples were in good agreement with independent dating, but still displayed a general overestimation using pIRIR signals. These overestimations may largely be due to the significant residual doses resulting from the harder to bleach nature of the elevated temperature signal, and present a considerable problem when dating waterlain sediments. A considerable challenge when using the pIRIR signal is to be able to separate the effects of both residual doses and fading and confirm that one is not masking the other. Despite this, the pIRIR protocols were successful at one site, although they offered no benefit compared to dating with more conventional luminescence signals. A comparison of De values derived from a standard IRSL signal to that from IRSL50/225, suggest that the latter overestimates by ∼10% due to a decrease in sensitivity of the sample prior to measurement of the test dose.

Ice keel seabed features in marine channels of the central Canadian Arctic Archipelago: evidence for former ice streams and iceberg scouring

The study area lies within the central part of the Canadian Arctic Archipelago; a region that was covered by the Laurentide Ice Sheet during the Late Wisconsinan glaciation and earlier. Multibeam imagery from widely spaced transects indicates the presence of linear groove and ridge features on the seabed at several localities in Peel Sound, Franklin Strait, northern Larsen Sound, and within M’Clintock Channel. These lineations resemble features in Antarctica and in several formerly glaciated regions that have been interpreted to be sole marks emplaced beneath fast-flowing ice streams. Based on these analogies, a similar origin is inferred for the lineations on the channel floors within the study area The lineations are oriented parallel to the channel axes and margins. They occur on all transects within the bathymetrically deeper area at the junction of Franklin Strait and Peel Sound. Northward in Peel Sound they occur extensively on the western and central transects, and more locally on the eastern transect. Their north-south orientation is normal to that of glacial flow features on Somerset Island and most of eastern Prince of Wales Island, which border Peel Sound to the east and west, respectively. The trend of the lineations is northeasterly (parallel to the channel axis) in Franklin Strait and mainly northerly in Larsen Sound and M’Clintock Channel. Elsewhere, the seabed imagery commonly displays scours of various sizes and orientations created by the keels of icebergs. Seabed sediments revealed by 3.5 kHz sub-bottom profiles are interpreted to consist primarily of ice-contact sediments, that in part are thinly mantled by draped water lain sediments. The age of the lineations has not been established. Possibly their formation was coincident with an ice stream in the M’Clintock Channel – eastern Victoria Island region, which formed an ice shelf in Viscount Melville Sound that grounded on southern Melville and Byam Martin islands at ca. 10.4–9.6 14C ka BP Alternatively, they could result from later glacial events.

Late Quaternary palaeohydrological changes in the northern Namib Sand Sea: New chronologies using OSL dating of interdigitated aeolian and water-lain interdune deposits

Ephemeral rivers today terminate in playas adjacent to the eastern part of the Namib Sand Sea, although there is evidence that these fluvial systems penetrated further west in the past. There are water-lain sediments exposed in interdune areas of the northern Namib Sand Sea associated with the former course of the Tsondab River, which are central to palaeoenvironmental reconstruction in the region. These deposits indicate that there was increased moisture availability in this presently hyper-arid region and/or the catchments of the rivers to the east of the Sand Sea in the Great Escarpment. Until now the chronology for the deposition of these sediments has been based on radiocarbon ( 14C) dates on carbonate materials. The validity of these ages is problematic and 14C limits the timescale to which these sediments can be dated. The water-lain units are bracketed by aeolian sand units, which are highly suitable for optically-stimulated luminescence (OSL) dating. Here, 24 OSL ages from three sites associated with the former course of the Tsondab River are presented, allowing a reassessment of the timing of sediment deposits and the west to east progression of the terminus of the Tsondab River during the late Quaternary. Narabeb, which is 60 km north-west of the current end point of the Tsondab River at Tsondab Vlei, contains eight mud units, six of which are shown to be of marine oxygen isotope stage (MIS 5, 128–75 ka) age. Water-lain units at Hartmut Pan, 55 km north-west of Tsondab Vlei, are dated by OSL to between 16.9 ± 0.9 ka and 12.7 ± 0.1 ka. At Ancient Tracks, closest to the Tsondab Vlei (6 km west), mud units are younger, and placed between 12.0 ± 0.7 and 12.8 ± 0.8 ka, 11.5 ± 0.5–10.5 ± 0.5 ka and after 10.5 ± 0.5 ka. This new chronology is compared with other key regional records to identify potential regional relationships and forcing factors. There is greatest correspondence with the records in the north of the summer rainfall zone. A revision of both old and young 14C ages on carbonate materials calls for revision of other 14C chronologies in the region and highlights the problems with the continued used of histograms of 14C-ages to indicate periods of increased humidity in southern Africa.

OSL dating of sediments from the Gobi Desert, Southern Mongolia

The present study focuses on the chronological relationship between alternating dune sand and silty water-lain sediments in the central part of the Khongoryn Els dune field in the Gobi Desert, Southern Mongolia. The 23 m high section evolved from the construction of a natural dam by west–east moving sand dunes and fluvial inundation by a river system from the mountain ranges in the south. To resolve the chronology of events, optically stimulated luminescence (OSL) dating was applied and from sedimentological and geochemical analysis the depositional processes could be characterised. Quartz OSL dating of these sediments is hindered by feldspar contamination. Thus, dating of coarse-grain K-feldspars is applied to provide a more reliable chronostratigraphy. As this fraction might be influenced by signal loss over geological time scales, the extent of fading is measured and corrected for. The resulting ages fit well in a supraregional reconstruction of Central Asian palaeoclimate. The data imply that the basal aeolian sediments were deposited 27 ka ago, while the major part of the profile was accumulated in a rather short period of time around ∼15 ka. The temporal differentiation implies that the stratification of aeolian and fluvial sediments is not caused by long term climatic variations. It rather represents arid conditions with episodical fluvial activity. Samples between 20 and 15 m depth could not be taken, but it is assumed that this part of the section represents an extremely arid time period with an intensive remobilisation of sand around LGM. A dune overlying the section was deposited during the Late Holocene and represents the ongoing aridity in this region.

Optically stimulated luminescence dating of young sediments: A review

Optically stimulated luminescence (OSL) dating of young (< 1000 years) sediments is used increasingly in a wide variety of late-Holocene studies as a mean of establishing contemporary sedimentation rates or the timing of sediment deposition. This paper provides a summary of the basic principles of OSL dating, outlines the problems specific to the dating of young material, and then uses recent applications to young sediments to illustrate the greatly increased scope and potential of the method in geomorphology and the geology of recent deposits. The overall reliability of this new generation of OSL ages is examined by comparing, where possible, OSL ages with independent age control. It is concluded that, the OSL ages are accurate, in that there is no evidence for systematic over- or under-estimation. It is our conclusion that OSL dating should be regarded as a reliable chronological tool for determining the time of deposition of water-lain sediments from the coastal zone, and aeolian deposits from both coastal and inland environments. Our conclusion is supported by the growing popularity of OSL dating in geomorphology and geology.

Devensian glacial events in Buchan (NE Scotland): A progress report on new OSL dates and their implications

Optically stimulated luminescence (OSL) dating of a series of glaciofluvial/glaciodeltaic sediments in central Buchan and Aberdeen has recently been undertaken. The aims of this project are to test the chronological model proposed by the most recent regional review and the suggestion that parts of Buchan may have remained ice-free during the last glacial maximum (late marine isotope stage (MIS) 3 and MIS 2 29–15 ka). The preliminary results indicate that during the Devensian (ca. 116–12 ka), extensive areas of Buchan may have been glaciated earlier than previously believed (possibly during MIS 4, 72–60 ka), but parts of the region show no depositional evidence of later glaciation. Some waterlain sediments from the Ugie Valley have yielded OSL ages indicating deposition during MIS 5d to MIS 5a (116–72 ka). We discuss whether the absence of overlying glaciogenic sediments at these locations raises questions about the reliability of the OSL ages or about existing models of the Devensian glaciation of Buchan.