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The analysis of exceptionally well-preserved visible clastic laminations in deep alluvial sediments at Kempsey, Worcestershire (UK), allows a new high-resolution analysis of late-Holocene flood-history in the largest UK catchment, as well as local human response. At the sample site over 4.5 m of sandy-silt overbank-alluvium accumulated on the floodplain and optically stimulated luminescence (OSL) dating of the upper 2.25 m demonstrates accretion from the late 14th century CE onwards. Sub-centimetre to centimetre resolution multi-proxy sediment analysis (loss on ignition, magnetic susceptibility, particle size, ITRAX and portable XRF) demonstrate clear variations in depositional history over the last millennium due to channel stability. Between c. 1380 and 1550 CE overbank sedimentation was driven by lower energy flood events, with negligible effect from climatic conditions during the Spörer Minimum (1460–1550 CE). After c. 1550 CE the magnitude of flooding events increased and by c. 1610 CE, the start of the visible sub-centimetre laminations, the accumulation rate regularly exceeded 3 mm year−1, which increased to 4.5 mm year−1 between c. 1690 and 1710 CE, and 3 and 3.5 mm year−1 between c. 1790 and 1840 CE before alluviation was altered by an embankment. The greatest extent of coarse overbank deposition and increased accumulation rate occur concurrently with periods of climatic instability associated with the Maunder (1645–1715 CE) and Dalton (1790–1820 CE) Minima, the periods of largest historical floods and during the intensification of arable cultivation across the middle Severn catchment. This data correlates well with other sites in the catchment suggesting that these are basin-wide forcing-responses. We also present evidence that this catchment-wide hydro-geomorphological history had local effects in shifting the geographical focus of an important settlement away from its historic floodplain edge location – which can be viewed as an adaptation to the flood risk. [ABSTRACT FROM AUTHOR]

We have studied laminated sediments from Lake Esmeralda, Vega Island, in order to reconstruct its history. We describe both inorganic and organic components of the sediment using a combination of the following analytical methods: x-ray fluorescence (XRF), x-ray diffraction (XRD), magnetic susceptibility measurement, chemical analysis for determination of cation exchange capacity, grain size determination, geochemical analyses (total inorganic carbon (TIC), total organic carbon (TOC), total sulphur (TS)), spectrophotometry, high-pressure liquid chromatography, and diatom assemblage and faunal remains characterization. The geochronology of the core was based on modelling optically stimulated luminescence ages and supported by laminae counting. The dating results imply a maximum age of ~400 years for the 177-cm long core and a period covered of ~200 years, suggesting (quasi-)annual laminae formation. Such a young age contradicts previous findings based on radiocarbon dating. Geomorphological evidence indicates that river capture isolated the lake catchment from upslope sediment delivery, effectively terminating accumulation ~230 years ago. Conversely, our short-term palaeoenvironmental record yields a subdecadal temporal resolution, which is unparalleled in comparison with other Antarctic palaeolimnological studies. Our interpretations of the geochemical and mineralogical proxy data give us insight into the past lake catchment and waterbody evolution, and lead us to recognize periods of enhanced weathering, bottom anoxia and to distinguish major lake level changes. [ABSTRACT FROM AUTHOR]

Instrumental/historic records have helped to understand the extreme flood–climate relationship in the modern environment; however, few studies are available to understand their long-term relation (102–103 years) due to the poor preservation and lack of dating techniques. It remains uncertain whether extreme flooding is linked with long-term wet phases of climate or a random event caused by an unusual downpour irrespective of climate. Luminescence analysis of quartz grains from river/floodplain sediments in the Kaveri basin, southern India, showed heterogeneous bleaching. We demonstrated the successful application of various statistical age models in estimating ages of heterogeneously bleached young sediments. This study shows distinct flood clusters occurred during the times of major shifts in the monsoon climate, from fluvial dormancy to sudden outburst of monsoons (~2 ka), from warmer to colder (onset of 'Little Ice Age' (LIA) ~ 14th century), from colder to warmer (end of LIA ~ 19th century) and ~20th century, indicating that climatic pattern can be associated with more frequent occurrences of extreme flood events. The study also shows that the two major flood events of the 20th century reported from the upper Kaveri were produced by high intensity short duration storms, suggesting that not all wet phases are associated with major floods and all dry phases with low floods/droughts. The excellent match of the chronology with the historical data, instrumental data and published literature based on proxy data on the Indian summer monsoon validates the chronology and the potential of sedimentary archives for future palaeoenvironmental reconstruction of the study area. [ABSTRACT FROM AUTHOR]

Cliff-top dunes are a locally important geomorphic features of sedimentary coasts. They are traditionally interpreted as being sourced by (or with) sand derived from the beach below the cliff. This paper presents the results of a stratigraphic and geochronological study of Carlo Sand Blow, a coastal blowout that has developed on top of a high sandy cliff in the Cooloola Sand Mass, south-east Queensland. We use a combination of sedimentological, pedological and geophysical techniques along with optically stimulated luminescence dating to determine the depositional history and evolution of the blowout. We demonstrate that the blowout is dominantly nourished by sand eroded from its floor rather than the adjacent beach. The original dune surface dates to the first half of the last glacial period (c. 40–70 ka) and this dune was deflated in the late-Holocene. Dune activity is directly associated with cliff undercutting because of coastal retreat in the late-Holocene, but coastal erosion on its own is not capable of maintaining aeolian activity. Blowout activity occurred between 2.6 and 2.3 ka and again at 0.3 ka with aeolian sand burying palaeosols. Both soil surfaces contained charcoal and tree stumps in growth position and our study suggests that fire is the immediate trigger for blowout reactivation. It is likely that these fires were anthropogenic in origin, because the site is somewhat protected from natural fire and the ages coincide with intensification of human use of coastal sites in the area. [ABSTRACT FROM AUTHOR]

The Nebraska Sand Hills is a stabilized dune field on the Great Plains of North America. Although it is well known that this dune field, like several others on the Great Plains, last experienced widespread activity during the Medieval Climatic Anomaly (MCA, ~AD 900–1300), spatial variation in the timing and nature of drought development is poorly constrained. To elucidate spatial trends in dune reactivation, samples potentially representing MCA activity across the Sand Hills were collected and dated using optically stimulated luminescence (OSL). Ages from the older part of the MCA were obtained from eolian sediments in the northwestern Sand Hills, while ages from later in the episode were obtained to the southeast, suggesting a geographic trend in the timing of revegetation of the dunes near the end of the drought. Revegetation likely occurred to the northwest initially as a result of renewed moisture availability from a rising water table in the interdunes, which serve as refugia for vegetation during times of drought. Vegetation then gradually spread to the southeastern Sand Hills. An additional spatial trend in ages is apparent in the chronology of linear dune mobilization across the Sand Hills. Linear dunes in the northwest are superimposed on megadunes and originated during the last reactivation, while linear dunes in the southeast are built around older cores of dunes and formed during several reactivations. Our geochronology reveals three episodes of eolian transport, including the MCA, in the formation of linear dunes in the southeast. [ABSTRACT FROM PUBLISHER]

For thousands of years, humans have inhabited locations that are highly vulnerable to the impacts of climate change, earthquakes, and floods. In order to investigate the extent to which Holocene environmental changes may have impacted on cultural evolution, we present new geologic, geomorphic, and chronologic data from the Qazvin Plain in northwest Iran that provides a backdrop of natural environmental changes for the simultaneous cultural dynamics observed on the Central Iranian Plateau. Well-resolved archaeological data from the neighbouring settlements of Zagheh (7170—6300 yr BP), Ghabristan (6215—4950 yr BP) and Sagzabad (4050—2350 yr BP) indicate that Holocene occupation of the Hajiarab alluvial fan was interrupted by a 900 year settlement hiatus. Multiproxy climate data from nearby lakes in northwest Iran suggest a transition from arid early-Holocene conditions to more humid middle-Holocene conditions from c. 7550 to 6750 yr BP, coinciding with the settlement of Zagheh, and a peak in aridity at c. 4550 yr BP during the settlement hiatus. Palaeoseismic investigations indicate that large active fault systems in close proximity to the tell sites incurred a series of large (MW ~7.1) earthquakes with return periods of ~500—1000 years during human occupation of the tells. Mapping and optically stimulated luminescence (OSL) chronology of the alluvial sequences reveals changes in depositional style from coarse-grained unconfined sheet flow deposits to proximal channel flow and distally prograding alluvial deposits sometime after c. 8830 yr BP, possibly reflecting an increase in moisture following the early-Holocene arid phase. The coincidence of major climate changes, earthquake activity, and varying sedimentation styles with changing patterns of human occupation on the Hajiarab fan indicate links between environmental and anthropogenic systems. However, temporal coincidence does not necessitate a fundamental causative dependency. [ABSTRACT FROM PUBLISHER]

This study presents an Optically Stimulated Luminescence (OSL) based chronology for the evolution of the barrier island Rømø and related back-barrier lagoon deposits in the Danish Wadden Sea. The chronology is constructed using 78 quartz OSL ages obtained using a Single Aliquot Regenerative dose (SAR) protocol; samples were retrieved from seven sediment cores, each up to 25 m long, taken from locations on the island and within the back-barrier lagoon. The reliability of the OSL results is assessed using preheat plateaus, thermal transfer tests, and dose recovery measurements, and by comparison with independent age control. The OSL ages compare favourably with three 14C age estimates, and range between 220±20 and 15 800±1200 years. Rømø appears to have developed as a progradational barrier system, and the island appeared for the first time approximately 8000 years ago. It then gradually expanded towards the west, north and south as a result of an abundant sediment supply. Luminescence dating is concluded to be well-suited for establishing precise and accurate chronologies for barrier island deposits, and the technique has provided an excellent basis for the reconstruction of barrier island evolution. [ABSTRACT FROM AUTHOR]

Post Nipissing-phase strandplains of the Great Lakes reflect late-Holocene water levels that are linked to climate variability, glacial isostasy, and changes in basin hydrology. This study examines a strandplain sequence at Bailey's Harbor, Door County, Wisconsin, along Lake Michigan, which contains a record of water-level variations during the past 1000 years, following the separation of the Lake Michigan-Huron basin from the Lake Superior basin. Vibracores are used to define the current elevation of the foreshore facies in 25 preserved beach ridges. Optical ages for five individual beach ridges are compared with radiocarbon ages on basal peats from nine swales collected in a previous study. The optical chronology yields a ridge formation/preservation rate of 30 ± 2 yr/ridge similar to that of previous assessments. This study further demonstrates the efficacy of optical dating for deciphering late-Holocene beach-ridge sequences, providing multidecadal resolution. Lake level meets or exceeds, by at least 0.5 m, historic metrics at c. ad 1125-1225. The maximum water level after c. AD 1225 is comparable with that recorded by the instrumental data. There is a noticeable high lake level from c. AD 1560 to 1725. Dating of additional sites along Lake Michigan is required to establish local rates of glacio-isostatic adjustment, identify possible erosion of the outlets and to resolve lake-level records for individual lakes following the separation of the upper Great Lakes currently constrained to have occurred c. 2400 to 1200 years ago. [ABSTRACT FROM AUTHOR]

An elevated valley-fill peat bog (Wilson Bog) near Mount Lofty, South Australia, failed in November 2005 following a flooding event, and exposed representative sections of the sediment infill. Two distinct units were revealed: 2 m of coarse-grained, siliciclastic sand/gravel, overlain by 2 m of peat.Asimple charcoal extraction technique based on floatation and skimming was developed to extract coarse charcoal from coarse-grained gravels to determine the palaeofire record at a proximal site of sedimentation. Optically stimulated luminescence (OSL) dating of basal sediments revealed a minimum age of deposition of 7.02 +0.50 -0.56 ka, while the oldest charcoal peak yielded a radiocarbon age of 6000-5740 cal. yr BP. The lower half of the siliciclastic unit contains three distinct charcoal peaks suggesting there were infrequent but intense fires associated with wetter conditions during the Holocene climatic optimum 8000-5000 years ago. The period from 4000 to 2000 cal. yr BP is characterised by more frequent charcoal peaks and higher background levels of charcoal, which is consistent withmore regular but less intense fires during drier, cooler conditions. The sharp transition from siliciclastic sedimentation to peat formation began ∼1200 cal. yr BP, which may relate to a return to wetter conditions. However, fire frequency appears to have increased in this time suggesting augmentation by anthropogenic or ENSO-related factors. Charcoal-rich layers in the siliciclastic unit are associated with poorly sorted, bimodal sediments with high proportions of clay, silt and gravel, which supports the hypothesis that there is an association between past fire events and rapid, coarse-grained, post-fire aggradation. By analogy with active colluvial aggradation following recent fires at nearbyMount Bold, it is evident that fire plays a significant role in hillslope destabilization and subsequent sediment movement, leading to rapid valley- fill aggradation - a chain of events to which we apply the term 'pyrocolluviation'. [ABSTRACT FROM AUTHOR]

A forested dunefield covers the Baraga Plains in western upper Michigan. The ages of five dunes, from across the dunefield, were determined by optically stimulated luminescence (OSL), employing the single-aliquot regenerative-dose (SAR) method on quartz grains. The results indicate that sand mobilization was restricted to the middle Holocene, at around 7 ka. Four environmental variables, rapid climatic oscillations, fire, strong winds and a dry climate are invoked as a combined cause of dune formation. This study provides further evidence for the wide extent of aeolian activity in the upper Midwest of North America during the middle Holocene. [ABSTRACT FROM AUTHOR]