Component-resolved bleaching spectra of quartz optically stimulated luminescence: preliminary results and implications for dating

Bleaching spectra of the ‘fast’ and ‘medium’ optically stimulated luminescence (OSL) components of quartz are reported. A dependence of photoionization cross-section, σ, on wavelength was observed for the fast and medium components and a significant difference in their responses to stimulation wavelength was found. The ratio of the fast and medium photoionization cross-sections, σfast/σmedium, varied from 30.6 when stimulated with View the MathML source light to 1.4 at View the MathML source. At View the MathML source the fast and medium photoionization cross-sections were found to be sufficiently different that infrared bleaching at raised temperatures allowed the selective removal of the fast component with negligible depletion of the medium. A method for optically separating the OSL components of quartz is suggested, based on the wavelength dependence of photoionization cross-sections.

Further investigations of the quartz optically stimulated luminescence components using linear modulation

The optically stimulated luminescence (OSL) from quartz is known to be the sum of several components with different rates of charge loss, originating from different trap types. The OSL components are clearly distinguished using the linear modulation (LM OSL) technique. A variety of pre-treatment and measurement conditions have been used on sedimentary samples in conjunction with linearly modulated optical stimulation to study in detail the behaviour of the OSL components of quartz. Single aliquots of different quartz samples have been found to contain typically five or six common LM OSL components when stimulated at View the MathML source. The components have been parameterised in terms of thermal stability (i.e. E and s), photoionisation cross-section energy dependence and dose response. The results of studies concerning applications of component-resolved LM OSL measurements on quartz are also presented. These include the detection of partial bleaching in young samples, use of ‘stepped wavelength’ stimulation to observe OSL from single components and attempts to extend the age range of quartz OSL dating.

Multiple phases of North African humidity recorded in lacustrine sediments from the Fazzan Basin, Libyan Sahara

The Fazzan Basin of south-west Libya is at present arid with less than 20 mm of rainfall per annum. However, regionally extensive limestones, lacustrine sands and coquina (fossiliferous carbonate rock) deposits show that the Fazzan Basin previously contained a large palaeolake, indicating that the climate in the past was more humid. Optically stimulated luminescence (OSL) dating techniques have been applied to key lacustrine deposits within the basin in an attempt to provide an internally consistent chronology for this humidity record. Results indicate that palaeolake sediments within the Fazzan Basin record a very long history of palacohydrological change, ranging from present day and conditions to humidity capable of sustaining a lake with an approximate area of 76,250 km(2). The existence of humid periods in mid oxygen isotope stage 5 and the early Holocene is confirmed. An older lacustrine event, tentatively correlated to oxygen isotope stage 11, is also recognized. In addition, evidence is presented for at least two humid phases beyond the age range over which the conventional OSL dating technique is applicable. This study demonstrates that OSL dating of palaeolake sediments within the Fazzan Basin offers the potential to provide a detailed record of North African humidity spanning several glacial-interglacial cycles. (c) 2006 Elsevier Ltd. All rights reserved.

Holocene palaeoenvironmental history and the impact of prehistoric salt production in the Seille Valley, Eastern France

The Seille Valley in eastern France was home to one of Europe’s largest Iron Age salt industries. Sedimentology, palynology and geochronology have been integrated within ongoing archaeological investigations to reconstruct the Holocene palaeoenvironmental history of the Seille Valley and to elucidate the human–environment relationship of salt production. A sedimentary model of the valley has been constructed from a borehole survey of the floodplain and pollen analyses have been undertaken to reconstruct the vegetation history. Alluvial records have been successfully dated using optically stimulated luminescence and radiocarbon techniques, thereby providing a robust chronological framework. The results have provided an insight into the development of favourable conditions for salt production and there is evidence in the sedimentary record to suggest that salt production may have taken place during the mid-to-late Bronze Age. The latter has yet to be identified in the archaeological record and targeted excavation is therefore underway to test this finding. The development of the Iron Age industry had a major impact on the hydrological regime of the valley and its sedimentological history, with evidence for accelerated alluviation arising from floodplain erosion at salt production sites and modification of the local fluvial regime due to briquetage accumulation on the floodplain. This research provides an important insight into the environmental implications of early industrial activities, in addition to advancing knowledge about the Holocene palaeoenvironmental and social history of this previously poorly studied region of France.

Holocene settlement shifts and paleoenvironments on the Central Iranian Plateau: investigating linked systems

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.

Geoarchaeology and the value of multidisciplinary palaeoenvironmental approaches: a case study from the Tehran Plain, Iran

Tepe Pardis, a significant Neolithic–Chalcolithic site on the Tehran Plain in Iran, is, like many sites in the area, under threat from development. The site contains detailed evidence of (1) the Neolithic–Chalcolithic transition, (2) an Iron Age cemetery and (3) how the inhabitants adapted to an unstable fan environment through resource exploitation (of clay deposits for relatively large-scale ceramic production by c. 5000 BC, and importantly, possible cutting of artificial water channels). Given this significance, models have been produced to better understand settlement distribution and change in the region. However, these models must be tied into a greater understanding of the impact of the geosphere on human development over this period. Forming part of a larger project focusing on the transformation of simple, egalitarian Neolithic communities into more hierarchical Chalcolithic ones, the site has become the focus of a multidisciplinary project to address this issue. Through the combined use of sedimentary and limited pollen analysis, radiocarbon and optically stimulated luminescence dating (the application of the last still rare in Iran), a greater understanding of the impact of alluvial fan development on human settlement through alluviation and the development of river channel sequences is possible. Notably, the findings presented here suggest that artificial irrigation was occurring at the site as early as 6.7±0.4 ka (4300–5100 BC).

New age estimates for the Palaeolithic assemblages and Pleistocene succession of Casablanca, Morocco

Marine and aeolian Quaternary sediments from Casablanca, Morocco were dated using the optically stimulated luminescence (OSL) signal of quartz grains. These sediments form part of an extensive succession spanning the Pleistocene, and contain a rich faunal and archaeological record, including an Acheulian lithic assemblage from before the Brunhes–Matayama boundary, and a Homo erectus jaw from younger cave deposits. Sediment samples from the sites of Reddad Ben Ali, Oulad J’mel, Sidi Abderhamane and Thomas Quarries have been dated, in order to assess the upper limits of OSL. The revision of previously measured mammalian tooth enamel electron spin resonance (ESR) dates from the Grotte des Rhinocéros, Oulad Hamida Quarry 1, incorporating updated environmental dose rate measurements and attenuation calculations, also provide chronological constraint for the archaeological material preserved at Thomas Quarries. Several OSL age estimates extend back to around 500,000 years, with a single sample providing an OSL age close to 1 Ma in magnetically reversed sediments. These luminescence dates are some of the oldest determined, and their reliability is assessed using both internal criteria based on stratigraphic consistency, and external lithostratigraphic, morphostratigraphic and independent chronological constraints. For most samples, good internal agreement is observed using single aliquot regenerative-dose OSL measurements, while multiple aliquot additive-dose measurements generally have poorer resolution and consistency. Novel slow-component and component-resolved OSL approaches applied to four samples provide significantly enhanced dating precision, and an examination of the degree of signal zeroing at deposition. A comparison of the OSL age estimates with the updated ESR dates and one U-series date demonstrate that this method has great potential for providing reliable age estimates for sediments of this antiquity. We consider the cause of some slight age inversion observed at Thomas Quarries, and provide recommendations for further luminescence dating within this succession.

Assessing the completeness of optical resetting of quartz OSL in the natural environment

Resetting of previously accumulated optically stimulated luminescence (OSL) signals during transport of sediment is a fundamental requirement for reliable optical dating. The completeness of optical resetting of 46 modern-age quartz samples from a variety of depositional environments was examined. All equivalent dose (De) estimates were View the MathML source, with the majority of aeolian samples View the MathML source, and fluvial samples View the MathML source. The OSL signal of quartz originates from several trap types with different rates of charge loss during illumination. As such, incomplete bleaching may be identifiable as an increase in De from easy-to-bleach through to hard-to-bleach components. For all modern fluvial samples with non-zero De values, SAR De(t) analysis and component-resolved linearly modulated OSL (LM OSL) De estimates showed this to be the case, implying incomplete resetting of previously accumulated charge. LM OSL measurements were also made to investigate the extent of bleaching of the slow components in the natural environment. In aeolian sediments examined, the natural LM OSL was effectively zero (i.e. all components were fully reset). The slow components of modern fluvial samples displayed measurable residual signals up to 15 Gy.

Optical dating of quartz from young samples and the effects of pre-heat temperature

The optically stimulated luminescence (OSL) signal within quartz may be enhanced by thermal transfer during pre-heating. This may occur via a thermally induced charge transfer from low temperature traps to the OSL traps. Thermal transfer may affect both natural and artificially irradiated samples. The effect, as empirically measured via recuperation tests, is typically observed to be negligible for old samples (<1% of natural signal). However, thermal transfer remains a major concern in the dating of young samples as thermal decay and transfers of geologically unstable traps (typically in the TL range 160–280°C) may be incomplete. Upon pre-heating such a sample might undergo thermal transfer to the dating trap and result in a De overestimate. As a result, there has been a tendency for workers to adopt less rigorous pre-heats for young samples. We have investigated the pre-heat dependence of 23 young quartz samples from various depositional environments using pre-heats between 170°C and 300°C, employing the single aliquot regeneration (SAR) protocol. SAR De's were also calculated for 25 additional young quartz samples of different depositional environments and compared with previous multiple aliquot additive dose (MAAD) data. Results demonstrate no significant De dependence upon pre-heat temperatures. A close correspondence between MAAD data and the current SAR data for the samples tested is also illustrated.

Timing and depositional environments of a Middle Pleistocene glaciation of northeast England: New evidence from Warren House Gill, County Durham

At various times during the Quaternary, north-eastern England was a zone of confluence between dynamic ice lobes sourced from the Pennines, northern Scotland, the Cheviots, and Scandinavia. The region thus has some of the most complex exposures of Middle to Late Pleistocene sediments in Britain, with both interglacial and glacial sediments deposited in terrestrial and marine settings. We investigated sedimentary sequences exposed on the coastline of County Durham at Warren House Gill, and present a new model of British and Fennoscandian Ice Sheet interaction in the North Sea Basin during the Middle Pleistocene. The stratigraphy at Warren House Gill consists of a lower diamicton and upper estuarine sediments, both part of the Warren House Formation. They are separated from the overlying Weichselian Blackhall and Horden tills by a substantial unconformity. The lower diamicton of the Warren House Formation is re-interpreted here as an MIS 8 to 12 glaciomarine deposit containing ice-rafted lithics from north-eastern Scotland and the northeast North Sea, and is renamed the ‘Ash Gill Member’. It is dated by lithological comparison to the Easington Raised Beach, Middle Pleistocene Amino Acid Racemisation values, and indirectly by optically stimulated luminescence. The overlying shallow subaqueous sediments were deposited in an estuarine environment by suspension settling and bottom current activity. They are named the ‘Whitesides Member’, and form the uppermost member of the Warren House Formation. During glaciation, ice-rafted material was deposited in a marine embayment. There is no evidence of a grounded, onshore Scandinavian ice sheet in County Durham during MIS 6, which has long been held as the accepted stratigraphy. This has major implications for the currently accepted British Quaternary Stratigraphy. Combined with recent work on the Middle Pleistocene North Sea Drift from Norfolk, which is now suggested to have been deposited by a Scottish ice sheet, the presence of a Scandinavian ice sheet in eastern England at any time during the Quaternary is becoming increasingly doubtful.

Glacial lake drainage in Patagonia (13-8 kyr) and response of the adjacent Pacific Ocean

Large freshwater lakes formed in North America and Europe during deglaciation following the Last Glacial Maximum. Rapid drainage of these lakes into the Oceans resulted in abrupt perturbations in climate, including the Younger Dryas and 8.2 kyr cooling events. In the mid-latitudes of the Southern Hemisphere major glacial lakes also formed and drained during deglaciation but little is known about the magnitude, organization and timing of these drainage events and their e ect on regional climate. We use 16 new single-grain optically stimulated luminescence (OSL) dates to de ne three stages of rapid glacial lake drainage in the Lago General Carrera/Lago Buenos Aires and Lago Cohrane/ Pueyrredón basins of Patagonia and provide the rst assessment of the e ects of lake drainage on the Paci c Ocean. Lake drainage occurred between 13 and 8 kyr ago and was initially gradual eastward into the Atlantic, then subsequently reorganized westward into the Paci c as new drainage routes opened up during Patagonian Ice Sheet deglaciation. Coupled ocean-atmosphere model experiments using HadCM3 with an imposed freshwater surface “hosing” to simulate glacial lake drainage suggest that a negative salinity anomaly was advected south around Cape Horn, resulting in brief but signi cant impacts on coastal ocean vertical mixing and regional climate.

Environmental control for layers

Light patterns have less effect on numbers of eggs laid by current stocks than on those of forty years ago, but the principles have not changed. Ovarian activity is stimulated by increasing photoperiods and suppressed by decreasing photoperiods. The light pattern used during rearing can still have large effects on age at 50% lay, even for modern stocks. Early sexual maturity maximises egg numbers but gives smaller eggs. Late maturity maximises egg size at the expense of numbers. The relationship between egg output (g/hen d) and age at first egg is curvilinear, with maximum yield occurring in flocks maturing in about the centre of their potential range. Fancy patterns of increasing daylength after maturity are probably not justified. A flock held on a constant 14h day will lay as many eggs as one given step up lighting. Intermittent lighting saves about 5% of feed consumption with no loss of output, provided that the feed has adequate amino acid content to allow for the reduced feed intake. Producers with light-proof laying houses should be taking advantage of intermittent lighting. The recommended light intensity for laying houses is still 10 lx, although the physiological threshold for response to changes in photoperiod is closer to 2 lx. Very dim (0.05 lx) light filtering into blacked out houses will not stimulate the hypothalamic receptors responsible for photo-sexual responses, but may affect the bird's biological clock, which can alter its response to a constant short photoperiod. Feed intake shows a curvilinear dependence on environmental temperature. At temperatures below the panting threshold, performance can be maintained by adjusting the feed so as to maintain an adequate intake of critical amino acids. Above the panting threshold, the hen is unable to take in enough energy to maintain normal output. There is no dietary modification which can effectively offset this problem. Diurnally cycling temperatures result in feed intake and egg production equivalent to that observed under a constant temperature equal to the mean of the cycle. When the poultry house is cooler at night than by day, it helps to provide light so that the birds can feed during the cooler part of the cycle.