The Potential Applications of Optical Dating to the Sandy Uplands of East Texas and Northwest Louisiana

The fine, sandy soils of East Texas and Northwest Louisiana have been the source of archaeological debate for some time. This discourse concerns the mode of burial of cultural material in the easily eroded soils and the mechanics of recent (Holocene) landform evolution. Because these deposits are typically well-drained, organic matter does not preserve well, thus hindering the dating of the geomorphic events that figure prominently in their development and the prehistoric occupations which lie buried throughout uplands of this region. A relatively new dating technique, optical dating, has much to offer this region and the archaeological community as it measures the period of time that has elapsed since sand grains were last exposed to sunlight. Hence, it directly dates the time of sediment transportation and deposition. This method is therefore applicable to a number of archaeological and geomorphic processes which may not be dated by traditional methods, owing to the lack of organic matter suitable for radiocarbon dating. In geomorphic contexts, optical dating may be preferred over radiocarbon as it directly dates the time of sedimentation rather than the age of organic matter in features such as buried soils that may be significantly different from the geomorphic event which fossilized the soil

Investigations into the potential effects of pedoturbation on luminescence dating

Much effort has been focussed on understanding the luminescence properties of natural minerals to achieve a reliable, accurate and precise dating technique. However, some field related aspects, such as the influence or effect of post-depositional disturbance on luminescence dates, are as yet underexplored. In the case of pedoturbation, depending on its intensity, the rate of sedimentation and unit thicknesses, potentially the whole sedimentary record at a site can be affected. This may lead to distorted OSL chronologies and erroneous sediment burial ages. Pedoturbation can result in sediment mixing and/or exhumation that affect luminescence both at the bulk and single grain level. Effects of these two principle processes on luminescence ages are examined using standard multigrain and single grain protocols. High resolution sampling of surface gopher mounds was used to determine the efficiency of bio-exhumation in resetting luminescence signal. Results show this is an inefficient mechanism for onsite sediment bleaching. The effects on luminescence signal of bio-mixing were explored by comparing a sample collected from within a krotovina (infilled burrow) to an adjacent undisturbed sample. Results show the difficulties in identifying pedoturbated samples at the single aliquot level and the possible inaccuracies in using the lowest palaeodose values to calculate OSL ages. Where pedoturbation of samples is suspected, use of probability plots of palaeodoses data is recommended. From these plots it is proposed that only data falling within a normal distribution centred on the peak probability be used to calculated OSL ages and to mitigate problems arising from pedoturbation

Comparative safety of anesthetic type for hip fracture surgery in adults: retrospective cohort study

Objective: To evaluate the effect of anesthesia type on the risk of in-hospital mortality among adults undergoing hip fracture surgery in the United States. Design: Retrospective cohort study. Setting: Premier research database, United States. Participants: 73 284 adults undergoing hip fracture surgery on hospital day 2 or greater between 2007 and 2011. Of those, 61 554 (84.0%) received general anesthesia, 6939 (9.5%) regional anesthesia, and 4791 (6.5%) combined general and regional anesthesia. Main outcome measure In-hospital all cause mortality. Results: In-hospital deaths occurred in 1362 (2.2%) patients receiving general anesthesia, 144 (2.1%) receiving regional anesthesia, and 115 (2.4%) receiving combined anesthesia. In the multivariable adjusted analysis, when compared with general anesthesia the mortality risk did not differ significantly between regional anesthesia (risk ratio 0.93, 95% confidence interval 0.78 to 1.11) or combined anesthesia (1.00, 0.82 to 1.22). A mixed effects analysis accounting for differences between hospitals produced similar results: compared with general anesthesia the risk from regional anesthesia was 0.91 (0.75 to 1.10) and from combined anesthesia was 0.98 (0.79 to 1.21). Findings were also consistent in subgroup analyses. Conclusions: In this large nationwide sample of hospital admissions, mortality risk did not differ significantly by anesthesia type among patients undergoing hip fracture surgery. Our results suggest that if the previously posited beneficial effect of regional anesthesia on short term mortality exists, it is likely to be more modest than previously reported

Late Wisconsin glaciation of Hadwen and Summer islands, Tuktoyaktuk Coastlands, NWT, Canada

The exact timing of the last major advance of the Laurentide Ice Sheet onto the Beaufort Sea coastlands of western Arctic Canada is unclear but significant to our understanding of landscape change and palaeo-ice stream chronology. Optical stimulated luminescence dating of preglacial and postglacial aeolian sand from Hadwen and Summer islands, in the Tuktoyaktuk Coastlands, indicates that glaciation took place between about 17.5 and 15 ka, and most likely between 16.6 and 15.9 ka, coinciding with Heinrich event 1. At this time the Mackenzie Trough palaeo-ice stream advanced into a cold-climate sandy desert, interrupting aeolian activity

Extending the aridity record of the Southwest Kalahari: current problems and future perspectives

An extensive luminescence-based chronological framework has allowed the reconstruction of expansions and contractions of the Kalahari Desert over the last 50 ka. However, this chronology is largely based on near-surface pits and sediment exposures. These are the points on the landscape most prone to reactivation and resetting of the luminescence dating ‘clock’. This is proving to be a limiting feature for extending palaeoenvironmental reconstructions further back in time. One way to obviate this is to sample desert marginal areas that only become active during significant arid phases. An alternative is to find and sample deep stratigraphic exposures. The Mamatwan manganese mine at Hotazel in the SW Kalahari meets both these criteria. Luminescence dating of this site shows the upper sedimentary unit to span at least the last 60 ka with tentative age estimates from underlying cemented aeolian units dating back to the last interglacial and beyond. Results from Mamatwan are comparable to new and previously published data from linear dunes in the SW Kalahari but extend back much further. Analysis of the entire data set of luminescence ages for the SW Kalahari brings out important inferences that suggest that different aeolian forms (1) have been active over different time scales in the past, (2) have different sensitivities to environmental changes and (3) have different time scales over which they record and preserve the palaeoenvironmental record. This implies that future optically stimulated luminescence work and palaeoenvironmental reconstructions must consider both site location and its relationship to desert margins and sediment depositional styles, so that the resolution and duration of the aridity record can be optimally understood

Late Quaternary sea-level changes of the Persian Gulf

Late Quaternary reflooding of the Persian Gulf climaxed with the mid-Holocene highstand previously variously dated between 6 and 3.4 ka. Examination of the stratigraphic and paleoenvironmental context of a mid- Holocenewhale beaching allows us to accurately constrain the timing of the transgressive, highstand and regressive phases of the mid- to late Holocene sea-level highstand in the Persian Gulf. Mid-Holocene transgression of the Gulf surpassed today's sea level by 7100–6890 cal yr BP, attaining a highstand of N1 m above current sea level shortly after 5290–4570 cal yr BP before falling back to current levels by 1440–1170 cal yr BP. The cetacean beached into an intertidal hardground pond during the transgressive phase (5300–4960 cal yr BP) with continued transgression interring the skeleton in shallow-subtidal sediments. Subsequent relative sea-level fall produced a forced regression with consequent progradation of the coastal system. These new ages refine previously reported timings for the mid- to late Holocene sea-level highstand published for other regions. By so doing, they allow us to constrain the timing of this correlatable global eustatic event more accurately

Syngenetic sand veins and anti-syngenetic sand wedges, Tuktoyaktuk Coastlands, western Arctic Canada

Sand-sheet deposits of full-glacial age in the Tuktoyaktuk Coastlands, western Arctic Canada, contain syngenetic sand veins 1-21 cm wide and sometimes exceeding 9 m in height. Their tall and narrow, chimney-like morphology differs from that of known syngenetic ice wedges and indicates an unusually close balance between the rate of sand-sheet aggradation and the frequency of thermal-contraction cracking. The sand sheets also contain rejuvenated (syngenetic) sand wedges that have grown upward from an erosion surface. By contrast, sand sheets of postglacial age contain few or sometimes no intraformational sand veins and wedges, suggesting that the climatic conditions were unfavourable for thermal-contraction cracking. Beneath a postglacial sand sheet near Johnson Bay, sand wedges with unusually wide tops (3.9 m) extend down from a prominent erosion surface. The wedges grew vertically downward during deflation of the ground surface, and represent anti-syngenetic wedges. The distribution of sand veins and wedges within the sand sheets indicates that the existence of continuous permafrost during sand-sheet aggradation can be inferred confidently only during full-glacial conditions