Edward J. Rhodes

82,000-year-old shell beads from North Africa and implications for the origins of modern human behavior

The first appearance of explicitly symbolic objects in the archaeological record marks a fundamental stage in the emergence of modern social behavior in Homo. Ornaments such as shell beads represent some of the earliest objects of this kind. We report on examples of perforated Nassarius gibbosulus shell beads from Grotte des Pigeons (Taforalt, Morocco), North Africa. These marine shells come from archaeological levels dated by luminescence and uranium-series techniques to ≈82,000 years ago. They confirm evidence of similar ornaments from other less well dated sites in North Africa and adjacent areas of southwest Asia. The shells are of the same genus as shell beads from slightly younger levels at Blombos Cave in South Africa. Wear patterns on the shells imply that some of them were suspended, and, as at Blombos, they were covered in red ochre. These findings imply an early distribution of bead-making in Africa and southwest Asia at least 40 millennia before the appearance of similar cultural manifestations in Europe.

Partial bleaching and the decay form characteristics of quartz OSL

Abstract Three exponential components have been isolated from observed high temperature OSL decay data of quartz. These components have been found to display differential bleaching and growth characteristics. It is postulated that changes in the ratio of the first two components (the “fast” and the “medium”) are responsible for the changes in decay form observed in partially bleached samples. Measurements have shown that a comparison of the observed ratios to the expected ratios (had a sample been fully bleached) may be able to differentiate sediments for which the OSL has only been partially reset prior to deposition.

Neanderthal exploitation of marine mammals in Gibraltar

Two coastal sites in Gibraltar, Vanguard and Gorhams Caves, located at Governors Beach on the eastern side of the Rock, are especially relevant to the study of Neanderthals. Vanguard Cave provides evidence of marine food supply (mollusks, seal, dolphin, and fish). Further evidence of marine mammal remains was also found in the occupation levels at Gorhams Cave associated with Upper Paleolithic and Mousterian technologies [Finlayson C, et al. (2006) Nature 443:850–853]. The stratigraphic sequence of Gibraltar sites allows us to compare behaviors and subsistence strategies of Neanderthals during the Middle Paleolithic observed at Vanguard and Gorhams Cave sites. This evidence suggests that such use of marine resources was not a rare behavior and represents focused visits to the coast and estuaries.

Charge movements in quartz and their relevance to optical dating

Abstract Combined thermoluminescence (TL), phosphorescence and optically stimulated luminescence (OSL) measurements have been used to trace the movement of charge within the lattice of a geological quartz sample when it is exposed to light (514 nm from an Ar ion laser). The evidence suggests that optical stimulation evicts charge from traps in the crystal lattice associated with the 325°C thermoluminescence (TL) emission and elevates it to the conduction band. Part of the charge recombines with luminescence centres to produce the observed optically stimulated luminescence (OSL), and a significant portion is re-trapped at the same or different localities in the lattice. Important implications for the optical dating of quartz are discussed, including the necessity of a pre-heat, the interpretation of the equivalent dose as a function of OSL measurement time and the ramifications of OSL recuperation.

Timing of Late Quaternary glaciations in the Himalayas of northern Pakistan

Optically stimulated luminescence dating of Late Quaternary glaciogenic sediments was undertaken in critical areas of the Himalayas of northern Pakistan in order to examine the timing of glaciation. The dates demonstrate that several glaciations occurred during the last glacial cycle. In Swat, the Grabral 2 Stade and the Kalam I Stade were dated at ca. 77 ka and ca. 38 ka, respectively. The error on the former date is large and it is conceivable that the moraines may have formed during the early part of Oxygen Isotope Stage 3 rather than during Oxygen Isotope Stage 4. The Kalam I Stade, however, clearly represents a glaciation during Oxygen Isotope Stage 3. The oldest moraines and those at the lowest altitude in the Indus valley at Shatial have an age of ca. 60 ka. These also relate to a major glacial advance during Oxygen Isotope Stage 3. A younger series of moraines, the Jalipur Tillite, and glaciofluvial sands at Liachar in the Indus valley, and moraines at Rampur-Tarshing have ages of ca. 27 ka, ca. 21-23 ka and ca. 15 ka, respectively. These dates show that glaciers also occupied parts of the Indus valley during Oxygen Isotope Stage 2. These dates and the morphostratigraphy show that glaciation in the Pakistani Himalaya was more extensive during the early part of the last glacial cycle and that the local last glacial maximum in Pakistan was asynchronous with the maximum extent of Northern Hemisphere ice sheets. Copyright

Methodological considerations in the optical dating of quartz

Abstract The optically-stimulated luminescence from quartz grains extracted from sediments at two archaeological sites has been studied. The sites were the Upper Palaeolithic site at Hengistbury Head, Dorset, U.K. and the Upper Aterian site at Chaperon Rouge, Morocco. Problems associated with the technique of optical dating are discussed, particularly the thermal treatment that is necessary to remove thermally unstable charge following artificial irradiation, and the extrapolation of growth curves to estimate the equivalent dose. The technique used is described and some preliminary dates are presented.

Observations of thermal transfer OSL signals in glacigenic quartz

Abstract The conclusions of Rhodes and Pownall (Rhodes, E.J., Pownall, L., 1994. Zeroing of the OSL signal in quartz from young glaciofluvial sediments. Radiation Measurements 23, 329–333) were somewhat discouraging for the prospects of using quartz OSL for dating glacigenic sediments, while the more detailed study of Rhodes and Bailey (Rhodes, E.J., Bailey, R.M., 1997. The effect of thermal transfer on the zeroing of the luminescence of quartz from recent glaciofluvial sediments. Quaternary Science Reviews (Quaternary Geochronology) 16, 291–298) provided more encouragement. Specifically, the latter authors were able to account for the relatively high D e values observed for recent glacigenic (dominantly glaciofluvial) sediments in terms of an anomalously high thermal transfer effect, rather than simply insufficient bleaching prior to deposition. In other locations, the OSL of quartz from glacigenic material appears to provide reliable age estimates, and does not suffer from these effects (Owen, L.A., Richards, B., Rhodes, E.J., Cunningham, W.D., Windley, B.F., Badamgarav, J., Dorjnamjaa, D., 1998. Relic permofrost structures in the Gobi of Mongolia: age and significance. Journal of Quaternary Science 13 (16), 539–548; Richards, B.W., Owen, L.A., Rhodes, E.J., 2000. Timing of Late Quaternary glaciations in the Himalayas of northern Pakistan. Journal of Quaternary Science 15, 283–297). In this paper, laboratory bleached samples from both the above studies are remeasured, using an experimental design to correct for OSL sensitivity changes, which has some similarities to the single aliquot regenerative dose (SAR) protocol of Murray and Wintle (Murray A.S., Wintle A.G., 2000. Luminescence dating of quartz using an improved single-aliquot regenerative-dose protocol. Radiation Measurements 32, 57–73). Clear evidence of thermal transfer OSL signals, generated during the preheating procedure, is presented. Further measurements, using the full SAR protocol, demonstrate that the source of this charge is related to natural dosing. For one sample, the apparent effect is subtracted effectively by the SAR protocol. Another sample studied in detail shows a striking relationship between the thermally transferred OSL signal and the total TL observed during the ramping of the preceding preheat treatment.

Timing of late Quaternary glaciations south of Mount Everest in the Khumbu Himal, Nepal

Moraines south of Mount Everest in the Khumbu Himal were dated using optically stimulated luminescence. Clustering of ages and morphostratigraphy allowed three advances to be dated: (1) the Periche Glacial Stage (ca. 18‐25 ka), (2) the Chhukung Glacial Stage (ca. 10 ka), and (3) the Lobuche Stage (ca. 1‐2 ka). The Periche Stage is coincident with Oxygen Isotope Stage 2; the Chhukung Stage represents a late glacial or early Holocene glacial advance; and the Lobuche Stage is a late Holocene glacial advance that predates the Little Ice Age.

Environmental dose rate heterogeneity of beta radiation and its implications for luminescence dating: Monte Carlo modelling and experimental validation

The recent development of rapid single sand-sized grain analyses in luminescence dating has necessitated the accurate interpretation of D-e distributions to recover a representative D-e acquired since the last bleaching event. Beta heterogeneity may adversely affect the variance and symmetry of D-e distributions and it is important to characterise this effect, both to ensure that dose distributions are not misinterpreted, and that an accurate beta dose rate is employed in dating calculations. In this study, we make a first attempt providing a description of potential problems in heterogeneous environments and identify the likely size of these effects on D-e distributions. The study employs the MCNP 4C Monte Carlo electron/photon transport model, supported by an experimental validation of the code in several case studies. We find good agreement between the experimental measurements and the Monte Carlo simulations. It is concluded that the effect of beta, heterogeneity in complex environments for luminescence dating is two fold: (i) the infinite matrix dose rate is not universally applicable; its accuracy depends on the scale of the heterogeneity, and (ii) the interpretation of D-e distributions is complex and techniques which reject part of the D-e distribution may lead to inaccurate dates in some circumstances

Australian desert dune fields initiated with Pliocene–Pleistocene global climatic shift

Development of continental aridity has been linked to late Cenozoic global cooling, but the evidence is indirect, based on terrestrial loess deposits and eolian silt in marine sediments, whereas direct dating of the inception of arid landforms has been frustrated by a lack of suitable methods. Here we report the first age determination of a major arid-zone dune field, based on cosmogenic 10 Be and 26 Al measurements of drill cores from dunes in the Simpson Desert, central Australia. Results show that the dune field began to form ca. 1 Ma, whereas dating using quartz optically stimulated luminescence indicates episodic dune building during late Quaternary ice ages. Less intense desertification began earlier; the previous cosmogenic exposure dating showed that neighboring stony deserts began to form at the onset of Quaternary ice ages 2–4 Ma. Aridity deepened and the dune field formed when ice age cycles increased their amplitude and switched their periods from 40 k.y. to 100 k.y. ca. 1 Ma.