Anne R. Skinner

Improvements in dating tooth enamel by ESR.

ESR dating requires that growth curves be determined by interpreting complex spectra. Spectra, however, can vary significantly in shape and field position between different samples, or occasionally between subsamples, even though the mineralogy remains the same. In some cases, this spectral variability does not affect the resulting accumulated dose calculation. In other cases, signal subtraction may be needed. However, some samples that until recently might have been considered unsuitable for dating are now shown to yield accurate and precise results because a broad interference peak is integral to the hydroxyapatite signal. By studying the spectrum at the Q-band frequency, it can be shown that the interfering signal in most cases is not a problem for dating. A second concern has been that artificially irradiating sample aliquots can introduce a short-lived component that is simply an unstable enhancement of the dating signal. The apparent accumulated dose from growth curves created immediately after irradiation is considerably greater than that after annealing, although the curves shape remains unchanged. Annealing both the natural and artificially irradiated signal shows the dating signals lifetime to be greater than 10(10) years.

New excavations at the site of Contrebandiers Cave, Morocco

PaleoAnthropology 2012: 145−201.

Q-band studies of the ESR signal in tooth enamel ☆

Abstract Tooth enamel is one of the most promising materials for electron spin resonance (ESR) dating because the X-band signal is large, easy to measure, and extremely stable. The mean lifetime at ambient temperature has been measured greater than the age of the Earth! However, the X-band spectrum in fossil teeth is, in fact, a composite of two signals that can be resolved if the sample is examined in the Q-band region. The relative size of the two signals appears to be a function of degree of fossilization; older teeth have a better-defined second signal. A study of the dependence of these signals on radiation dose, microwave power, and temperature strongly suggests that both signals are located in the hydroxyapatite crystal structures. As such, then, the X-band spectrum, measured at moderate modulation amplitude, is suitable for determining the age of fossil teeth.

ESR dating of terrestrial quaternary shells

Abstract Multiple geological processes over the last 100 ka have resulted in a complex stratigraphy for San Salvador Island, The Bahamas. A study of amino acid racemization in the land snail sp. Cerion was inconclusive in resolving this, and therefore an investigation of the same species using ESR was undertaken. Sample ages range from 4 to 150 ka. The newer shells represent one of the youngest ESR sample sets known, and the first attempt to use terrestrial species. The ages obtained correlate generally with stratigraphic expectations, but until further work is done on the environmental history, the numerical values should be considered relative rather than absolute.

The use of the E′ signal in flint for ESR dating

Abstract The E ′ signal in silica has been used to date quartz in geological applications. However, the behavior of this signal in flint is quite different. Resetting the signal by heating is difficult, and the signal intensity saturates both with respect to artificial dose and to microwave power. Nonetheless, ages determined for flints from north-western Florida are in reasonable agreement with C-14 ages, suggesting that the method should be studied further.

Combustion at the late Early Pleistocene site of Cueva Negra del Estrecho del Río Quípar (Murcia, Spain)

Abstract Control of fire was a hallmark of developing human cognition and an essential technology for the colonisation of cooler latitudes. In Europe, the earliest evidence comes from recent work at the site of Cueva Negra del Estrecho del Río Quípar in south-eastern Spain. Charred and calcined bone and thermally altered chert were recovered from a deep, 0.8-million-year-old sedimentary deposit. A combination of analyses indicated that these had been heated to 400–600°C, compatible with burning. Inspection of the sediment and hydroxyapatite also suggests combustion and degradation of the bone. The results provide new insight into Early Palaeolithic use of fire and its significance for human evolution.

ESR dating pleistocene barnacles from BC and Maine: a new method for tracking sea level change.

Barnacles have never been successfully dated by electron spin resonance (ESR). Living mainly in the intertidal zone, barnacles die when sea level changes cause their permanent exposure. Thus, dating the barnacles dates past sea level changes. From this, we can measure apparent sea level changes that occur due to ocean volume changes, crustal isostasy, and tectonics. ESR can date aragonitic mollusc shells ranging in age from 5 ka to at least 500 ka. By modifying the standard ESR method for molluscs to chemically dissolve 20 &mgr;m from off the shells, six barnacle samples from Norridgewock, Maine, and Khyex River, British Columbia, were tested for suitability for ESR dating. Due to Mn2+ interference peaks, the four Maine barnacle samples were not datable by ESR. Two barnacles from BC, which lacked Mn2+ interference, yielded a mean ESR age of 15.1 ± 1.0 ka. These ages agree well with 14C dates on the barnacles themselves and wood in the overlying glaciomarine sediment. Although stability tests to calculate the mean dating signal lifetime and more ESR calibration tests against other barnacles of known age are needed to ensure the methods accuracy, ESR can indeed date Balanus, and thus, sea level changes.

Dating human occupation at Toca do Serrote das Moendas, Sao Raimundo Nonato, Piaui-Brasil by electron spin resonance and optically stimulated luminescence

Excavation of Toca do Serrote das Moendas, in Piauí state, Brazil revealed a great quantity of fossil wild fauna associated with human remains. In particular, fossils of a cervid (Blastocerus dichotomus) were found, an animal frequently pictured in ancient rock wall paintings. In a well-defined stratum, two loose teeth of this species were found in close proximity to human bones. The teeth were independently dated by electron spin resonance (ESR) in two laboratories. The ages obtained for the teeth were 29 ± 3 ka (thousands of years) and 24 ± 1 ka. The concretion layer capping this stratum was dated by optically stimulated luminescence (OSL) of the quartz grains to 21 ± 3 ka. As these values were derived independently in three different laboratories, using different methods and equipment, these results are compelling evidence of early habitation in this area.

ESR Dating at Hominid and Archaeological Sites During the Pleistocene

In any fossil site, dating the site is essential to understanding the site’s significance, because chronological data permits comparisons with materials from other sites, and ultimately enables regional settlement patterns, migration, or evolutionary rates to be determined. A dating method’s ability to date significant fossil materials directly rather than just dating associated sedimentary or rock units adds to its archaeological and paleontological utility. Electron spin resonance (ESR) dating can provide chronometric ages for vertebrate teeth throughout the Pleistocene and late Pliocene. For mollusc shells and coral, ESR’s effective dating range spans much of the Pleistocene.

Monitoring tectonic uplift and paleoenvironmental reconstruction for marine terraces near Maǧaracik and Samandaǧ, Hatay Province, Turkey.

Near Hatay, the Antakya-Samandağ-Cyprus Fault (ASCF), East Anatolian and Dead Sea Fault Zones, the large faults that form the edges of the African, Anatolian, Cyprus and Arabian Plates, all produce large earthquakes, which have decimated Hatay repeatedly. Near Samandağ, Hatay, differential vertical displacement on the ASCF has uplifted the southeastern side relative to northwestern side, producing large fault scarps that parallel the Asi (Orontes) River. Tectonic uplift coupled with Quaternary sealevel fluctuations has produced several stacked marine terraces stranded above current sealevel. This study dated 24 mollusc samples from 10 outcrops on six marine terraces near Samandağ electron spin resonance (ESR). Ages were calculated using time-averaged and volumetrically averaged external dose rates, modelled by assuming typical water depths for the individual species and sediment thicknesses estimated from geological criteria. Uplift rates were then calculated for each fault block. At all the Mağaracık terraces, the dates suggest that many shells were likely reworked. On the 30 m terrace at Mağaracık IV (UTM 766588-3999880), Lithophagus burrows with in situ shells cross the unconformity. One such shell dated to 62 ± 6 ka, setting the minimum possible age for the terrace. For all the Mağaracık terraces at ∼30 m above mean sealevel (amsl), the youngest ages for the reworked shells, which averaged 60 ± 3 ka for six separate analyses, sets the maximum possible age for this unit. Thus, the terrace must date to 60-62 ± 3 ka, at the MIS 3/4 boundary when temperatures and sealevels were fluctuating rapidly. Older units dating to MIS 7, 6, and 5 likely were being eroded to supply some fossils found in this terrace. At Mağaracık Dump (UTM 765391-4001048), ∼103 m amsl, Ostrea and other shells were found cemented in growth position to the limestone boulders outcropping there <2.0 m above a wave-eroded notch. If the oysters grew at the same time as the wave-cut notch and the related terrace, the date, 91 ± 13 ka, for the oysters, this fault block has been uplifted at 1.19 ± 0.15 m ky(-1), since MIS 5c. At Samandağ Kurt Stream at 38 m amsl, molluscs were deposited fine sandy gravel, which was likely formed in a large tidal channel. Four molluscs averaged 116 ± 5 ka. If these molluscs have not been reworked, this fault block has uplifted at 0.34 ± 0.05 m ky(-1) since the MIS 5d/5e boundary. The differences in these uplift rates suggests that at least one, and possibly two, hitherto undiscovered faults may separate the Mağaracık Dump site from the other Mağaracık sites and from the Samandağ Kurt Stream site.