Bonnie A.B. Blackwell

Uranium series dating of travertine from archaeological sites, Nahal Zin, Israel

AT present, absolute dates of occupation can readily be determined for prehistoric sites no older than about 40,000 yr BP using conventional 14C techniques. Ages of older sites can be obtained with the K–Ar method, but only where volcanic deposits are interstratified with the archaeological deposits. The majority of Middle and Lower Palaeolithic sites contain no volcanic deposits. However, many of these sites are associated with synchronously deposited beds of calcium carbonate, occurring either as tufa mounds left by now extinct springs, or as layers of travertine (speleothem) in the mouths of formerly inhabited caves. We show here that such calcareous deposits can be dated by the 230Th–234U method, as long as they are relatively impermeable and free of detritus; ages in the range 5,000–400,000 yr BP are obtainable with a precision of 5–10%. When the carbonate is deposited, it invariably contains traces of uranium but essentially no thorium. Its age can be obtained from the extent to which 230Th has grown into radioactive equilibrium with its parent 234U. The technique of radiochemical analysis is given in ref. 1. The 230Th–234U method has been found to be less reliable for the dating of molluscs2; although it has also been applied to the dating of bones3, the method has often yielded contradictory results, probably attributable to continuous diffusion of radionuclides through the bone during burial4. Some permeable, very fine-grained tufas have also given poor results in earlier studies5; however, careful choice of dense, impermeable, coarsely crystalline travertines generally yields dates that are mutually consistent and coherent with other geochronological tests6.

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.

The geology and morphology of the Antakya Graben between the Amik Triple Junction and the Cyprus Arc

In southeastern Turkey, the NE-trending Antakya Graben forms an asymmetric depression filled by Pliocene marine siliciclastic sediment, Pleistocene to Recent fluvial terrace sediment, and alluvium. Along the Mediterranean coast of the graben, marine terrace deposits sit at different elevations ranging from 2 to 180 m above present sea level, with ages ranging from MIS 2 to 11. A multisegmented, dominantly sinistral fault lying along the graben may connect the Cyprus Arc in the west to the Amik Triple Junction on the Dead Sea Fault (DSF) in the east. Normal faults, which are younger than the sinistral ones, bound the graben’s southeastern margin. The westward escape of the continental İskenderun Block, delimited by sinistral fault segments belonging to the DSF in the east and the Eastern Anatolian Fault in the north caused the development of a sinistral transtensional tectonic regime, which has opened the Antakya Graben since the Pliocene. In the later stages of this opening, normal faults developed along the southeastern margin that caused the graben to tilt to the southwest, leading to differential uplift of Mediterranean coastal terraces. Most of these normal faults remain active. In addition to these tectonic movements, Pleistocene sea level changes in the Mediterranean affected the geomorphological evolution of the area.

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.

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.

Did Middle Stone Age Khargan Peoples Leave Structural Features? ‘Site J’, The Forgotten Settlement of the ‘Empty Desert’, Kharga Oasis, Egypt: 1933 and 2011

G. Caton-Thompson and E. W. Gardner designated new Pleistocene cultural units at Kharga Oasis in the 1930’s: both were originally termed ‘pre-Sebilian’, but were later locally named the ‘Levalloiso-Khargan’ and ‘Khargan’ industries. High on the Bulaq scarp face, a puzzling cluster of stone ‘alignments’ was discovered in 1931–32, with a reported, but discounted, association with ‘Levalloiso-Khargan’ artefacts. Gardner excavated some features in 1933. Members of the Kharga Oasis Prehistory Project relocated ‘Site J’ in January 2011, and verified the reported Khargan associations with the features. In 2008, the project found structural features associated with Khargan artefacts in the northern Gebel Yebsa survey area, confirming earlier finds in the southern oases of Kurkur and Dungul. Evidence there, and that found in Kharga and Dakhleh oases, is now designated as the Khargan Complex. The associated built stone features of the included cultural units appear to be unique in Late Pleistocene Africa, especially at Bulaq.

Amino Acid Racemization (AAR) Dating and Analysis in Lacustrine Environments

Amino acid racemization (AAR) dating depends on the natural diagenesis of organic components in proteins within fossils and in sediment containing organic matter. Unlike radiometric dating (e.g., etc.), this process depends on time, temperature, and, for some fossils, other paleoenvironmental conditions near the sample. Therefore, the process must be modelled extensively under various environmental conditions before it can be applied universally. If AAR does not function well as a dating technique for some fossil tissues, this reliance on environmental conditions may permit other applications that can provide important paleoenvironmental data. This chapter will concentrate on potential limnological applications, illustrated where possible by lacustrine examples. It necessarily omits most applications in non-limnological settings, although Table I does list references for many applications for readers interested in other uses. Other reviews (e.g., Rutter & Blackwell, 1995; Wehmiller & Miller, 1990) offer more general coverage. Two other important references are The Biogeochemistry of Amino Acids (Hare et al., 1980) and Perspectives in Amino Acid and Protein Geochemistry from the 1998 festschrift for Ed Hare (Goodfriend et al., 2000).