Naomi Porat

Desert pavement-coated surfaces in extreme deserts present the longest-lived landforms on Earth

All exposed rocks on Earth’s surface experience erosion; the fastest rates are documented in rapidly uplifted monsoonal mountain ranges, and the slowest occur in extreme cold or warm deserts—millennial submeterscale erosion may be approached only in the latter. The oldest previously reported exposure ages are from boulders and clasts of resistant lithologies lying at the surface, and the slowest reported erosion rates are derived from bedrock outcrops or boulders that erode more slowly than their surroundings; thus, these oldest reported ages and slowest erosion rates relate to outstanding features in the landscape, while the surrounding landscape may erode faster and be younger. We present erosion rate and exposure age data from the Paran Plains, a typical environment in the Near East where vast abandoned alluvial surfaces (10 2 –10 4 km 2 ) are covered by well-developed desert pavements. These surfaces may experience erosion rates that are slower than those documented elsewhere on our planet and can retain their original geometry for more than 2 m.y. Major factors that reduce erosion converge in these regions: extreme hyperaridity, tectonic stability, fl at and horizontal surfaces (i.e., no relief), and effective surface armoring by a clast mosaic of highly resistant lithology. The 10 Be concentrations in amalgamated desert pavement chert clasts collected from abandoned alluvial surfaces in the southern Negev, Israel (representing the Sahara-Arabia Deserts), indicate simple exposure ages of 1.5–1.8 Ma or correspond to maximum erosion rates of 0.25–0.3 m m.y. –1 . The 36

Radiometric dating of the Earlier Stone Age sequence in Excavation I at Wonderwerk Cave, South Africa: preliminary results

We present here the results of 44 paleomagnetic measurements, and single cosmogenic burial and optically stimulated luminescence ages for the Earlier Stone Age deposits from Wonderwerk Cave, Northern Cape, South Africa. The resulting paleomagnetic sequence: N>R>N>R>N constrains the Earlier Stone Age strata in this part of the site to between approximately 0.78-1.96 Ma. A single cosmogenic date of approximately 2.0 Ma from the base of the section offers some corroboration for the paleomagnetic sequence. Preliminary results indicate that the small lithic assemblage from the basal stratum may contain an Oldowan facies. This is overlain by several strata containing Acheulean industries. The preliminary radiometric dates reported here place the onset of the Acheulean at this site to approximately 1.6 Ma, which is roughly contemporaneous with that of East Africa.

Paleoseismic evidence for time dependency of seismic response on a fault system in the southern Arava Valley, Dead Sea rift, Israel

The Elat fault system in the southern Arava Valley (Dead Sea rift, Israel) is a complex fault zone, characterized by marginal normal faults and central sinistral strikeslip faults. Paleoseismic evidence shows that the Elat fault system has generated at least 15 earthquakes of magnitudes (M) larger than 6 during the late Pleistocene and the Holocene. At least two branches of the fault zone were tectonically active simultaneously, indicating that the seismic response over a period of 80 k.y. was time and space dependent. Late Pleistocene earthquakes displaced the surface by 1‐1.5 m; their magnitudes were between M 6.7 and M 7, and their average recurrence interval was 2.8 6 0.7 k.y. Movements along the fault system in the Holocene had a higher frequency and a recurrence interval of 1.2 6 0.3 k.y., but resulted in smaller displacement amounts (0.2‐1.3 m) and smaller earthquake magnitudes (M 5.9‐M 6.7). Historical records document the last seismic event along the Elat fault zone at ;1000 yr ago. The decrease in tectonic activity with time is inferred from the concentration of offset along the fault segments in the central part of the Elat fault zone and the decreased seismicity in the eastern and western margins. The magnitude range determined for the central zone (M 6.1‐M 6.7) was likely not high enough to activate the marginal faults. The average slip rate on the normal faults is 0.2 mm/yr. However, the slip rate has changed through time on different fault segments in the active wide shear zone and between clusters of events related to the same segment. The event-specific slip rates, therefore, have varied from 0.1 to 0.3 mm/ yr. The decrease in earthquake magnitudes with time, combined with the observations that the last large event occurred in A.D. 1068 and that no microseismicity has been detected during the past 15 yr, might signal locking of the Elat fault zone. This effect, if true, may result from episodic global reorganization of the system’s mode of strainenergy release, reflected in the configurational entropy of stress states on the fault. These results have significant implications for seismic hazard assessment in the southern Arava Valley, southern Israel, and underscore the possibility that the Elat fault may be a site of major earthquakes in the near future.

Mode and timing of kurkar and hamra formation, central coastal plain, Israel

ABSTRACT Porat, N., Wintle, A.G., Ritte, M. 2003. Mode and timing of kurkar and hamraformation, central coastal plain, Israel. Isr. J. Earth Sci. 53: 13–25. Kurkar ridges along the coastal plain of Israel are composed of alternating calcareousaeolianite (kurkar) and paleosol (hamra) units. Precise infrared-stimulated lumin-escence dating on alkali feldspars from both types of sediment confirms that all theunits comprising the most westerly kurkar ridge in the central coastal plain weredeposited during the last 65 ka. Calculated rates of accumulation for the kurkar give1–7 m/1000 years, with thick beds being deposited over periods as short as 2000–3000 years. On the other hand, accumulation rates for the hamra are at least one orderof magnitude lower, about 0.1 m/1000 years, implying long periods of relativeenvironmental stability. When these results are combined with measurements of thecarbonate content of each unit, it appears that high carbonate content alone is notsufficient for kurkar formation, but a high accumulation rate is essential. Thus thegoverning factor that controls the fate of a deposited aeolianite, whether it will cementinto kurkar or undergo pedogenesis, is the rate of accumulation.

Green stone beads at the dawn of agriculture

The use of beads and other personal ornaments is a trait of modern human behavior. During the Middle and Upper Paleolithic periods, beads were made out of shell, bone, ivory, egg shell, and occasionally of minerals. During the transition to agriculture in the Near East, stone, in particular green stone, was used for the first time to make beads and pendants. We observed that a large variety of minerals of green colors were sought, including apatite, several copper-bearing minerals, amazonite and serpentinite. There seems to be an increase with time of distance from which the green minerals were sought. Because beads in white, red, yellow, brown, and black colors had been used previously, we suggest that the occurrence of green beads is directly related to the onset of agriculture. Green beads and bead blanks were used as amulets to ward off the evil eye and as fertility charms.

Estimating the ages of fault scarps in the Arava, Israel

Abstract Systematic age estimations for the numerous fault scarps that rupture the alluvial fans in the southern Arava valley, Israel, are rare or nonexistent. Here we estimate the morphologic ages of several of these faults by the fault scarp degradation method and show that the ages agree well with ages estimated by the independent, earlier soil-geomorphic studies. The values we use for the coefficient of diffusion for the fault scarp degradation process are calibrated by a few numerical ages. These ages were determined by the Infrared Stimulated Luminescence (IRSL) method on one of the fault scarps and are the only numerical ages in the region. The morphologic ages are all in a correct stratigraphic order and in agreement with field stratigraphic relationships determined by earlier studies. They indicate that the studied fault scarps range in age from the latest Pleistocene to very recent times. The most recent fault scarps, which were analyzed are less than 2000 years old and perhaps much younger. They indicate that at least two earthquakes with magnitude > 6.5 have affected southern Israel and Jordan during that period. It is emphasized that so far we have studied only a limited number of fault scarps and therefore the number of large earthquakes during the last one to two millennia is a minimum.

Reconstructing the history of sediment deposition in caves: A case study from Wonderwerk Cave, South Africa

We applied cosmogenic isotope burial dating, magnetostratigraphy, and grain-size distribution analysis to elucidate the history of the sedimentary sequence, composed of fine quartz sands and silts, of Wonderwerk Cave, located on the southern edge of the Kalahari Desert, South Africa. The source for the quartz sand is the Kalahari sand dunes, presently located ∼100 km to the north of the cave. Field observations and grain-size analysis suggest a sediment transport scenario that includes eolian transport of Kalahari sand, abraded to a size of 70–100 µm, to the Kuruman Hills, temporary storage on the hill slopes and valleys surrounding Wonderwerk Cave, and later transport and deposition inside the cave. Our results suggest simple burial ages for sediments from both the front and back of the cave that range between 2.63 ± 0.17 Ma and 1.56 ± 0.10 Ma following initial exposure of 310–620 k.y. However, 26 Al/ 10 Be ratios of 3.98 ± 0.24 and 4.08 ± 0.22 measured in a sand sample collected from the surface outside the cave may imply an initial burial signal equivalent to 0.78 ± 0.15 Ma, thus reducing the possible age range of the buried samples to between 1.85 ± 0.23 and 0.78 ± 0.18 Ma. The paleomagnetic results for the front of the cave gave a polarity sequence of N > R > N||N, where N indicates normal polarity, and R indicates reverse polarity. This sequence can be correlated with both the older and younger cosmogenic burial age ranges. The correlation suggests that in the cave front, cosmogenic burial ages and the acquisition of stable remanent magnetization were not significantly affected by chemical and physical processes and that postburial production of cosmogenic isotopes was insignificant. In contrast, at the back of the cave, the paleomagnetic polarity sequence of R > N cannot be correlated with the cosmogenic burial ages, since the temporal gap between the initial penetration of the sediment into the cave and the final acquisition of a stable remanent magnetization may have been long (∼10 5 yr), and the single polarity transition can be correlated to any reverse-normal transition that occurred during the Quaternary. This highlights the need for caution when cosmogenic burial ages and paleomagnetic sequences are compared. The buried sediments in Wonderwerk Cave show similar grain-size distributions to the fine sand sediment presently exposed at the surface in the vicinity of the cave. Furthermore, calculated preburial 10 Be concentrations for the buried sediment are similar to those measured in sediment outside the cave. These similarities suggest that the environmental conditions and rates of geomorphic processes that persisted during sand deposition in Wonderwerk Cave during the late Pliocene and early Pleistocene may have been similar to those currently experienced in the southern Kalahari, the Kuruman Hills, and the western Ghaap Plain. These conditions favor the transport of fine-grained quartz sand to the vicinity of the cave.

Magnetostratigraphy of the Evron Member--implications for the age of the Middle Acheulian site of Evron Quarry.

The Institute of Earth Sciences, The Hebrew University, Jerusalem 91904, Israel The Geophysical Institute of Israel, P.O.Box 182, Lod 71100, Israel The Geological Survey of Israel, 30 Malkhe Israel St., Jerusalem 95501, Israel The Zinman Institute of Archaeology, The University of Haifa, Haifa 31095, Israel Department of Evolution, Systematics and Ecology, The Hebrew University, Jerusalem 91904, Israel

Archaeological investigations and OSL dating of terraces at Ramat Rahel, Israel

Abstract Dating terraces, the most prominent feature of the agricultural landscape in many parts of the world, is a problem for archaeologists. This study presents an interdisciplinary approach that combines archaeological survey and excavations with direct sediment dating of terrace fill using Optically Stimulated Luminescence (OSL). The study focuses on Ramat Rahel, a multi-period site located in the southern outskirts of modern Jerusalem, Israel, where, on a defined terraced slope chosen for a small-scale landscape archaeology project, three main phases of terrace construction and use were identified. The earliest phase dates to the Late Byzantine/Early Islamic period, the second to medieval times, and the last to the Ottoman period. The results enable a comprehensive reconstruction of the changing local landscape through time and demonstrate the validity of OSL, when combined with archaeological investigations, as a reliable method for terrace dating.

ESR dating of tooth enamel: comparison with 230Th234U speleothem dates at La Chaise-de-Vouthon (Charente), France

Abstract One way to assess a new dating methods reliability is by comparing its results with those from well established, independent techniques. A controlled test of the electron spin resonance (ESR) dating method as it is currently being applied to teeth was attempted for the time range 100–250 ka, beyond that of 14 C, at the archaeological site of La Chaise-de-Vouthon (Charente, France). Although absent in modern enamel, a single ESR signal with g = 2.0018 in fossil tooth enamel hydroxyapatite increases in amplitude with increasing irradiation doses. ESR ages are derived from the ratio of the AD, the radiation dose needed to produce the observed ESR signal, relative to the natural, environmental dose rate (ED) experienced by the tooth after deposition. Since the age depends on the uranium (U) uptake history assumed, three ages are calculated assuming: (1) early U uptake (EU); (2) continuous (linear) uptake (LU); (3) recent uptake (RU). Generally, the LU age agrees best with known ages determined by other methods, although the RU model is better for some teeth. ESR dating assumes that the fossil has not suffered recrystallization or significant diagenetic alteration. In the preliminary test, three teeth were dated. In Bourgeois-Delaunay, a bovid molar associated with Palaeolithic artefacts was collected from layers dated at 101 ± 12 to 114 ± 7 ka by 230 Th 234 U dating of the over- and underlying stalagmitic floors. From Suard, two Equus teeth were collected from beneath a stalagmitic floor dating 112 ± 12 ka. ESR dating teeth significantly underestimated the true age for the teeth: the mean ESR ages range from 37 to 94 ka with standard errors of 2–6 ka, and good replicability. Although more teeth at La Chaise need to be tested to ascertain that the underestimation does not result from random variation commonly seen among teeth within one unit, the consistent underestimation suggests a fault in one of the assumptions underlying the dating method. The most obvious source of error lies in the difficulty in modelling the external γ dose. Only U leaching, not incorrectly modelled U uptake, would cause the underestimation. Diagenetic alteration may also cause anomalous fading, thermal instability, variation in k , or ESR signal suppression. More study into the effects of diagenesis alteration on enamel ESR signals is needed, as is a reevaluation of the mean signal life and α efficiency for several more enamel samples.