Southwestern Desert Research Articles

Chemical mass balance source apportionment of fine and PM<sub>10</sub> in the Desert Southwest, USA

The Desert Southwest Coarse Particulate Matter Study was undertaken in Pinal County, Arizona, to better understand the origin and impact of sources of fine and coarse particulate matter (PM) in rural, arid regions of the U.S. southwestern desert. The desert southwest experiences some of the highest PM10 mass concentrations in the country. To augment previously reported results, 6-week aggregated organic speciation data that included ambient concentrations of n-alkanes, polycyclic aromatic hydrocarbons, organic acids, and saccharides were used in chemical mass balance modeling (CMB). A set of re-suspended soil samples were analyzed for specific marker species to provide locally-appropriate source profiles for the CMB analysis. These profiles, as well as previously collected plant and fungal spore profiles from the region, were combined with published source profiles for other relevant sources and used in the CMB analysis. The six new region-specific source profiles included both organic and inorganic species for four crustal material sources, one plant detritus source, and one fungal spore source. Results indicate that up to half of the ambient PM2.5 was apportioned to motor vehicles with the highest regional contribution observed in the small urban center of Casa Grande. Daily levels of apportioned crustal material accounted for up to 50% of PM2.5 mass with the highest contributions observed at the sites closest to active agricultural areas. Apportioned secondary PM, biomass burning, and road dust typically contributed less than 35% as a group to the apportioned PM2.5 mass. Crustal material was the primary source apportioned to PM10 and accounted for between 50–90% of the apportioned mass. Of the other sources apportioned to PM10, motor vehicles and road dust were the largest contributors at the urban and one of the rural sites, whereas road dust and meat cooking operations were the largest contributors at the other rural site.

Cenozoic rivers of northeast Africa: Evidence of trans-Saharan drainage

Radar imagery of the Sahara of Egypt and eastern Libya has dramatically changed previous concepts in regard to long term aridity of this region, revealing an extensive network of buried fluvial channels documenting the river systems that developed in the proto-Sahara during the Late Paleogene and Neogene, following the early Eocene regression of the Mediterranean Sea, and prior to Pleistocene aridification. The fall in base level associated with the end-Miocene Messinian desiccation of the Mediterranean led to deep down-cutting and extension of river systems throughout much of North Africa and South Europe. The deep, infilled canyons beneath the modern Rhone and Nile are well known, but the radar imagery identifies other deep canyons under the North African Sahara that are now invisible. In eastern Libya, drainage from Serir Tebisti (Tebisti Massif) into the Mediterranean via the Sirt Basin was channeled by two main rivers, the Sahabi in the west and the Kufra in the east; these were subsequently united in the Early Pliocene when the latter captured the former. The Gilf River was another important channel that drained north from the Uweinat-Gilf highland in southwest Egypt, in a system that may have been connected with the Kufra during the Neogene and enabling fish to move from the presently isolated Chad Basin to northern Libya and Egypt. The interplay of these north-flowing rivers and the constant northward retreat of the Mediterranean shoreline from Oligocene onward resulted in deposits of fluvial and marine sedimentation in every possible combinaton that have been described by many authors in the region between the Tebisti and the present Mediterranean shoreline. Prior to the establishment of the Nile, a southwestward drainage, the Qena River, was initiated by Oligocene uplift and lateral faulting along the Red Sea shoulder of the East African Rift. This river discharged into a distributive network known as the Radar Rivers near latitude 23° 30'N in the Southwestern Desert. It has been suggested that waters from the Qena River continued to flow southwestward to the Atlantic Ocean, in what is known as Trans African Drainage System (TADS).

The first evidence of paleo-wildfire from the Campanian (Late Cretaceous) of North Africa

Although the fossil record of plant macro- and mesofossils, including fossil charcoal, is patchy geographically and temporally, such remains play an important role for the interpretation of paleoenvironmental and paleoclimatic developments in the continental realm. In Egypt, previous palynological studies on the Upper Cretaceous (Campanian) deposits suggested presence of lush subtropical forests, dominated by angiosperms and pteridophytes, which developed under warm and wet climatic conditions. In the present study, the occurrence of paleo-wildfires during the Late Cretaceous (Campanian) is presented for the first time, based on samples from a surface exposure in the vicinity of the Baris Oasis, south Western Desert, Egypt. Macroscopic charcoal was collected and subsequently analyzed under a stereomicroscope and scanning electron microscope (SEM). The charred wood remains were identified as belonging to gymnosperms, which were important components of the North African paleoflora during the Cretaceous. These charcoal remains represent the first verified occurrence of paleo-wildfires in Africa during the Campanian.

Reply to Ruban and Zorina’s (2015) discussion on the paper: “Danian/Selandian unconformity in the central and southern Western Desert of Egypt” by S. Farouk and E. El-Sorogy (2015; Journal of African Earth Sciences, 103, 42–53)

A global sea-level fall during the Latest Danian Event (LDE) is observed in a regional and worldwide context in widely-separated locations with different tectonic and depositional settings (Clemmensen and Thomsen, 2005). A similar trend in the central and south-western Desert of Egypt is synchronous with a weak tectonic event, which results in the absence of the upper portion of the regressive phase during the LDE, of the P3b Subzone which is seen in “tectonically stable” areas. This weak tectonic event is linked to more intense deformation of the Syrian Arc (Swell) of the Bahariya Oasis, which is synchronous with the global Laramide orogeny. Over the entire Dakhla Basin, the similar vertical sequence tracks can be traced across the area and indicate relative sea-level changes rather than shoreline shifts, and consequently reflect a eustatic origin. Correlation with the Arabian Plate charts (Sharland et al., 2001, 2004; Haq and Al-Qahtani; 2005; Simmons et al., 2007) do not match with the regional reconstruction of Farouk and El-Sorogy (2015) because these Arabian Plate charts are based on mega-sequences controlled by a dramatic tectonic event with erosion along the northeast Arabian plate (Haq and Al-Qahtani, 2005). Recently, after recalibration of many eustatic charts the conclusions made by Farouk and El-Sorogy (2015) concerning the late Danian sea-level fall (e.g., Haq et al., 1987; Hardenbol et al., 1998; Lüning et al., 1998; Guasti et al., 2005; Clemmensen and Thomsen, 2005; Schmitz et al., 2011; Gradstein et al., 2012) have been confirmed.

The Climate and Its Impacts on Egyptian Civilized Heritage: Ei-Nadura Temple in El- Kharga Oasis, Western Desert of Egypt As a Case Study

Abstract Undoubtedly, El-Kharga Oasis monumental sites are considered an important part of our world´s cultural heritage in the South Western Desert of Egypt. These sites are scattered on the floor of the oasis representing ancient civilizations. The Roman stone monuments in Kharga represent cultural heritage of an outstanding universal value. Such those monuments have suffered weathering deterioration. There are various elements which affect the weathering process of stone monuments: climate conditions, shapes of cultural heritages, exposed time periods, terrains, and vegetation around them, etc. Among these, climate conditions are the most significant factor affecting the deterioration Archeological sites in Egypt. El- Kharga Oasis belongs administratively to the New Valley Governorate. It is located in the southern part of the western desert of Egypt, lies between latitudes 22º30'14" and 26º00'00" N, and between 30º27'00" and 30º47'00" E. The area of El Kharga Oasis covers about 7500 square kilometers. Pilot studies were carried out on the EI-Nadura Temple, composed of sandstones originating from the great sand sea. The major objective of this study is to monitor and measure the weathering features and the weathering rate affecting the building stones forming El- Nadora Roman building rocks in cubic cm. To achieve that aims the present study used analysis of climatic data such as annual and seasonal solar radiation, Monthly average number of hours of sunshine, maximum and minimum air temperatures, wind speed, which have obtained from actual field measurements and data Meteorological Authority of El-Kharga station for the period 1941 to 2000 (60 years), and from the period 1941-2050 (110 years) as a long term of temperature data. Several samples were collected and examined by polarizing microscopy (PLM), X-ray diffraction analysis (XRD) and scanning electron microscopy equipped with an energy dispersive X-ray analysis system (SEM-EDX). The results were in agreement with the observed values in the study area. The deterioration of El-Nadora temple is above 45 % of original temple (138-161 BC), these deteriorations have occurred not only due to the age of the structures, but also due to the climate elements. It was found that the climate is the most important elements influencing weathering. El-Nadora temple is highly influenced by wind action because it has built on a hill top 180 meter in hyper arid climate and exposed to wind without any obstruction. Finally, El-Nadora Temple has lost about 42.46 % of its original size, and if the rate of deterioration on those rates will disappear the major landmarks, symbols and inscriptions fully in 2150.

Altered granitic rocks, Nusab El Balgum Area, Southwestern Desert, Egypt: Mineralogical and geochemical aspects of REEs

Gabel Nusab El Balgum is located in the northern part of Bir Safsaf Area Southwestern Desert, Egypt (about 600km southwest of Aswan City) and covers an area of about 40km2. A few workers have investigated the Nusab El Balgum Area from the mineralogical and geochemical point of view. The area consists mainly of Devonian sandstone, Permo–Triassic volcanic rocks, altered granitic rocks and post-granitic dykes. The altered granitic rocks (silicified and kaolinized) have undergone several hydrothermal alteration processes and were subjected to different types of alteration (hematitization, carbonatization, kaolinization, sericitization and silicification) and are characterized by extreme enrichment in rare metals (such as Zr, Nb, Y and REEs).Bastnaesite, parisite, fergusonite, columbite, hydrothermal zircon, monazite and xenotime are common in the silicified and kaolinized granites. The silicified granite commonly contains more rare metals than the kaolinized granite. The REEs in Nusab El Balgum granites were introduced by hydrothermal fluids during alteration and occur in carbonate minerals such as bastnaesite (LREE) (CO3) F and parisite Ca (LREE) 2(CO3)3F2.The REE chondrite-normalized patterns of altered granites show an M-type tetrad effect and indicate higher LREEs, negative Ce anomaly (due to alteration by hydrothermal fluids) and negative Eu anomaly.

Electrical and geochemical properties of tufa deposits as related to mineral composition in the South Western Desert, Egypt

The geochemical, petrographical, and electrical properties of rocks are essential to the investigation of the properties of minerals. In this paper we will try to present a study of the A. C. electrical properties of carbonate rock samples and their relation to petrographical and geochemical properties. Samples were collected from four formations from the Bir Dungul area, in the South Western Desert, Egypt. The electrical properties of the samples were measured using a non-polarizing electrode, at room temperature (~28 °C), and at a relative atmospheric humidity of (~45%), in the frequency range from 42 Hz to 5 MHz. The changes in the electrical properties were argued to the change in mineral composition. Generally, the electrical properties of rocks are changed due to many factors e.g., grain size, mineral composition, grain shape and inter-granular relations between grains. The dielectric constant of samples decreases with frequency, and increases with conductor concentration. Also, the conductivity increases with an increase of continuous conductor paths between electrodes. The petrographical and geochemical studies reveal that the deposition of the tufa deposits occurred in shallow lakes accompanied by a high water table, an alkaline spring recharge and significant vegetation cover. Diagenetically, tufa deposits were subjected to early and late diagenesis. Petrography and geochemistry studies indicated that the area of tufa deposits was deposited under the control of bacterial activity. Geochemically, the Sr content indicates that the tufa deposits formed from dissolved bicarbonate under the control of microbes and bacterial activity.

Paleo-tectonic positions of Northeast Africa during Cretaceous–Paleocene: Paleomagnetic study on East Gilf Kebir Plateau basalts [59 Ma], Southwestern Desert, Egypt

The middle/late Paleocene basalts which cover the Late Cretaceous sandstone in the East Gilf Kebir Plateau were sampled for paleomagnetic investigation. The progressive thermal demagnetization revealed that−The hematite component was parallel to the present-day field and the goethite overprint. Its pole is considered as representing recent low-temperature martitization of the magnetite upon exposure to intensive chemical alteration.−The magnetite-anchored component was N–S dual-polarity with shallow equatorial inclinations. Based on its overwhelming existence, this component was considered as the characteristic remanence of the sampled basalt. Its north pole (71.7°N/203.5°E) was considered as representing the geomagnetic field during the eruption of the basalt.The reliability of the East Gilf Kebir basalt (59±1.7Ma) pole was constrained by its comparison with synchronous poles rotated from the main tectonic units using Euler Pole rotation. This basalt pole places NE Africa, along its present N–S azimuth at a far south tropical paleo-latitude. Cairo [30°N], was at paleo-latitude 11.8°N in middle/late Paleocene (59Ma), that is about 18° south to its present-day latitude.Comparing the present pole with the Mansouri ring complex (132±10Ma) Early Cretaceous pole (47°N/259°E) and two poles from the Wadi Natash volcanic field; the alkali basalt (104±7Ma) Middle Cretaceous pole [55°N/250°E] and the trachyte/Phonolite (86–78Ma) Late Cretaceous pole [66.5°N/229°E], a Cretaceous–Paleocene segment [132–59Ma] of the Apparent Polar Wander Path [APWP] of Africa could be traced. These poles can, concurrently, verify the paleo-azimuth and paleo-latitude evolution of the African plate during the Cretaceous and Paleocene.

Sedimentological characteristics of continental sabkha, south Western Desert, Egypt

Continental sabkha is recorded in the extreme middle part of the south Western Desert of Egypt representing one of the most promising areas for sustainable development, especially for agriculture. The geomorphologic units of the area are formed under the influence of structural, lithological, and/or climatic controls. These units include pediplain, depressions, mass-wasted blocks, residual hills, drainage lines, and aeolian landforms. The effective deflation process is reinforced by the lack of protective vegetation cover and the susceptibility of weakly consolidated rocks to wind removal. Different rock units covering the area range in age from Early Cretaceous to Quaternary. Quaternary deposits include playa/sabkha deposits where the continental sabkha is divided into four zones A, B, C, and D. Underground waters coming from the north and east were progressively enriched in solute by interaction with the surrounding sedimentary and igneous rocks. Most of the evaporite minerals grow displacively as a result of evaporative pumping. Mineralogically, the continental sabkha salt complex includes gypsum, natroalunite, tamarugite, bloedite, eugsterite, nitratine, halite, and D’ansite. Some of the major and trace elements (SiO2, Al2O3, Fe2O3, MgO, CaO, Na2O, K2O, as well as Rb, Ba, Zr, Sr, Y, V, and Zn) were measured. The correlation and enrichment of these major and trace elements indicate the origin of the salt complex in the sabkha.

Groundwater Flow Modeling in a Nubian Sandstone Aquifer, South Western Desert, Egypt

Groundwater Flow Modeling in a Nubian Sandstone Aquifer, South Western Desert, Egypt

Relationship between Selected Hydrochemical Parameters in Springs of Najaf Province, Iraq

Several springs exist at the south-western desert of Iraq in Najaf Province at latitude 31°00' - 32°15' and longitude 43°30' - 44°30'. They are almost parallel to Euphrates River on the eastern edge of western desert. General direction for the distribution of springs coincides with that of faults running northwest-southeast. The Hydrogen sulfide, temperature, pH and electrical conductivity were investigated in these springs. The analyses indicated that the concentration of H2S decreased from northwest toward southeast which is attributed to the escape of this gas to the atmosphere during the flow of groundwater near or on the earth surface. The surrounding geologic conditions did not affect the temperature and pH of the springs. Electrical conductivity showed an increase from northwest towards southeast which reflects dissolving more ions from the rocks of the aquifer. The electrical conductivity and hydrogen sulfide concentration had reverse relationship.

WITHDRAWN: Altered granitic rocks, Nusab El Balgum Area, Southwestern Desert, Egypt: Mineralogical and geochemical aspects of REEs

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Petrology and radioactivity of the famous Aswan monumental red granites new occurrence, Gebel Um Shaghir area, South Western Desert, Egypt

The basement rocks of Gebel Um Shaghir area are represented by amphibolites, gneissose granites, and small outcrop of coarse-grained younger red granites. The studied younger red granites have similar characteristics to the famous Aswan monumental red granites, such as morphology, color, mineralogical composition, and crystal size. Petrographically, Um Shaghir granites are coarse- to very coarse-grained and have subhedral granular texture. They are mainly composed of perthitic microcline, microcline, plagioclase, quartz, biotite, and arfvedsonite. Sericite, chlorite, and epidote are secondary minerals, while zircon, titanite, allanite, apatite, garnet, and opaques are accessories. Petrochemically, Um Shaghir red granites are alkaline A-type granites, generated in an extensional within-plate (WPG) environment. The probable origin of these granites is mainly fractional crystallization of calc-alkaline magma. Um Shaghir red granites could be recognized as uraniferous granites, where uranium mobilization post-magmatically could be indicated due to the wide range of eU contents (less than 2 to 21 ppm).

Foraging Populations of Tube Building Termites, Gnathamitermes perplexus (Banks), Associated With Termiticide Experiments in Southern Arizona (Isoptera: Termitidae)

In the southwestern desert region of Arizona, a common non-structure invading species is the tube building termite Gnathamitermes perplexus. It is a valuable species from an ecological point of view due to its role in the decomposition of dead wood in desert environments and its capacity to enrich and aerate vast quantities of soil. Since it has no economic importance, very little is known of the effects of termite control measures on it. However, G. perplexus is likely exposed to termiticides used to manage more damaging termite species with which it co-occurs. Since most common termiticides have relatively generalized modes of action, we hypothesized that G. perplexus populations would decrease significantly as a result of termiticide application. The results reported here are part of a larger study in which we were primarily interested in evaluating foraging termite populations of Heterotermes aureus, associated with circular grids that were treated with termiticides. Termites were collected monthly from 9 plots located at the Santa Rita Experimental Range (Pima Co., AZ) over a 3-year period. Plots were equally and randomly assigned to three treatments: a control and two insecticide treatments of either fipronil (Termidor®, BASF) or chlorfenapyr (Phantom®, BASF). Within the chlorfenapyr (Phantom®) treatment, we saw a significant increase in termite foraging populations after termiticide application. This effect showed a spatial pattern in which more termites were found near the center of plots. However, the number of G. perplexus collected in the fipronil (Termidor®) plots was reduced with respect to controls. This reduction in the number of termites also showed a spatial distribution with the decrease in termite numbers being stronger near the center of plots within the treated zone.

Desert Anuran Occurrence and Detection in Artificial Breeding Habitats

Abstract: One-third of known amphibian populations have become extinct, with habitat loss and degradation being the leading causes in the United States. Site occupancy has been suggested as one of the most effective state variables in describing population declines. The objectives of this study were to determine occupancy estimates of five southwestern desert anurans, accounting for imperfect detection, and to determine the main factors impacting detection. We conducted call and visual surveys on three consecutive nights after rain events at 21 breeding sites for Mexican Spadefoot (Spea multiplicata), Plains Spadefoot (Spea bombifrons), Couch's Spadefoot (Scaphiopus couchii), Great Plains Toad (Anaxyrus cognatus), and Green Toad (Anaxyrus debilis). We used occupancy modeling to estimate the proportion of sites occupied for all species detected during the sampling period. Spea multiplicata and A. debilis were most prevalent, followed by A. cognatus, Sp. bombifrons, and Sc. couchii, respectively. In additi...

Extraction of gadolinium from El-Garra El-Hamra rare-earth cake, South Western Desert, Egypt

The study area of El-Garra El-Hamra is one of the igneous masses located in the southern part of the Western Desert of Egypt. This work has been carried out to investigate the process of gadolinium separation from REEs cake obtained from El-Garra El-Hamra ore concentrate. It is considered as a new approach in the Nuclear Materials Authority of Egypt. Firstly; the optimum leaching conditions achieved are 200 gm/L H2SO4, 1/2 solid/liquid ratio, 4 h agitation time,−125 mesh size and at 90 °C temperature. Then by solvent extraction method using 1 mol/L D2EHPA middle REEs were extracted. The organic extractant was stripped by using 2 mol/L HCl and Gd pregnant solution was obtained. Then, the relevant optimum factors were 0.3 mol/L D2EHPA diluted by kerosene, 10 min contact time, and 4/1 organic/aqueous ratio giving 87 % Gd extraction. Then, the scrubbing of the loaded extractant was by 1 mol/L HCL followed by Gd stripping using 5 M HCl, contact time of 30 min and 1/3 organic/aqueous ratio. The strip solution was subjected to evaporation and little amount was dried to obtain GdCl3 powder having a purity of about 81 % associated with YCl3 4 %.

Petrographic, Radiometric and Paleomagnetic Studies for Some Alkaline Rocks, South Nusab El Balgum Mass Complex, South Western Desert, Egypt

Nusab El Balgum mass complex represents one of the alkaline igneous activities in the south Western Desert of Egypt. Petrographic investigations defined some different rock types in south of the complex represented by alkaline volcanics (pyroclastics [rhyolitic crystal tuffs], spherulitic rhyolites, alkaline rhyolite dykes), sub-volcanic peralkaline granites and structurally controlled mylonitic volcanoclastics. These rocks recorded significant concentrations in terms of the two radioactive elements Th and eU, which displayed considerable spatial variations, especially within the peralkaline granites. The abundance of Th and eU is mainly related to favorable combination of structural and pos-magmatic hydrothermal conditions. Paleomagnetic results give well-defined stable remanent magnetization directions of reliable VGP positions, which are presented and discussed in the context of the African APWP. Rock types, magnetization directions and VGP positions with the corresponding ages are as follows: 1) Rhyolitic crystal tuffs; D/I = 340.0°/—19.4°, α95 = 6.8°; VGP Lat./Long. = 51.4°N/240.5°E, A95 = 5.9° (Late Triassic). 2) Spherulitic rhyolites; D/I = 346.7°/—6.6°, α95 = 3.5°; VGP Lat./Long. = 60.4°N/237.0°E, A95 = 3.0° (Late Triassic/Early Jurassic). 3) Alkaline rhyolite dykes; D/I = 341.3°/16.7°, α95 = 5.4°; VGP Lat./Long. = 67.0°N/262.8°E, A95 = 4.2<span style="fo

Enteric Human Pathogens of Wild Boar, Feral Swine, and Javelina (Order: Artiodactyla)

Artiodactyls are even-toed ungulates that include domestic and wild ruminant herbivores (cattle, sheep, goat, deer, elk), pigs, and javelinas. There is increasing evidence that some wild ungulate species are important reservoirs of enteric human pathogens, and they may contribute to foodborne disease transmission directly through ingestion of undercooked game meat or indirectly via fecal contamination of fresh fruit and vegetable crops or agricultural water sources. To better understand zoonotic risks from feral swine and javelina in the U.S. southwestern desert, we conducted a prevalence survey of Shiga toxin-producing Escherichia coli (STEC) and Salmonella in colonic-fecal samples from animals collected through hunter-harvest or depredation. STEC O157:H7 was detected in feral swine, but not in javelina samples. Salmonella and non-O157 STEC serotypes of potential public health importance were found in both species. The findings underscore the importance of continued public health education efforts to protect hunters from exposure to these pathogens when handling game animals. Fresh fruit and vegetable growers should continue to prevent intrusions by wild and feral animals in the produce production environment to minimize transport of fecal-borne pathogens to crops intended for human consumption.

Images

Images Tony De Los Reyes Click for larger view View full resolution Tony de los Reyes, BORDER THEORY (CALEXICO SUPERMOON 3), 2015 Oil on muslin panel, 29 × 29 in. (Page 4) Click for larger view View full resolution Tony de los Reyes, BORDER THEORY (CALEXICO SUPERMOON 3), 2015 Oil on muslin panel, 29 × 29 in.(Page 5) Click for larger view View full resolution IMAGE (next pages): Tony de los Reyes, BORDER THEORY (INDEFINITE ZONE/BLACK), 2013 Dye and oil on linen, 77 × 116 in. (Page 24) (Page 25) Click for larger view View full resolution IMAGE: Tony de los Reyes, BORDER THEORY (RIO GRANDE/COLORSCALE 9), 2014 Dye, acrylic ink, and oil on linen with painted frame, 15 5/8 × 10 7/8 in. (Page 53) Click for larger view View full resolution Tony de los Reyes, BORDER THEORY (AMBIENT CROSSING/VINCULO AMBIENTAL), 2013 Dye and oil on linen, 60 × 70 1/2 in. (Page 78) Page 79) Click for larger view View full resolution IMAGE: Tony de los Reyes, BORDER THEORY (RIO GRANDE/YELLOW LIGHT), 2013 Dye and oil on linen, 45 × 31 in. Page 97 >> Border Theory Since 2013 I have been producing artwork that deals with issues arising from the US-Mexico border. My work addresses the implications associated with the delineation of this immense geographic space, either by the fortifications of the border wall, the Rio Grande, or sociopolitical transmissions that permeate collateral zones associated with the border. References to the political articulations of space, such as Henri Lefebvre’s statement, “the space of a (social) order is hidden in the order of space,” have influenced me to conceive of the US-Mexico border as a region of tragic architectures and ecstatic pathologies. Ultimately, my work begins to outline heterodoxies in political aesthetics that are tied to specific topographies. To date, the Border Theory series consists almost entirely of paintings that contain fragments of satellite images of the border. Many are completely abstracted, considering the border as hyperbolic zones of tension manifested in the border’s bifurcating line. The chromatic “colorscale” paintings contain similar examples of satellite images, this time with topographic information silk-screened onto the surface. The Calexico Supermoon paintings are works whose images come from personal photographs taken at midnight twenty miles east of Calexico, California, a border city in a rugged part of the south western desert, during the “super moon,” the closest distance between the earth and moon during the year. Here, the traditionally fixed notions of isolated colors are disrupted through the introduction of their complements, creating both attraction and repulsion. These, as well as all the works in the Border Theory series, continue to discuss the role of perception in the apprehension of space. They also reflect the current geopolitical climate, and investigate the interrelatedness of place, identity, and aesthetic production. >> Tony de los Reyes’s previous series was the subject of the exhibition and catalog Chasing Moby-Dick: Selected Works by Tony de los Reyes (2010) at the Santa Barbara Museum of Art, which traveled to the New Britain Museum of American of Art in Connecticut. Reviews and articles have appeared in such publications as Art in America, Artforum.com, X-TRA, Modern Painters, and the Los Angeles Times. De los Reyes received an MFA from the San Francisco Art Institute. He lives and works in Los Angeles. www.tonydelosreyes.com [End Page 98] Click for larger view View full resolution IMAGE: Tony de los Reyes, BORDER THEORY (RIO GRANDE/COLORSCALE 5), 2014 Dye, acrylic ink, and oil on linen with painted frame, 15 5/8 × 10 7/8 in. Page 99 Copyright © 2015 The Johns Hopkins University Press

Early and Middle Holocene Paleoclimates in the South Western Desert of Egypt - The World Before Unification

Abstract In the field seasons of 1990 to 2008 the Combined Prehistoric Expedition conducted an extensive archaeological, archaeozoological, archaeobotanical and geomorphological field work at more than a hundred sites in the Nabta, Kiseiba, El Kortain, Gebal El Beid, Gebel Ramlah and Berget El Sheb Areas, South Western Desert of Egypt. The research has helped to develop a long chronological sequence of Late Glacial and Holocene climatic changes in the region. The climatic sequence has been supported by more than 300 14C and OSL assays that permitted to place most of the climatic events in a firm chronological frame