Analytical and numerical modelling of air trapping during wetting of unsaturated soils

Acta Geotechnica - At high values of degree of saturation, the apparent soil water retention curve (SWRC) measured in a wetting test in the laboratory may differ from the true SWRC, because of the...     

A Palaeoenvironmental Investigation of Two Prehistoric Burnt Mound Sites in Northern Ireland

This paper provides a summary of the palaeoenvironmental evidence from a spread of late Mesolithic burnt material and two late Neolithic to early Bronze Age burnt mounds. The burnt mounds were up to 10 m diameter, had an amorphous shape, and were consistently less than 0.8 m thick. Monoliths were collected from two sites, Ballygawley and Roughan, in Co. Tyrone, Northern Ireland. This provided an opportunity to use a detailed palaeoecological approach for the first time to investigate the use and function of burnt mounds. Pollen, non‐pollen palynomorphs, micro‐ and macroscopic charcoal were used to place these features within their environmental context, and to establish if such an approach could provide further insights into their function. The palynological results shared similar characteristics: high microscopic charcoal values, repetitive fluctuations in tree and shrub taxa, increased Sphagnum, and the presence of non‐pollen palynomorphs (NPPs) HdV‐114 and HdV‐146, all of which could be diagnostic indicators of burnt mounds in palynological records. While the data do not allow us to ascribe a specific function for the burnt mounds, their environmental setting is discussed. A “see‐saw” pattern of arboreal pollen, combined with the macroscopic charcoal data, indicate possible species selection and management of local woodland for fuelwood.     

Isotopic Evidence for Long‐Distance Mammal Procurement,Chaco Canyon,New Mexico,USA

Previous research on the prehistoric communities of Chaco Canyon, New Mexico (ca. A.D. 800–1250) provides evidence of an extensive procurement system of nonlocal food and economic goods. In this paper, we use oxygen and strontium isotope analyses to establish whether animal protein followed a similar pattern. We contextualized our isotopic analyses of the archaeofaunas from recent excavations at Pueblo Bonito with data on modern faunas across an area of approximately 100,000 km² around the site. Our results show that most archaeological deer, rabbits, and prairie dogs were obtained from >40 km away from Pueblo Bonito with the latter two likely being garden hunted. The Chuska Mountains west of Chaco Canyon and more distant San Juan Mountains to the north were the main source areas. These results closely align with previous results on architectural wood, corn, and other key resources. The importation of small game animals suggests that the local supplies could not meet the needs of the community. Long‐distance meat procurement may have been embedded within a more complex network of ritual‐goods exchange or tribute that helped to offset the transport costs. Resource depletion may have contributed to the eventual abandonment of the region during the Medieval Warm Period.     

Characterization of Mason Gully (H5): The second recovered fall from the Desert Fireball Network

Mason Gully, the second meteorite recovered using the Desert Fireball Network (DFN), is characterized using petrography, mineralogy, oxygen isotopes, bulk chemistry, and physical properties. Geochemical data are consistent with its classification as an H5 ordinary chondrite. Several properties distinguish it from most other H chondrites. Its 10.7% porosity is predominantly macroscopic, present as intergranular void spaces rather than microscopic cracks. Modal mineralogy (determined via PS‐XRD, element mapping via energy dispersive spectroscopy [EDS], and X‐ray tomography [for sulfide, metal, and porosity volume fractions]) consistently gives an unusually low olivine/orthopyroxene ratio (0.67?0.76 for Mason Gully versus ~1.3 for typical H5 ordinary chondrites). Widespread “silicate darkening” is observed. In addition, it contains a bright green crystalline object at the surface of the recovered stone (diameter ≈ 1.5 mm), which has a tridymite core with minor α‐quartz and a rim of both low‐ and high‐Ca pyroxene. The mineralogy allows the calculation of the temperatures and ?(O₂) characterizing thermal metamorphism on the parent body using both the two‐pyroxene and the olivine‐chromite geo‐oxybarometers. These indicate that MG experienced a peak metamorphic temperature of ~900 °C and had a similar ?(O₂) to Kernouvé (H6) that was buffered by the reaction between olivine, metal, and pyroxene. There is no evidence for shock, consistent with the observed porosity structure. Thus, while Mason Gully has some unique properties, its geochemistry indicates a similar thermal evolution to other H chondrites. The presence of tridymite, while rare, is seen in other OCs and likely exogenous; however, the green object itself may result from metamorphism.     

Soils at the hyperarid margin: The isotopic composition of soil carbonate from the Atacama Desert, Northern Chile

We evaluate the impact of exceptionally sparse plant cover (0-20%) and rainfall (2-114 mm/yr) on the stable carbon and oxygen composition of soil carbonate along elevation transects in what is among the driest places on the planet, the Atacama Desert in northern Chile. δ¹³C and δ¹⁸O values of carbonates from the Atacama are the highest of any desert in the world. δ¹³C (VPDB) values from soil carbonate range from −8.2‰ at the wettest sites to +7.9‰ at the driest. We measured plant composition and modeled respiration rates required to form these carbonate isotopic values using a modified version of the soil diffusion model of [Cerling (1984) Earth Planet. Sci. Lett.71, 229-240], in which we assumed an exponential form of the soil CO₂ production function, and relatively shallow (20-30 cm) average production depths. Overall, we find that respiration rates are the main predictor of the δ¹³C value of soil carbonate in the Atacama, whereas the fraction C₃ to C₄ biomass at individual sites has a subordinate influence. The high average δ¹³C value (+4.1‰) of carbonate from the driest study sites indicates it formed—perhaps abiotically—in the presence of pure atmospheric CO₂.δ¹⁸O (VPDB) values from soil carbonate range from −5.9‰ at the wettest sites to +7.3‰ at the driest and show much less regular variation with elevation change than δ¹³C values. δ¹⁸O values for soil carbonate predicted from local temperature and δ¹⁸O values of rainfall values suggest that extreme (>80% in some cases) soil dewatering by evaporation occurs at most sites prior to carbonate formation. The effects of evaporation compromise the use of δ¹⁸O values from ancient soil carbonate to reconstruct paleoelevation in such arid settings.     

A reconstruction of Quaternary pluvial environments and human occupations using stratigraphy and geochronology of fossil‐spring tufas,Kharga Oasis,Egypt

We carried out a geologic survey and a preliminary archaeological survey of four fossil‐spring tufa localities in Kharga Oasis, Egypt, to constrain the timing of pluvial episodes in the Western Desert, and to document prehistoric occupation contemporaneous with times of increased rainfall. Uranium‐series dating of the tufas confirms that at least five episodes of tufa deposition are represented in Kharga, although not every event is represented at each locality. Across the region studied, tufas were most frequently deposited as part of a fluvial barrage system, characterized by terraced, vegetated pools impounded by arcuate tufa dams and separated by small waterfalls. Available water resources during pluvial phases would have included not only spring‐fed streams but also small freshwater lakes. While Earlier Stone Age (ESA) and Middle Stone Age (MSA) lithic artifacts may be found either as surficial lags on tufas, or, less commonly, encased within tufas, Epipalaeolithic and Neolithic artifacts are generally found in or on silts within surface deflation depressions in the tufas, principally at Wadi Midauwara. © 2004 Wiley Periodicals, Inc.     

A principal component analysis approach to assess CHIRPS precipitation dataset for the study of climate variability of the La Plata Basin,Southern South America

Natural Hazards - This article assesses the consistency of the satellite precipitation estimate CHIRPS v.2 to describe the spatiotemporal rainfall variability in the La Plata Basin (LPB), the...     

Process-oriented modeling studies of the 5500-km-long boundary flow off western and southern Australia

While the unique character of the coastal current system off the western and southern coasts of Australia has been recognized, this vast 5500-km-long boundary flow has been studied far less than other current systems of the world. Recent observational studies from satellite altimetry and climatology are consistent with a continuous current extending from its origin at the North West Cape to the southern tip of Tasmania. To date, coastal modeling studies have focused on either the western Australian coast to Esperance or on southern Australia. There has been no process-oriented modeling study of the entire region that would allow the systematic exploration of the two independent forcing mechanisms (i.e., wind-forcing and thermohaline gradients) and their interactions that have been noted to act in a synergistic manner to maintain the longest continuous coastal current system in the world.