The Red Sea depositional architecture: insights from 3D modeling

More than half a century of geological and exploration studies have taken place in the Red Sea area, and still very limited information is available to the geological community in regard to the lithological distribution and the stratigraphic architecture. In this study, extensive well data was used to build the first lithologic and stratigraphic 3D models of the entire Red Sea to better understand the lithological distribution. The potential models have been constrained by bathymetric and geophysical data. Studied data demonstrate that up to 5 km of sediments were deposited in the Red Sea. It is mainly comprised of limestones, evaporites, and shales. Our models show that the evaporite body represents more than 70% of the Red Sea succession. In particular, the evaporite succession seems to be well developed in the southern region. Salt dome features are present and developed close to the margins. The models suggest that domal formation did not enable thick carbonate accumulation in some parts of the basin but the carbonate generally follows the evaporite trend. The models help to identify the main controls leading to salt diapir by highlighting the distribution of this body and the geometry of geological structures. Syn-rift faulting and rifting has been one of the most prominent structural features. Complex interplay of tectono-stratigraphic events played a significant role in shaping the stratigraphic evolution of the Red Sea basin with multiple evolution phases of paleoenvironment and paleogeographic were recognized based on the models. Our synthesis and interpretation support that moderately deep marine conditions dominated in the Miocene, whereas shallow seas dominated the whole basin during the Plio-Pleistocene period as a result of episodic marine invasion. However, lacustrine environment may have prevailed at the Oligocene time in isolated half grabens.     

On the iron interpretation of the 6.4 keV emission line from SGR 1900+14

A 6.4 keV emission line was discovered in an unusual burst from the soft gamma repeater SGR 1900+14 with the Rossi X-ray Timing Explorer (RXTE). The line was detected in part of a complex multipeak precursor that preceded the unusual burst of 1998 August 29, i.e. two days after the giant flare of August 27 from the source. The origin of the line was not firmly identified and two possible interpretations were equally plausible including (a) Kα fluorescence from a small iron rich material that was ejected to the magnetosphere during the August 27 flare, and (b) proton or α-particle cyclotron resonance. If the iron scenario was correct, we expect to find evidence for the line during the intervening interval between the flare and the August 29 burst, i.e. on August 28. Here we present the results of the August 28 burst observation, taken with RXTE. We detect a total of seven bursts whose individual and joint spectra do not show evidence for spectral lines. We also investigated a sample of nine bursts before and after the August 29 burst (from 1998 June to December) that do not reveal evidence for a spectral line near 6.4 keV or elsewhere. These results disfavor the iron scenario and make the proton/α-particle cyclotron resonance interpretation more plausible. The appearance of the emission line in part of a complex burst and its absence from the studied sample indicate that the line is likely due to a transient phenomenon that may depend on the burst morphology, energetics and the properties of the emission region.      

Ecohydrographic constraints on biodiversity and distribution of phytoplankton and zooplankton in coral reefs of the Red Sea,Saudi Arabia

An integral concept of ecological research is the constraint of biodiversity along latitudinal and environmental gradients. The Red Sea features a natural example of a latitudinal gradient of salinity, temperature and nutrient richness. Coral reefs along the Red Sea coasts are supported with allochthonous resources such as oceanic and neritic phytoplankton and zooplankton; however, relatively little is known about how the ecohydrography correlates with plankton biodiversity and abundance. In this article we present the biodiversity of phytoplankton and zooplankton in Red Sea coral reefs. Oceanographic data (temperature, salinity), water samples for nutrient analysis, particulate organic matter, phytoplankton and zooplankton, the latter with special reference to Copepoda (Crustacea), were collected at nine coral reefs over ~1500 km distance along the Red Sea coast of Saudi Arabia. The trophic state of ambient waters [as indicated by chlorophyll a (Chl a)] changed from strong oligotrophy in the north to mesotrophy in the south and was associated with increasing biomasses of Bacillariophyceae, picoeukaryotes and Synechococcus as indicated by pigment fingerprinting (CHEMTAX) and flow cytometry. Net‐phytoplankton microscopy revealed a Trichodesmium erythraeum (Cyanobacteria) bloom north of the Farasan Islands. Several potentially harmful algae, including Dinophysis miles and Gonyaulax spinifera (Dinophyceae), were encountered in larger numbers in the vicinity of the aquaculture facilities at Al Lith. Changes in zooplankton abundance were mainly correlated to the phytoplankton biomass following the latitudinal gradient. The largest zooplankton abundance was observed at the Farasan Archipelago, despite high abundances of copepodites, veligers (Gastropoda larvae) and Chaetognatha at Al Lith. Although the community composition changed over latitude, biodiversity indices of phytoplankton and zooplankton did not exhibit a systematic pattern. As this study constitutes the first current account of the plankton biodiversity in Red Sea coral reefs at a large spatial scale, the results will be informative for ecosystem‐based management along the coastline of Saudi Arabia.     

Behavior of Weak Soils Reinforced with End-Bearing Soil-Cement Columns Formed by the Deep Mixing Method

This article reports on a series of small-scale, plane strain, 1 g physical model tests designed to investigate the bearing capacity and failure mechanics of end-bearing soil-cement columns formed via Deep Mixing (DM). Pre-formed soil-cement columns, 24 mm in diameter and 200 mm in length, were installed in a soft clay bed using a replacement method; the columns represented improvement area ratios, a_p, of 17%, 26%, and 35% beneath a rigid foundation of width 100 mm. Particle Image Velocimetry (PIV) was implemented in conjunction with close-range photogrammetry in order to track soil displacement during loading, from which the failure mechanisms were derived. Bearing capacity performance was verified using Ultimate Limit State numerical analysis, with the results comparing favorably to the analytical static and kinematic solutions proposed by previous researchers. A new equation for bearing capacity was derived from this numerical analysis based on the improvement area ratio and cohesion ratio of the soil column and ground model.     

Groundwater recharge in arid areas induced by tropical cyclones: lessons learned from Gonu 2007 in Sultanate of Oman

Younger groundwater found in some Omani aquifers is a result of recent recharge from cyclonic and storm events [Weyhenmeyer et al. (Science 287:842–845, 2000); Young et al. (J Appl Geophys 57:43–61, 2004)]. The analysis of the meteorological data in Oman indicates an anomalous rainfall on a decadal interval whereas cyclones frequency is expected to increase due to global climatic changes. The cyclone Gonu has severely struck the eastern Omani coasts in 2007 resulting in devastating floods. Huge volume of water (3,672 mm³) spread over the coastal plain calling for an assessment of potential groundwater recharge subsequent to this event. The present study evaluates groundwater recharge with respect to Gonu 2007 to assess the potential of recharge induced by such cyclones in the arid zones. The hydrographs of several piezometers sited along the coastal plain in Muscat Province have been studied and variation in water table rise has been analyzed. Significant water table rise is indicated for areas with geological and structural settings favoring rapid infiltration of water yielding considerable groundwater mound, whereas piezometers located in less favorable zones show minimum rise of water table. However, soon after the floods the aquifer hydrodynamics has readjusted to attain equilibrium and the groundwater mound dissipated. The cumulative rise of the water table on an areal extent does not exceed a few centimeters indicating lesser volume of recharge. Comparatively, recharge from frequent precipitation along favorable zones produces more significant recharge compared with cyclonic events where surface water residence time is shorter to allow for efficient infiltration.     

Seismic design and response evaluation of unbonded post‐tensioned hybrid coupled wall structures

This paper presents an analytical investigation on the seismic design and response of coupled wall structures that use unbonded post‐tensioned steel coupling beams. Both monolithic cast‐in‐place reinforced concrete wall piers and precast concrete wall piers are considered. Steel top and seat angles are used at the coupling beam ends for energy dissipation. The seismic design of prototype structures to achieve target displacement‐based performance objectives is evaluated based on nonlinear static and dynamic time history analyses. Additional recommendations are provided on shear design. Comparisons with ‘conventional’ structures that use embedded steel coupling beams as well as isolated walls with no coupling are provided. The results indicate that while the peak lateral displacements of unbonded post‐tensioned coupled wall structures are larger than the peak displacements of structures with embedded beams, the residual displacements are significantly reduced as a result of the restoring effect of the post‐tensioning steel. Copyright © 2008 John Wiley & Sons, Ltd.     

Solidification of Tank Bottom Sludge

Tank bottom oily sludge (S) is collected from tank bottoms during cleaning operations and contaminated soil is collected after spills and leakages. Disposal of tank sludge is a significant item of tank maintenance for producers, refiners and transporters of petroleum materials. The objective of this paper is to investigate the use of various additives in the solidification of tank bottom sludge. The sludge was solidified using various combinations of additives including ordinary Portland cement (OPC), cement by-pass dust (CBPD) and quarry fines (QF). Geotechnical and leachability properties of the mixtures were determined. The use of OPC alone as a solidifying agent yielded the best results. This was followed by blends S:OPC:QF of 1:0.5:1.5 and S:CBPD of 1:2. Economically, the latter two mixtures would be considered more cost-effective in solidifying the sludge as the additives are waste by-product materials. The Toxicity Characteristic Leaching Procedure (TCLP) results indicated that no extracts exceeded the threshold TCLP limits established by U.S. Environmental Protection Agency (USEPA). The solidified material can be used in construction of roads, embankments and landfill layers.     

Factors influencing determination of shale classification indices and their correlation to mechanical properties

The influence of sample preparation procedure on the measured classification indices such as clay-size fraction, liquid limit, and plastic limit of shales was investigated. Shale samples covering a wide range of composition and plasticity were tested using standard and modified preparation procedures to yield quantitative data required for this investigation. The study specifies the range of shale plasticity in which the measured values of clay-size fraction and liquid limit are sensitive to hydrometer specimen size and rehydration time, respectively. The study also revealed that the degree of shale particle disaggregation has an important influence on the measured clay-size fraction and liquid limit. This influence is maximized for shales with intermediate plasticity and can be interpreted in terms of particle size and shape. Correlations were established between classification indices derived from standard and modified sample preparation procedures. It is recommended to use these correlations to adjust shale classification indices derived from standard sample preparation procedures usually utilized by commercial laboratories. Such correlations help in creating a universally followed procedure for better estimation of shale engineering properties and reliable interpretation of case histories involving shale formations.     

Who participates in the Intergovernmental Panel on Climate Change and why: A quantitative assessment of the national representation of authors in the Intergovernmental Panel on Climate Change

This paper presents a quantitative analysis of international representation in the activities of the Intergovernmental Panel on Climate Change using expert authorship counts by country in each of the four IPCC assessment reports (1990, 1995, 2001 and 2007). Overall, we find that 45% of countries, all Non-Annex 1, have never had authors participate in the IPCC process; on the other hand, European and North American experts are make up more than 75% of all authors (N = 4394). Generalized linear models using negative binomial regression were used to quantitatively estimate the effect of a number of socio-economic, environmental and procedural factors influencing country-level participation in the IPCC. Per capita gross domestic product, population, English-speaking status, and levels of tertiary education were all found to be statistically significant drivers of authorship counts. In particular, participation by authors from English-speaking Non-Annex 1 countries is 2.5 times greater than those that are non-English speaking. Regionally small island nations of Oceania were the most severely under-represented group. South American and Asian countries had fewer authors, and African countries had more authors than what might be expected on the basis of demographic and socio-economic data. These differences across nations partly reflect existing scientific capacity that will be slow to change. However, the on-going under-representation of developing country scientists in the IPCC, particularly in the assessment of climate science (WGI) and climate mitigation (WGIII) warrants greater efforts to close the capacity gap.