Reflux stratabound dolostone and hydrothermal volcanism-associated dolostone: a two-stage dolomitization model (Jurassic, Lebanon)

The Kesrouane Formation, which is characterized by pervasive dolomitization, has a stratigraphic thickness that exceeds 1000 m. It is part of a broad carbonate platform deposited in the Levant region and represents 60% of the Lebanese Jurassic rocks. Two genetically distinct dolostones are recognized within this unit: (1) fine‐to‐medium crystalline non‐planar grey dolostone; and (2) coarse‐crystalline planar beige dolostone. The former is stratabound and of Early Jurassic age (⁸⁷Sr/⁸⁶Sr = 0·707455). This dolostone locally exhi‐bits pseudomorphs of evaporite nodules, pointing towards seepage‐reflux dolomitization by hypersaline‐ to marine‐related fluids. Exposures of the coarse‐crystalline dolostone are associated with regional pre‐Cretaceous faults, along which Late Jurassic volcanics also occur. Sedimentological and diagenetic considerations coupled with microthermometry support a hydrothermal origin for this dolostone, with T_H values of primary inclusions between 50 and 80 °C. The related dolomitizing fluids are mesosaline (3·5–12·0 eq. wt% NaCl), and are believed to result from the mixing of evaporative brines and sea water. Dolomitization is thus believed to have occurred in two stages, whereby fluids invaded the host rocks first by seepage‐reflux, explaining the resulting Early Jurassic stratabound dolostone, and later through fracture flow along the faults associated with the Late Jurassic volcanism, explaining the coarse‐crystalline hydrothemal dolostone.     

Paleoclimate reconstruction in the Levant region from the geochemistry of a Holocene stalagmite from the Jeita cave, Lebanon

Dated oxygen and carbon isotopic profiles from a Holocene stalagmite (11.9–1.1 ka) from the Jeita cave, Lebanon, are compared to variations in crystallographic habit, stalagmite diameter and growth rate. The profiles show generally high δ¹⁸O and δ¹³C values during the late-glacial period, low values during the early Holocene, and again high values after 5.8 ka. On the basis of the good correlation between the morphological and crystallographic aspect of the stalagmite and its isotopic records, as well as the isotopic response of speleothems from central and northern Israel, we relate high δ¹⁸O and δ¹³C values to drier conditions. Between 6.5 and 5.8 ka an increase in isotopic values, a decrease in growth rate and stalagmite diameter suggest a transition from wet conditions in the early Holocene towards drier conditions in the mid-Holocene. The transition occurred in two steps, first a progressive change to drier conditions started at 6.5 ka but was interrupted by a short ( 100 years) return to wetter conditions, followed by an equally rapid (< 200 years) change to drier conditions.     

Use of Sewage Sludge Ash and Hydrated Lime to Improve the Engineering Properties of Clayey Soils

Using various additives has been considered as one of the most common stabilization methods for improvement of engineering properties of fine-grained soils. In this research the effect of sewage sludge ash (SSA) and hydrated lime (HL) on compressive strength of clayey soil was investigated. For this purpose, 16 kinds of mixtures or treatments were made by adding different amounts of SSA; 0, 5, 10 and 15% by weight and HL; 0, 1, 3 and 5% by weight of a clayey soil. First, compaction characteristics of the treatments were determined using Harvard compaction test apparatus. So that, 12 unconfined compressive strength test specimens were made using Harvard compaction mold from each treatments taking into account four different curing ages, including 7, 14, 28 and 90 days in three replications. Therefore, a total of 192 specimens were prepared and subjected to unconfined compressive strength tests. The results of this study showed that the maximum dry density of the treated soil samples decreases and their optimum water content increases by increasing the amount of SSA and hydrated lime in the mixtures. It is also found that the adding of HL and SSA individually would increase the compressive strength up to 3.8 and 1.5 times respectively. The application of HL and SSA with together could increases the compressive strength of a clayey soil more efficiently even up to 5 times.     

Comparison of machine learning methods for copper ore grade estimation

In this study, machine learning methods such as neural networks, random forests, and Gaussian processes are applied to the estimation of copper grade in a mineral deposit. The performance of these methods is compared to geostatistical techniques, such as ordinary kriging and indicator kriging. To ensure that these comparisons are realistic and relevant, the predictive accuracy is estimated on test instances located in drill holes that are different from the training data. The results of an extensive empirical study in the Sarcheshmeh porphyry copper deposit in Southeastern Iran illustrate that specially designed Gaussian processes with a symmetric standardization of the spatial location inputs and an anisotropic kernel yield the most accurate predictions. Furthermore, significant improvements are obtained when, besides location, information on the rock type is included in the set of predictor variables. This observation highlights the importance of carrying out detailed studies of the geological composition of the deposit to obtain more accurate ore grade predictions.     

Optimal aquifers and reservoirs for CCS and EOR in the Kingdom of Saudi Arabia: an overview

An overview on the tectono-stratigraphic framework of the Arabian plate indicates obvious differences between two distinct areas: the hydrocarbon-prolific sector and non-hydrocarbon-prolific sector. These differences resulted from the interplay of a variety of factors; some of which are related to the paleo-geographic configuration (eustatic sea level fluctuations, climatic conditions, and salt Basins), others to differential subsidence (burial) and structural inversions. During the Paleozoic, the regional compression was caused by far field effects of the Hercynian orogeny. This led to major folded structures in central and eastern Saudi Arabia (e.g. Ghawar anticline). During the Mesozoic, the most important tectonic factor was the stretching of the crust (extension), accompanied with the increase in temperature, resulting in an increase of the accommodation space, and thicker sedimentary successions. Regional unconformities are mostly found where folded structures are dominant, and they acted as a carrier systems for the accumulation of hydrocarbon and groundwater. A good understanding of the stratigraphy and tectonic evolution is, thus, required to develop carbon capture and storage (CCS) and to design efficiently enhanced oil recovery (EOR) in both sectors. Oil and gas reservoirs offer geologic storage potential as well as the economic opportunity of better production through CO₂-EOR. The world greatest hydrocarbon reservoirs mainly consist of Jurassic carbonate rocks, and are located around the Arabian Basin (including the eastern KSA and the Arabian Gulf). The Cretaceous reservoirs, which mainly consist of calcarenite and dolomite, are located around the Gotnia salt Basin (northeast of KSA). Depleted oil and gas fields, which generally have proven as geologic traps, reservoirs and seals, are ideal sites for storage of injected CO₂. Each potential site for CO₂-EOR or CCS should be evaluated for its potential storage with respect to the containment properties, and to ensure that conditions for safe and effective long term storage are present. The secured deep underground storage of CO₂ implies appropriate geologic rock formations with suitable reservoir rocks, traps, and impermeable caprocks. Proposed targets for CCS, in the non-hydrocarbon-prolific sector, are Kharij super-aquifer (Triassic), Az-Zulfi aquifer (Middle Jurassic), Layla aquifer (Late Jurassic), and Wasia aquifer (Middle Cretaceous). Proposed targets for EOR are Safaniya oil field (Middle Cretaceous) (Safaniya, Wara and Khafji reservoirs), Manifa oil field (Las, Safaniya and Khafji reservoirs) (Late Jurassic), and Khuff reservoir (Late Permian-Early Triassic) in central to eastern KSA.     

Investigating 2-D MT inversion codes using real field data

There are currently a significant number of two-dimensional (2-D) and three-dimensional (3-D) inversion codes available for magnetotelluric (MT) data. Through various 2-D inversion algorithms suggested so far, the classical Occam's inversion, the data space Occam's inversion, the nonlinear conjugate gradient (NLCG) method, and the Gauss–Newton (GN) method are fundamental driving methods to find optimum earth models, and OCCAM, DASOCC, NLCG, and MT2DInvMatlab are possible candidates one can find in the public domain that implement these algorithms for 2-D MT inversions, respectively. In this study, we investigate the pros and cons (strength and weakness) of these codes to help one use them efficiently in practical works and, as an introductory guide, further develop (sophisticate or extend) them, especially for the 3-D case. To achieve this goal, we applied each one of the four aforementioned codes on a profile of real MT field dataset. Then, further investigations have been done by performing several inversion tests to see how each code can find the appropriate model to reconstruct the subsurface resistivity structure. Numerical experiments show that the two parameters, regularization and target misfit, in addition to the main criteria of inversion (such as the forward and the sensitivities calculation method, and the type of inversion algorithm), are very important to produce the expected model in inversion. The regularization parameter that acts to trade off between model norm and data misfit can affect the inversion process in terms of both the computational efficiency and the accuracy of the obtained model. Also, lack of insufficient precision to choose the target misfit can lead the inversion to produce and reach an incorrect model.     

Detection of Earth-mass and super-Earth Trojan planets using transit timing variation method

We have carried out an extensive study of the possibility of the detection of Earth-mass and super-Earth Trojan planets using transit timing variation method with the Kepler space telescope. We have considered a system consisting of a transiting Jovian-type planet in a short period orbit, and determined the induced variations in its transit timing due to an Earth-mass/super-Earth Trojan planet. We mapped a large section of the phase space around the 1:1 mean-motion resonance and identified regions corresponding to several other mean-motion resonances where the orbit of the planet would be stable. We calculated transit timing variations (TTVs) for different values of the mass and orbital elements of the transiting and perturbing bodies as well as the mass of central star, and identified orbital configurations of these objects (ranges of their orbital elements and masses) for which the resulted TTVs would be within the range of the variations of the transit timing of Kepler’s planetary candidates. Results of our study indicate that in general, the amplitudes of the TTVs fall within the detectable range of timing precision obtained from the Kepler’s long-cadence data, and depending on the parameters of the system, their magnitudes may become as large as a few hours. The probability of detection is higher for super-Earth Trojans with slightly eccentric orbits around short-period Jovian-type planets with masses slightly smaller than Jupiter. We present the details of our study and discuss the implications of its results.     

On the detection of (habitable) super-Earths around low-mass stars using Kepler and transit timing variation method

We present the results of an extensive study of the detectability of Earth-sized planets and super-Earths in the habitable zones of cool and low-mass stars using transit timing variation method. We have considered a system consisting of a star, a transiting giant planet, and a terrestrial-class perturber, and calculated TTVs for different values of the parameters of the system. To identify ranges of the parameters for which these variations would be detectable by Kepler, we considered the analysis presented by Ford et?al. (Transit timing observations from Kepler: I. Statistical analysis of the first four months. ArXiv:1102.0544, 2011) and assumed that a peak-to-peak variation of 20 s would be within the range of the photometric sensitivity of this telescope. We carried out simulations for resonant and non-resonant orbits, and identified ranges of the semimajor axes and eccentricities of the transiting and perturbing bodies for which an Earth-sized planet or a super-Earth in the habitable zone of a low-mass star would produce such TTVs. Results of our simulations indicate that in general, outer perturbers near first- and second-order resonances show a higher prospect for detection. Inner perturbers are potentially detectable only when near 1:2 and 1:3 mean-motion resonances. For a typical M star with a Jupiter-mass transiting planet, for instance, an Earth-mass perturber in the habitable zone can produce detectable TTVs when the orbit of the transiting planet is between 15 and 80 days. We present the details of our simulations and discuss the implication of the results for the detection of terrestrial planets around different low-mass stars.     

FAO-56 methodology for determining water requirement of irrigated crops: critical examination of the concepts,alternative proposals and validation in Mediterranean region

The present study evaluates firstly the ability of the FAO-56 methodology, based on the two-step approach “reference evapotranspiration (ET₀)—crop coefficient (K _c),” to accurately determine the actual evapotranspiration (ET) of irrigated crops and proposes, secondly, the alternative approaches for improving this determination. The FAO-56 methodology is supported by two hypotheses: (1) ET₀ represents all effects of weather and (2) K _c varies predominately with specific crop characteristics and only marginally with climate, which enables the transfer of K _c standard values among locations and climates. On the base of the theoretical analysis and experimental observations, a critical examination of the previous hypotheses demonstrates that they are not verified by reality. The first hypothesis is not verified for two reasons: (a) The formulation adapted by the Penman–Monteith equation and proposed in FAO-56 methodology for calculating ET₀ uses climatic variables determined at a 24-h average scale. However, in principle it is only valid in permanent regime, in other words at least on an hourly scale. (b) The FAO-56-proposed formulation attributes a constant value to the canopy resistance of the reference surface; but in reality, this resistance is variable in relation to the climatic variables. The second hypothesis, concerning the two-step approach, is also not verified because the values of K _c largely vary in relation to climatic variables (radiation, air vapour pressure deficit and wind speed). This fact does not support the possibility of the transferability of K _c values into locations where the local conditions deviate from the conditions where the adjusted values of K _c were determined. The weakness of the ET estimation, observed on several crops cultivated in the Mediterranean region, through the application of the FAO-56 methodology, is the result of errors accumulation, associated with that affects the determination of either ET₀ or K _c. The present study underlines the advantage of using a one-step approach in the calculation of ET, since it is based on fewer computation steps and, consequently, on fewer error sources than the two-step model. Two models adopting this approach are proposed and validated, one of which can be considered as operational, i.e. it only needs standard meteorological data as input. The use of these models enables an improvement of the ET estimation. This objective is a key component of any strategy to improve agricultural water management in Mediterranean region.