Arabian Journal of Geosciences

A good understanding of the caving mechanisms of loose top-coal is significant for longwall top-coal caving (LTCC) mining. In this paper, the equations of the particle motion, top-coal boundary, and drawing body were derived based on the stochastic medium theory. Then, the particles moving boundary and the shape of the top-coal loss were discussed, and the dynamic evolvement of the top-coal boundary and drawing body was analyzed. A theoretical model for calculating the top-coal recovery ratio was established, and the relationship between the top-coal recovery ratio and rock mixed ratio was studied and then the criterion for terminating the drawing cycle was proposed. Finally, model experiments were conducted to verify the theoretical analysis. It is concluded that the starting top-coal boundary keeps moving to the lower left with increasing drawing volume. The top-coal loss is zonal distribution and tilts toward the goaf and is composed of the top-coal surrounded by the floor, the starting top-coal boundary and the ending top-coal boundary between the drawing window and the lowest moving point in the starting top-coal boundary. The drawing body tilts toward the goaf and its deflection angle decreases with increasing drawing volume. The top-coal recovery ratio increases non-linearly with increasing rock mixed ratio, and the rock mixed ratio of 10–15% can be used as the criterion for terminating the drawing cycle. This work is the first attempt at demonstrating the caving mechanisms of the loose top-coal using the stochastic medium theory in LTCC mining.

In recent decades, the upgrading of information of human beings about the Earth’s climate and concern about climate change in the future has led to a better understanding of the components affecting the climate. One of the factors that has received much attention as a predictor of precipitation is teleconnection patterns, which is one of the topics of interest in hydrological, meteorological, and agricultural forecasts. Therefore, the main goal of the present study is to investigate the effect of teleconnection phenomena on autumn precipitation in Iran at different spatiotemporal scales including basin and different time lags using the Pearson correlation method and synoptical analysis. For this purpose, a network of 717 synoptic and rain gauge stations and 40 teleconnection indices at 1- to 6-month lags (from April to September) were utilized during the period 1987–2015. Finally, the type of correlation and frequency of significant signals or teleconnection (FSS) correlations were analyzed at basin and sub-basin scales. According to the results in most of the basins, the highest FSS correlations occurred at 1- to 3-month lags and in the Central Plateau basin occurred at 2- to 6-month lags. Simultaneous investigation of the effect of time lags and teleconnection indices on the FSS correlations also illustrated that the time lags and type of teleconnection indices were different in each basin. Overall, the results showed that most of the FSS correlations of autumn precipitation in most basins of Iran were well correlated to 3-month lag and Sea Surface Temperature (SST), Tropical North Atlantic (TNA), and Southern Oscillation Index (SOI) indices, which can be used to predict autumn precipitation using different statistical methods. Also, synoptic analysis showed that the El Niño Southern Oscillation (ENSO) family indices have the most significant correlation with most studied basins, especially the peripheral and western basins of Iran. The pattern of FSS correlations is consistent with the country’s topography and precipitation corridors. Also, the regional indices are intermediary to measure the impact of global indices such as ENSO, Pacific Decadal Oscillation (PDO), and Atlantic Multidecadal Oscillation (AMO) on the Iranian climate. Based on the results, the interpretation of high correlation of teleconnection patterns with Iran basins precipitation is difficult and requires separate work, but it seems to have relation with Madden-Julian Oscillation (MJO) index.

Postdepositional history of the Sanganeh Formation (Lower Cretaceous), in eastern Kopet-Dagh Basin in northeast of Iran was considered. The Sanganeh Formation mainly composed of shale, marl, siltstone, and interbeds of limestone. The study of limestone interbeds led to recognizing several diagenetic processes including micritization, cementation (including isopachous rim, syntaxial overgrowth, equant mosaic spary, blocky, and poikilotopic cements), neomorphism, compaction (including physical and chemical), dolomitization, pyritization, fracturing, and vein filling. Limestone samples were analyzed for major (Ca, Mg) and minor (Na, Sr, Fe, and Mn) elements as well as oxygen and carbon isotopic compositions (δ 18O and δ 13C). Many of diagenetic processes such as cementation, neomorphism, dolomitization, and pyritization happen in several diagenetic environments. In order to differentiate them, geochemical data (including element and isotopic) have been used. In addition, blocky, mosaic spar, and poikilotopic cements show different luminescence under the cathodoluminescence microscope that is accordant to their geochemical contents. Therefore, the luminescence was a guide for recognizing cements and neomorphed lime muds of different diagenetic environments of studied samples. The neomorphed lime muds and lime muds were differentiated by geochemical data. The marine lime muds and micrites includes mean δ 18O 0.04 ‰, δ 13C 1.95 ‰, Na mean 1491.21 ppm, Sr mean 5233.68 ppm, Fe mean 61.34 ppm, and Mn mean 35.96. The meteoric cements and includes mean δ 18O −1.02 ‰, δ 13C 8.85‰, Na mean 126.34 ppm, Sr mean 300.03 ppm, Fe mean 2883.88 ppm, and Mn mean 382.88. The burial cements and neomorphed lime mud samples contained mean δ 18O −9 ‰, δ 13C −6.33‰, Na mean 308.29 ppm, Sr mean 731.72 ppm, Fe mean 816.02 ppm, and Mn mean 37.28. Paragenetic sequence of the Sanganeh Formation carbonate rocks was interpreted and depicted using integration of petrographic, major and trace elements, and isotopic data in three phases including (i) eogenesis, (ii) mesogenesis, and (iii) telogenesis.

Beachrocks occur in present-day intertidal zones of the Arabian Gulf and the Gulf of Aqaba, on the eastern and northwestern coasts, respectively, of Saudi Arabia. The beachrocks occur as linear patches within beach deposits, which have variable grain size and detrital compositions. The Arabian Gulf beachrocks are composed of sand-sized bioclasts and siliciclastic grains, whereas the Gulf of Aqaba beachrocks are composed of sand- to pebble-size grains, which are dominated by igneous rock fragments and small amounts of skeletal carbonate grains. The cement includes micritic high-magnesian calcite and isopachous acicular/bladed aragonite. In addition to cements, intergranular pores are locally filled by a lime–mud matrix. Radiocarbon dating of beachrock samples from the Arabian Gulf yielded ages from ca. 655 to 2185 year bp, whereas the Gulf of Aqaba samples range in age between 2745 and 5075 year bp.

Due to the fact that most shale gas is stored in the adsorption state on organic compounds of the formation, better understanding of adsorption mechanism of CH4/CO2 in shale kerogen not only contributes to figure out the reserves of shale gas but also is beneficial to shale gas exploitation and carbon sequestration. Using the basic experimental data of shale core from Yanchang Formation, Ordos Basin, China, four types of kerogen structure are constructed and used as inputs to molecular simulation. The isothermal adsorption capacity of single-component and bi-component of CH4 and CO2 on kerogen is simulated and analyzed. The results indicate that the isothermal adsorption capacity of CH4/CO2 increases with the rising of maturity but decreases with temperature. The effect of kerogen type on adsorption capacity is as follows: type III > type II > type I. And the adsorption capacity of CO2 is larger than that of CH4, indicating the good potential of enhancing shale gas production and carbon sequestration.

The original version of this article unfortunately contained an error in the name of one of the co-authors. The corresponding author did not notice that the name of one of the co-authors, Hamid Reza Pourghasemi, was incorrectly presented as “Hamidreza Pourghasemi”. The correct author name is “Hamid Reza Pourghasemi”.

The effects of alteration on granites outcropping around Sivrihisar area within the Tavşanlı Zone (NW Turkey) were investigated considering minero-petrographical, geochemical, and geomechanical properties. For this aim, polarizing light microscope, scanning electron microscope, X-ray diffraction, chemical analyses, and geomechanical tests were conducted on the granitic samples. The new petrographic index, referred as feldspar alteration index, was developed from the quantitative ratios of total and altered constituents in feldspar minerals. Based on solution-precipitation processes, plagioclase and alkali feldspar were altered to smectite, sericite, and kaolinite along microfractures, cleavage, twinning, and zoning structure. Anorthite-rich core is more altered than the rim of zoned plagioclase due to higher solubility in water and selective alteration of calcic plagioclase. EDS studies indicate that Na, Si, and Ca decrease and Mg, Al, K, and Fe progressively increase. The normalized values of whole-rock chemical analyses of the granites show depletion of Si, Al, Na, and Ca reflecting the dissolution of plagioclase. Enrichment of Si, Al, Na, Ca, Mg, K, and Fe reveal precipitation of smectite, sericite, and kaolinite minerals during alteration. Minero-petrographical and geochemical changes led to an increase in water absorption and apparent porosity and a decrease in apparent density, P-wave velocity, Schmidt hammer rebound, and compressive strength. Significant relationships between FAI and geomechanical properties (R2 = 0.7116–0.8676), FAI and P-wave velocity index (Ivp) (R2 = 0.8676), and FAI and strength ratio (Rs) (R2 = 0.7614) demonstrate that FAI can be used to determine the alteration degree of granites.

Soil behaviour during earthquakes is just as important as the prediction of earthquakes. Seismic waves alter the soil strata that they traverse during earthquakes, and the strata may also change the properties of seismic waves. Conditions such as the type, stratification status, and combinations of the strata can also create different effects in the seismic wave. With dynamic soil behaviour analysis, the effects of earthquake ground motion and ground performance on general performance can be obtained by the change in acceleration parameters. In this study, one-dimensional dynamic analysis was carried out using the EERA (Bardet et al., EERA: A computer program for equivalentlinear earthquake site response analyses of layered soil deposits, University of Southern California, Los Angeles, 2000) program by using the drilling information of the Karaböğürtlen formation, which consists of alluvium, coastal sediment and siltstone, claystone, and sandstone units in the selected region. For this purpose, idealised soil profiles were created by using the drilling information from the region of Mesudiye in the province of Muğla, district of Datça. Acceleration values, which varied in depth and surface acceleration values, were obtained as a result of one-dimensional analysis using national and international characteristic earthquake acceleration records selected from the literature. Since the dynamic and kinematic structure related to the deformation in the region is extremely complex and there is no generally accepted model, different mechanism situations have been examined using the characteristic earthquake records that have happened in the world. According to the results, similar results were obtained in earthquakes with the same mechanism; it was observed that the acceleration values which were occurred in the earthquake records with different mechanisms had been changed. Moreover, it was calculated that the greatest amplification is in beach sediments composed of sand and clay units, and the highest amplification value was in the Parkfield earthquake, which increased the peak acceleration value by six times.