A study of erosion rates on salt diapir surfaces in the Zagros Mountains, SE Iran

Salt exposures and weathering residuum on several salt diapirs in different geographic/climatic settings were studied. Anhydrite, gypsum, hematite, calcite, dolomite, quartz, and clay minerals are the main constituents of the weathering residuum covering the salt diapirs in various thicknesses. Erosion rates of residuum as well as of rock salt exposures were measured at selected sites for a period of 5 years by plastic pegs as benchmarks. Recorded data were standardized to a horizontal surface and to long-term mean precipitation. For the rock salt exposures the following long-term denudation rates were determined of 30–40 mm a⁻¹ for coastal diapirs and up to 120 mm a⁻¹ for mountain salt diapirs. Long-term mean superficial denudation rate measured on weathering residuum of low thickness reached 3.5 mm a⁻¹ on coastal diapirs. The total denudation rate estimated for the thin residuum is close to 4–7 mm a⁻¹ based on apparent correlation with the uplift rate on Hormoz and Namakdan diapirs. Denudation of rock salt exposures is much faster compared to parts of diapirs covered by weathering residuum. The extent of salt exposures is an important factor in the morphological evolution of salt diapirs as it can inhibit further expansion of the diapir. Salt exposures produce huge amounts of dissolved and clastic load, thus affecting the surrounding of the diapir.     

Drought adaptation measures and their effectiveness at Barind Tract in northwest Bangladesh: a perception study

Natural Hazards - Drought is a natural calamity frequently occurs at Barind Tract in northwest Bangladesh and affects both the human and natural life. An initiative has been taken...     

Geochemistry of subsurface Late Quaternary ironstones in Rajshahi and Bogra Districts,Bangladesh: implications for genetic and depositional conditions

The present study deals with the geochemistry of Late Quaternary ironstones in the subsurface in Rajshahi and Bogra districts, Bangladesh with the lithological study of the boreholes sediments. Major lithofacies of the studied boreholes are clay, silty clay, sandy clay, fine to coarse grained sand, gravels and sands with (fragmentary) ironstones. The ironstones contain major oxides, Fe₂O₃* (* total Fe) (avg. 66.6 wt%), SiO₂ (avg. 15.3 wt%), Al₂O₃ (avg. 4.0 wt%), MnO (avg. 7.7 wt%), and CaO (avg. 3.4 wt%). These geochemical data imply that the higher percentage of Fe₂O₃* along with Al₂O₃ and MnO indicate the ironstone as goethite and siderite, which is also validated by XRD data. A comparatively higher percentage of SiO₂ indicates the presence of relative amounts of clastic quartz and manganese-rich silicate or clay in these rocks. These ironstones also have significant amounts of MnO (avg. 7.7 wt%) suggesting their depositional environments under oxygenated condition. Chemical data of these ironstones suggest that the source rock suffered deep chemical weathering and iron was mostly carried in association with the clay fraction and organic matter. Iron concretion was mostly formed by bacterial build up in swamps and marshes, and was subsequently embedded in clayey mud. Within the coastal environments, the water table fluctuates and goethite and siderite with mud and quartz became dry and compacted to form ironstone.

     

Assessing the impacts of climate and land use change on streamflow,water quality and suspended sediment in the Kor River Basin,Southwest of Iran

This research addressed the separate and combined impacts of climate and land use change on streamflow, suspended sediment and water quality in the Kor River Basin, Southwest of Iran, using (BASINS–WinHSPF) model. The model was calibrated and validated for hydrology, sediment and water quality for the period 2003–2012. The model was run under two climate changes, two land use changes and four combined change scenarios for near-future period (2020–2049). The results revealed that projected climate change impacts include an increase in streamflow (maximum increases of 52% under RCP 2.6 in December and 170% under RCP 8.5). Projected sediment concentrations under climate change scenarios showed a monthly average decrease of 10%. For land use change scenarios, agricultural development scenario indicated an opposite direction of changes in orthophosphate (increases in all months with an average increase of 6% under agricultural development scenario), leading to the conclusion that land use change is the dominant factor in nutrient concentration changes. Combined impacts results indicated that streamflows in late fall and winter months increased while in summer and early fall decreased. Suspended sediment and orthophosphate concentrations were decreased in all months except for increases in suspended sediment concentrations in September and October and orthophosphate concentrations in late winter and early spring due to the impact of land use change scenarios.     

Role of Multiple Décollement Horizons in the Structural Style of the Sefid-Zakhur Anticline in the Fars Province,Zagros Belt

Geotectonics - The geometry of the Sefid-Zakhur anticline, a gas reservoir in the Fars province, and the main controlling factors of the structural style in this anticline are studied in this...     

FEG-EPMA mapping and Fe-Ti oxide mineral chemistry of Brahmaputra River sediments in Bangladesh: provenance and petrogenetic implications

The present research deals with the FEG-EPMA mapping and Fe-Ti oxide mineral chemistry of Brahmaputra River sediments in Bangladesh. Major heavy minerals in the sediments consist of garnet (8.5–21.3%), kyanite (5.35–11.9%), monazite (2.3–5.3%), sillimanite (1.8–4.7%), zircon (3.6–9.1%), and a considerable amount of opaques mainly Fe-Ti oxide minerals (23.1–35.4%). The detrital Fe-Ti oxide minerals carry significant clues to the parent rocks or sources. In these contexts, detrital opaques (Fe-Ti oxides) have been analyzed with an electron probe microanalyzer (EPMA). These opaques (Fe-Ti oxide) display six types of textural patterns, dominantly seriate with granular, emulsion, and acicular sandwich structures and trellis type of textural patterns. These textural patterns belong to five intergrowths of Fe-Ti oxide minerals such as (1) ilmenite-hematite, (2) magnetite-ilmenite, (3) hematite-rutile, (4) ilmenite-hematite-rutile, and (5) ilmenite-rutile, where ilmenite-hematite intergrowth is common. Alteration is seen in both exsolved and unexsolved ilmenites. Textural patterns and mineral chemistry of the studied ilmenite minerals provide lines of evidence of low-temperature magmatic inheritance, later modified by diffusional processes. The estimated temperature and oxygen fugacity from the magnetite-ilmenite exsolution range from 547.6 to 558.2 °C and from 10^?21.4 to 10^?21.7, respectively. The data are also consistent with hematite-ilmenite temperature (between 537 and 540 °C) and oxygen fugacity (10^?21.7 to 10^?21.9) measurements in Cox’s Bazar beach placers. These temperatures and oxygen fugacities specify Fe-Ti oxide assemblages equilibrated in a T-fO₂ field very near to the FMQ buffer curve suggesting a crustal source (magmatic and/or metamorphic), which is modified significantly by metamorphic processes.     

A Bonded Particle Model Simulation of Shear Strength and Asperity Degradation for Rough Rock Fractures

Different failure modes during fracture shearing have been introduced including normal dilation or sliding, asperity cut-off and degradation. Attempts have been made to study these mechanisms using analytical, experimental and numerical methods. However, the majority of the existing models simplify the problem, which leads to unrealistic results. With this in mind, the aim of this paper is to simulate the mechanical behaviour of synthetic and rock fracture profiles during direct shear tests by using the two-dimensional particle flow computer code PFC2D. Correlations between the simulated peak shear strength and the fracture roughness parameter D _R1 recently proposed by Rasouli and Harrison (2010) are developed. Shear test simulations are carried out with PFC2D and the effects of the geometrical features as well as the model micro-properties on the fracture shear behaviour are studied. The shear strength and asperity degradation processes of synthetic profiles including triangular, sinusoidal and randomly generated profiles are analysed. Different failure modes including asperity sliding, cut-off, and asperity degradation are explicitly observed and compared with the available models. The D _R1 parameter is applied to the analysis of synthetic and rock fracture profiles. Accordingly, correlations are developed between D _R1 and the peak shear strength obtained from simulations and by using analytical solutions. The results are shown to be in good agreement with the basic understanding of rock fracture shear behaviour and asperity contact degradation.     

Electrokinetic Stabilization of Soft Soil Using Carbonate-Producing Bacteria

The carbonate (CO ₃ ^?2 ) produced by Sporosarcina pasteurii was injected electrokinetically to enhance the mechanical properties of soft clay soils. In this method the Ca²⁺ was injected into the anode chamber and moved towards the cathode by electromigration and electroosmotic flow. Then the released CO ₃ ^?2 from a blend of bacteria and urea was injected into the cathode chamber. The CO ₃ ^?2 ions were moved from the cathode to the anode under electromigration mechanism. The CaCO₃ was precipitated in the presence of calcium in porous medium of the soil, and consequently increased the shear strength of the soil. The polarity reversal was applied to have a homogeneous distribution of CaCO₃.     

Biodiversity and biomass of a natural and degraded mangrove forest of Peninsular Malaysia

Anthropogenic activities have always been the cause of most environmental degradation, and mangrove disappearance is no exception. A comparative assessment on the biodiversity of natural and degraded mangrove forests has been undertaken, looking at the biomass, both above-ground and below-ground. The natural and the degraded mangrove forests were situated at Kuala Selangor and Sungai Haji Dorani, respectively, both on the West coast of Peninsular Malaysia. A random sample scheme with quadrate sample plots (10 m × 10 m) was adopted for the measurement of the diameter at breast height and total height of individual tree species at both forests. Diversity indices and above- and below-ground biomass were estimated from this inventory. Eight mangrove tree species were identified at both study areas, namely: Bruguiera parviflora, Avicennia officinalis, Rhizophora mucronata, Sonneratia alba, Avicennia marina, Bruguiera cylindrica, Xylocarpus mekongensis and Excoecaria agallocha. The mangrove species in Sungai Haji Dorani showed high diversity with a Shannon–Weiner Index (H′) value of 0.91, compared to the natural mangrove of Kuala Selangor which has a lower value, H′ = 0.55. The dominant species in the natural mangrove area was B. parviflora, with the highest Important Value Index (IVI) of 70.96 %, as opposed to A. marina which was the most common species in the degraded mangrove area, with IVI of 49.16 %. An estimate of 305.46 t/ha of above-ground biomass was calculated for the natural mangrove, while 122.78 t/ha was obtained for the degraded mangrove forest. This contrasts with the below-ground biomass estimates, which were 14.09 t/ha for the natural mangrove and 36.35 t/ha for the degraded mangrove.