Genesis of Clastic Dykes and Soft-Sediment Deformation Structures in the Mamfe Basin, South-West Region, Cameroon: Field Geology Approach

This paper aims to investigate the genesis of clastic dykes and soft-sediment deformation structures in the Mamfe Basin, South West-Region, Cameroon. Results from this study portray the following: (1) The clastic dykes are extrusive and were generated from preexisting soft-sediments that penetrate fissures caused by seismic activity. It can be concluded that clastic dykes originate from seismic shacking, probably induced by volcanic-tectonic activity and magmatic dykes that cut across the Precambrian and Cretaceous formations of the Mamfe Basin. (2) The soft-sediment deformation structures (flexures, sheared foliations, anticlinal folds, load casts, and flame structures) are likely triggered by seismic shocks. The inferred influence of seismic activity results from rifting and rapid subsidence of basin-fill during the Cretaceous. Some of these soft-sediment deformation structures (SSDS) are induced by fluidization and liquefaction triggered by rapid sedimentation within tectonically active settings, as well as density variations illustrated by local occurrence of load casts with weak lateral extensions. (3) The synsedimentary features (joints, faults, filled fractures) are related to local stress triggered by gravitational sliding, because the fractures were filled by unconsolidated clastic materials.

Methane at the NW of Weddell Sea, Antarctica

The presence of gaseous hydrocarbons (from methane to n-pentane) in the seabed sediments and the bubbling of methane may suggest the presence of gas accumulations in the substrate of the NW Weddell Sea, Antarctica. The release of methane from the frozen ocean substrate adjacent to Seymour Island would be linked to climate instability during Late Cenozoic, when vast areas of the Antarctic continental shelf were flooded during the marine transgression that occurred c. 18,000 years ago, after the Last Glacial Maximum (LGM). As the ice melted, the sea again occupied the regions which it had abandoned. As the transgression was relatively rapid, the sub-air relief was not destroyed but was submerged and the ground had frozen (permafrost) along with it. Thus, the heat flow from the sea to the marine substrate, now flooded, would have destabilized frozen gas accumulations, which were originally formed into terrestrial permafrost during the LGM, similarly to what would have happened in the Arctic.

Combining Resistivity and Aeromagnetic Geophysical Surveys for Groundwater Exploration in the Maghnia Plain of Algeria

The Maghnia plain in western Algeria is filled by Plio-Quaternary and Miocene sediments that rest unconformably on a basement of Jurassic rocks. Electrical sounding (VES), magnetic data, well information, and hydrogeological data have been used to explore for groundwater potential in the Maghnia plain. The interpretation of Schlumberger sounding data was first calibrated with the lithology of available nearby wells. Four geoelectrical layers were identified within the study area. They are a thin near surface topsoil layer with variable resistivities, a moderate resistive aquifer (15–30 ohm-m), a resistive aquifer (40–70 ohm-m), and a conductive clay layer (1–10 ohm-m). Near Sidi Mbarek, the geoelectric section is reduced to three layers: a topsoil layer, a conductive layer corresponding to the Miocene marls, and a deep resistive layer that correlates with the Oxfordian sandstones. The interpretation of VES data and the enhancement techniques of magnetic data enabled the identification of a number of unmapped faults that occur near recharge zones close to adjacent mountains. This study enabled us to study the extension of the known Plio-Quaternary aquifer of the Maghnia plain and to explore the possible existence of a second deep groundwater aquifer in Oxfordian sandstones.

Depth Estimation Using the Tilt Angle of Gravity Field due to the Semi-Infinite Vertical Cylindrical Source

Tilt angle filter is an interpretation method that is used to determine the source borders locations from potential fields data. Moreover, the tilt angle is applied for estimation of the anomaly source depth, such as contact-depth method and tilt-depth method. In this paper an application of the tilt angle technique obtained from the first vertical and horizontal gradients of the gravity anomaly from semi-infinite vertical cylindrical source is described. The technique is based on the tilt angle and derivatives ratio. In this approach the depth estimates are proportional to the computed tilt angles and their distances from the cross section center of the anomaly cause on the surface. This new method is termed the tilt-distance-depth (TDD). The method is demonstrated using synthetic gravity data, with and without random noise, and real gravity data from Iran. The results are also compared with the solutions from Euler deconvolution technique and inverse modelling using Modelvision software.

Lidar-Based Detection and Interpretation of Glaciotectonic Features of the Morainic Topography of Finland

In Finland’s digital elevation model, marks of glaciotectonics as an important formation process of glacial geomorphology can be seen. This is a new finding to this extent regarding central parts of the former ice sheets. Deformational processes produced fragmented till surfaces probably mostly by brittle fracture of frozen till. Good signs of deformational effect to the till surfaces are the plucked edges or steps and semilinear or fan-like quarry edges in topography, which are often oblique compared with the main direction of the flow of the glacier. Plucked fractured steps of blocks of till can be so tight that they construct horizontal-like diamond patterned surfaces. Sometimes punctate proximal endings of fan-like hollows of transported rafts can be seen. Within main ice lobes or streams the glaciated terrain is often divided into longitudinal smooth looking drumlin terrain and into rough erosional slightly lower level situated zones, where the erosion has happened firstly by glaciotectonism and then by glaciofluvial streams. The eskers and different kind of hummocky moraines are often located in same zones. Among them deformational hummocky moraines and ribbed moraines are common. The abundance of glaciotectonic and plucking related features indicates that the base of the receding ice sheet was cold based in places or from time to time.

Caspian Sea Tidal Modelling Using Coastal Tide Gauge Data

The purpose of this paper is to model tidal conditions in the Caspian Sea using data from coastal tide gauges of Anzali, Noshahr, and Neka Ports. Harmonic analysis method was used to identify and examine 40 tidal components. The results illustrate that the annual (Sa) and semiannual solar (Ssa) components on all of the ports listed have the highest range in comparison with the other components which are, respectively, 16 cm, 18 cm, and 15 cm for annual components and 2.8 cm, 5.4 cm, and 3.7 cm for semiannual components.

Structural Overview and Morphotectonic Evolution of a Strike-Slip Fault in the Zone of North Almora Thrust, Central Kumaun Himalaya, India

The aim of the present research is to provide the base line details of the NNW-SSE trending Raintoli fault (RF) which is running parallel to the North Almora Thrust (NAT) along the Saryu valley from Seraghat-Naichun to Seri in the central sector of the Uttarakhand Himalaya, India. The RF is characterized as dextral strike slip fault and behaves as a ductile shear zone within the zone of NAT. The dextral sense of shear movement of RF is delineated by the fabric of the shear zone rocks including microscopically observed indicators such as sigma and delta porphyroclasts, quartz c-axis, and the field structural data. Additionally, in the quaternary period the dextral strike slip fault is reactivated with oblique slip component as characterized by various geomorphic indicators, for example, triangular facets, abandoned river channels, unpaired fluvial terraces, and V-shaped valleys with recurrent seismicity. Further, the morphometric parameters including Valley Floor Width to Valley Height (Vf), asymmetry factor (AF), and gradient index (GI) further prove active nature of RF as suggested by low values of hypsometric integration, V-shaped valley, higher gradient index, and tilting of Saryu basin.

Tunnel Probabilistic Structural Analysis Using the FORM

In this paper tunnel probabilistic structural analysis (TuPSA) was performed using the first order reliability method (FORM). In TuPSA, a tunnel performance function is defined according to the boundary between the structural stability and instability. Then the performance function is transformed from original space into the standard normal variable space to obtain the design point, reliability index, and also the probability of tunnel failure. In this method, it is possible to consider the design factors as the dependent or independent random parameters with arbitrary probability distributions. A software code is developed to perform the tunnel probabilistic structural analysis (TuPSA) using the FORM. For validation and verification of TuPSA, a typical tunnel example with random joints orientations as well as mechanical properties has been studied. The results of TuPSA were compared with those obtained from Monte-Carlo simulation. The results show, in spite of deterministic analysis which indicates that the rock blocks are stable, that TuPSA resulted in key-blocks failure with certain probabilities. Comparison between probabilistic and deterministic analyses results indicates that probabilistic results, including the design point and probability of failure, are more rational than deterministic factor of safety.

A Study on Preventing Spontaneous Combustion of Residual Coal in a Coal Mine Goaf

The effectiveness of grouting scheme has been simulated to prevent the coal spontaneous combustion at a goaf in Haizi Colliery, China. The colliery has been operated for long period over 27 years and has a complex ventilation network including airflow leakages which could possibly lead to the spontaneous combustion of coal at goafs. Firstly, the mine ventilation simulator MIVENA was used to analyze the mine ventilation network airflows to control airflows in and out of working faces and goafs. As the second approach, numerical simulations were carried by the simulator FLUENT in order to predict spontaneous combustion of residual coal with leakage flow in the #3205 goaf. It was cleared that the goaf can be divided into three zones based on oxygen concentration in the goaf area. Finally, the numerical simulation results show that the slurry grouting method is able to be an effective and economical method by reducing porosity in the goaf area to prevent spontaneous combustion of residual coal.

Comparative Analysis between Biogas Flow in Landfill and Electrical Resistivity Tomography in Rio Claro City, Brazil

The biogas originated from anaerobic degradation of organic matter in landfills consists basically in CH4, CO2, and H2O. The landfills represent an important depository of organic matter with high energetic potential in Brazil, although with inexpressive use in the present. The estimation of production of the productive rate of biogas represents one of the major difficulties of technical order to the planning of capture system for rational consumption of this resource. The applied geophysics consists in a set of methods and techniques with wide use in environmental and hydrogeological studies. The DC resistivity method is largely applied in environmental diagnosis of the contamination in soil and groundwater, due to the contrast of electrical properties frequent between contaminated areas and the natural environment. This paper aims to evaluate eventual relationships between biogas flows quantified in drains located in the landfill, with characteristic patterns of electrical resistivity in depth. The drain of higher flow (117 m3/h) in depth was characterized for values between 8000 Ω·m and 100.000 Ω·m, in contrast with values below 2000 Ω·m, which characterize in subsurface the drain with less flow (37 m3/h), besides intermediary flow and electrical resistivity values, attributed to the predominance of areas with accumulation or generation of biogas.