			Home About us Contact

Structural Relief (structural + relief)

Distribution by Scientific Domains

Earth and Environmental Science	80%

Selected Abstracts

Dynamics of soil erosion rates and controlling factors in the Northern Ethiopian Highlands , towards a sediment budget

EARTH SURFACE PROCESSES AND LANDFORMS, Issue 5 2008
Jan Nyssen
Abstract This paper analyses the factors that control rates and extent of soil erosion processes in the 199 ha May Zegzeg catchment near Hagere Selam in the Tigray Highlands (Northern Ethiopia). This catchment, characterized by high elevations (2100,2650 m a.s.l.) and a subhorizontal structural relief, is typical for the Northern Ethiopian Highlands. Soil loss rates due to various erosion processes, as well as sediment yield rates and rates of sediment deposition within the catchment (essentially induced by recent soil conservation activities), were measured using a range of geomorphological methods. The area-weighted average rate of soil erosion by water in the catchment, measured over four years (1998,2001), is 14·8 t ha,1 y,1, which accounts for 98% of the change in potential energy of the landscape. Considering these soil loss rates by water, 28% is due to gully erosion. Other geomorphic processes, such as tillage erosion and rock fragment displacement by gravity and livestock trampling, are also important, either within certain land units, or for their impact on agricultural productivity. Estimated mean sediment deposition rate within the catchment equals 9·2 t ha,1 y,1. Calculated sediment yield (5·6 t ha,1 y,1) is similar to sediment yield measured in nearby catchments. Seventy-four percent of total soil loss by sheet and rill erosion is trapped in exclosures and behind stone bunds. The anthropogenic factor is dominant in controlling present-day erosion processes in the Northern Ethiopian Highlands. Human activities have led to an overall increase in erosion process intensities, but, through targeted interventions, rural society is now well on the way to control and reverse the degradation processes, as can be demonstrated through the sediment budget. Copyright © 2007 John Wiley & Sons, Ltd. [source]

A geometric and kinematic model for double-edge propagating thrusts involving hangingwall and footwall folding.

GEOLOGICAL JOURNAL, Issue 5-6 2010
An example from the Jaca, Pamplona Basin (Southern Pyrenees)
Abstract A new geometric and kinematic model is proposed for a particular type of fault-related folding based on the study of a natural example developed in Palaeogene carbonate rocks from the Jaca,Pamplona Basin (Southern Pyrenees). The example consists of a hangingwall anticline related to a reverse fault with variable displacement and a gentle footwall syncline. A detailed structural analysis of the structure and a cross-section, perpendicular to its axis and parallel to the transport direction, reveals that none of the previous published models of fault-related folds is able to simulate its main characteristics and reproduce its geometry. The main features of the new model are: double-edge propagating fault and folding developed in both the hangingwall and the footwall. A MATLAB-based program was created to calculate structural parameters such as shortening, structural relief and fault slip; obtain graphs of different parameters such as shortening versus slip along the fault, shortening versus fault length, and produce sections across forward models showing the different stages of fold growth. The model presented here gives an acceptable geometrical fit to the studied natural structure and provides a reasonable evolutionary history. In addition, the results obtained using the model are similar to those measured on the cross-section. As a final step the subsurface portion of the natural fold was completed following the constraints imposed by the model. Copyright © 2010 John Wiley & Sons, Ltd. [source]

Post-impact structural crater modification due to sediment loading: An overlooked process

METEORITICS & PLANETARY SCIENCE, Issue 11 2007
Filippos Tsikalas
The analysis demonstrates that the geometry and the structural and stratigraphic relations of post-impact strata provide information about the amplitude, the spatial distribution, and the mode of post-impact deformation. Reconstruction of the original morphology and structure for the Mjølnir, Chicxulub, and Bosumtwi craters demonstrates the long-term subsidence and differential compaction that takes place between the crater and the outside platform region, and laterally within the crater structure. At Mjølnir, the central high developed as a prominent feature during post-impact burial, the height of the peak ring was enhanced, and the cumulative throw on the rim faults was increased. The original Chicxulub crater exhibited considerably less prominent peak-ring and inner-ring/crater-rim features than the present crater. The original relief of the peak ring was on the order of 420,570 m (currently 535,575 m); the relief on the inner ring/crater rim was 300,450 m (currently ,700 m). The original Bosumtwi crater exhibited a central uplift/high whose structural relief increased during burial (current height 101,110 m, in contrast to the original height of 85,110 m), whereas the surrounding western part of the annular trough was subdued more that the eastern part, exhibiting original depths of 43,68 m (currently 46 m) and 49,55 m (currently 50 m), respectively. Furthermore, a quantitative model for the porosity change caused by the Chesapeake Bay impact was developed utilizing the modeled density distribution. The model shows that, compared with the surrounding platform, the porosity increased immediately after impact up to 8.5% in the collapsed and brecciated crater center (currently +6% due to post-impact compaction). In contrast, porosity decreased by 2,3% (currently ,3 to ,4.5% due to post-impact compaction) in the peak-ring region. The lateral variations in porosity at Chesapeake Bay crater are compatible with similar porosity variations at Mjølnir crater, and are considered to be responsible for the moderate Chesapeake Bay gravity signature (annular low of ,8 mGal instead of ,15 mGal). The analysis shows that the reconstructions and the long-term alterations due to post-impact burial are closely related to the impact-disturbed target-rock volume and a brecciated region of laterally varying thickness and depth-varying physical properties. The study further shows that several crater morphological and structural parameters are prone to post-impact burial modification and are either exaggerated or subdued during post-impact burial. Preliminary correction factors are established based on the integrated reconstruction and post-impact deformation analysis. The crater morphological and structural parameters, corrected from post-impact loading and modification effects, can be used to better constrain cratering scaling law estimates and impact-related consequences. [source]

Tectonic modification of the Australian North-West Shelf: episodic rejuvenation of long-lived basin divisions

BASIN RESEARCH, Issue 2 2005
Mat Harrowfield
Neogene collision between Australia and the Banda Arc modified two adjacent depocentres within Australia's North-West Shelf, the Browse and Bonaparte Basins. We identify two components of this modification: (1) continuous long-wavelength amplification of Permo-Carboniferous basement topography, and (2) flexure and normal faulting of Triassic,Recent sedimentary cover. Although this deformation was continuous across the Browse and Bonaparte Basins, the degree of basement architectural control, mechanisms of fault linkage and distribution of syntectonic accommodation space varied significantly between the two basins. These variations reflect fundamental differences in the structural relief, amplitude and depth of rifted basement on either side of a rupture-barrier-style accommodation zone, the Browse/Bonaparte Transition. This long-lived architectural divide, of which there is no discrete structural expression, was amplified by Neogene collision. We examine tectonic rejuvenation of the Browse/Bonaparte Transition and describe a mechanism for actively sustaining long-lived segmentation of the continental shelf. [source]

Numerical models of growth-sediment development above an active monocline

BASIN RESEARCH, Issue 1 2004
Thomas L. Patton
The deposition, erosion and deformation of growth strata associated with an actively growing monocline are modelled using mechanically based numerical experiments. The results demonstrate that the nature of the growth-stratal record depends on (1) the interaction between the base-level rate of change and the rate of change of the accommodation space created due to structural relief across the limbs of the monocline; and (2) the progressive folding of the growth strata. With base-level elevation initially coincident with the upper surface of the pre-tectonic units, constant rates of base-level change create three growth-stratal preservation states. If the base level rises, a growth-sediment wedge covers both limbs of the monocline, with thinner sediment thicknesses on the upthrown limb, forming an on-structure wedge. If the base level falls at a rate less than the rate of accommodation space creation due to structural relief, growth-strata pinch out onto the dipping limb of the monocline, forming an off-structure wedge. If the base level falls at a rate greater than the rate of accommodation space generation due to structural relief, no syntectonic deposition occurs and pre-tectonic units on both sides of the monocline are eroded. Syntectonic unconformities develop within the growth-sediment packages when the rate of accommodation space generation changes during the course of the experiment. The bedding angularity across the unconformities is greatest in the region of the dipping limb of the monocline; off structure, the bedding across the correlative event becomes parallel, forming correlative conformities or disconformities. [source]