Geomorphological Evolution and Palaeoenvironmental Change in the Western Alashan Plateau, China

Although neotectonic activity is considered to be the main factor of the terrain evolution of the Qinghai Tibet Plateau and its surrounding high-altitude areas,further geomorphological analysis and literature analysis are needed for the understanding of the geomorphic evolution and the Quaternary environment change of the western area of the Alxa Plateau near the northern Tibet Plateau.The purpose of this study is to investigate the distribution of site-specific geomorphic units of the landforms developed in the vast topography of Ejina Basin(Western Alxa),in order to identify the geostructural and climatic causes of the geomorphic landscape and its impact on the change of paleoenvironment.At present,the climate and hydrological conditions in Ejina are relatively monotonous and stable.In addition to tectonic dynamic factors,the most widely distributed landform in the basin is climate landform.There are both geomorphological and sedimentological anomalies of Aeolian landforms occurred in the whole basin,indicating that the underlying surface effect(retention effect)of river(Ejina River)and its related uneven ground and weak wind erosion(deflation)process in the nearby area may be the important factors controlling the formation of Ejina dunes,rather than the arid climate.It is believed that the extensive interaction between the aeolian and fluvial processes is the main mechanism of the regional geomorphic difference in Ejina Basin.According to the comparability of regional geomorphology and sedimentology,the period of the formation of relic geomorphology in the edge of Ejina Basin can be reasonably attributed to the local glacial maximum of the last glacial.The geomorphic transformation from quasi plain and desert valley to desert plain,the appearance of widely moving sand dunes and the presence of large ancient lake geomorphology all indicate that the drought index of Ejina Basin is increasing on the scale of geomorphic formation.Paleogeomorphological and chronological evidences show that the climatic and hydrological conditions of the basin in the last glacial period and the early Holocene are much better than those at present.For example,the average annual precipitation in the area before 39-23ka BP is between 60-350 mm(about 36 mm today),but there are large waves in the Holocene.The coexistence of various climates and landforms in Ejina Basin and the resulting geomorphic diversity should be the composite result of various geomorphic processes and surface processes besides glaciation.The low aridity(relative humidity)in the Ejina Region in the late Pleistocene may be the result of the enhancement of the westerly rain belt and the weakening of the Asian Winter Monsoon in the arid region of Central Asia.

Geomorphology and Hydrology of the Benin Region, Edo State, Nigeria

This paper examines the geomorphology and hydrology of the Benin Region, Edo State, Nigeria. The major landform features and processes of the region are highlighted. This region is a strategic and significant landscape in Nigeria. Information was gathered on the various aspects of the landscape, including the Geology, Physiography (Relief) and Geomorphology, Geomorphic processes, Weathering, Drainage processes, Landforms, Surface Water Hydrology and Water Resources. The Benin Region is underlained by sedimentary formation of the South Sedimentary Basin. The geology is generally marked by top reddish earth, composed of ferruginized or literalized clay sand. Geologically, the Benin Region comprises of 1) the Benin formation;2) alluvium;3) drift/top soil and 4) Azagba-Ogwashi (Asuba-Ogwashi) formation. Several parts of the region are surrounded by the Benin historical moats. The region has been described as a tilled plain in the south western direction. The local relief of the region is 91 m. Boreholes records in the Benin Region show evidence of deep chemical weathering overtime. Soil profile reveals that the region is composed mainly of reddish brown sandy laterite. Intermittent layers of porous sands of sandy clays may reach a large depth as found in the borehole drilled in the region. These are products of deep chemical decay of the original parent rock materials. Three river systems drain the Benin Region. They are the Ikpoba River, the Ogba River and Owigie-Ogbovben River systems. The mean annual discharge of Ikpoba River for 1982-1983 and 1993-2002 was 1411 mm/yr, which was 1.019 × 109 m3 with a mean annual baseflow of 1256.23 mm (0. 907 × 109 m3). This constitutes 87.65% of the total flow. It has a mean annual surface runoff of 225.18 mm (0.112 × 109 m3) or 24.4 % of the total discharge. The water resources of the region include surface water and underground water.

Geomorphometric Features of the Alluvial Fans around the Chaka-Qinghai Lake in the Northeastern Tibetan Plateau

This article aims to study the geomorpometric features of alluvial fans since they act as a small-scale geomorphic unit response to tectonics and climate changes around the Chaka-Qinghai Lake area in the northeastern Tibetan Plateau. We quantitatively extracted geomorphic parameters, such as the surface area and slope of alluvial fans adjacent to the Qinghai Nan Shan and Ela Shan. Alluvial fans in the Chaka Lake partition area, south of the Qinghai Nan Shan, are featured by a small area and short length, but the largest slope. Geomorphic parameters of the alluvial fans in Ela Shan area are in- termediate in size, and the alluvial fans in the Qinghai Lake partition area north of Qinghai Nan Shan have the gentlest slope. Together with the regional faulting activity analysis, we suggest that the alluvial fans with the high slopes in the south of Qinghai Nan Shan are mainly controlled by the reverse faulting along the Qinghai Nan Shan faults, and the strike-slip movement of the Eia Shan fault zone plays a weak role. In contrast, due to the lack of active faults, the alluvial fans near the Qinghai Lake area north of the Qinghai Nan Shan only respond to regional erosion, transportation, and deposition proc- esses, thereby forming relatively gentle geomorphic units.

Morphological and Microstructural Evidences of Paleo-Seisminc Occurrences in an Earthquake Prone Zone of Tripura, India

Morphology and structure of a faulted zone not only express the present status but also preserve the evidences of early seismo-tectonic occurrences. The present paper aims to assess the morphological as well as subsurface evidences of early seismo-tectonic occurrences in an earth- quake prone zone of Baromura Hill, Tripura. Tectonically this is a part of Tripura-Mizoram fold belt and fall within Zone V of BIS seismic map. In the present research the tectonic lineaments of Baromura Hill was identified by using satellite data. For that purpose, Landsat TM shortwave in- frared, midwave infrared and near infrared was selected for preparing suitable band combination. A classified thermal infrared was used for final operation. From the remote sensing operation five clear tectonic lineaments were found. During the field work rock samples were collected for labora- tory testing. Thin sections of the rocks show that complex stress pattern was developed during the geological past which caused strong seismo-tectonic occurrences. From the study it can be assessed that though the nature of the paleo-seismic occurrences were almost same but the level of impact varied through spatial and temporal scales due different physical properties and arrangements. It is also clear from the study that the geological evolution of this place is more complex as it seems to be. Tectonic and geomorphic processes worked together through the Tertiary and Quaternary periods and played equally important role for landform evolution.