Quaternary Tectono Geomorphic Evolution of the Vaigai Delta as deduced from Geomorphic Mapping
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The well preserved landforms of the Vaigai river delta in Tamil Nadu stand testimony to the Quaternary sea level changes, fluvial dynamics of the river and the morphotectonic movements of the region. The geomorphic mapping performed using high resolution satellite images brought out the occurrence of unique set of landforms like beachrocks, abandoned channels, deltaic lobes etc. that indicate the dynamic evolution of the Vaigai delta during the Quaternary period assisted by the palaeo sea level fluctuations, preferential migration of the river and land upliftment due to neotectonic movements. The occurrences of extensive sand dunes further suggest the strong aeolian action in the geomorphic evolution of the delta and also the Quaternary climatic changes of the region.Keywords:
Landform
River delta
River terraces
Fluvial-lacustrine deposit is a kind of consolidation sediments that is one important geological basis for erosion landform.The erosion landform developed on alluvial plains composed of fluvial-lacustrine deposits is widely distributed.But its relevant studies,especially about the development process of erosion landform are very less.Based on the field survey information,theoretical analysis and some relevant articles,this paper comprehensively analyzed the exogenic forces action mechanism in the development process of erosion landform on alluvial plains composed of fluvial-lacustrine deposits in the Taklimakan Desert.The results show as the following:(1) These main exogenic forces including weathering,running water,aeolian erosion and gravity drive the erosion landform development on alluvial plains composed of fluvial-lacustrine deposits in the Taklimakan Desert.(2) Because aeolian activities in the Taklimkan Desert occur very frequent,so aeolian erosion plays a leading role in erosion landform development.(3)At the same time,weathering,running water and gravity also play important roles.Some records of summer strong rainfall events in the Taklimakan Desert indicate that the function of running water in erosion landform development can't be neglected.Rain infiltration and soil cracks,main weathering forms,loosen the surface soil structure,smash sediments to pieces,and make soil be eroded easily.Moreover,all these exogenic forces have different importance in different stages of erosion landform development.But they work co-operatively and mutually reinforce.Wind erosion breakthroughs can develop under aeolian erosion together with weathering and running water in the initial stage.A series of erosion landforms,including deflation furrow,wind erosion groove,blowout pit,wind erosion depression,erosion platform,wind erosion residual pier,and wind erosion plain,can rapidly develop under aeolian erosion together with gravity and weathering in the rest of stages.Sand wedges,composed of sand particles deposited in the wedge-shaped space of soil cracks,are of great importance in erosion landform development.Rainwater flows into sand wedges and is adsorbed by sand.Due to good penetrability of sand deposits,water can infiltrate quickly without evaporation loss and reach the bottoms of cracks.The deep soil can be destroyed by soil expansion of wetting and unfreezing;soil cracks widen and extend into deep soil further.Lateral erosion and undercutting are the main forms of wind erosion as well as sheet erosion,they make the sediments hang up.Lateral erosion,undercutting and sand wedges provide good conditions for gravity collapse and accelerate the negative erosion landform development on the sediments with nonhomogeneous texture.Collapse diluvium also can slow down the speed of wind erosion landform development.(4) The morphological characteristics of erosion landform depend on the special exogenic forces combination and the interbedded sedimentary structure of alluvial plains,namely,compact sediment and soft sediments are distributed in turn in vertical profile.
Landform
Alluvial fan
Water erosion
Alluvial plain
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The Segre River is one of the major streams in the southern Pyrenees that drains the elevated chain toward the Ebro basin foreland. Focusing on climatic, tectonic and structural controls, we aim to determine their relative importance for the Pliocene– Quaternary fluvial landscape evolution in the southern Pyrenees foreland. Along its course, the Segre River has a flight of fluvial cut-and-fill and strath terraces preserved that have been mapped based on DEM's and geomorphological fieldwork. This paper presents the first results of our study and reports on the Segre terrace staircase, which is characterized by seven major Quaternary terrace levels with elevations up to more than 110 m above the modern stream profile. In the upper and middle reaches, the (semi)parallel terraces of the Segre River feature anomalously thick gravel bodies and deformations of terraces caused by faulting, folding and local subsidence. In the foreland, the longitudinal terrace correlations disclose slightly increased vertical terrace spacing, which could originate from (i) delayed flexural isostatic uplift related to widespread foreland erosion after the endo-exorheic transition, or (ii) enhanced fluvial erosion after the Mid-Pleistocene climate transition in combination with base level lowering at the Ebro basin outlet in the Catalan coastal ranges. Since the basin opening (presumably late Miocene), the Catalan coastal ranges were progressively cut down and the exorheic drainage system gradually adjusted to Mediterranean sea-level. Both, the Segre terrace profiles and the morphology of the Ebro breach in the Catalan coastal ranges indicate a base level position of about 200 m asl for the onset of (Pleistocene) terrace staircase formation, implicating that the Catalan coastal ranges might have functioned as a local base level upstream of the sea outlet, potentially until the Middle– Late Pleistocene. This chapter is based on: Stange, K.M., van Balen, R.T., Vandenberghe, J., Pena, J.L., Sancho, C., 2013 (a). External controls on Quaternary fluvial incision and terrace formation at the Segre River, southern Pyrenees. Tectonophysics 602, 316–331.
River terraces
Terrace (agriculture)
Tectonic uplift
Landform
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Xinding Basin is a typical Cenozoic graben-type basin in the northern Fenwei graben system,which is surrounded by mountains of 2000 to 3000m high above sea level. Downward from the peak to the piedmont on the basin side are respectively peneplanes of Beitai stage and Dianziliang stage in Paleogene,peneplane of Tangxian stage in Neogene,and seven-level river terraces and six-level pediments in Quaternary. Loess and paleosol sequences on the landforms are correlative to typical loess section,which is an advantage for landform dating.A study has been made of the paragenetic relations of the pediments and river terraces on the northern piedmonts of Wutai Mountains and Xizhou Mountains via geomorphologic mapping on 1 ∶10,000 scale,and an analysis on the role of tectonic,climatic,and drainage factors in the parageneses. The Quaternary pediments and river terraces on the north piedmont of Wutai Mountains are united to constitute six steps of geomorphic surfaces. The episodic uplifting of fault blocks is deemed to be the dominant factor in the formation of the unified surfaces.Episodic uplifts result in longitudinal profiles of riverbeds alternated by cascade and gentle reaches one in mountainous areas. Terraces disappear upstream near the vertex of cascade reach. Cascade reaches represent quickly uplifting stages,and gentle ones represent stable stages. On condition that waterfalls between adjacent terraces recede at same speed,durations of active or stable stages can be estimated by ages of terraces and relative length of cascade reach and gentle one,and then ages of uplifting stages since 1.20Ma are estimated. The four quickly uplifting stages are from 1200 to 1059kaBP,from 600 to 501kaBP,from 130 to 103kaBP,and from 20kaBP to present. Other intervals are stable stages.
River terraces
Landform
Neogene
Alluvial fan
Lineament
Paleosol
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Landform
River terraces
Terrace (agriculture)
Chronology
Glacial landform
Alluvial fan
Coastal plain
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Landform
Desert (philosophy)
Water erosion
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In recent years,promoted by tremendous demands from national economic construction,great progress has been made in geomorphology and Quaternary geology in China.This article generalizes the recent progresses,mainly those in the period 2006-2008,including the progress in the fields of tectonic landforms,fluvial landforms,eolian landforms,glacial landforms,estuary and coastal landforms and Quaternary environmental evolution.Furthermore some suggestions are proposed to develop the discipline in the following aspects:(1) Studies of basic theories;(2) Research into applied geomorphology and Quaternary geology concerning the key construction projects;(3) Experimental studies,both in laboratories and in field surveys;(4) Training of young geomorphologists and Quaternary geologists.
Landform
Glacial landform
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The well preserved landforms of the Vaigai river delta in Tamil Nadu stand testimony to the Quaternary sea level changes, fluvial dynamics of the river and the morphotectonic movements of the region. The geomorphic mapping performed using high resolution satellite images brought out the occurrence of unique set of landforms like beachrocks, abandoned channels, deltaic lobes etc. that indicate the dynamic evolution of the Vaigai delta during the Quaternary period assisted by the palaeo sea level fluctuations, preferential migration of the river and land upliftment due to neotectonic movements. The occurrences of extensive sand dunes further suggest the strong aeolian action in the geomorphic evolution of the delta and also the Quaternary climatic changes of the region.
Landform
River delta
River terraces
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This paper presents the results of geomorphological investigations carried out on the Pinios River delta, which is a Late Holocene arcuate type delta, located in the southern Thermaikos Gulf (Central Greece). Digital elevation model (DEM) analysis and the study of maps of the last two centuries, accompanied by field survey and aerial photo interpretation have led to the production of a geomorphological map at 1:15,000 scale which outlines the features of the deltaic plain and coastal zone. The evolution and the associated morphology of the delta are the result of the complex interplay of fluvial sedimentation, wave activity and prevailing longshore currents. The dominant landforms of the delta are the numerous abandoned meandering channels, as the river has changed its course several times, and a series of sub-parallel linear sandy beach ridges (cheniers) occupy the lower delta plain. The shoreline of the delta is generally retreating due to marine processes, especially where former river mouths occur whereas the presently active mouth of the river and its immediate surrounds are prograding.
River delta
Landform
Beach morphodynamics
Progradation
River mouth
River terraces
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Remotely sensed images, maps, charts, and historical accounts document the evolution of the Lingayen Gulf bayhead plain in the northwestern Philippines. Beach ridges and relict channel patterns record delta progradation and switching that, together with meander belt migration, constructed the bayhead plain. The latest delta switching occurred after 1935, when the downstream portion of the Agno River, the largest river discharging into the bayhead, was artificially diverted to a more direct route. The shoreline retreated in the abandoned delta; in contrast, paired sets of beach ridges that diverge toward the new river mouth formed a cuspate delta. In the more landward portions of the coastal plain, similar but older pairs of wedge-shaped beach ridge sets occur between more continuous to parallel sets that also truncate their apical ends. The pair of wedge-shaped sets was used to map paleodelta lobes; the continuous-parallel sets record transgressive events. Within 7 kilometers of the bayhead plain, at least 15 paleodelta lobes were alternately, successively, or simultaneously built by three river systems. These paleodeltas formed during the sea level fall from 2.4 ka to the present. Before this, westward tilting because of movements along the two faults that bound the alluvial plain and switching of the main distributary channel of the Agno alluvial fan caused the lower Agno River to migrate episodically to the southwest. Continued channel avulsions in the alluvial fan changed the sediment loads of the multiple river pathways created by meander belt migration, leading to delta switching downstream. Contemporaneous 220-year recurrences of delta switching and high-magnitude Philippine Fault earthquakes indicate tectonic control of the bayhead plain evolution.
Progradation
Meander (mathematics)
River delta
Alluvial fan
Coastal plain
Alluvial plain
Marine transgression
River terraces
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Aggradation
River terraces
Bedrock
Landform
Tectonic uplift
Debris flow
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