Geological Excursion around Jaipur
Jaipur district is located in the eastern part of Rajasthan. It is bounded in the north by Sikar district, in the east by Alwar and Dausa districts, in the south by Tonk districts and in the west by Ajmer and Nagaur districts. It stretches between 26⁰ 26′ 08.11″ to 27⁰ 51′ 52.11″ north latitude and 74o 54′ 52.59″ to 76o 17′ 34.36″ east longitude covering an approximate area of 11,136 sq kms. The district is drained by several rivers viz., Banganga, Banas, Sabi and Shekhawati rivers and streams like: Bandi, Mashi, Dhund, Morel, Mendha, Gumti ka Nala, Madhobini, Sota etc. Administratively, Jaipur district is part of Jaipur division. This district is divided into 13 blocks, ranging in areas from 452 to 1925 km2.
Climate: Jaipur district has a semi-arid climate. There are three distinct seasons in a year. The winter season encompassing four months from November to February are mild and pleasant, with average temperatures in the 15-18° C range and low humidity. December and January are the coldest months when temperature varies between S and 10°C. There are however, occasional cold waves that lead to significant reduction of temperatures. March is a pleasant transition month to summer. The summer months of April to June record average daily temperature of around 35°C. May and June are the hottest months in Jaipur district. Temperature reaches up to 48°C in these months. Most of the annual rainfall is received in the monsoon months between June (end of June) and September.
Topography: The topography of Jaipur district is undulating in broad sense with largely even in the central and western parts but occasional hills in the east and north. The general topographic elevations in the district are between 300m to 400m above mean sea level. The narrow elongated hills rise above the adjacent plains and attain elevations to the extent of 750m amsl as a result escarpments of 100m to 200m are widely seen in the hilly regions which trend NE-SW. Hills are predominant in Jamwa Ramgarh, Shahpur, Viratnagar and Jaipur whereas the topography of rest of the district is undulating with occasional hills only.
Rainfall: The rainfall is however low, but has one of the high rainfall districts in Rajasthan. The general distribution of rainfall across can be visualized from isohyets presented in the Plate Ill. Interestingly, the eastern part receives more rainfall as compared to western part and it gradually reduces from east to west. The average annual rainfall was 823.2 mm based on the data of available blocks while highest average annual rainfall was 942.3 mm in Viratnagar block. Minimum annual rainfall was lowest in Kotputli block (540.6 mm). Kotputli block has received highest maximum annual rainfall of about 1,038.0 mm.
Geology: Geologic succession of Jaipur district is quite wide ranging in terms of age and rocks from Archean to Recent age are present in the area. Most of the north eastern part of the district is covered by younger and older alluvium which is predominantly sandy and clayey in nature. In some parts of western Jaipur eolian sand is also present as a thin cover above the alluvium sediments. Some parts in the northeastern region also show presence of Delhi Super Group quartzites, schists, phyllites and marbles. Most of the southern half of the district is occupied by Gneisses and schists of Bhilwara Super Group.
Geomorphology & Landforms: Landform features characterizing the area around Jaipur consist of structural hills, denudational pediments and intermontane valleys, and aeolian and fluvial plains. Structural hills occur as linear to arcuate uplands trending in a NNE-SSW direction with varying lithology associated with folding, faulting etc. The aeolian landforms comprise long stretches of eolian and sandy plains formed by aeolian activity. The eolian plains are made up of fine to medium grained sand and silt, occurring as dunes of varying heights, sizes and slopes. Th sandy plains are made uo of wind-blown sand with gentle sloping to undulating plain, comprising of coarse sand, fine sand, silt and clay. Denudational landforms comprise pediment, buried pediment and intermontane valleys. The pediments are represented by broad, gently sloping erosional surface of low relief between hills and plains, comprised of varied lithology, criss-crossed by fractures and faults. Pediments are often buried beneath relatively thick alluvial, colluvial or weathered materials.
The fluvial landforms in and around Jaipur are represented by alluvial plains, valley fills, flood plains, ravines, palaeochannels and salt encrustations or playas. The alluvial plains are represented by flat to gently undulating fluvial deposits of unconsolidated gravel, sand, silt and clay along rivers. Valley fills are also a result of fluvial activity comprising of boulders, cobbles, pebbles, gravels, sand, silt and clay. These units occur as consolidated to semi consolidated deposits. Flood plains occur as strips of relatively smooth land adjacent to river channels, which are sunjected to periodic flooding when rivers overflow their banks. Ravines occur as small, narrow, deep, depression, smaller than gorges, larger than gulley, usually carved by running water. Palaeochannels can be seen alongside river courses as buried, coarse textured material of variable sizes. Salt encrustations and playas are often found along with sand silt and clay in undrained topographic depressions devoid of vegetation.
Background Information - Aravalli
Craton and the Delhi Fold Belt
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Department of Geology
Aligarh Muslim University, Aligarh - 202 002 (India)