After reading this article you will learn about the geology of Indian arid zone.
The chief characteristic of the geology and rocks of India arid-zone is noticed in its remarkable succession of pre-Cambrian rocks which go far down towards the base of the Archaean. This sequence commences for the Bundelkhand gneiss, which is one of the oldest granites exposed anywhere upon the earth’ surface.
The early geologists call it a ‘fundamental gneiss’. The rock formations of Indian region range from Archaeans to Quaternary in age. The stratigraphic succession of the geological formations are given in table 3.1.
The oldest formations of granite, gneiss and chists are restricted near the Aravalli ranges towards the east. The Aravallis are tightly folded and highly metamorphosed rocks and belong to Aravallis (Archaean) and Delhi system. They also include considerable masses of granitic gneisses, granites, ultramafic rocks, and sills and bosses of amphiobolites and epidiorites.
The varieties of granites are Erinpura, Idar, Jalor and Siwana. Malani rhyolites are the representatives of volcanics. In Churu and Sikar districts extensive exposures are scattered with in the wind blown sands are termed as ancient crystalline’. Exposures of Malani rhyolites and their granitic equivalents called siwana granites occur extensively in Jodhpur, Pali, Barmer and Jalore districts.
Paleozoic Group – Vindhyan System:
The Vindhyan system is mostly represented by the consolidated to semi-consolidated sedimentary rocks in western Rajasthan. Rocks of Vindhyan system, which follows next in geological time scale are widely exposed in the Indian arid zone. They are most common in Jodhpur, Nagpur and Bikaner districts and partly in Pali and Jaisalmer districts.
The Vindhyan rocks are of late pre-Cambrian to early Cambrian age. The exposures are seen along Jodhpur-Pokaran road and around Jodhpur city. The rocks are well jointed and stratified. Glacial boulder beds in Bap-Pokaran are belonging to Permocarboniferous period, are present.
Rocks belonging to Jurassic and Cretaceous systems of Mesozoic group are exposed in Bikaner and Jaisalmer districts of western Rajasthan. Jurassic system is represented by Patcham, Chari, Katrol and Umia series in Kutch and Dhangadhra and Wadhawan sandstones in central Gujarat.
In Jaisalmer district of Rajasthan, the following succession has been established:
Abur Beds-Limestone with grits ad shales Parihar sandstones-Felspathic and ferruginous sandstones and quartzite’s.
Badesar Beds—Ferruginous grits ad sand-stones
Baisakhi formations—Shales with intercalation’s of sandstone
Jaisalmer limestone—Olitic and shell limestone with calcareous sandstone.
Lathi Beds—Sandstone with subordinate limestone’s towards top, available between Lathi and Jaisalmer near Bap and Nokha.
The Jurassic sequence in Kutch achieves thickness of 2150 metres which is attributed to gradual sinking of the basin of sedimentation as the deposition proceeded. Patcham and Chari series are predominantly calcareous while Wadhawan, Katrol, Umia formations are arenaceous with some limestone’s.
The exposures of Deccan Traps are observed over the western and southwestern parts of Kutch and Saurashtra. The traps achieve great thicknesses varying from 1000 meters in the east to 120 metres in the west. These are productive aquifers.
In Barmer the Balmir sandstones are of estuarine character and contain plant fossils. They are of Cretaceous age. The geological formations of Econe age are well represented in Jaisalmer and Bikaner. The strata consists of thick white and buff limestone’s and shales.
This group is mainly represented by the rocks belonging to Eocene period in western Rajasthan by Palana formations in Bikaner, Khuila formations in Jaisalmer which are of Laki age and Jagira and Bandah formations of Kirthan age. The tertiary group is represented by shales, with minor sandstone and limestone in Kutch and Saurashtra.
This group includes blown sand alluvium, Mar and Shumer series in western Rajasthan, alluvium and miliolite limestone of Gujarat and alluvium of Punjab and Haryana.
Geology of Cold Arid Zone:
The geology of arid cold region is mostly composed of consolidated sedimentary rocks of Palaeozoic and Mesozoic groups and intruded by the granites of tertiary era. These rocks are highly folded and faulted.