GEOLOGY of KUTCH Kutch—the largest district in Gujarat is bounded by the Great Rann on the north and east, Little Rann on the South-East, Gulf of Kutch on the south and the Arabian Sea on the west. It has a warehouse of impressive geological features. The people of Kutch have a rich cultural heritage which is very well acclaimed. The entire Kutch District has a unique landscape with highlands surrounded by vast plains which are extensive mudflats with salt covered white patches (Salinas). Highlands are structural uplifts which expose the rock formations in hilly region. Surrounding plains are structural lows between the uplifts covered by Quaternary and Rann sediments deposited in sea that transgressed into the lowlands and later receded during the structural uplift in recent past. During the marine incursion the uplifts were islands which are seen in the present landscape as uplands scattered over vast plains. These uplands are now described as “islands”. There are five such islands namely, Kutch Mainland (the biggest and most populated), Wagad, Pachham, Khadir, Bela and Chorar islands. The last four are collectively called “Island Belt” since they occur in one E-W linear belt. As seen from the geological map shown in Figure 1, Kutch basin is richly gifted with different deposits and structural features of the geological time scale since 200 million years. Detailed geology and tectonics of the region has been studied by various research workers (mainly S. K. Biswas’s papers). The basin started to form during late Triassic or early Jurassic during breakup of Gondwanaland. Mesozoic, Tertiary and Quaternary sediments were deposited in this basin. There were three phases of rift evolution. Deposition took place during the first phase. The first phase is the synrift phase with normal faulting when Mesozoic sediments were deposited. The next phase was the inversion phase when rifting was aborted as normal faults inverted as reverse faults causing upthrust of fault blocks. The third stage is the postbreak up northward drifting of the Indian plate when strike-slip movement along faults was initiated due to the dominant horizontal stress. From the map, the Mesozoic rocks are seen to be surrounded by Tertiary and Quarternary formations in all the uplifts. Deccan traps bordering the southern Mainland are the result of the volcanic activity following aborting of the rift during Late Cretaceous. There exist a number of formations like Kaladongar, Goradongar, Jhurio, Jumara, Jhuran and Khadir consisting of sandstone, shale and limestone in Middle to Upper Jurassic, Bhuj formation in Lower Cretaceous, overlain by Deccan Trap lava flows that erupted in Late Cretaceous to Early Paleocene time when Indian plate was passing over the Reunion hot-spot [8]. The region has unique geological features both on the onland and also on the offshore parts. Series of faults— Nagar Parkar, Island Belt, South Wagad, Kutch Mainland and North Kathiawar faults are responsible for the formation of uplifts (horsts), grabens, half-grabens. These features define the uniqueness of onland landscape of Kutch rift basin. The Island belt is broken into four blocks by wrench faults (Pachham, Khadir, Bela and Chorar). Uplifts along the aforementioned faults except the Kathiawar fault resulted in formation of sub-parallel E-W ridges (tilted horsts) while the uplift along the North Kathiawar fault is Saurashtra or Kathiawar horst which marks the southern rift-shoulder of the basin. The basin is bordered by Cambay petroliferous basin in the west and Nagar Parkar-Tharad ridge in the north (northern rift-shoulder). The Precambrian basement is exposed in the Nagar Parkar ridge. The basin extends across the offshore shelf almost upto the present continental slope. There are recent discoveries of petroleum deposits in the offshore part of the basin. Image: 1. Tectonic and geological map of Kutch showing major faults and stratigraphic units. 2. Dinosaur fossils in section in Kuar Bet (near India Bridge) 3. Lakhpat is a large area of wellexposed Middle Eocene Fulra limestone formation. The limestones are packed with varieties of fossils of Nummulites species. Nummulites are one of the important micro-fauna in the marine early Tertiary seas across the globe. This limestone belt extends from Lakhpat at the Western end to Vinjhan at the south-central region of the Mainland. The Nummulites are basically very unique fossils and can easily be recognized because of its coin shaped structure. 4. Paleo-channel in Khari Nadi section near crossing of Bhuj-Lodai road: Geologically old system of river channels filled up with sediments 5. Jara (23˚44N, 68˚59E): a) Location of Jara dome along the Lakhapar-Jara road as marked in the figure; b) The figure shows the jumara sediments at the core, doleritic dyke cutting through the hills, dhoosa oolite bed and strike-slip faults; c) Photo is taken at the marked location of Jara site viewing the Lakhapar ridges towards the south of Jara. (Courtesy: Dr. Bhawanisingh Desai, PDPU) REFERENCES 1. Wikipedia. en.wikipedia.org/wiki/Geotourism 2. Global Geotourism Blogspot. global-geotourism.blogspot.in/2011/09/father-of-modern-geotourism.html 3. National Geographic. travel.nationalgeographic/travel/sustainable/about_geotourism.html 4. S. K. Biswas, “The Miliolite Rocks of Kutch and Kathiawar (Western India),” Sedimentary Geology, Vol. 5, No. 2, 1971, pp. 147-164. dx.doi.org/10.1016/0037-0738(71)90029-7 5. G. Sen, M. Bizimis, R. Das, D. K. Paul, A. Ray and S. K. Biswas, “Deccan Plume, Lithosphere Rifting, and Volcanism in Kutch, India,” Earth and Planetary Science Letters, Vol. 277, No. 1-2, 2009, pp. 101-111. dx.doi.org/10.1016/j.epsl.2008.10.002 6. S. K. Biswas and S. V. Deshpande, “The Basement of the Mesozoic Sediments of Kutch, Western India,” Bulletin of Geology, Mining & Metallurgical Society of India, Vol. 40, 1968, pp. 1-7. 7. S. K. Biswas, “Structure of Kutch-Kathiawar Region, Wes- tern India,” Proceedings of the 3rd Indian Geological Congress, Pune, 1980, pp. 255-272. 8. S. K. Biswas, “A Review of Structure and Tectonics of Kutch Basin, Western India, with Special Reference to Earthquakes,” Current Science, Vol. 88, No. 10, 2005, pp. 1592-1600. 9. S. B. Shukla, “Late Quaternary Morphodynamic Evolution of the Northern Coast of Gulf of Kachchh Gujarat Western India,” Thesis, Maharaja Sayajirao University of Baroda, 2011.hdl.handle.net/10603/7485 10. Dinosaur Fossil Image, Web, 2013. newscenter.berkeley.edu/2011/02/22/t-rex-more-
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