Landscape and Geomorphology of the Impact Craters, India
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11th Planetary Crater Consortium 2020 (LPI Contrib. No. 2251) 2015.pdf LANDSCAPE AND GEOMORPHOLOGY OF THE IMPACT CRATERS, INDIA. Arindam Dutta1*, Debjani Raychaudhuri1, Aparajita Bhattacharya2, Anindya Bhattacharya3 and Sachin V. Pachpor4 1Geological Survey of India, Central Head Quarters, 29, J.L.N Road / 15, A & B Kyd Street, Kolkata-700016, India. 2Geological Survey of India, State Unit (SU): Punjab, Haryana and Himachal Pradesh, Chandigarh-160020, India; 3Geological Survey of India, State Unit – Karnataka and Goa, Bangalore – 560078, India, 4Geological Survey of India, State Unit - Maharashtra, Pune – 411006, India. Email: [email protected]*; [email protected]; [email protected]; anin- [email protected] and [email protected]. Introduction: An understanding of terrestrial im- on a topographic map (Survey of India topographic pact cratering is important as it addresses how the out- sheet no. 54K/3; 1:50,000; Figure 1c). er layer of the Earth has been modified due to impacts, and also its effect on the physical, chemical, and bio- a b logical systems. These studies also help in understand- ing the surface to sub-surface morphology, target ma- terial topography, ejecta emplacement and all other cratering mechanisms and processes. The present work has been taken up to identify and study the shock in- duced mesoscopic and microscopic deformation fea- c CEA tures in the three impact craters from India to compare their crater morphology of three different host rock units i.e. the basalts from Lonar crater, Maharashtra, the granite gneisses from Dhala (Mohar) crater, Mad- hya Pradesh and the sedimentary sequence from the GQV Granite Breccia Ramgarh crater, Rajasthan formed due to extra- terrestrial impacts. The envisaged studies in these three impact structures include systematic field survey and Figure 1a & b: Satellite imagery (IRS LISS III data sampling, detailed petro-mineraographic studies and with 3 – 2 – 1 band combination) and Digital Elevation image analysis for better understanding of the possible Model (DEM) of Dhala structure, Shivpuri Dist, M.P. deformation process(es) in response to meteorite / aste- Figure 1c: The Central Elevated Area (CEA) of Dhala roid impacts involving preservation and modification (Mohar) structure, Shivpuri dist, M.P. of crater landscape and morphology over the geologi- The Dhala area mainly comprises calc-silicate rocks, cal past. granitoids (including TTG lithologies), giant quartz Results: The deeply eroded Dhala structure is veins and reefs (GQVs), acid volcanics (dacite- hardly visible in Landsat (TM), Shuttle Radar Topo- rhyolite), meta-diorite and dolerite/amphibolite dykes, graphy Mission (SRTM), and Indian Remote Sensing as well as sandy siltstone intercalated with shale- Satellite (IRS)-1D hybrid [Linear Image Scanning Sys- sandstone unit (part of the Vindhyan Supergroup), tem, (LISS)-III + Panchromatic (PAN)] images. Off- with a small exposure of bedded ash and lateritic cover centre to the outline of the structure occurs a 426 m on the top of the central hill [1]. high, mesa-shaped hill, 2.5 km in diameter, to the northeast of Dhala village (Figure 1a & b). A number The Lonar crater (SOI toposheet no. 56 A/9) is a bowl- of roughly SW-NE to E-W trending linear to curvili- shaped, simple, hypervelocity impact structure with an near GQVs (Giant Quartz Vein)/ferruginous quartz average diameter of 1.88 km and an apparent depth of reefs with positive relief (up to 380 m high) are ob- 150 m [2]. It is one of the very few craters on Earth served on the eastern, western and southern sides of emplaced directly within basalts. This simple crater the Dhala (Mohar) structure. The present-day apparent formed entirely within the Deccan traps, making it a diameter of the structure is estimated at 11 km on the useful analogue for small craters on the basaltic sur- basis of the mapped distribution of monomict impact faces of the other terrestrial planets and the Moon [3]. breccias. The maximum elevation in the Dhala area Lonar crater is an excellent site for studies of impact has been recorded at the top of the central hill and the crater formation and shock deformation having flui- minimum elevation (295 m) near Bhaunti (4 km NW dized ejecta. The crater has a continuous, encircling, of Dhala village) in the vicinity of the Paronch River. raised rim, flanked by an ejecta blanket, extending for A weakly defined, annular drainage pattern in the vi- about 700 m to a km with a gentle slope of 2°-8°. cinity of the Central Elevated Area (CEA) is observed Three (03) set of fractures have been developed in 11th Planetary Crater Consortium 2020 (LPI Contrib. No. 2251) 2015.pdf impact basalts all along the crater rim, which are well The Ramgarh structure defines a circular shaped topo- evident in the LISS image of IRS map (Figure 2a). The graphic high, amidst the vast soil covered plains of the general topography of the Lonar crater is shown in Vindhyan Supergroup, near Ramgarh village, Baran Digital Elevation Model (DEM) (Figure 2b). The ejec- district, Rajasthan. It is characterized by a peripheral ta blanket or impact ejecta directly overlies the basaltic circular ridge and a central depression, with a level flow (mostly Flow No. 4) and contains unsorted basalt difference of 250 m (approx.), and the diameter meas- clasts / fragments (both massive and vesicular) embed- ures about 3.2 km. Close and intricate fracturing all ded within the pulverized basaltic matrix / ground- along the crest of the Ramgarh structure and subse- mass. The general thickness of ejecta blanket ~ 2 – 4 quent erosion of basal shale beds were responsible for meters, mostly exposed along nala cuttings, dug well the collapse of the roof, and formation of the depres- sections and farm/road excavation sites. The Lonar sion at the core of the Ramgarh structure as evident crater is a valuable analog site for studying degrada- from the Linear Image Scanning System (LISS-III) of tion processes with potential application to impact Indian Remote Sensing Satellite (IRS)-1D hybrid im- craters occurring on hydrologically active ancient age, Google Earth Image and DEM (Figure 3a & b). Mar’s surface, or to other impact craters on Earth, The dominant lithologies of Ramgarh structure are therefore, its geomorphic preservation is very impor- sandstone, shale and limestone of the Bhander Group tant [4]. belonging to the Vindhyan Supergroup. a b Kul River Figure 3a: The Ramgarh structure, Rajasthan with pe- Figure 2a: Satellite imagery (IRS LISS III data with 3 ripheral circular ridges and central depression, defines – 2 – 1 band combination) of Lonar crater, Buldhana a near circular shaped topographic high ( Source: district, Maharashtra (parts of toposheet no. 56 A/9). Google Earth Image). Figure 3b: Digital Elevation Model (DEM) of Ramgarh structure, Rajasthan. Conclusion: In this study we attempt to character- ize the landform, crater geomorphology, disposition of impacites and impact related structures (e.g. ejecta cover, breccia, fracture pattern etc.) which define the present day landscape of these impact craters over a geological milieu and provinves. References: Figure 2b: Digital Elevation Model (DEM) of Lonar [1] Pati J. K. et al. (2008) MAPS, 43, Nr 8, 1383–1398. crater, Buldhana district, Maharashtra. [2] Fredriksson K. et al. (1973) Science, 180, 862–864. Lonar crater interior shows signs of degradation in the [3] Maloof A. C. et al. (2010) Geol. Soc. Am. Bull., forms of gullies and debris flows, and the Dhar valley 122, 109–126. [4] Komatsu G. et al. (2014) Planetary (at Dhara Temple) is incising in the crater rim leading and Space Science, 95, 45–55. to form a fan delta. So keeping in view the geological importance of crater geometry and morphology it is recommended that the Lonar crater and lake may spe- cially be curated and protected from any sort of anth- ropogenic and/or agricultural activities. .