STUDY OF LATERITES AROUND TALMOD, MAHARASHTRA STATE, INDIA

STUDY OF LATERITES AROUND TALMOD, MAHARASHTRA STATE, INDIA Vadagbalkar Shrinivas Krishnaji Department of Geology, D.B.F. Dayanand College of Arts and Science, Solapur-413002, Maharashtra State, INDIA (Email: vadagbalkar@gmail.com) ABSTRACT: Inland laterisation in Deccan trap regions of part of Maharashtra state is not been attended and studied in details. Latertisation of the present study area belongs to the same. The Laterites of Talmod and surrounding area occur as primary Laterites i.e. directly resting on the parent rocks - Deccan traps with in situ alterations, under favorable conditions occurred in the past. Results of field setting, geomorphology and major geochemical characteristics further related with the probable genesis of these Laterites are presented in this paper. KEY WORDS: Laterites, Talmod, Maharashtra INTRODUCTION Laterites as defined by Schellman (1981) are the products of intense sub aerial rock weathering in which Fe and/or Al content is higher and Si content is lower than in merely Kaolinised parent rocks. They consist predominantly of mineral assemblages of goethite, hematite, aluminium hydroxides, kaolinite minerals and quartz. Laterites generally cap the Deccan Basalts and found on flat topped table lands, plateaus and coastal plains. Under the favourable conditions of Lateritisation the parent rock (Basalt) yield a residual product with relative or absolute enrichment of iron and aluminium along with titanium, accompanied by complete extraction of alkali, alkaline earth and silica along with other mobile elements. Inland Laterisation at relatively medium altitudes (~ 630 meters) in Deccan trap regions, are occurring in irregular and scanty patches especially in SE part of Maharashtra state in Marathwada upland areas, adjacent to Bidar district of Karnataka. This Lateritisation has not been attended and studied in details; therefore attempts are made to study part of these Laterites. The Laterites of Talmod and surrounding area i.e. the study area (latitude 76 0 42 N to 76 0 50 N and longitude 17 0 45 E to 17 0 53 E) occur as primary Laterites, directly resting on the Deccan traps. Results of field setting, geomorphology and major geochemical characteristics further related with the probable genesis of these Laterites are presented in this paper. GEOLOGY The area under study is situated in the south eastern part of Maharashtra. Talmod (76 0 45 15 N and 17 0 49 30 E) is a village in Osmanabad district of Maharashtra. It is 120 kms, SE of Osmanabad. The area in and around Talmod essentially consists of the Deccan Basalts of Cretaceous-Eocene age. The average precipitation is more than 1000 mm / year while the average temperature is 29 0 C. Alternately dry and humid weather conditions persist during the year. The area is consisting of elevated isolated plateau, and flat topped hillocks which are capped with Laterites and are essentially having the elevation above 620 meters. It is important to note that the adjacent lower elevation hillocks are void of Laterite capping. The average elevation is 640 meters. Moderate to gentle slope are characteristic of the area. The drainage is dendritic and intersected by shallow gullies / valleys. The Deccan Basalt flows of cretaceous Eocene age are horizontal in nature and show fairly uniformity in appearance. They are massive, hard and greenish to dark grey in colour. Horizontal and vertical joints/fractures are very common. Spheroid weathering is characteristic feature. Thermal and chemical action together weathers the Basalt to release the boulders of various sizes. The altered product is soft and greenish to yellowish brownish in colour called as Murom. During the temperate climate iron content in the silicate of the parent rock is liberated and oxidized to form goethite which imparts yellow and buff yellow colour to the products of weathering. The oxidation of iron gives red colouration reflecting the presence of hematite. (Chukrev, 1981). MATERIALS AND METHODS The lateritic ferricrust / duricrust which cap the traps are observed above 620 meters. The ferricrust / duricrust are hard and resistant at the top while comparatively softer below. The red iron oxides are dominating the crust. At Volume- 1 Issue-2 (2014) ISSN: 2348 604 X (Print); 2348 6058 (Online) 2014 DAMA International. All rights reserved 10

shallow places the loose lateritic soil which is reddish to brick red, granular in nature covers the duricrust. A Laterite profile comprises all stages from parent rock to the surface ferricrust / duricrust and therefore includes non-lateritic material too. The mature profile of weathering crust is remarkable in its unique monotony in various regions in the study area (Balsubramaniam and Vadagbalkar 1983; Chowdhury et al., 1965). Two main zones can be distinguished in this profile. The upper part of the profiles is usually red and lower part of the profiles is brownish yellow. The upper part is hard and mainly consisting of hematite material without any relics of original rock structure while the lower part is comparatively soft and mainly consisting of goethite material mixed with hematite material and showing at places relics of parent rock. The red products of weathering are affected by alteration into the climates (from humid to temperate) and become yellowish in colour, on account of hematite (Fe 2 O 3 ) changing to goethite (HFeO 2 ) by iron leaching process. This iron is added to the surface to convert it into ferricrust. The lower part of the goethite zone intermix with the lower clayey zone recognized as lithomarge clays or (Saprolite?). The lithomarge clays are soft, fragile and display various colours as red, yellow, green, brown etc. pockets of white kaolinitic clay (identified by stain technique) are commonly observed within the zone. At lower levels the relics of parent rocks are very common. Lithomarge zone thickness, in different profiles, varies from few centimeters to meter i.e. thinning and thickening of the zone is observed in some profiles. This zone exhibits a gradational contact with the altered Basalt zone below. The upper part of the altered Basalt is very soft and highly decomposed to term as clayey Basalt. The altered Basalt is further having gradational contact with fresh Basalts. The Laterite has average thickness of 5 to 10 meters. The Laterites appear more ferruginous in nature rather than aluminous. The Laterite formation is demarcating 620 meters level as the limit of Lateritisation, as below this level Laterites are not seen. The schematic diagram of a typical Laterite profile is represented in figure 1. From the various Laterite profiles in the area samples were collected at different levels/heights and used further for chemical analysis. GEOCHEMICAL STUDIES The various rocks in the Laterite profile were chemically analyzed for understanding the major element distribution, viz. Al 2 O 3, Fe 2 O 3, SiO 2, TiO 2 and LOI along with Na 2 O, K 2 O, CaO and MgO. The major elements were determined by the chemical methods, for 60 different samples. Out of these 20 representative analyses are taken to understand the chemical behavior of the major elements (Table 1). Volume- 1 Issue-2 (2014) ISSN: 2348 604 X (Print); 2348 6058 (Online) 2014 DAMA International. All rights reserved 11

RESULTS AND DISCUSSION The chemical analysis of the rocks in the Laterite profile from bottom to top, indicate the following variations. i) There is a gradual increase of alumina and decrease of Silica towards the top zone. ii) Fe 2 O 3 is at its maximum in the ferruginous Laterite (goethite) zone and again decreases towards the top zone, while near the surface crust again it shows its slight increases. iii) In general TiO 2 shows increase towards the top zone. The various rocks in the lateritic profile have been plotted on the Al 2 O 3, Fe 2 O 3, SiO 2 diagram (Figure 2). It is observed that there is a continuous de silication in the system and further probably there is a start of deferrification. The analyses reveal that the Laterites are more ferruginous in nature while slight increase in concentration of alumina than iron is observed in the samples of massive/granular zone below the duricrust. Al 2 O 3 is as high as 36. 30 %, Fe 2 O 3 is 50. 50 % maximum, silica ranges from 6. 5% to 11. 80%, LOI records higher values (22%) in alumina rich samples. The diagram further reveals that, the area has undergone strong Lateritisation as majority of Laterite samples are having silica % (computed) less than 12.50%. The geochemical variation diagram (Figure 2) reveals that Fe 2 O 3 and Al 2 O 3 are closer in initial stages while they diverge in the middle zone. Convergence of both is again observed near the top zone. This suggests the inverse relationship of Fe 2 O 3 and Al 2 O 3 with one another in the Laterite profile. The leaching is best seen in the chemical changes of Basalt to Laterite (Figure 2). The Basaltic Laterites are formed by extensive chemical weathering of Basalts during a geologic period (Cliff and 2008). Percolating waters caused degradation of the parent Basalt and preferential precipitation by acidic water through the lattice left the iron and aluminum composition. Primary plagioclase feldspars and augite with or without olivine were successively broken down and replaced by a mineral assemblage consisting of hematite, gibbsite, goethite, anatase, halloysite and kaolinite. During chemical weathering, processes like leaching, oxidation and hydration are involved, that lead to Volume- 1 Issue-2 (2014) ISSN: 2348 604 X (Print); 2348 6058 (Online) 2014 DAMA International. All rights reserved 12

the depletion of silica, leaching of alkalis, lime and magnesia and further conversion to iron and aluminum sesqui oxides (Balsubramaniam and Vadagbalkar 1983,1982); Schellmann (1981); Valeton (1983). A consideration of the chemical budget of the fresh rock to lateritic conversion reveals that nearly 43% silica is lost and 20.20% alumina is concentrated as enrichment. After considering the loss of material from the rock it is found that nearly 56 % of the parent material is leached out to produce a residuum of Laterite. CONCLUSION The area has undergone strong Lateritisation with nearly 56 % leaching of parent material i.e. Basalt The Laterites are more ferruginous in nature along with few pockets of aluminous Laterite. Physiographically the Laterite form an upland topography approaching pen plain and the drainage pattern suggest the presence of a water shade in this region which might have controlled the Lateritisation process. It is evident from the field appearance that Laterites overly the Basalts thereby suggesting the litho logical control and in situ alteration under favourable conditions of Lateritisation process. Field settings and studies reveal that probably normal rainfall followed by dry period, effective rock porosity (joints and fractures) in Basalts, the favorable geomorphological setting / relief-allowing free movement of water table with minimum erosion and long period of earth history have helped in formation of Laterites in the study area. REFERENCES Balsubramaniam K.S. and Vadagbalkar S.K. (1982). Mineralogy, Geochemistry and Genesis of Laterites around Kanhangad Region, Kerala State. J. Metals Mineral review, Calcutta. 21(5): 113-118. Balsubramaniam K S. and Vadagbalkar S.K. (1983). Geological studies relating to the weathering characteristics of Laterite and Bauxite profiles from Peninsular India, Prof. Kelkar Memorial volume, J. Indian Soc. Earth Scientists, Pune, 29-37. Chukrev P.V. (1981). On transformation of iron oxides by chemogenic eluvium in tropical and sub-tropical regions- Lateritisation Processes, oxford and IBH Publishing Co. Chowdhury M.K. Roy., Venkatesh V., Anandalwar M.A. and Paul D. (1965). Recent Concepts on the Origin of Indian Laterite, Report, Geol. Survey India, Calcutta, Retrieved April 17, 2010 Volume- 1 Issue-2 (2014) ISSN: 2348 604 X (Print); 2348 6058 (Online) 2014 DAMA International. All rights reserved 13

Cliff D., Ollier and Hetu C. Sheth (2008). The High Deccan duricrusts of India and their significance for the Laterite issue; J. Earth Syst. Sci. 117(5):537 551. Schellmann W. (1981). Considerations on the definition and classification of Laterites, Lateritisation processes, Oxford and IBH Publishing Co. Valeton Ida (1983). Palaeo environment of lateritic bauxites with vertical and lateral differentiation; Geological Society, London, Special publications (Geological Society of London) 11: 77dpo=10.1144/GSL.SP.1983.011.01.10. Retrieved April 17, 2010. Volume- 1 Issue-2 (2014) ISSN: 2348 604 X (Print); 2348 6058 (Online) 2014 DAMA International. All rights reserved 14