NOTES REPORT ON FIELD WORKSHOP ON INTEGRATED EVALUATION OF THE KALADGI AND BHIMA BASINS - OCTOBER 21-25,1999 Kaladgi and Bhima are the two important Proterozoic basins of northern Karnataka which have received considerable attention in the realm of stratigraphy, sedimentology and economic geology. In order to provide a forum for discussion on the integrated evaluation of data from these two basins and to provide an opportunity to examine critical geological sections, the Geological Society of India organised a field workshop for five days. The entire programme of field workshop was planned in consultation with key workers from organisations like Geological Survey of India, Department of Geology of the University of Pune and Atomic Minerals Directorate for Exploration and Research. Field Traverses: Broadly four field traverses were arranged, two in the Kaladgi basin and two in the Bhima basin. On each day, after the day's field work, delegates assembled in the evening for presentation of the results of their research. On our first traverse in the Kaladgi basin on October 22, we had the first stop at Gaddankeri where the Chikkasellikere Limestone Member of the Yendigere Formation (Lokapur Subgroup, Bagalkot Group, Kaladgi Supergroup) is exposed. Alternations of packstones and mudstones were observed in the sequence. The mudstones are characterised by internal cross-stratification. The presence of continuous parallel bedding, load casts, flame structures and convolute laminations were observed in the limestone sequence. In the down dip direction dolomites (Nagnaur Member) are followed by Jalikatti Argillite, PetIur Limestone and Bamanbudni Dolomite of the Muddapur Formation appear. The main ridge occupied by the Bevinmatti conglomerate marks the advent of the Sin~ikeriSubgroup. The next stop was at Chiksellikeri limestone mines of the Mysore Minerals. Limestone here analyses +52% CaO. We moved across the Chitrabhanukot Dome exposing the dolomite of the Yargatti Formation. The dolomite is characterised by strornatolites referable to Conophytoncyli~ldricus. Next we traversed across Lokapur folds and examined Jalikatti Argillite followed by Yadahalli Argillite (Muddapura Formation). Near Torgal Tanda we examined the angular unconformity between the Bagalkot Group and the Badami Group. The Badami is represented by thick horizontally bedded arenite lying unconformabl y over the steeply dipping Saundatti Quartzite and Manoli Argilli te (Rarndurg Formation - Lokapur Subgroup - Bagalkot Group). Ravi Korisettar acquainted us with prehistoric artefacts. In the evening the first technical session was held at the Bagalkot Camp. On the 23rd, the delegates visited the cave temples of Badami (a World Heritage site) representing one of the finest examples of rock-cut cave temples. The arenite in which cave temples are carved belongs to the Cave Temple Arenite of the Kerur Formation of the Badami Group. The arenite has preserved excellent trough cross bedding. At Chiknashi we examined the unconformity between the Archaean crystalline basement and the Bagalkot Group, the latter comprising the clast supported polymictic Salgundi Conglomerate followed by the Saundatti Quartzite and the Manoli Argillite. Bagalkot Group is unconformably overlain by conglomerates, gritty sandstones and arkoses of Badami Group which at places rest directly upon the crystalline basement. Theconglomerate is radioactive and according to S.A. Pandit the radioactivity is primarily due to thorium. JOUR.GEOL.SOC.INDIA,VOL.55, FEB. 2000 208 NOTES At Mahakoot the delegates were shown a section across a steeply dipping Saundatti Quartzite, Manoli Argillite and the Mahakoot Chertbreccia, unconformably overlain by the horizontalIy disposed conglomerate and arenite of the Badami. The nature of chertbreccia and polymictjc conglomerate of the Badami elicited considerable field discussion with views ranging from fauIting as the cause of breccia to sedimentary origin due to desiccation. There was some discussion on the origin of polymictic conglomerate of thc Badami Group, whether it was flu.vial or glacial. Near B.N. Jalihal, the delegates were shown the overturned limb of the anticline of the BagaIkot Group, over which the Badarni arenites rest with an angular ~nconforrnit~. The last stop of the traverse before returning to Bagalkot was at Konkankoppa where the youngest limestone member of the Badami sequence was seen. Here the Konkankoppa Limestone Member succeeds the Halkurki Shale. Limestone is bluish grey, at places reddish brown, and displays gently dipping ripple drift stratification truncated by erosional surface. The evening ~cientific~meetingwas held in the serene surroundings of the conference hall of the Almatti rest house of the Krishna Bhagya JaIa Nigam. On the 24th October; the delegates started with their baggage for the night halt at Shahapur. The Almatti railway cutting was our first stop where we examined the basement-cover relationship between the Archaean crystalline rocks and the Saundatti Quartzite of the Bagalkot Group as also the extension of the faults present in the basement into the cover rocks. This was explained as due to basement shear passing into the cover sediments in the form of a synsedimentary fault. However, the reverse nature of the fault and its curving along the contact between basement and cover was of the nature of a decollement along the base of the cover rock.. This was the last stop in the Kaladgi basin. We also had a look at one of the Palaeolithic sites with artefacts strewn around, thanks to initiative shown by Ravi Korisettar. As we moved along the Almatti-Muddebihal road we passed from Kaladgi to the younger Bhima basin towards northeast. However, it could not escape our attention that these two hasins are separated by a geomorphically subdued stretch of deeply weathered granitoids in strike extension of the Closepet granitoid batholith. At Muddebihal stop, the delegates had their first introduction to the sediments of the Bhima Group. We examined the conglomerates and quartzo-feldspilthic gritty sandstone of the Rabanpal I i Formation. Before reaching Ukinal, we had a look at the gradational change from clastic-argillaceous sequence of the Rabanpalli Formation to predominantly carbonate sequence of the Shahabad Formation. We examined grey, blocky limestone of the Shahabad Formation exposed in a prominent hill, about 1.2 km south of Ukinal. It was observed that the Shahabad limestone beds which are generally subhorizontal are deformed into folds close to the Gogi-Kuralagere reverse fault. Brecciation and rernobilisation of calcite along fault zone with radioactive lnineralisation is reported from this area. With the setting sun in the horizon we moved to Shahabad for the night halt. 25th October was the last day of our traverse. The delegates took keen interest in examining the nature of radioactive mineralisation discovered by the Atomic Minerals Directorate for Exploration and Research. The breccia marking the Gogi-Kuralagere fault contains fragments of limestone, sandstone and shale in calcite matrix. High radioactivity was detected in the fault breccia. According to S.A.Pandit radioactive minerals coffinite and pitchblende are present along with galena and pyrite. The delegates visited the core library of the Atomic Minerals Directorate and examined the cores of basement rocks and limestone. It was indeed a very useful visit. The last session of the scientific meeting was held at the lecture hall of the field camp of ;he Atomic Minerals Directorate. JOUR.GEOL.SOC.INDIA,VOL.55, FEB.2000 Scientific Sessions: Under the theme of stratigraphy there were three presentations; lithostratigraphic classification of Kaladgi basin (Jayaprakash and Sundaram), a reappraisal of their earlier classification which was based on regional geological mapping carried out by Geological Survey of India; the lithostratigraphy and inter-basinal correlation of the Kaladgi Group (Chandrasekhara Gowda) - a synthesis of earlier work of Mysore University; and a presentation based on a process-responsive li thostratigraphic classification of the Kaladgi basin (Kale and associates). In the absence of the much needed new mapping on 1:25,000 scale, the presentation was confined to a reappraisal of earlier work. No stratigraphic work is complete without a credible geological map based on lithostratigraphic classification. Thematic aspects should not be mixed up with lithostratigaphic classification. The session brought to the fore certain deficiencies with regard to nomenclature. Despite the Badami Group lying over the Bagalkot Group along an angular unconformity with a significant orogenic break, it is still grouped under the Kaladgi Supergroup and it is time the term Kaladgi is restricted to Pre-Badami Proterozoic sedimentary sequence as was first attempted by Viswanathiah (1977), and the term Bagalkot reduced in status appropriately. The two contributions on Konkan Kaladgi had different approaches; the one by Chitrao and Peshwa provided the classification of Konkan Kaladgi as Phonda and Kurli Formations constituting equivaIents of the Bagalkot and Badami Groups and also suggested their continuity with the main Kaladgi Basin beneath the Deccan Trap, while Kshirsagar and Jadhav oppose any physical continuity between these two and propose a regional domal structure separating these two. From Konkan Kaladgi there were other sandstone provenance discrimination studies suggesting serial downstripping of the Dharwar craton (Chitrao et al.) and a more detailed study