Chapter 1 Introduction Introduction 1.1 PROEM The key to effective basin analysis of any Proterozoic basin, lies in the assimilation of Proterozoic geohistory. Several sedimentary basins, which formed worldwide during the Proterozoic Eon, are the repositories of secular changes in the crustal, atmospheric, and oceanic processes as compared to the Archaean. The crustal evolution in Proterozoic was marked by stabilisation of crust, (during Late Archaean to Early Proterozoic) and formation of continental crust (by the accretion of Archaean cratonic nuclei). These continents were larger and more stable than the Archaean micro-continents, and had broad and relatively flat shelves and basins. Around Early to Middle Proterozoic, deposition in intracratonic and marginal basins of continental-sized cratons had commenced. Paleomagnetic and chronological data suggests that by Middle Proterozoic (around 1300 to 1000 Ma), all the continents coalesced to form a supercontinent called Rodinia surrounded by the Panthalassic ocean. All these evidences indicate that modern plate tectonic activity was operative even during the Proterozoic. Abundance of eukaryotes and other micro-organisms, in the ocean waters by ~ 2000 Ma, increased the free oxygen levels in the atmosphere and decreased the acidity of the oceans by the process of photosynthesis. As a result red beds and carbonates were deposited widely during Proterozoic. Around 1700 Ma stromatolites were also abundant, while Ediacaran fauna (multicellular soft bodied fauna) first appeared by ~ 900 Ma. In India, all these Proterozoic events are preserved in seven independent sedimentary basins collectively known as "Purana Basins" of Peninsular India. Radhakrishna (1987) proposed to retain the name "Purana" (originally designated by Holland, 1907) to all those sediments in India, within the age range of Middle and Upper Proterozoic (1600-600 Million years). These basins host sediments deposited on the continental crustal segments composed of Archaean to Palaeoproterozoic rocks, after a profound hiatus, known as the "Great Eparchean Unconformity". These Purana basins, fringing the Archaean Cratonic Nuclei of the Indian Peninsular Shield (Fig. 1.1) are mostly epicratonic and pericratonic basins (Kale & Phansalkar, 1991). The sediments of these basins were deposited in shallow marine settings. Though contemporary in nature, these are individual and apparently independent basins with comparable growth histories. Except for the Kaladgi and Bhima Basins, all the other basins have close association with the Middle Proterozoic Mobile Belt (MPMB), which in a way may throw light on their evolutionary history (Kale, 1995 and 1998). Strong signatures of an intrinsic alliance between global flooding events and regional tectonism during the Proterozoic Eon is manifested in these basins. Although containing thick succession of sediments, they rarely display strong deformation. Recurrence of quartzite-argillite-carbonate suites, absence of widespread metamorphism, little associated igneous activity and structural simplicity are some of the salient features of these basins. It has been observed that wherever deformation is present in these basins, it is-«rtfltTrw«astnrtfiH to thp Introduction IjCratonicnucleii; a) BM = Bundelkhand Massif; b) SC = Sighbhum Craton; c) BC = Bhandara Craton; d) WDC = Western Dharwar Craton. 2]Reworked Cratons; a) BBS=Bastar-Bhandara Sector; b) EDC=Eastern Dharwar Craton; c) ADB = Aravalli-Delhi Belt; d) CH = Chotanagpur Sector; e) EGB = Eastern Ghat Belt, f) SGT = Southern Granulite Terrain; 3]Proterozoic (Purana) Basins: a) VB = Vindhyanchal Basin; b) CB =Chattisgarh Basin; c) BB - Bastar Basins; d) PGB =Pranhita Godavari Basins e) CP =Cuddapah Basin; f) KB = Kaladgi Basin; g) BH = Bhima Basin. PC = Phanerozoic cover over the Precambrian terrains. Fig. 1.1: Major Precambrian terrains of the Peninsular Indian Shield. (adapted from Kale, 1995 and 1998). Introduction flanks (Kale and Phansalkar, 1991). The only basin, which perhaps stands out as an exception is the Kaladgi Basin, situated on the northwestern fringes of Dharwar craton (see: Fig. 1.1) and which has been chosen for the geological investigations in this study. It is an E-W trending ovate basin, displaying strong structural deformation in its central sector with relatively undeformed flanks. The flanks have unconformable contacts with the adjoining crystalline basement of Archaean- Palaeoproterozoic age. This structural discordance, is highlighted in the multispectral satellite imageries (see: Title Photo), in which the tonal patterns manifesting lithological differences and the large folds and lineaments give an overall picture of the challenges hidden in the study of this basin. Today, although large parts of the basin are concealed under basaltic flows of Cretaceous-Tertiary Deccan Traps, the exposed parts give concrete clues of an amazing interplay between basement dynamics and sea-level fluctuations responsible for the development of this basin. It is this unique feature of this basin, in terms of its settings, thick sedimentary pile and structural configuration that has attracted the attention of several geologists working in the Precambrians of India. The past 150 years, have thus been dedicated to the research, focusing on the various aspects (sedimentological, structural and partly evolutionary history) of this basin. The first remarkable study of this basin, was that by Robert Bruce Foote way back in 1876. The work of Foote (1987), was the first compilation on the Kaladgi sediments carried out with such an accuracy and depth of perception for the time when it was conducted. After Foote, this complex basin was studied in details by Viswanathiah and his group (1964,1966,1968, 1970,1976,1979 and 1983) from the Mysore University, the Geological Survey of India (compiled in Jayaprakash et al., 1987) and by the researchers of Pune University (Peshwa, Kale and others from 1978 till 1999). All these studies have contributed in the assimilation of this complex basin. However, the application of modern techniques in basin analysis and sequence stratigraphy (which has made tremendous impact on studies of sedimentary basins in the last two decades) have not yet been attempted in this basin. 1.2 PURPOSE OF STUDY While carrying out the literature survey, it was realised that several questions regarding basin evolution, complexities in sedimentation and structural patterns have remained unanswered so far, due to lack of elaborate justifications in the previous studies. Tremendous amount of data has been generated over the years from these studies. However very few of these studies (Kale and Phansalkar, 1991, Kale etal., 1996) have attempted to decipher the basin dynamics in light of modern perspectives of basin analysis. The compilation of this data and its analysis using these modern techniques for deciphering the overall evolutionary history of this basin has thus provided the main objective for conducting the present study. Introduction The work compiled in this thesis was thus undertaken in order to document: • Sedimentation patterns • Deformational patterns • Evaluation of the factors governing the evolution of this basin. In doing so, the data from the previous studies (duly acknowledged) was compiled along with the data generated during this study. On this background, the documentation of the contents of Kaladgi Basin and application of modern techniques has been attempted in this study, with the aim of unravelling the yet unknown aspects of this Proterozoic basin. However, it may be mentioned here, that this study is based purely on surface (outcrop) data. Hence the inferences drawn from this study may present a gross perspective of this basin. In absence of other data sources such as log data, seismic data, precise geochronological data and geophysical data (not available as yet for this basin), some of the inferences, which are of speculative nature may require further investigations in future studies. 1.3 CHOICE OF THE AREA To achieve these targets, it was realised that the area, which displays maximum amount of intricacies in terms of sedimentology and structure, would be an ideal candidate to conduct the desired investigations. It was hence decided to focus on the Bagalkot-Simikeri area, for the following reasons: 1. Previous workers have described "type" stratigraphic sections of this basin from this area. 2. This area displays significantly more deformation of the sediments than any other part of the basin and in doing so manifests the intricate relationships between hthologies and deformational structures. 3. Mappable contacts, conformable and unconformable, are well exposed in this area. The area of investigation has been designated as the "Bagalkot-Simikeri area" in conformity to the norms of Ph.D. registration by the University of Pune. In reality, the area covered in this study spans the entire eastern half of the contiguous exposures of this basin (Fig. 1.2). 1.4 AREA OF STUDY 1.4.1 GEOGRAPHICAL LocAnoN: The Kaladgi Basin spreads in the northern and northwestern parts of Karnataka State. More than 70% of the basin is present in the Belgaum, Bijapur, and Bagalkot, districts. Isolated outcrops of the Kaladgi rocks occurring as outliers, are present in the southern and southwestern regions of Maharashtra State (see: Fig. 1.2). The area under investigation, is bounded by: • Latitudes: 15°50' N and 16°25' N • Longitudes: 75°15' E and 75°45'E Introduction • tii-H >, CO 00 0\ m r~l bo "^ -d a 03 m •« r^ <u