Chapter-2:- LITERATURE REVIEW
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CHAPTER-II LITERATURE REVIEW 17 Chapter-2:- LITERATURE REVIEW 2.1 Introduction A detailed review presented in Chapter -II includes published and unpublished literature on general geology, stratigraphy, physical volcanology, geophysical aspects and engineering geology of DTB. The geological literature of DTB dates back to writings of British Officers from Geological Survey of India (GSI). In last fifty years, exponential growth in the literature is seen in the form of various memoirs published by Geological Society of India, Bengaluru, Gondwana Geological Society, Records of Geological Survey of India and many other academic institutes. Primary objective of present work is to understand engineering geology of basalt from parts of Western Maharashtra. The literature review presented in this chapter is subdivided into three parts. First part of chapter describes review on general geology including geomorphology, physical volcanology, petrology and stratigraphy of DTB. Second part includes geophysical aspects and third part includes engineering geology of DTB. Earlier writings of GSI officers and Gazzatier of Govt of India working in the Bombay Province (pre-independence India) have given good insight on morphology, petrology of DTB. Foot (1876) asserted that flatness of the Deccan country is a consequence of flat lying lava flows and negated the marine planation theory. Oldham (1893) compiled information available till 1890 on Deccan country and proposed usage of name Sahyādri instead of Western Ghats. Vast literature on DTB has been published since 1980. Geological Society of India (Geol. Socy of India), Bengaluru, has published various memoirs such as proceedings on Deccan Volcanism (1981), Volcanism-Radhakrishna volume (1994), Deccan Volcanic Province (1999), and Sahyādri- the Great Escarpment of Indian Subcontinent (2001). Agashe et al (1971), Karmarkar (1978) and Gupte et al (1980), have proposed alternate models of volcanicity, types of flows and various rock types of DTB. On the other hand Hawaii nomenclature scheme proposed by (Macdonald, 1953) and (Walker, 1971) is followed by Geological Survey of India and many others. After 2001, researchers such as Bondre et al, (2004a, b), Brown et al, (2011), Duraiswami 18 et al., (2003), (2004), (2009), (2014), Sheth et al , (2005), (2006), (2011), Sen et al (2011), Sen Bibhas (2012), (2017) have paid attention to physical volcanology of DTB to understand mode of emplacement. These researchers have also challenged earlier views of volcanological characters of `A`Ā and Pāhoehoe flows and promoted usage of rubbly pahoehoe instead of `A`Ā flows for most of Western DTB. Second part of the chapter discusses reviews from geophysical studies. These studies have been included in the thesis to develop a correlation between site conditions and local geophysical signatures. Many shallow subsurface infrastructure projects studied for this thesis are located in the river basins of Mula-Mutha with thick alluvial cover. This makes the locations / sites vulnerable if ground motions are associated with earthquake. Role of subsurface particularly extent of weathering, velocity of P and S waves are crucial parameters in the consideration of a stable site conditions. To understand this, a review of literature encompassing, probability of seismicity and nature of seismicity in and around the region was taken e.g. Verma et al (2014). Alongwith this, literature review, to undersatnad the crustal structure beneath the DTB, Glennie, (1951), Qureshy (1981), Kaila et al(1968),(1981) were reviewed and for Koyana-Warna region, Guha et al (1981) , Talwani (1995; Talwani et al (1997), (2000) were also reviewed to understand the phenomena., Third part of chapter describes the contributions on engineering geology of DTB. Earlier understating of DTB as a monolith has led to the misconceptions about the engineering geological problems in DTB. Most of the literature till date is restricted to estimation of various parameters as per different IS codes in laboratory conditions. These works lack inclusion of understanding of volcanological character of basalt and its engineering properties. This need was however addressed by Gupte et al (1980) who helped Public Works Department (PWD) of Govt. of Maharashtra, India to publish a handbook on engineering geology of projects in the state of Maharashtra. This work has discussed various flow types of basalts and their lithological variation based on presence of vesicularity. Handbook also throws light on lithological varieties of basalts and their laboratory tests such as UCS in kg.cm2, porosity%, specific gravity etc. This happens to be the first attempt to put lithological and engineering aspect together. Among other workers , Parthasarathy et al (1981) provided rock mass characteristics data for DTB, Ghosh (1987) provided 19 engineering geological zoning of India including DTB. GSI has carried out engineering geological investigation in many projects in Maharashtra. But these reports were seldomely published in the literature. Indra Prakash et al (1993), Chakraborty et al., (1996), Gupta et al., (2011), Ansari et al., (2014), Jain et al (2014), Kainthola et al (2015), Singh et al (2017) have published literature in the recent times on engineering geology of DTB. 2.2 Geology of Deccan Trap Basalt The Deccan Trap Basalt (DTB) occupies western and central part of India (Fig: 1.1). It is one of the remarkable Continental Flood Basalt (CFB) provinces in the world. The term ‗trap‘ was coined by Skyes in 1833 after a Swedish word- Trapp or Trappa meaning step like occurrence. These CFBs are also called as flood basalt because of the vast expanse or ―Plateau Basalts‖ as they often stand out as tableland. Eruption of DTB is also one of the most interesting events in the geological history as the lavas were erupted over the Cretaceous / Tertiary boundary (KTB), ~ 65 Ma as given by Cande et al (1995). This event is considered responsible for one of the largest mass extinctions in the geological time where about 40% of the genera extinguished (Sepkoski, 1996). The Western Ghats represent escarpment to the west, parallel to the west coast of India. Estimated extent of DTB prior to erosion, including their concealed extensions under Arabian sea may be of the order of 15, 00,000 km2 (Krishnan, 1963). Presently, it occupies more than 85% area of State of Maharashtra and parts of Gujarat, Madhya Pradesh, Karnataka, and Andhra Pradesh. At places along the western part of the province, a continuous vertical succession of basaltic flows with a thickness of more than 1, 600 m can be observed, and geophysical studies have indicated that the thickness attained by the lava pile is over 2,000 m in the western part of the province (Kaila et al., 1981). Its maximum exposed vertical thickness is about 1700 m in the Igatpuri area (Beane et al., 1986). Near Mahabaleshwar, roughly 300 km farther south, about 1200 m of flows are exposed (e.g. Deshmukh (1988), Najafi et al (1981)); southwest of Mahabaleshwar some 40 km, on the coastal lowland near Khed (elevation + 39 msl) 500 m of basalt thickness is reported (Mahoney, 1988). To the north, in the Cambay region, drill holes have encountered more than 1000 m of largely buried basalts, in some places lying beneath 4-6 km of younger sediments (West,1981). Drilling carried out near at Rasati village near Koyana dam site confirmed the occurrence of 20 granitic basement at 350 m below msl (Roy et al., 2013). Thickness of the basalt decreases from west to east as well as in the north and south. It reaches maximum thickness along the Western Ghats. Two different theories are proposed to explain the occurrence of this vast DTB. One is known as mantle plume hypothesis. This states that DTB formed around 65 Ma in response to the passage of the Indian plate over the Reunion hotspot. The eruption of the Deccan lavas is intimately related to the formation of the passive margin along the western coast of India, as the Seychelles micro-plate separated from the Indian plate. This view is endorsed by Beane et al., (1986), Cox et al , (1985). However, Senthil Kumar et al., (2007) have questioned apparent thermal trace of a Réunion plume or any other thermal anomaly responsible for the genesis of the Deccan basalts, in the present-day thermal regime. Another theory suggested by Sheth et al (2005) contradicting the plume hypothesis, suggests rifting in three different zones in the DTB, leading to widespread and extensive sedimentation. The DTB is constituted dominantly of tholeiitic basaltic lava flows, nearly horizontal, stacked one above the other and exhibits a low dip of about 1° to the southeast (Courtillot et al., 1986). The basaltic flows are intruded at a number of locations by doleritic dykes. 2.3 Geomorphology of the Deccan Trap Basalt In the early geomorphological studies of Deccan trap terrain, Foot (1876) suggested that flatness of scenery in the Upland Maharashtra is a consequence of structural factors such as flat lying lava and sedimentary succession beneath. Oldham (1893) inferred that the cliffs of Western Ghats are of marine origin based on parallelism to the sea cost as well as occurrence of Cremnoconchus - a genus of fresh water Mollusca in the hills of Western Ghats. The Imperial Gazetteer of India (1907) noted that greater wall of Western Ghats represents water divide of Peninsula and upheaval to the present altitudes is comparatively based on the gradients of westerly flowing river. According to Pascoe (1950) , differential erosion has played a vital role in the mountain formation as compared to earth movement as successive lava flows are practically undisturbed. He further noted that strike and dip of Archaean rocks which are concealed below the Deccan Trap have influence over the contours of Deccan 21 Trap country. King (1963) gave emphasis on deformation by tectonic movements which have elevated late – Cenozoic plateau leading to rejuvenation of river systems. Radhakrishna, (1965) pointed out following important observations that Western Ghats are not a true mountain range but represent the precipitous edge of the elevated plateau which appears to be the combined effect of uplift and erosion.