Department of Geology

Permanent URI for this collection

http://presiuniv.ndl.gov.in:4009/handle/123456789/2323

Browse

Browsing Department of Geology by Subject "Geology"

Now showing 1 - 5 of 5
  • No Thumbnail Available
    Item
    Evolution of Cambay Basin, western India during the Eocene from the study of gastropods and shell beds
    Halder, Kalyan
    During the early Palaeogene western India was flooded with extensive transgressions. The first marine sediments were deposited in the western marginal basins during the Ypresian, i.e., early Eocene. Molluscs, including gastropods, bivalves and scaphopods, appeared and flourished in these basins, within the transitional habitats between sea and land. The early Cenozoic time was important for the evolutionary history of gastropods because several of the gastropod groups, abundant in modern-day seas, either first appeared or went through rapid diversifications and distributions during this time. While comprehensive monographs about the Paleocene-Eocene gastropods are available from the European and North American basins, and even the adjacent Pakistan basins, the Indian basins remained relatively less explored. Among the western Indian basins, most of the published reports came from the Kutch Basin, a few from the Subathu and Rajasthan basins and none from the Cambay Basin. The gastropods present in the Ypresian Cambay Shale of the Cambay Basin are studied here. 32 caenogastropods and 9 heterobranchs are reported and described. 32 of them (24 caenogastropods and 8 heterobranchs) are new. 13 of them are microgastropod (< 4 mm). 3 new genera and 2 new subgenera are introduced. The fossils were collected from four lignite mines at Mangrol, Vastan, Tadkeshwar and Valia, Gujarat. The Camaby Shale is an argillaceous formation with intercalations of lignite seams and marine fossil bearing limestones. Glauconitic green shale layers and shell beds dominated by only one or a few opportunist molluscs yielded gastropods of eurytopic or marginal marine affinity. A change from the freshwater-dominated coastal swamp to a relatively open-marine condition in an overall marginal marine set-up could be deciphered from the sequence of lithologies and fossils. The composition, diversity-abundance pattern, environmental preference and trophic structure of the molluscs, especially gastropods, elucidate this transgressive sequence. The Cambay gastropod assemblage predominantly comprises endemic species and widespread genera. A similar pattern was unveiled by the Paleocene-Eocene gastropod faunas reported from all Indian and Pakistan basins, situated within the Western Indian Province (WIP). The wide distribution of the genera took place due to the faunal exchanges via the circum-tropical equatorial currents along the relict Tethys, Atlantic and Pacific oceans. The westerly flowing somewhat weak Tethys current was important for migration of western Indian faunas. However, the specific endemism is enigmatic because a large part of the fauna had planktotrophic development. The restricted nature of the basins might be a significant factor. The early developmental mode was not found to be a decisive factor in the geographic distribution of the WIP gastropods at both generic and specific levels. The maximum geographic distribution and also, temporal duration of these genera were found to be not significantly different among the WIP genera characterized by planktotrophy, non-planktotrophy (lecithotrophic/direct), and a combination of these. With greater time, the maximum geographic distribution became broader. Also, majority of these genera were found to attain their maximum geographic distribution at the early stages of their temporal ranges. The changes in the maximum latitudes of these genera support their migration towards higher latitudes during the warming and towards lower latitudes during cooling periods, in response to the climatic turnovers of the Palaeogene.
  • No Thumbnail Available
    Item
    Structural and AMS analyses of basement Granitoid rocks of the Chitrial Area and its bearing on unconformity proximal type Uranium mineralization Cuddapah Basin Telangana
    Ghosh, Gautam
    The 2.51-2.52 Ga age Paleoproterozoic (Mukherjee et al., 2018) basement granitoid rocks of the Chitrial area in the Eastern Dharwar Craton (EDC) are unconformably overlain by the Mesoproterozoic Srisailam Formation (Nagaraja Rao et al., 1987) of the Cuddapah basin. Pre-Srisailam dyke sets (1.9-1.8 Ga; French et al., 2008) of N-S, WNW-ESE and ENE-WSW orientations traverse the granites around the Chitrial outlier. The map scale WNW – ESE trending Dindi lineament marks the southern limit of the outlier. Atomic Minerals Directorate (AMD) in recent times has established several ‘Uranium deposits’ from the Cuddapah basin of which one such deposit has been reported from the Chitrial outlier. In this latter deposit, uranium is hosted in Arechaean to Paleoproterozoic porphyritic basement granite unconformably overlain by the Mesoproteozoic unmetamorphosed sediments of the Srisailam Formation. According to the concentration of uranium mineralization, AMD further divided the Chitrial outlier into five blocks namely the ‘Main block’, ‘Block 1’, ‘Block 2’, ‘Block 3’ and ‘Block 4’.
  • No Thumbnail Available
    Item
    Study of Geomorphic Features of Noachis Terra, Mars: An Insight to Martian Tectonic Processes
    Dasgupta, Nilanjan
    Early cessation of Mars’ internal dynamo has resulted in excellent preservation of geological and geomorphological structures on its surface through time, unlike Earth where almost all the tectonic and geomorphic signatures of antiquities have been destroyed and re-organized. The present study area, Noachis Terra, in the southern highlands of Mars, is one such terrain, where the morphotectonic structures are found to be fossilized within the rocks of all timeframe. These morphotectonic features are the key to the understanding of the palaeo-tectonism and hence are the primary objects of investigations of the present study. This research identifies these features and characterizes each of these in detail. The study presents a detailed morphotectonic map of Noachis Terra in a scale of 1:12,000,000, which was unavailable till date. The entire area was subdivided into four different tectonic domains, each of which was found to have unique tectonic characteristics. These four domains were explored in detail and mapped in the scale of 1:2,500,000 to 1:5,000,000 in this study. The tectonic evolution of the four tectonic domains has been described in this study with the aid of these maps. The control of both emergent and non-emergent tectonic structures on the courses of the Martian channels observed in Domain III and IV of the study area have been statistically tested by cross-correlation methods. Palaeostress analyses done from the orientations of the tectonic structures mapped clearly shows the nature of the shift of the principal stress directions both spatially and temporally in the Noachis Terra. This is significant as it hints to the changing nature of local stress fields vis-à-vis the global stress field of Martian crust. The present study also elaborates on the chronology of the structures, seen in the area, with special emphasis on Domains III and IV. Wrinkle ridges of the western part of Noachis Terra (Domain I) were formed during the early Noachian time under the influence of Tharsis volcano-tectonic province. Large scale grabens in the eastern part of Noachis Terra (Domain II) were formed due to lithospheric stretching related to isostatic adjustment of the Hellas basin during the late Noachian time. The present study reports a set of fossae from the central part of Noachis terra (Domain IV), which was formed in late Noachian time (~3.79 Ga), after the formation of grabens in Domain II. The fossae, identified in the north-western part of the Noachis Terra (Domain III), formed in early Hesperian (~3.69 Ga), are thought to be associated with the Valles Marineris formation. It, therefore, appears that Noachis Terra is a heterogeneous terrain with diverse history of tectonic evolution; the nature of tectonism quite dissimilar to the present day plate tectonism operative on earth.
  • No Thumbnail Available
    Item
    Tectono metamorphic and geochronological evolution of the Rengali Province in the Riamal Rengali Khamar sector Odisha India
    Bose, Sankar
    Rengali Province occupies a unique geographical position between the Archean Singhbhum Craton and the Proterozoic Eastern Ghats Belt of eastern India. This province was variably considered a part of the Singhbhum Craton and/or the Eastern Ghats Belt, but their metamorphic characters are grossly contrasting. This opens a possibility that the Rengali Province evolved as a separate orogenic belt that may be unrelated to the Eastern Ghats Belt. The most striking feature of this province is the occurrence of several linear WNW-ESE trending zones separated by major ductile faults or shear zones. The rocks of this province show varying degree of metamorphism from granulite to greenschist facies. Geological mapping of the central part of the Rengali Province reveals presence of a gneissic basement block intercalated with low-grade supracrustal sequences. The basement rocks are mostly of granitoid composition showing gneissic fabric and the rocks are metamorphosed to amphibolite facies. Enclaves of granulite facies rocks, represented by charnockite gneiss and mafic granulite, occur within the gneissic basement. A part of this gneiss basement, referred to here as the Central Gneissic Belt, is the prime focus of petrological, geochemical and geochronological study. Supracrustal rocks are represented by quartzite, mica schist and calc- silicate schist that belong to the Tikra Association. Detailed structural analyses of the rocks from the central part of Rengali Province suggest that deformation was regionally partitioned into fold-thrust dominated shortening zones alternating with zones of dominant transcurrent deformation bounded between the Barkot Shear Zone in the north and the dextral Kerajang Fault Zone in the south. The strain partitioned zones are further restricted between two regional transverse shear zones, the sinistral Riamol Shear Zone in the west and the dextral Akul Fault Zone in the east. The overall structural disposition can be interpreted as a positive flower structure bounded between the longitudinal and transverse faults with vertical extrusion and symmetric juxtaposition of mid-crustal amphibolite grade basement gneisses over low-grade upper crustal rocks emanating from the central axis of the transpressional belt. The Central Gneissic Belt is constituted of charnockite gneiss, migmatitic hornblende gneiss and felsic gneiss often showing gradational contacts. While mafic granulite occurs as enclave within the charnockite gneiss, amphibolite and calc-silicate granofels enclaves are present within the felsic gneiss. Petrological study shows that the charnockites and mafic granulites underwent granulite facies metamorphism, whereas the gneisses were subjected to amphibolite facies metamorphism. Mafic granulite shows peak metamorphic assemblage of garnet + clinopyroxene + plagioclase + quartz ± orthopyroxene which was stabilized at 10.6 ± 0.5 kbar and 860 ± 20 °C. Charnockite gneiss with the peak assemblage of orthopyroxene +quartz + plagioclase +K-feldspar was metamorphosed at 792 ± 48°C and 7.6 ± 0.4 kbar. Amphibolite and migmatitic hornblende gneiss contain hornblende along with plagioclase and garnet and these rocks were metamorphosed at 800 ± 20 °C, 8.5 ± 0.2 kbar and 695 °C, 8 kbar respectively. Later meta-dolerite dikes exhibit relic igneous textures which are slightly modified by greenschist facies metamorphism. Charnockite gneiss, migmatitic hornblende gneiss and felsic gneiss show similar trace and REE characteristics (moderate fractionation in terms of La and Yb, LREE enrichment and flat HREE pattern) implying the same protolith composition for these rock groups. Field, petrographic and geochemical data suggest that the protoliths for the charnockite gneiss, the migmatitic hornblende gneiss and the felsic gneiss crystallized as fractionated magma in within-plate syncollisional setting during a prominent phase of orogeny at the Rengali Province. Results of detailed zircon U–Pb (SHRIMP) geochronological study of the amphibolite to granulite facies rocks of the Central Gneissic Belt reveal a complex evolutionary history. Charnockitic gneiss has protolith age of 2861 ± 30 Ma and high-grade metamorphism occurred at 2818 ± 15 Ma. Migmatitic hornblende gneiss has a protolith age of 2828 ± 9 Ma. The leucogranite was emplaced at 2807 ± 13 Ma. The protolith of the felsic gneiss was emplaced at 2776 ± 24 Ma. Most of the zircon samples contain overgrowths of c. 2500 Ma, inferred to be the age of reworking of the Central Gneissic Belt. These data suggest that the Rengali Province evolved as an orogenic belt in the Neoarchean time (ca. 2800–2500 Ma) during southward growth of the Singhbhum Craton. These tectonothermal imprints at the margin of the Singhbhum Craton are possibly related to its inclusion within the supercontinent Ur. Interestingly, the rocks of the Central Gneissic Belt and the associated supracrustals do not record any age signatures of ca. 1000-900 Ma orogeny that evolved the Eastern Ghats Province, thus discarding any genetic link between the two adjacent orogenic belts. The later transpression, extrusion and juxtaposition of deep crustal section to shallower level was achieved due to reactivation of the fault-thrust system during ca. 530-500 Ma which can be linked to far field stresses of global Pan-African orogeny.
  • No Thumbnail Available
    Item
    Tectonothermal History of the Granulites and gneisses around Phulbani Odisha India and its bearing on the Evolution of the Proterozoic Eastern Ghats Belt
    Bose, Sankar
    The Proterozoic Eastern Ghats Belt of eastern India is a key terrane to understand the evolution of the India-East Antarctica blocks of the supercontinent Rodinia. This belt is known for lower crustal rocks that experienced ultrahigh temperature (UHT) metamorphism. Because of its geological diversity, this belt has been subdivided into several crustal provinces and domains each having discrete tectonometamorphic characters. Most of the petrological history of this belt is reported from the domains located at the central (Visakhapatnam domain) and the southern (Ongole domain) parts and while the vast area covering the northern part of this high-grade terrane remains unexplored. The present work has been carried out on the Phulbani domain which occupies a major portion of the north-western part of the belt. Apart from some isolated geochronological data, no systematic petrological, geochronological, structural and fluid investigation has been carried out from this domain. This poses severe constraints on the overall metamorphic history of the northern part of the Eastern Ghats Belt (Eastern Ghats Province) and its connection with the supercontinent Rodinia. In the present study, an attempt has been made to overcome these issues by constraining the geological history of the Phulbani domain in a holistic manner. Phulbani domain is composed of migmatitic felsic gneiss, felsic augen gneiss, fine-grained charnockite gneiss, aluminous granulite, calc-silicate granulite and mafic granulite which was metamorphosed at UHT condition and subsequently intruded by coarse-grained charnockite. The mineral assemblage formed at the peak-UHT metamorphic condition is best documented in the aluminous granulite as spinel+quartz-bearing mineral assemblage. Using textural, thermobarometric and phase equilibria data, it is inferred that the latter mineral assemblage stabilized at 950°C (at approximately 8 kbar) from a corundum-bearing mineral assemblage by chemical reactions during prograde heating. Scapolite-clinopyroxene-wollastonite-plagioclase bearing mineral assemblage in the calc-silicate granulite also indicates temperature in excess of 800°C which is corroborated by high anorthite content of scapolite. After attainment of peak-UHT condition, all the rocks including coarse-grained charnockite experienced pronounced phase of near-isobaric cooling along an almost isobaric prograde and retrograde path and produced coronal garnet in aluminous granulite, calc-silicate granulite, fine-grained charnockite gneiss and coarse-grained charnockite. From the fluid inclusion analyses, it is inferred that the peak- to post-peak metamorphic evolution of the Phulbani domain dominantly occurred in a CO2-dominated fluid regime as high-density (up to 1.03 gm/cm3) CO2-rich fluid inclusions are documented in aluminous granulite, coarse-grained charnockite and migmatitic felsic gneiss. Textures like K-feldspar micro-veins in migmatitic felsic gneiss, myrmekite-like intergrowth, Th-rich veins in monazite and the presence of pegmatoidal metasomatic rock at the contact of calc-silicate granulite and coarse-grained charnockite further point towards the presence of an additional fluid phase which was capable to transfer elements in micro- to mesoscopic-scale. In the present study such fluid phase is interpreted to be brine which escaped from the rock record perhaps due to its greater mobility. Phulbani domain is characterized by five phases of deformations (D1-D5) and related fabric developments (S1-S5S). Of these, the S1 fabric is found only as inclusion within porphyroblastic phases of aluminous granulite and migmatitic felsic gneiss and produced during D1. Being common in the aluminous granulite, calc-silicate granulite, migmatitic felsic gneiss and fine-grained charnockite gneiss, the S2/S3 gneissic fabric is interpreted to be the earliest recognizable planar fabric of the study area and resulted by successive D2-D3 deformations during UHT metamorphism. The S2/S3 gneissic fabric was transposed during D4 to form S4 and S4S fabrics which dominantly occur parallel to the axial plane of the folded S2/S3 fabric. The S4 fabric later on folded during D5 to form mylonitic fabric (S5S) of the Ranipathar shear zone. Pseudotachylite veins are always associated with this S5S fabric and dominantly occur parallel to this fabric. Outcrop-scale sheath folds also developed during ductile shearing in the Ranipathar shear zone and played a critical role during exhumation of the high-grade rocks of the Phulbani domain. Microstructural investigation of quartz grains of the migmatitic felsic gneiss showing the S4S fabric suggest dominant deformation by prism and rhomb slips. Quartz ribbons in the S5S mylonitic foliation suggest deformation by prism slip in the quartz grains. Microstructures in pseudotachylite veins of the Ranipathar shear zone indicate its origin by melt crystallization following development of mylonititic foliation. Deformed pseudotachylite matrix suggests at least one stage of deformation after pseudotachylite formation during reactivation of the RSZ. Zircon U-Pb (SHRIMP) and monazite U-Th-total Pb (EPMA) analyses obtained in the present study additionally put precise time constraints on the tectonothermal evolution of the Phulbani domain. Zircon from the coarse-grained charnockite shows crystallization age of ca. 970 Ma. Aluminous granulite possibly suffered UHT metamorphism at ca. 987 Ma as revealed from monazite included in porphyroblastic garnet. Monazite in the aluminous granulite and the migmatitic felsic gneiss grew dominantly at 966 ± 4 Ma and 968 ± 4 Ma ages respectively, which are interpreted as the cooling ages subsequent to the peak metamorphism. Oscillatory-zoned zircon grains of the felsic augen gneiss yield ca. 1173 Ma age which is interpreted as the crystallization age of the granitic protolith. This ca. 1173 Ma age granite possibly composed a part of the Proterozoic basement of the Eastern Ghats Province. Monazite age of ca. 781 Ma from aluminous granulite exposed at the N-S trending ductile shear zone and dates within the range of ca. 558–535 Ma from felsic augen gneiss exposed at the RSZ indicate localized shear-induced thermal process in the Phulbani domain. The presently studied rock suite thus recorded four distinct events (ca. 1173 Ma, ca. 1000–900 Ma ca. 781 Ma and ca. 558–535 Ma) of magmatism, metamorphism and deformation of the Eastern Ghats Belt. The tectonometamorphic and tectonothermal histories of the Phulbani domain during the time-frame of 1000–900 Ma appear to be similar if compared with the adjacent Visakhapatnam domain which argues against the domain-based classification of the Eastern Ghats Belt. Based on this, it is inferred that the shear zones marking the boundaries of the domains possibly formed during latter time and cannot be considered as domain boundaries. The metamorphic and the magmatic histories during the time-frame mentioned above additionally matches well with the Rayner complex of the East Antarctica indicating the contiguous nature of these terranes during the inferred ca. 950-900 Ma Rayner-Eastern Ghats orogeny.