Godavari Basin Research Articles

Main Deccan volcanism phase ends near the K–T boundary: Evidence from the Krishna–Godavari Basin, SE India

Recent studies indicate that the bulk (80%) of the Deccan trap eruptions occurred over less than 0.8 m.y. in magnetic polarity C29r spanning the Cretaceous–Tertiary (K–T) boundary. Determining where within this major eruptive phase the K–T mass extinction occurred has remained problematic. For this reason, models estimating the biotic and environmental consequences have generally underestimated the rate and quantity of Deccan gas emissions by orders of magnitude leading to conclusions that volcanism could not have been one of the major causes for the K–T mass extinction. In this study we report that the most massive Deccan trap eruption occurred near the K–T mass extinction. These results are based on sedimentologic, microfacies and biostratigraphic data of 4–9 m thick intertrappean sediments in four quarry outcrops in the Rajahmundry area of the Krishna–Godavari Basin of southeastern India. In this area two Deccan basalt flows, known as the Rajahmundry traps, mark the longest lava flows extending 1500 km across the Indian continent and into the Bay of Bengal. The sediments directly overlying the lower Rajahmundry trap contain early Danian planktic foraminiferal assemblages of zone P1a, which mark the evolution in the aftermath of the K–T mass extinction. The upper Rajahmundry trap was deposited in magnetic polarity C29n, preceding full biotic recovery. These results suggest that volcanism may have played critical roles in both the K–T mass extinction and the delayed biotic recovery.

An integrated geophysical approach for imaging subbasalt sedimentary basins: Case study of Jam River Basin, India

An integrated geophysical strategy comprising deep electrical resistivity and gravity data was devised to image subbasalt sedimentary basins. A 3D gravity inversion was used to determine the basement structure of the Permian sediments underlying the Cretaceous formation of the Jam River Basin in India. The thickness of the Cretaceous formation above the Permian sediments estimated from modeling 60 deep-electric-sounding data points agrees well with drilling information. The gravity effect of mass deficit between the Cretaceous and Permian formations was found using 3D forward modeling and subsequently removed from the Bouguer gravity anomaly along with the regional gravity field. The modified residual gravity field was then subjected to3D inversion to map the variations in depth of the basement beneath the Permian sediments. Inversion of gravity data resulted in two basement ridges, running almost east to west, dividing the basin into three independent depressions. It was found that the Katol and Kondhali faults were active even during post-Cretaceous time and were responsible for the development of the subsurface basement ridges in the basin. The inferred 3D basement configuration of the basin clearly brought out the listric nature of these two faults. Further, the extension of the Godavari Basin into the Deccan syneclise and the fact that the source-rock studies show the presence of hydrocarbons in the Sironcha block in the northern part of the Godavari Basin also shed some light on the hydrocarbon potential of the Jam River Basin.

Thickness, composition, and evolution of the Indian Precambrian crust inferred from broadband seismological measurements

We present seismological constraints to model the evolution of Indian Precambrian crust through receiver function analysis of teleseismic waveforms, recorded on 22 broadband seismographs along a N–S corridor, from southern granulite terrain to Delhi, on the Aravalli craton. Archean terrains (Eastern Dharwar, Bastar, Bundelkhand and Aravalli cratons) are underlain by crust with felsic-intermediate composition ( V p/ V s ∼ 1.65–1.75) in contrast to mafic composition ( V p/ V s > 1.78) of crust beneath Vindhyan basin, Godavari basin, and the Narmada-Son Lineament (NSL) of Proterozoic age. The Moho depth varies between 33 and 43 km with no definite relationship with age of the crust. Duplex Moho with highly mafic underplated lower crust is characteristic feature of the NSL, signifying its paleo-rift character. Present day felsic character of the Indian Archean crust could be a consequence of post-formation modification of the initial mafic lower crust through the process of lithospheric delamination. This major tectonic event also created layered lithosphere beneath parts of India imprinted as positive velocity contrast at a depth of ∼80 km, usually referred to as Hales discontinuity. The upper part of the lithosphere has shear velocity ( V s) ∼4.52 km/s and the lower one ∼4.77 km/s. We speculate that such a layered lithosphere could be due to a low-density, depleted spinel peridotite (with Archean affinity) lying over higher density fertile garnet peridotite of Proterozoic age.

40K– 40Ar dating of the Main Deccan large igneous province: Further evidence of KTB age and short duration

Most mass extinctions coincide in time with outpourings of continental flood basalts (CFB). Some 20 years ago, it was shown [Courtillot, V., Besse, J., Vandamme, D., Montigny, R., Jaeger, J.-J., Cappetta, H., 1986. Deccan flood basalts at the Cretaceous/Tertiary boundary? Earth Planet. Sci. Lett. 80, 361–374; Courtillot, V., Feraud, G., Maluski, H., Vandamme, D., Moreau, M.G., Besse, J., 1988. Deccan flood basalts and the Cretaceous/Tertiary boundary. Nature 333, 843–846; Duncan, R.A., Pyle, D.G., 1988. Rapid eruption of the Deccan flood basalts at the Cretaceous/Tertiary boundary. Nature 333 841–843] that the age of the Deccan traps was close to the Cretaceous–Tertiary (KT) boundary and its duration under 1 Myr. We have undertaken a new geochronological study, using the (unconventional) 40K– 40Ar Cassignol–Gillot technique which is particularly well suited to the potassium-poor Deccan lavas. The mean of 4 determinations from the topmost (Ambenali and Mahabaleshwar) Formations is 64.5 ± 0.6 Ma. They straddle the C29r/C29n reversal boundary for which they provide a new constraint. The mean age of 3 determinations from the oldest (Jawhar) Formation is 64.8 ± 0.6 Ma. The difference in age between top and bottom of a 3500 m composite section, probably comprising 80% of the total Deccan volume, is statistically insignificant, with the overall mean age being 64.7 ± 0.6 Ma ( N = 7). Our results are consistent with the most recent 40Ar/ 39Ar determinations [Knight, K.B., Renne, P.R., Halkett, A., White, N., 2003. 40Ar/ 39Ar dating of the Rajahmundry Traps, eastern India and their relationship to the Deccan traps. Earth Planet. Sci. Lett. 208, 85–99; Knight, K.B., Renne, P.R., Baker, J., Waight, T., White, N., 2005. Reply to ‘40Ar/39Ar dating of the Rajahmundry Traps, Eastern India and their relationship to the Deccan Traps: Discussion’ by A.K. Baksi. Earth Planet. Sci. Lett. 239, 374–382], confirming that there should be no systematic difference between the two methods when they are used in an optimal way. An earlier, smaller but significant, pulse of volcanism between 68 and 67 Ma, extending over at least 500 km in latitude in the northern part of the Deccan CFB has also been identified. After 2 to 3 Ma of quiescence, the second, major phase of volcanism occurred near 65 Ma, expanding over most of the area covered by the first pulse and another 500 km to the South, consistent with drift of India by 300 to 450 km at ∼ 150 mm/yr during the quiescence period. New paleontological data from the remote Rajahmundry section [Keller, G., Adatte, T., Gardin, S., Bartolini, A., Bajpai, S., Humler, E., in prep. The Cretaceous–Tertiary boundary in Deccan Traps of the Krishna–Godavari Basin of southeastern India. EPSL to be submitted] suggest that this second pulse can itself be divided into two major pulses, one starting in C29r and ending at the KT boundary, the second starting in the upper part of C29r and ending within C29n.

Impact of phase variations on quantitative AVO analysis: An example from Krishna Godavari Basin, India

Krishna Godavari Basin on the east coast of India is one of the country's most promising petroliferous basins, with commercial accumulations of hydrocarbons on land and offshore (Figure 1). Estimated resources in the basin are around 2000 million tons of oil or oil-equivalent gas. The reservoirs are in sediments of all ages, Permian to Pliocene.

Basin architecture and petroleum system of Krishna Godavari Basin, east coast of India

Krishna Godavari Basin is a peri-cratonic passive margin basin on the east coast of India (Figure 1). The onland part consists of 28 000 km2 and is mostly alluvium covered. Krishna and Godavari are the two major river systems which drain the area and discharge in the Bay of Bengal. The offshore basinal area covers 24 000 km2 to the isobath of 200 m. However, the basin extends into deeper water and covers a much larger area. The basin's characteristic feature is its en-echelon horst and graben system which is filled with a thick pile of sediments of Permian-to-Recent age and emerging as one of India's most promising petroliferous areas. Commercial accumulation of hydrocarbons occurs in sediments from the Permian to as young as the Pliocene.

Inorganic chemistry, petrography and palaeobotany of Permian coals in the Prince Charles Mountains, East Antarctica

Sampled outcrops of Permian coal seams of the Bainmedart Coal Measures in the Lambert Graben, eastern Antarctica, have been analysed for their proximates, ultimates, ash constituents and trace elements. A similar series of samples has been analysed for their principle maceral and microlithotype components and vitrinite reflectance. The coals are sub-bituminous to high volatile bituminous in rank; maturity increases markedly in southern exposures around Radok Lake where the oldest part of the succession is exposed and some strata have been intruded by mafic dykes and ultramafic sills. The coal ash is mostly silica and aluminium oxides, indicating that the mineral ash component is mostly quartz and various clay minerals. The ratio of silica to aluminium oxides appears to increase in an upward stratigraphic direction. The coal macerals include a relatively high liptinite content (mainly sporinite) that is significantly higher than for typical Gondwana coals. Greater degrees of weathering within the floodbasin/peat mire environments associated with climatic drying towards the end of the Permian might account for both preferential sporopollenin preservation and increased silica:aluminium oxide ratios up-section. Correlation of the coal maceral components to adjacent peninsula India coals indicates the closest comparative coals of similar age and rank occur within the Godavari Basin, rather then the Mahanadi Basin, which is traditionally interpreted to have been contiguous with the Lambert Graben before Gondwanan breakup. The petrological characteristics suggest that either previous interpretations of Palaeozoic basin alignments between Antarctica and India are incorrect, or that environmental settings and post-Permian burial histories of these basins were strongly independent of their tectonic juxtaposition. A permineralized peat bed within the succession reveals that the coals predominantly comprise wood- and leaf-rich debris derived from low-diversity forest-mire communities dominated by glossopterid and noeggerathiopsid gymnosperms.

Miocene deep water agglutinated foraminifera from offshore Krishna-Godavari Basin, India

Research Article| January 01, 2004 Miocene deep water agglutinated foraminifera from offshore Krishna-Godavari Basin, India Abiraman Govindan Abiraman Govindan Asian Biostratigraphic Services, H-53, Central Avenue, Chennai - 600 080, India, email: govindan@md2.vsnl.net.in Search for other works by this author on: GSW Google Scholar Micropaleontology (2004) 50 (3): 213–252. https://doi.org/10.2113/50.3.213 Article history received: 15 Sep 2003 accepted: 14 Oct 2004 first online: 06 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Twitter LinkedIn Tools Icon Tools Get Permissions Search Site Citation Abiraman Govindan; Miocene deep water agglutinated foraminifera from offshore Krishna-Godavari Basin, India. Micropaleontology 2004;; 50 (3): 213–252. doi: https://doi.org/10.2113/50.3.213 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu nav search search input Search input auto suggest search filter All ContentBy SocietyMicropaleontology Search Advanced Search Abstract The Krishna Godavari Basin is located in the East Coast Indian Peninsula containing 5 to 7 km of Cretaceous through Cenozoic terrigenous clastic sediments. The Miocene-Pliocene section in the offshore is known as the Ravva Formation, a major argillaceous facies with sandstone beds from which oil and gas are being produced. In this sequence, some cutting samples studied from four offshore wells were found to be rich in agglutinated benthic foraminifera, while planktic foraminifera were absent at these levels. These samples were studied in much detail for agglutinated foraminifera. A total of fifty-nine agglutinated foraminiferal species belonging to thirty-five genera have been identified. Two new species, Alveolophragmium indicum Govindan n. sp and Liebusella krishna Govindan n. sp., are described. All these species are reported for the first time from this region. The agglutinated benthic foraminiferal taxa bear close resemblance to those of Miocene agglutinated foraminifera assemblages reported from South Trinidad, the Falcon Basin of Venezuela, and offshore West Africa. The present report of alveolar genera, Alveovalvulina, Alveovalvulinella and Guppyella, and compressed, inner partitioned alveolar genera Pavonitina and Spiropsammia, together with other genera having complex reticulate inner structure as Cyclammina, Reticulophragmium and Alveolophragmium in this region are of great importance for the evaluation of biostratigraphy, paleoecology, paleobiogeography and burial history. Paleoecological analysis reveals three agglutinated foraminiferal biofacies/groupings, which characterize beyond outer shelf through bathyal slope (500 to 1500m) depth regimes in an oxygen minimum deep water setting for the deposition of these turbidite/debris flow sediments.A major marine transgression at the close of the Oligocene probably caused a moderately rich, more uniform distribution of deep water agglutinated species over this deep basin. Additional observations on the agglutinated benthic assemblage such as deformation of the tests, coloration of the tests and stratigraphic markers are also dealt with briefly. You do not currently have access to this article.

57Fe Mössbauer spectroscopic study of organic-rich sediments (source rocks) from test wells CTP-1 and MDP-1 located in Eastern Krishna–Godavari basin, India

A large number of sub-surface sedimentary samples using Mössbauer spectroscopy were obtained from various depths of wells CTP-1 and MDP-1 drilled in Eastern Krishna–Godavari basin (KG basin) of India. Results indicate that iron is distributed in pyrite, siderite and in clay minerals, apart from these minerals an anomalously large presence of sulfate minerals was also found. Their presence indicates oxidizing conditions in sediments. Significance of presence of minerals, which show oxidizing conditions in context of source rock characterization, is discussed.

Miocene deep water agglutinated foraminifera from offshore Krishna-Godavari Basin, India

Abstract The Krishna Godavari Basin is located in the East Coast Indian Peninsula containing 5 to 7 km of Cretaceous through Cenozoic terrigenous clastic sediments. The Miocene-Pliocene section in the offshore is known as the Ravva Formation, a major argillaceous facies with sandstone beds from which oil and gas are being produced. In this sequence, some cutting samples studied from four offshore wells were found to be rich in agglutinated benthic foraminifera, while planktic foraminifera were absent at these levels. These samples were studied in much detail for agglutinated foraminifera. A total of fifty-nine agglutinated foraminiferal species belonging to thirty-five genera have been identified. Two new species, Alveolophragmium indicum Govindan n. sp and Liebusella krishna Govindan n. sp., are described. All these species are reported for the first time from this region. The agglutinated benthic foraminiferal taxa bear close resemblance to those of Miocene agglutinated foraminifera assemblages reported...

Bouguer anomaly of the Godavari basin, India and magnetic characteristics of rocks along its coastal margin and continental shelf☆

The Bouguer anomaly map of the Godavari basin has delineated several transverse and median ridges that have divided this basin into several sub-basins. Modelling of a gravity profile in the central part of the basin suggests 5.0 km of Gondwana sediments and high density rocks along the shoulders which may represent upthrusted lower crustal rocks related to the Eastern Ghats orogeny. The total intensity magnetic map of the coastal part of the Godavari basin shows a well-defined magnetic anomaly of approximately 200 nT along the coast which coincides with the Kaza basement ridge. The modelling of this magnetic anomaly indicates 2–2.5 km of sediments over the Kaza ridge and 5.5–6 km thick sediments in the depressions towards the west of this ridge which are constrained from the basement configuration based on seismic sections in the surrounding region. The Kaza ridge, with a susceptibility of 10 −4 SI units, appears to be composed of basic rocks which may be part of the exposed Eastern Ghats towards the west. This magnetic map also shows several high amplitude short wavelength anomalies which are caused by sub-surface basic rocks. These basic rocks are related to the Rajahmundry trap, equivalent to the Deccan traps of late Cretaceous age, and are exposed nearby by. Modelling of the magnetic anomaly across the continental shelf, off the coast of the Godavari basin, suggests an almost 45° inclined contact away from shore at a depth of 2.5 km and having a thickness of 3.5 km. However, this magnetic anomaly could be matched only with a remanent magnetization with declination 310° and inclination −67° which corresponds to the direction of magnetization reported for the Rajmahal traps.

Triassic temnospondyls of the Pranhita–Godavari basin, India

The Pranhita–Godavari (P–G) basin of central India has yielded Early, Middle and Late Triassic temnospondyl families. Bracyops laticeps, the type for the family Brachyopidae was first described from the Lower Triassic ‘Mangli Beds’ of the northernmost extension of the P–G basin. In the northern and central parts of the P–G basin itself, the Middle Triassic Yerrapalli Formation has Stanocephalosaurus rajareddyi, a paracyclotosaurid, and the Upper Triassic Maleri Formation has Buettneria maleriensis, a metoposaurid and two other chigutisaurid taxa, Compsocerops cosgriffi and Kuttycephalus triangularis. A critical review of Triassic temnospondyls of the P–G basin indicates that the affinities of S. rajareddyi and K. triangularis are somewhat uncertain and discovery of further material is necessary to establish their relationships among similar temnospondyls of the world. It is also noted that B. maleriensis is displaced by the two chigutisaurid genera and species at the Carnian–Norian boundary. Thus, P–G basin is unique in having Pangaean metoposaurids and exclusively Gondwanan chigutisaurids in successive faunal zones within the same formation. Significantly, the end of Carnian is marked by the demise of metoposaurids in India as well as in Africa and Europe. In North America, their size appears to have diminished during that time.

Pamelaria dolichotrachela, a new prolacertid reptile from the Middle Triassic of India

A new genus and species Pamelaria dolichotrachela, belonging to the family Prolacertidae is reported for the first time from the Middle Triassic of India. The material consisting of associated skeletons and isolated bones has been excavated from the red mudstone of Yerrapalli Formation of Pranhita–Godavari Basin, South India. The nature of disposition of bones strongly suggests a catastrophic death and quick burial. The reconstructed skeleton of P. dolichotrachela strongly suggests that it was a quadrupedal sprawler. A detailed description of the new taxon and its comparison with other better known prolacertids of the world reveals a very close resemblance with Prolacerta broomi [Ann. Mag. Nat. History 16 (1935) 197], the type genus and species of the family. A number of characters like a relatively large skeleton; confluent nostril, lower jaw with a prominent coronoid and accessory neural spines in the posteriorcaudals with a sudden shift of neural spine position establish its distinctiveness.

Regional tectonic framework of the Pranhita–Godavari basin, India

The Pranhita-Godavari Gondwana rift (PGR) has a co-genetic relationship with Permo-Triassic reactivation of the Narmada–Son Geofracture (NSG). The Satpura Gondwana basin represents the terminal depocentre against the NSG, which restricted the northwestward propagation of the PGR. The NE–SW tensional stress responsible for the NW–SE trending PGR could not propagate beyond the ramp formed by uplift along the NSG and transformed kinetically into an ENE directed horizontal shear along the NSG, inducing large scale strike–slip movements. The latter dynamics were responsible for ENE extension of the Satpura rift as a pull-apart basin. The PGR extends up to the present east coast of India, where it is apparently terminated by the NE–SW trending Bapatla ridge along the Eastern Ghat Rift (EGR). The subsurface data, however, shows that the PGR extends across the Bapatla ridge and continues beneath the Cretaceous–Tertiary sediments of the Krishna–Godavari basin (KG) in the EGR. Thus, the Permo-Triassic PGR appears to have continued in the Indo-Antarctic plate before the Cretaceous break up. The EGR, during break up of the continents, cuts across the PGR and the KG basin was superimposed on it. The PGR site is located on a paleo-suture between the Dharwar and Bastar proto-cratons. The master faults developed bordering the rift, and the intra-rift higher order faults followed the pre-existing fabric. The transverse transfer zones manifested as basement ridges, divide the rift into segments of tectono-sedimentary domains. The major domains are the Chintalapudi, Godavari, and Chandrapur sub-basins, each of which subsided differentially. The central Godavari sub-basin subsided most and shows maximum structural complexity and sediment accommodation. The rifting started with initial half-graben faulting along the northeastern master fault and expanded by successive half graben faulting. This gave rise to intra-basinal horsts and grabens, which exercised control on the syn-rift sedimentation. The southeastern boundary fault developed as a strike–slip fault in response to plate rotation and the rift expansion was constrained by it.The basin fill sediments were deposited during two rifting events—Early Permian to (?) Early Jurassic Lower Gondwana rifting, and Early Cretaceous Upper Gondwana rifting. The Lower Gondwana sedimentation started with a pre-rift crustal sagging over the rift site and was filled by glaciogenic Talchir sediments. This was followed by syn-rift-fluvial sedimentation in repeating cycles during the early to late rift stages. Early Cretaceous Chikiala and Gangapur sediments were deposited during the Upper Gondwana rifting. The fluvial cycles were tectonically controlled during each rift stage. The absence of igneous intrusions indicates that the PGR is a passive rift in contrast to the rifts developed in the NSG zone.

Bouguer anomaly of the Godavari basin, India and magnetic characteristics of rocks along its coastal margin and continental shelf

The Bouguer anomaly map of the Godavari basin has delineated several transverse and median ridges that have divided this basin into several sub-basins. Modelling of a gravity profile in the central part of the basin suggests 5.0 km of Gondwana sediments and high density rocks along the shoulders which may represent upthrusted lower crustal rocks related to the Eastern Ghats orogeny. The total intensity magnetic map of the coastal part of the Godavari basin shows a well-defined magnetic anomaly of approximately 200 nT along the coast which coincides with the Kaza basement ridge. The modelling of this magnetic anomaly indicates 2–2.5 km of sediments over the Kaza ridge and 5.5–6 km thick sediments in the depressions towards the west of this ridge which are constrained from the basement configuration based on seismic sections in the surrounding region. The Kaza ridge, with a susceptibility of 10 −4 SI units, appears to be composed of basic rocks which may be part of the exposed Eastern Ghats towards the west. This magnetic map also shows several high amplitude short wavelength anomalies which are caused by sub-surface basic rocks. These basic rocks are related to the Rajahmundry trap, equivalent to the Deccan traps of late Cretaceous age, and are exposed nearby by. Modelling of the magnetic anomaly across the continental shelf, off the coast of the Godavari basin, suggests an almost 45° inclined contact away from shore at a depth of 2.5 km and having a thickness of 3.5 km. However, this magnetic anomaly could be matched only with a remanent magnetization with declination 310° and inclination −67° which corresponds to the direction of magnetization reported for the Rajmahal traps.

Deformation of the Proterozoic successions in the Pranhita–Godavari basin, south India—a regional perspective

A number of Proterozoic intracratonic basins, namely Cuddapah, Pranhita–Godavari (PG), Abujhmar, Indravati, Ampani, Chattisgarh and Khariar basins, occur to the immediate west of the Eastern Ghats granulite belt (EGGB) in India. Of these, the PG basin hosts an axial outcrop of late Paleozoic–Mesozoic Gondwana rocks flanked on either side by Proterozoic sedimentary successions. Among the latter, the Somanpalli Group in the eastern part and the Penganga and Yellandlapad Groups in the western part show contractional folds, imbricate thrusts and cleavage. These deformed rock groups and the Pakhal Group in the western belt include shallow to deep marine sedimentary successions. Stratigraphic relations indicate that the major episode of deformation in the PG basin occurred prior to deposition of the unconformably overlying Sullavai Group. The latter is a Neoproterozic, undeformed fluvial sequence with some aeolian intercalation. Deformed successions also occur in other Proterozoic basins of the south Indian craton, notably those in the Nallamalai fold belt (NFB) along the eastern part of the Cuddapah basin. The major fold–fault structures in the arcuate NFB vary in trend from NNW–SSE in the southern part to NE–SW in the northern part. At least one phase of folding and thrusting predates the ∼1000 Ma old event in the EGGB. Deformation associated with the Grenville and later Pan-African tectonic mobility has imprints on the Neoproterozic Kurnool Group in the Palnad sub-basin (northern NFB). The major structural trend in the PG basin is NW–SE, except for the Yellandlapad area in the southern part, where late superposed folds trend E–W. The deformation along the eastern margin of the Chattisgarh basin, its southern extension in Khariar, Ampani and Indravati basins may also be related with the main (Grenville) deformation in the EGGB. A regional, Mesoproterozic episode of basin closure and inversion is thus evident from the Proterozoic cratonic successions west of the Eastern Ghats. This occurred prior to a regional development of Neoproterozoic successions at these sites.

Taphonomy of some Gondwana vertebrate assemblages of India

The Gondwana formations of India, comprising a thick succession of Permo-Mesozoic continental sedimentary rocks, occur in rift basins formed within the Indian plate. Successions developed in some of the Gondwana basins namely—Pranhita–Godavari, Damodar, Satpura and Son–Mahanadi, contain an array of vertebrate fossil assemblages. Among the four basins, the Pranhita–Godavari basin contains vertebrate assemblages from Late Permian, Middle and Late Triassic and Early Jurassic sediments. An Early Triassic assemblage is known to occur in the Damodar basin. The Satpura basin has yielded a Middle Triassic assemblage while a Late Triassic assemblage is known from the Son–Mahanadi basin. All these assemblages are confined mainly to the fluvial red bed successions. Taphonomic aspects of some of the assemblages of these Gondwana basins are described here for the first time. On the basis of the nature of occurrences of the skeletal assemblages, six major taphonomic types (termed here as A–F) have been identified from the Gondwana basins of India. Type A includes complete articulated or semi-articulated skeletons. Type B exhibits disarticulated skeletons of a large number of monospecific individuals. Type C is characterized by disassociated bones of monospecific individuals in a “log jam” condition. Type D exemplifies disarticulated bone assemblage of mixed individuals, while isolated remains of single individuals belong to Type E. Type F typifies isolated fragmentary bones. Analyses of these skeletal assemblages provide considerable information of death, transportation and burial of the terrestrial vertebrates. These results, when integrated with the sedimentary features of the host rocks, provide additional palaeoenvironmental and palaeocological information.

Gravity anomalies, sediment loading and lithospheric flexure associated with the Krishna–Godavari basin, eastern continental margin of India

Gravity anomalies constrained by seismic data have been used to examine the long-term mechanical properties of the lithosphere beneath the Krishna–Godavari basin, a deltaic sedimentary basin on the eastern continental margin of India. The gravity effect of the rift crust, sedimentary loading and erosional unloading have been computed and the sum effect of these, when compared with the observed gravity anomalies, gives a best fitting Te of 30 km at the margin. The results suggest that the lithosphere, which was weak during the early rifting-stage, has gained strength during sedimentation. The onshore dipping doublet gravity anomaly at the margin reflects a weak rifted continental lithosphere abutting a strong oceanic lithosphere. Comparison with the results of similar investigations for the Bengal basin in the north and Cauvery basin in the south suggests increasing strength for the lithosphere from north to south.

Biostratigraphy of the exposed Gondwana and Cretaceous rocks of Krishna - Godavari Basin, India

Biostratigraphy of the exposed Gondwana and Cretaceous rocks of Krishna - Godavari Basin, India

Monsoon rainfall and its variability in Godavari river basin

Rainfall variability over a river basin has greater impact on the water resource in that basin. With this in view, the variability of the monsoon rainfall over the Godavari river basin has been studied on different time scales. As expected, the monsoon rainfall in Godavari basin is more variable (17%) than the all-India monsoon rainfall (11%) during the period of study (1951–90). Similarly, inter-annual variability of the monsoon rainfall on smaller time scales is found to be still higher and increases while going on from seasonal to daily scales. An interesting observation is that the intra-seasonal variability of the monsoon rainfall has a significant negative relationship (CC= −0.53) with the total seasonal rainfall in the basin.