The Krishna-Godavari basin is a rifted passive margin basin that developed orthogonally to the NW-SE trending Pranhita-Godavari graben along the central Eastern Continental Margin of India in response to the continental rifting process and the subsequent seafloor spreading between India and eastern Antarctica during the early Cretaceous period. The 3-D gravity interpretation of both the onshore and offshore sections of the basin integrated with detailed seismic reflection and refraction data provided significant new information about the crustal architecture and the early breakup history of the basin. The gravity-derived crustal models indicate that the crust at the eastern Indian shield margin is 39-41 km thick and thins to as much as 20-23 km at the Ocean Continent Transition (OCT) in the offshore. There is a significant variation in the nature of crust and the configuration along the margin between the three crustal domains encompassing the basin: the Cuddapah basin, Pranhita-Godavari Graben, and the Eastern Ghat Mobile Belt that indicates the lateral segmentation of the margin. A zone of high density (3.0 g/cm(3)) crustal material at the OCT separates the pure continental and oceanic crusts on either side. The Moho is shallowest along this zone and brought the upper mantle notably close to the surface, which indicates that it could be comprised of Proto-Oceanic Crustal rocks. Furthermore, the present study highlights a major basement structural high in the deep offshore area of the margin. The geophysical signatures over this structure suggest that it is a crustal scale feature that is characterized by intrusive volcanic rocks, comprised of low density crust, and lies close to the OCT towards offshore. Based on the inferred tectonic reconstruction, we believe that this structural high could be a continental fragment that was left behind during the process of breakup between India and the Elan Bank. (c) 2012 Elsevier Ltd. All rights reserved.

85° East Ridge is a prominent structural feature in the deep to ultra deep water regime of East coast of India. In the recent times a lot of scientific study has been done to understand the genesis and importance of this ridge system for hydrocarbon exploration. Many operators have acquired 2D and 3D seismic data set to understand the ridge geometry. The present paper focuses on the internal architecture of the ridge which could be helpful in characterizing the ridge genesis. Well developed prograding seismic reflectors have been found below the acoustic basement. These interesting features give an insight to the process which accompanied ridge formations. Prograding events identified in the seismic data can be due to delta formation in a clastic depositional regime or it can also form due to lava flow. The Present study supports the formation of lava delta in the region during the formation of the ridge. Characterizing these lava deltas has been helpful in predicting a hydrocarbon system in the region.

Due to the lack of clearly discernible magnetic anomaly identifications and fracture zones in the Bay of Bengal (BOB), the early Cretaceous plate reconstruction history of eastern Gondwanaland remains an unresolved issue with regard to the separation of the East Coast of India from the conjugate Enderby Basin of Antarctica. Based on the correlation of oceanic basement information obtained from a vast amount of deep reflection seismic data, we identified 16 NW–SE-trending fracture zones (FZ1–FZ16) in the BOB region. The trends of these fracture zones at the ECMI indicate two distinctly different sets, one set in the direction ~N25°W to N35°W in the southern part (FZ1–FZ7) and the other set in ~N50°W (FZ8–FZ15) direction along the northern part. These two sets of fracture zones further support the earlier inferences about the segmented nature of the ECMI into southern sheared/oblique rifted margin and the northern normal rifted margin. While, the southern part of the ECMI had formed under slow/asymmetric spreading and mixed transform setting with its conjugate western Enderby Basin, the northern part of the ECMI formed after the breakup of the Elan Bank from India at M2. Considering this scenario, we infer the presence of Late Mesozoic (younger to M4) anomalies along the ECMI and the subdued nature of magnetic anomalies in the western BOB can be explained by the obliquity of fracture zones with respect to the coast, as observed in many marginal smooth zones of the world oceans. The disposition of the 85°E ridge with respect to the pre-evolved BOB crust and early Cretaceous volcanic episodes in the region together indicate an emplacement of the ridge from ~105Ma onwards as a result of a hotspot source related to the Kerguelen super plume during its intense eruption activity.

E Ridge, one of the important N-S trending aseismic ridges lies in the Eastern offshore of India. The ridge has been interpreted to be formed during passage of Indian plate over stationary hotspot known as Kerguelen. Although several studies have been carried out to understand the evolution and genesis of ridge, its importance in hydrocarbon exploration is yet to be probed. In the present work the importance of 85° East Ridge in hydrocarbon potential has been discussed with the help of available seismic data as well as conceptual model in the deep Mahanadi Offshore Basin. Emplacement of ridge in the deeper oceanic crust has significant influence on sediment dispersal pattern from the early part of Late Cretaceous times till the end of Oligocene. The ridge acts as barrier for sediment transport at least till Oligocene time. The well developed lows between isolated highs related to the ridge are favorable for source rock generation and maturation. Well developed channel feature and the depositional fairway evident from seismic data and isopach maps point toward the reservoir potential in the area. On the other hand the isolated closure at the top of the ridge as well as onlap of Paleogene sediments are quite important for the entrapment condition. Published data from similar aseismic ridge elsewhere shows the possible exposure of ridge in shallow water / sub aerial condition hence chances of carbonate build up on the top of ridge is very much feasible. With systemic and careful approach the area can provide good locale for hydrocarbon potential for the country in future.

The study area encompasses the Eastern Continental Margin of India (ECMI) and the adjoining deep water areas of Bay of Bengal. The region has evolved through multiple phases of tectonic activity and fed by abundant supply of sediments brought by prominent river systems of the Indian shield. Detailed analysis of total field magnetic and satellite-derived gravity data along with multi channel seismic reflection sections is carried out to decipher major tectonic features, basement structure, and the results have been interpreted in terms of basin configuration and play types for different deep water basins along the ECMI. Interpretation of various image enhanced gravity and magnetic anomaly maps suggest that in general, the ENE–WSW trending faults dominate the structural configuration at the margin. These maps also exhibit a clear density transition from the region of attenuated continental crust/proto oceanic crust to oceanic crust based on which the Continent Ocean Boundary (COB) has been demarcated along the margin. Basement depths estimated from magnetic data indicate that the values range from 1 to 12 km below sea level and deepen towards the Bengal Fan in the north and reveal horst–graben features related to rifting. A comparison of basement depths derived from seismic data indicates that in general, the basement trends and depths are comparable in Cauvery and Krishna–Godavari basins, whereas, in the Mahanadi basin, basement structure over the 85°E ridge is clearly revealed in seismic data. Further, eight multichannel seismic sections across different basins of the margin presented here reveal fault pattern, rift geometries and depositional trends related to canyon fills and channel–levee systems and provide a basic framework for future petroleum in this under explored frontier.

Few Mass transport deposits (MTDs) or Mass transport complexes (MTCs) are identified in the deepwater, Krishnagodavari basin using near surface 3D seismic data set. The study aims at identifying mass transport complexes and their influence of paleo-topography. The area has been divided to into three regions namely, proximal, central and distal part. An effort to characterize the MTC in all the above three regions is being tried out in the study. Various features like striations, scour marks identified on the basal surface of the MTD suggests the highly erosional activity. This erosion leads to formation of various erosional remnants which can act as isolated reservoirs. The top surface of MTD is characterized by presence of set of normal as well as low angle imbricate thrust faults. These thrust faults resulted due to freezing of MTDs cause irregular topographic features on the top surface. Any sediment deposition on the top surface is controlled by this irregular topography. Sediment dispersal pattern identified from rms amplitude shows that the sediment fills the topography lows generated due to thrust faulting.

Presence of highly sinuous channel systems on the slope as well as abyssal plain part of deep water regime have been reported from almost all the deep water provinces around the world. Understanding the similarity and dissimilarity between these sinuous channels and the meandering fluvial channels can help in extrapolating the knowledge of land/shallow to deep water. Quantitative analyses of various geometrical parameters associated with the shape, form of the channels are being tried out. Deep water slope channels interpreted from closely spaced 3D seismic data set from east coast of India (Cauvery basin) are used in the study. A present day fluvial river interpreted from aerial photograph is also used for characterizing the fluvial environment. In the absence of any drilled well data the facies assemblages are interpreted based on the seismic amplitudes.

The eastern offshore of India covers a vast stretch of sedimentary tract fed by major rivers like Ganges, Brahmaputra and Mahanadi in the north, Krishna and Godavari in the center, and Cauvery and Palar in the south, which led to variations in shelf-slope characteristics, degree of slope and hence slope instability. The structure as well as seismic attribute maps prepared from multibeam bathymetry and high-resolution 3D seismic data set has been analyzed to identify various geohazards in the deep water offshore regions of the east coast of India. These can be categorized as slope instability, slope canyons, shallow gas, mass transport complexes, sediment waves, gas hydrates, gas chimney, mud volcanoes and shallow faults. The slope instability is primarily related to rapid sedimentation by the active river systems while the other geohazards are often developed in association with shallow gas flows and leakages. The bottom simulating reflectors (BSRs) identified in the seismic sections indicate the presence of gas hydrates. Rapid sedimentation, BSR formation, dissolution and expulsion of water as well as gas and their subsequent vertical migration are responsible for the formation of shallow gas-related hazards. The results from the above analysis are of immense help in minimizing the risk of shallow hazards during exploration, drilling and subsurface installation activities along the eastern Indian offshore.

The study area represents a NE-SW trending growth fault setting In Godavari offshore. The principal fault trends of the above deformed zone divide the area into different blocks which act as sub basins within a basin. An attempt has been made to identify various depositional processes active in these fault blocks. The upthrown fault block is characterized by more of erosional processes while the downthrown part is more like a depositional low collecting ponded type of deposits. The study is further extended to recognize various possible geohazards such as gas seeps, gas chimneys, shallow water flow, unstable sliding strata etc .Shallow 3D seismic data which is quite useful has been used in this study to identify the above anomalies. The geohazard study in the sub basins could preempt the expected drilling related problems prior to exploratory drilling.

Extensional crenulation cleavage marked by asymmetric kinks and ductile shears occurs at low angle to steep S-1 planes in the mica schist of Zawar area in the Aravalli mountain. It is developed due to extension along the S-1 planes consequent to large-scale ductile shearing. The compressive stress of such shearing is deduced to be subhorizontal in NNE-SSW direction. Early fold axes assume variable trend due to shearing.