Abstract
Analyses of the marine geophysical data collected in four oceanographic cruises during 1974–2008 inside the Gulf of Kachchh, northwest India was done, and geology and crustal structure were interpreted for the first time. Seabed topography deduced from satellite-derived bathymetry and bathymetric investigations has revealed the tide-dominated Gulf (> 6 m high) has ~50 m maximum depth along the axial part. The satellite-derived free-air gravity anomalies and their horizontal gradients together with earlier published results helped in noting major crust features like faults. Analyses of single and multi-channel seismic reflection data had enabled identifying reflection strata pattern and their continuity, wave-field and acoustic characters. 2-D model studies of ocean-bottom seismic refraction data (following ray-tracing technique), satellite-derived free-air gravity anomalies, magneto-telluric data along a profile in middle of the Gulf and magnetic anomalies near Gulf mouth have led to determine various physical properties: velocity, density, resistivity and the magnetic of the subsurface layers. They have been utilized in interpreting three-layered crust structure of the Gulf. Further, presence of ~3.0 km thick low, ~3.7 km/s velocity and 2.2 gm/cc density layer overlain by about 2.1 km thick high, 4.6 km/s velocity, and 2.55 gm/cc density layer noted. Considering the physical properties in correlation with mainland geology and crustal structure from onshore Suthri-1 and inner shelf GK-01-A1 well logs and coast parallel Mandvi–Mundra deep seismic study results, low and high-velocity layers have been noted as low velocity Mesozoic sedimentary rock formations overlain by high velocity Deccan volcanic rock formations. The volcanic rock thickness increases to the east are noted. The Tertiary sediments above them are ~1.2 km thick. The major crustal structures and geology identified contribute to understand regional geology, structure and tectonic framework of the Kachchh region and in particular, of the study area. The fractured Deccan volcanic rocks and their intervening intra-trappean sediments are possibly considered as potential hydrocarbon-bearing formations (?) in view of the underlying thick Mesozoic sediments.
Highlights
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1.
Seismic reflection, OBS, and magneto-telluric data revealed three layered crustal structure of the Gulf
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2.
We have identified fractured Deccan volcanic rocks and their intervening intra-trappeans sediments inside the Gulf
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3.
Presence of low velocity Mesozoic sedimentary rock formations overlain by high velocity Deccan volcanic rock formations
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Acknowledgements
We thank Secretary, DST, New Delhi for funding project no. ESS/16/313/2006 to study the Gulf of Kachchh. We would also like to thank the Director General, Hydrocarbons and Director General, CSIR, New Delhi for funding the marine seismic and marine magneto-tellurics project as R&D project. We equally thank the Director, CSIR-NGRI for continuously supporting the projects and Director General, ISR, Ahmedabad, Gujarat. The marine magneto-telluric data has been acquired by Scripps Institute of Oceanography (SIO) under the contract between CSIR-NGRI and SIO and the team was headed by Prof Steve Constable. We gratefully acknowledge the entire SIO team.
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D Gopala Rao and K S Krishna conceived the ideas and experimental design of the study. DGR has carried out conceptualization, planning, execution and wrote the manuscript. M Ismaiel has carried out literature review and preparation of the figures. KSK and MI have carried out the revision. Most authors have participated in compilation of different experiments in Gulf of Kachchh, data analysis and interpretation. And subsequently authors have provided valuable suggestions for improvement of the work.
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Communicated by N V Chalapathi Rao
** Passed away after the completion of this work.
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Gopala Rao, D., Krishna, K.S., Harinarayana, T. et al. Crustal structure of the Gulf of Kachchh, northwest India. J Earth Syst Sci 130, 136 (2021). https://doi.org/10.1007/s12040-021-01623-0
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DOI: https://doi.org/10.1007/s12040-021-01623-0