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Tidal rhythmites in offshore shale: A case study from the Palaeoproterozoic Chaibasa shale, eastern India and implications |
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| Authors: | L MallikR Mazumder BS MazumderM Arima P Chatterjee |
| Institution: | a Department of Geological Sciences, Jadavpur University, Kolkata 700032, India b Geological Studies Unit, Indian Statistical Institute, 203, B.T. Road, Kolkata 700108, India c Fluvial Mechanics Laboratory, Physics and Applied Mathematics Unit, Indian Statistical Institute, 203, B.T. Road, Kolkata 700108, India d Graduate School of Environment and Information Sciences, Yokohama National University, 79-7, Tokiwadai, Hodogaya, Yokohama 240-8501, Japan e Geoinformatics & Remote Sensing Cell, West Bengal State Council of Science & Technology, Department of Science & Technology, Bikash Bhavan, Kolkata 700091, India |
| Abstract: | Tidal rhythmites have been documented from modern continental shelves and distal offshore settings. In significant contrast to their modern counterparts, sedimentological studies of ancient tidal rhythmites formed in distal offshore settings and quantification of tidal rhythms encoded therein are, however, scarce. This paper presents sedimentological analysis of vertically accreted tidal rhythmites from the Palaeoproterozoic Chaibasa shale facies in India, and quantification of their tidal rhythms. The facies characteristics of the Chaibasa Shale coupled with harmonic analysis of the laminae thicknesses of the sandstone inter-layers corroborate a distal shelf palaeogeography for the generation of the vertically accreted tidal rhythmites. The latter are the distal counterparts of laterally accreted, tidal “bundle” deposits, well preserved within the shallow marine Chaibasa sandstones. The number of lunar days in a synodic month (∼23) estimated from the Chaibasa shale facies is, however, considerably lower than that estimated from the Chaibasa sandstone facies (∼32) suggesting that the tidal record encoded from the Chaibasa shale facies is incomplete. |
| Keywords: | Internal-tide deposit Turbidite Harmonic analysis Semidiurnal tide Palaeoproterozoic Chaibasa Formation |
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