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Abstract <p>The late Miocene–Pliocene argillaceous Boka Bil Formation, exposed at the outskirts of Aizawl town, Mizoram, records the depositional history of a wave-dominated clastic shelf, frequently infested by storms. In alternation with wave-rippled silty shale, lenticular siltstone/fine-grained sandstone interbeds with hummocky and swaley cross-stratifications and erosional sole feature like gutter bear undeniable proof for storm action. Process-based facies analysis allowed delineation of fair-weather and storm wave bases on the Boka Bil shelf that allowed categorization of depositional products as (i) above fair-weather wave base, (ii) between fair-weather and storm wave base, and (iii) close to or below storm wave base. Whereas <i>Cruziana</i> ichnofacies dominate the distal shelf, dwelling burrows of <i>Skolithos</i> ichnofacies are noticed in abundance in storm-infested proximal inner shelf sandstones. Additionally, recurring alternations between sandstone-hosted <i>Skolithos</i> ichnofacies and silty-shale-hosted <i>Cruziana</i> ichnofacies in shelf deposit bear indication of a storm-prone shelf setting. An operation of geostrophic current is inferred from near coincidence between fair weather wave ripple crest line orientation and gutter trend. Measurement of litholog and documentation of facies stacking pattern allowed identification of a shallowing-up progradational depositional trend in the course of Boka Bil sedimentation in the study area. Water depth range of 4–14 metres is estimated from fair-weather wave ripple data and sediment grain size using Bay of Bengal shelf as a modern analogue.</p> Research highlights <p><UnorderedList Mark="Bullet"> <ItemContent> <p>Wave- and storm-influenced sedimentation in Mio-Pliocene Boka Bil shelf of the Bengal basin.</p> </ItemContent> <ItemContent> <p>Operation of the geostrophic current on the shelf is inferred.</p> </ItemContent> <ItemContent> <p>Grazing and feeding (Cruziana) and dwelling (Skolithos) ichnofacies recorded.</p> </ItemContent> <ItemContent> <p>A progradational facies stacking is documented from the litholog and ichnofossil character.</p> </ItemContent> <ItemContent> <p>Considering the Bay of Bengal as a modern analogue and considering its wave parameters, a palaeo water-depth of 4–14 m is estimated for the Miocene Boka Bil shelf.</p> </ItemContent> </UnorderedList></p>

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Depositional history of a wave-dominated, storm-infested argillaceous late Miocene–Pliocene shelf from the Boka Bil Formation, Surma Group, Mizoram, India

  • 期刊论文

  • 发表日期：

    2026年5月23日

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  • Ujjwal Kr Singh,
  • Partha Pratim Chakraborty,
  • Lalramengi Fanai,
  • Lalremruata,
  • Alok Deep,
  • Paul Lalnuntluanga

摘要

Abstract

The late Miocene–Pliocene argillaceous Boka Bil Formation, exposed at the outskirts of Aizawl town, Mizoram, records the depositional history of a wave-dominated clastic shelf, frequently infested by storms. In alternation with wave-rippled silty shale, lenticular siltstone/fine-grained sandstone interbeds with hummocky and swaley cross-stratifications and erosional sole feature like gutter bear undeniable proof for storm action. Process-based facies analysis allowed delineation of fair-weather and storm wave bases on the Boka Bil shelf that allowed categorization of depositional products as (i) above fair-weather wave base, (ii) between fair-weather and storm wave base, and (iii) close to or below storm wave base. Whereas Cruziana ichnofacies dominate the distal shelf, dwelling burrows of Skolithos ichnofacies are noticed in abundance in storm-infested proximal inner shelf sandstones. Additionally, recurring alternations between sandstone-hosted Skolithos ichnofacies and silty-shale-hosted Cruziana ichnofacies in shelf deposit bear indication of a storm-prone shelf setting. An operation of geostrophic current is inferred from near coincidence between fair weather wave ripple crest line orientation and gutter trend. Measurement of litholog and documentation of facies stacking pattern allowed identification of a shallowing-up progradational depositional trend in the course of Boka Bil sedimentation in the study area. Water depth range of 4–14 metres is estimated from fair-weather wave ripple data and sediment grain size using Bay of Bengal shelf as a modern analogue.

Research highlights

Wave- and storm-influenced sedimentation in Mio-Pliocene Boka Bil shelf of the Bengal basin.

Operation of the geostrophic current on the shelf is inferred.

Grazing and feeding (Cruziana) and dwelling (Skolithos) ichnofacies recorded.

A progradational facies stacking is documented from the litholog and ichnofossil character.

Considering the Bay of Bengal as a modern analogue and considering its wave parameters, a palaeo water-depth of 4–14 m is estimated for the Miocene Boka Bil shelf.