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Abstract <p>The Late Cretaceous Mahadek Formation of the south Shillong Plateau, NE India, records a fluvial-to-marine transition produced by the combined influence of global sea-level rise and tectonism. Detailed facies mapping across multiple stratigraphic sections identifies four facies associations: FA 1–braided–to–meandering fluvial channels, FA 2– wave-dominated foreshore, FA 3– transition from lower shoreface to offshore and FA 4– Intertidal to storm-influenced subtidal environment. Their spatial arrangement reveals pronounced lateral facies variations linked to differential subsidence, uplift, and reactivation of basement faults. Tectonic structures created local topographic barriers and ancient coastal irregularities that affected the sediment flow, shoreline orientation, and the interaction between waves and tides. The vertical stacking from FA 1 to FA 3 reflects a transgressive systems tract, while direct marine onlap of FA 4 over the basement in some sectors indicates different subsidence rate. Paleocurrent data and facies stacking patterns indicate marine transgression from the southwest, producing wave-dominated shorelines with localized tidal embayment. This study highlights the interplay of eustatic sea-level rise and tectonics in shaping a complex coastal system in the south Shillong Plateau.</p> Research highlights <p><UnorderedList Mark="Bullet"> <ItemContent> <p>The Late Cretaceous&#xa0;Mahadek Formation records a fluvial-to-marine transition governed by global sea-level rise and tectonism.</p> </ItemContent> <ItemContent> <p>Facies associations (FA 1–FA 4) indicate fault-controlled uplift, subsidence, and topographic barriers that influenced sediment dispersal and shoreline orientation.</p> </ItemContent> <ItemContent> <p>The succession represents a retrogradational facies stacking patterns linked to differential subsidence and irregular coastal morphology&#xa0;of the basin.</p> </ItemContent> <ItemContent> <p>Marine transgression during the basin subsidence caused shoreline migration and spatial variation of energy regime from wave-to tide-domination.</p> </ItemContent> </UnorderedList></p>

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Fluvial to marginal marine transition and their spatial variation in response to tectonics and sea-level fluctuations: evidences from the Late Cretaceous Mahadek Formation, southern Shillong Plateau, NE India

  • 期刊论文

  • 发表日期：

    2026年7月1日

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  • Adrita Choudhuri,
  • Amlan Koner

摘要

Abstract

The Late Cretaceous Mahadek Formation of the south Shillong Plateau, NE India, records a fluvial-to-marine transition produced by the combined influence of global sea-level rise and tectonism. Detailed facies mapping across multiple stratigraphic sections identifies four facies associations: FA 1–braided–to–meandering fluvial channels, FA 2– wave-dominated foreshore, FA 3– transition from lower shoreface to offshore and FA 4– Intertidal to storm-influenced subtidal environment. Their spatial arrangement reveals pronounced lateral facies variations linked to differential subsidence, uplift, and reactivation of basement faults. Tectonic structures created local topographic barriers and ancient coastal irregularities that affected the sediment flow, shoreline orientation, and the interaction between waves and tides. The vertical stacking from FA 1 to FA 3 reflects a transgressive systems tract, while direct marine onlap of FA 4 over the basement in some sectors indicates different subsidence rate. Paleocurrent data and facies stacking patterns indicate marine transgression from the southwest, producing wave-dominated shorelines with localized tidal embayment. This study highlights the interplay of eustatic sea-level rise and tectonics in shaping a complex coastal system in the south Shillong Plateau.

Research highlights

The Late Cretaceous Mahadek Formation records a fluvial-to-marine transition governed by global sea-level rise and tectonism.

Facies associations (FA 1–FA 4) indicate fault-controlled uplift, subsidence, and topographic barriers that influenced sediment dispersal and shoreline orientation.

The succession represents a retrogradational facies stacking patterns linked to differential subsidence and irregular coastal morphology of the basin.

Marine transgression during the basin subsidence caused shoreline migration and spatial variation of energy regime from wave-to tide-domination.