Depositional processes and sedimentation pattern in an intermontane basin: Insights from the Imphal Basin, Indo‐Myanmar Range, NE India

Abstract

Intermontane basins make a distinct category of sedimentary basins, but nevertheless, the depositional processes and sedimentation patterns therein are not well understood. Quaternary sediment‐filled Imphal Basin in the Indo‐Myanmar Range provides us with an excellent opportunity of lending insight into these sedimentological aspects of an intermontane basin. Detailed facies analysis brings out that five distinct facies associations (“FAA”–“FAE”) have developed in different parts of the basin, each one of which indicates a specific subenvironment of deposition. Facies characters and spatial distribution of facies associations reveal that the basin fill records interlinked lacustrine, fluvial, and alluvial fan processes. Comprising mud and peat, the facies association “FAA” represents deposits of a lake and lakeshore swamp. The facies association “FAB” comprises mud interfingered with crudely bedded gravel and represents suspension fallout in a lake with intervening gravel‐rich, hyperconcentrated flows that diffusively plunged into the lakebed. The sand‐dominated facies association “FAC” and gravel‐dominated facies association “FAD” were deposited in fluvial domains of meandering and braided streams, respectively. Rimming the basin margin, the gravel‐dominated facies association “FAE” was deposited in the alluvial fan–interfan areas. Widespread development of the lacustrine facies (“FAA” and “FAB”) around the Loktak Lake along with extensive peat development over the lacustrine mud suggests lakeshore regression and development of vast swamps under humid conditions. The regression under humid conditions could be a result of fast and enhanced influx of finer sediments into the lake that transcended the creation of accommodation space and ultimately led to faster infilling of the lake margins favouring development of vast swamps in due course of time.

Stratigraphic response to fragmentation of the Miocene Andean foreland basin, NW Argentina

“…Similarly, the Miocene stratigraphic architecture of strata in the Vinchina Basin in the transition between the Precordillera fold-andthrust belt and the thick-skinned Sierras Pampeanas of central Argentina shows a similar fluvial stratigraphy (interpreted in terms of low and high accommodation space) related to the uplift along basin-border and intrabasin faults (Marenssi et al, 2015). Such relationships between tectonic processes and the development of facies architecture are also welldocumented in the Karakoram and the eastern Himalayan foreland basins (e.g., Burbank & Johnson, 1983;Goswami & Kshetrimayum, 2018). Moreover, the Miocene Alborz Basin of Iran records three coarsening upward cycles of clastic sediments indicating periods of high A/S and the retrogradational pattern of sedimentary facies with increments in flexural subsidence; conversely, low A/S and progradation of the sedimentary facies were interpreted to coincide with local intrabasin uplifts (Ballato & Strecker, 2014).…”

Sedimentation of open-framework gravels in alluvial-fan settings: Quaternary Poplar Fan, northwest China

“…Variations in grainsize reflect the hydrodynamics of streamflows around the bars. The bars accrete across pools when secondary currents wane (Cuevas Gozalo and Martinius, 1993;Chen et al, 2017;Goswami et al, 2018). Where OFGs occur near the top of compound bar deposits, they are commonly a product of the migration of coarse bar-head unit bars.…”

“…12). In the fan-head trench high-energy floods emanate from the catchment causing the deposition of massive gravels (G1) within the lateral confinement of the valley; here, OFG deposits are lacking (Blair, 1999;Alexander, 2001;Goswami, 2018). The overall unstratified lithofacies G1, with its poorly sorted and chaotic fabric, common presence of floating outsized boulders, and indistinct imbrications, is interpretable as the product of non-selective and partially en-masse deposition by hyperconcentrated flows (DeCelles et al, 1991;Blair and McPherson, 2009).…”