Late Quaternary landscape evolution of the frontal part of Tripura Fold Thrust Belt, India: Connecting climate and tectonics

The Tripura fold-thrust belt is located at the eastern fringes of the Bengal basin, which is also part of the Himalayan foreland basin. It is also considered situated at the outer wedges of deformation front of the Indo-Burmese ranges, eastern Himalayas. It has been developed due to the oblique collision of the Indian, Eurasian, and Burmese micro-plates over the past 2 million years, leading to new antifomal ridges in the western region. It comprises a series of N-S trending narrow antiformal ridges separated by wide synformal valleys. In North and East Tripura, the major rivers such as Khowai and Dhalai flow through the intermontane valley to the north, eventually merging with rivers in Bangladesh. Meanwhile, in West Tripura, rivers like Haora and Gomti flow westward, joining with rivers in Bangladesh.  The shifting of major rivers like Khowai and Haora northwards within the antiformal ridges indicates neo-tectonic activities along the transverse fault. Recent Earthquake activities in the area also emphasize that the area is tectonically active. However, due to its inaccessible location, dense vegetation, and ongoing border disputes have resulted in limited research attention. Based on previous structural studies, a series of N-S trending parallel antiformal ridges show a progressive decreasing structural complexity from East to West; however, limited or no systematic studies are available to understand the sequential development of these ridges and valleys concerning tectonic and chronological framework.
Our research aims to establish a geochronological framework in the late-quaternary geomorphic evolution of the Tripura fold-thrust belt which has been lacking. Using geomorphic studies and optically luminescence dating techniques, we provide a timeline of sediment deposition and new antiformal ridge formation in the westernmost part of the area during the Late Quaternary period, leading to a better understanding of the sequence of events operating in the landscape evolution. Primary field observation suggests a thick deposition of unconsolidated sand and silt layers showing a fining upward sequence preserved at the flank of ridges. In the westernmost part of Tripura, based on 22 luminescence ages dated from unconsolidated sand samples suggested that it was a plain depositional fluvial system during 87, 84, 79,76,74 ka or even older than that and continued to deposit around 68, 65,63 till 55 ka. During that time, there was a high sediment supply in the area. Due to tectonic activities, the Baramura and Atharamura ridges started to develop after 50 ka, evident from the luminescence dates from the top layer of sand deposits preserved in the crest of the ridges. Climate fluctuations significantly influenced sediment supply for fluvial deposition, which was subsequently affected by ongoing neo-tectonism in the Indo-Burmese ranges. Additionally, it also corresponds with the transition during arid-humid phases that prevailed over the Northern Hemisphere in the global scenario.