Mid–late Holocene fluvial aggradational landforms and morphometric investigations in the southern front of the Shillong plateau, NE India.

The present study is an attempt to understand the antiquity of the preserved fluvial landforms and its response to the climate–tectonics nexus through geomorphological investigations along the Jadukata, Umpung, Umngot and Umtongoi rivers in the southern front of the Shillong plateau (SP), NE India. Sedimentological characteristics, chronological analyses and morphotectonic parameters were used to describe the spatial and temporal variability in the patterns of aggradation, landform evolution and neotectonic influences in the study. Our results indicate that valley aggradation processes occurred around the transitional zone in the southern front of the SP during the mid–late Holocene era along with a hiatus in sediment deposition after 4.3 ka. Sediment generation and aggradation is modulated by precipitation anomalies associated with the Indian Summer Monsoon (ISM) variability whereas morphometric analysis suggests that activity along the Dauki–Dapsi fault has been contributing to the uplift-related deformation. Sedimentological observation supported by optically stimulated luminescence chronology obtained on palaeoflood deposits, valley-fill fluvial terraces and alluvial fans indicate their deposition during three pluvial phases: (i) 5.3–4.3 ka, (ii) 2.4–1.0 ka and (ii) 0.7–0.3 ka. Our data indicate that valley aggradation and geomorphic processes in the southern part of SP responded to short-term changes in the ISM variability with contributions from the morphotectonic activities associated with the Dauki–Dapsi fault during the late Holocene period. [ABSTRACT FROM AUTHOR]