Reconstruction of Middle Miocene Surma Basin as Two Arcs Derived Sedimentary Model: Evidence from Provenance, Source Rock Weathering and Paleo-Environmental Conditions

Abstract

Surma Basin in Northeast India is characterized by a thick Cenozoic sedimentary succession that initiated due to the collision between Indian and Burmese plates. Variability in the litho-association of a thick sedimentary column in this robust terrain represents the distribution and deposition of enormous sediments that supplied throughout the entire basin evolution, especially during the Middle Miocene. This makes Middle Bhuban sandstone as the best aspirant for this study. Miocene Bhuban sandstones collected from parts of Aizawl and Champhai Districts of Mizoram, NE India have been studied for the whole rock geochemistry to understand the nature of source rocks, probable source areas and paleoclimatic conditions. The geochemical behavior of studied sandstones represent a felsic nature (TiO2/Zr: 15.03–37.09; La/Sc: 1.80–6.52, La/Co: 0.39–5.48, Th/Sc: 0.56–2.05; Cr/Th: 4.19–28.00; Al2O3/TiO2: 13.13–28.09), fractionated granitoid provenance [(La/Lu)N: 15.06–22.25; (La/Yb)N: 14.09–19.96; (La/Sm)N: 3.17–3.99; (Gd/Yb)N: 2.00–2.84] and moderately weathered sediments (CIA: 65; CIW: 73; PIA: 69; WIP: 41; ICV: 0.87; Rb/Sr: 1.07). The deposition of these sediments took place in an oxic condition (sharp positive Ce anomaly) during a regressive phase with contribution from various granitoid plutons. Synthesizing the data available for different plutons around the Himalayan and Indo-Burmese Ranges (IBR), they show close similarity with Middle Bhuban geochemical signatures. Ladakh granite, Yangbajin granite and Jirong Granodiorite of Himalaya along with Wuntho-Mt. Popa and Banmauk granitoids are the most influential sources of the Surma sediments before the cessation of Paleo-Irrawaddy and then Paleo-Brahmaputra River courses. This is also evident by the paleo-current directions of sediments from various parts of the Surma Basin. Rise of Shillong plateau, Mikir massif and Naga hills in the north and IBR in the east caused the flow migration and lithological changes. Therefore, the present study ultimately invokes a significant supply of the sediments from the granitoids of neighbouring Indo-Burmese arc in the east in addition to their contribution from the Himalayan ranges in the north.