Geomorphic evolution of the craton-derived Sone megafan in the southern Ganga plain, India: A tectono-climatic interplay

• Published in: Catena (Giessen) 2024-01, Vol.234, p.107636, Article 107636
• Main Authors: Verma, Aditya K, Patel, Narendra K., Pati, Pitambar, Jaiswal, Manoj K., Kashyap, Rajkumar, Narzary, Belligraham
• Format: Article
• Language: English
• Subjects: middle Ganga plain; neotectonics; Quaternary; Sone megafan; subsurface faults
• ISSN: 0341-8162; 1872-6887
• DOI: 10.1016/j.catena.2023.107636

•Formation of the Sone megafan in the Ganga plain is tectono-climatically controlled.•The peninsular climate and the Himalayan tectonics effect the megafan’s evolution.•Tectonic tilting and twisting is controlling the fluvial geomorphology of the megafan.•Shifting of fluvial processes promotes soil development on the abandoned surface.•The Sone and the Gandak megafans behave similarly to the Himalayan neotectonics. The Ganga plain neotectonics has been studied from surface and sub-surface faults, frequent geomorphic readjustment, changing sedimentation pattern, piedmont progradation, pedological variation, and frequent earthquake occurrences. However, being neotectonically stable, the peninsular region’s geomorphic changes are governed by climatic fluctuations, contributing to the Ganga plain’s sedimentation. Therefore, peripheral craton sourced marginal alluvial deposits in the Ganga basin are appropriate features to study the control of both the Himalayan tectonics and climate of core peninsular region away from their respective source areas. This study uses a process-response approach model to describe the geomorphic development of the Sone megafan, located at the marginal part of the Ganga plain to the south of the Ganga River, bordering the Indian craton. Geomorphological mapping, field investigation of the depositional features, soil profiles, and Optical Stimulated Luminescence (OSL) chronology suggest four phases of geomorphic evolution, i.e., in 22-8 Ka, 8.0 Ka -7.3 Ka, 7.3 Ka -2.4 Ka, and 2.4 Ka– 0.5 Ka on the Sone megafan. The different evolutionary phases are marked by channel and floodplain abandonment and soil profile development. The megafan surface is divided into four distinct geomorphic units (OdSP– Oldest Sone Plain, OSP– Old Sone Plain, YSP– Young Sone Plain, and AFP– Active Floodplain) based on OSL ages and soil properties. Geomorphology and soil suggest a mixed climate in the source and sink area. The arid climate in the catchment contributed to the sediment production, and the humid climate promoted its transport, which resulted in the largest depositional unit of the megafan, even during the arid period in the Ganga basin. Contrast to the north of the Ganga River, no surface faults are found on the Sone megafan. However, the tectonic activity of the bounded basement faults, i.e., the East and the West Patna faults, are well pronounced in the sediment distribution and fluvial response. Tilting and twisting the fault-bounded block con