Neotectonic Activities and Its Significance to River-Course Evolution: Implication for the Cai River Catchment, Ninh Thuan Province, South-Central Vietnam

Abstract

The Cai River catchment of the Ninh Thuan province locates in the South-central portion of Vietnam. This area is underlain by various rock types, including Mesozoic to Cenozoic sedimentary and volcanogenic sequences and a large volume of magmatic complexes. The Cenozoic sedimentary cover comprises thin units that are commonly deposited within small deltaic or fault-controlled alluvial basins, and along discontinuous narrow coastal plains. Pliocene-Quaternary basaltic bodies are locally covered part of the coastal zone or form small offshore volcanic islands. These assemblages are variably deformed and dismembered as consequence of long-lived tectonic movements. Recent tectonic activities are evident by numerous indicators, which include brittle fracture and fault systems straddling Quaternary sedimentary covers and recent weathering profiles, numerous fault scarps, abrupt local land uplift and/or subsidence, disruption of drainage systems, occurrence of earthquake, exposure of hot spring water and mud/sand volcanos. Other morpho-tectonic features such as the presence of Quaternary terraces, exposure and displacement of coral reef, and the development or significant modification of drainage patterns and modern basinal architecture have also resulted from active tectonic activities. Dating of the deformed materials, including fault gauge, uplifted, or subsided sediments reveal that the recent tectonic movements have taken place continually during the Late Holocene to recent. The combination of diverse lithologies, multiple tectonic fracturing and displacement of the rock units, tectonic uplift, and subsidence, in conjunction with the surface processes and sea action, have resulted in complex river course and coastal morphology. Active faulting and local tectonic movements have created long-term effects on the river flow pattern and coastal zone stability, including the shifting of flow direction, the formation of subsided or uplifted structures, sea-shore modification. Lateral tectonic movements, on the other hand, have led to the modification of the flow pattern, which consequently creates local complex flow patterns and associated hazards along the Cai River and its tributary.