Introduction

The present landforms, geomorphic processes and sedimentary deposits in the tropics have been influenced by events which took place in the Neogene. Events in the Tertiary included the building of two huge mountain chains, the Himalaya and Andes, which in turn modified the tropical climate. For example, the origin of the Himalayan Ranges and the uplift of the Tibetan Plateau either created the South Asian Monsoon system, or strengthened it immensely from its previous state. This gave rise to a strong seasonality and storminess in regional rainfall that translated into seasonal river discharges and high-magnitude floods in the rivers of South, Southeast and East Asia. Prell and Kutzbach (1992) associated the rising of the eastern Himalaya with an east–west decrease in precipitation along the mountain chain, enhanced aridity in Rajasthan and western Sahara, and cooler conditions over northern Asia and Europe. The very high mean elevation of the Tibetan Plateau (4000–5000 m) prevented the influx of the monsoon from the south, leading to aridity and a low level of glaciation north of the Himalayan chain (Gasse and Derbyshire, 1996; An et al., 2001). The world subsequently went through a repeated pattern of glacial and interglacial times in the Quaternary.