Paleoclimatic significance of the late Quaternary plant macrofossils from the Gokarna Formation, Kathmandu Valley, Nepal

Late Quaternary plant macrofossils from fluvial, fluvio-deltaic and lacustrine sediments of the Gokarna Formation in the Besigaon, Mulpani, and Dhapasi sections in the Kathmandu Valley, Nepal were analyzed. The obtained plant macrofossils allowed us to reconstruct the late Pleistocene paleoenvironment in central Nepal, which was influenced strongly by the SW Indian monsoon system and tectonic movements of the Himalayas. In total, 102 taxa from 52 families were identified to genus or species levels. The dominance of Eurya, Ficus, Morus, Zizyphus, Stephania, Rubus, Quercus subgen. Cyclobalanopsis, Pyracantha, and Carpinus in the lower and middle plant macrofossil assemblages indicates influence of a warm climate. In the upper plant macrofossil assemblages, the higher contents of cooler climatic taxa such as Abies, Pinus, Picea smithiana, Tsuga dumosa, Taxus wallichiana, Quercus subgen. Lepidobalanus, and Betula indicate a climatic deterioration. The higher diversity and common occurrence of aquatic plants indicate rich wetland vegetation in the Kathmandu basin. The plant macrofossil analysis shows at least three cycles of climate fluctuation between warm and cool phases during the deposition of the Gokarna Formation between 53,170 ± 820 yrs. BP and 49,300 ± 2100/1700 yrs. BP. These cycles seem to be fairly local or regional, but this can also be correlated with the overall global cooling context in GISP2 oxygen isotope curve in the late Pleistocene.