POLLEN AND SPORE ASSEMBLAGES FROM THE MIOCENE MALADUN FORMATION AT HONGTUPO, SONGPAN COUNTY, WESTERN SICHUAN PLATEAU AND THEIR BEARING ON PALAEOENVIRONMENTS
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Abstract:
Up to now, little is known about the palaeovegetation of the most northeastern part of the great Qinghai-Xizang (Tibet) Plateau during the Neogene time. In this study, we report Miocene pollen and spore assemblages from the Maladun Formation at Hongtupo, a small mountain about 50 km southwest of Songpan County town, Sichuan Province. The palynoflora is characterized by rich presence of Ulmaceae, Betulaceae and abundant Pinaceae pollen with rare spores. Angiosperm pollen occupies 52.9%–84.4% of the total tally. Gymnosperm pollen form 13.8%–44.1% of total pollen and spores. Spores only amount to 1.9%–5.1% of the total assemblage. Other elements in the pollen flora include common Fagaceae (Quercus, Castanea), Salix, Juglandaceae (Juglans, Carya) and minor Liquidambar, Sporotrapoidites, Lonicera, Ephedra, Compositae (Asteraceae), Rosaceae, Leguminosae (Fabaceae), Polygonaceae, Ranunculaceae, Lythraceae etc. Such a pollen flora represents a mixed broadleaved and conifer forest. The pollen flora of the Hongtupo is of late Early Miocene to early Middle-Miocene age based on the correlation with the similar pollen assemblage from the Lengshuigou Formation of Weihe Basin which was dated by the associated vertebrate fossils. The palaeoclimate derived from the pollen flora should be of cold temperate to temperate with an annual temperature of about 8℃–13℃. The present pollen flora shows a much less warm appearance than those of the similar age pollen floras from northern and eastern China, which leads to a deduction of palaeoaltitude at the fossil locality of over 1000 m to about 2000 m above sea level. It is interesting that the pollen flora also contains some warm-loving elements such as Liquidambar and Juglandaceae pollen, which probably implies the Miocene Hongtupo area was neighbored by a low terrace or valley landscape.
