Abstract:

In Qinghai-Tibet Plateau, no Paleozoic fish fossils have been found so far due to limited studies.Recently, the second comprehensive scientific expedition to Qinghai-Tibet Plateau-paleontological expedition selected several areas in Southern Tibet with good Devonian exposure to conduct investigations, in which the Pali area in Yadong County of South Tibet is located in the hinterland of the southern Himalayan orogenic belt, and the Devonian sequence was only found in the western and southern parts of Pali Town.Using field paleontological section measurements, fossil sampling, recording and photography, we report a new section of Lower Devonian Liangquan Formation which is enriched in paleontological fossils located in Southwest Pali.We also discussed the sedimentary characteristics during Early Devonian of the study area.The lithology of the lower member of The Lower Devonian Liangquan Formation is interbedded within the coarse-grained and medium-fine grained clastic rocks.The lower part of the middle section is medium-thick bedded limestone, and the upper part is mainly bioclastic limestone.The lithology of the upper strata is mainly clastic rock and marl.From the lower member to the lower part of the middle member in the section, the regressive sedimentary sequence of coarse sands at the bottom and fine at the top reflects a process of seawater deepening in the coastal and shallow sea.The coral-bearing bioclastic limestone in the upper part of the middle member indicates that the seawater begins to be shallower.The clastic rock and marl assemblage in the upper member of Liangquan Formation reflects a coastal sedimentary environment.There are rich paleontological fossils in clastic rocks in the upper member, including cephalopods, aminoids, brachiopods, bivalves, and plant fragments, and bone fragments, and fossils of suspected placodermi are also found.These new data provides a comparative study with the sedimentary characteristics of Early Devonian in the study area.The discovery of the suspected placodermi remains effectively provide a guide to the further work searching for fossil fishes in this area.It also provides potential clues for studying the paleogeographic pattern in the southern Tibet of Paleo-Tethys.

Key words: Pali, South Tibet, Devonian sequence, placodermi, Paleo-Tethys