Helenifore Robustum Radiolarian Fauna from the Hanjiga Formation, Middle Tianshan, Xinjiang, China and the Chronostratigraphic Significance
摘要
The Hanjiga Formation is a Devonian stratigraphic unit in Wenquan area of Middle Tianshan,Xinjiang,China which consists of marine clastic deposits with the intercalary of the volcanic clastic rocks.Rich Middle Devonian coral and brachiopod fossils have been found in the limestone lumps and gravels of this formation.Recently,the Helenifore robustumradiolarian fauna of late Frasnian,Late Devonian,is discovered in the cherty lens of the upper Hanjiga Formation.Therefore,regarding the age of the Hanjiga Formation,we suggest(1)because the Middle Devonian coral and brachiopod fossils were separately found in the limestone lumps and gravels in the Hanjiga Formation,they do not represent the age of the formation;(2)the late Devonian radiolarians reported herein most likely represent the age of the Hanjiga Formation,i.e.,late Frasnian.Five radiolarian genera and 11 species,belonging to 3 orders and 4 families,are described in this paper.