陕南早中侏罗世勉县群植物组合面貌

APPEARANCE OF THE FOSSIL PLANT ASSEMBLAGE ABOUT MIANXIAN GROUP OF SOUTH SHANXI PROVINCE IN LOWER AND MIDDLE JURASSIC

勉县群为陕南勉县至紫阳一带早中侏罗世陆相含煤沉积；自下而上分为三个组，即洪水沟组、沔水组、堰河组．该群含有丰富的植物化石，该植物群是典型的南方型Ｐｔｉｌｏｐｈｙｌｌｕｍ—Ｃｏｎｉｏｐｔｅｒｉｓ植物群。根据沉积特征及植物化石分布规律分析，勉县群三个组的形成时代依次为：早侏罗世、早中侏罗世、中侏罗世。有趣的是，在沔水组中下部发现了有花植物中华木兰（Ｍａｇｎｏｌｉａｍｉｏｃｅｎｉｌａ），为研究被子植物早期起源历史提供了一份新的材料。

Mianxian Group is coaly continental deposit of Lower and Middle Jurassic from Mianxian to Ziyangxian of South Shaanxi Puovince. It may be divided into three Formations from the lowest stratum to the uppermost, i. e. Hongshuigou Formation, Mianshui Formation and Yanhe Formation. The fossil plant of this Group is very abundant. The flora is a typical Southern Ptilophyllum-Coniopteris flora. According to the depositional characteristics and the distribution law of the fossil plant, the formed tines are respectively Lower Jurassic, Lower dnd Middle Jurassic, Middle Jurassic. It is interesting that Anthophyta Magnolia miocenica is discorered from the middle and lower parts of Mianshui Formation. It provides a new material for studying the Angiosperm origin in its early stage.