华北板块大羽羊齿植物的成煤古气候含义

IMPLICATION OF COAL-FORMING PALAEOCLIMATE OF GIGANTOPTERID PLANTS IN THE NORTH CHINA PLATE

华北板块存在3个大羽羊齿分布区:Ⅰ—大羽羊齿植物贫乏区;Ⅱ—Gigantonoclea分布区;Ⅲ—Gigantonoclea—Gigantopteris共存分布区。根据大羽羊齿植物的地理限制、叶相特征和其他标志重建了华北板块早二叠世晚期至晚二叠世早期的古气候分带格局:其东南部(Ⅲ区)处于无季节性分化的热带雨林气候,并逐渐向西北过渡为萨旺纳气候(Ⅱ区)和热带草原气候(Ⅰ区)。上述古气候分带的现今取位方向(北东向)是华北板块于二叠纪的北向漂移过程中,伴随35°～45°逆时针旋转造成的。正是这种运动机制,使得华北板块逐渐脱离赤道附近的热带雨林成煤气候带,导致早二叠世早期广泛存在的聚煤作用,在早二叠世晚期—晚二叠世早期收缩至现今华北地台的东南一隅。

Based on the variability of genus taxon, three different regions in the plate are well recognized as follow: Ⅰ-rare gigantopterid region, Ⅱ-Gigantonoclea region and Ⅲ-con-currented Gigantonoclea-Giganto pteris region The evidence furnished by the geographical limitation of genus taxon and foliar physiognomy feature of this plant group appearantly indicates that a changed trend northwestwardly from an unseasonal rain tropical forest climate in Ⅲ region into savanna climate in Ⅱ region and steppe climate in Ⅰ region is continuesely transformed. The present emplacement direction of the Permian palaeoclimatic zones in the North China Plate suggests that it underwent a northward movement from low to middle latitude in north Hemisphere, accompaneied with a conterclockwise retation of about 35°-45°. The main part of the plate was away from the rain tropical forest climate zone, which is favorable to form coal, into the savanna and steppe climate zones to be difficut to forming coal. In this way, the late Early/early Late Permian coal resourse is contracted to the southeastern coner of the North China Plateform.