北京永定河谷中新元古界雾迷山组叠层石生长控制因素探讨

INVESTIGATION OF CONTROLLING FACTORS FOR GROWTH IN STROMATOLITES OF THE MIDDLE NEOPROTEROZOIC WUMISHAN FORMATION,YONGDING RIVER VALLEY,BEIJING

北京永定河谷庄户洼剖面中新元古界雾迷山组产出大量叠层石。本文对其形态进行分析测量,获得叠层石优势生长方向的雷达图,结合雾迷山组时期古板块方位、波痕构造所指示古水流方向及当时的构造应力方向等信息进行分析,对叠层石形态生长控制因素进行综合探讨。分析表明,因雾迷山组形成时期华北板块位于赤道附近,永定河谷庄户洼剖面雾迷山组叠层石形态不受阳光控制,控制其形态的主要因素是古水流。另外,构造应力活跃所引起的古地震频发导致了软沉积物向深海滑塌也影响了叠层石的生长形态,硅质填充物在后期破坏了叠层石的形态。对叠层石形态生长控制因素进行分析探讨,可帮助理解叠层石形态生长机理和古环境,具有重要的地球生态学意义。

A large amount of stromatolites occur in the Wumishan Formation of Yongding River Valley in Beijing, which provide great materials for this study. In order to investigate the controlling factor for growth in stromatolites, the shape of stroma- tolites was measured and analyzed, and the radar map of dominant growth directions of stromatolites was gained, and then it was combined with the location of the North China palaeoplate, the direction of palaeo-currents inferred from ripplemark structures, the direction of palaeo-tectonic stress. This study indicates that the growth of stromatolites of Wumishan Formation in Zhuang- huwa Section, Yongding River Valley was not controlled by sunlight mainly, because the location of North China palaeoplate was near the equator, and the main controlling factor was palaeo-current. Besides, soft-sediment deformations toward the deep sea induced by the seismic activities which were caused by palaeo-tectonic stress overlaid on stromatolites influenced the shape of them, and siliceous chert filling damaged stromatolites subsequently. By analyzing the controlling factors for growth in stromatolites, we can understand the mechanism of growth of stromatolites and the palaeoenvironment, it has important ecological significance.