贵阳花溪地区下三叠统大冶组中Phycosiphon形态结构分析及其古环境意义

贵阳花溪地区下三叠统大冶组二段Phycosiphon数量丰富、保存完整,为研究其行为习性提供了良好材料。对61个样品中的267个“U”型叶片的宽、高和边缘管直径统计分析表明,“U”型叶片宽、高比一般在0.5–0.6之间,边缘管直径和叶片高之比在0.12–0.18之间,据此推测Phycosiphon造迹生物大小与叶片大小存在一定的关系。对Phycosiphon造迹生物行为习性进行了研究分析,认为叶片的凹曲方向可以指示造迹生物的觅食方向。Phycosiphon基本形态由“U”型觅食迹和线形爬行迹构成,“U”型觅食迹和线形爬行迹可以构成鹿角状、团状、不规则状以及链状四种组合类型。鹿角状和团状多形成于浊流事件之前,指示低能静水环境;不规则状一般形成于浊流事件之后,指示沉积速率较快和相对高能的水体环境;链状在这两种环境中都有发育,体现了Phycosiphon造迹生物随机性觅食的特点。Phycosiphon发育特征表明研究区在早三叠世处于浅海碳酸盐台地前缘斜坡地带,浊流频发,但整体处于贫氧、低能的环境。

Morphological analysis and palaeoenvironmental significance of Phycosiphon from the Early Triassic Daye Formation in the Huaxi area, Guiyang

Abundant and well-preserved samples of Phycosiphon from the Member II of the Lower Triassic Daye Formation in the Huaxi area of Guiyang provide good materials for studying the behavior of the ichnogenus. Statistical analysis of the width, height and marginal tube diameter of 267 U-shaped leaves in 61 samples show that the ratio of the width to the height of the U-shaped leaves generally ranges from 0.5 to 0.6, and the ratio of the marginal tube diameter to the leaf height ranges from 0.12 to 0.18. It is assumed that there is a certain relationship between the size of the Phycosiphon-making organisms and that of the leaves. The behavior of the Phycosiphon-making organisms was analyzed, and the results suggest that the concave direction of leaves may indicate the foraging direction of the Phycosiphon-making organisms. The basic structure of Phycosiphon consists of U-shaped pascichnia and linear repichnia. The U-shaped pascichnia and linear repichnia can form four combinations: antler-shaped, cluster-shaped, irregular-shaped, and chain-shaped. The antler-shaped and cluster-shaped combinations are formed before the turbidity events, indicating low-energy hydrostatic environments. The irregular-shaped combination is generally formed after the turbidity events, indicating an environment with rapid sedimentation rate and relatively higher energy. However, the chain-shaped combination is developed in both environments, reflecting the random foraging characteristics of the Phycosiphon-making organisms. The development characteristics of Phycosiphon indicate that the study area was located on the slope of the front of a shallow carbonate platform during the Early Triassic, where turbidity current occurred frequently, but the overall environment was oxygen-poor and low-energy.