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