Abstract:

8 fresh samples of carbonaceous mudstone were featured from Xiaoping Formation, Late Triassic epoch in Gaoming area of the western Guangdong Province. The constant of whole-rock main element, trace element and REE content were determined using X-ray fluorescence spectrometer and ICP-MS. The values of m (m=100×MgO/Al₂O₃) and  Ca/Mg , B/Ga and Rb/K are used to study the paleosalinity in this area. The result shows that the Fenggang Member of Xiaoping Formation is brine neritic facies sedimentation. The paleosalinity showed low-high-low-change process. The paleosalinity reaches the highest value in the middle-upper part and decreases to the lowest value at the top. The values of P and Sr/Cu reflect the change of the paleoclimate. Fenggang period is mainly affected by warm-humid climate. And the dry-hot climate occurred in the central and upper part of the period. The discrimination diagrams of Zr-Th and La-Th-Sc and REE show that the tectonic setting of Gaoming area was the depression basin on passive continental margin. All the samples were characterized with high ∑REE(214.15-455.85)，LREE enrichemnt(LREE/HREE =7.51-12.02) and Eu negative anomaly（δEu=0.47-0.60）. The source rocks are mainly granite partially mixed with basalt and sedimentary rock based on the data.

Key words: western Guangdong Province, Gaoming area, Late Triassic epoch, Xiaoping Formation, carbonaceous mudstone, elemental geochemistry