Abstract:

The marine and transitional sediments were dominated during Early or Middle Jurassic in the Qiaoyuan Formation of Kuitan area in Huilai. The samples were analyzed by the whole rock analysis and the ICP-MS trace elements analysis. The paleosalinity and the change of water depth are showed by the main and trace elements and their ratios, which are impacted by the change of sea-level and positively correlated. Using the values which reflect the paleosalinity and the water depth of m, Sr/Ba,Ca/Mg,B/Ga and Rb/K, the curve of relative change of sea-level of Qiaoyuan Formation was established. The Qiaoyuan Formation shows the sedimentary cycle of two transgressions and the transgressions takes place in the lower and upper part of Qiaoyuan Formation. The samples were analyzed by the ICP-MS trace element analysis and the sandstone mineral composition analysis. The source rocks are mainly from sedimentary rock, basalt and granite of the upper crust with the REE distribution patterns and the La / Yb-ΣREE source rock discrimination diagrams. Based on the Dickinson diagram, Zr-Th, La-Th-Sc, Th-Co-Zr/10 discrimination diagrams and the eigenvalues comprehensive analysis for trace elements, the tectonic setting is the backarc extrusion basin, which with the characteristics of a continental island arc and few passive continental margin component. The sediments are from the volcanic arc belt.

Key words: Huilai area, Early-Middle Jurassic, Qiaoyuan Formation, change of sea-level, element geochemistry, tectonic setting