Abstract:

Provenance analysis of sedimentary rocks has an important significance on revealing the composition of basins, qualities of
reservoirs and sedimentary environment. Trace elements of Middle Permian carbonaceous mudstone samples in Jiaomuri area,
Qiangtang Basin were analyzed and discussed. The study of trace element content，characteristic ratios and REE distribution indicates
that the samples are moderately differentiated in LREE((La/Sm)N=2.50~5.41), while the HREE shows flat pattern ((Gd/Yb)N=1.32~2.47)
and all samples have slight Eu abnormity. The ratios of Sr/Ba, V/Cr, Ni/Co, Ceanom and δEu values are used to reveal the redox of
paleo-ocean. Our data show that the Middle Permian sedimentary environment where mudstones deposited was mainly oxidizing marine
conditions. Ratio of Rb/Sr and La/Th-Hf, La/Sc-Co/Th, Th/Sc-Zr/Sc diagrams show that the provenance area underwent weak
weathering and the source rocks are probably mainly andesitic rocks. La/Sc-Ti/Zr，La-Th-Sc and Th-Sc-Zr/10 discrimination
diagrams suggesting that the carbonaceous mudstone of the Longge Formation formed probably in an oceanic island arc tectonic setting.

Key words: Qiangtang Basin, Middle Permian, Longge Formation, carbonaceous mudstone, element geochemistry, tectonic setting