Sediment recycling in the northern Qaidam Basin margin during the Cenozoic: A case study from the Dahonggou section

This paper is the result of geological survey engineering.

Objective Recently, more studies show that the sediment recycling plays an important role in the inversion of the tectonic events, the identification of sediment source areas and the sources of eolian dust.

Methods In order to explore the Cenozoic sediment recycling in the Qaidam Basin, this paper conducts thin section identification, detrital framework grain composition and heavy mineral analysis of sandstones, and major, trace, and rare earth elements, and clay minerals of mudstones of the Dahonggou section in the northern Qaidam Basin.

Results The major, trace, and rare earth elements of mudstones are similar to the standard distribution patterns of upper continental crust (UCC) and chondrite, which may indicate that the sediments have been completely mixed or recycled; Sandstone is mainly composed of quartz, and a small amount of feldspar and lithic grains which are mainly composed of sedimentary ones. Sandstone framework detrital mode indicates a provenance type of recycled orogenic belt; The content of stable heavy minerals and ZTR (zircon, tourmaline, and rutile) index suddenly decrease in the upper portion of the section, indicating a closer source area to the section during the late stage; On the contrary, the contents of chlorite, which is easy to decompose, suddenly increase in the upper portion of the section. This observation might also shows that its source area was closer at this time.

Conclusions Based on the analysis of sedimentary facies, sandstone thin section and detrital zircon U−Pb age, it was suggested that the Jurassic and Cretaceous sedimentary rocks in the thrust−fold belt of the northern Qaidam Basin experienced large−scale sediment recycling and were one of the important provenances of the Cenozoic strata in the basin; Then, the fission−track analyses of detrital apatite show that the Cenozoic sedimentary rocks in the northern margin of the Qaidam basin have experienced significant recycling at 9−7 Ma; After about 3 Ma, with fold−thrusting propagating into the basin center, the uplifted sedimentary rocks in the northern basin experienced recycling, which form the important provenance of the Quaternary lakes within the center of the Qaidam Basin and of the Quaternary loess deposits in China Loess Plateau.