Identification of greigite in the late Pleistocene sediments of Lake Qinghai and its environmental implications

Lake Qinghai, the largest lake in China, is situated in an important climate-sensitive zone on the northeastern margin of Tibetan Plateau. In this study, the magnetic mineralogy of a late Pleistocene sediment core (1F, 18.6 m long) from the southern sub-basin deposition center of Lake Qinghai was studied using multiple rock-magnetic and non-magnetic measurements. There are two distinct magnetic susceptibility peaks at the depths of 8.15∼8.96 m and 15.50 ∼ 17.28 m. High- and low-temperature magnetic measurements, coupled with scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) analyses, suggest that the sediments from these two intervals contain a large number of single domain (SD) and some superparamagnetic (SP) greigite particles, which is the primary cause for the enhancement of magnetic susceptibility. Greigite particles are mainly formed due to sulfate reduction, an early stage of diagenesis. Therefore, the occurrence of greigite in 1F core implies that the Lake Qinghai could have experienced two intervals favorable for early diagenesis during the late Pleistocene.