Formation of greigite (Fe ₃ S ₄ ) in the sediments of saline lake Lop Nur, northwest China, and its implications for paleo-environmental change during the last 8400 years

We present the results of rock magnetic and SEM/EDX analyses of the sediments of Lop Nur, a former saline lake in the Tarim Basin, China. The aim of the study was to assess the impacts of authigenic iron sulfide minerals (e.g., greigite) on the sedimentary magnetic properties and their possible relationship with environmental and climate change. Five layers with relatively high values of χ, χ _ARM , SIRM, S-ratio, χ _ARM /χ and SIRM/χ are identified within organic-rich sediments; the five layers are dated to ca. 8150–7000, 5300–4900, 3600–3100, 2750–2550 and 1820–1680 cal. yr BP. Authigenic greigite is the dominant magnetic mineral within the five layers and it is present in the stable single domain state. The magnetic properties of the intervening layers are dominated by detrital multidomain magnetite. Combined with results of a previous study, we infer that the greigite-bearing sediments were deposited during cold and wet periods which were probably related to the North Atlantic cold events during the past 8400 yr. During these periods, greigite formation was likely driven by an enhanced organic matter supply, but pyritization was constrained by the decreased sulfate content and high sedimentation rate. The greigite and its diagnostic magnetic parameters (e.g., SIRM/χ) can be regarded as an indicator of the hydrological and climatic evolution of the Tarim Basin.