Mid-late Holocene climatic changes recorded by loess deposits in the eastern margin of the Tibetan Plateau: Implication for human migrations

Implications of the loess record for Holocene climate and human settlement in Heye Catchment, Jiuzhaigou, eastern Tibetan Plateau, Sichuan, China

“…We used AMS to measure the graphitized carbon dioxide for 14 C/ 12 C ratios. In addition to new radiocarbon ages, we include analysis of 27 previously published radiocarbon ages (Henck et al, 2010;d'Alpoim Guedes et al, 2015;Wen et al, 2017). We calibrated new and previously published radiocarbon ages to calendar years with CALIB v. 8.2 using the IntCal20 data set (Reimer et al, 2020;Stuiver et al, 2022).…”

“…Resumption of loess deposition in the Heye Catchment corresponds to a post-MHCO cooling and drying regionally (An et al, 2000;Feng et al, 2006) and locally (Hong et al, 2003;An et al, 2006;Zhao et al, 2011;Wen et al, 2017); loess deposition in western China increased in 6-3 ka (Lehmkuhl et al, 2000(Lehmkuhl et al, , 2014Porter, 2001;Huang et al, 2002;Maher et al, 2003;An et al, 2006;Stauch et al, 2012). On the eastern TP, multiproxy analyses of lake and peat cores corroborate cooling and drying after 6-3.7 ka (Zhang and Mischke, 2009;Zhao et al, 2011;Chen et al, 2014), with a slight warming after 3.7 ka (Zhang and Mischke, 2009), which we cannot evaluate in our data, because we have only two dates in younger loess that are older than 3.7 ka.…”

“…There is uncertainty about when the younger loess deposited, whether and how it may have been modified syn-or postdeposition, and what role landsliding and human occupation may have played in any modification. Prior work on the younger, gravelly loess used radiocarbon dates of bulk charcoal, grain-size analyses of the loess (i.e., excluding the coarse lithic component), and rare earth element analysis at the Ashaonao archaeological site to determine that the loess is likely derived from fine-grained glaciofluvial deposits in eastern Tibet during the Late Holocene and was deposited continuously over the last ∼5000 years (Wen et al, 2014(Wen et al, , 2017, but considers neither the older loess nor the source of gravel in the younger loess. Henck et al (2010) interpret the older loess below the paleosol as primary loess deposition, which they date to the late Pleistocene/Early Holocene (11.1 ± 0.7 and 18 ± 1.4 ka), and younger gravelly loess above the paleosol as material remobilized by Late Holocene landslides, with the gravel as having been incorporated during landsliding.…”

“…In addition, the region's oldest archaeological site (d'Alpoim Guedes et al, 2015) is in Jiuzhaigou loess deposits on hillslopes subject to landsliding and co-seismic faulting. Previous investigations of loess in Jiuzhaigou (Wen et al, 2014(Wen et al, , 2017 left unanswered questions about the depositional history and provenance of the loess and also the role of hillslope processes and seismic activity in modifying the loess and hillslope topography. Thus, in addition to enhancing understanding of Holocene climate and loess provenance in western China, analysis of the Jiuzhaigou loess record can also provide insight into causal connections between climate, loess deposition, hillslope deformation by landslides and co-seismic faulting, and human inhabitance.…”

“…However, the widespread landslide hazards reported in loess regions (Dijkstra et al, 1994;Derbyshire, 2001;Wen et al, 2005;Zhang and Wang, 2007;Schmidt et al, 2017) also compromise safety (Schmidt et al, 2017). Conversely, human inhabitance can modify the loess record; for example, farming can inflate the rate of loess deposition (Roberts et al, Wen et al [2014]) and previous studies on loess grain size in the region (Lei, 1998;Wang et al, 2003;Sheng, 2010;Yang et al, 2010a;Stauch et al, 2012;Lehmkuhl et al, 2014); size of point indicates reported mean grain size. Background elevation is from World Wildlife Fund (2008).…”