Text S9. Ca analysis
Variations in biogenic calcium (Ca) are a proxy of environmental change in coastal areas (e.g. Delaine et al., 2015). The relative intensity of a suite of 47 elements, including Ca, was determined (as counts per second, cps) in 40.3 m sediment samples at 0.01m interval using XRF core scanner (GEOTEK, MSCL-S). The abundance of Ca, expressed as the ratio of Ca intensity divided by the intensity of all 47 elements, is reported as percent (%). The results of Ca abundance from KhqS, KHQ-14 and Xiasun-1603 are showed in Figs. 2c, 3 and Fig. S5, respectively.
The low level of Ca content is the most prominent feature of the basal unit U1. Ca content increases in the upper parts of U2 at KHQ-14 and KhqS, although it is still low in their lower parts, as does the Ca content at XS-1603. Up to U3, as occupation layer appeared at KhqS and XS-1603, the Ca content is generally slightly higher than that of adjacent parts of U2. The uppermost U4, is represented at all three sites and has relatively high but varying Ca content. At KHQ-14, intercalations of relatively dark, organic-rich horizons contained in U4, which are not evident at the other two sample sites, have significant lower Ca content comparing to the stacks developing parallel-bedding. In the upper part of the sequence at KhqS, the lower Ca content is caused by the absence of samples due to soil crack caused by well developing rythmites and oxidation over the more than 15 years since the profile was first exposed. In sum, the higher Ca content arise together with foraminifera and marine/brackish diatom in upper U2 and U4 in both KHQ-14 and KhqS, while the low Ca content corresponds to the segment, lower part of U2 and intermission of U4, dominating by freshwater diatom and absence of foraminifera. The high/low value of Ca content is quite consistent with the appearance/absence of foraminifera and marine-brackish/freshwater diatom, and therefore can be used to reflect hydrologic conditions.