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.