## 3 Results  
### Concentration of REEs  
The REE data and relevant parameters of the two profiles are listed in Table 2. The total REE (\(\Sigma\)REE) in the SC profile ranged from 313.47 to 608.95 ppm and the average value was 381.19 ppm. The \(\Sigma\)REE of SC bedrock was 12.65 ppm. The REE concentration was 30 times higher than in the bedrock. For the TG profile, \(\Sigma\)REE ranged from 281.15 to 776.56 ppm (average 386.26 ppm), which is closer to that of SC profile. The \(\Sigma\)REE of limestone in the TG profile was 29.237 ppm, which is significantly higher than in the dolomite stone in SC. The \(\Sigma\)REE in both SC and TG profiles showed fluctuating increases from top to bottom, as shown in Figure 2. For example, at the upper layer of SC profile (from 0 to \(-\)100 cm), the \(\Sigma\)REE was 313.47\(-\)356.24 ppm, whereas at the weathering front (-120 cm), the value was 608.95 ppm. For the TG profile, the \(\Sigma\)REE in the upper layer (from 0 to -180 cm) was 281.15-347.13 ppm, reaching 776.56 ppm at RSI. This suggests that the REEs gradually leached away above the RSI and accumulated at the RSI Table 2.  
The \(\Sigma\)LREE/\(\Sigma\)HIREE ratio is the fractionation indicator for light REE (LREE, from La to Eu) and heavy REE (HREE, from Gd to Lu and Y). The fractionation of \(\Sigma\)REE in the SC profile is slightly higher than in the TG profile. In the SC profile, the \(\Sigma\)LREE/\(\Sigma\)HIREE ratio ranges from 2.12 to 3.23 from topsoil to RSI (average: 2.94), showing a generally declining trend with the highest value at \(-\)100 cm (3.24), and the lowest (2.12) at \(-\)120 cm (RSI) (Figure 2). For the TG profile, the trend declined with the lowest value at the RSI (-210 cm) (Figure 2). This indicates that the leaching rate of LREE increased from top to bottom with the highest value at the RSI. The HREE gradually gathered from topsoil to bottom and peaked at the RSI. This result was confirmed at the subtropical weathering crusts covering on carbonate rocks by [PERSON] [30], [PERSON] [31], and [PERSON] et al. [32]. Geochemical parameters such as Ce and Eu of sedimentary rocks can be used to judge material source and sedimentary environment [21]. Normally, Ce \(>\) 0.78 is a positive anomaly, and Ce \(<\) 0.78 is a negative anomaly; Eu \(>\) 1 is a positive anomaly, and Eu \(<\) 1 is a negative anomaly [27]. Ce showed a positive anomaly at the top of the SC profile, with the \(\delta\)Ce value ranging from 1.19 to 1.30 (average: 1.22). Its negative anomalies were lower at the weathering front of RSI, where the \(\delta\)Ce value was 0.76. The TG profile shows that the highest positive anomaly (\(\delta\)Ce = 1.31) was at the surface soil, with the lowest negative anomaly was at the RSI (\(\delta\)Ce = 0.29). \(\delta\)Eu was a relatively stable negative anomaly. The \(\delta\)Eu values for SC were 0.68 (ranging from 0.64 to 0.71) and 0.67 in the soil and bedrock, respectively. For the TG profile, \(\delta\)Eu was 0.63, equal to the \(\delta\)Eu value for bedrock (Figure 3). Figure 2: Variation curve of \(\Sigma\)REE (the sum of REEs), \(\Sigma\)LREE (the sum of light REE from La to Eu), \(\Sigma\)HIREE (the sum of heavy REE from Gd to Lu and Y), and the ratios of \(\Sigma\)LREE/\(\Sigma\)HIREE with depth in SC and TG profiles. UL, RSI, DLM, and LMS denote upper layer, rock–soil interface, dolomite, and limestone, respectively. LREE and HREE denote the light REE and heavy REE as illustrated in Table 2.  
The specific elements ratios such as (La/Yb)N, (La/Sm)N, and (Gb/Yb)N, which can indicate the differentiation characteristics of LREE and HREE, are shown in Figure 4. The (La/Yb)N in SC profile is 4.10-8.47, with the average value of 6.87 (from 0 to \(-\)120 cm), which was lower than that of sandstone, granite, and gneiss (10.39, 7.65, and 8.17, respectively) as reported by [PERSON] et al. [33].