Table S1.
Detailed carbon and other information for dated phytoliths
| Lab ID | Sample code | Dry soil weight (g) | Extracted (mg) | Analyzed (mg) | Graphite (mg C) | Carbon yield rate (%) | Fraction modern ± 1σ |
| 434204 | SH-8-P | 130.974 | 241 | 219.1 | 0.34 | 0.15 | 0.3567 ± 0.0018 |
| 434203 | SH-5-P | 131.880 | 232 | 207.5 | 0.17 | 0.08 | 0.4040 ± 0.0020 |
| 438410 | HHS-5-P | 150.000 | 1,000 | 463.7 | 0.80 | 0.20 | 0.3648 ± 0.0014 |
| 438409 | HHS-3-P | 150.000 | 1,313 | 455.1 | 0.80 | 0.20 | 0.3676 ± 0.0018 |
| 434202 | HX-4-P | 107.608 | 267 | 239.1 | 0.17 | 0.07 | 0.4025 ± 0.0020 |
| 438411 | HX-5-P | 150.358 | 1,144 | 415.3 | 0.50 | 0.10 | 0.4091 ± 0.0020 |
| 434199 | HX-6-P | 110.907 | 485 | 417.9 | 0.34 | 0.08 | 0.3916 ± 0.0015 |
| 406654 | HX-7-P | 201.773 | 726 | 688.0 | 1.02 | 0.15 | 0.3844 ± 0.0014 |
| 434200 | HX-8-P | 132.451 | 932 | 416.9 | 0.34 | 0.08 | 0.3754 ± 0.0019 |