"1. OSL dating sample collection and measurement When collecting OSL dating samples, try to avoid light as much as possible, use black cloth to block the sun, select fine silt sand and sandy soil on the section to sample, and then knock a stainless steel tube (50mm in diameter, 30 cm in length) horizontally into the sampling level, fill it up, take it out and seal it with black plastic tape. In a dark room, take out the sample and scrape off the surface layer by 2-5 mm, place it in a container to soak, stir, and wash. Then add 20% H2O2 to remove organic matter, add 10% HCl to remove calcium carbonate, and stir until there is no foam. Sieve and extract the coarse particle components (select 90-125 μm particle components) and place them in the drying oven. Remove 20-30g of dried sample, place it into a test tube protected from light, add 2.72 of heavy solution, shake and precipitate for 24-36 hours. Remove the floating part separated from the heavy liquid, wash it, place it into a light-protected container, dry it, add 40% FH solution, shake and dissolve for 40-45 minutes, and wash it. Add 1M HCl solution to remove fluoride, wash it with distilled water, dry it, and then use a magnet to absorb heavy minerals to obtain purer quartz mineral particles. Use silicone oil to stick it on a stainless steel disk with a diameter of about 1mm to make a test sample. The OSL dating De value testing instrument is Risø TL/OSL-DA-15 reader made in Denmark. The dating material is potassium feldspar 90-150um. The environmental dose rate radioactive elements U, Th, and K are measured using the neutron activation method (NAA). When calculating the internal dose rate of potassium feldspar, the potassium content of 12.5±0.5%, and the estimated water content of the sample is 5%±3%. 2. Collection and testing of environmental proxy indicators Collect powder samples of about 100g at moderate intervals in the section (borehole) and record the number. The sample was dried at 45°C for 24 hours before magnetic susceptibility measurement to remove the effect of moisture on the magnetic susceptibility. Then 10g of the dried sample was taken to measure the low frequency on a Bartington MS2 type magnetic susceptibility meter (0.47kHz); Before sample chromaticity measurement, take 5g of the dried sample and grind it until the particles are uniform, and measure it on a CM700d spectrophotometer produced by Minolta Corporation of Japan. The instrument uses a Lab color system. The measurement spectral range is 400-700nm visible light, and the resolution is 10nm. TOC was determined by potassium dichromate spectrophotometry. Particle size analysis uses a Mastersizer 2000 laser particle size analyzer produced by Malvern Company in the United Kingdom, which requires pretreatment. Weigh a suitable amount of sample and add it to a beaker. First add 10ml of H2O2 solution with a concentration of 10% and heat it to remove organic matter, and then add 10ml of 1:3 to remove carbonate. After sufficient reaction, remove the beaker and fill it with distilled water and let it stand for about 12 hours. Then use a rubber tube to withdraw the supernatant from the beaker until about 20ml of solution remain. Finally, add 10ml of sodium hexametaphosphate with a concentration of 0.05 mol/L, place the beaker in an ultrasonic cleaner and shake for 5 minutes, and then disperse it can be tested on the machine. "

In the data set, Risø TL/OSL-DA-15 reader produced in Denmark is used for measuring the De value of OSL age. The dating material is potassium feldspar 90-150um. The contents of radioactive elements U, Th and K in environmental dose rate are measured by neutron activation method (NAA). When calculating the internal dose rate of potassium feldspar, the potassium element content of 12.5±0.5% is adopted, and the estimated water content of samples is 5%±3%. The chromaticity measurement uses the CM700d spectrophotometer produced by Minolta Corporation of Japan. The instrument uses a Lab color system and measures visible light in the spectral range of 400-700nm with a resolution of 10nm. Magnetic susceptibility is measured by Bartington magnetic susceptibility meter made in England according to GB/T 35690-2017 Method for measuring permeability of weak magnetic materials. TOC is determined by potassium dichromate spectrophotometry, refer to GB/T 32116-2015 Total organic carbon (TOC). Particle size analysis uses a Mastersizer 2000 laser particle size analyzer produced by Malvern Company in the United Kingdom. The instrument measurement range is 0.02-2000µm, with an error of less than 1%. This data is in accordance with the national standard of People's Republic of China, Particle Size Distribution Laser Diffraction Method GB/T 19077-2016/ISO13320:2009. The particle size analysis data are exported by Mastersizer 2000 supporting software, and the particle size parameters can be calculated according to the Folk-Ward formula (Ren Mingda and Wang Nailiang, 1981;Folk and Ward, 1957).