Siltstone is a clastic sedimentary rock consisting of grains with sizes of 0.0039–0.0625 mm. It contains at least 50% silt, and its clastic composition is relatively simple: mainly quartz and small amounts of feldspar, mica, chlorite and clay minerals but little detritus. Based on the particle size, siltstone can be divided into coarse siltstone (0.0312–0.0625 mm) and fine siltstone (0.0039–0.0312 mm). According to the clastic content, it can be divided into feldspar siltstone, quartz siltstone, detritus siltstone (very rare) and other transitional types. Based on the cementing material, sandstone can be divided into clayey, ferrous, calcareous and dolomitic siltstones. Based on the composition, it can be categorized as argillaceous siltstone, ferrous siltstone and calcareous siltstone. The grains in siltstone are usually angular. Siltstone forms under weak hydrodynamic conditions, and it often contains thin horizontal bedding with thin sand beds and convoluted bedding.