Description

The facies association IV is characterized by more internal structures containing Sr, Fl, Si, Fr, and C (Figure 7A). Fine-grained sediments and coal are developed extensively, while sandy sediments range in thickness between 0.5 and 2 m. It is quite common to see tidal bedding such as flaser bedding, wavy bedding and lenticular bedding (Figure 7G,I–K), as well as various bioturbation structures (Figure 7F,H). The coaly fragments and plant pieces, predominantly sub-rounded to rounded, are common in the sandstone. The size of these clasts are in range from small pebbles to large cobbles (4~256 mm), occasionally boulders (Figure 7C). The most common occurrence of ORC is loaded as the wavy discontinuous lamination (Figure 7B–D).

**Figure 7.** Sedimentary characteristics of the organic-rich clasts in the sand flat (log SM-5). (**A**) Schematic sedimentary succession with gamma-ray response of the sand flat, showing the occurrence of ORC. (**B**–**J**) Photos of typical lithofacies and ORC types in the sand flat, noting the sedimentary structures and bioturbation. (**K**) Location of logA in the schematic barrier coast sedimentary model.
