Interpretation

Thin wavy bedding sandstone of this facies association typifies the sand flat deposit in a tidal flat environment (Figure 7N). The thick coal seams and organic-rich mud shales (Figure 7L,M), which develop in marsh and lagoon, supply sufficient source for ORC. Two main mechanisms exist on the formation of ORC: basal erosion under the effect of tide and detachment due to synaeresis cracking (Figure 7I,M), while the transport of the broken ORC from the origin site is operated by the processes of tide currents. At the level of high tide, some large particles of ORC are trapped by sandy deposits; whereas most ORC would break up repeatedly under the action of tide currents. With the ebb of tide, the residual granule ORC would load and form into wavy lamellar aggregates. The circular coaly ORC, having a grain size of >10 cm in Figure 7C, should be a cross-section of the plant stem, which probably formed directly after depositing in the sand.

#### *4.5. Facies Association V*
