Bedding structure

There are many kinds of sedimentary structure in the sedimentary rocks, of which the most macro structure is bedding structure. It is one of the most important features of the sediments, which usually reflects in the change of sediment composition, color, grain and size in the direction perpendicular to the surface of sediments (i.e., bedding plane). Bedding structure is the main basis of the analysis of sedimentary environment and paleo-geographic restoration. 

Tabular cross-bedding 

It develops in the sandy or conglomerate layer of Yardang body in the Yardang scenic spot. Tabular cross-bedding (Figure 4-17) is composed of a series of internal oblique laminated group interface, which is roughly parallel to each other. The lamina is 2 to 10 mm thick, inclining to the same direction. The inclination of lamina represents the direction of flow. In the direction parallel to the flow direction, its prograding lamina intersects with the interface while it parallel to the interface in the direction perpendicular to the flow direction, which reflects the strong medium energy sedimentary environment. In the Pleistocene era, the climate was humid and rainy and there is abundant water. In the lacustrine and fluvial sediments, tabular cross-bedding due to the water flow can be found.

Figure 4-17 tabular cross-bedding

Trough cross-bedding 

It develops in the sandy or conglomerate layer of Yardang body in the Yardang scenic spot. The interface is like trough, which cuts or intersects with each other. The lamina, thicker than 5mm, intersects with the total interface. Parallel to the direction of flow, the lamina is slower arc and the inclination is consistent. However, perpendicular to the flow direction, the lamina is like trough, the long axis direction of which is the same as the flow direction. Trough cross-bedding reflects the energy dynamic environment.

Figure 4-18 trough cross-bedding

Wedge cross-bedding 

It develops in the sandy layer of Yardang body in the Yardang scenic spot. The lamina of the wedge cross-bedding (Figure 4-19) are almost perpendicular to each other, displaying like the wedge. The lamina can intersect with the laminated total interface at different angles. In the direction of flow, the lamina intersects with the laminated interface group. It is almost parallel or oblique to the profile perpendicular to the flow direction, which reflects the sedimentary environment of strong medium energy. 

Figure 4-19 wedge cross-bedding

Parallel bedding

It develops in the coarse sand and conglomerate layer of Yardang body in the Yardang scenic spot, which is formed in the strong hydrodynamic conditions with its lamina parallel to each other. It corresponds to stronger water carrying capacity than that corresponds to large cross-bedding. It is usually formed in the flat bed with high flow condition and of symbiosis with large cross-bedding, which belongs to the product of typical jet sedimentary environment such as river and flood (Figure 4-20).

Figure 4-20 parallel bedding

Wavy bedding 

It develops in the silty sediments of Yardang body in the Yardang scenic spot. When fine grain sediment deposits, the wavy sediment layer formed due to the fluctuation of water is called wavy bedding. It is a sign of weak turbulence in the aquatic environment, which often occurs in the flood land, shallow lakes and former delta.