Fig. 1

Maps showing the sampling locations and regional geology of the Yanchang Formation in the Ordos Basin， Wufeng-Longmaxi formations in northern Guizhou， Niutitang Formation of central Guizhou， and Shanxi Formation in the Southern North China Basin ［29，51］"

Fig. 2

Composition characteristics of the shale samples from the Yanchang Formation in the Ordos Basin， Wufeng-Longmaxi formations in northern Guizhou， Niutitang Formation of central Guizhou， and Shanxi Formation in the Southern North China Basin"

Fig. 3

SEM images of organic-clay composites in the shale samples from the Yanchang Formation in the Ordos Basin， Wufeng-Longmaxi formations in northern Guizhou， Niutitang Formation of central Guizhou， and Shanxi Formation in the Southern North China Basin"

Fig. 4

Sketch diagrams showing the card-house and band-like architectures of the clay layers［54］"

Fig. 5

SEM images showing typical organic-clay composites selected for focus ion beam （FIB） slicing from the shale samples of the Yanchang Formation in the Ordos Basin， Wufeng-Longmaxi formations in northern Guizhou， Niutitang Formation of central Guizhou， and Shanxi Formation in the Southern North China Basin"

Fig. 6

Transmission electron microscopy （TEM） images of organic-clay composites in the shale samples from the Yanchang Formation in the Ordos Basin， Wufeng-Longmaxi formations in northern Guizhou， Niutitang Formation of central Guizhou， and Shanxi Formation in the Southern North China Basin"

Fig. 7

SEM images showing the deformation of organic-clay composites caused by stress in the shale samples from the Longmaxi Formation in northern Guizhou and Niutitang Formation in central Guizhou"

Fig. 8

TEM images showing the element mapping of the organic-clay composites in the shale samples from the Chang 7 Member in producing well 941# （at a depth of 716 m）， Ordos Basin"

Fig. 9

TEM images showing the element mapping of the organic-clay composites in the shale samples from layer ② （at a burial depth of 0.5 m） of the first member of the Longmaxi Formation in northern Guizhou"

Fig. 10

Occurrence of organic matter in the organic-clay composites in the shale samples from the Yanchang Formation in the Ordos Basin， Wufeng-Longmaxi formations in northern Guizhou， Niutitang Formation of central Guizhou， and Shanxi Formation in the Southern North China Basin"

Fig. 11

SEM images showing the differences of pore development in organic particles and organic-clay composites in the shale samples from the Niutitang Formation in well ZK 105 （at a burial depth of 701 m）"

Fig. 12

The pore development characteristics of organic-clay composites under different stress for the shale samples from the Longmaxi Formation in northern Guizhou， and Niutitang Formation in central Guizhou"