dolomitization; porosity origin; overdolomitization; dissolution; Feixianguan formation
2. Geological setting
The Jiannan area Kartogenin geotectonically located in Shizhu synclinorium zone in the eastern Sichuan Basin, southwestern China (Fig. 1). The Sichuan Basin is a large intracratonic basin with 12 km thickness of sediments deposited from the Cryogenian on the metamorphic basement of the Yangtze Paraplatform which formed during the Jinning and Chengjiang orogenies (Fig. 2; Hao et al., 2008). Generally, the Sichuan Basin experienced early marine basin and later continental basin development stages divided by the Indosinian tectonic movements (Fig. 2; Xu et al., 2013). Marine sequences from Pre-cambrian to Middle Triassic are relatively well preserved, whereas the tectonic movement that occurred between the Early and Late Cretaceous during the continental basin development stage marked the intensive uplift and folding of the eastern Sichuan, resulting in no sediment deposition in the study area (Ma et al., 2008).