The discovery and significance of a sedimentary hiatus within the Carboniferous Taiyuan Formation, northeastern Ordos Basin, China: Reply

The paper by Jiang et al. (2012) documented a hiatus and overlying incised-valley fill between the Lower Pennsylvanian Taiyuan Formation (Ct1) and the Upper Pennsylvanian Taiyuan Formation (Ct2). Herein, we provide credible evidence suggesting that the incised-valley fill mentioned by Jiang et al. (2012) is a barrier island. Our work also indicates that the contact between Ct1 and Ct2 is continuous and without hiatus. The Paleozoic Ordos Basin has two stages of sedimentary environments: the early Paleozoic marine carbonate deposition and the Late Paleozoic (Carboniferous to Permian) transformation from paralic to terrestrial. Most scholars believe that the Carboniferous Taiyuan Formation is a barrier–lagoon–tidal flat system (Zhao and Liu, 1990; Hao et al., 2007; Luo et al., 2011) that formed during the relatively large-scale transgression at the North China block. The predominant sedimentary environment of the Taiyuan Formation is the barrier shoreline and has been documented as a barrier island, lagoon, and swamp (Chen et al., 2001; Yang et al., 2005; Hao et al., 2007; Luo et al., 2011). In particular, Jiang et al. (2012) confirmed the facies of Ct1 as a barrier–tidal system and interpreted the interval of Ct2 as a northeast–southwest-trending incised-valley fill and further claimed a hiatus between the Ct1 and Ct2 units. Well D23 locates in the incised-valley fill, as mentioned in figure 14 of Jiang et al. (2012). Its core of the lower Ct2 (above the bottom coal of D23; Figure 1) suggests that it is tidal in origin based on the following sedimentary structures: lens (starved ripples), ripples, and flaser beddings; herringbone bedding; and tidal bundles (couplet) (Figure 1). The fining-upward succession with erosive-based structures of tidal origin is a tidal inlet (Figure 1C, H). The coarsening-upward succession with parallel …