COMMENT TO LEHRMANN ET AL. NEW SECTIONS AND OBSERVATIONS FROM THE NANPANJIANG BASIN, SOUTH CHINA

In the study of Earth-surface environmental processes during the events associated with the Permian–Triassic boundary, a key issue is the nature of the latest Permian pre-extinction surface in shallow marine limestones in numerous sites, principally within the Tethyan realm. Sediments below this surface pre-date the extinction event, so that the limestones comprising these latest Permian facies contain diverse fossil remains of organisms that lived just before the extinction. At all reported sites, this surface is disconformably overlain by post-extinction sediments, which contain microbialites in many places, particularly in Tethys. The nature of the youngest pre-extinction surface remains controversial, originating by either physical erosion or dissolution. Furthermore, if the surface was created by dissolution, this could reflect ocean acidification or, alternatively, subaerial dissolution. These arguments were discussed by Collin et al. (2009) and Kershaw et al. (2012a). In an attempt to solve the problem of the origin of the youngest pre-extinction surface, Lehrmann et al. (2015) provided a comprehensive treatment of the associated facies in the Nanpanjiang Basin in southern China, which although is of considerable value, contains some aspects we consider require further attention. Our comment primarily addresses their views regarding the environment of formation of calcium carbonate grain-coating cements in the boundary deposits. We also consider some other aspects of their paper, all presented under several subheadings on specific points listed below. Thus, in this comment, we aim to clarify some of their reported observations and interpretations of the boundary deposits. In preparing this comment, we reviewed thin sections used by Collin et al. (2009) and present further photographs showing the fabrics in better detail. Figure 1 shows outcrop views of a key site in the Great Bank of Guizhou (for location see Lehrmann et al. 2015, fig. 1). Figure 1C is a polished block showing …