Cover Story
Bentonite discovered at the base of the Upper Ordovician Linxiang Formation in the Zhaotong area on the western margin of the Yangtze Block. As a claystone formed by the sedimentation and subsequent diagenetic alteration of volcanic tephra, the spatial distribution of bentonite pro-vides an objective constraint on the areal extent, magnitude, and frequency of volcanic activity throughout geological history. Formed instanta-neously and laterally, bentonite serves as a criti-cal material for isochronous stratigraphic correla-tion and geochronological research. The discov-ery of bentonite at the base of the Linxiang Formation in the Western Yangtze Block provides essential geochronological constraints to refine the chronostratigraphy of the Linxiang For-mation and its underlying Baota Formation, de-fine the timing of pre-Silurian volcanism across the Ordovician–Silurian transition, and recon-struct the evolution of depositional environments. The research achievement was led by Senior En-gineer YUAN Yongsheng, Kunming General Sur-vey of Natural Resources Center, China Geolog-ical Survey. For details, see pp. 733-749 of this issue. (Photo by YUAN Yongsheng)
