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封面故事：扬子西缘昭通地区奥陶系上统临湘组底部发现的斑脱岩。斑脱岩是火山凝灰物质经沉积、蚀变作用形成的黏土岩, 它的空间分布特征能够客观反映地史时期火山活动的影响范围、规模和频率, 短时间形成和分布广泛的特性使得它成为地层等时对比和年代学研究的重要载体。扬子西缘临湘组底部斑脱岩的发现, 为临湘组及下伏宝塔组的 年代地层厘定、奥陶纪—志留纪之交火山活动时限和沉积环境演化提供重要的年代学参考。这项由中国地质调查局昆明 自然资源综合调查中心袁永盛高级工程师取得的研究成果, 详见本期733-749页。 (图片提供: 袁永盛)
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)
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