湘西北龙山地区下奥陶统桐梓组潮坪风暴岩的发现及其意义

报道了湘西北地区早奥陶世桐梓组地层中的风暴岩，并对该套事件沉积体的区域展布及表现形式进行了系统阐述。通过对野外剖面的仔细观测和室内资料的综合研究，普遍见指示潮坪环境的半球状叠层石、羽状交错层理等，并识别出各种侵蚀-撕裂构造、粒序层理、韵律层理、变形层理及沙纹-波状层理等风暴沉积标志，丘状交错层理常保存不全，综合分析后认为该风暴岩为潮坪风暴沉积，并进一步划分出4种类型的风暴沉积序列。同时，区内桐梓组见有大套滑塌重力流沉积，经对比，可能为同一飓风事件在不同环境中产生的不同物质记录。该套风暴岩具有重要的地质意义:风暴沉积特征的变化蕴含了丰富的气候变化信息，反映出晚寒武世至早奥陶世时期全球温室继承、转型的一种气候响应。风暴岩、风暴浊积岩及滑塌角砾岩的发现，为该时期“鄂西台洼”的存在提供了新的沉积学证据；也为区内含矿段地层的精细划分和对比提供实际参考；同时，对分析华南板块的向北漂移提供了更仔细、更可靠的参考数据。

Characteristics of Tempestite of Lower Ordovician Tongzi Formation,in the Longshan Area,Northwestern Hunan and Its Geological Significance

This is the first time to report storm deposit in the Tongzi Formation, Lower Ordovician in the northwest Hunan Province. Meanwhile, the author demonstrates the distribution and manifestation of the sedimentary deposits systematically. Based on careful field observation and laboratory analysis, indications of the tidal flat environment such as hemispheric stromatolites, Herringbone cross bedding are widely present in the succession. The sedimentary structures of the storm deposit such as erosion -tear structure, graded bedding, rhythmic bedding, deformed bedding and the sand grain-wave bedding have been identified, excluding hummocky cross-stratification. Based on the analysis, the storm deposit in this Formation is the tidal flat storm deposit. And, four types of storm deposits have been recognized. Meanwhile, big slump gravity flow deposits are identified in Tongzi Formation, which must be the different material records of the same hurricane in different environments. Study of the storm deposit indicates that the tempestites carry important poleoclimate inFormation and frequent occurrences of storms responded to climate changes from late Cambrian to lower Ordovician. The discovery of tempestite, the storm turbidite and slump breccias provide new lines of evidence for the Western Hubei platform depression in this period and suitable reference for fine stratigraphic division and correlation of ore-containing block Formation as well as more reliable reference data for the analysis of the north draft of the South China Plate.