Abstract:

This paper investigates storm deposit characteristics in tidal flat environments of the Early Ordovician Yeli Formation in southern North China to elucidate their implications for palaeolatitude and palaeoclimate. Through comprehensive field sedimentological observations and carbonate microfacies analysis,five distinct microfacies were identified: intraclastic dolomite,quartz-bearing sandy dolomite,sandy dolomite,medium-crystalline dolomite,and fine-crystalline dolomite. These microfacies,combined with macroscopic sedimentary features,indicate an environmental transition from subtidal through intertidal to supratidal zones. Storm-generated sedimentary structures include scoured surfaces,storm gravel layers,graded bedding,massive bedding,hummocky cross-stratification,rip-up clasts,load and flame structures. Through systematic analysis of structure-environment relationships,six distinct storm deposition sequences were classified based on their formative hydrodynamics: subtidal vortex-dominated,subtidal combined vortex-wave,intertidal hybrid gravity flow-wave,intertidal debris flow,intertidal vortex-controlled,and supratidal tidal current sequences. The established depositional model demonstrates that storm flow dynamics primarily controlled the sequence architecture. The recorded increase in both storm frequency and intensity during the Early Ordovician corresponds to a climatic warming phase within the broader cooling trend. Regional synthesis indicates the eastern North China Block margin faced an open ocean at paleolatitudes of 15°~24°S. The research results not only deepen the understanding of the storm deposition sequence,but also provide key sedimentary data for the reconstruction of the Early Ordovician palaeoclimate and palaeogeography in southern North China.

Key words: southern North China, Lower Ordovician, storm deposits, tidal flat environment, palaeoclimate, palaeolatitude

摘要：

为了深入理解潮坪环境风暴沉积特征及其古纬度与古气候指示意义,本研究以华北南部下奥陶统冶里组风暴沉积层为研究对象,通过详尽的野外沉积学观察与室内碳酸盐岩微相分析,识别出砾屑白云岩、含石英砂屑白云岩、砂屑白云岩、中晶白云岩和细晶白云岩等5类碳酸盐岩微相,并结合宏观沉积特征,推测沉积环境经历了潮下带→潮间带→潮上带的演变过程。其中风暴沉积构造主要由侵蚀、破坏与沉积作用形成,包括风暴冲刷面、风暴砾屑层、粒序层理、块状层理、丘状交错层理、撕裂构造、负载和火焰状构造等。依据这些沉积构造组合与沉积环境的对应关系,按照风暴水动力类型,划分出6类风暴沉积序列: 潮下带风暴涡流沉积序列; 潮下带风暴涡流+风暴浪沉积序列; 潮间带风暴重力流+风暴浪沉积序列; 潮间带风暴碎屑流沉积序列; 潮间带风暴涡流沉积序列; 潮上带风暴潮流沉积序列。建立华北南部下奥陶统冶里组潮坪环境碳酸盐岩风暴沉积模式,并认为风暴沉积序列结构主要受控于风暴流作用方式。冶里组风暴沉积记录显示出早奥陶世风暴活动频率与强度的增加,是对气候变暖的响应,说明奥陶纪气候在总体变冷的初期存在波动。结合前人在华北板块报道的同期风暴沉积,推断华北板块东缘应面向广海,其古纬度位置为南纬15°~24°。研究成果不仅深化了对风暴沉积序列的认识,亦为华北南部早奥陶世古气候与古地理重建提供了关键的沉积学数据。

关键词: 华北南部, 下奥陶统, 风暴沉积, 潮坪环境, 古气候, 古纬度

CLC Number: 

• P534.42

• P588.2