丘状和似丘状交错层理成因机制研究进展  

Advances in genetic mechanism research on hummocky and hummocky-like cross-stratifications

作　　者：李向东[1] Li Xiang-Dong(School of Land Resource Engineering,Kunming University of Science and Technology,Kunming 650093,China)

机构地区：[1]昆明理工大学国土资源工程学院,云南昆明650093

出　　处：《古地理学报》2020年第6期1065-1080,共16页Journal of Palaeogeography：Chinese Edition

基　　金：国家自然科学基金项目(编号:41272119)资助。

摘　　要：丘状交错层理多和风暴沉积相关,似丘状交错层理多和浊流沉积相关,随着研究的深入,早已打破了丘状(似丘状)交错层理分别只存在于浅水(深水)沉积环境中的界线,故近年来丘状(似丘状)交错层理在作为沉积环境判别标志方面出现了很大的争议和混淆,究其原因则在于对丘状交错层理和似丘状交错层理的成因机制缺乏明确的认识。在详细总结丘状(似丘状)交错层理的结构、形态特征和垂向序列的基础上发现:(1)丘状交错层理底界常为剥蚀面,内部削切关系发育且与洼状交错层理关系密切;垂向序列常出现层段缺失和丘状交错层理叠置。(2)似丘状交错层理纹层厚度变化多样;丘状层可镶嵌于平行层理或小型交错层理之中,且为连续沉积;垂向序列往往出现高流态沉积构造与低流态沉积构造交替叠置。依据这些特征并结合水槽实验的相关研究成果,从流体力学角度可将丘状(似丘状)交错层理的形成机制分为水动力机制和沉积机制两部分。两者的水动力机制完全相同,即为立轴漩涡形成,在自然界中一般为斜压波动引起。两者的沉积机制完全不同:丘状交错层理为剥蚀悬砂沉积机制,而似丘状交错层理则为悬砂降落沉积机制。由于2种沉积机制所形成的沉积物悬浮浓度及其对沉积流体能量的要求不同,故形成丘状和似丘状交错层理各自不同的沉积特征。这对于从流体演化方面判断沉积环境具有非常重要的意义。Hummocky and hummocky-like cross-stratification(HCS and HCS-like)as the identification criteria for sedimentary environments have recently become confused because of the little knowledge on their genetic mechanism based on the following facts:HCS and HCS-like are often associated with storm deposits and turbidity current deposits,respectively;the views on HCS produced in shallow water environments and HCS-like produced in deep-water environments have been abandoned recently.According to the detail reviews on structural and morphologic characteristics and vertical sequence of HCS and HCS-like from literatures,here we found that:(1)the special features of HCS include the sharp or erosional basal contact,the internal truncation surface,close relationship with swaley cross-stratification,and the missing zone or amalgamation of HCS in vertical sequence;(2)the special features of HCS-like often include various thickness of individual lamina,hummocky layer interbedded with parallel bedding or small-scale cross-bedding under continuous deposition,and alternating sedimentary structures of upper and lower flow regime in vertical sequence.According to hydrodynamic theory and flume experiment achievements,these results show that the genetic mechanism of HCS and HCS-like could be divided into two parts,hydrodynamic mechanism and depositional mechanism.The hydrodynamic mechanism of HCS and HCS-like is same and could be interpreted by vertical vortex generated by baroclinic wave in nature.However,depositional mechanism of HCS and HCS-like is very different:HCS and HCS-like could be interpreted by erosion suspending sand mechanism and suspending sand settling mechanism,respectively,and the special features in HCS and HCS-like are due to the different sediment suspension concentration and depositional flow energy.The division for hydrodynamic and depositional mechanism of HCS and HCS-like is very significant in determining sedimentary environments from depositional flow evolution perspective.

关 键 词：丘状交错层理 似丘状交错层理 沉积机制 沉积环境 

分 类 号：P512.2[天文地球—地质学]