摘要
深水环境下等深流沉积研究已经开展50多年,在这50多年里虽然取得了一些成果,但对等深岩的形成机理和沉积环境研究较少。通过野外剖面实测、详细描述和碳氧同位素特征分析,对研究区形成等深岩的环流的特征及不同类型等深岩的形成环境进行了探索。根据其岩性特征,研究区下奥陶统盘家咀组发育有灰泥等深岩、粉屑等深岩、砂屑等深岩、砾屑等深岩和生物屑等深岩5种等深岩相,在垂向上主要发育由单一灰泥等深岩叠置组成的层序、灰泥等深岩与生物屑等深岩组成的层序和灰泥等深岩与砂屑等深岩组成的层序3种不完整等深岩层序和少量的完整等深岩层序。为了研究该等深流沉积形成时的古环境,分别对研究区不同类型等深岩与原地沉积进行系统采样做碳、氧同位素分析。研究表明,工区下奥陶统盘家咀组等深岩的碳同位素δ13C值分布于0.18‰~2.31‰,氧同位素δ18O值的范围为-10.93‰^-9.54‰,盐度指数Z值介于122.91~127.14,温度T值为16.98~24.81℃。与原地沉积相比,研究区等深岩的δ13C值、Z值、T值均较高,且随着等深岩的粒度增大,其δ13C值、Z值、T值均逐渐增高。这表明等深流沉积环境与原地沉积完全不同,等深岩主要形成于高盐度的较深水环境中,且盐度、水温越高,越有助于高能等深流沉积物砂屑等深岩和生物屑等深岩的形成。等深岩层序的形成周期均表现为古盐度、古水温、海平面先增大后减小的周期性变化。
The literature on deep-water contourites is extensive after more than 50 years of research.However, many unknowns exist in terms of their forming mechanism and sedimentary settings.The article explores the characteristics of circulation and environment for forming various contourites in the Panjiazui Formation of the Lower Ordovician in the study area based on field measured section,detailed description and analyses of carbon and oxygen isotope characteris-tics.Lithologic analyses show that the formation contains 5 kinds of contourite lithofacies：calearenitie,calcilutite,caleilu-titie,gravel and bioclastic contourities.Vertically,three types of incomplete vertical contourite sequences and some com-plete contourite sequences are recognized.The incomplete sequences include superimposed single calearenitie contourite sequence,interbedding calearenitie contourites and bioclastics contourite sequenceand interbedding calearenitie contou-rites and caleilutitie contourites sequencece.Systematically sampling and carbon/oxygen isotope analyses of the various contourites and autochthonous deposits indicate δ^13 C values varying between 0.18‰and 2.31‰,δ^18 O values changing from -10.93‰to -9.54‰,salinity index Z shifting from 122.91 to 127.14,and temperature（T） ranging between＆amp;nbsp;16.98 and 24.81 ℃.Compared with the autochthonous deposits,the contourites in the formation have higher values of δ^13 C,Z and T.With the grain size of the rock getting bigger,these values continue to increase,showing that the sedimen-tary environment of contourites is totally different from that of the autochthonous deposits.The contourites were mainly formed in relative deep water environment with high salinity,and higher salinity and temperature were more favorable for the formation of certain high-energy contourites, such as caleilutitie and bioclastic contourities.The forming periods of contourite are all characterized by the periodical changes of first increasing and then decreasing palaeo-salinity,palaeo-temperature,and sea level.
出处
《石油与天然气地质》
EI
CAS
CSCD
北大核心
2015年第5期745-755,共11页
Oil & Gas Geology
基金
国家自然科学基金项目(41172105)
关键词
碳、氧同位素
等深岩
盘家咀组
下奥陶统
中扬子台地
carbon/oxygen isotope
contourite
Panjiaju Formation
Lower Ordovician
Mid-Yangtze platform
