长周期层序形成机制的探索_层序地层学进展之二

第12卷 第6期2010年 12月古地理学报J OURNA L O F PALAEOGEOGRA P HYVol 12 N o 6D ec .2010文章编号:1671-1505(2010)06-0711-18长周期层序形成机制的探索:层序地层学进展之二*梅冥相中国地质大学(北京)地质过程与矿产资源国家重点实验室,北京100083摘 要 将不整合面所限定的地层单位定义为层序,赋予这种层序以 构造旋回 的概念;将 不整合面及其可以对比的整合面 所限定的地层单位定义为 沉积层序 ,简称为 层序 ,并将沉积层序的形成过程解释为海平面变化过程。

如果将前者作为 构造层序 ,则这种层序代表了二级层序,新定义的 沉积层序 则属于三级层序。

概念的调整和变化意味着层序存在一个级别或序次问题。

地质学家长期研究的结果表明,海平面变化主要存在两种基本的驱动机制,一种是由于构造运动所造成的 洋盆体积 的变化,另一种是气候变化所造成的地球极地冰盖消长而最终产生的海水体积的变化;前者所造成的变化以周期长、速度慢为特征,被简称为 构造型海平面变化 ,后者所产生的变化则以高频率和高速率为特征,被简称为 冰川型海平面变化 。

根据上述概念,显生宙可识别出两个一级旋回,并可以进一步划分为6个二级层序(S loss 模型)或13个二级层序(Vail 模型),显生宙二级层序划分的差别反映了长周期层序形成机制研究的一些重要变化和进展。

对长周期层序形成机制的研究,除了考虑地球本身的构造活动所造成的洋盆体积的变化以外,地质学家们还将一级旋回与银河年旋回对应、二级旋回与银道面旋回对应、三级旋回与奥尔特星系旋回对应起来进行更大范围的思考和探索,也为研究长周期层序形成的最终驱动机制提供了一个重要的思考途径。

如果把对Exx on 层序地层模式概念体系不协调的研究而产生的各种层序地层模式作为层序地层学的第1个进展,长周期层序形成机制的研究则可以作为层序地层学的第2个进展。

包括:(1)把来自于显生宙的一些重要模型和概念应用到前寒武纪,由此在更长的时间框架内探索一级旋回与超大陆旋回的成因联系;(2)二级旋回与地球水圈和大气圈演变的成因关联;(3)进一步总结三级旋回的形成机制。

追索这方面的进展,可以更加深入地理解当年Exxon 科学家们将层序形成机制归因于海平面变化的初衷以及所包含的科学意义,从而有利于今后的深入研究。

关键词 层序级别 形成机制 层序地层学进展作者简介 梅冥相,男,1965年生,教授,博士生导师,从事沉积学和地层学研究工作;E m ail :m ei m i ngxiang @263 net 。

中图分类号:P534 文献标识码:A*国家自然科学基金项目(编号:40472065)和中国石油化工股份有限公司海相前瞻性项目(编号:C0800-07-ZS-164)联合资助收稿日期:2010-06-23 改回日期:2010-08-20Research on for m i ng m echanis m of long ter m sequences :The second advance in seque nce stratigraphyM e iM ingx iangS t ate K ey Laboratory of G eological P rocesses and M ineral Resources ,Chi na Universit y of G eosciences (B eij i ng ),Beijing 100083Abstract S trati g raphic un its t h at are only bounded by unconfor m ities are defi n ed as sequences ,w hich are endo w ed w ith the m eaning of tectonic cyc les .Those strati g raphic successi o ns bounded by un古 地 理 学 报 2010年12月confor m ities and the correlati v e con for m ities are a lso defi n ed as sequences t h at belong to depositional se quences i n sequence strati g raphy,and these sequences are interred as the pr oducts o f globa l sea leve l changes.If t h e f o r m er can be ca lled as tecton ic sequences,they are act u ally t h e second order sequences;f u rther,t h e latter belongs to the th ird order sequences.Thus,change and m od ification on the concept of sequences represent a proble m of sequence h i e rarchy.There are t w o f u nda m ental dri v en m echan i s m s for sea leve l changes,the firstm echan is m re fers to the change resulted fro m the vo lu m e change of the oceanic basi n that is caused by tecton ic acti o n,wh ich is m ar ked by long period and sl o w chang ing rate and is grouped into tecton i c eustasy;and the second refers to the g lacial eustasy resulted fro m the vo l u m e change of sea w ater caused by the i n creasi n g and decreasi n g of icecap in polar reg i o ns o f the earth due to palaeo cli m ate change,wh ich ism arked by short per i o d and rapid chang i n g rate and is g r ouped into glacia l eusta sy.The t w o funda m enta lm echan is m s beco m e a co mm on cogn ition through long ter m researches by geolo g i s ts.On the basis o f the above concepts,t w o first order cyc les can be d iscer ned in the Phaner ozo ic and can f u rther be subdivided into6second order sequences(t h e S loss s m odel)or13second order se quences(the V ail s m odel),and t h e difference on the div isi o n o f second o r der sequences i n t h e Phanero zoic de m onstrates so m e changes and progresses on stud ies of for m ing m echan is m s o f l o ng ter m sequences.I n additi o n to the study of vo l u m e change of ocean ic basi n caused by tecton ic action that is thought as a m a i n m echan is m for long ter m sequence,m any geolog ists th i n k that there is a general relati o nship bet w een t h e for m ing period o f long ter m sequences and the ti m e duration period of different astroa l cyc les,such as t h e relati o nship bet w een galactic year and the first o r der cyc le,the second order cycle t h at is generally re lated to ga lactic p lane cycle and response o f the th ir d cycle to the Oort cycle,a ll ofw hich prov ide an i m portant thi n king appr oach for f u rther research.I m po rtantly,if studies on i n consistence of conceptua l sys te m o f the Exxon m odel of sequence stratigraphy t h at result i n m any sequence stratigraphic m ode ls can be t h ought as the first advance in sequence strati g raphy,st u dies on for m i n g m echan is m s o f long ter m se quences can be though t as the second advance,wh ich contains the f o llo w i n gs:(1)t h e study on the gene t ic re lationsh i p bet w een the first order sequence and the superconti n enta l cyc l e thr ough usi n g o f the concept and m odel i n the Phanerozoic to the Preca m bri a n;(2)research on the for m i n g m echanis m of the second order sequence that is genetically related to the evo l u tionary feat u res o f hydrosphere and at m osphere;(3)f u rther su mm arizati o n for t h e for m i ng m echanis m o f the third order sequence.There f o re,traci n g these pr ogresses is very helpful to further understand th ei n itia l i n tension of the Exxon schoo l i n sequence stratig raphy,that is,the for m ing process of sequences can be attri b uted to sea level change,and is helpful for f u rther researches in t h e future.K ey w ords seque nce hier archies,for m ing m ec hanis m,advance i n sequence strati g raphyAbout the aut hor M ei M i n gx ia ng,bor n in1965,gr aduated fro m Chi n a University o f Geosciences (Beijing)i n1993w ith a Ph D degree.No w he i s a professor at School ofEarth Sciences and Resource,Chi na University of Geosciences(Beijing),and is engaged i n sedm i e nto l o gy and strati g raphy.1 概述符合Steno叠覆律(La w of Superposition)的成层岩石所组成的地层记录(H edberg,1959;Salva dor,1994;NACSN,2005;张守信,2006),多年来对其研究的积累表明其具有4大特性:复杂性、不完整性、非渐变性和旋回性(梅冥相,1996;梅冥相和高金汉,2005),旋回性的研究是从复杂而不完整的地层记录中寻找出更多规律性的有效途径之一。