利用Matlab函数识别沉积物中的米兰柯维奇旋回信号

针对旋回分析中需要对数据进行的各种处理,利用Matlab中集成的滤波（filter）函数、插值（interp1）函数、求均值（mean）函数、去线性趋势（detrend）函数、求方差（variance）函数及谱分析（pwelch）函数等的组合,编制了识别沉积物中米兰柯维奇旋回信号的程序。选择窗口宽度(window)约等于有用信号中最低频率信号的波长、交叠点数(noverlap)为窗口宽度的50％、傅里叶变换的数据点数(nfft)大于全部采样数据的长度且为2的最小整数次幂时,可获得较好的谱估计结果。其不足之处是不能估计背景的红噪声谱及给出谱峰值的置信水平。     

泥盆系弗拉阶／法门阶之交米兰柯维奇旋回及高分辨率地层对比

在广西泥盆系弗拉阶－法门阶（F－F）之交盆地相－斜坡相碳酸盐地层（桂林杨堤剖面，阳朔龙门剖面，德保都安剖面和横县六景剖面）中识别出超层序组、层序组、层序和纹层4级旋回层，它们在牙形石带内的级序结构、数量关系和排列顺序在时间上持续、稳定，在空间上可进行跨相、跨盆地的远距离对比。我们的资料表明，超层序组、层序组、层序和纹层旋回分别相当于长偏心率、偏心率、斜度或岁差和亚米兰柯维奇旋回。泥盆纪时它们的周期值分别为400，000年100，000年、33，333年或16，667年和8，000－17，000年。长偏心率与偏心率、偏心率与斜度、偏心率与岁差的比例关系分别为1：4、1：3和1：6。与第四纪相比，泥盆纪时斜度和岁差周期变短，偏心率周期基本保持恒定，表明地球自转至少自泥盆纪以来变慢。在研究剖面上，F－F事件前后超层序组与层序组间的级序结构存在明显的差别，即F－F事件前为1：4，F－F事件后为1：3。造成这种变化的原因可能与F－F事件期间多次陨击事件对地球长偏心率周期的影响有关。利用米兰柯维奇旋回的研究结果可使弗拉阶－法门阶之交年代地层的划分对比达到十万年级和万年级的分辨率，并可对上泥盆统国际通用的标准牙形石带进行数字标定，即上rhenana带、linguiformis带、下、中、上triangularis带的时间延续分别为0．6Ma、0．8Ma、0．3Ma、0．3Ma和0．3Ma。在十万年级和万年级分辨率基础上弗拉期－法门期之交的海平面变化不具一致性和同步性。     

米兰柯维奇韵律层及其年代地层意义

本文简要介绍了米兰柯维奇轨道三要素（岁差、黄赤交角及偏心率）及其变化周期，并对因轨道要素的变化引起的韵律沉积层的研究现状进行了综述，由于气候变化的全球性以及轨道参数的相对稳定性，本文认为，米兰柯维奇韵律层可以作为盆际，盆内地层对比的重要辅助手段，并可用来测定地层单元的延续时间，实际应用结果表明，其精度要高于现行的生物地层学对比及同位素测龄法。     

碳酸盐旋回地层研究现状

地层纪录中的韵律性很早就引起了人们的关注,本世纪60年代此项研究曾形成了一个小的热潮(Merriam,1964)[1],但直到70年代随着DSDP计划的实施,通过大量深海沉积纪录与米兰柯维奇气候韵律的对比,才使得旋回(或韵律)的轨道控制论得到证实(Hays et al.,1976[2];Imbrie,1985[3];Berger,1984[4]),并被普遍接受。80年代中后期,随着全球沉积计划(GSGP),特别是CRER项目的酝酿和实施,为这种高频沉积旋回的研究注入了新的催化剂,并正式提出了\"旋回地层\"(cyclostratigraphy)的概念(Fischer et al.,1988,1990)[5,6],其着重点就是研究10-400Ka范围内的旋回沉积,包括沉积旋回的形成机制,旋回在地层对比和地层定年、古海洋重建、占气候系统演变和盆地分析中的意义和作用,是当代沉积学和地层学极富挑战性、涉及范围广泛的前沿课题。     

旋回年代学及其应用意义—华北地台寒武世碳酸盐岩鲕滩高频旋回的年代学研究

华北地台中寒武世鲕滩碳酸盐岩沉积序列中发育大量分属4－7级的高频层序，依据旋回平均厚度的频率分布、不同级别旋回叠加样式和比率、沉积发育样式和跨越整个地台的可对比等特征认为，它们受控于地球轨道参数变动，是典型的米兰柯维奇旋回，其中Ⅳ、Ⅵ级分别对应于长、短偏心率旋回，时限分别为0．4Ma和0．1Ma。应用轨道旋回规则的周期间隔给出了中寒武世各级层序、地层阶和相应界面的年龄值。     

利用采样定理与沉积速率确定旋回分析最佳采样间隔

旋回地层学方法近年来被成功应用于年代确定及重大地质事件天文影响因素的判别.采样是旋回分析中最重要的一步, 目前大多使用地球物理、地球化学替代性指标, 采样频率过高, 会大大增加测量和计算的工作量, 同时也会增加随机干扰或其他非气候因素的干扰; 采样频率过低, 可能识别不出其中所包含的米兰柯维奇旋回成分.为确定一个最佳的采样间隔, 通过对80~100 Ma理论日照量曲线及两个实测剖面3种采样间隔(密集采样间隔与约等于一个岁差周期沉积厚度四分之一和一半的采样间隔)数据分别进行谱估计并比较谱估计结果.发现在满足采样定理的前提下, 以一个岁差周期沉积厚度的约一半作为采样间隔, 既可以分析出全部的米兰柯维奇旋回信号, 又具有最少的工作量, 是旋回分析的最佳采样间隔.实际采样中需根据平均沉积速率来确定这个最佳采样间隔.      

恭城地区法门期地层高频旋回的划分及特征

文章以恭城县西岭乡挖掘沟村晚泥盆世法门期地层为例,应用层序地层学理论,进行高频旋回地层研究,将其详细地划分出五级旋回９４个,四级旋回３６个,初步总结了各种旋回地层的空间叠复关系,强调指出高频旋回地层出现的原因很可能与地球轨道变化周期有关。     

Devonian Frasnian-Famennian Transitional Milankovitch Cycles and High-Resolution Stratigraphic Correlation

Four hierarchical cyclothems, superbundlesets, bundlesets, bundles and laminae, have been identified from the Devonian Frasnian-Famennian carbonate strata in Guangxi, South China. Their hierarchical structures, ratio relationships and sequence in conodont zones are continuous and stable and can be traced across different facies zones and sedimentary basins. Our data show that hierarchically organized superbundlesets, bundlesets, bundles and laminae correspond to the long eccentricity, eccentricity, obliquity or precession and sub-Milankovitch cycles respectively. Their periods were 400,000, 100,000, 33,333, 16,667 and 8,000-17,000 a, respectively. The ratios of long eccentricity to eccentricity, eccentricity to obliquity, and eccentricity to precession in the Devonian are 1:4, 1:3 and 1:6 respectively. Using these hierarchical Milankovitch cyclothems, chronostratigraphical division and correlation can be realized at a resolution of 100 ka or 10 ka at the Frasnian-Famennian transition. The time intervals     

认识偏心率周期的地层古气候意义

介绍了偏心率周期在地层和古气候研究方面的新发展.现有地球轨道模式对250Ma以来的轨道运算误差能控制在0.2%之内, 使基于偏心率周期来划分地层年代成为可能.新的国际标准地层年代表以405ka长偏心率周期为基础来划分主要地层界线.新生代将包括E1-E162偏心率长周期, 底界年龄(65.5±0.3) Ma.这一地层年代表的建立, 标志着轨道地层学时代的到来.偏心率的100ka短周期和405ka长周期在诸多地质记录中都有反映, 特别是来自深海钻孔的物理化学古气候指标.很多古气候重大事件往往发生在偏心率周期的弱振幅时期, 表明弱振幅时期易受其他因素的干扰影响, 这些因素包括碳储库、冰盖和海平面变化、电磁场, 以及区域构造重组等等.越来越多的研究发现碳同位素在偏心率周期上与地球轨道驱动相关, 且常领先于氧同位素的变化, 表明热带碳循环过程是影响全球气候变化的关键因素之一.      

Recognition of Milankovitch Cycles in the Natural Gamma—Ray Logging of Upper Cretaceous Terrestrial Strata in the Songliao Basin

Spectrogram analysis of seven natural gamma-ray logging of Member 1 of the Qingshankou Formation (K2qn1) and Member 1 and 2 of the Nenjiang Formation (K2n1-2) of Late Cretaceous age in the Songliao Basin reveals sedimentary cyclicities controlled by Milankovitch climate periodicities. The recognition of Milankovitch cycles allows estimation of an average accumulation rate of ~7.55–8.62 cm/ka for the K2qn1 sections, and ~6.69–10.16 cm/ka for the K2n1-2 sections. Two marine transgression events occurred during the deposition of K2qn1 and K2n1-2 and their ages are at ~0.74–1.10 Ma and ~2.38–4.84 Ma, respectively. Identification of Milankovitch cycles from fine-grained deep lake sedimentary rocks in the Songliao Basin may provide great potential for high-resolution stratigraphic subdivisions and correlations.     

High-frequency cyclicity (Milankovitch and millennial-scale) in slope-apron carbonates: Zechstein (Upper Permian), North-east England

The Upper Permian (Zechstein) slope carbonates in the Roker Formation (Zechstein 2nd‐cycle Carbonate) in North‐east England consist of turbidites interbedded with laminated lime‐mudstone. Studies of turbidite bed thickness and relative proportion of turbidites (percentage turbidites in 20 cm of section) reveal well‐developed cyclicities consisting of thinning‐upward and thickening‐upward packages of turbidite beds. These packages are on four scales, from less than a metre, up to 50 m in thickness. Assuming that the laminae of the hemipelagic background sediment are annual allows the durations of the cycles to be estimated. In addition, counting the number and thickness of turbidite beds in 20 cm of laminated lime‐mudstone, which is approximately equivalent to 1000 years (each lamina is 200 μm), gives the frequencies of the turbidite beds, the average thicknesses and the overall sedimentation rates through the succession for 1000 year time‐slots. Figures obtained are comparable with modern rates of deposition on carbonate slopes. The cyclicity present in the Roker Formation can be shown to include: Milankovitch‐band ca 100 kyr short‐eccentricity, ca 20 kyr precession and ca 10 kyr semi‐precession cycles and sub‐Milankovitch millennial‐scale cycles (0·7 to 4·3 kyr). Eccentricity and precession‐scale cycles are related to ‘highstand‐shedding’ and relative sea‐level change caused by Milankovitch‐band orbital forcing controlling carbonate productivity. The millennial‐scale cycles, which are quasi‐periodic, probably are produced by environmental changes controlled by solar forcing, i.e. variations in solar irradiance, or volcanic activity. Most probable here are fluctuations in carbonate productivity related to aridity–humidity and/or temperature changes. Precession and millennial‐scale cycles are defined most strongly in early transgressive and highstand parts of the larger‐scale short‐eccentricity cycles. The duration of the Roker Formation as a whole can be estimated from the thickness of the laminated lithotype as ca 0·3 Myr.     

Quaternary Fourier stratigraphy: Orbital templates and Milankovitch anomalies

A simple template-generating algorithm using summer insolation at 65°N as input provides a timeseries for the last 2 million years that can be compared directly with the oxygen isotope record in deep-sea sediments. Discrepancies between template and record are diminished by representing both series as Fourier expansions, and importing the power spectrum of the record to the template, without changing phase. The remaining differences between the hybrid template and the record contain messages about time spans of unusual behavior of the system. The most striking anomalies in the Quaternary are the unusually cold period following the mid-Pleistocene climate shift at 900 ka (Stage 22) and much of Stage 11 near 400 ka, representing excess warming. The present interglacial also is too warm, compared with expectations. Anomalies are thought to be the result of stabilization of unusually cold periods (by albedo feedback) and unusually warm periods (by carbon dioxide feedback). It is proposed that there is a connection between surplus ice buildup (after the mid-Pleistocene climate shifi at 900 ka) on marine shelves and subsequent extra-large transgressions, which stabilize warm periods by shallow-water carbonate production (coral reef hypothesis).     

塔里木盆地塔中-巴楚地区上奥陶统良里塔格组米兰科维奇旋回性沉积记录研究

通过露头、钻井岩芯沉积相观察及高频旋回识别,结合全岩碳氧同位素旋回、自然伽玛能谱测井ln(Th/K)值频谱分析及地震反射特征,研究了塔里木盆地塔中—巴楚地区分布的上奥陶统良里塔格组开阔台地及外缓坡相碳酸盐岩中发育的四～六级高频层序(旋回)特征及其叠置关系。认为其六级米级旋回、五级准层序及四级准层序组可能分别与20～40ka、100ka及400ka周期的Milankovitch日-地轨道气候旋回有关,并识别出该区良里塔格组由11～12个400ka周期的准层序组构成。提出海相碳酸盐岩全岩或生物壳碳同位素值可作为反映全球海平面相对变化的指标及识别形成三级层序的主控因素(全球海平面变化、地区性构造沉降-抬升运动)的方法——碳同位素-沉积旋回对比分析法。晚奥陶世良里塔格组沉积时期,塔中台地北缘总体表现为向上变浅的加积型沉积叠置型式,主要与塔中I号断裂活动控制形成的高陡型镶边台地边缘有关;巴楚台地西北缘则表现为向上变浅的加积-进积复合型沉积叠置型式,主要与其断裂活动弱、受沉积作用控制为主的缓坡台地边缘有关。塔中-巴楚台地良里塔格组表现为一个完整三级层序的形成与演化,主要受控于该台地的构造(沉降-抬升)运动而不是全球海平面变化,属于典型的地区性构造层序及不具有全球对比意义。     

频谱分析法在识别米兰科维奇旋回及高频层序中的应用——以塔里木盆地塔中－巴楚地区下奥陶统鹰山组为例

在巴楚地区露头高频层序研究及塔中地区钻测井三级层序划分的基础上,对塔里木盆地塔中地区塔中162井和塔中43井下奥陶统鹰山组层序OSQ2的自然伽马能谱测井ln（Th/K）曲线进行了滤波处理、快速傅里叶变换处理、小波时频分析以及调谐处理,识别出具有米兰科维奇旋回特征的高频旋回。结果表明：斜度（黄赤交角）旋回最为明显,周期为37.0 ka,是以向上变浅为主的六级米级旋回的主要控制因素,其主旋回平均厚度在台地边缘相带的塔中162井及塔中43井中分别为4.55 m及3.97 m,在巴楚地区半局限-开阔台地相带中为2～4 m;95 ka的短偏心率周期是形成五级准层序的主要控制因素,而大致代表四级准层序组形成时限的413 ka长偏心率周期在地层记录中表现并不明显。据高频层序叠置关系分析及平均主旋回个数初步估算,塔中-巴楚地区下奥陶统鹰山组层序OSQ2的形成时限大约为4.92 Ma,塔中43井鹰山组层序OSQ2受后期构造隆升而被剥蚀约192  m。结合四级层序（准层序组）发育时限（413 ka）及其叠置关系,以及与其调谐的小波变换曲线特征,初步将塔中-巴楚地区鹰山组层序OSQ2划分出12个准层序组。自然伽马能谱测井ln（Th/K）曲线包含沉积古水深相对变化的信息,是反映气候变化生成的米兰科维奇旋回层序的良好指标。