藏北雁石坪夏里组高频岩相旋回的驱动机制研究

Walsh频谱分析引用不连续的方波代替傅里叶频谱分析中连续的正弦波和余弦波,由于Walsh函数的不连续性,它广泛应用于地层旋回周期的检测。藏北雁石坪地区中侏罗统夏里组发育一套以砂岩、泥岩为主的高频岩相旋回,在地层颜色上也表现出较好的旋回性。对该组地层岩性和颜色进行Walsh频谱分析对比发现,岩性频谱曲线及颜色频谱曲线的主频周期与米兰科维奇旋回周期之间均具有极好的对应关系,认为海平面的周期性变化是夏里组高频岩相旋回的驱动机制。同时根据岩性旋回频谱和颜色旋回频谱计算得出夏里组的沉积速率约为0．111m／ka,沉积持续时间约为3．689Ma。     

米兰科维奇冰期旋回理论中的“4万年周期问题”：回顾与展望

米兰科维奇理论认为地球轨道的天文周期调控北半球高纬地区夏季接收太阳辐射的强度,进而驱动第四纪地表的冰期-间冰期旋回。20世纪60年代以来,米兰科维奇理论预测的天文周期在第四纪海洋沉积物中得到了印证,看似证明了该理论的正确性。但大量新记录的出现给经典米兰科维奇理论带来了挑战,早更新世的“4万年周期问题”——即为何早更新世的冰期旋回中没有岁差周期——就是其中之一。目前对于该问题的两种回答包括：1)南、北半球冰盖分别受当地夏季太阳辐射强度的驱动;2)早更新世冰期受北半球夏季累积太阳辐射量驱动。不难发现,这两种假说均默认了米兰科维奇理论中“高纬地区是驱动地球气候演变关键区域”的假设,争议的点仅在于岁差是否影响了高纬度冰盖的变化,这或许是“4万年周期问题”至今悬而未决的原因。未来要解决早更新世乃至整个第四纪冰期旋回的问题,或许目光要跳出高纬地区,考虑低纬过程以及高-低纬之间的相互作用。

     

Metre‐scale cycles in shallow water carbonate successions: Milankovitch and stochastic origins

Metre‐scale cycles are a common feature in Precambrian and Phanerozoic shallow water carbonate successions, and astronomically forced changes in sea‐level (Milankovitch cycles) may have been an important driver controlling their deposition. Nevertheless, the degree to which potentially low amplitude astronomically paced sea‐level oscillations may have controlled carbonate accumulation in deep time is unclear. In this study, a stochastic model of carbonate accumulation demonstrates how metre‐scale exposure‐bound sequences can be generated under conditions of random sea‐level change. These sequences have characteristic durations close to Milankovitch cycles, despite the absence of any astronomical control on their formation. Metre‐scale sequences with sub‐Milankovitch (millennial‐scale) durations can also be generated by the model, potentially shedding light on the origin of sub‐Milankovitch sequences such as those recorded on the Middle Triassic Latemar platform of Northern Italy. Sensitivity tests demonstrate how shallow water carbonates may be very sensitive to weak (i.e. low amplitude) astronomically forced sea‐level oscillations. Notably, strong statistical evidence (P < 0·01) for astronomical cycles can be preserved in modelled successions even when astronomical forcing contributes <1% of the sea‐level variance on million year timescales. Taken together, metre‐scale cycles with Milankovitch‐scale durations in ancient carbonate successions may reveal very little about the amplitude, or even the existence, of astronomical forcing as a sea‐level driver.     

Climate Changes and Cyclic Sedimentation in the Mid-Late Permian: Kennedy Group, Carnarvon Basin, Western Australia

Climate has an important direct and indirect influence of sedimentation, and especially on the development of cyclic sedimentation. Climate influences both accommodation and supply, the major controls on the architecture of sedimentary sequences. The Permian paleoclimate is the subject of increasing controversy, giving rise to numerous differing models developed and an expanding database of fossil evidence for climatic conditions.Western Australian basins, in particular the Carnarvon Basin, are unique among nearby Gondwanan basins in that they do not have extensive coal measures within their Permian successions. The Kennedy Group, the uppermost unit in the onshore Carnarvon Basin Permian succession, has a detrital composition indicative of arid weathering conditions. Within the Kennedy Group, even lagoonal and very nearshore sediments are devoid of plant debris or indications of the nearby presence of extensive flora. Presumed surfaces of subaerial exposure do not show paleosol development or root-traces. There has been little development of clay and chemical grain degradation is almost entirely related to diagenetic cementation and dissolution phases, rather than transport and source weathering. Nearby basins, at similar latitudes, in India and East Australia contain coal measures, consistent with the humid climates that are predicted for this latitude. It is suggested therefore that the inferred aridity in the climate of the Carnarvon Basin and other Western Australian Basins is due to local climatic effects, probably related to an interruption in atmospheric circulation caused by tectonic rifting and uplift to the west.Cyclicity in the Kennedy Group indicates regular Late Permian, Milankovitch scale eustatic sea-level change, and may signify the presence of some ice at the poles. The development of cycles may have been enhanced by shifting climate belts controlled by Milankovitch cyclicity.     

Orbitally induced cycles in the chalk facies of the United Kingdom

The characteristic rhythmic bedding of the Upper Cretaceous pelagic carbonate sequences of the United Kingdom is interpreted as the result of orbital variations. A 23,000 year and a 41.500 year cycle have been recognised and can be used to confirm the dating of late Cretaceous events, especially in the Cenomanian.     

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。     

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.     

The 100-kyr ice-age cycle: internal oscillation or inclinational forcing?

The ice-age hypothesis of Muller and MacDonald (1995, 1997a, 1997b) has two parts: (a) The 100-kyr cycle does not owe its existence to Milankovitch forcing; and (b) variations in inclination of Earth's orbit (i.e., the orbit's angle with the solar system invariable plane) provide the mechanism sought. In support of the first proposition, Muller and MacDonald point to the paradox that the spectrum of oxygen isotope series from deep-sea sediments contains no power for two prominent eccentricity cycles, 125 and 400 kyr. In support of the second proposition, they offer a match between the SPECMAP record (Imbrie et al. 1984) and a plot of the amplitude of orbital inclination, shifted by 33 kyr. The hypothesis of Muller and MacDonald is rejected in both parts, although an influence of inclination forcing is not precluded entirely. The paradox of the missing eccentricity cycles (125 and 400 kyr) is explained by suppression of the two longer cycles, and enhancement of the one near 96 kyr, as a result of internal oscillation. A Muller–MacDonald machine for making the 100-kyr ice-age cycles, however conceived, would have to have a memory near 30 kyr to provide for phase shift between input and output. Precisely this amount of memory is sufficient to produce the needed oscillation in Milankovitch machine here applied; thus, there is no advantage, from the point of view of either necessity or simplicity, in replacing Milankovitch forcing, with its precise phasing (despite the fuzzy physics), with inclination forcing, and with its severe problems in phasing (and, thus far, no physics at all). Received: 10 June 1998 / Accepted: 2 February 1999     

冻融循环作用下泥质白云岩力学特性及损伤演化规律研究

针对饱水状态下的泥质白云岩,采用BCD–218 C低温数控恒温箱、WDW3100型微机控制电子万能试验机进行不同冻融循环状态下的单轴压缩试验,对其在单轴状态下应力-应变曲线变化特征以及抗压强度、峰值应变、弹性模量、泊松比的变化规律进行了分析。在现有的损伤力学理论基础上,引入斜率增大趋势系数,建立了以冻融循环次数和应变为控制变量的本构模型。结果表明,在冻融循环过程中,单轴抗压强度、峰值应变、弹性模量参数呈指数下降趋势,泊松比呈线性增加的趋势;受冻融循环的影响,应力-应变全过程曲线在第一阶段后出现短暂的线形平缓阶段,具有岩石局部滑移现象;岩石破坏形态从脆性向延性转化,具有峰前塑性硬化和峰后应变软化等行为特征。理论本构模型与试验结果相符合。     

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。     

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.     

前寒武纪旋回地层学研究进展与展望

旋回地层学是利用已知的地球轨道天文周期, 对地层记录的周期性变化进行识别、解释的地层学新兴分支学科。在过去近30年, 旋回地层学研究取得了一系列重要进展, 对于认识地质历史时期的气候变化、重大地质事件的天文驱动、天文运行规律等诸多科学问题做出了重要贡献;同时, 基于此研究建立的天文年代标尺, 也成为一种新的高精度地质定年方法, 被应用于国际地质年代表的编制以及地表地质过程年代及持续时间的精确标定。然而, 全球旋回地层学研究主要集中在显生宙, 并以中、新生代最为详细。对于更早的占地球历史约7/8 的前寒武纪时期, 相关研究较少, 但一些新研究显示了可靠的天文沉积旋回可能存在的证据。因此, 前寒武纪有可能成为旋回地层学研究新的突破方向。中国华北克拉通北缘元古代地层沉积旋回非常发育, 具有开展旋回地层学研究的潜力。     

冻融循环条件下片麻岩蠕变特性试验研究

为探讨寒冷地区隧道围岩的长期稳定性,选取吉林省辉白隧道中的片麻岩进行冻融循环条件下的三轴蠕变试验,分析了冻融循环作用对片麻岩蠕变特性的影响机制。试验结果表明：随着冻融次数的增加,片麻岩的蠕变变形量逐渐增加,而蠕变破坏应力、蠕变时长、长期强度均有明显降低的趋势。同时冻融循环温度的幅度对片麻岩的各蠕变参数也有一定影响,表现为冻融循环次数相同时,温度越低,岩样的初始瞬时蠕变越大,而蠕变时长与长期强度越小。同时基于试验结果,利用1stOpt优化软件对Burgers模型参数进行辨识,可得模型理论曲线与试验曲线在蠕变减速段和稳定段吻合较好。最后通过SEM扫描和能谱EDS分析了冻融循环对片麻岩微细观结构的影响机制。岩样在长期荷载作用下的破坏模式均为剪切破坏,随着冻融次数的增加,岩石的破裂程度越来越严重、破坏块度越来越小。研究结果为寒区岩石工程的支护设计和防冻害设计提供了参考和依据。     

A general method for defining the number of cycles of repeated loading

In geotechnical engineering designs and safety checks, the number of cycles of repeated loading N is frequently used as a parameter for calculating the response of soil structures under the repeated loading. However, there appears to be a lack of rational methods for calculating N for repeated loadings along general stress paths. A new method for defining N is proposed in this paper, based on the assumption that a yield surface may be identified for the material. It is demonstrated that the proposed method provides a rational and useful means for engineering calculation of soil deformations under repeated loadings. Copyright © 2001 John Wiley & Sons, Ltd.     

冻融循环过程中土体的孔隙水压力测试研究

冻融循环对土的结构以及物理力学性质有着重要影响,其变化与冻融过程中的孔隙水压力变化有密切关系。但土体冻结过程中的孔隙水压力测试一直是冻土土工测试试验的技术难题。针对这一难题,研发了一种适用于冻结土体孔隙水压力测试的探头,并对砂土和粉质黏土在冻融循环过程中的孔隙水压力发展变化进行了实时监测,获得了圆柱试样冻融循环过程中不同深度处的孔隙水压力变化过程。在冻结过程中,粉质黏土形成冻结缘区及可视的分凝冰,而砂土则无冻结缘及分凝冰的形成。冻融循环过程中土体内部的孔隙水压力变化受温度、冻结速率、冻融循环以及土质等因素的影响。孔隙水压力随温度的循环变化而经历周期性变化：冻结过程中,孔隙水压力不断下降,吸力不断增加;融化过程中,孔隙水压力增大。而冻结速率、冻融循环及土质主要对孔隙水压力降的幅值变化产生影响。此外,冻结锋面位置附近孔隙水压力的下降、吸力的增加,正是水分由未冻区向冻结区迁移的主要驱动力。根据以上试验结果及其理论分析发现,所研制的孔隙水压力探头具有一定的实用性。     

Griesbachian Cyclostratigraphy at MajiashanSection, Anhui Province, China

INTRODUCTIONAs a large regression continued over the world at the endof the Paleozoic, a new remarkable transgression was intrudinginto the Lower Yangtze located in the eastern Tethys duringthe Late Permian, resulting in many excellent continuous marine Permian-Triassic sequences in this region. But the middleTriassic indosinian movement transformed this region from marine to continental factes, resulting in the deposition of theLower Triassic in the marked regression setting prior to …     

Climatic Versus Tectonic Control on Storm Cyclicity in Mesoproterozoic Koldaha Shale, Vindhyan Supergroup, Central India

The 1.2 Ga-old Koldaha shale, central India reveals three orders of depositional cyclicities in its basal storm-dominated shelf succession. Visual appraisal as well as Fourier and MEM analyses concurs in this respect. Only the major storm events at intervals of a few thousands of years have left recognizable imprints. Interbedding of storm sandstones and fairweather shales is apparently climate-controlled. Packaging of about seven such climatic cycles results the second-order cyclicity befitting eccentricity cycles of contemporary scale. Nonetheless, for the erratic storm bed-thickness trends within the cycles some other factor/s might have played a role. The third order cycles are, more dominantly, correlatable with basinal tectonics.     

云冈石窟砂岩循环冻融试验研究

风化是云冈石窟目前所面临的严重的地质病害之一,温度和水分的变化是造成石窟岩体风化的重要原因,尤其是在循环冻融条件下岩体更易风化,因此,利用室内试验研究循环冻融条件下云冈石窟砂岩的物理力学性质,对于石窟岩体的稳定性评价和保护具有重要的意义。将取自云冈石窟的砂岩岩样分为饱水组、干燥组和对比组3组,通过对饱水组和干燥组岩样进行35次循环冻融试验,模拟云冈石窟砂岩的风化过程。在冻融循环开始前以及每5次冻融循环结束后,量测岩样的质量、体积,并利用超声检测分析仪对各岩样进行超声纵波测试;利用INSTRON－1346岩石伺服试验机对上述3组砂岩岩样进行单轴压缩试验,并对试验后的岩样进行SEM微观结构分析。通过试验研究,得到不同含水状态下云冈石窟砂岩岩样的冻融破坏特征以及不同循环冻融次数后岩样体积、质量、超声波纵波波速、砂岩的单轴应力-应变全过程曲线、抗压强度、抗冻系数以及微观结构的变化,分析归纳出循环冻融条件下云冈石窟砂岩的主要物理力学特性。     

Orbitally forced sedimentary rhythms in the stratigraphic record: is there room for tidal forcing?

The imprint of orbital cycles, which result from the varying eccentricity of the Earth’s orbit and changes in the orientation of its axis, have been recognised throughout the Phanerozoic rock record. Variations in insolation and their effect on climate are generally considered to be the sole transfer mechanism between the orbital variables and cyclic sedimentary successions. Common oceanographic principles, however, show that the ocean tide also responds to variations in the orbital parameters. The ocean tide has not yet been considered to be a valid, additional transfer mechanism for the orbital variations. In geological studies of Milankovitch cycles in sedimentary successions the insolation paradigm offers satisfying explanations, and the role of long‐term variations of the ocean tide has not yet been appreciated. Variations in the ocean tide, related to changing eccentricity (at present 0·0165, theoretical maximum 0·0728), affect a variety of oceanographic and sedimentary processes. In addition to the widely accepted paradigm of orbitally forced insolation changes, the tidal transfer of orbital signals may explain certain less well‐understood aspects of orbitally induced cycles in the stratigraphic record related to ocean mixing, organic productivity, and tidal processes in shallow seas and deep water. Variations of the ocean tide in relation to the 18·6 year lunar nodal cycle, which has no insolation counterpart by which they may be obscured, indeed show that these relatively small variations can produce significant effects in sedimentary environments that are sensitive to variations in the strength of the ocean tide. In analogy with the 18·6 year lunar nodal cycle, orbital variations of the tide on Milankovitch time scales are likely to have affected sedimentary systems in the past.