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1.
J. Hohenegger S. Ćorić M. Khatun P. Pervesler F. Rögl C. Rupp A. Selge A. Uchman M. Wagreich 《International Journal of Earth Sciences》2009,98(4):915-930
The scientific borehole Baden-Sooss penetrates a succession of Badenian (Langhian, Middle Miocene) sediments at the type locality
of the Badenian, the old brickyard Baden-Sooss in the Vienna Basin. The sedimentary succession of the 102-m-cored interval
consists of more than 95% bioturbated, medium-to-dark gray marly shales with carbonate contents between 11 and 25% and organic
carbon contents between 0.35 and 0.65%. Biostratigraphic investigations on foraminifera (mainly lower part of Upper Lagenid
Zone) and calcareous nannoplankton (standard zone NN5) indicate an early Badenian (Langhian) age. Cycles in carbonate content,
organic carbon content, and magnetic susceptibility have been identified by power spectra analysis. Correlations between the
three variables are extremely significant. Using cross-correlation, periods around 40 m correlate significantly with the 100 kyr−1 eccentricity cycle, the ∼20 m periods with the obliquity cycle, and the 15 to 11-m periods with both precession cycles. Wavelet
transformation and decomposition of composite periodic functions were used to obtain the position of the cycle peaks in the
profile. Cross-correlation with orbital cycles (La2004) dates the Baden-Sooss core between −14.379 ± 1 and −14.142 my ± 9 kyr. 相似文献
2.
《Quaternary Science Reviews》2007,26(17-18):2042-2066
A review of seven outstanding issues on Mediterranean palaeoenvironments is presented. These are related to the dominant orbital pacing of climate variability, the length of the interglacial vegetation succession, the influence of the African summer monsoon, the seasonality of precipitation during boreal insolation maxima, the moisture balance during glacial maxima and the appearance of the mediterranean-type climate rhythm and evolution of mediterranean sclerophyllous plants. What emerges is that (1) marine δ18Oplanktonic and SST records show that precession has been a fundamental tempo of Mediterranean climate change, representing both a low-latitude signal (runoff from North Africa) and the direct influence of insolation at Mediterranean latitudes, but high-latitude glacial effects (41-kyr and 100-kyr cycles) became superimposed after 2.8 Ma. Sapropel and dust deposition patterns in marine cores reveal that obliquity also has an effect on Mediterranean climate through dry–wet oscillations, which are independent of glacial–interglacial variability. (2) The temperate part of interglacial vegetation succession has a duration of approximately half a precession cycle. This persisted during the interval of obliquity-dominated glacial cycles (∼2.8–1 Ma), with distinct forest successions following the precessional cycles. However, these are not always separated by an open vegetation phase because of minimal ice growth, producing an impression of a prolonged interglacial forest interval. (3) The effect of an enhanced African monsoon during summer insolation maxima has been mainly indirect, in terms of Nile discharge and runoff along the North African coast, leading to increased freshwater input into the Mediterranean Sea, reduced deep-water ventilation and sapropel deposition. (4) The notion of an accentuated summer rain regime in the northern Mediterranean borderlands also contributing to a freshening of the Mediterranean Sea during boreal insolation maxima is not supported by the available evidence, which suggests increased summer aridity. (5) Recent improvements in chronological precision and data resolution point to an increase in aridity and decreased temperatures during the Last Glacial Maximum (21±2 ka), but suggest an increase in effective moisture during the immediately preceding interval of 24–27 ka. (6) The mediterranean-type climate is not exclusively a post-3.6 Ma phenomenon, but may have appeared intermittently during the course of the Tertiary (or before). (7) If that is the case, then the paradigm that the sclerophyllous evergreen habit represents a pre-adaptation to summer drought may need re-evaluation. 相似文献
3.
Larry A. Mayer Cyril Gobrecht Nicklas G. Pisias 《International Journal of Earth Sciences》1996,85(3):505-512
Recent developments in continuous core-logging techniques now permit us to recover the high-resolution time series necessary
for the detailed spectral analyses of paleoclimatic proxy records. When applied to long records recovered by scientific drilling
(5–10 Ma) they enable us to look at the long-term history and evolution of the ocean's response to orbital forcing. A serious
limitation in these studies is the need to display the complex, multidimensional spatial and temporal interactions of the
ocean-climate system in an easily comprehensible manner. We have addressed this issue by developing a series 3D visualization
tools which permit visualization of the role of the orbital parameters in determining the latitudinal variation of insolation
as well as the interactive exploration of multidimensional data sets. The ORBITS tool allows us to visualize the effect of
orbital eccentricity, precession, and tilt on the latitudinal distribution of insolation on the earth at the solstices and
the equinoxes for any time over the past 5 Ma (for Berger's orbital model) or 10 Ma (for Laskar's orbital model). The effect
of the orbital parameters on insolation can be viewed individually, in pairs, or all three together. By moving the model steadily
through time, the rate at which orbitally induced changes in insolation occur can also be visualized. To look at the ocean's
response to orbital forcing we take the long time series generated from our paleoclimatic proxies and calculate their spectrum
over a fixed, but sliding, time window. To view the complex multidimensional relationships found in these evolutionary spectral
analyses, we use another interactive 3D data exploration tool developed at the University of New Brunswick (Canada). This
tool (FLEDERMAUS) uses a six-degrees-of-freedom input device (BAT) and a series of software modules for color coding, shading,
and rendering complex data sets, to allow the user to interactively "fly" through the multidimensional data. Through the use
of color, texture, and 3D position, as many as six or seven variables can be explored in a simple and intuitive manner. With
special liquid-crystal-display glasses, the scene can be viewed in true "stereo." We use these tools to explore the relationship
between orbital forcing and the response of the benthic isotope and calcium carbonate record at ODP Site 846 (90°W and 5°S)
This analysis shows an equatorial Pacific carbonate record which has a large component of linear response to tilt, but little
linear response to precession. There is a major shift in response, from a carbonate-dominated response to an isotope (ice
volume)-dominated response at approximately 4.5 Ma, and as expected, there is a large nonlinear response at the lower frequencies
(400 and 100 kyr) during the past 800 kyr to 1 Ma
Received: 22 June 1995 / Accepted: 29 January 1996 相似文献
4.
Katalin Báldi 《International Journal of Earth Sciences》2006,95(1):119-142
Benthic foraminifera and stable isotopes analyses revealed changes emerging in the paleoceanographic scenery in the Paratethys.
The percentage of inbenthic, oxyphylic taxa and diversity in the benthic foraminiferal assemblage showed increasing food supply
(organic matter), decreasing oxygen level and growing stress on the sea floor. Oxygen isotopes measured in planktonic and
benthic foraminifera pointed to strengthening stratification during the Badenian period. The carbon isotopes indicated intensified
accumulation of light marine organic matter. This increasing stratification trend is especially pronounced by Late Badenian
(13.5–13 Ma) when surface water oxygen isotope values are rather negative. A simple two-layer circulation model was worked
out for the Badenian Paratethys explaining these characteristic environmental changes. An antiestuarine (lagoonal) circulation is assumed for the Central Paratethys during the Early (16.4–15 Ma) and mid Badenian (15–13.5 Ma). The mid Badenian
period of time comprises the short episode of evaporite formation in the Carpathian Foredeep and the Transylvanian Basin.
Evidence presented here supported a reversal of circulation to estuarine type after the deposition of salts by Late Badenian (13.5–13 Ma). The Early Badenian antiestuarine circulation is suggested
to associate with the high temperatures of the Mid-Miocene Climatic Optimum, and the Late Badenian estuarine circulation with
the cooler period following it. 相似文献
5.
全球大洋深海有孔虫碳同位素(δ13C)记录中广泛发现40万年周期,这一周期可能与偏心率长周期的轨道驱动有关.1.6 Ma以来,δ13C的这一长周期拉长到50万年,且重值期不再与偏心率低值对应.目前对δ13C 40万年周期的成因及其周期拉长的机制还不明确.这里使用了包含9个箱体的箱式模型,用于研究热带过程与冰盖相互作用及其对大洋碳循环的影响.模拟结果显示当北半球高纬海区海冰迅速增大时冰盖迅速融化,进入冰消期,而当海冰快速消失后,冰盖则重新缓慢增长.冰盖变化具有冰期长,间冰期短的非对称形态.在季节性太阳辐射量的驱动下冰盖变化具有10万年冰期-间冰期旋回.当冰盖融化速率受北半球高纬夏季太阳辐射量控制时,冰盖变化的岁差周期明显加强,相位与地质记录一致,说明轨道驱动可以通过非线性相位锁定机制使冰盖变化与其在相位上保持一致.海冰的阻隔效应使大气中CO2在冰消期时增多.冰期时大洋环流减弱使大气中CO2逐渐减少.当模型只有ETP驱动的风化作用而不考虑冰盖变化时,模拟的δ13C记录显示极强的40万年周期,体现了大洋碳储库对热带风化过程的响应.当同时考虑冰盖变化和风化作用时,模拟的δ13C结果中40万年周期减弱而10万年周期加强,并且40万年周期上碳储库与偏心率的相位与不考虑冰盖变化时的相位也存在差异,反映了冰盖变化引起的洋流改组压制了大洋碳循环对热带过程的响应. 相似文献
6.
Northeast Sichuan basin is a Mesozoic-Cenozoic basin in the northern margin of the Yangtze plate which has a complex tectonic
background and hydrocarbon accumulation history. By means of the analysis method of wave processes, major cycles of sedimentary
wave process in this basin have been studied. The results show that there are five-order cycles corresponding to 760, 220,
100, 35 and 20 Ma respectively, two first-order sedimentary cycles (220 Ma) and four secondorder sedimentary cycles (100 Ma).
The authors find that the second-order sedimentary cycles are well matched with reservoir formation cycles through studying
the relationship between second-order sedimentary cycles and reservoir formation cycles, and divide three reservoir formation
cycles in this basin.
__________
Translated from Journal of Jilin University (Earth Science Edition), 2007, 37(3): 513–518 [译自: 吉林大学学报(地球科学版)] 相似文献
7.
The origin of third-order depositional sequences remains debatable, and in many cases it is not clear whether they were controlled by tectonic activity and/or by eustatic sea-level changes. In Oxfordian and Berriasian–Valanginian carbonate-dominated sections of Switzerland, France, Germany and Spain, high-resolution sequence-stratigraphic and cyclostratigraphic analyses show that the sedimentary record reflects Milankovitch cyclicity. Orbitally induced insolation changes translated into sea-level fluctuations, which in turn controlled accommodation changes. Beds and bedsets formed in rhythm with the precession and 100-kyr eccentricity cycles, whereas the 400-kyr eccentricity cycle contributed to the creation of major depositional sequences. Biostratigraphical data allow the correlation of many of the 400-kyr sequence boundaries with third-order sequence boundaries recognized in European basins. This implies that climatically controlled sea-level changes contributed to the formation of third-order sequences. Furthermore, this cyclostratigraphical approach improves the relative dating of stratigraphic intervals. 相似文献
8.
内蒙古苏尼特右旗白乃庙地区徐尼乌苏组的形成时代及其地质意义 总被引：1，自引：1，他引：0
本文对白乃庙地区徐尼乌苏组沉积特征、原岩建造、变质火山岩及变质碎屑岩的年代学和地球化学进行了研究,探讨了白乃庙地区早古生代构造演化。本次研究采集了徐尼乌苏组中具有代表性的变质含砾粗粒杂砂岩、变质英安质晶屑凝灰岩和变质长石石英细砂岩样品,进行了锆石LA-ICP-MS U-Pb年代学和岩石地球化学分析。结果显示,2个变质英安质晶屑凝灰岩锆石的加权平均年龄分别为440.9±1.8Ma(MSWD=0.10)和440.9±1.7Ma(MSWD=0.15),锆石Th/U比值为0.46~1.59,自形程度较好,发育有典型的岩浆锆石振荡环带结构,显示为岩浆成因锆石的特点,表明徐尼乌苏组的形成时代为早志留世。变质含砾粗粒杂砂岩的碎屑锆石年龄在452.0±1.3Ma~535.0±1.0Ma之间,最高峰值年龄为490Ma左右;变质长石石英细砂岩碎屑锆石年龄则在440.1±5.7Ma~3268.9±57.7Ma之间,最小谐和年龄为440.1±5.7Ma,峰值年龄为490Ma左右,另有1.0Ga、1.6Ga、1.8Ga和2.5Ga四个明显的峰值年龄。根据研究区徐尼乌苏组岩性组合与结构构造,可将该组划分为3个不同的沉积旋回。结合白乃庙地区徐尼乌苏组测年结果、岩石地球化学特征、原岩建造及区域岩浆岩资料,白乃庙弧后盆地沉积可划分为三个演化阶段:早期快速堆积阶段(452.3~440.9Ma),形成了一套成熟度较低的粗碎屑岩建造,物源主要来源于白乃庙岩浆弧中的岩浆岩;中期火山喷发阶段(440.9~440.1Ma),以火山沉积作用为主,为火山碎屑岩建造夹有碳酸盐建造和少量碎屑岩建造,碎屑物质主要来源于该时期的火山活动;晚期稳定沉积阶段(440.1Ma),形成一套细碎屑岩建造和碳酸盐建造,为浅海相稳定沉积,此时物源广泛,分别来源于华北克拉通基底、兴蒙造山带和白乃庙早古生代火山弧。根据徐尼乌苏组的沉积建造和火山建造特征,结合白乃庙火山弧岩浆活动特征,认为徐尼乌苏组形成于早古生代弧后盆地中,此时华北板块北缘属于安第斯型活动大陆边缘。 相似文献
9.
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. 相似文献
10.
Nd Isotopic Composition and Material Source of Pre—and Post—Sinian Sedimentary Rocks in Xiushui Area,Jiangxi Province 总被引：4，自引：1，他引：4
Reported in this paper are the Nd isotopic compositions of the pre-Sinian and Sinian-Cambrian sedimentary rocks in the Xiushui area,Jiangxi Province.Significant differences are noticed between them in their Nd isotopic dompositions.As for the pre-Sinian lightly metmorphozed sedimentary rocks,^143Nd/^144Nd=0.512000-0.512214,CNd(T)=-8.04-9.99,and TDM=18332426Ma are suggested for the Sinian-Cambrian sedimentary rocks .These differences would reflect the diversity of material source for the sedimentary rocks deposited before and after the Sinian period.Mantle material ap-pears to have been involved in the formation of the pre-Sinian sedimentary rocks while the post-Sinian sedimentary rocks are composed mainly of recycled detritus from the continental crust. 相似文献
11.
Utilizing a sequential extraction technique this study provides the first quantitative analysis on the abundance of sedimentary
phosphorus and its partitioning between chemically distinguishable phases in sediments of the Bering Sea, the Chukchi Sea
and the Mackenzie River Delta in the western Arctic Ocean. Total sedimentary phosphorus (TSP) was fractionated into five operationally
defined phases: (1) adsorbed inorganic and exchangeable organic phosphorus, (2) Fe-bound inorganic phosphorus, (3) authigenic
carbonate fluorapatite, biogenic apatite and calcium carbonate-bound inorganic and organic phosphorus, (4) detrital apatite,
and (5) refractory organic phosphorus. TSP concentrations in surface sediments increased from the Chukchi Sea (18 μmol g−1 of dried sediments) to the Bering Sea (22 μmol g−1) and to the Mackenzie River Delta (29 μmol g−1). Among the five pools, detrital apatite phosphorus of igneous or metamorphic origin represents the largest fraction (~43%)
of TSP. The second largest pool is the authigenic carbonate fluorapatite, biogenic apatite as well as CaCO3 associated phosphorus (~24% of TSP), followed by the Fe-bound inorganic phosphorus, representing ~20% of TSP. The refractory
organic P accounts for ~10% of TSP and the readily exchangeable adsorbed P accounts for only 3.5% of TSP. Inorganic phosphorus
dominates all of phosphorus pools, accounting for an average of 87% of the TSP. Relatively high sedimentary organic carbon
and total nitrogen contents and low δ13C values in the Mackenzie River Delta together with the dominance of detrital apatite in the TSP demonstrate the importance
of riverine inputs in governing the abundance and speciation of sedimentary phosphorus in the Arctic coastal sediments. 相似文献
12.
Sediment production and accumulation on shallow carbonate platforms are controlled by allogenic, externally controlled processes
(such as sea level, climate, and/or platform-wide subsidence patterns) as well as by autogenic factors that are inherent to
the sedimentary system (such as lateral migration of sediment bodies). The challenge is to determine how and in which proportion
these processes interacted to create the observed sedimentary record. Here, a case study of Middle Berriasian, shallow-marine
carbonates of the Swiss and French Jura Mountains is presented. Based on vertical facies evolution and bedding surfaces, different
orders of depositional sequences (elementary, small-scale, medium-scale) have been identified in the studied sections. The
hierarchical stacking pattern of these sequences and the time span represented by the investigated interval imply that eustatic
sea-level fluctuations in the Milankovitch frequency band were an important controlling factor. The small-scale and medium-scale
sequences relate to the 100 and 400-kyr orbital eccentricity cycles, respectively. The elementary sequences are attributed
to the 20-kyr precession cycle. Differential subsidence additionally produced accommodation changes. The present study focuses
on one specific small-scale sequence situated at the base of the transgressive systems tract of large-scale sequence Be4,
which is identified also in other European basins. This small-scale sequence has been logged in detail at eight different
outcrops in the Jura Mountains. Detailed facies analysis reveals that different depositional environments (tidal flats, internal
lagoons, open lagoons, carbonate sand shoals) were juxtaposed and evolved through time, often shifting position on the platform.
The boundaries of the small-scale (100-kyr) sequence can be followed over the entire study area and thus must have formed
through predominantly allogenic processes (eustatic sea-level fall, the effect of which was locally modified by differential
subsidence). In two sections, five well-developed elementary sequences constitute the small-scale sequence. In the other sections,
the identification of elementary sequences often is difficult because sedimentation was dominated by autogenic processes that
overruled the influence of sea-level fluctuations. In low-energy, tidal-flat and internal-lagoonal settings, orbitally induced
sea-level changes were recorded more faithfully, while high-energy shoals were mainly submitted to autogenic processes and
the allogenic signal is masked. Consequently, the studied Jura platform experienced a combination of auto- and allogenic processes,
which created a complex facies mosaic and a complex stacking of depositional sequences. Nevertheless, the 100-kyr orbital
signal was strong enough to create correlatable sequence boundaries. Within a 100-kyr sequence, however, the unambiguous definition
of sequences related to the 20-kyr orbital cycle is often difficult and the prediction of their lateral or vertical facies
evolution impossible. 相似文献
13.
北京延庆千沟中元古代高于庄组第三段:一个典型的前寒武纪非叠层石碳酸盐岩沉积序列 总被引：2，自引：0，他引：2
在前寒武纪碳酸盐岩中,最为普遍的是叠层石碳酸盐岩沉积序列,而以潮下相沉积为主的非叠层石碳酸盐岩沉积序列与前者形成了较大的差异;因此,与叠层石碳酸盐岩沉积序列一样,非叠层石序列成为了解前寒武纪复杂多变的碳酸盐世界的重要线索。燕山地区中元古代高于庄组为一套厚度千余米的碳酸盐沉积序列,包括四大部分:第一段（或称为官地亚组）为发育在海侵砂岩上的叠层石白云岩地层;第二段（或称为桑树鞍亚组）为发育少量叠层石的含锰白云岩地层;第三段又称为张家峪亚组,为一套以发育灰岩为主的非叠层石碳酸盐岩沉积序列;第四段以叠层石岩礁和叠层石礁白云岩为特征。延庆千沟剖面的高于庄组第三段的非叠层石碳酸盐岩沉积序列,贫乏叠层石是其基本特点,包含3个三级层序,在三级层序的海侵体系域和早期高水位体系域中,层面上发育席底构造的中层均一石灰岩（隐藻泥晶灰岩）和灰黑色薄层泥灰岩组成若干潮下型米级旋回,晚期高水位体系域则以厚层块状纹理石灰质白云岩和白云质灰岩为特征;三级层序的凝缩段单元则以薄层泥灰岩和泥页岩构成的L-M型米级旋回为特征。因此,每一个三级层序均以一个有序的沉积相序列为特征。高于庄组的分布时限大致为200 Ma（1 600～1 400 Ma）,考虑到下伏的大红峪组和高于庄组之间的地层间断时限大致为50 Ma至100 Ma,所以推断高于庄组的堆积作用时限为100 Ma（1 500～1 400 Ma）左右,其中高于庄组第一段与第二段的分界线正好处于该组的中部而可以推断该界线的大致为1 450 Ma左右;因此,高于庄组第三段非叠层石碳酸盐岩沉积序列的发育表明,在1 450 Ma左右可能发生过一次可以与前寒武纪其他已经被识别出的三次叠层石衰减事件（2 000 Ma、1 000 Ma和675 Ma）相比拟的又一次叠层石衰减事件。延庆千沟剖面高于庄组第三段的非叠层石碳酸盐岩沉积序列,可以大致与北美地区的起始时限为1 450 Ma左右、Belt超群中的Helena组非叠层石碳酸盐岩沉积序列相对比,表明了1 450 Ma左右的叠层石衰减事件具有全球性,从而赋予高于庄组第三段非叠层石碳酸盐岩沉积序列重要的沉积学意义。延庆千沟剖面高于庄组第三段非叠层石碳酸盐岩沉积序列,特别的岩石类型和沉积构造,成为前寒武纪碳酸盐岩沉积中非叠层石碳酸盐岩沉积序列的典型代表,由其所代表的沉积学特点将有助于深入理解漫长的前寒武纪碳酸盐沉积作用的变化规律而具有重要意义。 相似文献
14.
MEI Mingxiang 《《地质学报》英文版》2008,82(2):295-309
In the long Precambrian period, stromatolitic carbonate successions were very common. However, the non-stromatolitic carbonate succession that is marked by subtidal deposits shows a sharp contrast to the stromatolitic carbonate succession. Both the non-stromatolitic and the stromatolitic carbonate successions are important clues for the further understanding of the evolving carbonate world of the Precambrian. The Mesoproterozoic Gaoyuzhuang Formation at the Qiangou section in northwestern suburb of Beijing is a set of more than 1000 m-thick carbonate strata that can be divided into four members （or subformations）, in which a non-stromatolitic carbonate succession marked by the scarcity of stromatolites makes up the third member of the formation. This non-stromatolitic carbonate succession can further be subdivided into three third-order sequences that are marked by the regular succession of sedimentary facies. In third-order sequences, a lot of subtidal carbonate meter-scale cycles made up of medium-bedded leiolite limestones and thin-bedded marls constitute their transgressive system tracts （TSTs） and the early high-stand system tracts （EHSTs）, a lot of meter- scale cycles made up by thin-bedded limestones and marls constitute their condensed sections （CSs）, and thick-bedded to massive dolomitic limestones or lime dolomites make up the late high-stand system tracts （LHSTs）. The particularly non-stromatolitic carbonate succession making up the third member of the Mesoproterozoic Gaoyuzhuang Formation at the Qiangou section might be the representative of the non-stromatolitic carbonate succession of the Precambrian because of its special lithological features and particular sedimentary structures, and its general sedimentary features are helpful and meaningful for the further understanding of the evolution rules of the sophisticate and evolving carbonate world of the Precambrian. The time scale of the Gaoyuzhuang Formation is deduced as that from 1600 Ma to 1400 Ma; thus, the non-stromatolitic 相似文献
15.
Hayfaa Abdul Aziz Madelaine B?hme Alexander Rocholl Jerome Prieto Jan R. Wijbrans Valerian Bachtadse Albert Ulbig 《International Journal of Earth Sciences》2010,99(8):1859-1886
A detailed integrated stratigraphic study (biostratigraphy and magnetostratigraphy) was carried out on five sections from
the western part of the Bavarian Upper Freshwater Molasse of the North Alpine Foreland Basin (NAFB), greatly improving the
chronostratigraphy of these sediments. The sections belong to the lithostratigraphic units Limnische Untere Serie (UL) and Fluviatile Untere Serie (UF) and contain 19 (mostly new) small-mammal bearing levels, significantly refining the local biostratigraphy. Radiometric
ages obtained from glass shards from tuff horizons are used together with the biostratigraphic information for constructing
and confirming the magnetostratigraphic correlation of the studied sections to the Astronomical Tuned Time Scale (ANTS04;
Lourens et al. in Geologic Time Scale 2004, Cambridge University Press, 2004). This correlation implies that the UL lithostratigraphic
unit corresponds to the latest Ottnangian and the Early Karpatian, whereas the UF corresponds to the Karpatian and the Early
Badenian. This indicates that the Brackish- to Freshwater Molasse transition already occurred during the late Ottnangian.
The pre-Riesian hiatus occurred in the latest Karpatian and lower Early Badenian in Eastern Bavaria and Bohemia and in the
Late Karpatian and earliest Badenian in Western Bavaria. The geochemical and Ar–Ar data of volcanic ashes suggest that highly
evolved silicic magmas from a single volcano or volcanic center, characterized by a uniform Nd isotopic composition, erupted
repetitively over the course of at least 1.6 Myr. Three phases of eruptive activity were identified at 16.1 ± 0.2 Ma (Zahling-2),
15.6 ± 0.4 Ma (Krumbad), and 14.5 ± 0.2 Ma (Heilsberg, Hegau). The correlation of the local biostratigraphic zonation to the
ANTS04 enables further the characterization of both the Ottnangian–Karpatian and Karpatian–Badenian boundaries in the NAFB
by small-mammal biostratigraphy. According to these results the Ottnangian–Karpatian boundary is contemporaneous with the
first appearance datum of Megacricetodon
bavaricus (in the size of the type population) and the first common occurrence of Keramidomys thaleri, whereas Ligerimys florancei, Melissiodon dominans and Prodeinotherium aff. bavaricum have been already disappeared during the late Ottnangian. The Karpatian–Badenian boundary is characterized by a significant
size increase of the large Megacricetodon lineage and possibly a (re-)immigration of Prodeinotherium bavaricum. 相似文献
16.
The Aptian-Albian 'Scisti a Fucoidi' varicoloured pelagic sediments in central Italy, show a 'couplet' alternation of carbonate-rich/carbonate-poor layers, which are interpreted as the sedimentary expression of precession (frequency 19–23 kyr). Carbonate content, chromatic variation, and planktonic foraminiferal abundance were analysed at a 1-cm spacing for a 10-m interval of the Piobbico core, specifically drilled through this formation. Spectral analysis of these parameters shows a prominent signal equated to the c . 100 kyr cycle of orbital eccentricity at a sedimentation rate of 5 mm kyr−1 . The coherency of the spectral response of each parameter suggests that a single mechanism controlled the whole sedimentary record. Detailed study of planktonic foraminiferal distribution of the same section at 1-mm scale resolves the Milankovitch frequencies of 41 kyr and 18 to 23 kyr, equated with the obliquity and precessional cycles. But foraminiferal abundance is not in phase with carbonate content, which was largely controlled by calcareous nannofossils, but peaked at intermediate carbonate values. The proposed model for explaining the discrepancy at the precessional level is that foraminifera thrived at intermediate values of the precession index, when the environment was only moderately fertile but stable, while during highs of the precession index, mixing of the water column increased fertility and caused calcareous nannofossil blooms and restriction of planktonic foraminifera to few and tolerant species. The resulting bimodality of foraminiferal abundance per precessional cycle appears to be recorded in the spectrum by peaks at the 11 and 14 kyr levels. Cross correlation of foraminiferal abundances with the calcium carbonate curve over 1–2 Myr intervals produces discrepant results (apparent phase lags) which we attribute to differences in the response to the fundamental eccentricity cycles. 相似文献
17.
We present a high-resolution sedimentological analysis of Barremian–Aptian shallow-water carbonates from two cores (S. Maria 6 and 4) that were drilled in the central Apennines (central Italy) and one section (Monte Faito) that crops out in the southern Apennines (southern Italy). The aims of this work are (a) to propose a high-resolution correlation of sections that are located approximately 170 km apart in different tectonic units and paleogeographic domains using a microstratigraphic (cm-scale) approach and (b) to reveal global and regional mechanisms that control the stratigraphic architecture of these carbonate platform strata.A composite S. Maria section was assembled by integrating the sedimentologic and biostratigraphic analyses of the two cores, which overlap each other across the Barremian–Aptian boundary. Both the S. Maria and the Monte Faito sections show repetitive facies patterns that are expressed as elementary cycles, which are hierarchically grouped into bundles and superbundles. The elementary cycles are meter-scale sedimentary units that are bounded by subaerial erosion surfaces, which directly overlie subtidal deposits. This implies that they formed under the influence of relative sea-level fluctuations. In both sections, the superbundles are organized into Transgressive/Regressive Facies Trends (T/RFTs), which are considered to be expressions of lower-frequency relative sea-level changes.These deposits, like their Cretaceous analogues of other areas of the Apennines, show evidence of astronomically controlled eustatic oscillations, which are reflected in the hierarchical organization of their stacking patterns. They also exhibit a sequence-stratigraphic configuration that is best recognizable in the superbundles and T/RFTs. Based on integrated stratigraphic criteria, a high-resolution regional correlation between S. Maria and Monte Faito was developed and compared with the reference section of Monte Raggeto (M. Maggiore, southern Apennines, Italy), where biostratigraphic and cyclostratigraphic studies have been complemented by magneto- and isotope-stratigraphy.We also propose a chronostratigraphic correlation between our T/RFTs and the Tethyan stratigraphic cycles of Hardenbol et al. (1998). Based on the cyclostratigraphic interpretation and orbital chronostratigraphy of the studied interval, we estimate a minimum duration of 5.2 my for the Barremian interval, which is similar to the 4.5 my duration from the Geological Time Scale of Gradstein et al., (2012). 相似文献
18.
Vein-type tin mineralization in the Dadoushan deposit, Laochang ore field, Gejiu district, SW China, is predominantly hosted in Triassic carbonate rocks (Gejiu Formation) over cupolas of the unexposed Laochang equigranular granite intrusion. The most common vein mineral is tourmaline, accompanied by skarn minerals (garnet, diopside, epidote, phlogopite) and beryl. The main ore mineral is cassiterite, accompanied by minor chalcopyrite, pyrrhotite, and pyrite, as well as scheelite. The tin ore grade varies with depth, with the highest grades (~1.2 % Sn) prevalent in the lower part of the vein zone. Muscovite 40Ar–39Ar dating yielded a plateau age of 82.7 ± 0.7 Ma which defines the age of the vein-type mineralization. Measured sulfur isotope compositions (δ 34S = −4.1 to 3.9 ‰) of the sulfides (arsenopyrite, chalcopyrite, pyrite, and pyrrhotite) indicate that the sulfur in veins is mainly derived from a magmatic source. The sulfur isotope values of the ores are consistent with those from the underlying granite (Laochang equigranular granite, −3.7 to 0.1 ‰) but are different from the carbonate wall rocks of the Gejiu Formation (7.1 to 11.1 ‰). The calculated and measured oxygen and hydrogen isotope compositions of the ore-forming fluids (δ 18OH2O = −2.4 to 5.5 ‰, δD = −86 to −77 ‰) suggest an initially magmatic fluid which gradually evolved towards meteoric water during tin mineralization. 相似文献
19.
《Quaternary Science Reviews》2007,26(1-2):56-69
We describe the evolution of climate system dynamics by examining the climate response to changes in obliquity and precession over the last 5.3 Myr. In particular, we examine changes in the shape of glacial cycles and the power of obliquity and precession response in benthic δ18O. When the exponential trend in δ18O variance is removed, its spectral power exhibits strong, proportional responses to amplitude modulations in orbital forcing over most of the Plio–Pleistocene. Precession responses correlate with modulations in forcing for the last 5 Myr, but 41-kyr response is sensitive to obliquity modulation only before 1.4 Myr. Where responses are sensitive to modulations in forcing, we demonstrate that glacial cycles are orbitally forced rather than being self-sustained or paced by orbital changes. The shapes of glacial cycles have several nonlinear properties, which may be indicative of glacial–interglacial differences in climate sensitivity or response time. The “saw-tooth” asymmetry of glacial cycles first appears shortly after the onset of major northern hemisphere glaciation, and the relative duration of interglacial stages decreases at 1.4 Myr. Collectively, trends in the shape of glacial cycles and the sensitivity of δ18O to obliquity and precession are suggestive of major transitions in climate dynamics at approximately 2.5 and 1.4 Myr but show no significant change associated with the appearance of strong 100-kyr cycles during the mid-Pleistocene transition. 相似文献
20.
柴西西岔沟新近系磁组构特征对环境变化的响应 总被引：1，自引：0，他引：1
通过对柴达木盆地西部(简称柴西地区)的干柴沟背斜南西翼的西岔沟层型剖面进行系统测制和2～3 m等间隔磁性地层学、磁化率各向异性系统采样,并进行精确测量,利用在该区建立的高分辨率、高精度磁性地层年代资料,结合沉积学等研究,讨论了磁化率各向异性参数变化趋势对环境的指示,并揭示在约23～6.2 Ma期间环境演化经历了三个阶段:Ⅰ阶段(22.4～13.4 Ma)为湿润环境;Ⅱ阶段(13.4～8.2 Ma)为温干环境向干冷转型;Ⅲ阶段(8.2～6.2 Ma)气候转冷变干且变化更复杂。认为7.8 Ma以来气候转型及有规律的变化与现代季风形成有关。为青藏高原的隆升过程及其环境效应提供可靠资料。 相似文献