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1.
The Late Jurassic Kimmeridge Clay Formation (KCF) is an economically important, organic-rich source rock of Kimmeridgian–Early Tithonian age. The main rock types of the KCF in Dorset, UK, include grey to black laminated shale, marl, coccolithic limestone, and dolostone, which occur with an obvious cyclicity at astronomical timescales. In this study, we examine two high-resolution borehole records (Swanworth Quarry 1 and Metherhills 1) obtained as part of a Rapid Global Geological Events (RGGE) sediment drilling project. Datasets examined were total organic carbon (TOC), and borehole wall microconductivity by Formation Microscanner (FMS). Our intent is to assess the rhythmicity of the KCF with respect to the astronomical timescale, and to discuss the results with respect to other key Late Jurassic geological processes. Power spectra of the untuned data reveal a hierarchy of cycles throughout the KCF with ～ 167 m, ～ 40 m, 9.1 m, 3.8 m and 1.6 m wavelengths. Tuning the ～ 40 m cycles to the 405-kyr eccentricity cycle shows the presence of all the astronomical parameters: eccentricity, obliquity, and precession index. In particular, ～ 100-kyr and 405-kyr eccentricity cycles are strongly expressed in both records. The 405-kyr eccentricity cycle corresponds to relative sea-level changes inferred from sequence stratigraphy. Intervals with elevated TOC are associated with strong obliquity forcing. The 405-kyr-tuned duration of the lower KCF (Kimmeridgian Stage) is 3.47 Myr, and the upper KCF (early part of the Tithonian Stage, elegans to fittoni ammonite zones) is 3.32 Myr. Two other chronologies test the consistency of this age model by tuning ～ 8–10 m cycles to 100-kyr (short eccentricity), and ～ 3–5 m cycles to 36-kyr (Jurassic obliquity). The ‘obliquity-tuned’ chronology resolves an accumulation history for the KCF with a variation that strongly resembles that of Earth's orbital eccentricity predicted for 147.2 Ma to 153.8 Ma. There is evidence for significant non-deposition (up to 1 million years) in the lowermost KCF (baylei–mutabilis zones), which would indicate a Kimmeridgian/Oxfordian boundary age of 154.8 Ma. This absolute calibration allows assignment of precise numerical ages to zonal boundaries, sequence surfaces, and polarity chrons of the lower M-sequence.  相似文献   

2.
The foraminiferal δ 18O and δ 13C records for the past 5 Ma at ODP Site 1143 reveal the linear responses of the Plio-Pleistocene climatic changes in the southern South China Sea to orbital forcing at the obliquity and precession bands. The phase of the δ 18O variations with the orbital forcing is opposite to that of the δ 13C, which may be caused by the frequent El Niño events from the equatorial Pacific. The amplification of the Northern Hemisphere Ice Sheet at ñ3.3 Ma probably affected the development of the 100-ka climatic cycles. Its further spreading may spur the 100-ka climatic cycle to become the dominant cycle in the late Pleistocene. The “Mid- Pleistocene Transition” event has localized influence on the isotopic variations in the southern South China Sea. The foraminiferal δ 13C records for the past 5 Ma at Site 1143 are highly coherent with the orbital forcing at the long eccentricity band, and lead the δ 18O records at the shorter eccentricity band, highlighting the importance of the carbon cycle in the global climate change.  相似文献   

3.
The middle Miocene Valdearenas–Muduex section in the internally-drained, continental Madrid Basin (central Spain) is dated bio-magnetostratigraphically between 15.2 Ma and 11.5 Ma. The section contains two formation-scale, sedimentary sequences, that both consist of a siliciclastic lower part and a calcareous upper part. Siliciclastic sedimentation took place in distal floodplain and fluvial environments, while limestones resulted from carbonate precipitation in calcic soil profiles and in ephemeral lacustrine water bodies. Spectral analysis of the L* colour time series points to the influence of the ～ 405-kyr and 0.97-Myr eccentricity cycles, while the bases of the two calcareous intervals correlate to successive minima of the 2.4-Myr eccentricity cycle. The 405-kyr cycle lags maximum eccentricity, whereas the 0.97 and 2.4-Myr cycles lag minimum eccentricity, each by approximately a quarter of a cycle. No obliquity forcing is detected. The observed orbital configuration of 2.4-Myr minima at the base of limestone-dominated intervals is similar to a previously documented Late Miocene shift in the Teruel Basin of northeast Spain. Our results indicate that long-period eccentricity climate forcing may well be a significant player on long, tectonic time scales in continental basin fill.  相似文献   

4.
The Milankovi theory stresses that the summer insolation in the high northern latitudes that is dominated by the precession cycle controls the glacial/interglacial cycles in global climate change.If the climate system responds linearly to the external insolation forcing,the precession cycle of 23 or 19 ka should dominate the variations in the climatic proxy records.I performed spectral and evolutive cross spectral analyses on the high resolution benthic 18O and 13C records from the South China Sea and the North Atlantic,the proxies of global ice volume and ocean carbon reservoir respectively.I found that the obliquity instead of the eccentricity or the precession is the most marked cycle in the global ice volume and ocean carbon reservoir variations over the past 5 Ma.The analysis further reveals that only at the obliquity band instead of the eccentricity or the precession band does the global ice volume and ocean carbon reservoir display consistently high coherency and stable phase relationship over the past 5 Ma.The consistently positive or near-zero phases of the benthic 18O relative to the benthic13C at the obliquity band suggest that the global carbon cycle is involved in the polar ice sheet growth as an important internal feedback,not a determinative driving factor.The obliquity instead of the precession or the eccentricity takes the dominant role of driving the global climate change during the Pliocene and Pleistocene.  相似文献   

5.
The loess–paleosol sequences of China, Siberia, Alaska and many other regions, along with lake sediments and glaciers, provide the only accurate paleoclimatic terrestrial records for intervals of thousands to hundreds of thousand years. The frequency dependence (FD) of magnetic susceptibility (MS) in such sequences has become the leading parameter for analyzing climatic change and Milankovitch (astronomical) periodicity in Siberian sequences; it is always higher in soil horizons than in loess. The enhanced FD parameter in soils is associated with ferromagnetic minerals, mostly magnetite, produced during pedogenesis. The MS and FD parameters of 670 samples from five sections in Siberia are reported here. Inter-section correlation is used to produce a combined FD time series for the studied sections. Chronological control is established by absolute dating and stratigraphic correlation. Spectral analysis of the FD time series reveals the presence of Milankovitch signals at ～100 kyr (eccentricity), ～40 kyr (obliquity) and ～23 kyr (precession) and demonstrates that Siberian loess–paleosol sequences are excellent continental recorders of long-term paleoclimatic changes. This suggests that the FD parameter can potentially be used more widely for evaluation of climate periodicity in loess/paleosol sequences in other parts of the world.  相似文献   

6.
The variations of the Earth’s geometry (ETP) pre-dominate climate changes such as monsoon on the Earth[1], serving as its external forcing. The loess/ paleosol sequence in Central China provides a good record of terrestrial deposition to study the evolution of the east Asian monsoon[2―4]. However, the deep sea deposition, due to its high resolution dating and abun-dant climate proxies, should be able to provide more climatic information in the geological time, such as the forcing mechanis…  相似文献   

7.
A mutual climatic range method is applied to the Mediterranean marine pollen record of Semaforo (Vrica section, Calabria, Italy) covering the period from ∼2.46 Ma to ∼2.11 Ma. The method yields detailed information on summer, annual and winter temperatures and on precipitation during the nine obliquity and precession-controlled ‘glacial’ periods (marine isotope stages 96 to 80) and eight ‘interglacial’ periods (marine isotope stages 95 to 81) characterising this time interval. The reconstruction reveals higher temperatures of at least 2.8 °C in mean annual and 2.2 °C in winter temperatures, and 500 mm in precipitation during the ‘interglacials’ as compared to the present-day climate in the study area. During the ‘glacials’, temperatures are generally lower as compared to the present-day climate in the region, but precipitation is equivalent. Along the consecutive ‘interglacials’, a trend toward a reduction in annual and winter temperatures by more than 2.3 °C, and toward a higher seasonality is observed. Along the consecutive ‘glacials’, a trend toward a strong reduction in all temperature parameters of at least 1.6 °C is reconstructed. Climatic amplitudes of ‘interglacial–glacial’ transitions increase from the older to the younger cycles for summer and annual temperatures. The cross-spectral analyses suggest obliquity related warm/humid–cold/dry ‘interglacial–glacial’ cycles which are superimposed by precession related warm/dry– cold/humid cycles. A time displacement in the development of temperatures and precipitation is indicated for the obliquity band by temperatures generally leading precipitation change at ∼4 kyr, and on the precession band of ∼9.6 kyr in maximum.  相似文献   

8.
It is apparent that there are three periods in various Quaternary paleoclimate records, the pe-riod of the Earth抯 orbital eccentricity cycles, ~100 ka, the period of the Earth抯 obliquity cycles, 41 ka, and the periods of the precession cycles, 23 ka and…  相似文献   

9.
The Marathousa Member, Middle Pleistocene strata in the fluvio-lacustrine Megalopolis basin, southwest Greece, displays distinct but complicated lithological cycles comprising first-order alternation of lignites and detrital muds and second-order alternation expressed by frequent intercalation of organic layers. Palynological evidence indicates that the lithological cycles are driven by the Earth’s orbital forcing. All the lignite seams yield temperate oak forest whereas the detrital beds provide semi-arid steppe mainly of Artemisia. This means that the first-order lithological cycle represents the glacial/interglacial cycle (i.e., the 100-kyr eccentricity cycle), providing a timescale of at least 350 kyr to the Marathousa Member. Pollen also detects smaller-scale climate fluctuations in many of the subordinate organic layers, with the total number of fluctuations being five in a complete lignite-detritus couplet. This means that the second-order lithological cycle reflects the 21-kyr insolation cycle. A tentative phase relation between the lithological cycles and the astronomical cycles is shown based on palynostratigraphy and electron spin resonance dating. Lacustrine environments with increased water tables are implied for the glacial periods sedimentologically, in contrast to local swamp vegetation for the interglacial periods. The subordinate organic layers were formed under intermediate environments (climate, water depth, etc.) between full glacials and interglacials.  相似文献   

10.
The loess record in southern Tajikistan and correlation with Chinese loess   总被引：12，自引：0，他引：12  
In the present study, the Chashmanigar loess–soil sequence in southern Tajikistan is studied; this loess section has a paleomagnetic basal age of about 1.77 Myr. Magnetic susceptibility, color reflectance and grain size were systematically measured for closely spaced samples from the section. Paleosols consistently have a finer grain size distribution, higher magnetic susceptibility, redder color reflectance and lower dust sedimentation rate than loess horizons, suggesting a colder, drier and dustier environment during glacial periods than in interglacial periods. The grain size record was tuned to variations in obliquity and precession of the Earth’s orbit. The resulting magnetic susceptibility, grain size and color reflectance time series all show well-expressed astronomical periodicities during the Pleistocene. The mid-Pleistocene climate transition, characterized by a shift of dominant climatic periods from 41 kyr to 100 kyr at about 1.0–0.8 Myr, is clearly documented in these proxy records. Comparison of the Chashmanigar loess record with the Lingtai loess section in China and the ODP site 677 δ18O record shows that during the entire Pleistocene, the climate cycles recorded by the Central Asian loess can be well correlated to the Chinese loess and deep-sea oxygen isotope records. It is suggested that alternations of loess and soil horizons both in Central Asia and China could be basically forced by global ice volume variations, although different wind systems have controlled the Pleistocene loess transport and sedimentation in the two areas.  相似文献   

11.
One of the most striking features of the Quaternary paleoclimate records remains the so-called 100-kyr cycle which is undoubtedly linked to the future of our climate. Such a 100-kyr cycle is indeed characterised by long glacial periods followed by a short-interglacial (10–15 kyr long). As we are now in an interglacial, the Holocene, the previous one (the Eemian, which corresponds quite well to Marine Isotope Stage 5e, peaking at 125 kyr before present, BP) was assumed to be a good analogue for our present-day climate. In addition, as the Holocene is 10 kyr long, paleoclimatologists were naturally inclined to predict that we are quite close to the next ice age. Simulations using the 2-D climate model of Louvain-la-Neuve show, however, that the current interglacial will most probably last much longer than any previous ones. It is suggested here that this is related to the shape of the Earth's orbit around the Sun, which will be almost circular over the next tens of thousands of years. As this is primarily related to the 400-kyr cycle of eccentricity, the best and closest analogue for such a forcing is definitely Marine Isotopic Stage 11 (MIS-11), some 400 kyr ago, not MIS-5e. Because the CO2 concentration in the atmosphere also plays an important role in shaping long-term climatic variations – especially its phase with respect to insolation – a detailed reconstruction of this previous interglacial from deep sea and ice records is urgently needed. Such a study is particularly important in the context of the already exceptional present-day CO2 concentrations (unprecedented over the past million years) and, even more so, because of even larger values predicted to occur during the 21st century due to human activities.  相似文献   

12.
Our understanding of the chronological sequence of Pleistocene land mammal faunas (including hominids) preserved in caves and fissures in the karstic terrain of subtropical southern China has been greatly impeded by the discontinuous nature of the strata yielding the fossils. A contributory issue is the lack of suitable elements for numerical dating, especially for the Early Pleistocene cave sediments. Here we present new magnetostratigraphic dating results for five cave sedimentary sequences in the Bubing Basin, Guangxi Zhuang Autonomous Region, which contain the typical Pleistocene Gigantopithecus fauna and Ailuropoda–Stegodon fauna of southern China. The five karstic caves are situated at elevations ranging from 252 m to 191 m above sea level. The integrated dating results reveal that the five cave sedimentary sequences span an age range from the late Gauss normal Chron to the early Brunhes normal Chron. The faunas are assigned to >2.6 Ma (Mohui–houshan Cave), 1.95–1.78 Ma (Mohui Cave), 0.99–0.78 Ma (Baolai Cave) and ∼0.7 Ma (Upper Wuyun and Ganxian Caves). Furthermore, by combining our new magnetostratigraphy work with previously published magnetostratigraphic, U–series and electron spin resonance dating results, a chronological sequence of the Plio–Pleistocene mammalian faunas from cave sites in southern China has been established. The chronological sequence contributes to an improved understanding of the evolutionary processes of Plio–Pleistocene land mammals, as well as of early humans in subtropical southern China.  相似文献   

13.
The magnetostratigraphy of a 54-m-long section above the Cretaceous-Tertiary boundary at the sea-cliff section of Zumaia in the Basque basin (northern Spain) has been established. The section encompasses the entire Danian and the lower part of the Selandian stages as indicated by calcareous plankton biostratigraphy. The studied interval consists of (hemi)pelagic limestone-marl alternations in the form of couplets and bundles, which range from centimetre/decimetre to metre scale respectively and a few thin-bedded calcareous turbidites. The magnetostratigraphy, based on samples from about 200 stratigraphic levels, allows the identification of six reversal boundaries from chron C29r to C26r at a bed level. The spatial (or temporal) evolution of periodicities from a lithologically coded series is studied with the continuous wavelet transform technique. A preliminary age model based on the standard CK95 GPTS indicates that the basic lithologic carbonate-marl couplet corresponds to the 19-23-kyr precession cycle (21-31-cm cycle in the depth domain) and that a bundle cycle (usually groups of four to six basic couplets) with global periodicity centred at 1.22 m corresponds to the ∼110-kyr eccentricity cycle. We have tuned the bundle cycles to the Va03_R7 eccentricity orbital solution [Astrophys. J. 592 (2003) 620-630] following an initial match of a node of the ∼2.4-Ma eccentricity modulatory cycle in the target time series to particularly carbonate-rich bundles from the upper part of the Zumaia section that displays significant power of a 4.4-m-period cycle corresponding to the ∼404-kyr eccentricity cycle. Consistency between lithologic patterns and characteristics in the eccentricity target is reasonably met although the ∼404-kyr eccentricity cycle is not persistent throughout. The tuning, however, appears robust as it brings the age of the K/T boundary at ∼65.8 Ma. It is argued that a sea-level signal (tectonically driven?) is superimposed on the climatic forcing at the Milankovitch band masking the full expression of the low-frequency astronomical periods. We provide a cycle-tuned duration for all intervening Early Palaeocene polarity chrons and estimate relative ages for bioevents. The cycle-tuned chronology indicates that the CK95 GPTS overestimates the duration of chrons C28 and C27 by 20 and 26% respectively. Our data may prove useful to better constrain Early Palaeocene biostratigraphy of calcareous plankton and in the redefinition of the boundary between the Danian and Selandian stages.  相似文献   

14.
The Induan sequence in the West Pingdingshan Section, Chaohu, Anhui Province, displays a series of superimposed mudstone/limestone cycles. The lithological character of the cycles, combined with power spectral and wavelet analysis of magnetic susceptibility readings, reveals 12 short eccentricity and 56 precession Milankovitch cycles - obliquity cycles are not apparent. The uniformity of cycle thicknesses indicates a stable depositional setting making this section ideal to perform various geo-logical studies. Accordingly, the Induan Stage is estimated to have lasted 1.1 Ma, and the depositional rate for this part of the section is about 3.7 cm/ka. This places the Induan-Olenekian boundary in the West Pingdingshan Section at about 251.5 Ma based on an age of 252.6 Ma for the Permian-Triassic boundary.  相似文献   

15.
In the later part of the Pleistocene, variations in global ice volume have been dominated by an approximate 100,000-year cycle. Analysis of 2-Myr-long oxygen isotope record from an equatorial Pacific core indicates that this is true only for the last 900,000 years. Prior to this time the amplitude of the 100,000-year cycle is much reduced, as is the variance of all oscillations with periods greater than 60,000 years. Based on results of time series analysis of this 2-Myr-long record, the Pleistocene glacial cycles can be divided into three sections: (1) the late Pleistocene (0–900 kyr B.P.) where the variations in the isotope record are dominated by the 100,000-year cycle; (2) the middle Pleistocene (900–1450 kyr B.P.) in which low-frequency components are not as important as in the later period of the Pleistocene, and (3) the early Pleistocene/late Pliocene (1450–2000 kyr B.P.) where general reductions of importance at all frequencies is seen as compared to the later intervals. Recent modeling efforts which describe variations in global ice volume show that the dominant low-frequency component observed in the late Pleistocene can result from different time constants for the rate of glacial growth and decay in response to variations in the Earth's orbital parameters. It is hypothesized that during the early Pleistocene the rate of growth and decay of glaciers were more similar and that continental erosion by successive glacial advances lowered the land surface in areas of ice-cap formation to below sea level. When the ice caps became marine-based, more rapid decay of the ice became possible.  相似文献   

16.
天文气候学10万年问题的研究   总被引：8，自引：1，他引：7       下载免费PDF全文
为了研究第四纪晚更新世(约100万年前到2万年前)古气候的周期变化以及在轨道尺度上气候系统对太阳辐射的响应,本文发展了适合于非线性非平稳数据的分析方法即经验模态分解(EMD),对太阳辐射古气候记录进行了分析,进而重新认识了地球轨道周期变化影响下的太阳辐射的气候意义.研究结果表明,太阳辐射中偏心率的影响是相当大的,而不是以前认为的不到1%的影响,至少它是和太阳辐射的黄赤交角,岁差波段的信号是可以相比拟的.  相似文献   

17.
柴达木盆地东部三湖地区四系米兰柯维奇旋回分析   总被引：6，自引：4，他引：2       下载免费PDF全文
自然伽马曲线包含丰富的地质信息,能够很好地反映由气候变化引起的地层旋回.本文采用频谱分析对柴达木盆地三湖地区第四系自然伽马测井曲线进行了系统分析.作为频谱分析方法之一的快速傅里叶变换能够将自然伽马曲线从时间（深度）域转换为频率域,然后分析每一个峰值频率的波长及其相互之间的比率关系,寻找那些波长比率与米兰柯维奇周期比率相同或相似的频率,从而捕获高频旋回信息.研究结果表明第四系地层中很好地保存了高频的米兰柯维奇旋回,这样的沉积旋回主要由地球轨道的周期性变化而导致的古气候变化引起的.偏心率周期引起的地层旋回厚度变化范围在92.00~115.00 m之间,黄赤交角引起的地层旋回厚度变化范围在24.55~63.43 m之间,岁差引起的地层旋回厚度变化范围在16.8~26.35 m之间.黄赤交角和岁差是影响该区米兰柯维奇旋回的主要因素,其中岁差的影响最大,而偏心率的影响最小.  相似文献   

18.
Challenges and pitfalls for developing age models for long lacustrine sedimentary records are discussed and a comparison is made between radiocarbon dating, visual curve matching, and frequency analysis in the depth domain in combination with cyclostratigraphy. A core section of the high resolution 284-ka long temperature record developed from Lake Fúquene in the Northern Andes is used to explore four different age models (a–d). (a) A model based on 46 AMS 14C dates of bulk sediment is hampered by low concentrations of organic carbon. (b) A model based on the comparison of the radiocarbon dated pollen record to the well-established record from Cariaco Basin using curve matching and visual tie points. For the upper 26 m of the core this approach yields an age interval of 28–59.5 ka. (c) Another age model is based on curve matching and the Intcal09 radiocarbon calibration curve, yielding an age range of 22.5–80.4 ka for the same core interval. (d) Finally, a model is developed based on spectral analysis in the depth domain of the temperature-related altitudinal migrations of the upper forest line. This method identifies periodicities without a pre-conceived idea of age. The main frequency of 9.07 m appears to reflect the 41-kyr orbital signal of obliquity, which is tuned to the filtered 41-kyr temperature signal from the well-constrained LR04 marine benthic ∂18O stack record (Lisiecki and Raymo, 2005). Using this last age-modelling approach, the upper 26 m of core Fq-9C yields a temporal interval of 27–133 ka. Problems arising from radiocarbon dating carbon poor sediments from a large lake are addressed and the visual curve matching approach is compared to the analysis of cyclic changes in sediment records in developing an age model. We conclude that the frequency analysis and cyclostratigraphy model is the most reliable one of the four approaches. These results show that cyclostratigraphy may provide a useful method for developing an age model for long terrestrial records including multiple orbital cycles.  相似文献   

19.
During the Mesozoic (250–64 Ma) intervals of about 0.5 Myr were subject to severe environmental changes, including high sea-surface temperature and very low oxygen content of marine water. These Oceanic Anoxic Events, or OAEs, occurred simultaneously with profound disturbance to the carbon cycle. The carbon-isotope anomaly in the Early Jurassic that marks the Toarcian Oceanic Anoxic Event (T-OAE) at ~ 182 Ma is characterized in marine sections by a series of dramatic steps towards lighter values. Herein we present new carbon-isotope data from terrestrial organic matter (phytoclast separates), collected through a Late Pliensbachian–Middle Toarcian coastal and marginal marine succession in the Polish Basin, a setting where hinterland climate and sea-level change are well recorded. The results show that the shift to light carbon-isotope values in the woody organic matter, and therefore also in atmospheric carbon dioxide, similarly occurred in major steps. The steps are here correlated with those identified from marine organic matter, where they have previously been attributed to 100 kyr eccentricity forcing of climate. The results provide strong support for orbitally and climatically controlled release of isotopically light carbon from gas hydrates into the ocean–atmosphere system in a series of rapid bursts. Additionally, a link between the carbon-isotope steps and shoreline movements can be demonstrated. Individual peaks of the negative excursion are mostly associated with facies indicative of sea-level rise (flooding surfaces). However, at the same time inferred higher atmospheric carbon-dioxide content may be expected to have resulted in increased rainfall and temperature, leading to accelerated weathering and erosion, and consequently increased sediment supply, progradation and regression, causing some mismatches between isotope shifts and inferred sea-level changes. Enhanced abundance of megaspores derived from hydrophilic plant groups, and marked increase in kaolinite, are coincident with the overall development of the negative isotope excursion. The combined data suggest that each 100-kyr cycle in carbon-isotope values was characterized by increasingly severe palaeoclimatic change, culminating in extremely hot and humid conditions co-incident with the peak of the final most negative carbon-isotope excursion. The chemostratigraphic correlation allows very precise dating of the Late Pliensbachian–Middle Toarcian coastal and marginal marine sedimentary succession in the Polish Basin.  相似文献   

20.
A much improved high-resolution magnetostratigraphy is presented for the interval between 8.5 and 12.5 Ma in the deep marine astronomically tuned Monte dei Corvi Beach section in northern Italy. This section contains the formally designated boundary between the Middle and Upper Miocene defined by the Tortonian GSSP. The natural remanent magnetization is carried by an unusual low-temperature component of primary origin. According to interpretations of isothermal remanent magnetization (IRM) acquisition curves, the palaeomagnetic signal is most probably carried by iron sulphides, such as greigite or pyrrhotite. The resultant magnetostratigraphy is reliable and can be straightforwardly calibrated to the Astronomically Tuned Neogene Time Scale (ATNTS2004) showing that the section ranges from Chron C5An.2n up to C4.2r-1. The inferred correlation of the Tortonian GSSP to the older part of Chron C5r.2n is confirmed, thereby guaranteeing global correlation potential. In addition, the Monte dei Corvi Beach section has been re-tuned to the new numerical solution La2004 for the interval between 8.5 and 12.9 Ma. This exercise shows that the characteristic cycle patterns are not consistent with a single solution with fixed values for dynamical ellipticity and tidal dissipation. For the younger part of the section, sedimentary cycles show an excellent fit with intricate details of precession/obliquity interference in the nominal La2004(1,1) solution. However, this solution produces serious mismatches between the sedimentary cycles and the precession/obliquity interference in the interval older than ∼ 10.2 Ma. For this interval changes in tidal dissipation value (while keeping dynamical ellipticity constant at its present-day value) are necessary to maintain a perfect fit. A detailed visual comparison reveals a very good to excellent fit with La2004(1,1.2) and, to lesser extent, with La2004(1,0.5). However, La2004(1,1.2) is the preferred tuning target for the moment in the interval older than 10.2 Ma. The astronomical (re)tuning on precessional scale to La2004(1,1) yielded slightly different astronomical ages for each basic cycle and, hence, also for the calcareous plankton events and magnetic reversal boundaries with uncertainties ranging within a few thousand years. The age of the Tortonian GSSP turns into 11.625 Ma instead of the previously published 11.608 Ma. Our ages should replace existing ages in the Astronomically Tuned Neogene Time Scale (ATNTS2004).  相似文献   

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