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1.
Silvia N. Csari 《Gondwana Research》2007,11(4):529-536
Absolute radiometric data obtained recently in Upper Paleozoic basins of South America and Southern Africa are available to constrain the age of some palynological biozones defined in the Western Gondwana. Some dates obtained from Argentina coincide with southern Africa's and are useful to constrain the palynological associations. In this way, the Permian Argentinian Lueckisporites–Weylandites (LW) Biozone is compared with the Lueckisporites virkkiae Biozone of Brazil and Zone 3 of South Africa. On the other hand, the palynofloras from Dwyka (South Africa) are comparable with Argentinian and Brazilian associations recovered near the Carboniferous–Permian boundary. Tuffaceous intervals of the Dwyka Group in South Africa suggest the beginning of that sequence at 307 Ma reaching the 290 Ma at the top. The available palynological, paleoenvironmental and radiometric data from these three western Gondwanan areas are analyzed and compared. 相似文献
2.
The numerical age of the Albian/Cenomanian (A/C) boundary (=Early/Late Cretaceous Epoch boundary) has recently been updated using new radiometric dates from Hokkaido, Japan. Yet, an element of uncertainty still remains in the age scaling due to inaccurate chronostratigraphic contexts surrounding the tuff beds that have been geochronologically studied in the Oyubari and Soeushinai areas. To ensure stability in the Cretaceous time scale, this paper rigorously reevaluates the current status of Hokkaido A/C chronology, clarifying the limitations and making refinements via proper reintegration of published chronostratigraphic data. In the case of the Oyubari area, its A/C biostratigraphic scheme is limited by near-absence of ammonites and planktonic foraminifera at the Albian–Cenomanian transition, resulting in a large discrepancy in the proposed boundary levels based on these macro- and microfossil taxa. These problems can be solved by solid data integration aided by event- and δ13C-sratigraphy from the adjacent Ashibetsu area, wherein the A/C boundary is well documented by the superior planktonic foraminiferal record. Based on the resultant A/C boundary redefinition for the Oyubari area in conjunction with a simple linear interpolation from two published UPb ages, the A/C boundary age can be independently calibrated to be 100.8 Ma [with ±1.4 Myr uncertainty (=analytical precision)], which is consistent with that currently in use in the Geologic Time Scale 2012 (100.5 ± 0.4 Ma). In the case of the Soeushinai area, its chronostratigraphic framework is limited by rather complex geological structure and vertically/laterally variable lithologies. Moreover, the accuracy of geochronological data from this area is undermined by the fact that the dated tuff levels do not bracket the inferred A/C boundary. 相似文献
3.
山东济阳坳陷始新统-渐新统天文地层界线年龄分析 总被引：2，自引：2，他引：0
YAO Yi-min ) XU Dao-yi ) HAN Yan-ben ) YIN Zhi-qiang ) ZHANG Hai-feng ) ) Geological Scientific Research Institute of Shengli Oilfield Company SINOPEC Dongying ) Institute of Geology China Earthquake Administration Beijing ) National Astronomical Observatories Chinese Academy of Sciences Beijing 《地层学杂志》2007,(Z2)
山东济阳坳陷沙河街组上部天文地层研究是以牛38井沙三段中亚段顶界年龄34.892Ma作为标定,分析和计算出沙二段下亚段底年龄为33.799Ma、沙段二段上亚段底为33.338Ma、沙一段底为32.940Ma和东营组底为31.829Ma。从天文地层界线年龄分析,沙三段-沙二段界线的年龄大致可对比为"国际地层表(2004)"始新统-渐新统界线年龄33.90Ma,而沙二段下亚段-上亚段界线年龄比国际始新统-渐新统界线的滞后大约600ka。在"中国区域地层表"始新统-渐新统界线年龄(32Ma)和"国际地层表"的始新统-渐新统界线年龄(33.9Ma)之差的1.9Myr,大致相当于本区计算的沙一、二段的持续时间。SP数据的小波分析表明,在沙二段-沙三上亚段界线附近,即约33.8Ma之后,约405ka周期开始变得不明显、不规则,幅度亦下降,剧烈突变发生时间在33.4Ma左右。上述界线对应偏心率周期的理论值突变的时间。因此推论始新世-渐新世转折期是偏心率多个理论周期重迭而导致的一个特殊的时期,也是本区沙二段下亚段这段地层形成不整合面的时间,大约在33.8—33.4Ma期间。 相似文献
4.
富饶阶地表地层剖面 总被引：11，自引：5，他引：6
黑龙江省嘉荫县乌云镇地区中生代结束前后连续沉积了两套含煤地层,即上部的古新统乌云组和下部的马斯特里赫特阶富饶组。富饶阶相当于富饶组上段地层,但由于其代表剖面顶、底不全,且可参照的钻孔岩心已不复存在,因此有必要在原命名地区寻找新的地表露头剖面。乌云镇西北白头山黑龙江沿岸出露富饶阶上部地层,其上部含有丰富的孢粉化石,自下而上初步确定了两个孢粉组合:杉粉(Taxodiaceaepollenites)-红杉粉(Sequoiapol-lenites)孢粉组合和鹰粉(Aquilapollenites)-肋桦粉(Betulaepollenites)孢粉组合。这两个孢粉组合都有鹰粉类(Aquilapollis)化石,计有5属10多种化石,其中除了小刺鹰粉(Aquilapollenites spinulosus)一种可由上白垩统上延入古近系下部地层外,其他多数出现在环太平洋的上白垩统最上部地层中(马斯特里赫特阶)。由于富饶组下段相当于明水阶(马斯特里赫特阶中、下部),因而富饶组上段,即富饶阶,相当于马斯特里赫特阶的上部。对该剖面下部的流纹质晶屑沉凝灰岩采样进行SHRIMP锆石U-Pb法测年,定年结果为66±1Ma,与上述孢粉生物地层学结论相吻合。由此可以推测白垩系-古近系界线似在乌云组与富饶组之间,即厚层含砾砂岩的底部,但需进一步证实。 相似文献
5.
Previous palaeomagnetic results from Tertiary volcanic rocks of Sardinia suggest that the island underwent a quick counterclockwise rotation between 20.5 and 19 Ma. In order to test this hypothesis, a new palaeomagnetic study was carried out on sediments and volcanic rocks with well-controlled biostratigraphic or radiometric ages younger than the suggested age for the end of the rotation.
Unrotated palaeomagnetic directions obtained from the Upper Ignimbrites (radiometric age: 18.5–19.7 Myr) and the Aquitanian tuffs collected in the Anglona region (N Sardinia) would suggest that the rotation ended earlier than 20.5 Myr. The directions found in the volcanics are perhaps the result of secular variation, rather than differential rotation of the Anglona region with respect to surrounding regions.
Two sites belonging to the upper ignimbritic unit (SI2 ) in the Monte Traessu-Monte Rispisu area (Logudoro region) exhibited a large amount of rotation ( D =320.4°, I =60°) which may be age related (radiometric age: 19.9 Myr). Four dikes (radiometric age: 18.3–16.7 Myr) in the Arcuentu volcanic complex (Arburese region) yield results ( D =348.4°, I =33.8°) that indicate a further amount of rotation after their emplacement.
Stable end-point directions were successfully isolated from three Upper Burdigalian/Langhian sedimentary sites (biostratigraphic age: 18–15Ma) from the Marmilla and Logudoro regions. Consistent paleomagnetic directions obtained from these sites ( D =352°, I =49°) indicate that a small amount of rotation was still to be completed in the Langhian time. This result is consistent with the history of Sardinian volcanism, which did not end until 13 Ma. 相似文献
Unrotated palaeomagnetic directions obtained from the Upper Ignimbrites (radiometric age: 18.5–19.7 Myr) and the Aquitanian tuffs collected in the Anglona region (N Sardinia) would suggest that the rotation ended earlier than 20.5 Myr. The directions found in the volcanics are perhaps the result of secular variation, rather than differential rotation of the Anglona region with respect to surrounding regions.
Two sites belonging to the upper ignimbritic unit (SI
Stable end-point directions were successfully isolated from three Upper Burdigalian/Langhian sedimentary sites (biostratigraphic age: 18–15Ma) from the Marmilla and Logudoro regions. Consistent paleomagnetic directions obtained from these sites ( D =352°, I =49°) indicate that a small amount of rotation was still to be completed in the Langhian time. This result is consistent with the history of Sardinian volcanism, which did not end until 13 Ma. 相似文献
6.
《Geodinamica Acta》2013,26(3-4):239-253
The precise ages of the sedimentary successions within two prominent NE-SW-trending basins, the Gördes Basin and the Selendi Basin, are critical to an understanding of the Neogene evolutionary setting of western Turkey and associated calc-alkaline magmatism. Early radiometric dating was not always sufficiently precise to resolve alternative interpretations. During this study, high-precision Ar40-Ar39 radiometric ages were determined on single crystals of biotite and sanidine from silicic tuffs and associated intrusive rocks. Finegrained tuffaceous sediments near the top of the sedimentary succession in the Selendi Basin gave ages of 18.89 ± 0.58 Ma to 16.42 ± 0.09 Ma. Coarser-grained tuffaceous sediments near the top of the equivalent sedimentary succession in the Gördes Basin to the NW yielded ages of 18.78 ± 0.3 Ma to 17.04 ± 0.35 Ma. Associated intrusive rocks were dated at 20.86 ± 0.08 Ma to 17.62 ± 0.07 Ma. An andesitic body on the northern margin of the Gediz (Ala?ehir) Graben further south gave ages of 16.08 ± 10.91 to 14.65 ± 0.06 Ma. Combined with published radiometric age data, these new results confirm an Early Miocene age for the clastic sedimentary fills of the Gördes and Selendi basins. The results from the Gediz Graben are consistent with its formation in Early Miocene time, earlier than the Late Miocene or Plio-Quaternary ages suggested in some interpretations. 相似文献
7.
Ammonite-based biostratigraphic schemes for the Lower Cretaceous are fairly well refined across the world, from the standard zonation in the West Mediterranean province to the Boreal and Austral provinces in the northern and southern hemispheres, respectively. However, the lack of radioisotopic ages associated to the fossil-rich, Lower Cretaceous marine successions has hindered the accurate establishment of the numerical ages for the lower boundaries of its several stages (from Berriasian to Albian). Geochronological dating by U–Pb SHRIMP of a tuff layer that occurs within beds belonging to the Holcoptychites neuquensis Zone in the Pilmatué Member of the Agrio Formation in the Austral province (Neuquén Basin, Argentina) has resulted in an absolute age of 130.0 ± 0.6 Ma (2 sigma internal errors only) or 130.0 ± 0.8 Ma (including calibration and decay constant uncertainties). This age is interpreted to represent the time of eruption and thus the timing of the pyroclastic deposit. The H. neuquensis Zone is the equivalent of the A. radiatus Zone in the West Mediterranean province. Therefore, the obtained age is the first numerical data that could help constrain the Hauterivian lower boundary. Indeed, there is reasonable agreement with the latest proposed lower boundary of the Hauterivian at ∼132.9 Ma. On the other hand, the duration recently established for this stage would be hard to reconcile with the stratigraphic record of the entire Hauterivian in the study region (northeastern Neuquén Basin). Therefore, the results of this contribution could also help to assess the extent of the Hauterivian and associated stages. 相似文献
8.
Ulf Linnemann Maria Ovtcharova Urs Schaltegger Andreas Grtner Michael Hautmann Gerd Geyer Patricia Vickers‐Rich Tom Rich Birgit Plessen Mandy Hofmann Johannes Zieger Rita Krause Les Kriesfeld Jeff Smith 《地学学报》2019,31(1):49-58
The replacement of the late Precambrian Ediacaran biota by morphologically disparate animals at the beginning of the Phanerozoic was a key event in the history of life on Earth, the mechanisms and the time‐scales of which are not entirely understood. A composite section in Namibia providing biostratigraphic and chemostratigraphic data bracketed by radiometric dating constrains the Ediacaran–Cambrian boundary to 538.6–538.8 Ma, more than 2 Ma younger than previously assumed. The U–Pb‐CA‐ID TIMS zircon ages demonstrate an ultrashort time frame for the LAD of the Ediacaran biota to the FAD of a complex, burrowing Phanerozoic biota represented by trace fossils to a 410 ka time window of 538.99 ± 0.21 Ma to 538.58 ± 0.19 Ma. The extremely short duration of the faunal transition from Ediacaran to Cambrian biota within less than 410 ka supports models of ecological cascades that followed the evolutionary breakthrough of increased mobility at the beginning of the Phanerozoic. 相似文献
9.
利用激光剥蚀电感耦合等离子质谱(LA-ICP-MS)对三峡地区二叠系茅口组牙形石的U-Th-Pb同位素年龄进行测定。结果表明该地层中牙形石的208Pb/232Th放射年龄为269±44,Ma,207Pb/235U放射年龄为256±39,Ma,接近二叠系茅口组的生物地层年龄。206Pb/238U的年龄为196±6,Ma,虽然准确度较高,但与前人推测的地层年龄相比偏低。此外,作者对牙形石的稀土元素(REE)组成进行了分析,并且发现牙形石的REE组成和Ce异常与古海水氧化还原条件有一定的相关性,可以指示古海水的信息。 相似文献
10.
四川盆地东部海相下—中三叠统界线的锶同位素年龄标定 总被引：5，自引：0，他引：5
中国西南地区海相下—中三叠统以火山碎屑岩为其直观界线,该年龄的标定可为区域地层年表和国际地层委员会全球标准年表研究提供重要的下—中三叠统界线年龄参考值.基于此,本文测试了四川盆地东部华蓥山下—中三叠统界线火山碎屑岩附近的石膏和硬石膏样品87Sr/86Sr比值,以及相应的Si、Ca、Mg、Mn、Sr以及SO42-的含量,根据锶同位素地层学的原理,尝试对下—中三叠统界线进行了年龄标定;同时评估了样品的成岩蚀变性、对海水信息的代表性以及年龄标定结果的可靠性.火山碎屑岩附近5个样品的87Sr/86Sr比值变化在0.708243~0.708391之间,标定的年龄值在240.5~242.5Ma的范围内,2个紧靠火山碎屑岩样品的年龄值在242Ma左右(分别为241.9Ma和242.5Ma),从而为华南地区以火山碎屑岩作为海相下—中三叠统界线的合理性提供了重要的化学地层学依据,也为全球下—中三叠统界线提供了一个新的年龄值. 相似文献
11.
Multiple provenance of detrital zircons from the Permian–Triassic boundary in the Bükk Mts., Hungary
Norbert Zajzon Zsófia Szabó Tamás Gábor Weiszburg Teresa Elizabeth Jeffries 《International Journal of Earth Sciences》2011,100(1):125-138
Detailed zircon analyses were carried out on samples from the Bálvány North section, which contains the Permian–Triassic boundary.
A fine-grained sandstone bed within the “boundary shale” contains a significant amount of zircon crystals. Pupin morphological,
scanning electron microscopy [secondary electron, back-scattered electron, cathodoluminescence (CL)] and laser ablation inductively
coupled mass spectrometry (LA-ICP-MS) investigations were done in selected single grains to combine morphological information
with radiometric ages, and infer the provenance of zircons. Three populations are distinguished on the basis of Pupin morphology.
Their centres of gravity are S17, S2 and P1. The LA-ICP-MS radiometric ages reveal three main age groups and a smaller one,
apart from a few scattered old ages. The largest group, comprising ca. 50% of the measured grains, has an age of 470–440 Ma.
The two other main groups, which together represent ca. 25% of the measured grains, are around 280 and 600 Ma. The 280 Ma
group contains slightly more grains than the 600 Ma group. A small group has an age of 370–340 Ma. In addition, there are
some older grains with ages of 850, 969, 1,050 and 2,150 Ma. Based on the zircon morphology no clear separation of the different
age groups could be made. Both the 280 Ma and the 470–440 Ma age groups tend to show zircon crystals derived from three types
of sources: crustal granites, calc-alkaline granitoids and alkali granites and/or their volcanic equivalents. Zircons in the
450 Ma group have a magmatic rim around their altered, relict core, as revealed by CL images. Post-magmatic processes also
affected the rim. The age of the core is possibly reset during the formation of the magmatic rim. This suggestion is supported
by the LA-ICP-MS data, because no difference was seen between the core and the rim. The different roundness of the zircons,
the well-sorted crystals and the at least five different source rocks indicate previous concentration of the grains, before
their transportation into the “boundary shale”. Austroalpine and Southern Alpine rocks could be the sources of the zircon
crystals, which fit well into the paleogeographical model of the area, which suggests that the Bükk Mts. was located in the
foreground of the Alpine units. 相似文献
12.
YAO Yi-min ) XU Dao-yi ) ZHANG Hai-feng ) HAN Yan-ben ) ZHANG Shou-peng ) YIN Zhi-qiang ) HE Qing-fang ) BIAN Xue-mei ) ) Geological Scientific Research Institute of Shengli Oilfield Company SINOPEC Dongying ) Institute of Geology China Earthquake Administration Beijing ) National Astronomical Observatories Chinese Academy of Sciences Beijing 《地层学杂志》2007,(Z2)
东辛2-4井钻取岩芯0—530.1m,明化镇组上段的上亚段至平原组划分为18个层,其中,下更新统平原组一段(简称平一段)的底作为第四系下界;同时进行了古地磁研究,测定出布容、松山、高斯和吉尔伯特等4个极性时。由于天文地层研究的需要,对90年代古地磁的年龄与"国际地层表"(2004)对比,作了相应调整,确定井深242.5m处的年龄为781ka,274.5m处的为2581ka,452.0m处的为3596ka和529.5m处的为4493ka,井深242.5m和452.0m这两个界线的年龄值作为天文地层计时的标定。研究大致分为两步:①以磁化强度(MI)数值曲线的频谱和小波分析,选定平原组一段102.4m周期和明化镇组上段68.36m周期分别对应于天文偏心率404ka旋回,求出了堆积速率为0.1584mm/a和0.1692mm/a及其他各层位的年龄:井深274.5m处上新统明上(上)亚段顶界的年龄为2546ka,平一段底界的年龄是970ka,不整合的延续时间大约为1.6Myr。②推测明上(上)亚段顶2546—1806ka期间可能沉积了129m地层;而在1806—908ka期间,由于构造活动上升,把原沉积又剥蚀掉了,形成井深274.5m处的一个大的不整合面,对储层孔隙的扩张和压实有重要影响,成为最后二次烃源物质的卸载和封堵。 相似文献
13.
Stephan Königer Volker Lorenz Harald Stollhofen Richard A. Armstrong 《International Journal of Earth Sciences》2002,91(2):341-356
Thin, widespread, fallout tuff layers interbedded within fluvio-lacustrine successions of the Carboniferous-Permian Saar-Nahe Basin provide important tephrostratigraphic markers. In addition, radiogeochronometric data derived from the tuffs serve as calibration points for the adjustment to regional chronostratigraphy and to numerical time scales. The Pappelberg-Tuff in the Meisenheim Formation (Glan Group) has been dated by U/Pb zircon SHRIMP technique at 297.0Dž.2 Ma. Taking the Carboniferous/Permian boundary at 296 Ma, the Meisenheim Formation coincides approximately with this boundary. Consequently, underlying strata, lithostratigraphically regarded as the basal part of the 'Rotliegend', chronostratigraphically belong to the Upper Carboniferous. Bed thicknesses, grain size and sorting characteristics of the tuffs and the absence of contemporaneously emplaced volcanics within the Saar-Nahe Basin point to an extrabasinal derivation of the wind-drifted volcanic ash. Decreasing grain sizes of juvenile pyroclastic particles towards the north suggest source areas south of the basin within 300 km distance. The majority of the tuffs are rhyolitic to rhyodacitic and indicate petrographic and geochemical affinities to Moldanubian S-type granitoids, in particular to highly differentiated two-mica granites, and related volcanic effusives. Within the time frame considered here, such potential source rocks were emplaced in the northern and central Black Forest (SW Germany) and the northern Vosges (E France) at 100-150 km distance south of the Saar-Nahe Basin. 相似文献
14.
兰中伍 《沉积与特提斯地质》2023,43(1):180-187
华南南华系对应于国际上的成冰系,关于其沉积时限长期存在争议。近十余年来,通过高精度锆石U-Pb定年,已经基本敲定南华系的重要时间节点。长安组底界年龄被限定在ca. 717 Ma,莲沱组顶部沉积时间被限定在ca. 714 Ma。长安冰期中期暂时冰退的时间被限定在ca. 690 Ma,冰期终止时间限定在ca. 659 Ma。小行星撞击地球可能导致了长安冰期中期的暂时冰退,这期间形成的风暴沉积构造和丘状交错层理可以提供最直接的沉积学证据。结合世界其它地区报道的年龄,斯图特（长安）冰期的起止时间限定在了717～659 Ma。马力诺（南沱）冰期的启动时间被大致限定为649 Ma,终止时间被限定在ca. 635 Ma。结合世界其它地区年龄数据,马力诺冰期的启动时间可限定在649～639 Ma。随着后续工作的深入,马力诺冰期的启动时间范围应会被进一步缩小。华南南华系沉积时限的准确厘定对于理解全球成冰纪地质-生物-环境事件具有重要意义。马力诺冰期持续时间约14 Myr,远远小于长安冰期的持续时间（约58 Myr）。冰期末期大规模岩浆作用是导致这两次冰期持续时间不同的直接原因。通过模拟计算发现,扬子北缘... 相似文献
15.
白垩纪年代地层学研究简述 总被引：7，自引：2，他引：5
简述国际白垩纪年代地层和地质年表研究现状,介绍马斯特里赫特阶、土仑阶和赛诺曼阶底界的GSSP及其生物地层学标志,其他阶推荐的GSSP定义标准以及中国陆相白垩系建阶进展。评述白垩系地质年表方案,根据我国辽西地区义县组尖山沟层研究的最新进展,提出考虑以12 5 Ma作为白垩系底界的年龄标准 相似文献
16.
Few studies exist in the geologic literature that show the distribution of seismic facies and depositional sequences within a lacustrine basin. The Pannonian Basin of Central Europe offers a unique opportunity to evaluate the influence of the eustatic signal on lacustrine deposition.
Seismic stratigraphie and sedimentological studies indicate that the Middle Miocene-Early Pliocene infill of the transtensional Pannonian Basin was formed by large delta systems. Systematic sequence stratigraphie analysis of 6000 km of reflection seismic data and more than 100 hydrocarbon exploration wells in Hungary allowed the identification of twelve third-order sequence boundaries in the late Neogene sedimentary fill. This number of depositional sequences corresponds to that of the published global eustatic curve for this time period. Furthermore, based on magnetostratigraphic and radiometric data, the ages of these depositional sequences can be tentatively correlated with the global eustatic curve.
The Pannonian Basin became isolated from the world sea at the Sarmatian/Pannonian (11.5 Ma) boundary and formed a large lake. The stratal patterns and sedimentary facies of individual systems tracts within the lacustrine sequences display the same characteristics as marine depositional sequences. The relatively low rate of thermal subsidence and the high rate of sediment supply resulted in a good sequence resolution. Within the third-order sequences higher-order sequences can be recognized with an average duration of about 0.1–0.5 Ma. 相似文献
17.
Diffusion modeling of zoning profiles in eclogite garnets from three different tectonic units of Mt. Dabie, UHPM unit, HPM unit and northern Dabie, was used to estimate the relative time span and cooling rates of these rocks. Modeling result for the Huangzhen eclogite garnet shows that the maximal time span for the diffusion-adjustment process is about 22 Ma since the peak-temperature metamorphism, which is the maximum time span from amphibolite facies metamorphism to greenschist facies metamorphism. The Bixiling eclogites had subjected to a cooling process at a rate of - 10℃/Ma from 750℃ to 560℃ during 20 Ma. The second cooling stage of the Raobazhai eclogite following granulite-facies metamorphism is an initial fast cooling process at a rate of about 25℃/Ma and then slowed down gradually. All these belong to a coherent Dabie collision orogen with differences in subduction depth and exhumation/uplifting path. 相似文献
18.
陆相红层因为其含古生物化石稀少给高精度生物、年代地层的对比带来了较大的困难。旋回地层学可以将地层与地时结合起来,解决地层沉积的时限问题。基于前人在对胶莱盆地K/Pg界线识别的基础上,主要利用了一维连续小波变换尺度分析法与频谱分析法对胶莱盆地胶州组K/Pg界线之下、晚白垩世红土崖组玄武岩夹层之上的陆相红层进行旋回地层分析,认为胶莱盆地晚白垩世的陆相红层中保存有米兰科维奇旋回,岁差、斜率和偏心率各个周期在不同的层段响应程度略有不同。根据旋回识别结果及K/Pg界线建立了“浮动天文年代标尺”,推测在66~67.77 Ma期间,胶莱盆地陆相红层的平均沉积速率约为5.15 cm/kyr,胶州地区［（67.77~73）±0.3］ Ma期间为玄武岩岩浆冷凝固结形成玄武岩进而遭受风化剥蚀及构造沉降的时期,红土崖组与胶州组的时间界线约为67.28 Ma,红土崖组玄武岩夹层的年龄应早于67.77 Ma。 相似文献
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作者对相当于晋宁运动岩浆活动产物的湖北峡东黄陵岩体和江西九岭岩体分别进行了40Ar/39Ar快中子定年。对采自宜昌莲沱地区的黑云母斜长花岗岩体和黄陵庙黑云母花岗闪长岩体的样品测得两条年龄谱,HH-01黑云母的高温坪年龄为893.7±6.7Ma,HH-05角闪石坪年龄为886.4±4.6Ma。对采自江西宜丰黄岗口的九岭岩体中黑云母测得的高温坪年龄为937.1±6.4Ma。从上述三个年龄值,并综合以前测定的晋宁期侵入体的年龄值以及不整合面上覆盖层和基底最上部沉积层的一些年龄值认为,以900Ma作为震旦系底界年龄是合适的。 相似文献