Estimation of the Mesozoic geological time scale

Geological time scales are constructed by combining the stratigraphic record with radiometric dates and their standard deviations. The stratigraphic record encompasses litho-, bio-, chrono-, and magnetostratigraphy. The statistical methods employed should embody concepts and data available for the systems considered. Recently, in order to estimate the ages of 31 Mesozoic stage boundaries, use was made of a database with chronostratigraphic classifications for 340 dates, biostratigraphic data including ammonite subzones, and information on seafloor spreading. This paper is primarily concerned with the propagation of errors through the successive steps of the data analysis. The following stepwise approach was taken for combining the different types of data: (1) maximum likelihood estimation with windows set around prior stage boundary estimates, (2) averaging of estimates with variable precision including magnetochronologic data, and (3) calibration by means of cubic smoothing splines assuming equal duration of ammonite subzones. The end product is a time-scale in which the stage boundary ages are accompanied by approximate 95 per cent confidence intervals.     

我国陆相渐新世哺乳动物群的划分及排序

亚洲渐新世不是原认为的三分，而是仅包括两个期：早渐新世三达河期和晚渐新世塔奔布鲁克期。我国渐新世的地方动物群排序为：早渐新世包括（从早到晚）克克阿木、乌兰布拉格早期和乌兰布拉格晚期３个动物群；晚渐新世包括（从早到晚）４个动物群：沙嘎特动物群、塔奔布鲁克动物群、伊克布拉格动物群和索索泉动物群。“始新世末事件”在亚洲也很明显，主要表现为较原始的古老的哺乳动物在渐新世初就大量迅速绝灭。在渐新世期间，哺乳动物的变化主要表现为进化程度上的演变和替代。上述演变主要与当时全球的气候变冷、变干燥和亚洲地形的变化有关。     

晋东北侏罗纪盆地早中侏罗世沉积充填记录及其构造意义

侏罗纪/白垩纪之交是中国中东部乃至东亚地区构造活动的重要时期,发生了构造变形、岩浆-成矿、气候环境突变等一系列重大的构造事件,被称为"燕山运动",但对于其启动时限的认识却一直存在着争议。本文以晋东北侏罗纪盆地为研究对象,在早中侏罗世沉积序列划分和重矿物组合特征变化研究的基础上,结合重点层位火山岩夹层锆石U-Pb同位素测年,详细刻画了这期构造事件启动的具体时限。研究认为,中侏罗统云岗组(J2yg)底部砾岩沉积时期,沉积序列由早期的湖进序列向湖退序列转换,碎屑岩的成分由早期的以石英、长石为主过渡为以长石、岩屑为主,重矿物组合由早期的以锆石为主过渡为以石榴子石为主,预示着侏罗纪构造活动进入了启动阶段。通过下侏罗统永定庄组(J1y)火山碎屑岩的年龄(179.2±0.79)Ma和中侏罗统云岗组(J2yg)顶部凝灰质碳酸盐岩年龄(160.6±0.55)Ma的制约,推测中侏罗统云岗组(J2yg)底部砾岩沉积时间大约为168 Ma,这个时间代表了侏罗纪构造活动(燕山运动)的起始时限。该成果在沉积学方面为燕山运动的起始时限提供了新的制约。     

Astronomical time-scale for physical property records from Quaternary sediments of the northern North Atlantic

Deep sea sediment cores taken between 50° and 75°N in the North Atlantic, in water depths varying between 1340 and 3850 m, were examined to provide an astronomically calibrated late Quaternary time-scale based on physical property records. Magnetic susceptibility and gamma ray attenuation porosity evaluator (GRAPE) density changes of these cores revealed significant responses to orbital forcing in the eccentricity (100 kyr), obliquity (41 kyr) and precessional (23, 19 kyr) bands. At 75°N (Greenland Sea), a response to obliquity forcing was weak despite the fact that it should become more pronounced in sediments at high latitudes. Application of bandpass filtering at the obliquity period (41 kyr), however, showed that variance at this period did exist in the magnetic susceptibility record, but at a very low power. At 50°N stacked curves of magnetic susceptibility correlated strongly with the SPECMAP curve for the past 500 ka. Since about 65 ka, dropstone layers are recorded in both magnetic susceptibility and GRAPE data of Rockall Plateau sediments. Although Rockall Plateau sediments show peaks in physical properties that correlate with Heinrich events (H₁, H₂, H₄, H₅, H₆), such a relationship was not readily observed in Norwegian-Greenland Sea records. Heinrich events at Rockall Plateau sites indicate a northward flow of icebergs in the eastern North Atlantic. This flow pattern and the presence of Heinrich events during the past 65 ka raise the questions of whether similar events occurred before this time period, and to what kind of ice sheet dynamics and climatic-oceanographic conditions favoured major iceberg surges from the Laurentide ice sheet to the North Atlantic at 50°N.     

中国南方海、陆相侏罗系的划分与对比

对自21世纪以来中国南方海、陆相侏罗系的研究进展进行了总结,依据地层发育的总体特征,将中国南方侏罗系划分为4个地层区和14个地层分区,文中着重介绍了中国南方海、陆相侏罗纪年代地层划分、底界界线层型及各统之间的界线生物标志和与全球年代地层的对比关系.此外,对全球年代与生物地层的研究进展也作了扼要介绍.     

新疆准噶尔盆地中、晚侏罗世多重地层研究

对新疆维吾尔自治区沙湾县玛纳斯河红沟侏罗系剖面开展了生物地层学、同位素年代地层学、旋回地层学和磁性地层学等的综合研究。研究结果表明,头屯河组的时代为中侏罗世中晚期到晚侏罗世早期,包括巴通阶的最顶部、卡洛维阶和牛津阶的中下部;其底界年龄约为166.2 Ma,顶界线年龄约为160.8 Ma,沉积时间约5.4 Ma。齐古组顶部年龄值为155.3 Ma,沉积时间约5.5 Ma,包括了牛津阶的上部和基默里奇阶的中下部,其顶部与东部冀北、辽西地区髫髻山组顶部大体相当,比土城子组层位低。喀拉扎组的时代为晚侏罗世基默里奇期晚期,而其上覆地层吐谷鲁群的时代为早白垩世早期,两者之间存在一个相当大的不整合,缺失了晚侏罗世提塘期以及可能包括早白垩世最早期的地层,有超过了7 Ma的地层缺失量。侏罗系与白垩系的界线为此不整合面,侏罗纪/白垩纪之交的地层未保存。     

Jurassic sediments in the Irkut basin and southwestern Transbaikalia: correlations based on paleobotanical and geochronological data

The Jurassic growth of mountain ranges along the southern edge of the Siberian platform occurred in an active tectonic setting related to the closure of the Mongol-Okhotsk Ocean. The oceanic subduction and subsequent continent collision events induced compressive deformations at the platform boundary. Understanding the paleogeography related to the Mesozoic closure of the Mongol-Okhotsk Ocean requires dating and correlation of the Jurassic Prisayan Formation in the Irkut basin and Tugnuyskaya Formation in southwestern Transbaikalia. This work presents structural and paleobotanic results within both formations. ⁴⁰Ar/³⁹Ar dating of underlying volcanics from the upper member of the Ichetuyskaya Formation is used to refine the age of the sediment series and provide probable correlation. The results show that the Tugnuyskaya Formation initiated at the end of the Middle Jurassic-beginning of the Late Jurassic and was not coeval with the Prisayan Formation, whose upper fine-grained members were deposited in the early Middle Jurassic. ⁴⁰Ar/³⁹Ar dating of volcanics from the upper member of the Ichetuyskaya Formation yielded a Middle Jurassic age of 167.7 ± 1.2 Ma (Bajocian to Bathonian). The paleogeographic data analysis based on facies and mineralogical composition of sediments and on a study of source areas from Sm-Nd data and the U-Pb ages of detrital zircons from the deposits in the southern Irkut basin indicates that the deposition of the Prisayan Formation was followed by the intensification of relief building along the southern edge of the Siberian Platform. Our geochronological data show that active tectonic deformations in southwestern Transbaikalia evidenced in the volcanoclastic Ichetuyskaya Formation in the Tugnuy basin also occurred during the Middle Jurassic. The uppermost sediments of the Tugnuy basin were deposited at the end of the Middle Jurassic-Late Jurassic in a quiet tectonic setting with low relief and lacustrine-boggy depositional environments.     

珠江口盆地晚侏罗世中基性火山岩的岩石成因与构造意义：来自年代学和地球化学的约束

位于南海北部陆缘的珠江口盆地发育中生代岩浆岩,记录了古太平洋板片俯冲消亡的动力学过程。本项研究以钻井揭露的晚侏罗世火山岩为研究对象,开展系统的岩石学、岩相学、年代学和地球化学研究,探讨其成因机制和动力学背景。岩石学及地球化学分析显示,这套火山岩由玄武岩、玄武安山岩、安山岩和粗面安山岩组成。LA-ICP-MS锆石U-Pb年代学分析表明,玄武安山岩的结晶年龄为154.0±3.2 Ma。岩石的SiO₂含量为49.54%～58.22%,K₂O含量为0.71%～3.00%,MgO含量为5.29%～11.05%,Mg^#值介于52～66之间,属于高钾钙碱性系列中基性火山岩。岩石的轻重稀土元素分馏明显,(La/Yb)_N比值为5.00～6.93,且具有轻微的铕负异常,δEu值为0.73～1.04。样品显著富集大离子亲石元素Rb、Ba、Th和U等,相对亏损高场强元素Nb、Ta、Ti和P等。岩石成因分析表明,晚侏罗世中基性火山岩主要起源于受俯冲板片流体交代的富集岩石圈地幔熔融,且岩浆经历了辉石、角闪石等矿物的分离结晶。综...     

Stratigraphy and Geochronology of Vertebrate Fossil‐Bearing Jurassic Strata from Linglongta,Jianchang County,Western Liaoning,Northeastern China

Northeastern China contains widely distributed Jurassic terrestrial strata that have yielded many spectacular mammal and pterosaur fossils, in addition to feathered dinosaur fossils and more recent discoveries from Jianchang, particularly from western Liaoning. However, the fossil-bearing stratigraphic succession, regional correlation, and age estimates of the fossils found in Jianchang County and nearby areas have been contentious. Here, we report on the vertebrate fossil-bearing Jurassic stratigraphy from Linglongta, Jianchang County, western Liaoning, including a SHRIMP U-Pb zircon date unambiguously associated with the fossil horizons. The primary goal was to determine the vertebrate fossil-bearing succession. A further aim was to provide age estimations for the fossil-bearing horizon as well as the earliest appearance of feathered dinosaurs, the eutherian–placental clade, and transitional pterosaurs. Field investigations showed that the vertebrate fossil-bearing stratigraphic succession in Jianchang County mainly consists of basal andesites overlain by rhythmic tuffs and tuffaceous lacustrine sediments, with the upper intermediate or acidic lavas interbedded with laminated more or less tuffaceous lacustrine deposits. This sequence correlates well with the Middle Jurassic Lanqi/Tiaojishan Formation in northeastern China. Detailed and accurate field observations showed that the well-preserved vertebrate fossils were buried in either the middle or the upper fine-grained laminated lacustrine deposits. Previous and current SHRIMP U-Pb zircon dates provide an age estimation of 161–159 Myr for the fossil-bearing horizon and vertebrates. This indicates that the earliest appearance of feathered dinosaurs here was more than 159 Myr ago and unquestionably older than Archaeopteryx from Germany, making these the earliest known feathered dinosaurs in the world. Furthermore, the eutherian–placental clade and the known transitional pterosaurs first emerged no later than 161 Myr. The vertebrate assemblage unearthed recently from Linglongta and neighboring areas in Jianchang County belongs to the Daohugou Biota. In addition to feathered dinosaurs, this biota was characterized by mammals, primitive pterosaurs, insects, and plants and was present in Inner Mongolia, western Liaoning, and northern Hebei in northeastern China during the Middle–Late Jurassic.     

Early Jurassic granitoids from deep drill holes in the East China Sea Basin: implications for the initiation of Palaeo-Pacific tectono-magmatic cycle

The timing of the Palaeo-Pacific Plate (PPP) subduction in East Asia, following the amalgamation of the North and South China Blocks (NCB and SCB), remains equivocal despite several investigations on the widespread subduction-related Mesozoic magmatism in this region. Here we report newly discovered granodiorites in the East China Sea Basin (ECSB) from deep boreholes (2945–2983 m), which yield SHRIMP zircon U–Pb age of 174 ± 1.1 Ma. The rock shows relatively high Sr/Y and La/Yb ratios, low contents of Ni, Cr, and MgO, and markedly negative values of εHf(t) (21.0 to ?27.0). These geochemical and isotopic features are similar to those of the tonalite-trondhjemite-granodiorite (TTG) suites produced by the partial melting of the thickened lower continental crust. Our data, together with the ca. 190–180 Ma I-type granites reported from the eastern Zhejiang–Fujian and Taiwan areas, lead us to conclude that the continental crust in the coastal areas of South China underwent some degree of thickening during the Early Jurassic. A comparison with the coeval magmatic rocks in South Korea and Japan suggests that a large NE-trending continental arc (ca. 190–170 Ma) might have been constructed along the eastern margin of Asia at this time. Our study provides insights into the initiation of the Palaeo-Pacific tectono-magmatic cycle immediately following the consolidation of the SCB and NCB.     

准噶尔盆地的侏罗系

简介了准噶尔盆地周边侏罗系各岩组的沉积特征及所含生物群面貌。根据生物群纵向演变规律和横向对比，将八道湾组的时代归于早侏罗世早期，不排除其底部为晚三叠世的可能；三工河组为早侏罗世晚期至中侏罗世早期；头屯河组与盆地东北缘五彩湾组相当，属中侏罗世晚期。早、中侏罗世准噶尔盆地气候温暖潮湿，盆地边缘以河流沼泽相为主，是重要成煤时期，中侏罗世晚期以后，盆地开始抬升，盆地边缘以河流相为主，气候变干热，除东北缘外，生物贫乏；晚侏罗世时，盆地受燕山运动影响，激烈抬升，边缘形成河流相或山麓河流相粗碎屑沉积，伴随有强烈的火山活动。     

柴达木盆地侏罗系分布的主控因素研究

探讨了柴达木盆地现今上、中和下侏罗统的残余分布及控制因素,指出侏罗纪为连续的沉积过程,下侏罗统的断陷盆地原始沉积中心集中在阿尔金、红山和冷湖构造带以南的地区;中侏罗世为坳陷型盆地,沉积面积大于早侏罗世;晚侏罗世和早白垩世为范围广阔的大型坳陷盆地。晚白垩世大面积隆升,侏罗系剥蚀量最大的地区位于冷湖一带。新生代晚期的走滑冲断作用对于侏罗系的分布有着决定性的影响,赛什腾山和北部的南祁连山隆升使侏罗系被分割成南北两个残余分布区。     

浙南龙泉地区晚侏罗世火山岩的厘定及成因探讨

浙江晚中生代大规模火山活动始于晚侏罗世还是早白垩世,长期以来存在争议。本文对浙南龙泉地区火山岩进行了锆石U-Pb定年,获得一批高精度的年代学数据,其SHRIMP锆石U-Pb和LA-ICP-MS锆石U-Pb年龄集中于163～145 Ma,确认浙江晚中生代火山活动始于晚侏罗世。地球化学特征和Sr-Nd同位素特征表明这套晚侏罗世火山岩具有高硅、高钾、低磷、贫铁镁的特征,属于过铝质高钾钙碱性岩石系列。由于晚中生代太平洋板块的俯冲作用,导致了下部地壳物质(基底变质岩)广泛熔融,形成了本区晚侏罗世火山岩浆活动。为了便于表达、对比,笔者建议新建"晚侏罗世黄茅尖群"地层单位。     

大别山侏罗纪变形及其构造意义

大别山造山带作为三叠纪华北与扬子大陆碰撞成因并形成超高压变质岩石已经没有异议。然而,对侏罗纪的变形性质和大地构造背景的认识还未取得一致意见。通过前陆早侏罗世地层褶皱,前陆深部反射地震探测,造山带内SE角闪岩相线理变形以及160～120Ma岩浆岩记录和同位素年代学研究等新的研究成果,证实中侏罗世大别山曾发生强烈的造山运动。这次造山运动相当于“燕山运动”,由于扬子与华北陆块在三叠纪已经拼合成一个大陆,所以侏罗纪变形属于陆内造山性质。将侏罗纪变形事件从大别山碰撞造山过程中分离出来可以合理地解释大别山超高压岩石第二次折返（从壳幔边界到地壳浅部）机理,150Ma的混合岩化作用和广泛的130～120Ma花岗岩．火山岩成因,以及大剐山前陆MOHO错断等现象。     

浙中地区晚侏罗世花岗斑岩LA-ICP-MS锆石U-Pb年龄、地球化学特征及其地质意义

在华南大陆东北缘浙中地区后山店及曹娥地区零星分布有小规模的花岗斑岩体,其LA-MC-ICP-MS技术测得的锆石U-Pb年龄分别为(149.1±1.1)Ma和(150.3±1.6)Ma,表明其均为中生代晚侏罗世岩浆活动的产物,属于燕山早期晚阶段形成。两个岩体均为高钾钙碱性系列,A/CNK值介于0.96~1.28,多小于1.1,属准铝质-弱过铝质花岗岩类;稀土含量中等,具明显的轻重稀土分馏,中等至强的Eu亏损(0.10~0.40),总体表现出略呈右倾的"海鸥型"稀土配分曲线,富集Rb、Th、U等大离子亲石元素(LILE)和Nd、Hf、Y等高场强元素(HFSE),而明显亏损Ba、Sr、P、Ti等元素。后山店岩体为高分异的S型花岗岩,曹娥岩体为A型花岗岩。锆石Hf同位素的εHf(t)值变化范围主要集中于-9.5~-2.9之间,均为负值,二阶段模式年龄tDMC变化范围主要集中于1364~1783 Ma,反映其物质来源可能为中元古代上地壳基底物质。结合前人成果,本文认为浙中晚侏罗世花岗斑岩形成于后碰撞环境下的后造山板内拉张阶段,其形成年龄可能代表了古特提斯构造域向古太平洋构造域转换的晚阶段。