Cenozoic stratigraphy of Taiwan: Window into rifting, stratigraphy and paleoceanography of South China Sea

Shallow marine sequences of the northern South China Sea (SCS) are uplifted and exposed by plate convergence in the Taiwan mountain belt. These deposits provide detailed geological information about the rifting event, stratigraphy, sedimentology, paleoclimate and paleoceanography of the shallow SCS to compare with what are recorded in the ODP 1148 deep-sea core. Seismic surveys and marine micropalentological studies show that Eocene sequences in the offshore Taiwan Strait and onland Taiwan mountain belt are all deposited in rifting basins and are covered unconformably by the Late Oligocene-Neogene post-rifting strata. Between syn-rifting and post-rifting sequences, there is a regional break-up unconformity throughout the island. Early Oligocene and Late Eocene strata are missing along the break-up unconformity equivalent to the T7 unconformity in the Pearl River Mouth Basin off south China. This may suggest that the SCS oceanic crust could have initiated between 33 and 39 Ma. Neither obvious stratigraphic gap nor slumping features are found in the Oligocene-Miocene transition interval of Taiwan. This observation highly contrasts with what has been documented from the ODP 1148 deep-sea core. This suggests that the stratigraphic gap and slumping features could only be recorded in the SCS deep sea region, but not in the shallow shelf near Taiwan. Compared to the Middle Miocene paleoceanographic re-organization events in the SCS deep sea, the geological history of the Taiwan shallow sequence shows changes of in sedimentation and faunal composition. Due to the Antarctic glacial expansion at~14 Ma, Middle to late Miocene strata of the Western Foothills show progressive regression sedimentations associated with a decrease of benthic foraminif-eral abundance and a sharp faunal turnover event. Many Early-Middle Miocene endemic benthic foraminifers were extinct in 14-13 Ma and new benthic foraminifers of the Kuroshio Current fauna appeared from 10.2 Ma, comparable with new occurrence of Modern benthic foraminifers at 9 Ma in the Java Sea area. This reveals that the Western Boundary Kuroshio Current in the North Pacific could initiate from 10-9 Ma due to closures of the Indo-Pacific seaways by convergent tectonics between the Australian Continent and the Indonesian Arc in 12-8 Ma. Subduction of the SCS oceanic lithosphere since the Middle Miocene resulted in formation of the Hengchun Ridge accretionary prism and the North Luzon Arc. Occurrence of these two bathymetric highs ( 2400 m) since the Middle Miocene and closures of the inter-arc passages in the North Luzon arc in the last 3.5 Ma would control the water exchanges between the West Pacific and the deep SCS. Accordingly, the tectonic evolution in the Central Range-Hengchun Peninsula accretionary prism and the arc-forearc Coastal Range not only control directly the route for water exchanges between the West Pacific and the SCS, but also indirectly shows a great influence on the geochemistry of deep SCS waters. The latter is best shown by much negative carbon isotope values of benthic foraminifers in the ODP 1148 deep-sea core than the West Pacific records in the last 14 Ma.     

U-Pb dating of detrital zircons from the Wudangshan Group in the South Qinling and its geological significance

U-Pb dating was made by the LA-ICP-MS method for detrital zircons from the Wudangshan volcanic-sedimentary succession in the South Qinling. Samples comprise quartz sandstones of the Wudangshan Group collected from the base of the Yangping Formation and an upper layer of the Shuangtai Formation overlain its volcanic sequence, and two river-sand collections from the drainage systems cutting across the two formations, respectively. The results show that the Yangping detrital zircons are dominated by 830–780 Ma grains with a minor population of ~1.0–0.84 Ga and sporadic grains of ~2.6, ~2.4 and 2.0 Ga, whereas the Shuangtai zircons yield an upper intercept age of 763±33 Ma, identical to the timing of the Wudangshan volcanism within error, with few concordant grains of 1.9 and 0.86 Ga. Age spectra for the two river-sand samples are similar to those of the Yangping and Shuangtai Formations, respectively. It thus suggests that the Wudangshan strata are less than 780 Ma, whereas their major detrital zircon populations of 1.0–0.85 Ga and 830–780 Ma are consistent with timing of the Hannan magmatic activities along the northwestern margin of the South China Block. This suggests a Hannan or adjacent area provenance for the Wudangshan strata. The Wudang area is characterized by rift-related igneous events at ~755 and ~680 Ma, respectively, pointing to a tectono- magmatic history different from the Hannan area. It is inferred that the ~755 Ma magmatism is likely to indicate a separation of the South China Block from the supercontinent Rodinia, while the ~680 Ma event suggests a further split between the South Qinling and some unknown continent.     

中新世以来滇西高原内红河流域区的古高程反演

流经滇西高原的红河水系将高原内被剥蚀下来的物质输送到莺歌海盆地与琼东南盆地中堆积.滇西高原隆升剥蚀区与莺歌海盆地和琼东南盆地堆积区构成了一个相对封闭系统.采用质量平衡法,将莺-琼盆地内的堆积物回剥至隆升剥蚀区,重建了中新世以来滇西高原内红河流域区所达到的可能高程.16.2～19.6 Ma前红河流域区海拔高度低于560 m,16.2～11 Ma前的隆升使高程升至860～950 m.经过11～5.3 Ma前的剥蚀夷平后,海拔高度降为800m.距今5.3～1.6 Ma前的快速隆升,使海拔高度曾达到2600～2725 m,隆升幅度达1800～1925 m,滇西高原形成.近1.6 Ma以来则主要是剥蚀削低,海拔高度从2560 m降为2300m.中新世以来红河流域区被剥蚀掉约3900 m.     

Timing of the Wudangshan, Yaolinghe volcanic sequences and mafic sills in South Qinling: U-Pb zircon geochronology and tectonic implication

The Wudangshan, Yaolinghe volcanic-sedimentary sequences and doleritic-gabbroic sills comprise the largest exposed Precambrian basement in South Qinling. Zircons separated from 5 volcanic-pyroclastic samples of the Wudangshan Group, 2 volcanic samples of the Yaolinghe Group and one sample for the mafic sills were used for U-Pb dating by laser ablation-inductively coupled plasma mass spectrometry （LA-ICPMS）. The results reveal that the Wudangshan volcanic sequence was formed at （755±3） Ma （a weighted mean from the 5 samples, MSWD=0.47）, whereas the Yaolinghe volcanic suite and the mafic sill were crystallized at （685±5） （2 samples, MSWD=0.36） and （679±3） Ma （MSWD=1.6）, respectively, which are equal to each other within analysis errors. These ages are markedly younger than those previously documented for the rocks. The newly obtained ages for the Wudangshan and Yaolinghe Groups are Identical to those of the bottom Liantuo and slightly older than those of the Nantuo Formations, respectively, lower strata of the Nanhua （middle to late Neoproterozoic） stratotype section in eastern Three Gorges, Yangtze creton. A range of inherited magmatic zircons was recognized with ages of 830 to 780 Ma, which are typical of Neoprotzrozoic magmatisms recorded along the margins and interior of the Yangtze craton. Thus, there is Neoproterozoic basement comprising 830-780 Ma igneous suites in South Qinling; the inherited zircons were detrital sediments derived from the northern margin of the Yangtze craton. Accordingly, it is suggested that the South Qinling is a segment of the Yangtze creton before the Qinling Orogeny.     

Synchronous drying and cooling in central Asia during late Oligocene

Aridification of central Asia during late Oligocene and Early Miocene has been documented by numerous eolian records from the North Pacific and central Asia. However, direct evidence of aridity from the interior of the arid zone is still rather scarce. To better reconstruct the climate history in central Asia during the late Oligocene, we have analyzed ostracod assemblages and gypsum content in the sediments from the lacustrine Jingou River section in the northern Tianshan Mountains. Our results show that the cold water species Candona cf. Neglecta and Pseudocandona albicans replaced the warm water species Ilyocypris bradyi and Ilyocypris sp. to become the dominant species at 23.8 Ma, indicating significant cooling in central Asia at that time. At the same time, a substantial increase in gypsum content indicates the intensification of central Asian drying. The synchronous cooling and drying approximately coincided with the Oi2b.1 and/or Mi1 events, implying a causal linkage between late Oligocene global cooling and central Asian aridity.     

Methoxy n-fatty acids in surface soils from the Gongga and Kunlun Mountains: Ecological implications

GC-MS characteristics of surface soil samples from the eastern and northern Tibetan Plateau provide tentative identification of 8(–14)-Methoxy hexadecanoic acid (iME-16:0) and 9(–17)-methoxy octadecanoic acid (iME-18:0). Sixty surface soil samples were collected from the eastern slope of Gongga Mountain, at elevations ranging from ~1230 to 4500 m (eastern Tibetan Plateau), and from the northern slope of West Kunlun Mountains, ranging from ~1300 to 5500 m (northern Tibetan Plateau). This study also analyzed the methoxy n-fatty acids (MFAs) of Gongga Mountain tree leaves from six common living species, at the elevation of 2900–4200 m. MFAs dominate these samples, with more centrally located methoxy groups eluting earlier than those with methoxy groups located closer to the end of the main carbon chain. MFAs occur prominently in most of the Gongga Mountain soil samples (and from six tree samples) from dominantly coniferous and deciduous broadleaved forests. Other than in two narrow vegetation zones between 4000–4350 m and 2900–3300 m, no MFAs were found in 19 Kunlun Mountains soil samples from areas covered mainly with montane desert and alpine desert steppe vegetation. Based on the inventory of plants and soils from which MFAs have been isolated, we conclude that the MFAs most probably originate from specific woody plants. If we can exclude some particular grasses as sources, MFAs may be specific woody plants-derived biomarkers; thus they would serve as an important additional proxy for comprehensive and precise ecological reconstructions.     

Crustal evolution of the Shiwandashan area in South China: Zircon U-Pb-Hf isotopic records from granulite enclaves in Indo-Sinian granites

U-Pb dating coupled with Hf isotope analyses on zircon from metasedimentary granulite enclaves in the Jiuzhou peraluminous granite from the Shiwandashan area in southeastern Guangxi Province, South China are presented in this paper. The results show that the protoliths of these granulite enclaves were mainly composed of Neo-Mesoproterozoic (564–1061 Ma) clastic materials with a peak age at ~822 Ma. These materials were probably derived from the igneous rocks that were emplaced during the Neoproterozoic breakup of Rodinian Supercontinent. Subordinate sediments include the Paleoproterozoic (1778–2227 Ma) and even the Meso-Paleoarchean materials with the oldest U-Pb age at 3551±8 Ma, indicating the existence of ancient crustal rocks in the area and/or its surrounding regions. Younger grains include the early Mesozoic (234±2 Ma) magmatic zircon populations and the late Permian (253±3 Ma) metamorphic zircon populations. Further zircon Hf isotope analyses reveal that their protoliths were complex, containing both recycled crustal rocks and juvenile materials. Combined zircon U-Pb ages and Hf isotope compositions indicate that at ~253 Ma, the Shiwandashan area experienced an intensive thermal event that resulted in the granulite-facies metamorphism; and that crustal remelting occurred at ~234 Ma to form the S-type granitoids during the uplifting stage. The metasedimentary granulite enclaves are resitites of these granitoids.     

Depositional architecture and developing settings of large-scale incised valley and submarine gravity flow systems in the Yinggehai and Qiongdongnan basins, South China Sea

In the Ying-Qiong basins in the South China Sea developed a set of giant inner shelf slope and submarine gravity flow deposits in the Ying-Huang formations since the Late Miocene. These deposits can be classified into 9 sequences in which slope slump-debris flow, slope fan and particularly, the large-scale axial basin-floor incised valley fills have been recognized. They were distributed in a distinctive pattern attributed to tectonic control. The development of shelf slopes and abyssal plains in the basins was related to the last episode of rapid subsidence and a large amount of sediment inputs. Large-scale basin-floor incised valleys, formed during the late Miocene and Pliocene, indicate several major sea level falls that occurred in the South China Sea.     

Magnetostratigraphic dating of mammalian fossils in Junggar Basin, northwest China

The first detailed chronology for the late Oligocene to early Miocene continental record in northern Junggar Basin is presented,based on rock magnetic experiments and magnetostratigraphic investiga-tions of a 192 m thick mammal-bearing section in the Ulungur River area. Magnetites and hematites were identified as the main carriers for the characteristic remanent magnetization,and the resulting polarity sequence allows an unambiguous correlation to the geomagnetic polarity time scale (GPTS). Furthermore,the Tieersihabahe fauna layer occurs below the Paleocene/Neocene boundary,and the Suosuoquan fauna layer is just above the Neocene onset. Therefore,the age of the Tieersihabahe fauna and Suosuoquan fauna layers can be definitely estimated to be about 25.2 Ma and 22.5 Ma,respectively.     

Magnetic characteristics and their paleoclimatic significance of Fengzhou loess in the Qinling Mountains of China

The Fengzhou loess section is very typical in the Qinling Mountains. The section, about 82 m thick and underlain by the Neogene red clay, consists of 33 layers of loess and 33 layers of paleosol. The section covers Brunnes normal polarity zone and Matuyama reversed polarity zone, and the B/M boundary is located in the middle of L₈. Matuyama reversed polarity zone records Jaramillo, Olduvai and Reunion normal polarity subchrons. The boundary between Matuyama reversed polarity zone and Gauss normal polarity zone (M/Ga) appears in the lithological boundary between loess and the Neogene red clay. Loess accumulation in Fengzhou started before 2.48 Ma. The magnetic susceptibility curve indicates 33 cold-dry and humid-warm cycles of paleoclimatic variation in the Qinling Mountains during the last 2.48 Ma. The above climatic fluctuation may be well compared with that of the oxygen isotopic records from deep-sea deposits.     

南海深海盆的沉积充填

 依据大洋钻探井及地震剖面资料，定量确定南海同扩张期和后扩张期深海盆沉积充填差异及沉积物来源变化。研究显示，南海深海盆自渐新世（32 Ma）开始形成，随着南海二次扩张海盆范围逐渐扩大，海盆内主要充填火山碎屑角砾岩及火山灰，碳酸盐岩、超微化石软泥，泥质粘土、粉砂质粘土、泥岩及粉细砂岩。深海盆充填主要沉积物为晚中新世（11.6Ma）以来的陆源碎屑沉积，丰富陆源碎屑的供给与南海闭合过程中同期区域构造事件（如青藏高原快速隆升、菲律宾板块俯冲）密切相关，也与晚中新世以来东亚季风增强以及源区强烈的风化剥蚀有关。     

陕西秦岭泥盆纪盆地群构造沉积动力学研究

陕西秦岭泥盆纪盆地群是在早泥盆世扬子板块北缘陆内裂谷沿勉略一线进一步发育成有限洋盆，而后分裂出秦岭板块，勉略洋盆与商丹洋盆的并存导致秦岭造山带出现了三个板块（扬子、华北及秦岭板块）共存的格局，由此形成了秦岭泥盆纪盆地群．在这种复杂的板块构造格局下，整个秦岭造山带出现了构造动力学成因不同的一系列盆地．在秦岭板块北缘发育了刘岭边缘盆地，在其中堆积了含火山岩的巨厚碎屑岩系（最大厚度超过１１ｋｍ）．在秦岭板块内部，由于广泛发育的伸展断裂而形成了一系列地堑和半地堑型盆地，在其中堆积了反映以陆表海为主的一套碳酸盐和碳酸盐碎屑沉积．在扬子板块与秦岭板块之间的勉略有限洋盆中发育了夹超基性至酸性火山岩、硅质岩的碳酸盐碎屑沉积．在扬子板块北缘的高川一带还发育了以细碎屑岩碳酸盐岩为主的陆表海沉积．总之，秦岭在泥盆纪发育了一个多种构造沉积动力学成因性质完全不同的盆地集合群     

Eolian sand deposition and its environmental significance in the northeastern margin of the Qinghai-Xizang Plateau

The dry climate which appeared about 8#x2013;7 Ma ago in South Asia has been interpreted as results of the intensification of Asian monsoon caused by the uplift of the Qinghai-Xizang Plateau at its maximum altitude around that time. Whether it is or not, it is a critical problem. A total of 55 samples were taken from the Tertiary red earth and Quaternary lacustrine deposits and loess in the Linxia Basin which is located in the northeastern margin of the Qinghai-Xizang Plateau, for the analysis of quartz types and contents using electron probe microanalyzer. The results indicate that the eolian sands have existed since 15Ma and reached its maximum content at 8 and 6#x2013;5 Ma, respectively. This means that the climate was very dry during 8-5 Ma period in western China, which was regarded as the result of global climatic change at that time. Mean size of quartz sand grains was about 0.4 mm during 15#x2013;3.6/2.6 Ma period and dropped to 0.1–0.07 mm dramatically after 3.6–2.6 Ma. This demonstrates that the local eolian deposition was decreased significantly and even disappeared since Late Pliocene and was replaced by dust deposits from distal source, suggesting the uplift of Qinghai-Xizang Plateau and the change of air circulation after 3.6–2.6 Ma.     

Magnetostratigraphy and pavleo-environmental record of Tertiary deposits of Lanzhou Basin

The Tertiary deposits of the Yongdeng section, the Lanzhou Basin were studied by means of magnetostrati-graphy. The magnetostratigraphic sequences from Paleocene to Miocene were established, and the time scale for the corresponding stratigraphy and mammalian faunas was also established by referring to their correlation to the GPTS of BKSA95 (The geomagnetic polarity time scale which was thoroughly revised and updated by Berggreen et al. in 1995). In the end the paleoenvironmental records and their relationship with the uplifting of the Tibetan Plateau were discussed. The results are as follows. The top boundary of the Xiliugou Formation is dated to be 51 Ma, i.e. Eocene. TheYehucheng Formation covers the time span of 51-31.5 Ma, i.e. from late Early Eocene to early Early Oligocene. The Xianshuihe Formation covers the time span of 31.5-15 Ma, i.e. from Early Oligocene to Middle Miocene. The lower member of the Xianshuihe Formation spans from 31.5 to 20.0 Ma, i.e. from Early Oligocene to early Early Miocene. The middle member is from 20.0 to 16.5 Ma, i.e. in the middle Early Miocene.     

鄂尔多斯盆地西缘差异抬升的裂变径迹证据

目的探讨鄂尔多斯盆地西缘从南至北不同地区的差异抬升时期及抬升速率。方法利用磷灰石和锆石裂变径迹年龄的综合分析,研究盆地西缘的构造差异抬升。结果西缘北部汝箕沟地区中生代以来有两次较大的抬升时期,分别为晚白垩世和始新世,抬升速率分别为29.5 m/Ma和46.5 m/Ma。中部石沟驿地区抬升时期较早,为晚侏罗世和晚白垩世,抬升速率分别为40.0m/Ma和21.9 m/Ma。南部的差异抬升最为强烈,最早的抬升时期为晚侏罗世,在炭山地区表现明显;早白垩世末—晚白垩世南部地区发生整体抬升;中新世末期六盘山地区发生快速抬升。罗山、炭山地区相对抬升速率和后期抬升速率为46.3 m/Ma和25 m/Ma,六盘山地区则分别为22.5m/Ma和283.3 m/Ma。结论在鄂尔多斯盆地西部,最早的抬升时期为晚侏罗世,晚三叠世并没有抬升事件,故西部前陆盆地的形态始显现于晚侏罗世。西部的差异抬升导致了不同地区前陆盆地构造发展的不平衡。     

Paleomagnetic dating of the topmost terrace in Kouma,Henan and its indication to the Yellow River＇s running through Sanmen Gorges

In the east of Xiaolangdi, many river terraces are developed at the exit of the Yellow River Gorges. Among them the terraces in Kouma, Yanshi of Henan Province are most typical, where the Yellow River developed three staircase terraces, among which the altitude of gravel stratum of the topmost terrace is 30-35 m higher than the river level.The top of the gravel stratum was covered by 60 m eolian loess deposits which have many brownish-red paleosol strips.And the paleosol $14 is at its bottom. Research on systematic magnetostratigraphy and paleosol-loess matching indicates that the bottom age of the loess on the topmost terrace is 1165 ka. Therefore, it can be concluded that the terrace develops no later than 1.165 Ma and the situation that the Yellow River runs through Sanmen Gorges and inpours into East China Sea happened at least before 1.165 Ma.     

青藏高原盆地系统演化与高原形成时间

青藏高原在以时间为坐标的隆升过程中,高原的范围、高度都是呈阶段性递增的.随着青藏高原的构造隆升,在高原的内部和外围发育了众多的沉积盆地,在这些沉积盆地中详细地记录了青藏高原的隆升过程.高原北部盆地的演化显示出向北递进增长的特征,以南北挤压为动力背景的北部前陆盆地演化代表了盆地对高原周缘造山带的响应关系:金沙江缝合带、昆仑山、祁连山的新生代逆冲抬升的时间分别为53 Ma、46 Ma和29.5 Ma.对高原南北盆地-造山带的构造演化对比发现:祁连山和高喜马拉雅的逆冲时间相同,说明青藏高原在渐新世基本定型.     

Pollen evidence from Baode of the northern Loess Plateau of China and strong East Asian summer monsoons during the Early Pliocene

The red clay eolian sequence on the Chinese Loess Plateau (CLP) is an important archive for paleoclimate change from the late Miocene to Pliocene,and can provide significant information for the controversial problems of East Asian monsoon evolution and its forcing mechanism.In this study,we present a pollen record from Baode,northern CLP.The record shows four stages of paleoecological evolution.From 5.6-4.4 Ma,a forest steppe ecosystem developed under an extremely warm period with high seasonal precipitation.Since 4.4 Ma,a drier episode occurred,which prompted parkland landscapes to develop.During 3.5-3.05 Ma,the environment changed to a rather open steppe ecosystem with a much cooler and drier climate.After 3.05 Ma,the vegetation evolved to forest steppe.Using the percentages of arboreal plants to mirror precipitation,and comparing with other published pollen data from the CLP,we find the existence of S-N directionality of the precipitation change and high percentage of arboreal plants in the entire CLP during the Early Pliocene,which suggest the CLP was characterized by a strong East Asian summer monsoon.The strong summer monsoon corresponds well to the low global ice volume,which may illuminate global climate mechanism for the summer monsoon evolution in the early Pliocene.     

天水盆地古近纪地层年代及其意义

天水盆地位于青藏高原东北缘六盘山与西秦岭二重要构造带交汇处,该盆地充填的新生代沉积序列记录着该区构造变形历史,因此研究该盆地沉积记录对探讨青藏高原东北缘新生代构造活动事件具有重要意义.通过对天水盆地古近纪砾石层砂质透镜体中碎屑颗粒磷灰石裂变径迹热年代学研究,获得样品地层的最大沉积年龄为24.8士1.5 Ma.结合前人的工作,厘定该套古近纪地层最顶部地层年龄为22～24.8 Ma,并确定天水盆地古近纪沉积物源区在24.8 Ma左右发生了构造冷却事件,推断印度板块与欧亚大陆碰撞的远程效应在古近纪末-新近纪初已传递到青藏高原的最东北缘.     

<Superscript>40</Superscript>Ar/<Superscript>39</Superscript>Ar isochron ages of lawsonite blueschists from Jiuquan in the northern Qilian Mountain,NW China,and their tectonic implications

Using laser ⁴⁰Ar/³⁹Ar dating method, we have gotten the metamorphic ages of lawsonite blueschist and epidote blueschist from Jiuquan, northern Qilian Mountain, NW China. The high quality laser ⁴⁰Ar/³⁹Ar dating of glaucophane from lawsonite blueschist gives an isochron age of 413±5 Ma. The isochron age obtained from phengite in epidote blueschist is 415±7 Ma. These data, combining with peak metamorphic P-T conditions and regional geological setting, allow us to infer that the lower limit of the ages of the prograde subduction metamorphism from lawsonite blueschist facies to epidote blueschist facies occurred at ca. 413–415 Ma, which also suggests that the formation of lawsonite blueschist in the northern Qilian Mountain maybe resulted from the corner flow in the cold subduction zone. This study shows that the final closing time of the northern Qilian remnant oceanic basin is about 413–415 Ma, which also represents the convergent age between the North China Craton and the Qaidam block.