Late Carboniferous – Middle Permian arc/forearc‐related basin in Central Asian Orogenic Belt: Insights from the petrology and geochemistry of the Shuangjing Schist in Inner Mongolia,China

The Solonker Suture Zone is thought to record the terminal evolution of the Central Asian Orogenic Belt (CAOB) in Inner Mongolia. However, two contrasting interpretations of the timing of suturing of the Solonker Suture Zone exist: (i) Permian to Early Triassic; and (ii) Middle Devonian or Late Devonian to Carboniferous. The Shuangjing Schist is exposed in the Linxi area along the Xar Moron Fault Zone, which marks the southern boundary of the Solonker Suture Zone in the eastern section of the CAOB, and thus provides insight into the timing of suturing of the Solonker Suture Zone. Detailed and systematic analysis of the petrology and geochemistry of the Shuangjing Schist shows that the Shuangjing Schist developed by greenschist facies prograde metamorphism of a volcanisedimentary rock series protolith. The volcanic parts of the Shuangjing Schist are a calc‐alkaline series with large volumes of intermediate members and subordinate acidic members. Volcanism occurred in a magmatic arc on the continental margin and was induced by subduction‐related magmatism resulting from mantle metasomatism. The sedimentary parts of the Shuangjing Schist reflect a transition from continental shelf to abyssal plain sedimentation. The formation of the Shuangjing Schist is suggested to be related to closure of an arc/forearc‐related ocean basin. The timing is constrained by a laser ablation inductively coupled plasma–mass spectrometry (LA‐ICP–MS) U–Pb magmatic zircon age of 298 ± 2 Ma from a carbonaceous biotite–plagioclase schist that was intruded by granite at 272 ± 2 Ma. In the Linxi area, southward subduction of the arc/forearc basin led to uplift, thickening, collapse, and erosion of the overriding continental crust. Collapse induced extension and widespread magmatism along the volcanic arc at the northern margin of the North China Craton. The closure of the arc/forearc‐related oceanic basin led to the formation of Late Permian to Middle Triassic collisional granites and the subsequent end of the collision of the Solonker Suture Zone.     

Emplacement age and tectonic implications of the brecciated limestone at the edge of the Longmenshan klippe

The Longmenshan thrust belt (LMTB) is one of the best natural laboratories for thin-skinned tectonics and has developed a series of NE-SW trending fold-and-thrust structures represented by a series of nappes and klippes, exemplified by the Tangbazi and Bailuding klippe. However, the timing and emplacement mechanism of these klippes are still in dispute. Three possible mechanisms have been proposed: (1) a Mesozoic-Cenozoic southeastward thrusting, (2) a Cenozoic gravity gliding, and (3) glacial deposition. Almost all of these klippes are tectonic and overlaid on folded Late Triassic sandstone except the Tangbazi klippe, which is located in the center of the LMTB and has a narrow tail extending southeastward and covering Jurassic-Quaternary rocks. This geometric relationship is considered the most important stratigraphic evidence to support the post-Cenozoic emplacement of the Longmenshan klippe. Our structural and petrological observations show that the rocks at the front of the Tangbazi and Bailuding structures are brecciated limestone, which is assumed to have been generated by a gravitational collapse and is not characteristic of the massive Permian strata. Artemisia pollen, which has been exclusively recognized in post-Late Eocene strata in Central Asia, was found in the matrix of this brecciated limestone. Therefore, our discovery indicates that the brecciated limestone was deposited after the Late Eocene rather than during the Permian as annotated on the geological map. In contrast, unbrecciated, massive Permian limestone overlaid on the folded Late Triassic rocks. Hence, the anomalous relationship of Permian strata overlaying Late Triassic rocks cannot be evidence of Cenozoic emplacement. According to currently recognized bulk strata relationships, we can only be sure that the klippe was emplaced in the post Late Triassic. The petrological characteristics of the brecciated limestone show that it was crumbled before the re-sedimentation of the breccia, implying that the LMTB might have experienced a rapid uplift during the Late Eocene.     

Depositional model of Early Permian reef-island ocean in Eastern Kunlun

Many fusulinid fossils have been found in thin- to middle-bedded limestones which are distributed between the Early Permian limestone hills and formerly considered as Early Triassic. The fusulinid fossils, identified asNeoshwagerina sp.,Verbeekina sp. andSchwagerina sp., can also be found in massive limestone hills. At the same time, Early Permian radiolarian chert of deep basin facies was discovered in Animaqing. All the above show that the massive limestone hills, thin- to middle-bedded limestones and radiolarian chert belong to syndeposits in Early Permian ocean. The sediments in the study area can roughly be divided into three types: shallow facies, basin facies and transitional facies. The carbonate buildup can be subdivided into massive bioclastic limestone and reef framestone. Basin facies contains thin- or middle-bedded limestone, abyssal red mudstone or ooze, blue-green mudstone and radiolarian chert. Transitional facies includes reef talus and platformal skirt facies. The Early Permian ocean in Eastern Kunlun is recognized as a kind of reef-island ocean environment according to distribution and composition of different facies. The reef-island ocean in Eastern Kunlun is characterized by reef islands (or carbonate buildups) alternating with basins, complicated sea-floor topography, sharp facial change and well-developed reefs.     

Depositional model of Permian Luodianian volcanic island and its impact on the distribution of fusulinid assemblage in southern Qinghai, Northwest China

Pan-riftizational tectonic activity reached climax at Luodianian (Permian) in the East Tethyan Domain, Qinghai-Tibet Plateau. Because of eruptive volcanics and influence of terrigenous materials, a complex volcanic-sedimentary landform formed on the sea floor in southern Qinghai. Four sedimentary facies types were recognized based on detailed field mapping. Spatially, platform facies volcanic-limestone type was located at the center belt approximately trending NWW, surrounded by shallow water slope facies tuff/tuffite type at the two flanks and deep water slope facies breccia/calcirudite at the most outside. The depression facies sandstone-mudstone type, which comprised mainly mudstone, de-posited between volcanic islands (platform facies volcanic-limestone type). Based on the field map-ping and stratigraphic section data, seven rift-related sedimentary facies were recognized and a depo-sitional model for volcanic island was proposed. It is revealed that some volcanic island chain formed quickly and intermittently in the Qamdo Block during violent eruption, and small carbonate reef, shoal, platform occurred above or on edge of volcanic island, and some slope sedimentary facies surrounded volcano island chain during dormant period of volcanic activities. Three types of fusulinid assemblages were distinguished in the carbonate rocks, which deposited in varied positions of a palaeo-volcanic island: (1) Misellina-Schwagerina assemblage occurred above or on edge of volcanic island, (2) Para-fusulina assemblage was located at restricted depression facies among volcanic islands or carbonate platform, and (3) the reworked Pseudofusulina-Schwagerina assemblage occurred at slope facies near margin of volcanic island, which originally deposited in the shallow-water carbonate platform, then collapsed along the volcanic island margin with fusulinid-bearing grain-supported carbonate con-glomerate or calcirudite, and finally re-deposited on the deeper slope. The sedimentary sequence re-sulting from calm shallow water was deposited at the interior of the Qamdo Block from the Devonian to early Early Permian. At the beginning of the peak period of activity of pan-riftzation (Luodianian), al-ternate volcanic island and shallow marine environment within continent crust came into being. Uni-form and stable shallow-water carbonate platform was formed during the Xiangboan. This suggested that the activity of rift basin was evidently weakened. Subsequently the instability of the basin appre-ciably increased with the occurrence of basalt in late Kuhfengian. At last the whole Qamdo Block turned into the closure period of rift during the Late Permian.     

Uplift and evolution of Helan Mountain

The Helan Mountain lies in the northwest margin of Ordos Basin and its uplift periods have close relations with the tectonic feature and evolution of the basin. There are many views on the uplift time of Helan Mountain, which is Late Triassic and Late Jurassic. It is concluded by the present strata, magmatic rock and hot fluid distribution that the Helan Mountain does not uplift in Late Triassic to Middle Jurassic but after Middle Jurassic. Through the research of the sedimentary strata and deposit rate in Yinchuan Graben which is near to the Helan Mountain, it is proved that the Helan Mountain uplifts in Eocene with a huge scale and in Pliocene with a rapid speed. The fission track analysis of apatite and zircon can be used to determine the precise uplift time of Helan Mountain, which shows that four stages of uplifting or cooling: Late Jurassic to the early stage of Early Cretaceous, mid-late stage of Early Cretaceous, Late Cretaceous and since Eocene. During the later two stages the uplift is most apparent and the mid-late stage of Early Cretaceous is a regional cooling course. Together with several analysis ways, it is considered that the earliest time of Helan Mountain uplift is Late Jurassic with a limited scale and that Late Cretaceous uplift is corresponding to the whole uplift of Ordos Basin, extensive uplift happened in Eocene and rapid uplift in Pliocene.     

Uplift and evolution of Helan Mountain

The Helan Mountain lies in the northwest margin of Ordos Basin and its uplift periods have close relations with the tectonic feature and evolution of the basin. There are many views on the uplift time of Helan Mountain, which is Late Triassic and Late Jurassic. It is concluded by the present strata, magmatic rock and hot fluid distribution that the Helan Mountain does not uplift in Late Triassic to Middle Jurassic but after Middle Jurassic. Through the research of the sedimentary strata and deposit rate in Yinchuan Graben which is near to the Helan Mountain, it is proved that the Helan Mountain uplifts in Eocene with a huge scale and in Pliocene with a rapid speed. The fission track analysis of apatite and zircon can be used to determine the precise uplift time of Helan Mountain, which shows that four stages of uplifting or cooling Late Jurassic to the early stage of Early Cretaceous, mid-late stage of Early Cretaceous, Late Cretaceous and since Eocene. During the later two stages the uplift is most apparent and the mid-late stage of Early Cretaceous is a regional cooling course. Together with several analysis ways, it is considered that the earliest time of Helan Mountain uplift is Late Jurassic with a limited scale and that Late Cretaceous uplift is corresponding to the whole uplift of Ordos Basin, extensive uplift happened in Eocene and rapid uplift in Pliocene.     

The thermal history of the Sichuan Basin,SW China: Evidence from the deep boreholes

The Sichuan Basin is a superimposition basin composed of terrestrial and marine sediments that is well known for its abundant petroleum resources. Thermal history reconstruction using paleogeothermal indicators, including vitrinite reflectance and thermochronological data, shows that different structural subsections of the Sichuan Basin have experienced various paleogeothermal episodes since the Paleozoic. The lower structural subsection comprising the Lower Paleozoic to Middle Permian (Pz-P₂ successions experienced a high paleogeothermal gradient (23.0–42.6°C/km) at the end of the Middle Permian (P₂, whereas the upper structural subsection comprising Late Permian to Mesozoic strata underwent a relatively lower paleogeothermal gradient (13.2–26.9°C/km) at the beginning of the denudation (Late Cretaceous or Paleocene in the different regions). During the denudation period, the Sichuan Basin experienced a successive cooling episode. The high paleogeothermal gradient resulted from an intensive thermal event correlated to the Emeishan mantle plume. The heat flow value reached 124.0 mW/m² in the southwestern basin near the center of the Emeishan large igneous province. The low geothermal gradient episode with heat flow ranging from 31.2 to 70.0 mW/m² may be related to the foreland basin evolution. The cooling event is a result of the continuous uplift and denudation of the basin.     

Paleostructural geomorphology of the Paleozoic central uplift belt and its constraint on the development of depositional facies in the Tarim Basin

Inclined eastward and consisting of the Hetianhe, Hetianhedong, Tazhong paleouplifts and Bachu paleoslope, the central paleouplift belt in the Tarim Basin was a large composite paleouplift and paleoslope belt with complicated palaeogeomorphic features during the Middle to early Late Ordovician. A number of paleostructural geomorphic elements have been identified in the paleouplift belt and surrounding areas, such as the high uplift belts, the faulted uplift platforms, the marginal slopes and slope break zones flanking the paleouplift belt, the surrounding shelf slopes or low relief ramps, the shelf slope break zones and deep basin plains. They exerted great influence on the development of paleogeography of the basin. The marginal slopes and slope break zones flanking the uplift belt constrained the formation and deposition of the high-energy facies including reefal and shoal deposits during the Late Ordovician, which comprise the major reservoirs of the Lower Paleozoic in the basin. Toward the end of the Ordovician, the Tazhong paleouplift hinged westward and became a westward-dipped nose as the southeastern margin of the basin was strongly compressed and uplifted. The tectono-paleogeomorphic framework of the central northern basin during the Early Silurian and the Late Devonian to Early Carboniferous changed remarkably in topography from the initial low in east and high in west to high in northeast and low in southwest. The major paleogeomorphic elements developed in these periods included the strong eroded uplift high, the uplift marginal slope, the gentle ramp of the depression margin and the depression belt. The sandstones of the lowstand and the early transgressive systems tracts were deposited along the uplift marginal slopes and the gentle ramps of the depressions comprise the prolific reservoirs in the basin. The study indicates that the distribution patterns of the unconformities within the basin are closely related to the paleogeomorphic features and evolution of the paleouplift belt. From the high uplift belt to the depression, we found the composed unconformity belts at the high uplift, the truncated and onlap triangular unconformity belts along the uplift marginal slopes, the minor angular unconformity or discontinuity belts along the transitional zones from the uplift marginal slopes to depression and the conformity belt in the central depression. The truncated and the onlap triangular unconformity belts are the favorable zones for the formation of stratigraphic trap reservoirs. Supported by National Basic Research Program of China (Grant No. 2006CB202302), National Natural Science Foundation of China (Grant No. 40372056) and Frontier Research Project of Marine Facies     

南海南部礼乐盆地礁体发育区的构造热演化特征

礼乐滩是礼乐盆地的重要组成部分,自晚渐新世礼乐地块裂离北部陆缘后开始发育礁灰岩.为认识这些长期浸没海水中的礼乐礁体及其下伏地层的热状态与热演化特征,在详细分析礼乐滩钻井测温数据和镜质体反射率数据的基础上,对一条穿过礁体的骨干剖面进行了构造热演化数值模拟.结果显示,礁体区钻井2000～4500 m深度范围内温度介于30～90℃之间,井底与海底之间的平均地温梯度仅10℃·km^-1左右,地温梯度随深度逐渐增加,3000～4000m深度段地温梯度介于32～37℃·km^-1;礁体下伏地层有机质曾经经历了比现今所处温度更高的古温度.进一步分析表明,高孔高渗的礁体上部因与周围低温海水发生热交换,导致地层温度降低、地温梯度和热流降低甚至为负值;与海水热交换作用随深度增加而减弱并最终停止,地层温度逐渐升高,地温梯度和热流值趋于正常;现今钻井3000～4000 m深度段地温梯度约为35℃·km^-1,基底热流可能介于65～75 mW·m^-2,平均约为70 mW·m^-2;礁体发育区有机质热成熟度主要是...     

Coral reef health and effects of socio-economic factors in Fiji and Cook Islands

This research focuses on coral reef health in the South Pacific region, an area of high global coral diversity. Coral reef health surrounding four island case studies in the Cook Islands and Fiji have been assessed in areas that have not been previously surveyed. This study compares four islands with barrier and fringing reefs that have different levels of economic development, population pressure, land-use practices, and marine management practices. This interdisciplinary research methodology includes both ecological and social data collection to further understanding of human environment interactions. In comparing the reefs with different socio-economic factors, this research shows that reefs with traditional systems of resources management are healthier, population pressure is not the main factor causing the demise of the reefs and agro-industry is the main industry causing the degradation of the reef in these four South Pacific Islands. In addition, researchers need to use a whole reef perspective to examine coral reef health.     

Community replacement sequences and paleoenvironmental changes in reef areas of South China from Late Permian to Early Triassic exemplified by Panlongdong section in northeastern Sichuan Basin

The well-known Permian Changhsingian calcisponge reef located at Panlongdong section,Xuanhan county,northeastern Sichuan Basin has attracted wide attention.Due to severe dolomitization and poor quality of the fossils,the P-T boundary in this section is difficult to determine.This study,for the first time,recognized six communities in the Upper Permian Changhsingian Changxing Formation through the Lower Triassic Induan Feixianguan Formation of the Panlongdong section.They are Bryozoan-Archaeolithoporella-calcisponge Community,Calcareous green algae-foraminifer-crinoid Community,Microgastropod-foraminifer Community,Ostracod-microgastropod-cystic microbe Community,Ostracod-small brachiopod Community,and Non-calcified cyanobacteria Community.By using community replacement and palaeoenvironmental analysis,for the first time,we set the P-T boundary of the Panlongdong section at the middle of the calcimicrobialite containing cystic microbes.The community replacement sequence in the Panlongdong section is similar to that in other contemporaneous sections in reef areas of South China,indicating universal palaeoenvironmental changes during the Permian-Triassic transition.The results show that:(1)Changhsingian calcisponge reefs in South China generally vanished before the mass extinction and may be related to the large regression in the Late Permian.(2)The Calcareous green algae-foraminifer-crinoid Community replaced reef community and continued till the mass extinction.The mass extinction was probably related to the global sea-level drop.(3)The first aftermath community was dominated by specialized microgastropods,followed by the microbes,and then by the specialized microgastropods and small brachiopods.The succession of the three communities reflected the change in environmental conditions from dysoxic to anoxic and again to dysoxic.(4)In the Early Triassic,the relict community in shallow sea had very low diversity and low abundance,and was dominated by crinoids,gastropods,and bivalves.     

SEISMIC INTERPRETATION OF UPPER ELK POINT (GIVETIAN) CARBONATE RESERVOIRS OF WESTERN CANADA1

The seismic signatures of three reefs of the Upper Elk Point Subgroup (Givetian Stage) of the Western Canada Sedimentary Basin are documented and analysed on the basis of variations in seismic image of particular lithologic units, lateral amplitude and/or phase changes, structural relief and velocity-generated relief, as rendered by the reflection data. The effects on seismic signatures of spatial geological variations resulting from such phenomena as differential compaction, reef-focused salt dissolution, palaeotopography, lateral and vertical facies variations, regional dip, and reservoir morphology are discussed. The usefulness of seismic data in clarifying relationships between reefs and their adjacent sedimentary sections, particularly in cases where well control is sparse, is also considered. Such documentation of seismic signatures from known reefs using geophysical and geological analysis can establish criteria to enable recognition of similar buildups elsewhere. Three example reefs are presented, each typical of a particular area and environment of W. Canada. The first is from the Winnipegosis Formation of SE Saskatchewan, the second and third from the Rainbow Member and Upper Keg River Reef Member, respectively, of the Keg River Formation of NW Alberta. All three of these carbonate buildups developed in the evaporitic Elk Point Basin. However, the degree of salt encasement and subsequent dissolution varied greatly, as do the resulting seismic effects. For these three reef types, the typical elements of their seismic signatures have been compiled and are here summarized.     

Depositional environments of well‐sorted detrital limestone from the Minatogawa Formation in the southern part of Okinawa Island,the Ryukyu Archipelago,Japan

Well‐sorted detrital limestone is one of the typical lithofacies of the latest interval of the Pleistocene Ryukyu Group, which is exposed in the Ryukyu Archipelago in southwestern Japan. The depositional environments of the limestone are interpreted to be extremely shallow and to include back‐reef lagoons or moats and subaerial sand dunes. However, detailed micropaleontological analyses have not been performed on this limestone. In this study, the interpretation of the depositional environments and paleo‐water depths was improved by quantitative examination of foraminiferal assemblages for the well‐sorted detrital limestone of the Minatogawa Formation in the southern part of Okinawa Island. Thin sections of limestone collected from the Minatogawa (Horikawa) quarry were subjected to sedimentological and foraminiferal analyses. Comparison with modern foraminiferal distribution within the Ryukyu Archipelago indicates that back‐reef and fore‐reef dwelling foraminifers characterize the fossil assemblages from the well‐sorted detrital limestone (bioclastic grainstone). Three ratios of indicator foraminiferal taxa (ratios of back‐reef to fore‐reef taxa, planktonic foraminifers to Amphistegina lobifera and Amphistegina lessonii, and Calcarina gaudichaudii to other Calcarina species), as well as multivariate analyses suggest that the well‐sorted detrital limestone was deposited in fore‐reef setting shallower than 40 m in water depth. A comparable depth range was reconstructed from the coral assemblage in the associated coral limestone, suggesting that the Minatogawa Formation was deposited in a gently inclined ramp setting with patch reefs and/or fringing reefs. Stratigraphic changes in paleo‐water depth, together with evidence of several unconformities associated with paleosol layers suggest that there were repeated transgressions and regressions, with an amplitude up to several tens of meters, when the Minatogawa Formation was deposited.     

Paleomagnetism of Carboniferous-Permian and early jurassic geological complexes in Mongolia

Paleomagnetic characteristics of Carboniferous-Permian and Early Mesozoic geological complexes in Mongolia are studied. The studied rocks are shown to possess a multicomponent magnetization. Lowtemperature overprinting components of normal polarity discovered in nearly all of the studied strata were acquired after main deformation stages of the rocks, apparently in the Cenozoic. High-temperature overprinting components of reversed polarity identified in rocks of an active continental margin (ACM) were acquired when bimodal magma melts moved through ACM volcanic sequences. Late Carboniferous and Early Permian paleomagnetic poles of Mongolia calculated from directions of primary magnetization components are, respectively (Λ = 154.6, Φ = 32.2, A = 7.8) and (Λ = 95, Φ = 71, A = 8.7). Apparently, the territory of Mongolia in the Early Permian was a margin of the Siberian craton and was separated from the Northern China block by a basin extending for no less than 2000 km in the E-W direction. The strike of a marginal-continental volcanic belt was submeridional and a plate subducted under the continent from the east. Late Carboniferous-Permian intraplate magmatic complexes of Mongolia formed at various latitudes from various mantle sources during the northward movement of the Mongolian part of the Siberian continent. The oldest bimodal sequences of the Gobi-Tien Shan zone (318–314 Ma) formed at more southern latitudes (40°–47°–54°N) as compared with the 275-Ma complexes of the Gobi-Altai zone (51°–58°–67°N). Thus, sources of the Carboniferous-Permian intraplate magmatism in Central Asia either occupied a vast mantle region (up to 1000 km in the latitude direction) or moved together with the Asian continent.     

Integrated Radiolaria,benthic foraminifera and conodont biochronology of the pelagic Permian blocks/tectonic slices and geochemistry of associated volcanic rocks from the Mersin Mélange,southern Turkey: Implications for the Permian evolution of the northern Neotethys

Blocks and tectonic slices within the Mersin Mélange (southern Turkey), which are of Northern Neotethyan origin (Izmir–Ankara–Erzincan Ocean (IAE)), were studied in detail by using radiolarian, conodont, and foraminiferal assemblages on six different stratigraphic sections with well‐preserved Permian succesions. The basal part of the Permian sequence, composed of alternating chert and mudstone with basic volcanics, is assigned to the late Asselian (Early Permian) based on radiolarians. The next basaltic interval in the sequence is dated as Kungurian. The highly alkaline basic volcanics in the sequence are extremely enriched, similar to kimberlitic/lamprophyric magmas generated at continental intraplate settings. Trace element systematics suggest that these lavas were generated in a continental margin involving a metasomatized subcontinental lithospheric mantle source (SCLM). The middle part of the Permian sequences, dated by benthic foraminifera and conodont assemblages, includes detrital limestones with chert interlayers and neptunian dykes of middle Wordian to earliest Wuchiapingian age. Higher in the sequence, detrital limestones are overlain by alternating chert and mudstone with intermittent microbrecciated beds of early Wuchiapingian to middle Changhsingian (Late Permian) age based on the radiolarians. A large negative shift at the base of the Lopingian at the upper part of section is correlated to negative shifts at the Guadalupian/Lopingian boundary associated with the end‐Guadalupian mass extinction event. All these findings indicate that a continental rift system associated with a possible mantle plume existed during the late Early to Late Permian period. This event was responsible for the rupturing of the northern Gondwanan margin related to the opening of the IAE Ocean. When the deep basinal features of the Early Permian volcano‐sedimentary sequence are considered, the proto IAE oceanic crust formed possibly before the end of the Permian. This, in turn, suggests that the opening of the IAE Ocean dates back to as early as the Permian.     

南黄海盆地基底及海相中、古生界地层分布特征

南黄海盆地是大型海相中、古生界和陆相中、新生界两期叠合型盆地,本文根据最新地震资料结合钻井资料及与海陆地质资料的对比研究对盆地内地震层序进行了划分,得到了陆相中、新生界盆地基底即中、古生界海相盆地的顶界埋深、三叠系和上二叠统的残留厚度,推断了陆相层基底地层分布,并根据磁力异常资料推测了海相中、古生界盆地结晶基底埋深,推断了海相中、古生界整体残留情况.下三叠统青龙组和上二叠大隆及龙潭组在南黄海盆地南部坳陷及勿南沙隆起广泛存在,而在北部坳陷的分布则狭窄,中部隆起则由于隆起和剥蚀作用导致这两套地层几乎没有残余.对中-古生界海相盆地和中-新生界陆相盆地的基底特征进行了比较,认为海相中、古生界在南黄海地区区域性存在,海相层厚度分布特征受基底起伏控制,同时受到印支板块运动的影响,中部隆起区是海相中、古生界比较稳定的地区.下古生界可能在南黄海盆地广泛分布,但受资料限制,还难以获知其残余地层的特征.     

The Piedmont landscape of Maryland: A new look at an old problem

The Piedmont upland of Maryland has been variously interpreted as a peneplain, a series of peneplains, a surface of marine planation, and a landscape in dynamic equilibrium. These different perspectives of landform evolution are related to different scales of time and space. Both equilibrium and episodic erosion features can be recognized in the modern landscape. An equilibrium condition is suggested by adjustment of first and second order streams to rock structure and lithology, entrenchment of some streams against gneiss domes, altitudinal zonation of rock types around gneiss domes, correlation of lithology with overburden thickness on uplands, decreasing overburden thickness on uplands related to decreasing degree of metamorphism of crystalline rocks, and correlation of secondary mineral assemblages with subsurface drainage and slope. The long-term episodic character of erosion is suggested by clastic wedges on the adjacent Coastal Plain, an upland of low relief that truncates non-carbonate rocks of different lithologies, isovolumetric chemical weathering of alumino-silicate rocks, clastic deposition in marble valleys, and weathering profile truncation by modern drainage. The Maryland Piedmont may have been an area of positive relief subject to subaerial erosion since Triassic and possibly Permian time. The upland surface preserved in the eastern Piedmont developed by the Late Cretaceous. In the interval from the Late Cretaceous to the Late Miocene, low input of terrigenous sediments to the Coastal Plain, dominance of marine sedimentation, and spotty evidence of saprolite formation on crystalline rocks, suggest that the Maryland Piedmont was an area of low relief undergoing intense weathering. Incised valleys were formed during a cycle of erosion probably initiated in the Late Miocene and extensive colluvial sediments were deposited on hillslopes by periglacial processes during the Pleistocene.     

南海西北部沉积盆地晚新生代沉降、沉积特征:对深部异常过程的响应

南海西北部雷琼区域出露大量晚新生代碱性玄武岩,且地震层析成像结果显示其地幔存在类似地幔热柱特征的低速异常体.为了揭示该异常体的活动信息及其对表层地质过程的影响,本文选择位于雷琼区域的北部湾盆地和珠三坳陷为研究对象,系统分析了它们早中新世以来的构造沉降、与基底隆升有关的剥蚀面和岩浆活动特征.结果显示,研究区晚中新世构造沉降速率表现为低速异常;晚中新世以来,研究区发育了2个因基底隆升形成的局部剥蚀面,剥蚀范围大致以雷琼火山区为中心呈环状分布,中心区域剥蚀量较大,累积厚度100～200m;中中新世后研究区部分区域因岩浆活动导致上覆地层隆起和沉积环境变化.分析表明雷琼地区深部低速异常体对表层升降影响有限,推测该深部异常体规模较小,可能是深部更大规模异常体的一个分支.     

Introductory perspective on the COREF Project

Abstract Coral reefs are tropic to subtropic, coastal ecosystems comprising very diverse organisms. Late Quaternary reef deposits are fossil archives of environmental, tectonic and eustatic variations that can be used to reconstruct the paleoclimatic and paleoceanographic history of the tropic surface oceans. Reefs located at the latitudinal limits of coral‐reef ecosystems (i.e. those at coral‐reef fronts) are particularly sensitive to environmental changes – especially those associated with glacial–interglacial changes in climate and sealevel. We propose a land and ocean scientific drilling campaign in the Ryukyu Islands (the Ryukyus) in the northwestern Pacific Ocean to investigate the dynamic response of the corals and coral‐reef ecosystems in this region to Late Quaternary climate and sealevel change. Such a drilling campaign, which we call the COREF (coral‐reef front) Project, will allow the following three major questions to be evaluated: (i) What are the nature, magnitude and driving mechanisms of coral‐reef front migration in the Ryukyus? (ii) What is the ecosystem response of coral reefs in the Ryukyus to Quaternary climate changes? (iii) What is the role of coral reefs in the global carbon cycle? Subsidiary objectives include (i) the timing of coral‐reef initiation in the Ryukyus and its causes; (ii) the position of the Kuroshio current during glacial periods and its effects on coral‐reef formation; and (iii) early carbonate diagenetic responses as a function of compounded variations in climate, eustacy and depositional mineralogies (subtropic aragonitic to warm‐temperate calcitic). The geographic, climatic and oceanographic settings of the Ryukyu Islands provide an ideal natural laboratory to address each of these research questions.     

Upper Jurassic and lower cretaceous of Sanjiang-Middle Amur basin: Non-marine and marine correlation

A comparative analysis of Late Jurassic-Early Cretaceous strata have been done for the Sanjiang-Middle Amur basin, a coal- and oil-bearing area spanning the eastern Heilongjiang of northeastern China and southeastern Far East of Russia. On the basis of various fossils occurring in the formations, particularly by means of the Tithonian-Valanginian index Buchia and the late Barremian-middle Albian indicator Aucellina assemblages, the marine and non-marine Late Jurassic-Early Cretaceous strata in the basin are correlated. The Mesozoic international chronostratigraphic chart () is established basically based on the marine rocks. To accurately date the non-marine strata, it is necessary to correlate them with the marine deposits. This study sheds new light on the dating and correlation of non-marine Upper Mesozoic. Additionally, the results would help understand the tectonics and paleogeography and thus aid the exploration of energy resources.