Why is stromatactis so rare in Mesozoic carbonate mud mounds?

The sedimentary–diagenetic structure stromatactis is widespread in Palaeozoic spiculitic carbonate mud mounds, but occurs only sporadically in Mesozoic sponge carbonate mud mounds. Comparative analysis of Palaeozoic and Mesozoic stromatactis limestones suggests that this variation results from the degree of siliceous sponge skeletal rigidity and the amount of internal sediment accumulation in the original cavity network. Partial to entire filling by internal sediment resulted in a continuum, from a small amount of internal sediment and large amount of cement (stromatactis, common in the Palaeozoic), to only internal sediments (aborted stromatactis, common in the Mesozoic). These observations match independent lines of evidence concerning the siliceous sponge evolution and sediment recycling (e.g. bioerosion) across the Palaeozoic to Mesozoic biotic revolution.     

Tectonothermal history of the Holy Cross Mountains (Poland) in the light of low‐temperature thermochronology

The low‐temperature thermal history of the Holy Cross Mountains (HCM) is investigated by apatite fission track and apatite and zircon (U–Th)/He thermochronology. Our results provide constraints on the deformation history of Palaeozoic basement rocks in the transition area from Precambrian to Palaeozoic Europe that are exposed from beneath Permian–Mesozoic sediments within the HCM. Late to post‐Variscan cooling of the Palaeozoic strata from maximum temperatures is shown to be a major feature of the HCM. This cooling likely followed a heating event related to burial and/or hot fluid circulation along the Holy Cross Fault in the late Carboniferous. The central part of the HCM shows a rapid cooling event caused by tectonic inversion, which started in the Late Cretaceous. However, this event was less pronounced in the western margin of the HCM, where slow cooling continued throughout the Mesozoic with only minor acceleration of the cooling rate since the latest Cretaceous.     

Diversity and faunal changes in the latest Cretaceous dinosaur communities of southwestern Europe

Characterization of macroecological patterns for latest Cretaceous dinosaur communities is essential to understand how those faunas were changing during the run-up to the Cretaceous-Paleogene extinction event, and thus the cause of the extinction. Outside of the well-studied latest Cretaceous dinosaurs of North America, southwestern Europe (France, Spain and Portugal) preserves one of the richest end-Cretaceous dinosaur fossil records, as it has produced hundreds of dinosaur fossil localities. We compiled a comprehensive database of all dinosaur fossil occurrences from the uppermost Cretaceous of the Ibero-Armorican region and analyze it statistically, providing the first numerical study of the ecological and taxonomic diversities of these communities. Our study corroborates previous work that has identified a major faunal change in the latest Cretaceous terrestrial vertebrate assemblages, and places this event around the C31r-C31n reversal, in the early late Maastrichtian (c. 69 Ma). Significant differences in ecological diversity metrics (dominance, Shannon and Simpson) characterize the pre- and post-turnover assemblages. The turnover event, therefore, did not only lead to a taxonomic replacement but also important reorganizations in the structure of dinosaur communities. Herbivorous dinosaurs suffered the most dramatic alterations across the turnover, in terms of relative dominances, by shifting their contributions within the communities (hadrosauroids replacing titanosaurids as the dominant taxon in the medium-to large-bodied herbivore niche) or even disappearing (rhabdodontids and nodosaurids). The carnivores apparently maintained similar relative abundances before and after the turnover, and the relative proportions between carnivorous and herbivorous taxa remained static through time. Further improvement of the present database might allow for the identification of new ecological patterns, and higher-resolution comparison with the North American records.     

A look with μCT technology into a treasure trove of fossils: The first two fossils of the millipede order Siphoniulida discovered in Cretaceous Burmese amber (Myriapoda,Diplopoda)

Millipedes (Diplopoda) are an important fossil group of land arthropods in the Palaeozoic. However, there is a gap in the Mesozoic, with only slightly more than a dozen fossils being known, until the much more recent fossil records mainly from Cenozoic Dominican and Baltic ambers become available. Burmese amber, precisely dated to the Late Cretaceous, is known for an apparently rich but still undescribed millipede fauna, and might represent the ideal bridge to close this gap in the millipede fossil record. In addition, modern micro-computed tomography (μCT) technology allows complex 3D reconstructions of objects fossilized in amber. Here we utilize μCT technology to describe the first millipedes from Burmese amber, which are also the first two fossil representatives of the order Siphoniulida. Siphoniulida, with two known species and just nine recorded specimens, are the rarest and least known of the 16 extant orders of the Diplopoda. Records are known from Sumatra, Guatemala and Mexico. The two new fossils described here represent two distinct species, Siphoniulus muelleri sp. nov. and S. preciosus sp. nov., and indicate a wider distribution of this order in the Cretaceous. The holotype of S. muelleri sp. nov. was well-enough preserved so that characters of the head, such as the incisura lateralis, not investigated before in extant representatives of the order, could be studied. This study highlights the possibilities and challenges provided by μCT technology in investigating Diplopoda fossilized in amber.     

华北克拉通东部南北缘中生代火山-沉积格局及其构造转折过程

通过华北克拉通东部北缘和南缘盆地充填序列和盆地分布演化对比研究,解析了该区中生代构造转折过程。研究发现两侧盆地均大致从早侏罗世开始发育,约以晚侏罗世为界,之前盆地充填记录反映以挤压作用、岩石圈增厚为主,之后以陆内伸展、岩石圈减薄为主,显示晚侏罗世明显的构造转折,并且地壳浅部的构造体制转变均滞后于岩石圈深部构造环境的变化。然而,两侧盆地演化也有明显差别：①北缘燕辽地区从早侏罗世到白垩纪,发育了多层系的从基性、中基性到中酸性的火山岩及火山碎屑岩组合,而南缘合肥盆地仅在晚侏罗世早白垩世产出钙碱性火山岩及火山碎屑岩组合,反映出不同的深部构造过程和源区特征;②北缘的岩石圈减薄可能始于约163 Ma,南缘明显的岩石圈减薄则始于约149 Ma,而反映在盆地构造与充填尺度上的伸展作用分别对应于大约145 Ma和132 Ma;③晚侏罗世构造转折期,北缘燕辽地区粗碎屑沉积以河流体系为主,反映盆山地势高差较小;而南缘该期发育冲积扇体系,盆山地势高差较大;④北缘盆地沉积中心迁移规律复杂,而南缘总体呈现由南向北的迁移趋势。显然,大别山碰撞造山和后造山期强烈的隆升和剥露对南缘盆地演化具有极大的主导和制约作用,而北缘则显示出强烈的壳幔相互作用并伴有区域性的陆内挤压推覆（转折前）和张裂 伸展（转折后）交替的特点。华北克拉通晚中生代构造转折的时限北缘较南缘早,说明诱发这一转折事件的区域构造动力可能首先与华北北部壳幔相互作用密切关联。     

A new afrograptid (Diplostraca: Estheriellina) from the Lower Cretaceous of southern England

The Family Afrograptidae is a ‘conchostracan’ group with multiple radial costae reaching to the umbo on their carapaces. It comprises four described genera: Afrograpta, Camerunograpta, Congestheriella and Graptoestheriella with a total of thirteen described species which are occasionally reported from the Jurassic and the Cretaceous in Africa, Europe and South America (i.e. Afrograpta from the Upper Cretaceous of Cameroon; Camerunograpta from the Jurassic to Cretaceous of Cameroon; Congestheriella from the Jurassic to Upper Cretaceous of the Congo Basin, Brazil, Bulgaria, Venezuela and Argentina; and Graptoestheriella from the Upper Jurassic to Lower Cretaceous of Brazil). A new genus and a new species, Surreyestheria ockleyensis gen. et sp. nov., belonging to the Family Afrograptidae from the Lower Cretaceous (lower Barremian) Upper Weald Clay Formation of Ockley Village, Surrey County, southern England is described in this paper. The new genus mainly differs from the other four genera by the special reticulate ornamentation on its carapace. It indicates that the Family Afrograptidae was more diverse and more widely distributed in the late Mesozoic than previously supposed. Afrograptidae is a special branch of Estheriellina the latter originating in the late Palaeozoic and the former in the early Mesozoic. Afrograptids, as a whole had been widespread across Pangea in the Early Jurassic.     

苏北盐阜地区中、古生界地层分布特征

应用钻井、测井及古生物资料,对下扬子苏北盐阜地区中、古生界地层进行研究,同时综合了重、磁、电、二维地震、MT二维剖面等资料,探讨盐阜地区中生界残留地层展布规律。研究结果表明,中生界白垩系浦口组在研究区广泛分布,厚度较大,且分布稳定,而赤山组、葛村组及侏罗系、三叠系局部零星分布;上古生界地层残存在滨海隆起—建湖隆起引水沟凸起一带,下古生界地层残存在淮阴凹陷—盐城凹陷地区。     

中国贵州中生代四足类足迹化石的回顾与新发现*

贵州省拥有丰富的中生代脊椎动物化石记录,多为三叠纪海生爬行类化石,侏罗纪和白垩纪的脊椎动物化石较少。目前,贵州省已发现中生代爬行类足迹点9处,分别为贞丰牛场、贞丰龙场、安顺幺铺、赫章辅处、毕节响水(2处)、仁怀茅台、赤水宝源和习水同民足迹点。文中除描述了贞丰龙场新增的一批足迹化石外,整理并总结了所有足迹点的发现史、研究现状、足迹类型与特征以及所反映的古生态信息。已发现的遗迹记录由69条行迹和420个孤立足迹组成,足迹总数达991个。所有的遗迹化石指示了至少477个造迹者,包括海生爬行类、手兽足迹类、非鸟兽脚类、鸟类、蜥脚类和鸟臀类等,其中三叠纪以海生爬行类主导,侏罗纪和白垩纪以蜥臀类主导。这个数据集为贵州中生代古生物类群的多样性提供了重要的信息,是晚中生代稀缺骨骼化石记录的良好补充,为研究贵州省中生代脊椎动物群的古生态与古环境提供了更多的证据。     

Tectonic setting, petrology and geochronology of jadeite + glaucophane and chloritoid + glaucophane schists from north-west Turkey

The north-west Turkish blueschists represent a subducted passive continental margin sequence dominated by metaclastic rocks and marble. The depositional age of the blueschist protoliths are probably Palaeozoic to Mesozoic, while the age of the high-pressure/low-temperature metamorphism is Late Cretaceous. Blueschists are tectonically overlain by a volcanosedimentary sequence made up of accreted oceanic crustal material that locally shows incipient blueschist metamorphism and by spinel peridotite slices. The metaclastic rocks with regional jadeite and glaucophane, which comprise the lower part of the blueschist unit, make up an over 1000-m-thick coherent sequence in the Kocasu region of north-west Turkey. Rare metabasic horizons in the upper parts of the metaclastic sequence with sodic amphibole + Iawsonite but no garnet indicate lawsonite blueschist facies metamorphism. The blueschist metaclastics in the Kocasu region are practically free of calcium and ferric iron and closely approximate the NFMASH system in bulk composition. Two low-variance mineral assemblages (with quartz and phengite) are jadeite + glaucophane + chlorite + paragonite and chloritoid + glaucophane + paragonite. The metaclastics comprise up to several-metres-thick layers of jadeite schist with quartz, phengite and nearly 100 mol% jadeite. Phase relations in the metaclastics show that the chloritoid + glaucophane assemblage, even in Fe²⁺-rich compositions, is stable in the jadeite stability field. In the NFASH system the above assemblage without the accompanying garnet has a narrow thermal stability field. Mineral equilibria in the metaclastics involving chloritoid, glaucophane, jadeite, paragonite and chlorite indicate metamorphic P-T conditions of 20 ± 2 kbar and 430 ± 30 d? C, yielding geothermal gradients close to 5d? C km^-1, one of the lowest geotherms recorded. Blueschists in the Kocasu region, which have been buried to 70 km depth, are tectonically overlain by the volcanosedimentary sequence and by peridotite buried not deeper than 30 km. Phengites from two jadeite schists were dated by Ar/Ar laser probe; they give an age of 88.5 ± 0.5 Ma, interpreted as the age of metamorphism. Blueschists and the overlying peridotite bodies are intruded by 48-53-Ma-old granodiorite bodies that were emplaced at 10 km depth. This suggests that the exhumation of blueschists by underplating of cold continental crust, and normal faulting at the blueschist-peridotite, interface occurred during the Late Cretaceous to Palaeocene (88-53 Ma).     

Pollen diagrams from the Shumagin Islands and adjacent Alaska Peninsula, southwestern Alaska

Pollen diagrams of 10 peat sections taken in sedge tundra span as much as 10.730 radiocarbon years and show a varied sequence of pollen assemblages dominated by herbs and shrubs. Taxa, for the most part. belong to the Gramineae. Cyperaceae. Salix, Abuts, Beiula and Empelrum. The assemblages indicate scral changes in the vegetation, resulting from interaction of climate and of successive ashfalls from regional volcanoes, and suggest a patchwork of late Quaternary plant communities. This record from southernmost Beringia enlarges upon previous pollen records from the Aleutian Islands and from the southern part of the Bering land bridge region in western Alaska.     

The Cretaceous/Palaeogene (K/P) boundary at Aïn Settara, Tunisia: restructuring of benthic foraminiferal assemblages

Benthic foraminiferal assemblages, in contrast to planktic foraminifera, generally did not suffer mass extinctions at the Cretaceous/Palaeogene (K/P) boundary; extinctions were fewer in deeper water. However, the outer shelf, upper bathyal section at Aïn Settara, Tunisia, records a dramatic change in the structure of benthic foraminiferal assemblages across the K/P boundary. At the level of extinction of planktic assemblages and enrichment in Ir and other geochemical anomalies, highly diversified, low-dominance Upper Maastrichtian assemblages with infaunal and epifaunal morphogroups were suddenly replaced by taxonomically impoverished assemblages, strongly dominated by epifaunal morphogroups. This extinction or temporary emigration of most infaunal morphogroups is interpreted to be the result of a sudden breakdown in food supply. This, in turn, is the consequence of a sudden collapse in primary productivity, probably resulting from the impact of the K/P asteroid.     

Seismostratigraphy and structural framework of the SW Baltic Sea

The SW part of the Baltic Sea between Scania, Rügen, Bornholm and Mön constitutes a complex crustal transition between the Baltic Shield and the accreted Phanerozoic provinces of the West European Platform. An integrated interpretation of marine reflection seismic data sets from the BABEL AC line and two commercial surveys offshore NE Germany and S Sweden have resulted in a complete view of the structural framework in the area. The general seismic picture can best be detected by two characteristic sets of reflection phases. The lower set is dominated by slightly dipping and vertically displaced prominent reflectors corresponding to downfaulted Lower Palaeozoic strata on top of the Precambrian basement. The upper set represents Mesozoic and Cenozoic coherent reflection phases including a thick Upper Cretaceous unit. The Caledonian deformation front is identified in the southern part of the investigated area as the border against which basement rocks have been affected by Caledonian metamorphism and deformation. Major structural elements also include the N–S trending Agricola–Svedala Fault and North Rügen-Skurup Fault. Several NW–SE trending faults are also identified including the Nordadler–Kamien Fault, Jutland–Mön Fault, Carlsberg Fault, Romeleåsen Fault Zone and the Fyledalen Fault Zone. The sedimentary record from NE German offshore wells and Scanian boreholes is compared with the seismic data. The Cambro-Silurian strata are composed mainly of quartzitic sandstones, shales and biomicritic limestones. The Silurian is dominated by grey, micaceous shale and micaceous siltstone deposited in a marginal basin. Upper Palaeozoic strata are merely encountered in the southernmost part of the investigated area. These include Zechstein strata. The Mesozoic deposits are dominated by a thick Cretaceous sequence of mainly limestones with interbedded sandstones.     

华南衡阳盆地上白垩统黄土类似物的初步研究

中国新生代黄土序列具有沉积速率高、连续性好等特点,记录了东亚地区持续的古气候动力学演化和重大地质事件信息。受区域构造-地貌和大气环流格局影响,中生代晚期华南发育了众多盆山型古沙漠系统且出露了巨厚的风成砂,但几乎未有学者提及黄土/黄土类似物的存在。本文通过粒度端元解析、野外露头的构型分析等手段,对衡阳盆地上白垩统红花套组进行了初步研究,识别出风成砂丘、砂席和泥滩等环境类型;并在泥滩环境中提取到黄土类似物的粒度组分信号,同时提出了黄土类似物的风成成因,总结了其形成-堆积过程。这项工作旨在探索白垩纪黄土类似物存在的可能性,为未来开展华南陆块中生代风尘记录研究提供契机。     

内蒙古西部额济纳旗地区X井油气显示特征与油气源探讨

根据内蒙古额济纳旗地区X井白垩系额济纳旗组、侏罗系麻木鸟苏组、古生界顶面风化壳等不同层段的油气显示特征和钻井泥浆烃类气体组分、甲烷C同位素的分析结果,认为侏罗系和白垩系油气显示特征相同,为油与气显示,气体样品的干燥系数(C_1/C_总)为0.80～0.87,甲烷C同位素δ~(13)C_1为-48.19‰～-50,87‰,表现了低成熟热解气的特征;古生界风化壳为气显示,天然气干燥系数(C_1/C_总)为0.91～0.92,甲烷C同位素δ~(13)C_1为-21.56‰-30.91‰,表现了高成熟热解气的特征.该井及邻区的中生界、古生界烃源岩干酪根类型及其演化程度具有显著的差别,中生界烃源岩以低成熟混合型干酪根为主,古生界烃源岩为成熟-高成熟(或过成熟)的混合型-腐泥型干酪根.表明该区存在以中生界侏罗系-白垩系低成熟烃源岩为油气源的油气系统和古生界高成熟(或过成熟)烃源岩为气源的油气系统,指示了古生界油气资源前景.     

鄂尔多斯盆地西南地区蓟县系古地温演化历史及岩浆热事件的影响

深层油气成藏机理研究的首要前提是要明确烃源岩的热演化历史,这对区域油气勘探潜力的评价有着重要的指导意义。鄂尔多斯盆地西南缘蓟县系烃源岩在中生代以来的热演化史有何特征,是否受早白垩世岩浆热作用的影响,影响程度如何等问题的不明确,制约着人们对该地区中元古界烃源岩的生烃潜力的认识及进一步勘探开发的思路。通过对安口—铜城地区出露的三叠系、侏罗系及铜城岩体进行磷灰石裂变径迹、磷灰石/锆石(U-Th)/He测试,结合镜质组反射率数据,分别恢复了该地区沉积岩在中三叠世以来和侵入岩在早白垩世以来的冷却历史,结合岩浆岩体的空间分布特征和泥页岩镜质组反射率,估算蓟县系烃源岩古地温。热年代学模拟表明,蓟县系烃源岩自中生代以来先后经历了三叠纪—侏罗纪的正常埋深增温,达到了生烃温度门限,自早白垩世约130～110 Ma开始冷却,其中个别样品表现为自始新世中期至45 Ma微弱加速冷却,中新世晚期至8 Ma以来快速冷却。研究表明,中晚侏罗世是鄂尔多斯盆地西南缘蓟县系生烃的关键时期,烃源岩处于主生油温度范围,之后的早白垩世晚期岩浆侵入事件的热作用范围有限,对蓟县系烃源岩古地温的影响仅发生在局部地区。鄂尔多斯盆地西南缘...     

Paleogeography of the Southern Baltic Region in the late Mesozoic: Implications of foraminifers

Foraminifers from Middle-Upper Jurassic and Upper Cretaceous sediments of the Kaliningrad basin located in the southwestern part of the East European platform are studied. During the greater part of the Late Mesozoic, the study region represented a northern margin of a spacious epicontinental sea in the Boreal zoogeographic realm. The analyzed composition and quantitative distribution of foraminifers, ratio between planktonic and benthic species, ornamentation degree of tests, and their preservation are used to reconstruct paleogeography and history of eustatic sea-level changes. The upper Callovian through Upper Jurassic zonation based on distribution of Epistomina species is proposed. Defined foraminiferal assemblages are correlated with coeval assemblages from the East to West European platforms and North Atlantic     

吉林果松盆地早白垩世果松组火山岩年代学及其地质意义

以果松盆地果松组火山岩为研究对象,对标准剖面安山岩进行了精确的锆石U-Pb定年分析,旨在确定其形成时代。样品中的锆石多呈自形-半自形晶,振荡环带发育,Th/U比值在0.48~2.77之间,显示其典型的岩浆成因。锆石U-Pb定年结果显示,原定中晚侏罗世的果松组火山岩形成于130 Ma(加权平均年龄为130±2 Ma,MSWD=0.48)或129 Ma(加权平均年龄为129±2 Ma,MSWD=0.14),应划归为早白垩世。根据果松盆地中生界岩石组合特点,结合新获得的火山岩测年数据和生物化石种群特征,重新厘定果松盆地中生代地层序列,进而讨论了果松盆地与邻区白垩纪地层单元的地层对比关系。     

Geomagnetic reversal history

The history of geomagnetic polarity reversals in the Cenozoic and Late Mesozoic is well known since the Late Jurassic (Oxfordian). A continuous record of polarity has been derived for this time interval from the interpretation of oceanic magnetic anomalies. Most of the polarity chrons in this oceanic record have been verified and dated in coordinated magnetostratigraphic and biostratigraphic studies. This has led to the generation of progressively refined and improved geomagnetic reversal time-scales that provide a framework for absolute dating of palaeontological zonations. By serving as a basis for statistical analysis of reversal frequency they provide information relevant to processes in the Earth's core. The rate of reversals since the Late Cretaceous shows a steady increase on which a cyclical variation appears to be superposed. A stochastic model for reversals predicts a Poisson distribution of polarity interval lengths. The polarity time scales contain many fewer short (± 50 kyr) polarity chrons than a Poisson distribution, and it has been suggested that a gamma renewal process with index greater than unity is a more appropriate statistical model. The statistical arguments give no convincing reason for abandoning the model and other, physical reasons must be sought to explain the incompleteness of the reversal record. The discovery and verification of short chrons in the oceanic record may best be investigated by deep-tow magnetometer surveys. The reversal history before the Late Jurassic is not well known. Magnetostratigraphy in coeval Early Jurassic sections has not given correlatable records and it has not been possible to compile a definitive polarity sequence. Evaluation of geomagnetic polarity history for the Early Mesozoic and the Palaeozoic will require unambiguous magnetostratigraphy in well-dated sections where verification of the polarity pattern is possible at the fossil zone or stage level.     

鲁西隆起晚中生代盆地重矿物组合分析及其构造响应

本文以鲁西隆起区盆地及周边盆地砂岩中碎屑重矿物为研究对象,通过重矿物的稳定性分析,以及通过不同源区重矿物组合的差异,探讨了鲁西隆起及周边地区晚中生代以来的物源及构造演化过程。研究结果显示,鲁西盆地中生代早期早中侏罗纪时期主要源区为鲁西隆起,中晚侏罗纪时期主要物源为胶东地区和鲁西隆起,而早白垩世时期主要物源为胶东地区,其次才是鲁西隆起。晚白垩世沂沭断裂带盆地物源主要是鲁西隆起和胶东地区,鲁西隆起贡献量大于胶东地区。重矿物的稳定性也折射出源区构造演化历史。早-中侏罗世至中-晚侏罗世,鲁西盆地重矿物物源由鲁西隆起向胶东地区的显著转变,暗示着苏鲁造山带自三叠纪形成之后,经折返抬升,至晚侏罗世之前已经到达地表。重矿物的含量变化显示,早白垩世中期和晚白垩世中期鲁西盆地内沉积了大量的鲁西变质岩矿物组合,并且不稳定重矿物含量急剧增加,我们推测鲁西在早白垩世晚期、晚白垩世中期存在两次构造抬升。