Jurassic ammonite faunas from Nepal and their bearing on the palaeobiogeography of the Himalayan belt

From the Upper Bathonian up to the Tithonian–Berriasian, six main faunas and twelve basic faunal assemblages within them are distinguished in Nepal. The successive faunas show (1) low taxonomic diversity and (2) the dominance of a small number of genera and the subordinate place of the associated taxa.The assemblages include: (1) strictly Tethyan (e.g., Mediterranean or European Tethyan) species and/or genera, very few in number and occurring as isolated individuals or discontinuous faunal horizons; (2) Indo-Malagasian components, some scattered, others with a wide occurrence in the SW Pacific, some as far as Antarctica and/or Patagonia; (3) indigenous genera endemic for the Himalayas and the SW Pacific region. Faunas of the same age for the Sula Islands, Papua-New Guinea, Australia, New Zealand, Antarctica and South America are also considered.In spite of common components, the Himalayan faunas contrast with the relatively higher diversity of the Indo-Malagasian faunas. Low diversity and dominance of indigenous genera mean that the faunas extending from the Himalayas to Antarctica and Patagonia represent an actual biogeographical unit, the Indo Pacific (faunas and) Realm.Indo Pacific and Tethyan faunas show a less marked contrast than the Tethyan and Boreal. Transitional or mixed faunas of subaustral type developed in the Indo-Malagasian and Andean regions. This is explained by the absence of a geographical trap comparable to the land-locked palaeogeography of the Arctic Basin. The palaeogeography of the Arctic amplified the role of the other environmental factors. Among these the high latitude seasonal effects are likely to have resulted in environmental instability, controlling trophic resources and therefore the structure of the ecosystems, for instance low diversity and high density of the high latitude ammonite faunas.     

Palaeobiogeographic implications of Late Bajocian-Late Callovian (Middle Jurassic) dinoflagellate cysts from the Central Alborz Mountains, northern Iran

The Dalichai Formation with an age of Late Bajocian-Late Callovian was sampled in Central Alborz Mountains of northern Iran and studied for palynological, palaeobiogeographical and palynocorrelation purposes. Palynological studies revealed diverse and well-preserved dinoflagellate cyst assemblages and lead to identification of three zones i.e., Cribroperidiniumcrispum (Late Bajocian), Dichadogonyaulaxsellwoodii (Bathonian to Early Callovian) and Ctenidodiniumcontinuum (Early to Middle Callovian) Zones. Subzone a of the D. sellwoodii Zone (Early to Middle Bathonian) was also differentiated. This biozonation corresponds to those recognised in Northwest Europe. Furthermore, the ammonoid families recorded including Phylloceratidae, Oppeliidae, Reineckeiidae, Perisphinctidae, Haploceratidae, Parkinsoniidae and Sphaeroceratidae, which confirm the Late Bajocian to Late Callovian age, are quite similar to those of Northwest Europe and the northwestern Tethys. The close similarities of the dinoflagellate cyst assemblages and ammonite fauna of northern Iran with those of Northwest Europe and the northwestern Tethys during the Middle Jurassic indicate direct but episodic marine connection and faunal exchange between the two areas.     

A New Genus of Fossil Cycads Yixianophyllum gen. nov. from the Late Jurassic Yixian Formation, Western Liaoning, China

A new genus of fossil Cycads, Yixianophyllum gen. nov., is reported here. The specimens were collected from the southern hill of Jinjiagou village, Toudaohezi Town, Yixian County, western Liaoning Province, China. The fossil plant-beating bed belongs to the lower part, the Zhuanchengzi bed, of the Upper Jurassic Yixian Formation （Yixianian）. The new genus in leaf shape, venation and epidermal structure shows a transitional form between Mesozoic Cycads （Ctenis, Nilssonia） and modem Cycads （Stangeria and Encephalartos）. Since the features of these specimens differ from any known genera of Cycads, a new generic name Yixianophyllum is proposed for these leaves. Typical species, Yixianophyllum jinjiagouense gen. et sp. nov. is described here. A supposed evolutionary tendency of Cycadean leaf-forms with Taeniopteris-type is discussed.     

西藏南部下鲁硅岩晚侏罗世罩笼虫(放射虫)新材料

下鲁硅岩为藏南日喀则地区雅鲁藏布蛇绿岩南侧的晚侏罗世—早白垩世硅质岩系。本文补充描述了该岩系中 4块标本的罩笼虫亚目放射虫化石 1 6属 2 3种 ,包括 8个新种。加上这些标本原已描述过的 1 8属 3 3种 ,共有 3 4属 56种。所有的属和近一半的种见于北美西部 ,可与那里的晚侏罗世放射虫分带很好地对比 ,它们分别相当于那里牛津期的 2 γ亚带和晚启莫里期—早提索期的 3 β亚带。动物群具特提斯生物地理区特征 ,但与西特提斯的地中海地区同期动物群显然不同 ,可能当时东特提斯与太平洋联系密切。     

Arm hooks of coleoid cephalopods from the Jurassic succession of the Wessex Basin,Southern England

The Jurassic succession of the Wessex Basin – especially that cropping out within the Dorset and East Devon Coast World Heritage Site – contains important lagerstätten for coleoid cephalopods. The Blue Lias and Charmouth Mudstone formations of West Dorset, the Oxford Clay Formation of North Wiltshire and the Kimmeridge Clay Formation of Purbeck have provided large numbers of important body fossils that inform our knowledge of coleoid palaeobiology, including the hooks present in the arms. Isolated hooks are also found in the processed residues studied by micropalaeontologists and these occurrences can be used – in some cases – to record the presence of key taxa in the absence of well-preserved body fossils. While some hook morphotypes can be attributed to known species, there are many forms of hook described where the parent animal remains unknown. The present state of our knowledge of the Jurassic assemblages in the Wessex Basin is presented and remaining issues identified.     

晚侏罗世承德盆地砾岩碎屑源区分析及构造意义

河北承德及寿王坟盆地在晚侏罗世土城子期堆积了大量的粗碎屑沉积.砾石成分统计结果显示,承德-寿王坟盆地充填的土城子组碎屑母岩组合主要有三种,其中火山岩、花岗质岩石和变质岩组合在承德盆地占绝对优势,反映了当时盆地以北的“内蒙地轴”为主要的蚀源区.向北逆冲的双庙断裂将承德盆地分成南北两个部分,断裂两侧的砾石成分组合基本相同,显示出碎屑物质共同来源于北部,同时也暗示了该断裂在土城子期可能没有强烈的活动（强烈活动期可能在土城子组之后？）.分析表明,承德盆地南部的不对称向斜构造两侧砾石成分截然不同,说明该向斜构造控制了碎屑分布,是同沉积期形成的.该盆地南侧的碎屑供应量远远小于北侧,反映了控制盆地南缘发育的向北逆冲的灰窑断层可能是一条次要的同沉积断裂.在晚侏罗世整体向南推进的逆冲断裂系统中,灰窑断裂和双庙断裂应属于背向逆冲断层.承德盆地中大量的粗碎屑堆积与同期冲断带的耦合关系分析,指示了这一时期盆地北侧存在强烈的逆冲断裂活动.作为主要物源区,北部的“内蒙地轴”在晚侏罗世发生了强烈的隆升-剥蚀作用,推测当时在地貌上可能存在近E-W走向的古山系（或古高原？）.     

塔里木板块西南缘晚侏罗世古地磁研究

塔里木板块西南缘托云、奥依塔格晚侏罗世古地磁研究,获得了托云地区特征磁化方向:Ds=1.5°,Is=50.8°;古地磁极:λ=81.0°,ψ=247.0°,古纬度31.5°N。奥依塔格地区特征磁化方向:Ds=118.4°,Is=55.9°;古地磁极:λ=4.9°,ψ=120.6°,古纬度=36.4°N。从古地磁结果认为:①托云和奥依塔格相对托云地区产生顺时针旋转;②这两个地区古纬度为31°～36°左右,与塔里木平均古纬度30°N是基本一致的,但与现在纬度差达8°～10°左右,造成纬度差主要原因是构造运动造成的;③塔里木晚侏罗世古地磁亦与华北、华南基本一致,说明晚侏罗世塔里木、华北、华南三板块已联合成一个整体,拼合成统一的中国大陆,其位于热带—亚热带古气候环境。     

大兴安岭北端晚侏罗世花岗岩类地球化学及其地质和找矿意义

大兴安岭北端的龙沟河、二十一站等岩体形成于晚侏罗世,与斑岩型铜金矿化关系密切.这些岩体的主要岩石类型为石英闪长岩、石英二长闪长岩、花岗闪长岩,总体属高钾钙碱性系列,少量属橄榄玄粗岩系列.其SiO2含量介于61.37%～66.59%,Al2O3含量为15.35%～17.06%,MgO含量介于2.02%～3.47%,Mg#指数高达44～59.(La/Yb)N介于16.85～81.73之间,δEu介于0.68～0.93,给出强分异的稀土元素配分型式,与埃达克岩的特征一致.Ba、Sr和LREE强烈富集,Nb和Ta强亏损,Rb和Ti弱亏损;岩石Yb含量介于0.31～1.32μg/g,Y含量介于4.32～12.07μg/g,贫Yb低Y特征显著;Sr/Y介于67.74～220.60,高Sr低Y特征清楚.上述特征也与埃达克岩地球化学特征一致.由于古亚洲洋和蒙古-鄂霍茨克洋分别于古生代末期和二叠纪-中侏罗世闭合,因此,所研究的埃达克岩应形成于中朝-蒙古大陆与西伯利亚大陆之间的陆陆碰撞造山环境,是碰撞造山带加厚下地壳拆沉-熔融的产物.     

大兴安岭北段伊勒呼里山晚侏罗世二长花岗岩LA-ICP-MS锆石U-Pb年龄、地球化学特征及其地质意义

对大兴安岭北段伊勒呼里山地区二长花岗岩进行了LA-ICP-MS锆石U-Pb年龄和岩石地球化学研究,确定其形成时代、岩石成因,揭露区域大地构造环境。测年数据显示,二长花岗岩于158.1±0.7Ma前形成,为晚侏罗世早期岩浆演化事件的产物。地球化学结果显示,二长花岗岩具有高Si、富Na、K、Al,低Fe、Mg的特点,A/CNK值为0.83~1.09,属高钾钙碱性花岗岩;富集大离子亲石元素K、Rb,贫高场强元素Hf、Th;稀土元素总量较高,稀土元素配分曲线右倾,具弱的负Eu异常,为Ⅰ型花岗岩。岩浆起源于下地壳玄武质成分的岩石部分熔融,为同碰撞期陆壳加厚过程的产物。研究区晚侏罗世早期二长花岗岩的形成与蒙古-鄂霍茨克缝合带闭合过程中的陆-陆碰撞环境有关,其形成时代限定了大兴安岭北段伊勒呼里山地区蒙古-鄂霍茨克洋的闭合时间应为晚侏罗世早期。     

Mesozoic (Late Jurassic) palynomorphs and charcoal from a sandstone pebble from Quaternary glacial deposits of the North Sea

The palynological contents as well as macroscopic charcoal fragments from a calcareous sandstone pebble from Quaternary glacial deposits of the North Sea (80 km SW of the Dogger Bank) are described. The taxonomic composition of the palynoflora points to a Late Jurassic (or Late Jurassic/Early Cretaceous) age of the sandstone. The charcoal is interpreted as direct evidence of palaeo‐wildfire occurring during this period in the source area of the sediments of this particular sandstone. This finding, together with already published data on Mesozoic deposits, allows to conclude that wildfires were obviously widespread during this period in the area of the modern day North Sea and adjacent areas. Copyright © 2012 John Wiley & Sons, Ltd.     

Sedimentary Conditions of Evaporites in the Late Jurassic Xiali Formation, Qiangtang Basin: Evidence from Geochemistry Records

The Qiangtang Basin (QB), located in the central Tibetan Plateau, is a Jurassic marine basin and one of the most important prospective salt resource belts in China. In recent decades, many outcrops of gypsiferous?bed have been found in the Jurassic marine strata in the basin. Salt springs with abnormally high sodium (Na+) contents had been identified in the Late Jurassic Xiali Formation (Fm.) in the basin in the last years. However, to date, no potash or halite deposits have been identified in the QB. Gypsum outcrops and salt springs are very important?signs in the investigation of halite and potash deposits. Therefore, the Xiali Fm. is?a potentially valuable layer to evaluate for the possible presence of halite and potash deposits in the basin. However,?few studies?have explored the formation?conditions of evaporites in the unit. Here, we present detailed geochemical records from the Yanshiping section related to the study of the formation?conditions of evaporites in the Xiali Fm. of the QB. Climate proxies based on the obviously increased anion concentrations of SO42? and Cl? and the significant correlation?coefficients of Ca2+-SO42? (R = 0.985) and Na+-Cl? (R = 0.8974) reveal that the upper member of the Xiali Fm. (the upper Xiali Fm.) formed under an arid climate and evolved into the sulfate phase or early chloride phase. Provenance proxies based on the obviously increased K+ and Na+ ion concentrations and the significant correlation?coefficient of Na+-Cl? (R = 0.8974) suggest that the upper Xiali Fm. featured optimal provenance conditions for the possible formation of halite deposits. The regression and the semi-closed tidal?flat environment in the upper Xiali Fm. were favorable for the formation of potash and halite deposits. The low Mg2+ /Ca2+ values (mean value = 1.82) and significant Na+-Cl? correlation?coefficient (R = 0.8974) also suggest that the upper Xiali Fm. is the layer most likely to contain potential halite deposits. In addition, the macroscopic correlations of tectonism, provenance, paleoclimate, saliferous strata and sedimentary?environment between the QB and the adjoining Amu Darya Basin in Central Asia reveal that the two basins shared similar geologic settings that were favorable for the formation of evaporites during the Late Jurassic. Therefore, the upper Xiali Fm. is a valuable layer to explore for halite deposit and may be potentially valuable in the future exploration for potash deposits in the QB.     

辽宁西部及邻区中侏罗世燕辽生物群脊椎动物化石研究进展

近年来,在中国辽宁西部、内蒙古东南部、河北北部中侏罗世髫髻山组和九龙山组中发现了丰富的脊椎动物、无脊椎动物和植物化石,这一化石群被称为燕辽生物群。燕辽生物群已正式命名的脊椎动物26属28种,包括鱼类1属1种、两栖类4属4种、有鳞类1属1种、翼龙类10属12种、兽脚类恐龙5属5种、哺乳类5属5种。燕辽生物群的脊椎动物化石对研究长羽毛兽脚类恐龙的演化、翼龙类的分类演化、滑体两栖类的分异等具有重要意义。虽然辽宁西部及邻区燕辽生物群脊椎动物的多样性不及同一地区早白垩世的热河生物群,但它为认识这一地区晚中生代生物群的演替提供了极为重要的依据。     

藏东波密-察隅地区晚侏罗世花岗岩的成因及构造意义

西藏东部的波密-察隅地区是拉萨地体的南东向自然延伸,其中生代以来的演化一直被认为是处于北部的班公湖-怒江洋和南部的雅鲁藏布洋两个动力学系统中。相应地,该区广泛分布的晚中生代-新生代岩浆岩也被认为与两个大洋的发展演化及随后拉萨-羌塘、拉萨-印度的碰撞和后碰撞作用直接相关。本研究在波密-察隅地区中北部的伯舒拉岭岩浆带中发现了晚侏罗世的花岗岩,锆石LA-ICP-MSU-Pb测年表明其形成时代为151～153Ma,地球化学显示较强的δEu负异常,锆石εHf(t)值基本在误差范围内波动,平均值为-7.75和-7.77,表明这期花岗岩为古老地壳重熔的产物,与传统认为的该时期岩浆活动对应怒江洋的俯冲岛弧背景相矛盾。结合该区发现的早侏罗世壳源花岗岩及区域沉积特征,本文认为波密-察隅地区侏罗世的壳源花岗岩应该是拉萨地体内新发现的印支期或早中生代造山事件后地壳增厚或伸展阶段岩浆活动的反映或继续,而和传统认为的怒江洋俯冲没有关系,拉萨地体东部的波密-察隅地区在演化方面可能有其特殊性。有关藏东波密-察隅地区中生代构造演化的研究还需大量地质工作以及多学科的研究去证实。     

内蒙古中部达来地区晚侏罗世A型花岗岩:地球化学特征、岩石成因与地质意义

A型花岗岩的成因研究是揭示重要壳幔相互作用和伸展型地球动力学过程的重要窗口。离子探针锆石U-Pb测年指示内蒙古中部达来地区的达来庙钾长花岗岩岩株大约于晚侏罗世(160.1±1.8Ma)侵位。岩体Si O2含量介于69.8%~73.9%,富碱铁,贫钙镁;富集大离子亲石元素和Nb、Ta、Zr、Hf等高场强元素,发育明显的Eu负异常(Eu/Eu*=0.20~0.68)。这指示达来庙花岗岩具有A型花岗岩的元素地球化学特征。同时岩石具有低全岩Sri(87Sr/86Sri=0.70504~0.70523),低正全岩εNd(t)(+2.1~+2.3)以及高正的锆石εHf(t)(+7.0~+11.5)和高锆石δ18O(6.7‰~7.7‰)等同位素特征。元素同位素地球化学示踪指示达来庙花岗岩可能源于新增生中基性地壳物质的部分熔融及其后的结晶分异作用。一方面,达来庙花岗岩和蒙古-华北北部地块分散分布的其他A型花岗岩共同见证了有别于早白垩世大规模上地壳伸展的中晚侏罗世弥散状中下地壳伸展行为;另一方面,蒙古-华北北部地块晚中生代两段式的地壳伸展轨迹记录了蒙古-鄂霍茨克构造域造山后的重力垮塌过程。     

Heritage and landscape change: Recording,archiving and engaging with photogrammetry on the Jurassic Coast World Heritage Site

The Jurassic Coast World Heritage Site is a landscape defined by change and process. As such, the approach to its heritage must be similarly flexible and active. A balance must be found between celebrating these processes of change, whilst also conserving those invaluable discoveries and features that so define this coast, as well as encouraging ongoing research and public engagement. This delicate task can be aided firstly by thinking about this geologically defined World Heritage Site as a landscape. In this way it is possible to develop rich and nuanced narratives between the human and geological. Secondly, by embracing new technologies and methodologies to record, archive and communicate features and finds, as well as the process of change itself. Here, we explore these ideas through two unique sites of geological and palaeontological interest discovered in the process of quarrying. To balance keeping the sites open to the public with the risk of natural and human damage to the sites, Structure-from-Motion photogrammetry was used to create accurate, high-resolution, georeferenced 3D models. The process and potentials of the technique are discussed, alongside a discussion of the broader ideas of heritage and approaches already at play on this coastline.     

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...     

冀西北尚义盆地对晚侏罗世构造活动的沉积响应

尚义盆地位于走向近东西的中生代燕山冲断带前缘盆地群的西段,在晚侏罗世土城子时期堆积了大量的粗碎屑。盆地中土城子组沉积相变明显,自北向南从粗砾质变为粉砂质沉积,具比较典型的非对称相带分布特征。土城子早一中期,从北向南总体上形成砾质冲积扇(包括泥石流)-辫状河流-洪泛平原或干化湖泊等古环境布局。晚期则以砂砾质辫状河流沉积为主,可能夹有发育大型风成交错层理的砂质沙丘沉积。土城子组碎屑成分以变质岩和花岗质岩石为主.物源主要来自盆地北侧的"内蒙地轴",沉积充填具有同构造砾岩的性质。尚义盆地北缘发育一系列呈叠瓦状排列的逆冲断裂。断裂与盆地耦合关系的初步分析显示.北缘逆冲断裂的构造载荷是控制尚义盆地形成和演化的主要因素。靠近北部冲断带一侧沉积相序的中—下部具有向上变粗的特点.可能指示了土城子组沉积受前进式的冲断载荷和岩石圈挠曲控制的过程。根据尚义盆地与其北侧相关断裂的空间配置、沉积碎屑北粗南细的变化、盆地横断面北厚南薄的楔状体特征等分析.盆地属于陆内的前陆式盆地,推测是在自北向南的近水平挤压构造背景下形成的.     

黑龙江伊春地区晚三叠世—早侏罗世铝质A型正长-碱长花岗岩地球化学特征及其构造意义

黑龙江伊春地区晚三叠世-早侏罗世正长-碱长花岗岩的岩石学和主、微量元素及同位素分析结果表明,岩石中大多含有高温自形或锥形石英、副矿物萤石和文象结构、晶洞构造等;岩石化学特征上具有高硅、富碱和低钙镁、偏铝质-过铝质特点,稀土元素配分模式呈轻稀土元素略微富集的、缓向右倾斜而重稀土元素较为平坦、铕亏损的海鸥型,富集高场强元素(HFS)Zr和Ga,亏损Ba、Sr、Eu等;岩石中的石英包裹体均一温度为750～950℃,具有高温岩浆浅成被动就位的特征.岩石富SiO2、K2O、Al2O3,δ18O值为5.1‰～10.3‰,属正常略偏低δ18O值花岗岩类;ISr值较高、εNd值较低,暗示了其源区物质来源主要与古老下地壳变质基底物质有关,并涉及到一定程度的壳幔岩浆混合作用.综合这些特征,首次提出伊春地区晚三叠世-早侏罗世正长-碱长花岗岩属于铝质A2型花岗岩,这说明此后该地区进入了古亚洲洋最终闭合之后大陆碰撞后跨塌、伸展动力学体制的构造背景.