Aptian–Albian rudist bivalves (Hippuritida) from the Chilean Central Andes: Their palaeoceanographic significance     

《Cretaceous Research》2015

The study of Aptian–Albian rudist faunas from the Chilean Central Andes documents the presence of two forms, ascribed to the Monopleuridae: Douvillelia skeltoni an early Aptian species known hitherto from Mexico, and Jerjesia chilensis, an endemic Albian species from Chile and Peru, with a complex taxonomic history. The regional stratigraphy of the Central Andes, combining ammonites and rudists, is consistent with the Caribbean stratigraphic distribution of Jerjesia and Douvillelia. Andean occurrences of the two genera broaden their distributional area on the Pacific side of Americas, and testify their biostratigraphic value. Oceanographic conditions of the Chilean Pacific margin during the Aptian–Albian, including moderate but effective cold oceanic current, upwellings, high productivity and thermal instability, may acknowledge the low taxonomic diversity of rudist assemblages, which look impoverished when compared to their low latitude homologues from the Caribbean regions which were functioning as a dispersal centre.  相似文献   

Cretornis hlavaci Frič, 1881 from the Upper Cretaceous of Czech Republic (Pterosauria,Azhdarchoidea)     

《Cretaceous Research》2015

Cretornis hlavaci Frič, 1881 from the Upper Cretaceous (Turonian) of Czech Republic is a valid taxon referred to Azhdarchoidea based on having a saddle-shaped humeral head, pneumatic foramen on proximal humerus present on anterior side and absent on posterior side, elongate deltopectoral crest with subparallel proximal and distal margins, pneumatic foramen absent on distal side of humerus, metacarpals I–III not articulated with carpus and displaced on anterodorsal side of wing metacarpal, and wing metacarpal much longer than humerus. Absence of a pneumatic foramen on posterior side of proximal humerus suggests attribution of Cretornis hlavaci to Neoazhdarchia. It has a unique construction of the distal ulna with a dorsal articulation surface placed distinctly proximal to the tuberculum shared only with the non-azhdarchid azhdarchoid Montanazhdarcho minor from the Campanian of North America. Cretornis hlavaci differs from the latter taxon by the structure of its humerus and distinctly longer wing metacarpal. It is more derived than “Tapejaridae” but shares with Azhdarchidae the deltopectoral crest of the humerus displaced distally from humeral head. Cretornis cannot be assigned to Azhdarchidae because of the oval cross section of the second wing phalanx. A unique rhombic outline of the distal humerus of Cretornis hlavaci is a possible autapomorphy for this taxon. Its wing span estimated as 1.5–1.6 m. This is the first taxon of non-azhdarchid pterosaurs known from the Upper Cretaceous of the Eastern Hemisphere.  相似文献   

40Ar/39Ar geochronology and palynology of the Cerro Negro Formation,South Shetland Islands,Antarctica: A new radiometric tie for Cretaceous terrestrial biostratigraphy in the Southern Hemisphere     

B. Hathway  A. M. Duane  D. J. Cantrill  S. P. Kelley 《Australian Journal of Earth Sciences》2013,60(4):593-606

The upper part of the Jurassic‐Cretaceous Byers Group, exposed on Byers Peninsula in the South Shetland Islands, Antarctica, consists of 1.4 km of non‐marine strata assigned to the Cerro Negro Formation. Silicic pyroclastic units close to the base of the formation have yielded new ⁴⁰Ar/³⁹Ar ages of 120.3 ± 2.2 Ma on plagioclase from one horizon, and 119.4 ± 0.6 and 119.1 ± 0.8 Ma on biotite and plagioclase from a second horizon. Plagioclase from a welded ignimbrite close to the topmost exposed part of the formation has given an ⁴⁰Ar/³⁹Ar age of 119 ± 3.0 Ma. These ages indicate that the Cerro Negro Formation was deposited during a relatively short period in early Aptian times. The identification of palynomorph taxa has enabled us to propose correlations for the Cerro Negro Formation with spore/pollen zonations of South America and Australia. The presence of Interulobites pseudoreticulatus, Appendicisporites and F. wonthaggiensis in the Cerro Negro Formation supports correlation with the Interulobites‐Foraminisporis and the lower part of the tectifera‐corrugatus zones in southern South America. The presence of Foraminisporis asymmetricus and other palynomorphs suggests correlation with the Cyclosporites hughesii Interval Zone of early to late Aptian age in Australia. These data represent a valuable addition to the few radiometric ties available for Mesozoic terrestrial palynostratigraphy in the Southern Hemisphere.  相似文献   

Conceptualization of the hydrogeological system of some sedimentary aquifers in Savelugu–Nanton and surrounding areas,Northern Ghana     

Nelson Attandoh  Sandow Mark Yidana  Aliou Abdul‐Samed  Patrick Asamoah Sakyi  Bruce Banoeng‐Yakubo  Prosper M. Nude 《水文研究》2013,27(11):1664-1676

Groundwater resources play a pivotal role in the rural water delivery system in Ghana. The hydrogeological system of Middle Voltaian terrain was simulated using available data on hydraulic heads and boundary conditions. The objective was to characterize the general groundwater flow pattern and provide local estimates of the distribution of hydraulic conductivity and recharge fields. The results suggest a predominant NE–SW flow direction, which ties in with the general regional structural trend and indicates that the hydrogeological conditions of the rocks are controlled by structural entities created in the wake of fracturing and/or weathering of the rocks whose primary permeabilities are considerably reduced because of high compaction and low‐grade metamorphism. Calibrated hydraulic conductivities range between 1.90 and 10.81 m/d. The spatial distribution appears to reflect the intensity of fracturing and/or weathering of the rock and the proportion of the clay fraction of the weathered zone. Vertical groundwater recharge has been estimated to range between 0.3% and 4.1% of the annual rainfall. This recharge rate is quite low and reflects the imperviousness of the thick overburden because of high clay content in some places and high compaction in others. Despite this apparently low recharge rate, groundwater resources potential in the area appear to be high, and increased abstraction from existing abstraction wells by up to 50% does not appear to register significant effects on groundwater budgets at the simulated recharge rates. This suggests that the well yields are much lower than the potential of the aquifer system. The apparently low yields might be associated with poor well development and the choice of inappropriate well completion materials. This study recommends a monitoring system to be developed for a much more regional groundwater flow simulation under transient conditions. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

大兴安岭北段诺敏大山地区早白垩世侵入岩地球化学特征及其构造意义     

任永健  张成信  张明明  程烁  高立湧  于汪  赵寒  王畅  张伟胜 《地质论评》2022,68(6):2103-2114

笔者等选择大兴安岭北段诺敏大山地区早白垩世侵入岩进行了锆石U- Pb年代学和地球化学研究,探讨该区域侵入岩成因类型、岩浆来源及构造环境。该区侵入岩岩性主要为正长花岗岩、正长花岗斑岩和似斑状正长花岗岩,对其中正长花岗岩样品进行LA- ICP- MS锆石U- Pb测年表明,正长花岗岩侵位年龄为129. 5±0. 4 Ma,应为早白垩世岩浆活动的产物,结合区内侵入岩与地层相互接触关系,本区侵入岩形成时代为早白垩世。区内侵入岩具有富硅（SiO2= 67. 36%~74. 09%）、富碱（K2O+Na2O= 8. 88%~9. 34%）、高铝（Al2O3= 12. 56%~16. 15%）,低MgO、TiO2、CaO的特点,属于高钾钙碱性岩石系列;铝饱和指数（A/CNK）为0. 94~1. 31,为准铝质—过铝质岩石。微量元素富集Rb、U、Th、K等大离子亲石元素,强烈亏损Ti、Nb、Sr、P等高场强元素,具有明显的Eu负异常,属于高分异I型花岗岩。岩石Rb/Sr为0. 9~2. 0,Sr/Y为4. 2~7. 2,显示出高Sr、低Y的特点,指示岩浆源区为地壳物质的部分熔融。结合区域研究成果,蒙古—鄂霍茨克构造域在早白垩世之前已结束碰撞,诺敏大山地区早白垩世岩浆活动可能发生在蒙古—鄂霍茨克造山后的伸展环境。  相似文献   

鄂尔多斯盆地早白垩世构造-热事件与铀成矿的关系——来自玄武岩锆石U-Pb年代学的约束     

韩美芝  李子颖  邱林飞  骆效能 《铀矿地质》2022,(1):13-24

鄂尔多斯盆地北部纳岭沟铀矿床以北,大营及巴音青格利铀矿床以东的黑石头沟发育一层玄武岩,为探讨这期玄武岩与鄂尔多斯盆地北部铀成矿的关系,文章对该玄武岩进行了地球化学与年代学的分析。该玄武岩切穿下白垩统东胜组,SiO₂含量较低(46.99%),里特曼指数σ为8.69,显示出碱性玄武岩的特征;其锆石U-Pb定年结果为(126.7±2.4) Ma,表明黑石头沟玄武岩形成于早白垩世,反映鄂尔多斯地块在早白垩世发生了一次构造-岩浆-热事件,与大区域的华北地区乃至中国东部在早白垩世发生的较普遍的构造-岩浆-热事件具有一致性。结合前人的研究成果,这次构造-岩浆-热事件是由于岩石圈地幔减薄造成的。该事件使地下深部热流体上涌及板内运移,导致早白垩世古地温梯度增高,这一过程为铀元素在鄂尔多斯盆地北部的迁移、沉淀、富集成矿创造了条件。  相似文献   

辽东凤凰山正长花岗岩SHRIMP U-Pb年龄、地球化学特征与陆内伸展作用          下载免费PDF全文

宋运红  杨凤超  郝立波  闫国磊  赵东芳  张哲寰 《中国地质》2022,49(5):1687-1698

【研究目的】 辽宁丹东地区发育着一期A型花岗岩,因其特殊的成因演化,特定的构造背景及其重要的地球动力学意义而备受关注。【研究方法】 本文通过对辽宁丹东凤凰山岩体SHRIMP锆石U-Pb年代学、岩石地球化学特征的分析,探讨了该岩体形成时代、岩石成因及地球动力学背景。【研究结果】 辽东凤凰山黑云母正长花岗岩锆石U-Pb年龄分别为（122.3±1.7）Ma、（125.0±1.7）Ma、 （122±2）Ma,代表岩浆结晶年龄,凤凰山正长花岗岩侵位时代属于早白垩世。地球化学分析结果显示,SiO₂含量为65.65%～73.62%,K₂O为3.52%～5.76%,Na₂O为3.64%～4.26%,Al₂O₃为13.4%～15.49%,A/CNK值1.02～1.46,属铝过饱和型。碱度率AR在2.71～5.13,基本在铝质A型花岗岩AR值范围内,FeO_t/MgO比值为4.69～18.05,表现为A型花岗岩的A1和A2过渡类型。Rb/Nb比值为6.02～8.64,明显高于大陆壳的Rb/Nb比值2.2～4.7,说明陆壳物质对岩体成岩影响较大,从而导致Rb的含量增加。相对富集大离子亲石元素Rb、Th, Zr、Hf,亏损Sr、P、Ba、Ti、Nb。稀土总量较高,轻重稀土之间的分馏不明显,Eu具明显的负异常。【结论】 综上,凤凰山正长花岗岩可能产生于陆内剪切相关的伸展环境,应为自中侏罗世开始由板块俯冲引起的东亚大陆边缘构造过程的响应。  相似文献   

古亚洲洋东段洋盆闭合与后造山伸展——来自内蒙古苏尼特右旗中三叠世A型花岗岩的证据     

王帅  李英杰  孔星蕊  许展  王金芳  董培培  鞠文信  王晓东 《岩石矿物学杂志》2022,41(3):555-568

内蒙古苏尼特右旗查干楚鲁A型二长花岗岩位于索伦-林西缝合带内,侵位于早二叠世哈冷岭SSZ型蛇绿构造混杂岩(带)中。本文对其进行系统的野外地质特征、岩石学、地球化学和锆石U-Pb年代学研究,旨在厘定岩体成因和形成的构造背景,为古亚洲洋东段洋盆闭合时限提供证据。LA-ICP-MS锆石U-Pb测年结果显示查干楚鲁二长花岗岩侵位于中三叠世(245.9±1.3 Ma);岩体含较多碱性长石,暗色矿物以黑云母为主,见晶洞构造;地球化学研究显示,该岩体高硅(SiO₂=76.75%～77.18%)、富碱(Na₂O+K₂O=8.19%～8.62%),贫钙(CaO=0.40%～0.44%)和镁(MgO=0.03%～0.05%);负Eu异常显著(δEu=0.03～0.09), Rb、Th、U、K、Ga元素较富集,而Ba、Sr、P、Ti元素相对亏损,且10 000 Ga/Al(2.72～3.52)、~TFeO/MgO(29.16～57.82)、(Na₂O+K₂O)/CaO(15.08～21.39)值较高...  相似文献   

河北围场地区发现早白垩世七鳃鳗化石     

郭新宇 《江苏地质》2022,46(3):260-265

七鳃鳗是一种古老而原始的特殊无颌类脊椎动物。因其仅发育脊索上的小软骨片及口腔内的角质齿,一般很难保存为化石。国内外现存的七鳃鳗化石记录很少,例如南非晚泥盆世的Priscomyzon riniensis、北美石炭纪的Mayomyzon pieckoensis和Hardistiella montanensis,还有我国内蒙古下白垩统义县组的Mesomyzon mengae。近几年,在河北承德围场地区早白垩世地层中发现了丰富的鱼类化石,其中就有七鳃鳗化石,表明围场地区是继内蒙古宁城之后我国第二个重要的早白垩世七鳃鳗化石产地。研究了产自围场地区早白垩世九佛堂组的3件七鳃鳗化石标本（MHGU4270、MHGU4271、MHGU4272）,化石保存基本完整,可见吸盘、眼、鳃囊、肌节、背鳍、后背鳍、尾鳍等构造。成年期个体（MHGU4270、MHGU4271）体长为24～27 cm,体高为1.9～2.0 cm;非成年期个体（MHGU4272）体长约为17.0 cm,体高约为1.2 cm,明显大于内蒙古宁城地区发现的孟氏中生鳗。根据形态结构特征,认为这3件七鳃鳗化石应为一个新的属种,将其命名为围场河北鳗（Hebeimyzon weichangensis gen. et sp. nov.）。围场中生鳗（新属、新种）的发现不仅为我国早白垩世七鳃鳗化石的研究增添了新材料,扩大了研究的区域范围,而且对进一步深化研究早白垩世七鳃鳗的演化历史、生活习性、生态环境和古地理分布具有重要科学价值。  相似文献   

白垩纪羌塘地体西南缘的陆-陆碰撞:来自班怒带西段的花岗岩约束     

付顺  赵应权  王进军  余瑜  朱迎堂  傅星劼 《地学前缘》2022,29(2):416-430

羌塘地体西南缘布木错—雄巴日—羌多—赛登地区分布着大量呈岩株或岩枝状的中酸性-基性侵入岩,其岩石地球化学特点是低SiO₂(67.99%~73.32%)、高Al₂O₃(12.82%~15.02%),属于过铝质花岗岩,里特曼指数(2.09~2.63)σ<3.3,属钙碱性花岗岩类;稀土元素显示为轻稀土较强富集和重稀土强亏损的特征,岩浆结晶分异程度较高。岩石地球化学特征和稀有元素特征图解指示花岗岩构造环境有一定的差异性,以I型为主,其形成及侵位应与古特提斯洋的闭合、新特提斯洋的扩张有关,属同碰撞型造山花岗岩。通过对该区多个花岗岩体锆石LA-ICPMS 测定,测得其形成年代为116~107 Ma,与早白垩世晚期羌塘地体南缘的陆-陆碰撞作用时间相吻合。  相似文献