Formation of subglacial till under transient bed conditions: deposition, deformation, and basal decoupling under a Weichselian ice sheet lobe, central Poland   总被引：1，自引：0，他引：1  

J. A. PIOTROWSKI  N. K. LARSEN  J. MENZIES†  W. WYSOTA‡ 《Sedimentology》2006,53(1):83-106

A multi-proxy approach involving a study of sediment architecture, grain size, grain roundness and crushing index, petrographic and clay mineral composition, till fabric and till micromorphology was applied to infer processes of till formation and deformation under a Weichselian ice sheet at Kurzetnik, Poland. The succession consists of three superposed till units overlying outwash sediments deformed at the top. The textural characteristics of tills vary little throughout the till thickness, whereas structural appearance is diversified including massive and bedded regions. Indicators of intergranular bed deformation include overturned, attenuated folds, boudinage structures, a sediment-mixing zone, grain crushing, microstructural lineations, grain stacking and high fabric strength. Lodgement proxies are grooved intra-till surfaces, ploughing marks and consistently striated clast surfaces. Basal decoupling by pressurized meltwater is indicated by undisturbed sand stringers, sand-filled meltwater scours under pebbles and partly armoured till pellets. It is suggested that the till experienced multiple transitions between lodgement, deformation and basal decoupling. Cumulative strain was high, but the depth of (time-transgressive) deformation much lower (centimetre range) than the entire till thickness ( ca 2 m) at any point in time, consistent with the deforming bed mosaic model. Throughout most of ice overriding, porewater pressure was high, in the vicinity of glacier floatation pressure indicating that the substratum, consisting of 11 m thick sand, was unable to drain subglacial meltwater sufficiently.  相似文献   

藏北龙木错东部三岔口地区下奥陶统与泥盆系的不整合界面   总被引：7，自引：6，他引：7  

夏军钟华明  童劲松鲁如魁 《地质通报》2006,25(1):113-117

在北羌塘三岔口一带采获丰富的腕足类:汉伯矮正形贝及比较种Nanorthis cf.hamburgensis(Walcott).建立了早奥陶世岩石地层单位--三岔口组,是羌塘地区目前有化石控制的最低层位.中、晚泥盆世拉竹龙组与下伏志留系、奥陶系不整合接触关系的进一步确定,证明了羌北-昌都板块与扬子板块的亲缘性,为羌北-昌都板块属性的确定提供了重要证据.  相似文献   

小秦岭(陕西境内)高山河群与小河岩体接触关系及时代探讨     

冯明伸 《陕西地质》1998,(1)

本文对小秦岭（陕西境内）高山河群与小河岩体的接触关系性质,从点到面,从微观到宏观进行了扼要的论述,并明确指出二者非侵入接触,而应是沉积不整合接触,在此基础上探讨了小河岩体的时代。  相似文献   

哈密坡子泉地区石炭系研究的新认识     

彭湘萍  白云山 《新疆地质》1998,(3)

通过野外工作 ,在前人所划的坡子泉地区石炭系白山组内新发现三个角度不整合 ,而将白山组解体成四个组。结合古生物化石和同位素年龄资料 ,将狼泉组和坡子泉组划归下石炭统 ,黑石山组和马庄山组划归上石炭统。在此基础上 ,研究了新划四个组的沉积环境 ,总结了坡子泉地区石炭纪地壳演化简史 ,建立了地层组合模式  相似文献   

被动大陆边缘碳酸盐生长序列与盆山转换耦合   总被引：3，自引：0，他引：3  

许效松 《地球学报》1996,17(1):41-53

碳酸盐作为盆地堆积物整体的一部分，剖析达到碳酸盐清水环境的先决条件、保持条件和中止消亡条件就可判别盆地中碳酸盐沉积与其他堆积作用之间的关系，恢复盆地性质、演化历史和盆转山的过程。碳酸盐生长的４个边界条件：碳酸盐生长的基座、碳酸盐沉积前后的转换面、碳酸盐生长序列的内部结构和碳酸盐中止和消亡方式、不同板块部位的盆地和盆转山过程，这４个边界条件均不相同。在被动大陆边缘转为前陆盆地过程中，碳酸盐生长发育的４个边界条件也随之而变化。其过程为：早期裂谷充填；晚期裂谷、碎屑岩陆架形成；碳酸盐陆架；热沉降和镶边碳酸盐台地  相似文献   

Debris from the basal ice of the Agassiz ice cap,Ellesmere Island,arctic Canada     

A. M. D. Gemmell  M. J. Sharp  D. E. Sugden 《地球表面变化过程与地形》1986,11(2):123-130

This article describes the characteristics of debris obtained from the basal ice in a borehole in the Agassiz ice cap, Ellesmere Island, Northwest Territories by the Canadian Polar Continental Shelf Project in 1979. The debris appears to have been incorporated by basal freezing at a time when the base of the glacier upstream was near the pressure melting point and some 19°C warmer than at the present site. Such an occurrence may be explained by a different flow regime, by a thicker ice sheet, by the influence of irregular bedrock topography on basal ice conditions at some stage in the past, or by a combination of these factors.  相似文献   

Devonian-Carboniferous unconformity in Argentina and its relation to the Eo-Hercynian orogeny in southern South America     

O. R. López-Gamundí  E. A. Rossello 《International Journal of Earth Sciences》1993,82(1):136-147

The Devonian-Carboniferous contact in southern South America, characterized by a sharp unconformity, has been related to the Late Devonian-Early Carboniferous Eo-Hercynian orogeny. The Calingasta-Uspallata basin of western Argentina and the Sauce-Grande basin (Ventana Foldbelt) of eastern Argentina have been selected to characterize this unconformity. The Eo-Hercynian movements were accompanied in western Argentina by igneous activity related to a Late Devonian—Early Carboniferous magmatic arc mainly exposed today along the Andean Cordillera. This magmatic activity is partly reflected also in eastern Argentina (Ventana Foldbelt), where isotopic dates suggest a thermal event also related to the intrusions present to the west in the North Patagonian Massif and Sierras Pampeanas. The scarcity of Lower Carboniferous deposits in the stratigraphic record of southern South America suggests that the Early Carboniferous was a time interval dominated by uplift and erosion followed by widespread subsidence during the Middle and Late Carboniferous. The origin of the Eo-Hercynian orogeny can be linked with the convergence between the Arequipa Massif, and its southern extension, and the South American continent. Its effects are best represented along the Palaeo-Pacific margin, although distant effects are discernible in the cratonic areas of eastern South America. Correspondence to: O. R. López-Gamundí  相似文献   

扬子西缘东吴伸展运动   总被引：22，自引：2，他引：20       下载免费PDF全文

梁定益  聂泽同 《地球科学》1994,19(4):443-453

扬子西缘二叠系中震积岩十分发育,笔者根据震积岩、震积－伸展不整合的存在,厘定了它的时代,确认了东吴运动的存在。指出它是该区晚古生代以来最重要的一次伸展构造事件,多旋回震积岩、化石有序混积与水下边界正断层的多次活动有关。在木里地区,从东吴运动开始,地震、伸展－裂陷。火山活动持续到三叠纪,形成裂陷槽（晚二叠世－早三叠世达到高峰）。在这里,东吴运动实际是裂陷造槽运动。  相似文献   

再论震积岩及震积不整合——以川西-滇西地区为例   总被引：45，自引：1，他引：44  

梁定益  聂泽同 《地球科学》1994,19(6):845-850

震积岩是“灾变事件岩”的典型代表,震积岩一般由原地相的地震扰动层与上覆的滑来震积层组成,无论后者是否发育,震积不整合都是存在的。伸展构造环境下形成的区域性震积不整合,属于伸不整合,地震扰动层可以进一步分为软沉积及液化变形段,半固结变形的微褶皱和微断层段、脆性变形的震碎角砾岩段及韵律断层段等序列;群震型（多震旋回）剖面也可划分出出前震、主震、后震等序列。地震扰动序列对识别震积岩很关键,群震型剖面及化  相似文献   

Geometrical relationships between unconformities and subsequent folding: the Arro fold system (southern Pyrenees)Relations entre discordances et plissement dans le système de plis et chevauchements d'Arro (bassin de Graus-Tremp,Pyrénées)     

Antonio M Casas  Ruth Soto  Begoña Martı́nez-Peña 《Comptes Rendus Geoscience》2002,334(10):765-772

The Arro system is an oblique fold system involving the Eocene sediments of the Graus-Tremp basin. It consists of westward-verging folds, trending NNW–SSE, some of them related with thrusts, in piggyback sequence. Seismic profiles allow to infer the geometry of structures at depth: folds and thrusts are ‘decolled’ over an unconformity between turbiditic and platform sediments. Re-activation of bedding surfaces by folding in the underlying units resulted in folding and thrusting in the upper series. To cite this article: A.M. Casas et al., C. R. Geoscience 334 (2002) 765–772.  相似文献