DOCSLIB.ORG

Seismic Evidence for Blind Thrusting of the Northwestern Flank of the Venezuelan Andes Bruno De Toni

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Seismic Evidence for Blind Thrusting of the Northwestern Flank of the Venezuelan Andes Bruno De Toni University of South Carolina Scholar Commons Faculty Publications Earth, Ocean and Environment, School of the 12-1993 Seismic evidence for blind thrusting of the northwestern flank of the Venezuelan Andes Bruno De Toni James N. Kellogg University of South Carolina - Columbia, [email protected] Follow this and additional works at: https://scholarcommons.sc.edu/geol_facpub Part of the Earth Sciences Commons Publication Info Published in Tectonics, Volume 12, Issue 6, 1993, pages 1393-1409. De Toni, B. & Kellogg, J. N. (1993). Seismic evidence for blind thrusting of the northwestern flank of the Venezuelan Andes. Tectonics, 12 (6), 1393-1409. ©Tectonics 1993, American Geophysical Union This Article is brought to you by the Earth, Ocean and Environment, School of the at Scholar Commons. It has been accepted for inclusion in Faculty Publications by an authorized administrator of Scholar Commons. For more information, please contact [email protected]. TECTONICS, VOL. 12, NO. 6, PAGES 1393-1409, DECEMBER 1993 SEISMIC EVIDENCE FOR BLIND La Fria andE1 Vigia (Figures1 and 2). In thispaper we THRUSTING OF THE NORTHWESTERN presentgeological and geophysical evidence for basement- FLANK OF THE VENEZUELAN ANDES involvedthrusting of the VenezuelanAndes toward the Maracaibo Basin. Bruno De Toni INTEVEP, S.A., Caracas, Venezuela GEOLOGIC SETTING JamesKellogg The regionalgeologic setting of thearea can be describedas Departmentof GeologicalSciences, University of South a mountainfront adjacentto a foredeepbasin. The mountain Carolina, Columbia frontrepresents a Precambrian-Paleozoic igneous-metamorphic complexpartially covered with sedimentsof Mesozoicand Abstract. Surfacegeology and seismicand well datafrom Cenozoicages. The foredeepis an asymmetricstructural basin the northwestern flank of the Venezuelan Andes indicate thatcontains up to 12 km of sedimentarysection. The early overthrustingof Andeanbasement rocks toward the adjacent Miocene to Pleistocenemolasse deposits up to 6 km in MaracaiboBasin along a blind thrustfault. The frontal thicknessdominate the sedimentarysection. The oldest monoclineis interpretedas the forelimbof a northwestward sedimentaryrocks that crop out in the mountainfront are vergingfault-related fold deformedover a crustal-scaleramp. Jurassicred bedswhich are unconformablyoverlain by a The Andean block has been thrust 20 km to the northwest and Cretaceoussequence up to 2 km in thickness.From early uplifted 10 km on a rampthat dipsabout 20o-30 ø Cretaceousto middleEocene, sediments were deposited in an southeastward.The thrustfault rampsup throughcrystalline extensivepassive continental margin setting (Figure 3). basementrocks to a decollementhorizon within the shaly Coarseclastic sediments of the Rio Negro Formation, units of the Cretaceous Colon-Mito Juan formations. bioclasticcarbonates of the Apon Formation,and siliciclastic Backthrustsin themonocline produce a wedgegeometry and sedimentsof the AguardienteFormation were depositedfirst in reducethe amountof blind sliprequired on the decollement the initial stageof the Cretaceoustransgressive event. northwestof the Andes. The rigid Andeanuplift wascaused Limestones,calcareous shales, and black shalesof the Capacho by northwest-southeastcompressive tectonic forces related to andLa Luna formationsrepresent anoxic facies deposited theconvergence of theCaribbean plate, the Panama volcanic duringthe maximummarine transgressiol•of late Cretaceous arc,and northwestern South America. The thick(up to 6 km) (Cenomanian-Campanian)age. Regressionbegan in the latest molassedeposits accumulated in the foredeepbasin indicate Cretaceous(Maestrichtian) with marinedeposition of the shaly thatthe Venezuelan Andes started to riseas earlyas the early Colon Formation and the sandier Mito-Juan Formation. This Miocene.However, a lateMiocene intramolasse unconformity regressionevent continued through the Paleocene and middle marksthe beginningof the formationof the monoclineand the Eocenewith depositionof sandstones,siltstones, shales, and greatestuplift. Thecrustal-scale fault-related fold modelmay coalsof the OrocueGroup in a deltaicenvironment followed explain structuralfeatures seen in otherareas of basement- by fluvial sandstonesof the Mirador Formation. involved foreland deformation. Unconformablyoverlying this is the upperEocene paralic facies of the Carbonera Formation which is in turn INTRODUCTION transitionallycovered by lacustrineshales of the Oligocene Leon Formation. Mioceneto Recentaged sediments represent Over thepast several years, diverse tectonic models have continentaldeposits (Guayabo Group) derived mainly from beenproposed to explainthe Venezuelan Andes uplift. Bucher erosionof the VenezuelanAndes uplift. [ 1952],Gonzalez de Juana [1952], Ilargraves and Shagam The sedimentsin the mountainfront are foldedinto a steep [1969],and Shagam[1972] described the VenezuelanAndes as northwestwarddipping monocline. The dip of strataranges a mega-anticlinecontaining a horst-grabenblock complex and from 25 ø to overturned, and the strike is northeast-southwest. limitedat bothflanks by high-anglereverse faults. Rod Numerousfaults, mainly orientednorth northwest-south [ 1960], Deratmiroff [ 1971], Schubert[ 1985], White [ 1985], southeastand northeast-southwest,cut and offset the Boesiet al. [1988],and Monsalve [ 1988]proposed that the outcroppingstratigraphy. The Rio Mocotiesfault is VenezuelanAndes is a "mushroomlike"transpressional uplift considered to be the southwestern continuation of the Bocono withshear deformation in theBocono fault system and right-lateralstrike-slip fault. imbricatethrusting toward both Andean fronts. Hospers and The gravity field of the area showsa Bougueranomaly in Van Wijnen [ 1959],Kellogg and Bonini [1982, 1985], the northAndean trough of nearly- 150 mGal [Bonini et al., Giegengack[1984], and Kohn et al. [1984] notedthe 1977]. This large negativeanomaly in the southernedge of asymmetryof the gravityfield [Belliziaet al., 1976] and the Maracaibo Basin indicates that the basin and the Andes are suggestedthat the Venezuelan Andes uplift was caused by not in local isostaticequilibrium. crustalshortening along a southeastdipping "Wind River type" thrustfault. TectonicSetting This paperfocuses on the structuralinterpretation of seismic The intra-Mioceneunconformities indicate a majorAndean sectionstraversing the northwesternflank of the Venezuelan orogenywhich has been relatedto thecollision of thePanama Andesand the southernedge of theMaracaibo Basin between island arc with the South American continent [Mann and Burke, 1984; Eva et al., 1989]. The resultingcollision and Copyright 1993 by the American GeophysicalUnion. the obliquesubduction of the Carnegieridge beneath the Andes in Ecuadormay havecaused the upliftof theEastern Cordillera Paper number 93TC01893 of Colombia and the detachment of the North Andes block or 0278-7407/93/93TC-01893510.00 microplatealong the Boconoand the East Andean frontal fault 1394 DeToni and Kellogg: Venezuelan Andes C•RIBBE•N SEA C•RIBBœ•N Sœ• 12 ø I VENEZUELA COLOMBIA 11 ø MARACAIBO BASIN CARIBBEAN 10 o MOUNTAINS STUDY AREA •- APURE-BARINASBASIN __ _..,.,. _• r.,'"' •--X.,,, j_. o o, ,o,o ß I 75 ø W 72 ø 71 ø 70 ø 69 ø 68 ø 67 ø Fig. 1. Locationmap of the studyarea. system[Pennington, 1981' Kellogg et al., 1985]. The limited (1988-1991) showof the orderof 1 to 2 cm/yr convergence cumulativedisplacement on the Boconofault [Stephan,1977; betweenthe Caribbean,Panama, and North Andeanplates Gonzalezde Juanaet al., 1980; Schubert,1982; Giegengack, [Vegaet al., 1991]. "Thick-skinned"basement-involved 1984], despitethe relativelyrapid present-day slip rate of 1 deformationhas been correlated with magmaticgaps and low- cm/yr [Schubert,1980; Aggarwal, 1983], suggeststhat most angleor flat subductionin thePampeanas Range of Argentina of the northeastward movement of the North Andes block [Jordanet al., 1983;Jordan and Allmendinger, 1986] andthe occurredin the last 5 or 10 m.y. [Kellogg, 1984; Macellari, North AmericanCordillera [Lipman et al., 1971; Burchfieland 1984]. Davis, 1975; Coney, 1976; Dickinsonand Snyder, 1978]. Globalplate motionmodels predict west northwest-east southeastconvergence for the Caribbeanand South American Comparisonsto OtherBasement-lnvolved Foreland plates[Jordan, 1975; Minster and Jordan,1978; DeMets et al., Deformations 1990]. The north-southvector component is even greaterfor Caribbean-NorthAndean convergence when the NorthAndean Structural features in the Venezuelan Andes are similar to movement northeastward relative to South America on the thoseassociated with theLaramide orogeny (40-70 m.y.) in Boconofault systemis added. The directionof maximum the centraland southernRocky Mountains of the United shorteningin the VenezuelanAndes is northwest-southeast. States. The basementblock tectonicstyle of the Laramide Kellogg and Bonini [1982, 1985] and Kellogg [1984] orogenyis characterizedby the movementof basementblocks suggestedthat this vectorof deformationis relatedto slow alongreverse faults. The overlyingsediments in many areas convergence(1.7 + 0.7 cm/yr) betweenthe Caribbeanplate and fold overreverse faulted basement blocks forming the the North Andeanmicroplate at the SouthCaribbean marginal monoclines[Steams, 1971; Steamsand Weinberg, 1975; fault (Figure4). This compressivedeformation was also Matthews,1978; Narr, 1993;Narr and Suppe,submitted responsiblefor the upliftsof the Sierrade Perijaand the Sierra manuscript]analogous to thebruchfalten (fault folds)of Stille Nevadade SantaMarta.
Load more

Recommended publications
  • Memorial to Carlos Schubert 1938-1994 THO M a S W
    Memorial to Carlos Schubert 1938-1994 THO M A S W. DONNELLY Dept, o f Geological Sciences, State University o f New York, Binghamton, NY 13902-6000 Friends of Carlos Schubert Paetow were shocked and saddened upon hearing of his death in Caracas, Venezuela, on July 22, 1994, following an aneurism and a mesenteric stroke. Carlos, a longtime Fellow of the Geological Society of America, was one of the dominant figures of Venezuelan geology, specializing in his later years in neotectonics and in Quaternary geology. His untimely passing leaves a large void in Latin American—and in Quaternary—geology. His publications were voluminous and spanned a wide range of topics, but dominantly centered in Venezuelan studies. Carlos was bom in Hamburg, Germany, on October 9, 1938, and went to Caracas as an infant. He had a youthful interest in many subjects, but not especially in geology. His decision to pursue this field was the result of parental advice that geology and chemistry were the major fields of the future. Because he was uncom­ fortable with chemistry, he chose geology. Undoubtedly one of his important inspirations was the German explorer Alexander von Humboldt. Indeed, one of Carlos’s most prized possessions was his German 1815 edition of Humboldt’s Travels. In much of Carlos’s later work we can find a thread linking him to the founder of South American earth science. When he completed his high school studies in Caracas in 1957, he faced the problem that Pérez Jiménez, the president of Venezuela, had closed all Venezuelan universities. Fortunately, Carlos was awarded a scholarship from the Shell Oil Company to attend the University of Arizona, where he received his bachelor’s degree in geology in 1961.
    [Show full text]
  • Monoclinal Flexure of an Orogenic Plateau Margin During Subduction, South Turkey
    Non-peer reviewed preprint submitted to EarthArXiv Monoclinal flexure of an orogenic plateau margin during subduction, south Turkey Running title: Monoclinal flexure plateau margin David Fernández-Blanco1, Giovanni Bertotti2, Ali Aksu3 and Jeremy Hall3 1Tectonics and Structural Geology Department, Faculty of Earth and Life Sciences, Vrije Universiteit Amsterdam, De Boelelaan 1085, 1081 HV Amsterdam, the Netherlands [email protected] 2Department of Geotechnology, Faculty of Civil Engineering and Geosciences, Delft University of Technology, Stevinweg 1, 2628CN, Delft, the Netherlands 3 Department of Earth Sciences, Centre for Earth Resources Research, Memorial University of Newfoundland, St. John's, Newfoundland, Canada A1B 3X5 Non-peer reviewed preprint submitted to EarthArXiv Abstract Geologic evidence across orogenic plateau margins helps to discriminate the relative contributions of orogenic, epeirogenic and/or climatic processes leading to growth and maintenance of orogenic plateaus and plateau margins. Here, we discuss the mode of formation of the southern margin of the Central Anatolian Plateau (SCAP), and evaluate its time of formation, using fieldwork in the onshore and seismic reflection data in the offshore. In the onshore, uplifted Miocene rocks in a dip-slope topography show monocline flexure over >100 km, few-km asymmetric folds verging south, and outcrop- scale syn-sedimentary reverse faults. On the Turkish shelf, vertical faults transect the basal latest Messinian of a ~10 km fold where on-structure syntectonic wedges and synsedimentary unconformities indicate pre-Pliocene uplift and erosion followed by Pliocene and younger deformation. Collectively, Miocene rocks delineate a flexural monocline at plateau margin scale, expressed along our on-offshore sections as a kink- band fold with a steep flank ~20–25 km long.
    [Show full text]
  • Polyphase Laramide Tectonism and Sedimentation in the San Juan Basin, New Mexico Steven M
    New Mexico Geological Society Downloaded from: http://nmgs.nmt.edu/publications/guidebooks/54 Polyphase Laramide tectonism and sedimentation in the San Juan Basin, New Mexico Steven M. Cather, 2003, pp. 119-132 in: Geology of the Zuni Plateau, Lucas, Spencer G.; Semken, Steven C.; Berglof, William; Ulmer-Scholle, Dana; [eds.], New Mexico Geological Society 54th Annual Fall Field Conference Guidebook, 425 p. This is one of many related papers that were included in the 2003 NMGS Fall Field Conference Guidebook. Annual NMGS Fall Field Conference Guidebooks Every fall since 1950, the New Mexico Geological Society (NMGS) has held an annual Fall Field Conference that explores some region of New Mexico (or surrounding states). Always well attended, these conferences provide a guidebook to participants. Besides detailed road logs, the guidebooks contain many well written, edited, and peer-reviewed geoscience papers. These books have set the national standard for geologic guidebooks and are an essential geologic reference for anyone working in or around New Mexico. Free Downloads NMGS has decided to make peer-reviewed papers from our Fall Field Conference guidebooks available for free download. Non-members will have access to guidebook papers two years after publication. Members have access to all papers. This is in keeping with our mission of promoting interest, research, and cooperation regarding geology in New Mexico. However, guidebook sales represent a significant proportion of our operating budget. Therefore, only research papers are available for download. Road logs, mini-papers, maps, stratigraphic charts, and other selected content are available only in the printed guidebooks. Copyright Information Publications of the New Mexico Geological Society, printed and electronic, are protected by the copyright laws of the United States.
    [Show full text]
  • Tectonic Evolution of Structures in Southern Sindh Monocline, Indus Basin, Pakistan Formed in Multi-Extensional Tectonic Episodes of Indian Plate
    Tectonic Evolution of Structures in Southern Sindh Monocline, Indus Basin, Pakistan Formed in Multi-Extensional Tectonic Episodes of Indian Plate Sarfraz Hussain Solangi, Shabeer Ahmed, Muhammad Akram Qureshi, Mohammad Shahid, Uzair Hamid Awan Universityof Sindh, Pakistan Summary There are number of structures and structural styles found in extensional tectonic settings of the world but the evolution of these structuresis still needful and a big challenge as well. Evolution of structures in extensional settings have been studied by Yuan Li et al., (2016)and many other reserachers on different extensional basins of the world. Sindh Monocline lies on the western corner of Indian Plate and the tectonic history of Indian plate has been well described by Chatterjee et al., (2013) while tectonic history of Sindh Monocline has been studied by Zaigham, and Mallick, (2000), Chatterjee et al., (2013) (Fig.1). The aim of this study is the evolution of structures in the subsurface of Southern Sindh Monocline, Pakistan using the seismic data interpretation and faltenning of horizons approach. Jamaluddin et al., (2015) and others have also testified such approach. Southern Sindh Monocline is charaterized and experienced by different tectonic episodes of Indian plate while rifting from Gondwanaland, rifting from other plates at different geological times and to its collision with the Asia. Basic structures with in study area are classified into nine types whilethe structural styles have been classified into six types as horst and grabens,dominos,crotch,synthetic
    [Show full text]
  • Geology and Stratigraphy Column
    Capitol Reef National Park National Park Service U.S. Department of the Interior Geology “Geology knows no such word as forever.” —Wallace Stegner Capitol Reef National Park’s geologic story reveals a nearly complete set of Mesozoic-era sedimentary layers. For 200 million years, rock layers formed at or near sea level. About 75-35 million years ago tectonic forces uplifted them, forming the Waterpocket Fold. Forces of erosion have been sculpting this spectacular landscape ever since. Deposition If you could travel in time and visit Capitol Visiting Capitol Reef 180 million years ago, Reef 245 million years ago, you would not when the Navajo Sandstone was deposited, recognize the landscape. Imagine a coastal you would have been surrounded by a giant park, with beaches and tidal flats; the water sand sea, the largest in Earth’s history. In this moves in and out gently, shaping ripple marks hot, dry climate, wind blew over sand dunes, in the wet sand. This is the environment creating large, sweeping crossbeds now in which the sediments of the Moenkopi preserved in the sandstone of Capitol Dome Formation were deposited. and Fern’s Nipple. Now jump ahead 20 million years, to 225 All the sedimentary rock layers were laid million years ago. The tidal flats are gone and down at or near sea level. Younger layers were the climate supports a tropical jungle, filled deposited on top of older layers. The Moenkopi with swamps, primitive trees, and giant ferns. is the oldest layer visible from the visitor center, The water is stagnant and a humid breeze with the younger Chinle Formation above it.
    [Show full text]
  • Horst Inversion Within a Décollement Zone During Extension Upper Rhine Graben, France Joachim Place, M Diraison, Yves Géraud, Hemin Koyi
    Horst Inversion Within a Décollement Zone During Extension Upper Rhine Graben, France Joachim Place, M Diraison, Yves Géraud, Hemin Koyi To cite this version: Joachim Place, M Diraison, Yves Géraud, Hemin Koyi. Horst Inversion Within a Décollement Zone During Extension Upper Rhine Graben, France. Atlas of Structural Geological Interpretation from Seismic Images, 2018. hal-02959693 HAL Id: hal-02959693 https://hal.archives-ouvertes.fr/hal-02959693 Submitted on 7 Oct 2020 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. Horst Inversion Within a Décollement Zone During Extension Upper Rhine Graben, France Joachim Place*1, M. Diraison2, Y. Géraud3, and Hemin A. Koyi4 1 Formerly at Department of Earth Sciences, Uppsala University, Sweden 2 Institut de Physique du Globe de Strasbourg (IPGS), Université de Strasbourg/EOST, Strasbourg, France 3 Université de Lorraine, Vandoeuvre-lès-Nancy, France 4 Department of Earth Sciences, Uppsala University, Sweden * [email protected] The Merkwiller–Pechelbronn oil field of the Upper Rhine Graben has been a target for hydrocarbon exploration for over a century. The occurrence of the hydrocarbons is thought to be related to the noticeably high geothermal gradient of the area.
    [Show full text]
  • Proceedings Chapter Reference
    Proceedings Chapter Detailed Structural and Reservoir Rock Typing Characterisation of the Greater Geneva Basin, Switzerland, for Geothermal Resource Assessment CLERC, Nicolas, et al. Abstract A large, multistage program (GEothermie 2020) for developing the deep geothermal energy resources of the trans-border (Swiss- French) Greater Geneva Basin has been initiated in 2013 by the State of Geneva (Switzerland). In this framework, two PhD research projects have been initiated to study the subsurface geology of the region focus on both geothermal and hydrothermal energy prospection. The first project aims at characterizing facies distribution, petrophysical and thermal properties of the sedimentary sequence ranging from Permo-Carboniferous to Lower Cretaceous units. The second project investigates the basin structural evolution, fault-related fractures and their geometrical characteristics and properties. This information is being integrated in 3D geological models at both regional and local scale, derived from 2D seismic lines and well data. Detailed rock typing description from petrophysical measurements and laboratory analysis of core and outcrop samples (facies and micro-facies description; geochemical, petrophysical and thermal properties) are being carried out in order to assess the lateral variations of [...] Reference CLERC, Nicolas, et al. Detailed Structural and Reservoir Rock Typing Characterisation of the Greater Geneva Basin, Switzerland, for Geothermal Resource Assessment. In: Proceedings World Geothermal Congres. 2015. Available
    [Show full text]
  • The Venezuelan Hydrocarbon Habitat, Part 1: Tectonics, Structure, Palaeogeography and Source Rocks
    Journal of Petroleum Geology, vo1.23(1), January 2000, pp 5-53. 5 THE VENEZUELAN HYDROCARBON HABITAT, PART 1: TECTONICS, STRUCTURE, PALAEOGEOGRAPHY AND SOURCE ROCKS K. H. James* Venezuela forms part of an important hydrocarbon province, defined by the presence of prolific Cretaceous source rocks, which extends across northern South America. By early 1997, the country had produced 53 billion barrels of oil. Reserves are estimated to total 73 billion barrels of oil and 146 TCF of gas with 250 billion barrels recoverable in the Heavy Oil Belt. Most reserves are located within the intermontane Maracaibo and foreland Barinas-Apure and Eastern Venezuela BasinxThey correspond to more than 1.5 trillion BOE originally in place. The province S hydrocarbon history began with a broad passive margin over which the sea transgressed throughout much ofthe Cretaceous. Limestones and shales followed basal sands and included rich source rocks. Convergence between the distal part of the area and the Caribbean Plate created an active margin that migrated southwards, so that flysch and wildflysch followed the transgressive facies. The process culminated in Lute Cretaceous to Middle Eocene orogeny with the emplacement of southward-vergent nappes and the development of northward-deepeningforedeeps. Flysch and wildflysch formed in the north while important deltaic - paralic reservoir sands accumulated in the south. Major phases of hydrocarbon generationfrom Jurassic-Cretaceoussource rocks occurred across the entire margin of northern South America during the orogeny. They are recorded by Jurassic - Middle Cretaceous graphitic marbles, schists and quartzites (metamorphosed, organic limestones and shales and oil-bearing sandstones) in the Coastal and Northern Ranges of Venezuela and Trinidad.
    [Show full text]
  • Raplee Ridge Monocline and Thrust Fault Imaged Using Inverse Boundary Element Modeling and ALSM Data
    Journal of Structural Geology 32 (2010) 45–58 Contents lists available at ScienceDirect Journal of Structural Geology journal homepage: www.elsevier.com/locate/jsg Structural geometry of Raplee Ridge monocline and thrust fault imaged using inverse Boundary Element Modeling and ALSM data G.E. Hilley*, I. Mynatt, D.D. Pollard Department of Geological and Environmental Sciences, Stanford University, Stanford, CA 94305-2115, USA article info abstract Article history: We model the Raplee Ridge monocline in southwest Utah, where Airborne Laser Swath Mapping (ALSM) Received 16 September 2008 topographic data define the geometry of exposed marker layers within this fold. The spatial extent of five Received in revised form surfaces were mapped using the ALSM data, elevations were extracted from the topography, and points 30 April 2009 on these surfaces were used to infer the underlying fault geometry and remote strain conditions. First, Accepted 29 June 2009 we compare elevations extracted from the ALSM data to the publicly available National Elevation Dataset Available online 8 July 2009 10-m DEM (Digital Elevation Model; NED-10) and 30-m DEM (NED-30). While the spatial resolution of the NED datasets was too coarse to locate the surfaces accurately, the elevations extracted at points Keywords: w Monocline spaced 50 m apart from each mapped surface yield similar values to the ALSM data. Next, we used Boundary element model a Boundary Element Model (BEM) to infer the geometry of the underlying fault and the remote strain Airborne laser swath mapping tensor that is most consistent with the deformation recorded by strata exposed within the fold.
    [Show full text]
  • Tetonic Inheritance and Structural Styles in the Merida
    Third ISAG, St Malo (France), 17-19/9/1996 TECTONIC INHERITANCE AND STRUCTURAL STYLES IN THE MERIDA ANDES (WESTERN VENEZUELA). Bernard COLLETTA( l ) , Franqois ROURE( l) Bruno DE TONI(~),Daniel LOLTREIRO(~)Herminio PASSALACQUA(~)~~~Yves GOU(~). (I hnstitut Franqais du PCtrole, BP3 1 1, 92506 Rueil-Malmaison, France (2)~ntevep,Apartado 76343, Caracas 1070-A, Venezuela (3)~eicipFranlab, 92506 Rueil-Malmaison, France KEY WORDS: Venezuela, Merida Andes, tectonic inversion, crustal scale balanced sections INTRODUCTION Unlike the adjacent Caribbean and Central Andean orogens, the Merida Andes (Fig. 1) do not relate to direct interactions between the South American craton and either arc terranes or oceanic domains, but represent only minor intraplate readjustements between the Eastern Cordillera in the south and the South Caribbean transform margin in the north.Although no deep seismic profiling has yet been attempted across the Venezuelan Andes, a large set of conventional seismic reflection profiles has been recorded by the petroleum industry in the Maracaibo and Barinas-Apure basins, respectively along the North and South Andean foothills. In addition, isolated refraction and magnetotelluric data are available. However, only the gravimetric coverage is really complete, thus providing a relatively coherent image of the basement architecture. STRUCTURE OF THE SOUTH ANDEAN FLANK The Barinas-Apure basin extends from the Andean foothills in the northwest to the Guyana shield in the southeast, thus encompassing most of the drainage area of the Rio Apure, a tributary of the Orinoco River. Southwards, it connects directly with the Llanos basin in Colombia. The Barinas basin hardly compares with a flexural basin. It is largely dominated by either north- or south-verging basement- involved structures.
    [Show full text]
  • Late Quaternary Deglacial History of the Mérida Andes, Venezuela
    JOURNAL OF QUATERNARY SCIENCE (in press) Copyright ß 2007 John Wiley & Sons, Ltd. Published online in Wiley InterScience (www.interscience.wiley.com) DOI: 10.1002/jqs.1109 Correspondence the terminal and lateral moraines of the El Caballo and Reply: Late Quaternary deglacial La Mucuchache glaciers. A chemically untreated organic history of the Me´rida Andes, sample from 1.5 m above the base of the section yielded a conventional age of 22 750 cal. yr BP (19 000 14C yr BP), Venezuela: response whereas a peat sample immediately below the top of the section yielded an age of 19 960 cal. yr BP (16 500 14C yr BP). to comment We recognise that other workers (e.g. Mahaney et al., 2001, 2004; Dirszowsky et al., 2005) have re-analysed the Pedregal fan complex. For example, the sedimentology was described in detail by Dirszowsky et al. (2005). However, the chronology in We welcome the opportunity to respond to Mahaney et al.’s these papers is questionable and not useful for constraining the critique of our article on the deglacial history of the LGM. All of the recently published dates are on refractory Venezuelan Andes (Stansell et al., 2005). The source of our organic matter isolated using a cellulose extraction technique disagreement appears to stem primarily from differences in which concentrates refractory carbon, resulting in ages research strategies and methodology. Our work in the between 47 000 and 60 000 14C yr BP. These ages include mul- Venezuelan Andes employs lake sediment archives that record tiple reversals and are at the very edge of interpretability as continuous sedimentary sequences and can be dated using finite radiocarbon ages; nonetheless, the authors have inter- accelerator mass spectrometry (AMS) radiocarbon dating of preted them as valid ages.
    [Show full text]
  • Grand Canyon
    U.S. Department of the Interior Geologic Investigations Series I–2688 14 Version 1.0 4 U.S. Geological Survey 167.5 1 BIG SPRINGS CORRELATION OF MAP UNITS LIST OF MAP UNITS 4 Pt Ph Pamphlet accompanies map .5 Ph SURFICIAL DEPOSITS Pk SURFICIAL DEPOSITS SUPAI MONOCLINE Pk Qr Holocene Qr Colorado River gravel deposits (Holocene) Qsb FAULT CRAZY JUG Pt Qtg Qa Qt Ql Pk Pt Ph MONOCLINE MONOCLINE 18 QUATERNARY Geologic Map of the Pleistocene Qtg Terrace gravel deposits (Holocene and Pleistocene) Pc Pk Pe 103.5 14 Qa Alluvial deposits (Holocene and Pleistocene) Pt Pc VOLCANIC ROCKS 45.5 SINYALA Qti Qi TAPEATS FAULT 7 Qhp Qsp Qt Travertine deposits (Holocene and Pleistocene) Grand Canyon ၧ DE MOTTE FAULT Pc Qtp M u Pt Pleistocene QUATERNARY Pc Qp Pe Qtb Qhb Qsb Ql Landslide deposits (Holocene and Pleistocene) Qsb 1 Qhp Ph 7 BIG SPRINGS FAULT ′ × ′ 2 VOLCANIC DEPOSITS Dtb Pk PALEOZOIC SEDIMENTARY ROCKS 30 60 Quadrangle, Mr Pc 61 Quaternary basalts (Pleistocene) Unconformity Qsp 49 Pk 6 MUAV FAULT Qhb Pt Lower Tuckup Canyon Basalt (Pleistocene) ၣm TRIASSIC 12 Triassic Qsb Ph Pk Mr Qti Intrusive dikes Coconino and Mohave Counties, Pe 4.5 7 Unconformity 2 3 Pc Qtp Pyroclastic deposits Mr 0.5 1.5 Mၧu EAST KAIBAB MONOCLINE Pk 24.5 Ph 1 222 Qtb Basalt flow Northwestern Arizona FISHTAIL FAULT 1.5 Pt Unconformity Dtb Pc Basalt of Hancock Knolls (Pleistocene) Pe Pe Mၧu Mr Pc Pk Pk Pk NOBLE Pt Qhp Qhb 1 Mၧu Pyroclastic deposits Qhp 5 Pe Pt FAULT Pc Ms 12 Pc 12 10.5 Lower Qhb Basalt flows 1 9 1 0.5 PERMIAN By George H.
    [Show full text]