Thesis
Reference
Lithostratigraphical and tectono-sedimentary study of the Plio-Pleistocene infill of the Interandean North Cauca Valley Basin
(Colombia)
NEUWERTH, Ralph
Abstract
This investigation focus on the study of the Plio-Plesitocene deposits in a zone covering parts of the Quindío, Risaralda and Valle del Cauca departments in Central Colombia. The results can be summarized as follows : In the initial phase, a vast field campaign, a detailed sedimentological study and facies analyses have led to the differentiation of various lithological units within the Zarzal Formation, allowing the stratigraphical redefinition of the Plio-Pleistocene sediments deposited in the northern part of the Cauca Basin, on both sides of the Serranía de Santa Barbara. This sedimentological study has demonstrated the existence of soft-sediment deformations interpreted as seismites. They demonstrate an intense synsedimentary seismic activity during the Plio-Pleistocene. The last part of this research presents a tectonic study at a larger scale than the studied North Cauca Basin. A dextral strike-slip zone has been evidenced. This deformation zone seems to be responsible for the closing of the North Cauca Basin studied here.
NEUWERTH, Ralph. Lithostratigraphical and tectono-sedimentary study of the
Plio-Pleistocene infill of the Interandean North Cauca Valley Basin (Colombia). Thèse de doctorat : Univ. Genève, 2009, no. Sc. 4141
URN : urn:nbn:ch:unige-189486
DOI : 10.13097/archive-ouverte/unige:18948
Available at:
http://archive-ouverte.unige.ch/unige:18948
Disclaimer: layout of this document may differ from the published version.
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UNIVERSIDAD DEL QUINDÍO FACULTAD DE INGENERÍA CEIFI Profesor A. Espinosa
L ITHOSTRATIGRAPHICAL AND T ECTONO -S EDIMENTARY S TUDY OF THE P LIO -P LEISTOCENE I NFILL OF THE I NTERANDEAN
N ORTH C AUCA V ALLEY B ASIN (C OLOMBIA )
_______________________________________________________________
THESE
Présentée à la Faculté des Sciences de l’Université de Genève pour obtenir le grade de Docteur ès sciences, mention Sciences de la Terre
par
Ralph Neuwerth
deMonthey (VS)
Thèse No 4141
GENEVE
Atelier de reprographie ReproMail 2012
Terre & Environnement, vol. 106, viii + 157 pp. (2012)
ISBN 978-2-940472-06-2
Section des sciences de la Terre et de l'environnement, Université de Genève, 13 rue des Maraîchers, CH-1205 Genève, Suisse Téléphone ++41-22-379.66.28 - Fax ++41-22-379.32.11
http://www.unige.ch/sciences/terre/
Abstract
This investigation is the result of a collaboration agreement between the Universities of Geneva (Switzerland) and Quindío (Colombia), initiated by Profs. Georges Gorin (Geneva) and Armando Espinosa (Quindío). It is part of a larger research project funded by the Swiss National Science Foundation and studying the Plio-Plesitocene deposits in a zone covering parts of the Quindío, Risaralda and Valle del Cauca departments in Central Colombia. Within the framework of the latter project, four Ph.D. and six M.Sc. theses have been carried out and six papers have been so far published in international journals. The thesis presented here attempts to integrate in an optimal way the results already obtained by other contributors to the project.
Because the North Cauca Basin studied here was significantly lacking reliable data, a multidisciplinary approach has been applied throughout the investigation. The results have improved the geological knowledge of the area and can be summarized as follows :
In the initial phase, a vast field campaign, a detailed sedimentological study and facies analyses have led to the differentiation of various lithological units within the Zarzal Formation. The latter are interstratified with each other, as well as with the volcaniclastic deposits of the Quindío-Risaralda Fan. These new data, as well as radiometric datings, have permitted the stratigraphical redefinition of the Plio-Pleistocene sediments deposited in the northern part of the Cauca Basin, on both sides of the Serranía de Santa Barbara (paper submitted to Geologica Acta).
This sedimentological study of various outcrops has demonstrated the existence of spectacular soft- sediment deformations interpreted as seismites. They demonstrate an intense synsedimentary seismic activity during the Plio-Pleistocene. These results have been published in 2006 in Sedimentary Geology.
The last part of this research presents a tectonic study at a larger scale than the studied North Cauca Basin. Because a sedimentary depositional model for the lithostratigraphical units was established, it has been necessary to take a more regional view at tectonic lineaments in order to understand the geometry of the basin in a wider context. A dextral strike-slip zone has been evidenced, comprised between the EENE-WWSW trending, dextral, transtensional Cucuana and Istmina faults. This deformation zone seems to have led to the clockwise rotation of the Romeral Fault System and the formation of NW-SE trending normal faults. The latter are probably responsible for the closing of the North Cauca Basin studied here, but also for that of the Amagá and Upper Magdalena basins.
Resumen
La presente investigación es el resultado del convenio existente entre las Universidades de Ginebra (Suiza) y del Quindío (Colombia), iniciado por los profesores Georges Gorin (Suiza) y Armando Espinosa (Colombia). Dicho proyecto a sido sostenido por el Fondo Nacional Suizo de la Investigación, el cual fue consagrado al estudio sedimentológico y estructural de los depósitos de edad Pliopleistocena que cubren parte de los departamentos del Quindío, Risaralda y la parte norte del departamento del Valle del Cauca. La realización de este proyecto permitió producción de cuatro tesis de doctorado, seis tesis de master y la publicación de seis artículos en revistas internacionales.
El trabajo aquí presentado intenta integrar de la mejor forma los estudios realizados previamente en el marco de dicho proyecto.
La cuenca septentrional del Valle del rio Cauca carecía de estudios detallados hasta la elaboración del presente estudio. Esta problemática fue abordada de una manera multidisciplinaria y los resultados obtenidos contribuyen en el mejoramiento de los conocimientos geológicos del área de la siguiente manera.
Gracias al trabajo de campo; al estudio sedimentológico detallado y al análisis de facies las diferentes unidades litoestratigráficas existentes al interior de la Formación Zarzal pudieron ser diferenciadas.
De la misma manera que las relaciones existentes con el Abanico Volcaniclástico del Quindío- Risaralda. Estos resultados junto con las dataciones radiométricas efectuadas nos permiten proponer una redefinición estratigráfica de los sedimentos Plio-Pleistocenos depositados en la parte norte de la cuenca del valle del rio Cauca; de lado y lado de la Serranía de Santa Bárbara (articulo remitido a Geológica Acta).
Esta descripción sedimentológica a la escala del afloramiento permitió igualmente de identificar impresionantes estructuras de deformación de sedimentos blandos; que fueron interpretadas como sismitas. Estas últimas, son una prueba de la actividad sísmica de la zona durante el Plio-Pleistoceno.
Estos resultados fueron publicados en el año 2006 en la revista “Sedimentary Geology”.
La parte final de esta tesis propone un estudio tectónico a gran escala. Dado que el modelo de depósito de las diferentes unidades litoestratigráficas había sido previamente elaborado (en el seno de este proyecto); un análisis de las principales estructuras existentes en el área era necesario con el fin de precisar la geometría de dicha zona. La existencia de una zona de cizallamiento dextral fue evidenciada entre las fallas de componente dextral y normal de Cucuana e Itsmina orientadas EENE-WWSW. Esta zona de deformación parece ser la responsable de la rotación en sentido horario del sistema de fallas de Romeral y de la creación de las fallas normales de orientación NW – SE.
Estas últimas no solo permitieron el cierre de la cuenca del Valle del río Cauca en la zona de estudio, sino que probablemente influyeron en el cierre de las cuencas de Amagá y del Valle superior del Magdalena.
Résumé
Cette recherche est le fruit d’un accord de collaboration entre les Universités de Genève (Suisse) et du Quindío (Colombie), initié par les Professeurs Georges Gorin (Genève) et Armando Espinosa (Quindío). Elle s’insert dans un vaste projet de recherche, soutenu par le Fond National Suisse de Recherche Scientifique, portant sur l’étude des dépôts plio-pléistocènes dans une zone couvrant une partie des départements du Quindío, Risaralda et Valle del Cauca en Colombie centrale. Ce projet a permis la réalisation de quatre thèses de doctorat, six thèses de master et six articles dans des revues scientifiques internationales. Le présent travail a essayé d’intégrer de manière optimale les études préalablement réalisées dans le cadre de ce grand projet.
Cette étude a pour but de comprendre la formation ainsi que l’évolution du bassin du Cauca Nord, comprenant deux bassins sédimentaires intra-montagneux (North Cauca Valley and Quindío- Risaralda Fan) durant le dernier million d’années. Ces derniers, situés entre les cordillères centrale et occidentale de la Colombie centrale, sont séparés par une chaine montagneuse d’âge Oligo-Miocène, nommée la Serranía de Santa Barbara. Cette zone est géologiquement intéressante car tectoniquement très active. En effet, ce projet a vu le jour suite au séisme d’Armenia survenu le 20 janvier 1999 d’une magnitude de 6.2, faisant plus d’un millier de victimes. Tectoniquement, cette région est sous l’influence de trois plaques convergentes, à savoir Nazca, Caraïbes et Amérique du Sud. Les dépôts étudiés dans le cadre de ce projet représentent la plus ancienne unité stratigraphique n’ayant pas subi de déformation majeure. Leur étude détaillée permet ainsi d’améliorer la connaissance de l’évolution des Andes colombiennes entre le Néogène tardif et le Pléistocène.
Le bassin du Cauca Nord étudié ici manquant fondamentalement de données pertinentes, une approche multidisciplinaire a été nécessaire et constitue la trame de ce manuscrit. Les résultats obtenus semblent objectivement améliorer les connaissances géologiques et peuvent être résumés de la manière suivante :
Dans un premier temps, une large campagne de terrain et une étude sédimentologique détaillée de la Formation Zarzal ont permis de décrire : (1) de nombreux faciès qui n’apparaissent pas dans la littérature. Cette formation a donc été redéfinie sur la base des environnements de dépôts rencontrés : (a) fluvio-lacustre, (b) mass-flows, (c) Gilbert-type delta et (d) fan alluvial ; (2) une relation stratigraphique avec les dépôts volcaniclastiques du fan du Quindío-Risaralda, qui ont été étudiés et décrits notamment par Fernando Guarin dans ses travaux de diplôme et de doctorat liés à ce projet.
En conséquence, un nouveau groupe lithostratigraphique, nommé le Santa Barbara Group a été proposé. Celui-ci inclus la Formation Zarzal et la nouvelle Formation Quindío-Risaralda. La Formation Zarzal a été redéfinie en trois membres (Membres Obando, Ansermanuevo and Holguín) selon leurs environnements de dépôt et l’origine de leurs éléments lithologiques.
Les dépôts affleurant sur la zone d’étude ont été datés palynologiquement et géochronologiquement (méthode 40Ar/39Ar). Des pollens d’Alnus, apparus en Colombie il y a 0.8 Ma, ont été identifiés dans
plusieurs échantillons d’argile sur l’ensemble de la zone d’étude. Les datations absolues réalisées sur des biotites prélevées dans dépôts de cendre révèlent des âges compris entre 1,06 ± 0,17 and 2,79
± 0,5 Ma. Les sédiments du Groupe de Santa Barbara affleurant dans la zone d’étude se sont donc déposés durant le Plio-Pléistocène.
Cette description sédimentologique à l’échelle de l’affleurement a permis également de rencontrer des structures de déformation de sédiments meubles (sables de faible à moyenne granulométrie, limons et argiles) très spectaculaires qui ont fait l’objet d’une publication dans la revue Sedimentary Geology (2006).
Les différentes structures de déformation rencontrées ont été décrites morphologiquement puis classifiées dans 4 groupes comprenant 14 catégories, à savoir (1) structures de charge (simple load cast, pendulous load cast, flame structure, attached pseudonodules, detached pseudonodules) ; (2) structures d’échappement d’eau (water escape cusp, dish and pillar, pocket and pillar) ; (3) intrusions de sédiment meuble (clastic dykes and sills) ; (4) autres structures (disturbed laminites, convolute laminations, slumping, synsedimentary faults). Les mécanismes et forces de déformation sont essentiellement liés aux instabilités gravitationnelles, déshydratation, liquéfaction et déformations cassantes.
Plusieurs mécanismes sont susceptibles de déclencher de telles déformations. Les plus connus sont la surcharge sédimentaire, les courants de tempêtes et la sismicité. Aucune évidence à l’affleurement ne permettant de lier ces structures à une surcharge sédimentaire ni à des tempêtes (swalely et hummocky cross-stratification), celles sont ont donc été interprétées comme sismites. Cette interprétation est supportée par les arguments suivants : (1) l’activité sismique géologique et récente est clairement démontrée dans la zone d’étude qui est sous l’influence du système de faille Cauca-Romeral ; (2) l’intercalation d’intervalles déformés dans des couches non-déformées reflète des événements catastrophiques suivis de période de relative stabilité ; (3) les sédiments meubles de faible à moyenne granulométrie de la Formation Zarzal sont particulièrement sujets à la liquéfaction durant des épisodes sismiques ; (4) les structures rencontrées sont similaires, tant en en taille que dans leur forme, à celles décrites comme sismites dans la littérature ; (5) la large répartition géographique de déformations sont compatibles avec des sismites.
Par conséquence, l’existence de ces sismites dans les sédiments de la Formation Zarzal confirme une activité tectonique dans la zone d’étude durant le Plio-Pléistocène. Des tremblements de terre d’une magnitude supérieure à 5 sur l’échelle ouverte de Richter peuvent être admis, se basant sur la proximité de failles actives ainsi que sur le type de structures de déformation rencontrées.
La stratigraphie et l’âge des dépôts remplissant la dépression du Cauca Nord étant définis, l’activité sismique durant leur dépôt étant démontrée, l’ultime étape de cette étude a été de comprendre la formation d’un tel bassin intra-montagneux. Plusieurs modèle ont été présentés dans la littérature : graben ; bassin de pull-apart ; soulèvement de la Serranía de Santa Barbara,…
La dernière partie de cette thèse propose ainsi une étude tectonique à plus grande échelle, une vision des grandes structures étant nécessaire pour comprendre la géométrie d’une manière globale. Pour ce faire, une large campagne de mesure de miroirs de faille sur le terrain, une interprétation minutieuse de modèles numériques et une analyse morphométrique ont été réalisées.
La cartographie des dépôts holocène et des failles principales a permis de mettre en évidence la géométrie à large échelle autour de la zone étudiée. Celle-ci montre que les bassins du Cauca Nord, du Quindío-Risaralda, d’Amagá et du Magdalena sont délimités par des failles et donc d’origine tectonique. Ce résultat ainsi que l’analyse des linéaments (1’300) ont permis de mettre en évidence une zone de cisaillement située entre les failles de Cucuana et Istmina, ou le système de failles de Cauca-Romeral a subi une rotation horaire comprise entre 9° et 16°. Cette déflexion crée des failles transtensionnelles orientée NW-SE, telle que le système de faille Otún. Le mouvement normal de ces dernières génère ainsi une surrection de la partie nord de la zone d’étude, qui produit un effet de barrage, créant en conséquence un espace d’accommodation pour le dépôt des sédiments de la Formation Zarzal. Cette interprétation semble confirmée par les résultats d’étude morphométrique sur un MNA de 30m qui démontrent une importante activité tectonique dans la zone d’étude, spécialement dans la région de La Virginia.
De plus, l’analyse structurale des dépôts de la Formation Zarzal démontre l’activité simultanée des failles d’Otún et Ibagué et du système de faille Cauca-Romeral durant le Plio-Pléistocène. Ceci est confirmé par les structures de déformation rencontrée dans ces dépôts, attestant ainsi de l’importante activité sismique durant cette période.
L’ensemble des résultats de notre équipe de recherche, associés aux données décrites dans la littérature, ont permis de proposer un modèle d’évolution cinématique simplifié du Cauca Nord, illustré dans le chapitre 7.
La période allant de l’Oligocène Tardif au Miocène précoce voit la plaque Farallon se séparer en deux nouvelles plaques : Nazca et Cocos. Cet événement coïncide avec l’initiation du système de faille Ibagué et des failles orientées ENE. La conséquence tectonique est l’augmentation du taux de surrection de la Cordillère Centrale, de développement de la vallée du Cauca et le dépôt de la Formation Cartago.
Le plissement de cette dernière commença entre l’Oligocène tardif et le Miocène précoce et la Formation La Paila s’y déposa de manière discordante. Cette période correspond à la collision du bloc Chocó-Panamá contre la plaque sud-américaine.
La Formation Zarzal s’est ensuite déposé en discordance sur la Formation La Paila durant le Plio- Pléistocène, suite à la rotation du système de faille de Cauca-Romeral.
De nos jours, la partie nord de la zone d’étude, ainsi que la Serranía de Santa Barbara, sont toujours en surrection, entrainant la phase actuelle de remplissage sédimentaire du bassin du Cauca Nord.
Cette thèse de doctorat ne prétend pas donner toutes les réponses aux questions posées sur la géologie de la zone d’étude. En effet, l’étude sédimentologique des dépôts plio-pléistocènes n’a été réalisée que sur les affleurements en surface et ne permet donc pas de déterminer avec exactitude la géométrie et les épaisseurs des unités lithostratigraphiques. Des données sismiques sont nécessaires pour affiner cette stratigraphie et pour proposer un modèle de facies.
De plus, le modèle de déformation proposé est dérivé d’une analyse d’un modèle numérique d’altitude.
Il serait ainsi indiqué d’acquérir des données structurales sur le terrain, spécialement concernant les failles Otún, Cucuana et Istmina, ainsi qu’au pied de la Cordillère Occidentale, où les problèmes d’insécurité nous ont empêchés de nous y rendre.
Finalement, de meilleures datations des Formations Cartago et La Paila contribueraient à l’amélioration du modèle d’évolution cinématique proposé.
Acknowledgments
La présentation des résultats de ce travail de recherche me donne l’occasion d’exprimer ma profonde gratitude à l’égard de tous ceux qui ont, de près ou de loin, contribué à son élaboration.
Je tiens tout d’abord à exprimer mes plus vifs remerciements au Pr. Georges Gorin, mon directeur de thèse, sans qui ce projet n’aurait jamais vu le jour et que je considère non seulement comme un collègue, mais comme un ami Je tiens à relever son talent dans son domaine et à le remercier pour ses précieux conseils prodigués tout au long de cette étude. Ses fantastiques qualités humaines et sa grande disponibilité m’ont fourni une motivation supplémentaire à la réalisation de mon diplôme.
Mes remerciements s’adressent également au Pr Armando Espinosa de l’Université du Quindío (Colombie), co-directeur de thèse, et également instigateur du projet. Il m’a été d’un grand secours lors de mes nombreux déplacements en Colombie, tant par ses connaissances de la géologie locale que sur son aide logistique indispensable.
Je remercie également le Dr Mario Sartori, notre maître structuraliste à tous, pour tous ses conseils avisés, son œil sur le terrain, mais également pour sa motivation, ses anecdotes, son humour et sa constante bonne humeur.
Je remercie par anticipation le Pr. Olivier Parize pour sa participation en qualité de jury de ce travail, tout en me réjouissant de ses commentaires, sûrement pertinents, qui contribueront à l’amélioration de ce manuscrit.
Un grand merci s’adresse tout particulièrement à Fiore Suter, avec qui j’ai non seulement pu partager des mois de terrain, mon bureau dans lequel de grandes discussions ont largement contribué au présent travail, mais également un appartement et parmi les plus beaux moments de ma vie.
Un pensée chaleureuse se tourne également vers Fernando Guarin, Lina Ospina et Olivier Pahud, avec qui une réelle amitié c’est nouée, et avec qui j’ai réalisé une partie de mes missions de terrain.
Je tiens à exprimer ma plus grande reconnaissance à Rayo et Hubert, Lalo et Don Daniel pour leur aide précieuse, voire indispensable.
Plus que mes remerciement mais mon amour s’adressent à Katia, qui a été et reste mon soutien le plus précieux au monde, bacissimi !
Mille mercis également à tous mes amis, mis hermanos colombianos, particulièrement à Solecita, JuanK, LaCif, Alejo y Aleja, Lucho, Desisy y Mario, las Hermanas Negritas, Ingé Hugo.
Tous mes remerciements aussi à mes compagnons de volée, particulièrement Anouk, Jo, Julien et Fiore, avec qui le contact est toujours resté et le restera pour de nombreuse années encore je l’espère.
Un grand merci également non seulement au bureau 308 qui a vu se succéder, entre autre, David, Fiore, Chadia et Lina, mais également tous mes collègues du 3ème !
Je remercie aussi tous les personnes qui ont collaboré scientifiquement et techniquement : Carlos Guzmán, Richard Spikings, Rossana Martini, François, Pierrot et Peter, Olivier, Luc et Roelant, etc….
Pour finir, je tiens à remercier mes parents et mon frère Frank pour leurs encouragements et leur amour, tous mes amis, et tout spécialement Fiore Suter, mi hermanito et colocataire.
Abstract i
Resumen ii
Résumé iii
Acknowledgments vii
CHAPTER I - IntRoductIon 1
1.1. Description of project 2
1.2. Aims of study 2
1.3. Organisation of manuscript 4
CHAPTER II - methods 7
2.1. Field study 8
2.2. Fault inversion method 8
2.3. Morphometry 8
References 10
CHAPTER III - GeoloGIcalbackGRound 11
3.1. Location of study area 12
3.2. Geodynamic evolution of Colombia from Jurassic to recent times 13
3.3. Stratigraphy of the studied area 17
3.4. Structural geology of the studied area 23
3.5. The Cauca Depression 28
References 35
CHAPTER IV - sedImentaRyInfIllofandeanIntRamountanebasIns: casehIstoRyof PlIo-PleIstocenedePosItsInthe noRth cauca Valley (colombIa) 51
4.1. Introduction 52
4.2. Geological setting 54
4.4. Methods 58 4.5. Results and interpretation: New lithostratigraphical subdivision of Late Tertiary-Recent
sediments 58
4.6. Discussion 74
4.7. Conclusions 76
References 77
CHAPTER V - soft-sedImentdefoRmatIonInatectonIcallyactIVeaRea: the PlIo- PleIstocene ZaRZal foRmatIonInthe cauca Valley (WesteRn colombIa) 85
5.1. Introduction 86
5.2. Geology of Zarzal Formation 87
5.3. Overview of soft-sediment deformations and classifications 91
5.4. Soft-sediment deformations in the Zarzal Formation 93
5.5. Discussion 101
5.6. Conclusions 108
References 110
CHAPTER VI - tectonIcs 117
6.1. Introduction 118
6.2. Large scale geometry 119
6.3. Morphometry 126
6.4. Structural analysis 130
6.5. Discussion and conclusions 145
References 147
CHAPTER VII - conclusIons 151
7.1. Sedimentary infill of Andean intramountane basins: case history of Plio-Pleistocene deposits in
the North Cauca Valley (Colombia) (chapter 4) 152
7.2. Soft-sediment deformations in a tectonically active area: The Plio-Pleistocene Zarzal
Formation in the Cauca Valley (Western Colombia) (chapter 5) 152
7.3. Tectonics (chapter 6) 153
7.4. Cinematic reconstruction 153
References 156
CHAPTER I
Fig. 1.1: Geodynamics of NW South America: velocities and direction of motion for the different plates and blocks with respect to South America (after (Suter et al., 2008). Location of figure 1.2. 3 Fig. 1.2: 30-meter resolution DEM based on radar photographs (USGS, 2005) showing departmental boundaries and location of the areas studied in the general project(in red: zone one studied by Guarin, 2008; zone II studied by Suter, 2008; zone III studied in this work).
A: Ansermanuevo; Ar: Armenia; C: Cartago, V: La Virginia; P: Pereira; Z: Zarzal. CC: Central Cordillera; SSB: Serranía of Santa Barbara; WC: Western Cordillera. 4
CHAPTER III
Fig. 3.1: (A) Geodynamics of NW South America: velocities and direction of motion for the different plates and blocks with respect to South America (after (Suter et al., 2008). Location of study area.
Abbreviations: B: Bogotá; C: Cali; CC: Central Cordillera; EC: Eastern Cordillera; WC: Western Cordillera; EFFS: Eastern Frontal Fault System; IBF: Ibagué Fault; GF: Garrapatas Fault; RFS:
Romeral Fault System.
(B) Digital elevation model (DEM, (USGS, 2005)) of western central Colombia showing the course of the Cauca River. The study area is located upstream of La Virginia town, at the northern termination
of the Cauca Valley Basin (after (Suter et al., 2008). 12
Fig. 3.2: 30-meter resolution DEM based on radar photographs (USGS, 2005) showing Plio- Pleistocene deposits and faults in the studied area.
Abbreviations: A: Ansermanuevo; Ar: Armenia; C: Cartago, V: La Virginia; P: Pereira; Z: Zarzal.
CC: Central Cordillera; SSB: Serranía of Santa Barbara; WC: Western Cordillera. AB: Aguas Bonitas Fault; Asmn: Ansermanuevo Fault; C-A: Cauca Almaguer Fault, C-P: Cauca Patía Fault;
Csta: Consota Fault; Mont: Montenegro Fault; Nav: Navarco Fault; Otún: Otún Fault; Plst: Palestina Fault; Qnueva: Quebradanueva Fault; Rob: El Roble Fault; RV: Río Verde Fault; Sal: Salento Fault;
San J: San Jeronimo Fault; Sev: Sevilla Fault; SR: Santa Rosa Fault; Tor: Toro Fault. 13 Fig. 3.3: Simplified cross-section across the Cauca depression and the Quindío-Risaralda Basin, see
figure 3.2 for location. After (Suter et al., in review). 14
Fig. 3.4: Middle Cretaceous to Miocene plate reconstruction of northwestern South America showing two models: (A) arrival and oblique docking of the Pacific Terranes, followed by accretion of San Jacinto, Sinú , Guajira-Falcon, and Caribbean Mountain terranes and finally collision of the Chocó Arc. Grey shaded areas in all time slices represent paleotopographic swells, elevated and/or emergent areas. Red crosses represent magmatism (after (Cediel et al., 2003)).
Abbreviations: BAU: Baudó terrane; CAM: Caribbean Montaine terrane; CG: Cañas-Gordas terrane;
DA: Daguá-Piñon terrane; EC: Eastern Cordillera; GA: Garzón massif; GOR: Gorgona terrane; GU- FA: Guarija-Falcon terrane; MSP: Macacaibo sub-plate; PA: Panamá terrane: RO: Romeral terrane;
SJ: San Jacinto terrane; SM: Sinú terrane.
(B) backarc extension followed by accretion (after (Moreno and Pardo, 2002)). 15 Fig. 3.5: Compilation of the five 1:100'000 geological maps of INGEOMINAS (Caballero and Zapata, 1983; Parra, 1983; McCourt et al., 1984; Nivia et al., 1995; Estrada and Viana, 1998) which
cover the study area (after (Suter et al., 2008). 18
Fig. 3.6: 90-meter resolution DEM based on radar photographs (USGS, 2005) showing the 45 mass
Abbreviations: A: Armania; C: Cartago; P: Pereira; V: La Virginia; CC: Central Cordillera; SSB:
Serranía de Santa Barbara. 22
Fig. 3.7: 90-meter resolution DEM based on radar photographs (USGS, 2005) showing faults in the studied area (modified after (Ingeominas, 1999; Nivia, 2001; Suter et al., 2008)). 24 Table 3.1: Compilation of published literature about fault characteristics in the study area and its surroundings. These faults are located in Fig. 3.7 (modified after (Suter et al., 2008)). 34
CHAPTER IV
Fig. 4.1: (A) Geodynamics of NW South America and location of study area. Velocities and direction of motion for the different plates and blocks with respect to South America (after (Suter et al., 2008b).
Abbreviations: B: Bogotá; C: Cali; CC: Central Cordillera; EC: Eastern Cordillera; WC: Western Cordillera; EFFS: Eastern Frontal Fault System; IBF: Ibagué Fault; GF: Garrapatas Fault; RFS:
Romeral Fault System.
(B) Digital elevation model (DEM, (USGS, 2005)) of western central Colombia showing the course of the Cauca River. The study area is located upstream of La Virginia town, at the northern termination
of the Cauca Valley Basin (after (Suter et al., 2008b). 54
Fig. 4.2: Compilation of the five 1:100’000 geological maps of INGEOMINAS (Caballero and Zapata, 1983; Parra, 1983; McCourt et al., 1984b; Nivia et al., 1995; Estrada and Viana, 1998) which
cover the study area (after (Suter et al., 2008b)). 55
Fig. 4.3: Simplified tentative cross-section (after Suter et al. (2008b)) across the Cauca depression and the Quindío-Risaralda Basin (see figure 4.2 for location). The two zones highlighted by a frame (Cauca depression and La Vieja River) are detailed below in figure 4.6. 56 Fig. 4.4: 30-meter resolution DEM (USGS, 2005) with location of studied field sections. Three zones are highlighted: 1: the Cartago Fan (CF) (sections 1 to 8, Fig. 4.16); 2: the eastern foothills of the Western Cordillera (WC) (sections 9 to 17, Fig. 4.10); 3: the western foothills of the Serranía of Santa Barbara (SSB) (sections 18 to 22, Fig. 4.8).
Abbreviations: CC: Central Cordillera; QRF: Quindío-Risaralda Fan. 59 Fig. 4.5: Obando Member. A: stacked, trough cross-bedded bodies of black sands interpreted as braided-river channel infill; B: planar stratifications in fine silts to clays interpreted as floodplain deposits; C: diatomaceous deposits interbedded with very fine sandy beds. The white arrow indicates ash fall deposits, dated with 40Ar/39Ar method at 1.32 ± 0.07 Ma (see figure 4.7). 60 Fig. 4.6: Simplified tentative cross-sections from the Western Cordillera (WC) to the Quindío- Risaralda basin. This interpretation illustrates the interfingering of the Plio-Pleistocene units defined in this study (see Figure 4.3 for location and legend).
Abbreviations: AM: Ansermanuevo Member; HM: Holguín Member; OM: Obando Member; QRFm:
Quindío-Risaralda Formation; SSB: Serranía of Santa Barbara. 61
Fig. 4.7: (A) 40Ar/39Ar plateau age from the ash layer of section 18-20 in figure 4.8. 62 Fig. 4.8: Field sections in the western foothills of the Serranía of Santa Barbara (SSB) (see figure 4.4 for location and legend). In each section, the first occurrence of detritic sediments and mass flows sourced from the SSB is correlated with a black line in order to highlight the change in lithological composition. This line does not correspond to a time line. See figure 4.7 for Ar/Ar datings. 63 Fig. 4.9: Palaeocurrent directions measured in trough cross-bedded black sands, sigmoid stratifications (rose diagramme 8) and imbricated pebbles (rose diagramme 4) of Zarzal Formation.
Cordillera; CF: Cartago Fan; O: Obando; QRF: Quindío-Risaralda Fan; SSB: Serranía of Santa Barbara; Vict: La Victoria; Vir: La Virginia; WC: Western Cordillera; Z: Zarzal. The base map is the
same DEM as that of figure 4.4 where sections are located. 64
Fig. 4.10: Field sections in the eastern foothills of the Western Cordillera (WC) (see figure 4.4 for location of sections). The first occurrence of alluvial conglomerates rich in black cherts, white quartz and volcanic clasts at each location is correlated with a black line in order to highlight the change in lithological composition. This line does not correspond to a time line. Legend is the same as that in
figure 4.8. 65
Fig. 4.11: Ansermanuevo Member: clast-supported conglomerate rich in black chert, white quartz and volcanic elements interfingering with typical black sand deposits of the Obando Member (section
17, Fig. 4.10). Hammer for scale. 66
Fig. 4.12: Holguín Member: bottomset deposits: (A) pinching out towards the south and showing an erosive contact with the overlying foreset unit; (B) containing plant fragments (section 23, Fig. 4.8)
67 Fig. 4.13: Holguín Member: erosive contact between foreset and topset units (section 23, Fig. 4.8).
68 Fig. 4.14: Holguín Member: foreset facies (section 23, Fig. 4.8): (A) dip section of steeply dipping, sandy foresets separated by siltstone intercalations resulting from deposition of suspended load; (B) sandy foresets containing clayey soft pebbles; (C) strike-parallel section of foresets, which consist of
parallel flat-lying sandstone beds. 69
Fig. 4.15: Holguín Member: topset unit consisting of stacked, trough cross-bedded alluvial deposits (well to moderately sorted sands and gravel) and mass-flow deposits. 70 Fig. 4.16: Field sections in the N-Cartago Fan (see figure 4 for location). The first occurrence of volcanic mass flows at each location is correlated with a black line in order to highlight the change in sedimentary regime. This line does not correspond to a time line, because mass flows were first deposited in the eastern part of the Quindío-Risaralda Basin before moving westwards (Espinosa, 2000; Guarin et al., 2006). Numbers associated with palaeocurrents refer to those in figure 4.9. The base map is the same DEM as that of figure 4.4 where sections are located. Legend is the same as that
in figure 4.9. 72
Fig. 4.17: Quindío-Risaralda Formation. A: stratigraphical contact between (1) clast-supported conglomerates showing horizontal stratification and (2) coarse-grained sands with inverse grading;
B: photograph of (2) interpreted as hyperconcentrated flow deposits; C: matrix-supported, poorly sorted conglomerates (1) interpreted as debris-flow deposits with dm-size, angular, basaltic clasts
(section 6, Fig. 4.16). 72
Fig. 4.18: Example of field section in the Quindío-Risaralda Formation (after Guarin (2008)). 73 Table 4.1: Published subdivisions for the Zarzal Formation. 75 Table 4.2: Proposed new lithostratigraphical scheme of the Cauca depression and Quindío-Risaralda
Basin. 76
Fig. 5.1: Megatectonic framework and location of study area. 86 Fig. 5.2: Regional distribution of Plio-Pleistocene sediments in the Valle del Cauca, Risaralda and
Quindío Departments. Location of Figs. 5.3 and 5.4. 87
Fig. 5.3: Geological cross-section across the Valle del Cauca and Quindío Departments. See Fig. 5.2
for location. 88
Fig. 5.4: Detailed geological and location map of study area. See Fig. 5.2 for location. 89 Fig. 5.5: E–W and N–S trending correlations of field sections in the Zarzal Formation. See Fig. 5.4
for location of field sections. 90
Table 5.1: Comparison between some classifications of soft-sediment deformation (SSD) structures
showing nomenclatures and classification criteria. 91
Fig. 5.6: Types of soft-sediment deformation structures observed in the Zarzal Formation. 92 Fig. 5.7: Load structures. (A) Simple load cast (a) (section 8, see Figs. 5.4 and 5.5 for location) associated with convolute laminations (b) and water escape structure (c). (B) Pendulous load cast (section 8, see Figs. 5.4 and 5.5 for location). This structure is associated with a subvertical synsedimentary fault.
Part of the deformed fine sand–clay is liquefied, probably as a result of slumping. (C) Pendulous load cast (section 8, see Figs. 5.4 and 5.5 for location) showing internal deformations (a) associated with
gravity loading. 94
Fig. 5.8: Load structures. (A) Pendulous load cast (drop structure, Alfaro et al., 1997), near section 8 (see Figs. 5.4 and 5.5 for location). It forms a pocket of medium-grained sands overlying deformed, finely laminated sands. The upper part of the latter is affected by flame structures (a). (B) Attached pseudonodule made of fine-medium-grained sands, which sank into coarse-grained sands (section 8, see Figs. 5.4 and 5.5 for location). (C) Attached pseudonodule (a), water escape structure (b), simple load cast (c), convolute lamination (d) (section 8, see Figs. 5.4 and 5.5 for location). The attached pseudonodule (a) displays slightly deformed laminations. Note the clay layer within (a) which seems
to have been dislocated by the water escape. 95
Fig. 5.9: Load and water-escape structures. (A) Attached (a) and detached (b) pseudonodule (section 8, see Figs. 5.4 and 5.5 for location). Note that the clayey silt has a greater density than the liquefied sand. (B) Water escape cusps (a) (section 8, see Figs. 5.4 and 5.5 for location) formed by mediumgrained sands intruding fine-grained sands. Observe the laccolith shape of the fine-grained- sand intrusion into medium-grained-sands and silts (b). This structure is capped by hardly deformed silts, which have been penetrated by a sandy sill (c). (C) Dish and pillar structure (section 8, see Figs.
5.4 and 5.5 for location). The undisturbed laminations of the overlying medium-coarse-grained sand lense proves that the underlying deformation occurred prior to its deposition and is not related to
loading. 96
Fig. 5.10: Water escape and soft-sediment intrusion structures. (A) Pocket and pillar structure (section 8, see Figs. 5.4 and 5.5 for location). (B) Ptigmatic and bifurcated clastic dyke (section 6, see Figs.
5.4 and 5.5 for location). (C) Medium-grained sand, rooted vertical dyke intruding silty clays (near section 8, see Figs. 5.4 and 5.5 for location). This intrusion seems to be partially controlled by
fractures (a). 98
Fig. 5.11: Soft-sediment intrusion and other deformation structures. (A) Medium-grained sand, subvertical disconnected dyke (near section 8, see Figs. 5.4 and 5.5 for location) showing downward bending of intruded, fine-grained sediments (a) in the lower part. This feature indicates the lateral movement of the injection. (B) Disturbed laminites (near La Victoria, see Fig. 5.4 for location). (C) Convolute laminations (section 6, see Figs. 5.4 and 5.5 for location). 99 Fig. 5.12: Other soft-sediment deformation structures. (A) Slump with subhorizontal axial plane
to a flower structure indicative of strike-slip movements. Small-size load cast (c) and flame (d)
structures are also observed. 100
Fig. 5.13: Post-depositional extensional tectonics in the Zarzal Formation (section 7, see Figs. 5.4
and 5.5 for location). 105
Fig. 5.14: Post-depositional strike-slip tectonics in the Zarzal Formation (section 8, see Figs. 5.4 and
5.5 for location). 106
Fig. 5.15: Injection dykes (section 8, see Figs. 5.4 and 5.5 for location) are a proof of extension
(Rodríguez-Pascua et al., 2000). 107
CHAPTER VI
Fig. 6.1: Idealized model of the Quindío-Risaralda Fan and Serranía de Santa Barbara. Black and green arrows indicate respectively horizontal and vertical direction of rotation. (After (Guarin, 2008).
Abbreviations: A: Armenia, M: Montenegro, F.MTG: Montenegro fault, F.MTA: Matecaña fault, F.ARM: Armenia fault, F. PTS = Potrerillos fault, C: compresion, E: extension. 118 Fig. 6.2: (A) Summary of the data obtained in (Suter et al., 2008) and (B) comparison with the theoretical fault pattern developed under right-lateral shear system (after (Tchalenko, 1970)). (After
(Suter et al., 2008)). 119
Fig. 6.3: (A) Map of relative uplift rates of the SSB fold-and-thrust range and its surrounding, Plio- Pleistocene to Recent deposits; (B) Cross-section of the SSB passing between Obando and La Victoria
(see 6.3A for location) (After (Suter et al., in review)). 120
Fig. 6.4: 90-meter resolution DEM based on radar photographs (USGS, 2005) showing Holocene depocenter areas (yellow), bounded by main faults.
Abbreviations: BSFS: Bituima-La Salina Fault System; CF: Cucuana Fault; CPF: Cali-Patía Fault;
DF: Doima Fault; IBF: Ibagué Fan; IF: Ibagué Fault; IST: Istmina Fault; GF: Garrapatas Fault; LSFS:
La Salina Fault System; OFS: Otún Fault System; PAF: Palestina Fault; PF: Potrerillos Fault; PG:
Piedras Girardot Basin; QNF: Quebradanueva Fault; QR: Quindío-Risaralda Basin; RFS: Romeral Fault System; SDL: Santo Domingo lineament; SRF: Santa Rosa Fault. Green lines represent the new faults mapped in this study (see figure 6.11 for their inferred kinematics). 121 Fig. 6.5: 90-meter resolution DEM based on radar photographs (USGS, 2005) showing the “en- échelon” Otún Fault mapped in this study. Letters a, b and c refer to fault segments forming the Otún
Fault (see figure 6.11 for kinematics). 123
Fig. 6.6: 90-meter resolution DEM based on radar photographs (USGS, 2005) showing lineaments in the Central Cordillera and its surroundings, between 4°N and 7.4°N. 124 Fig. 6.7: Quantity-dependent rose-diagram illustrating the orientation of lineaments interpreted in
figure 6.6. 126
Fig. 6.8: Summary of figure 6.6, where the principal lineaments affecting this area are grouped into families according to their strike.
Abbreviations: AF: Arma Fault; GF: Garrapatas Fault; IF: Ibagué Fault; OF: Otún Fault; PF: Palestina
Fault; SF: Salento Fault; SRF: Santa Rosa Fault. 127
Fig. 6.9: Simplified map drawn from figure 6.4 showing main faults and Holocene depocenters (yellow). The hatched area represents the shear zone. (See figure 6.4 for abbreviations). 128 Fig. 6.10: Quantity-dependent rose-diagram illustrating the orientation of the RFS lineaments of
Fig. 6.11: (A) Simple shear associated with strike-slip faulting produces preferred orientation of faults, as well as different fault movements (after (Wilcox et al., 1973; Sylvester and Smith, 1976)).
(B) Summary of the data obtained in this study. Grey areas represent extensional zones.
Abbreviation: Ψ: shear angle. 129
Table 1: Morphometric data calculated of the studied area. 130 Fig. 6.12: 30-meter resolution DEM based on radar photographs (USGS, 2005) showing the drainage basin asymmetry of the North Cauca Depression (yellow) and the Risaralda Basin (red).
Abbreviation: Ψ: shear angle. 131
Fig. 6.13: 30-meter resolution DEM based on radar photographs (USGS, 2005) showing the mountain- front sinuosity (Smf) of the eastern border of the Risaralda Valley (black lines), the western border of the Risaralda Valley (yellow lines), the western border of the Cauca Valley (red lines) and its eastern
border formed by the SSB foothills (green lines). 132
Fig. 6.14: 30-meter resolution DEM based on radar photographs (USGS, 2005) covering the study area. White circles indicate the location of faults where striae have been observed, and white squares the location of faults in the Plio-Pleistocene deposits.
Abbreviations: A: Ansermanuevo; Bel: Belalcazar; C: Cartago; Ob: Obando; R: Roldanillo; T: Toro;
U: La Union; Vict: La Victoria; Vir: La Virginia; Z: Zarzal. 134 Fig. 6.15: 30-meter resolution DEM based on radar photographs (USGS, 2005) showing (A) the distribution of the calculated palaeostress tensors and (B) the distribution of maximum horizontal σ
(in red) in area A. 134
Fig. 6.16: Stereoplots representing the dip, dip azimuth, and kinematics of fault planes at each site numbered in figures 6.15 and 6.20, as well as the orientation of their calculated paleostress tensors
(Wulff stereograms, lower hemisphere). 135
Fig. 6.17: Fault plane: s: slip fibers; f: crystallization fibers. The white arrow shows the motion of the
missing compartment with respect to that in the picture. 136
Fig. 6.18: Histogram representing the number of tensors from area A (see figure 6.15) belonging to stress regimes versus their respective ellipsoid form parameter Ф=(σ2−σ3)/(σ1−σ3). 136 Table 2: Parameters of the 19 calculated stress tensors, with the name of the site, the orientations of σ1, σ2 and σ3, the corresponding ellipsoid form parameter (Ф) and the stress regime the tensor belongs to. The number of faults used for the calculation appears in the “n” column; Var (°) indicates the average misfit angle after the final calculation. A quality criterion between 1 (good) and 3 (bad)
is given for the result. 137
Fig. 6.19: Fault plane: s: slip fiber. The white arrow shows the undeterminable motion of the missing
compartment with respect to that in the picture. 138
Fig. 6.20: 30-meter resolution DEM based on radar photographs (USGS, 2005) showing (A) distribution of the calculated palaeostress tensors and (B) distribution of maximum horizontal σ (in
red) in area B. 139
Fig. 6.21: Histogram showing the number of tensors from area B (see figure 6.15) belonging to stress regimes versus their respective ellipsoid form parameter Ф=(σ2−σ3)/(σ1−σ3). 140 Fig. 6.22: Histogram showing the number of tensors from the whole studied area (see figure 6.15) belonging to stress regimes versus their respective ellipsoid form parameter Ф=(σ2−σ3)/(σ1−σ3).
141 Fig. 6.23: Quantity-dependent rose-diagram illustrating the orientation of the 513 faults and joints
: 30-meter resolution DEM (USGS, 2005) with location of the sites where conjugate normal faults planes were measured in the Plio-Pleistocene Zarzal Formation and Quindío-Risaralda volcaniclastic Fan. The black dots in the plots (Wulff stereonets, lower hemisphere) are projections of the fault plane poles. The dip of their mean vector indicating the direction of elongation (local σ3) is represented by the black asterisks. The dip and dip azimuth of mean vectors is shown besides each plot. The values given for the sites where only one single fault plane could be measured (numbers 4, 6, 10, 14, 17 and 18; black arrows on map) correspond to the dip and dip azimuth of the fault planes.
The directions of local σ3 are symbolized on the DEM by arrows.
Abbreviations: A: Ansermanuevo; C: Cartago; CF: Cartago Fan; O: Obando; QRF: Quindío-Risaralda Fan; SSB: Serranía de Santa Barbara; T: Toro; Vict: La Victoria; Vir: La Virginia; WC; Western
Cordillera; Z: Zarzal. 143
Fig. 6.25: Examples of synsedimentary extensional features observed in the Zarzal Formation. They are (A) covered by unfaulted beds (a) or (B) characterized by the variable thickness of the faulted
blocks (b). 144
Fig. 6.26: Schematic block diagram showing main faults and Holocene depocenters (yellow) of the studied area.
Abbreviations: AF: Armenia fault; CAF: Cartago Fan; CF: Cajamarca fault; PF: Potrerillos fault;
QNF: Quebradanueva fault; SF: Sevilla fault. 146
CHAPTER VII
Fig. 7.1: Oligocene to present-day, schematic, simplified reconstruction of faults in the studied area.
(A) Representation of the Romeral Fault System before initiation of the Ibague Fault System and other ENE trending right-lateral strike-slip fault systems. (B) Clockwise block rotation induced by EENE dextral strike-slip faulting. The latter induced initialization of NNE elongation, NW transtensional faulting and Plio-Pleistocene deposition (hatched area). (C) Present day geometry showing active, faulting, NNE elongation, shear zone and local subsidence and Holocene deposits (yellow). 154
I
ntRoductIonRalph Neuwerth
1.1. Description of project
After many years of research and numerous publications on the historical seismicity of Colombia, Prof. Armando Espinosa of the Quindío University published a revision of the seismic catalogues (Espinosa, 2004). Aware of the potential risk of a dramatic earthquake in the Armenia region, he had proposed repeatedly the need for a microzonification of the Quindío Department. Unfortunately, his proposal had not gone very far when the terrible Armenia earthquake struck the coffee region of Colombia on 20 January 1999 with a magnitude of 6.2. It killed 1230 people and destroyed more of 5600 homes. The economic impact of this earthquake led to a direct economic loss of approximately US$ 1.8 billion (Cardona, 1999). Following this tragic event and discussions between Prof. Armando Espinosa and Prof. Georges Gorin of the University of Geneva, a scientific collaboration agreement was established between the Quindío and Geneva universities. Six M. Sc. theses (Guarin, 2002;
Suter, 2003; Duque, 2005; Ospina, 2007; García Londoño, 2008; Pahud, 2009) and four Ph.D theses (Guarin, 2008; Suter, 2008; Neuwerth, this work; Duque, ongoing work) have been or are being carried out within the framework of this collaboration.
This research has been supported by the Swiss National Science Foundation (grants nos. 21-67080.01 and 200020-107866) within the framework of a general project entitled: “Tectonics, neotectonics and sedimentation in active fault zone: examples of Plio-Pleistocene deposits in the Northern Andes of Central Colombia”. This investigation aimed at improving the geological knowledge about Plio- Pleistocene sediments in an area covering the Colombian Departments of Quindío, Risaralda and Valle del Cauca (Fig. 1.1), at the northern termination of the interandean Cauca Depression. This zone lies at the collision front of the Chocó-Panamá Block, where the major N-S trending Romeral Fault System (active since Cretaceous times) changes its kinematics from right-lateral in the south to left-lateral in the north (Fig. 1.1).
The studied area is located in Central Western Colombia (Figs. 1.1 and 1.2). It comprises two sedimentary basins separated by a belt of folded, pre-Pliocene continental clastic sediments (the Serranía of Santa Barbara or SSB): the North Cauca Depression to the west and the Quindío-Risaralda Basin to the east (Fig. 1.2). These two basins are filled by subhorizontal Pleistocene sediments. In the North Cauca Basin, this infill consists principally of fluvio-lacustrine deposits (the so-called Zarzal Formation), which interfinger with alluvial fans derived from the Western Cordillera in the west and from the Serranía of Santa Barbara in the east. Moreover, towards the northeast, they interfinger with the volcaniclastic mass-flow deposits which form a vast fan that infills the Quindío-Risaralda Basin and is sourced from the Cerro Bravo-Machin volcanic complex in the Central Cordillera. This area has been studied by the three PhD students involved in the project, i.e., Fernando Guarin (Guarin, 2008; area I in Fig. 1.2), Fiore Suter (Suter, 2008; area II in Fig. 1.2) and Ralph Neuwerth (area III in Fig. 1.2).
1.2. Aims of study
The North Cauca Valley Basin is a 200km long alluvial plain extending from Cali up to La Virginia (Fig. 1.1) at an altitude of 900m. It is subdivided in its northern part in the two sub-basins described
above. These sub-basins are separated by the Serranía of Santa Barbara (SSB), an active pop-up structure forming a topographic barrier. The Oligo-Miocene rocks forming the SSB are folded and are unconformably overlain on both sides by Pliocene to Recent rocks which are subhorizontal and show extensional dislocations (Cardona and Ortiz, 1994; Pardo et al., 1994; Suter et al., 2008a; Suter et al., 2008b).
The North Cauca Valley Basin is under the influence of the N to NNE trending Romeral faults, which, in this area, presents a compressive kinematics (Paris et al., 2000; Suter et al., 2008b).
Fig. 1.1: Geodynamics of NW South America: velocities and direction of motion for the different plates and blocks with respect to South America (after (Suter et al., 2008). Location of figure 1.2.
The aims of this study are twofold: 1) to attempt to understand how such an intramountane basin has been formed; 2) to refine the existing poor stratigraphical and sedimentological knowledge of the Pliocene to Recent sediments.
1.3. Organisation of manuscript
Because this thesis deals with a multidisciplinary approach, it has been subdivided into chapters
Fig. 1.2: 30-meter resolution DEM based on radar photographs (USGS, 2005) showing departmental boundaries and location of the areas studied in the general project(in red: zone one studied by Guarin, 2008;
zone II studied by Suter, 2008; zone III studied in this work).
A: Ansermanuevo; Ar: Armenia; C: Cartago, V: La Virginia; P: Pereira; Z: Zarzal. CC: Central Cordillera;
SSB: Serranía of Santa Barbara; WC: Western Cordillera.
corresponding to the different investigated geological fields.
The second chapter presents a short overview of field work carried out to collect sedimentological and structural data, of fault inversion analysis and morphometry.
The third chapter aims at presenting the high tectonic complexity of the studied area, which is situated in an accommodation zone between three tectonic plates and at the front of the Chocó-Panamá Block indentation. The stratigraphical units cropping out in the studied area are described and related with the geodynamical evolution of northwestern South America. Finally, interrogations and hypothesis about the formation of the intramountane basin studied are exposed.
The fourth chapter focuses on sedimentology and lithostratigraphy. Twenty-two field sections have been described. They comprise data on palaeocurrents, sedimentary structures, bedding, palynological and geochronological analysis. They have permitted the identification of numerous gaps existing at present day and the proposition of a revisited lithostratigraphy of the Plio-Quaternary deposits in the North Cauca Valley. This chapter has been submitted as a manuscript to Geologica Acta.
The fifth chapter has been published in 2006 in Sedimentary Geology (Neuwerth et al., 2006). It describes soft-sediment deformations encountered at large scale and demonstrates the high level of paleosismicity that have affected the deposits in the studied area.
The sixth chapter gets into the tectonic, neotectonic and geomorphological aspects and tries to explain the northern closure of the basin.
References
Cardona, J. F. and Ortiz, M., 1994. Aspectos estratigráficos de las unidades del intervalo Plioceno Holoceno entre Pereira y Cartago. Propuesta de definición para la Formación Pereira. Manizales, Colombia, Universidad de Caldas: 155.
Cardona, O. D., 1999. The earthquake of Armenia, Colombia, January 25, 1999, Special Report, Geohazards International, pp. 9.
Duque, A. L., 2005. Geology of the urban zone of Armenia and its application to land management (Colombia). M. Sc. thesis, Université de Genève, Geneva, Switzerland, 153 p.
Espinosa, A., 2004. Historia sísmica de Colombia (Academia Colombiana de Ciencias Exactas, Físicas y Naturales, Universidad del Quindío), CD-ROM.
García Londoño, L. F., 2008. Etude néotectonique de la Faille Armenia entre les villes de Circasia et Filandia (Quindío - Colombie). Travail de diplôme inédit.
Guarin, F., 2002. Etude du fan fluvio-volcanique du Quindío (Colombie). Geneva, Univ. of Geneva, Switzerland: 92.
Guarin, F., 2008. Etude sédimentologique du cône volcanoclastique du Quindío-Risaralda (Colombie Centrale) et sa relation avec la morphotectonique. Terre et Environnement (Université de Genève), 29, 146 p.
Ospina, L. M., 2007. Morphotectonique des dépôts quaternaires dans la région de Calarcá, Quindío (Colombie centrale). M. Sc. thesis, Université de Genève, Geneva, Switzerland, 96p.
Pahud, O., 2009. Etude sédimentologique et morphotectonique dans le Quaternaire du Valle del Cauca (Colombie). M. Sc. thesis, Université de Genève, Geneva, Switzerland.
Pardo, T. A., Moreno, S. M. and De J. Gómez, C., 1994. Evidencias de actividad neotectonica en la carretera Cartago-Ansermanuevo (Valle del Cauca, Colombia). III Conferencia colombiana de geología ambiental. Armenia, Quindío (Colombia): 181-191.
Suter, F., 2003. Géologie de la région de Playa Azul, partie occidentale distale du fan fluviovolcanique du Quindío (Serranía de Santa Barbara, Quindío et Valle del Cauca, (Colombie), Université de Genève, Suisse: 133.
Suter, F., 2008. Tectono-Sedimentary Study of the Interandean North Cauca Valley Basin, Central Western Colombia. Terre et Environnement (Université de Genève), 78, 145 p.
Suter, F., Neuwerth, R., Gorin, G. E. and Guzman, C., 2008a. Depositional model of (Plio-)Pleistocene sediments in a tectonically active zone of Central Colombia. Geologica Acta 6(2), 1-19.
Suter, F., Sartori, M., Neuwerth, R. and Gorin, G. E., 2008b. Structural imprints at the front of the Chocó-Panamá indenter: field data from the North Cauca Valley Basin, Central Colombia.
Tectonophysics 460, 134-157.
m
ethodsRalph Neuwerth
2.1. Field study
Extensive field work has been the most important component of this research. It corresponds to a period of some eight months over four years. It has been principally dedicated to sedimentological and structural data acquisition. The former encompasses the sedimentary logging of twenty-two field sections, the sampling of sands and silts for mineralogical study, of clays for palynological analysis and ash layers for geochronological dating. Because of the dense tropical vegetation cover, the best outcrops have been encountered near roads and urban constructions.
Structural field work has consisted of fault measurements, i.e., strike and dip of fault planes in soft sediments and strike and dip of fault planes and slickenside striae in consolidated rocks. Fracture strikes were also measured. Because of vegetation cover and strong rock weathering, this field work has been essentially carried out in river beds. Furthermore, because of the high level of insecurity in the Western Cordillera, only the foothills of the latter have been investigated.
Field work was preceded by the extensive interpretation of aerial photographs in order to locate outcrops and surface fault traces and to carry out geomorphological analysis.
2.2. Fault inversion method
This section focuses only on data analysis and quality criteria. A detailed outline of the method, its merits and limitations can be found in Angelier and Mechler (1977) and Angelier (1994). Faults data have been collected to determine palaeostress axis directions using the direct inversion method of Angelier (1990) implemented in the TectonicsFP software (Sperner et al., 1993; Ortner et al., 2002).
The stability and quality of each tensor has been estimated from the following criteria:
(1) coherency test by comparison with the right-dihedra method of Angelier and Mechler (1977);
(2) number of faults used in the inversion: a dataset consisting of less than eight faults would give a low quality result;
(3) average misfit angle: if too many faults have to be removed, the result is considered as bad, (4) the stability of the result with respect to particular faults: when some faults have a strong influence on the result when added or removed from the dataset, the quality criterion would be bad.
Tensors were classified from 1 (excellent) to 3 (low quality).
2.3. Morphometry
Two geomorphic parameters have been used in order to estimate or quantify the neotectonic activity:
the Drainage Basin Analysis and the Mountain-Front Sinuosity. Theoritical considerations can be found in Keller and Pinter (2002). Only equations are presented here in order to understand the
values presented in chapter 5:
The Asymmetry Factor (AF) is defined as
AF = 100(Ar=At)
where Ar is the area of the basin to the right (facing downstream) of the trunk stream, and At is the total area of the drainage basin.
The mountain-front sinuosity (Smf) is defined as
Smf = Lmf/Ls
where Lmf is the length of the mountain front along the foot of the mountain, and Ls is the straight-line length of the mountain front.
References
Angelier, J., 1990. Inversion of field data in fault tectonics to obtain the regional stress - A new rapid direct inversion method by analytical means. Geophys. J. Int. 103, 363-376.
Angelier, J., 1994. Palaeostress analysis of small-scale brittle structures. Chapter 4 in: ‘Continental Deformation’, edited by P. Hancock, Pergamon Press, 421 p. (p. 53-100). In.
Angelier, J. and Mechler, P., 1977. Sur une méthode graphique de recherche des contraintes principales également utilisable en tectonique et en séismologie: la méthode des dièdres droits. Bull. Soc. Géol.
France 7(6).
Keller, A. and Pinter, N., 2002. Active Tectonics, Earthquakes, Uplift, and landscape. Prentice Hall, New Jersey, United States. pp. 362
Ortner, H., Reiter, F. and Acs, P., 2002. Easy handling of tectonic data; the programs TectonicVB for Mac and TectonicsFP for Windows. Shareware and freeware in the geosciences; II, A special issue in honour of John Butler. Pergamon, New York-Oxford-Toronto, International.
Sperner, B., Ott, R. and Ratschbacher, L., 1993. Fault-striae analysis: a turbo pascal program package for graphical presentation and reduced stress-tensor calculation. Computers Geosciences 19, 1361- 1388.
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3.1. Location of study area
The study area covers parts of three Colombian departments: Quindío (city of Armenia), Risaralda (city of Pereira) and Valle del Cauca (cities of Cartago and Zarzal). It is located between the Central and Western Cordilleras at a latitude of 4.4 – 4.8°N and a longitude of 75.8 – 76.1°W and (Figs. 3.1 and 3.2).
The North Cauca Valley Basin is subdivided in two sub-basins by a fold and thrust belt (called the Serranía de Santa Barbara or SSB): the Cauca Depression to the west and the Quindío-Risaralda Basin to the east (Fig. 3.2). These two basins are infilled by subhorizontal Pleistocene sediments. The latter consist principally of fluvio-lacustrine deposits in the Cauca Depression (the so-called Zarzal Formation), which interfinger with the volcaniclastic mass-flow deposits forming the Quindío- Risaralda Fan. The latter is sourced from the Cerro Bravo-Machin volcanic complex in the Central Cordillera (Fig. 3.2).
The intramountane North Cauca Valley Basin studied here is located immediately west of the Romeral Fault System (RFS), a palaeosuture where Palaeozoic and Cretaceous continental rocks in the east
Fig. 3.1: (A) Geodynamics of NW South America: velocities and direction of motion for the different plates and blocks with respect to South America (after (Suter et al., 2008). Location of study area.
Abbreviations: B: Bogotá; C: Cali; CC: Central Cordillera; EC: Eastern Cordillera; WC: Western Cordillera;
EFFS: Eastern Frontal Fault System; IBF: Ibagué Fault; GF: Garrapatas Fault; RFS: Romeral Fault System.
(B) Digital elevation model (DEM, (USGS, 2005)) of western central Colombia showing the course of the Cauca River. The study area is located upstream of La Virginia town, at the northern termination of the Cauca Valley Basin (after (Suter et al., 2008).
are adjacent to Cretaceous accreted oceanic terranes in the west (Fig 3.1 and 3.3).
3.2. Geodynamic evolution of Colombia from Jurassic to recent times
The Western Colombia geological history started with an extensive phase in the Jurassic, followed by a long period of tectonic activity associated with the movement of three distinct tectonic plates: the South American, the Pacific and the Caribbean Plates. The studied area having been affected mainly by Cenozoic tectonics, the emphasis in this description has been put on the Andean Orogeny.
Triassic and Jurassic units exposed in the Colombian Andes encompass a complex association of calcareous, siliciclastic, volcaniclastic and plutonic rocks (Bayona et al., 2006). Two tectonic settings have been proposed for these Mesozoic rocks:
(1) a backarc extension occurring behind a subduction-related magmatic arc (McCourt et al., 1984a;
Pindell and Erikson, 1993; Pindell and Tabbutt, 1995; Toussaint, 1995b; a; Meschede and Frisch, 1998; Pindell and Kennan, 2001; Moreno-Sanchez and Pardo-Trujillo, 2003)
(2) an intracontinental rifting regime associated with the break-up of Pangea (Pindell and Dewey John, 1982; Ross and Scotese, 1988; Cediel et al., 2003).
Three alternative hypotheses have been proposed for the processes that might have been active during the Cretaceous (Sarmiento-Rojas et al., 2006):
Fig. 3.2: 30-meter resolution DEM based on radar photographs (USGS, 2005) showing Plio- Pleistocene deposits and faults in the studied area.
Abbreviations: A: Ansermanuevo;
Ar: Armenia; C: Cartago, V: La Virginia; P: Pereira; Z: Zarzal. CC:
Central Cordillera; SSB: Serranía of Santa Barbara; WC: Western Cordillera. AB: Aguas Bonitas Fault; Asmn: Ansermanuevo Fault;
C-A: Cauca Almaguer Fault, C-P:
Cauca Patía Fault; Csta: Consota Fault; Mont: Montenegro Fault;
Nav: Navarco Fault; Otún: Otún Fault; Plst: Palestina Fault;
Qnueva: Quebradanueva Fault;
Rob: El Roble Fault; RV: Río Verde Fault; Sal: Salento Fault; San J:
San Jeronimo Fault; Sev: Sevilla Fault; SR: Santa Rosa Fault; Tor:
Toro Fault.
1. Backarc extension (McCourt et al., 1984a; Fabre, 1987; Toussaint and Restrepo, 1989; Cooper et al., 1995; Meschede and Frisch, 1998),
2. Passive margin (Pindell and Erikson, 1993; Pindell and Tabbutt, 1995),
3. Intracontinental rifting related to the opening of the Caribbean (Cediel et al., 2003).
These hypotheses will be better developed in the next section, where the terranes present in the studied area are described.
The Andean Orogeny started with the convergence of the Pacific Plate in the western part of Colombia.
It is marked by four main events:
(1) Accretion and/or obduction along the western margin of Colombia during the Cretaceous.
(2) Relative divergence to convergence between the Americas during the Paleogene to Early Eocene.
(3) Break-up of the Farallon Plate into the Nazca and Coco plates during the Oligo-Miocene.
(4) Collision of the Chocó-Panamá-Block (CPB) into the NW corner of South America during the Miocene.
(1) The emplacement of the terranes situated west of the RFS is still a matter of debate (Fig. 3.4) .For some authors they were accreted (McCourt et al., 1984a; Restrepo and Toussaint, 1988; Restrepo- Pace, 1992; Taboada et al., 1998; Ramos and Aleman, 2000; Taboada et al., 2000; Moreno-Sanchez and Pardo-Trujillo, 2003; Chicangana, 2005b; Nivia et al., 2006), whereas others think they were obducted (Bourgois et al., 1987; Kellogg et al., 1995; Kerr et al., 1997; Kerr et al., 1998; Cediel et al., 2003).
The timing of accretion/obduction is also still debated. Most authors have recognized two major accretionary/obducting episodes in the Cretaceous on the western side of the Central Cordillera
Fig. 3.3: Simplified cross-section across the Cauca depression and the Quindío-Risaralda Basin, see figure 3.2 for location. After (Suter et al., in review).
