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Stratigraphy of the Ordovician La Cristalina Formation, Puerto Berrío (Colombia)

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Stratigraphy of the Ordovician La Cristalina Formation, Puerto Berrío (Colombia) ____________________________ Director Doc. Rer. Nat., P.Doc. Pedro Calixto Patarroyo Gama ____________________________ Codirector Ph.D. José María Jaramillo Mejía II Stratigraphy of the Ordovician La Cristalina Formation, Puerto Berrío (Colombia) Stratigraphy of the Ordovician La Cristalina Formation, Puerto Berrío (Colombia) María Fernanda Almanza Meléndez Geologist, Universidad Nacional de Colombia Sede Bogotá Universidad Nacional de Colombia Facultad de Ciencias, Departamento de Geociencias Bogotá D. C., Colombia 2017 Stratigraphy of the Ordovician La Cristalina Formation, Puerto Berrío (Colombia) María Fernanda Almanza Meléndez Geologist, Universidad Nacional de Colombia-Sede Bogotá Thesis presented as partial requisite to get the title of: Mágister en Ciencias-Geología Director: Doc. Rer. Nat., P.Doc. Pedro Calixto Patarroyo Gama Co-Director: Ph.D. José María Jaramillo Mejía Research field: Stratigraphy Universidad Nacional de Colombia Facultad de Ciencias, Departamento de Geociencias Bogotá D. C., Colombia 2017 To those who enjoy each piece of the cake, who love researching and never forget to be a good human being. To my beloved father, mother and brother Acknowledgments The main reason to do this master theses was the curiosity I had for some poorly-known old rocks. So, I feel deeply grateful with those Ordovician complicated rocks for allowing me discover something new. I am grateful with my advisor Pedro Patarroyo for accompanings me during field work, and with my co-advisor professor José María Jaramillo, firstly, for the enlightining discussions during the best researching-breakfasts, secondly for guiding me to unlock dreams and build this master theses and its related peer-reviewed publications, lastly for introducing me to such metamorphic rocks and to encourage me to study them. I am also grateful with Francisco Javier Muñoz, Master candidate at Genève University, for their valuable assistance during field work. Thanks to my friends, fellow geologists, professors and my family for listening to my changing geological models. Thanks to the Academic Vice-Rectory of the Universidad Nacional de Colombia (UN) for the Honours Degree Scholarship, the Welfare Science Faculty of the UN for supportting part of the academic exchange to Johannes Gutenberg Universität, the Geosciences Department of the UN for supportting geochemical analyses, the Spanish Mineco (CGL 2012- 39471) of the CSIC (Spain) for financing a research trip, and GmasLab (Bogotá) for supportting laboratory measurements. Finally, many thanks in advance to those who will be next to me not only in the process of improving the geological model here proposed, but also for continuing publishing the information relevant to La Cristalina Formation. As Philippe ROSSI (President of the Commission for the Geological Map of the World) reflected about maps but here applied to the geological model of La Cristalina Formation: “(…) never achieved just abandoned” Paul Valery Resumen y Abstract IX Abstract La Cristalina Formation is a low-grade polimetamorphic sedimentary unit that crops out in the eastern flank of the Central Cordillera, mainly to the south of La Cristalina Railway Station from which its the name was coined, and corresponds to the northwesternmost Ordovician sedimentary unit of Colombia. La Cristalina has not been defined according to the international procedure, despite “La Cristalina” term has been used for more than 87 years, when was published the first Ordovician sedimentary rocks of Colombia. Here 109 samples were handed, there were made 6 field trips, 8 creeks-sections, 5 cross-sections, 4 general composed stratigraphic columns, photo-geology, 64 thin sections, 39 geochemical and 2 geochronological analyses in order to correctly define the unit, following the international procedure of the International Commission on Stratigraphy. The unit was studied from the stratigraphic point of view, but as during the research fossils were found and igneous rocks analized, special studies were carried out. La Cristalina Formation is a very useful stratigraphic unit if considering the paleography of Gondwana and the tectonic location and its deformation meaning for the understanding of the tectonic processes that have occurred since Ordovician times. Here is suggested to continue using the name “La Cristalina” as a lithostratigraphic unit with a “Formation” rank. La Cristalina is defined here as all the strata concordant with Ordovician graptolitic metamudstones, composed of at least 4 facies and facies associations: metamudstones, siliciclastic intercalations, metamicrites and calcareous intercalations, those suggest an off shore and shoreface epicontinental marine sequence. Fossils occurrences reported here correspond to an assemblage of graptolites determined as Didymograptus cf. murchisoni (Beck), Pseudamplexograptus latus (Bulman) and Glossograptus hincksii (Hopkinson), together with phyllocarids and the first occurrences of Colombian foraminifera identified as Astrorhiza? sp. of international interest. La Cristalina overlies, with a faulted contact and an unconformity some Precambrian paragneisses, and underlies the Middle Jurassic rhyolites and andesites with a fault or an unconformity; besides with an unconformity underlies some Lower Cretaceous marine rocks (Fuquen et al., 2009) and Cenozoic alluvial deposits. Importantly, La Cristalina has an overspread low grade metamorphism that reached biotite isograde. It was intruded by 3 different igneous rocks: granodioritc to dioritic rocks (likely, related with the Middle to Upper Jurassic Segovia Batholith), rhyodacitic porphyries and granitoids with s-type affinities. These igneous rocks allow constraining the relative age of the metamorphism of La X Stratigraphy of the Ordovician La Cristalina Formation, Puerto Berrío (Colombia) Cristalina as pre-Jurassic and are the responsible of the La Cirstalina contact metamorphism. Structural complications and lacking of fossils makes complicated to unequivocally identify the sequence and calculate the total thickness. Lastly, metamudstones of La Cristalina can be correlated with the mudstones of El Hígado Formation. According to all the above, the Chapter 1 of this theses corresponds to the proposal to formally define the unit. Contenido XI Resumen La Formación La Cristalina es una unidad metasedimentaria polimetamórfica de bajo grado, que aflora en el flanco oriental de la cordillera Central, principalmente al sur de la Estación La Cristalina del Ferrocarril de Antioquia del cual proviene su nombre, además corresponde a la unidad ordovícica sedimentaria más noroccidental de Colombia. La Cristalina no había sido definida formalmente de acuerdo al procedimiento internacional recomendado, a pesar de que el término “La Cristalina” ha sido usado por más de 87 años, cuando fueron publicadas las primeras rocas ordovícicas de Colombia. Para este estudio se colectaron 109 muestras de mano y se hicieron 6 salidas de campo, 8 secciones por quebrada, 5 cortes geológicos, 4 columnas estratigráficas generalizadas, 64 secciones delgadas, 39 medidas geoquímicas y 2 geocronológicas. Lo anterior con el objetivo de definir formalmente la unidad estratigráfica, de acuerdo al procedimiento internacional recomendado por la Comisión Internacional Estratigráfica. A pesar de que el principal objetivo fue estudiar la unidad desde el punto de vista estratigráfico, durante el trabajo de investigación fueron encontrados fósiles y se analizaron rocas ígneas, por lo que se hicieron estudios adicionales. La Formación La Cristalina es una unidad estratigráfica muy útil si se consideran las reconstrucciones paleogeográficas de Gondwana y el significado que tiene su posición tectónica y su deformación en el entendimiento de los procesos tectónicos que han ocurrido desde el Ordovícico en la esquina noroccidental de Suramérica. Aquí se propone seguir usando el témino “La Cristalina” como una unidad litoestratigráfica con un rango de “Formación”. La Cristalina se define como todos los estratos concordantes con metalodolitas graptolíticas, que incluyen al menos 4 facies y asociaciones de facies: metalodolitas, intercalaciones siliciclásticas, metamicritas e intercalaciones calcáreas. Estas facies representan una secuencia epicontinental marina de costa afuera y de frente de playa. Las ocurrencias de fósiles reportadas aquí corresponden a una asociación de graptolitos determinados como Didymograptus cf. murchisoni (Beck), Pseudamplexograptus latus (Bulman) y Glossograptus hincksii (Hopkinson) con filocáridos, además de las primeras ocurrencias de foraminíferos en Colombia, Astrorhiza? sp., de interés internacional. La Cristalina suprayace con un contacto fallado e inconforme a unos paraneises precámbricos, e infrayace a riolitas y andesitas del Jurásico Medio con posiblemente un contacto fallado o una inconformidad, además infrayace con un contacto inconforme a unas rocas marinas del Cretácico inferior (Fuquen et al., 2009) y a depósitos aluviales del Cenozoico. De XII Stratigraphy of the Ordovician La Cristalina Formation, Puerto Berrío (Colombia) forma escencial, La Cristalina tiene metamorfismo de bajo grado en toda la secuencia que incluso alcanza la isógrada de la biotita. La unidad fue intruída por al menos 3 unidades ígneas: rocas granodioriticas a dioriticas (probablemente, relacionadas con el Batolito de Segovia del Jurásico Medio a Superior), pórfidos riodacíticos de edad desconocida y granitos tipo-S del Paleoceno, estas rocas ígneas permiten inferir que el metamorfismo de La Cristalina
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