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marinas del Neógeno en la bahía de Tumaco, Nariño
Jorge GÓMEZ and Daniela MATEUS–ZABALA
Table of Contents
Only the abstracts and keywords of the manuscripts accepted up to now have been included.
The Cretaceous/Paleogene Boundary Deposits on Gorgonilla Island
By Hermann Darío BERMÚDEZ, Ignacio ARENILLAS, José Antonio ARZ, Vivi VAJDA, Paul R. RENNE, Vicente GILABERT and José Vicente RODRÍGUEZ
Manuscript accepted October 29, 2018
A ~20 mm thick spherule bed representing Chicxulub impact ejecta deposits and marking the Cretaceous/Paleogene (K/Pg) boundary was recently discovered on Gorgonilla Island (Gorgona National Natural Park, Pacific of Colombia). This discovery represents the first confirmed record of the K/Pg event in Colombia, South America and the eastern Pacific Ocean. The deposit consists of extraordinarily well–preserved glass spherules (microtektites and microkrystites) reaching 1.1 mm in diameter. Importantly, the Gorgonilla spherule bed is unique relative to other K/Pg boundary sites in that up to 90% of the spherules are intact and not devitrified, and the bed is virtually devoid of lithic fragments and microfossils. The spherules were deposited in a deep marine environment, possibly below the calcite compensation depth. The preservation, normal size–gradation, presence of fine textures within the spherules, and absence of bioturbation or traction transport indicate that the Gorgonilla spherules settled within a water column with minimal disturbance. Thus, the spherule bed may represent one of the first parautochthonous primary deposits of the Chicxulub impact known to date. 40Ar/39Ar dating and micropaleontological analysis reveal that the Gorgonilla spherule bed resulted from the Chicxulub impact. Intense soft–sediment deformation and bed disruption in Maastrichtian sediments of the Gorgonilla Island K/Pg section provide evidence for seismic activity triggered by the Chicxulub bolide impact, 66 million years ago. It is also notable that the basal deposits of the Danian in the Colombian locality present the first evidence of a recovery vegetation, characterized by ferns from a tropical habitat, shortly following the end–Cretaceous event.
K/Pg boundary, Chicxulub, microtektites, seismites, Gorgonilla Island, Colombia.
Formation and Evolution of the Lower Magdalena Valley Basin and San Jacinto Fold Belt of Northwestern Colombia: Insights from Upper Cretaceous to Recent Tectono–Stratigraphy
By Josué Alejandro MORA–BOHÓRQUEZ , Onno ONCKEN, Eline LE BRETON, Mauricio IBANEZ–MEJIA , Gabriel VELOZA, Andrés MORA, Vickye VÉLEZ and Mario DE FREITAS
Manuscript accepted October 29, 2018
Using a regional geological and geophysical dataset, we reconstructed the stratigraphic evolution of the Lower Magdalena Valley Basin and San Jacinto fold belt of northwestern Colombia. Detailed interpretations of reflection seismic data and new geochronology analyses reveal that the basement of the Lower Magdalena Basin is the northward continuation of the basement terranes of the northern Central Cordillera and consists of Permian – Triassic metasedimentary rocks intruded by Upper Cretaceous granitoids. Structural analyses suggest that the NE–SW strike of faults in basement rocks underlying the northeastern Lower Magdalena is inherited from a Jurassic rifting event, while the ESE–WNW—striking faults in the western part originated from a Late Cretaceous to Eocene strike–slip and extensional episode. The Upper Cretaceous to lower Eocene sedimentary rocks preserved in the present–day San Jacinto fold belt were deposited in a submarine, forearc basin formed during the coeval oblique convergence between the Caribbean and South American Plates. A lower to middle Eocene angular unconformity at the top of the upper Paleocene to lower Eocene San Cayetano sequence, the termination of the activity of the Romeral Fault System, and the cessation of arc magmatism are all interpreted to indicate the onset of low–angle orthogonal subduction of the Caribbean Plateau beneath South America between 56 and 43 Ma. Flat subduction of the plateau has continued to the present and would be the main cause of amagmatic post–Eocene deposition and formation of the Lower Magdalena Valley Forearc Basin. Extensional reactivation of inherited, pre–Oligocene basement faults was crucial for the tectonic segmentation of the basin and the formation of its two depocenters (Plato and San Jorge). Late Oligocene to early Miocene fault–controlled subsidence allowed initial infill of the Lower Magdalena, while uplift of Andean terranes made possible the connection of the Lower and Middle Magdalena Valleys, and the formation of the largest Colombian drainage system (Magdalena River system). This drainage system started delivering enormous amounts of sediments in middle Miocene times, as fault–controlled subsidence was gradually replaced by sedimentary loading. Such dramatic increase in sedimentation and the huge volume of sediment being delivered to the trench caused the formation of forearc highs in San Jacinto and of an accretionary prism farther to the west. Our results highlight the fundamental role of plate kinematics, inherited basement structure and sediment flux on the evolution of forearc basins such as the Lower Magdalena and San Jacinto.
Keywords: forearc basin, basement, flat–slab subduction, tectono–stratigraphy, Lower Magdalena, San Jacinto fold belt, Caribbean, subsidence, sedimentation.
Construction of the Eastern Cordillera of Colombia: Insights from the Sedimentary Record
By Brian K. HORTON, Mauricio PARRA and Andrés MORA
Manuscript accepted October 29, 2018
A continuous, long–lived sedimentary record contains important evidence bearing on the geologic evolution of the Eastern Cordillera in the northern Andes of Colombia. Today, this largely isolated NNE–trending mountain range forms a ~1–3 km–high topographic barrier separating the Magdalena Valley hinterland basin from the Llanos Foreland Basin. A Mesozoic – Cenozoic history of marine and non–marine sedimentation affected the Eastern Cordillera and flanking Magdalena and Llanos provinces during contrasting tectonic regimes. (i) Jurassic to earliest Cretaceous extension led to the development and linkage of extensional sub–basins (commonly half graben features governed by normal faults) in selected regions. (ii) A subsequent phase of postextensional thermal subsidence generated a thermal sag basin across a broader region. (iii) In latest Cretaceous to Paleocene time, initial crustal shortening in the Central Cordillera created a regional flexural basin that was successively broken by the Paleocene – Oligocene emergence of thrust/reverse–fault related uplifts within the Eastern Cordillera and the partitioning of the original regional basin into the Magdalena hinterland basin and Llanos Foreland Basin. (iv) Major Neogene uplift and establishment of an effective topographic barrier occurred as continued shortening became focused along the bivergent eastern and western flanks of the fold–thrust belt comprising the Eastern Cordillera. Shortening commonly involved contractional reactivation of preexisting normal faults and inversion of pre–foreland basin elements. This geologic history is largely expressed in the clastic sedimentary archives of the Eastern Cordillera, Magdalena Valley Basin, and Llanos Basin. Growth strata and cross–cutting relationships among fold–thrust structures and basin fill provide essential timing constraints for individual structures, particularly when integrated with thermochronological data. Regional stratigraphic correlations and sediment accumulation histories help to identify shared and divergent stratigraphic histories during progressive basin compartmentalization. Substantial shifts in sediment provenance, identified through U–Pb geochronology, demonstrate the changes in sediment source regions and paleodrainage patterns during several changes in tectonic conditions.
Keywords: Eastern Cordillera, fold–thrust belt, foreland basin, provenance, U–Pb geochronology.
Late Cretaceous to Cenozoic Uplift of the Northern Andes: Paleogeographic Implications
By Andrés MORA, Diego VILLAGÓMEZ, Mauricio PARRA, Víctor M. CABALLERO, Richard SPIKINGS, Brian K. HORTON, Josué Alejandro MORA–BOHÓRQUEZ, Richard A. KETCHAM and Juan Pablo ARIAS–MARTÍNEZ
The Eastern Foothills of Colombia
By Andrés MORA, Eliseo TESÓN, Jaime MARTÍNEZ, Mauricio PARRA, Álvaro LASSO, Brian K. HORTON, Richard A. KETCHAM, Antonio VELÁSQUEZ and Juan Pablo ARIAS–MARTÍNEZ
Structural Styles of the Eastern Cordillera of Colombia
By Andreas KAMMER, Alejandro PIRAQUIVE, Cristhian GÓMEZ, Andrés MORA and Antonio VELÁSQUEZ
Manuscript accepted April 15, 2019
The Eastern Cordillera of Colombia is bracketed between the moderately west–dipping flank of the Central Cordillera on its western side and the little disturbed to gently bent Guiana Shield on its eastern side. Unlike other Andean foreland–oriented belts, it is completely disconnected from the main Andean trunk system. Transverse shortening of 4 mm/y records a considerable displacement transfer to the upper plate; this is twice the long–term rate of 2.2 mm/y, which is the average for a shortening of 65 km over a period of 30 Ma and suggests an increased recent shortening phase. We differentiate three structural domains. The southern domain records significant shortening by penetrative strain at lower structural levels and folding at higher structural levels, which supports the idea of partitioning into pure–shear deformation within the pre–Cretaceous basement and into buckling in the Upper Cretaceous to Paleogene units. Similar constellations of a relatively weak crustal welt enclosed between domains with backstop characteristics have been examined in analogue and numerical experiments (“vise model”). A northern intermediate domain is characterized by large–scale, basement–cored antiforms, whose formation may be ascribed to the partial reactivation of Late Triassic normal faults. The northernmost domain comprises the Cocuy Syntaxis, which constitutes an antiformal lobe with significant topographic relief. It is affected by secondary folds with a down–slope vergence. These changes in structural style record increased support by the subducting slab, according to the spatial coincidence of the outer slab hinge and the highest topographic relief within this northern Andean flat slab segment.
To examine a possible cause for a rheological break between deformable cordilleran crust sandwiched between relatively rigid and strong surrounding basement blocks, we review the Cretaceous back–arc setting. Tectonic subsidence and sedimentation patterns suggest its division into a forebulge and flanking basins that may be ascribed to the framework of an impinging mantle plume. Temporal constraints further suggest that forebulge evolution may have been triggered by an initial foundering of the slab at the onset of a Cretaceous subduction cycle. In such a small–scale convection system, downwelling mantle flow between the back–arc region and the stable shield may maintain a relatively well–defined rheological limit over long periods. This situation complies with the model of an edge–driven convective flow.
Rheological contrasts between the back–arc basin and the shield persisted into the Cenozoic and contributed to a protracted evolution of the Andean cordilleran mountain fronts. The eastern mountain front accumulated structural relief of more than 10 000 m during an initial Oligocene to late Miocene shortening phase. Fold growth incited by the buttressing of the strong foreland block of the shield can be tested by the tri–shear model, in which propagation of faulting is halted, and displacement is consumed by fold amplification. During a Pliocene stress reorganization, this Miocene mountain front was breached by a shallowly dipping thrust, which gave rise to a more foreland–oriented deformation front. During this outward–stepped faulting, proximal foreland sequences became involved in a wedge–top position and were exhumed at the thrust tip along emergent ramps. These second–cycle erosion products were widely dispersed into the Llanos Basin and were incorporated into modern fluvial terraces.
Keywords: back–arc basin, fault reactivation, gravitational collapse, Eastern Cordillera of Colombia.
Cenozoic Evolution of the Sierra Nevada de Santa Marta, Colombia
By Mauricio PARRA, Sebastián ECHEVERRI, Ana María PATIÑO, Juan Carlos RAMÍREZ, Andrés MORA, Edward R. SOBEL, Ariel ALMENDRAL and Andrés PARDO
Cenozoic Geologic Evolution of the Southern Tumaco Forearc Basin (SW Colombian Pacific)
By Andrés PARDO–TRUJILLO, Sebastián ECHEVERRI, Carlos BORRERO, Alejandro ARENAS, Felipe VALLEJO, Raúl TREJOS, Ángelo PLATA, José Abel FLORES, Agustín CARDONA, Sergio RESTREPO, Ángel BARBOSA, Hugo MURCIA, Carlos GIRALDO, Sergio CELIS, Jairo A. OSORIO and Sergio A. LÓPEZ
Cenozoic Marine Carbonate Systems of Colombia
By Juan Carlos SILVA–TAMAYO, Daniel RINCÓN–MARTÍNEZ, Lina M. BARRIOS, Juan C. TORRES LASSOand Chixel OSORIO–ARANGO
From Facies Analysis, Stratigraphic Surfaces and Depositional Sequences to Stratigraphic Traps in the Eocene – Oligocene Record of the Southern Llanos and Northern Magdalena Basin
By Víctor M. CABALLERO, Guillermo RODRÍGUEZ, Julián F. NARANJO, Andrés MORA and Felipe DE LA PARRA
Oligocene – Miocene Coal–Bearing Successions of the Amagá Formation, Antioquia, Colombia: Sedimentary Environments, Stratigraphy and Tectonic Implications
By Juan Carlos SILVA–TAMAYO, Mario LARA and Ana Milena SALAZAR–FRANCO
Manuscript accepted October 29, 2018
The Amagá Formation is an upper Oligocene – middle Miocene tropical siliciclastic succession that was deposited along several semi–isolated intramontane (pull–apart) sedimentary basins in the northernmost part of the Colombian Andes. Despite the fact that these coal–bearing sedimentary records constitute one of the most complete upper Oligocene – middle Miocene continental successions deposited along the hinterland of the northern Andes convergent margin, limited geologic information is available in the literature about their sedimentology and stratigraphy. In this contribution, we report new detailed stratigraphic information from the Amagá Formation in the Santa Fe de Antioquia–San Jerónimo Basin and integrate it with previously published sedimentologic, sequence stratigraphic, biostratigraphic, geochronologic and thermochronologic information about the sedimentary successions in this formation, which crop out along the Amagá–Venecia, Fredonia–La Pintada–Valparaíso and Santa Fe de Antioquia–San Jerónimo Basins. This integrative approach allows us to assess the mechanisms controlling the sedimentologic evolution of tropical hinterland/intramontane successions along Andean–type convergent margins.
Our approach allows us to subdivide the Amagá Formation into two members, i.e., the lower and upper members. Regionally, the lower member records a change in sedimentary environments from a braided river system to a meandering river system. This change occurred during a period of increasing sediment accommodation space, which coincides with the late Oligocene (28–25 Ma) break–up of the Farallón Plate into the Nazca and Cocos Plates. The upper member of the Amagá Formation displays a facies association typical of braided river systems, and it was deposited during a period of decreasing sediment accommodation space. This decrease in sediment accommodation space likely resulted from a major regional uplift event associated with the early Miocene change from oblique to orthogonal convergence between the Nazca and South American Plates and the early Miocene (23–21 Ma) docking of the Panamá–Chocó Block to northern South America.
Miocene Tholeiitic and Calk–alkaline Magmatism from the Northern Colombian Andes–Implications for Magma Petrogenesis in the Northern Volcanic Zone
By Marion WEBER, José Fernando DUQUE, Susana HOYOS, Andrés L. CÁRDENAS–ROZO, Jorge GÓMEZ TAPIAS and Rob WILSON
The Morales Formation (New Unit): Record of Fluvial–Lacustrine Environments and the Beginning of the Miocene Explosive Volcanism in the Patía Sub–basin (SW of Colombia)
By Andrés F. GALLEGO–RÍOS, Andrés PARDO–TRUJILLO and Guillermo A. LÓPEZ–PLAZAS
New Contributions to the Knowledge of the Chocó–Panamá Arc in Colombia, Including a New Segment South of Colombia
By Gilberto ZAPATA–GARCÍA and Gabriel RODRÍGUEZ–GARCÍA
Isthmian Bedrock Geology: Tilted, Bent, and Broken
By Camilo MONTES and Natalia HOYOS
October 29, 2018
A review of the bedrock geology of the Isthmus of Panama highlights tectonic deformation—tilting, bending and breaking—, as major controlling factors in the sites and modes of Cenozoic sedimentation. Deformation in Paleocene – early Eocene times folded and faulted a basement complex composed of plateau basalts, pelagic and hemipelagic sequences, and an overprinted magmatic arc. This deformation episode brought parts of the Isthmus from lower bathyal depths to subaerial exposure, bringing about basement cooling and eroding the plutonic bodies that make up the roots of a Campanian to Eocene arc. A clastic–carbonate, less deformed, upper Eocene and younger sedimentary sequence onlaps non–conformably the basement complex. Southward tilting of the Isthmus controlled the accumulation of the clastic wedge, recording first shallow marine depositional environments, followed by deepening, and then by shoaling. This sequence resulted from basin tilting that simultaneously raised the San Blas range, eroding it, while deepening the axis of the Chucunaque Basin. Bending and breaking of the Isthmus took place as it was being detached from the trailing edge of the Caribbean Plate, and marked the start of left–lateral offset of the Isthmus in late Eocene times.
Keywords: Panama, isthmus, deformation.
Zircon U–Pb and Fission–Track Dating Applied to Resolving Sediment Provenance in Modern Rivers Draining the Eastern and Central Cordilleras, Colombia
By Cindy Lizeth URUEÑA SUÁREZ, Mary Luz PEÑA URUEÑA, Jimmy Alejandro MUÑOZ ROCHA, Lorena del Pilar RAYO ROCHA, Nicolás VILLAMIZAR ESCALANTE, Sergio AMAYA FERREIRA, Mauricio IBANEZ–MEJIA and Matthias BERNET
October 29, 2018
Determining the crystallization and cooling ages of detrital zircon from ancient sedimentary rocks or modern river sediments is a powerful method for tracing the sediment provenance and exhumation of orogenic mountain belts. Here, we present a study of the U–Pb and fission–track dating of detrital zircons from: (i) the sedimentary cover units of the Eastern Cordillera between Bogotá and Villavicencio and (ii) the modern river sediments of the Guatiquia and Guayuriba Rivers, which drain the eastern flank of the Eastern Cordillera, and those of the Magdalena River at Girardot, which drains the western flank of the Eastern Cordillera and the eastern part of the Central Cordillera. We use our data to highlight the advantages and limitations of using zircon U–Pb and fission–track dating in provenance studies, including the identification of original source areas, sediment recycling and the difficulty of detecting amagmatic orogens in the detrital zircon record. The data obtained in this study allow us to better understand the association between the exhumation of sources and their detrital zircon signatures in the modern rivers that drain part of the Eastern Cordillera.
Different Levels of Exhumation across the Bucaramanga Fault in the Cepitá Area of the South–Western Santander Massif, Colombia: Implications for the Tectonic Evolution of the Northern Andes in North–Western South America
By Sergio AMAYA FERREIRA, Carlos A. ZULUAGA and Matthias BERNET
Apatite and zircon fission track data from crystalline rocks collected along an east–to–west elevational profile across the Bucaramanga strike–slip fault in the Cepitá area and thermal history modeling show the four–stage thermal history of the south–western Santander Massif of the northern Andes in Colombia. A 60 my phase of burial heating from the Late Jurassic to the Late Cretaceous was followed by three cooling phases beginning in approximately 65–60 Ma, which were related to regional tectonic events. The Late Cretaceous – early Paleocene accretion of an island arc and interactions of the Caribbean Plate with the north–western South America Plate first triggered the surface uplift and erosional exhumation of the Santander Massif. During the late Oligocene – early Miocene, the collision of the Panamá–Chocó Block with north–western South America caused an acceleration in the cooling and exhumation of the Santander Massif and differential surface uplift to the east and west of the Bucaramanga Fault in the Cepitá area. The present–day topography of the Santander Massif probably formed at this time. Locally recorded late Miocene cooling may be related to movement on the secondary fault pattern in the study area or minor magmatic activity.