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Über dieses Buch

This book provides a comprehensive overview of the geological evolution of the Northern Andes and contiguous shield areas, with a focus upon Colombia. Updated geological interpretations are supported by modern lithogeochemical, seismic, gravity and magnetic data and radiogenic isotope and radiometric age determinations. The composite data permits a detailed interpretation of the tectono-magmatic history of the Northern Andean Block, including the Andes of Colombia, northern Ecuador, western Venezuela and eastern Panamá.

Tectonic reconstructions based upon characterization of more than thirty litho-tectonic and morpho-structural units, terrane assemblages and tectonic realms, and their bounding suture and fault systems, highlight the intimate and complementary Mesozoic-Cenozoic history of the Northern Andean Block and the Pacific and Caribbean Plates.

The complex nature of Northern Andean assembly contrasts with ‘‘classical’’ Central Andean ‘‘Cordilleran-type’’ orogenic models. Differences render the application of typical Cordilleran-type models inappropriate for the Colombian Andes.

The importance of underlying Proterozoic through mid-Mesozoic elements, in the development of Meso-Cenozoic Northern Andean orogeny-phase tectonic configurations is analyzed in the light of spatial-temporal studies and reconstructions related to basin formation, sedimentation, deformation, uplift mechanisms, structural style and magmatic evolution. The pre-Andean architecture of north western South America has played a pre-determinative role in the development of the Northern Andean orogenic system.

16 contributions analyze key stratigraphic, structural, metamorphic, magmatic and tectonic questions, and provide solutions as far as the most recent published field-based studies permit. The volume provides geological interpretations and tectonic models which contrast with repetitive theoretical proposals frequently found in the available literature.



Regional Overview


Chapter 1. Phanerozoic Orogens of Northwestern South America: Cordilleran-Type Orogens. Taphrogenic Tectonics. The Maracaibo Orogenic Float. The Chocó-Panamá Indenter

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Fabio Cediel

Chapter 2. Proterozoic Basement, Paleozoic Tectonics of NW South America, and Implications for Paleocontinental Reconstruction of the Americas

This paper summarizes geological data from the basement massifs of the northern Andes, which constrains their evolution since Late Proterozoic time. Regional associations, age, and tracer isotopic data suggest that two orogenic episodes—Orinoquiense-Grenvillian (~1.0 Ga) and Quetame-Caparonensis (~0.47 Ga)—consolidated the basement of the northern Andes, here referred to as the Chicamocha terrane. The Paleozoic paleogeography has been refined by establishing connections between provincial fauna. Faunal constraints indicate a Gondwanan affinity in the Cambro-Ordovician and an Appalachian character for the Siluro-Devonian assemblages. In a broader context, the proto Andean Grenvillian-Orinoquiense (~1.0 Ga) and Quetame-Caparonensis-Famatinian (~0.5–0.43 Ga) orogens may be traced from the Andes of Venezuela down to Argentina. A fragment of the Chicamocha terrane and its Cambro-Ordovician cover was “transferred” to southern Mexico in Late Paleozoic time. Permian magmatic belts running along active margins in Mexico and northern South America place a time limit for this connection at the onset of the assemblage of Pangea.
Pedro A. Restrepo-Pace, Fabio Cediel

The Guiana Shield and the Andean Belt


Chapter 3. The Proterozoic Basement of the Western Guiana Shield and the Northern Andes

Proterozoic metamorphic and igneous rocks belonging to the Guiana Shield form the basement of the Colombian territory from its eastern borders westwards to at least the eastern flanks of the Central Cordillera. A small part of the Amazonian basement underlain by felsic metavolcanics records the Trans-Amazonian Orogeny (2.26–1.98 Ga), the major orogenic event that shaped most of the Guiana Shield. The main part of the Colombian Amazonian and Orinoquian basement and of the adjacent Venezuelan and Brazilian territories consists of high-grade, largely supracrustal metamorphic rocks which accreted onto the Trans-Amazonian basement during the Querarí Orogeny (1.86–1.72 Ga) and was intruded by Mesoproterozoic anorogenic plutons around 1.59–1.51 Ga. The Andean Precambrian basement crops out in upthrust blocks all along the Eastern and eastern Central Cordillera, from the Garzón Massif in the south to the Guajira Peninsula in the north, and continues further northeast into Venezuela and eastwards into the Subandean basins. The Andean basement consists mainly of granulites and other high-grade metamorphic rocks, mainly of supracrustal origin, as well as minor plutons, formed during the Grenvillian Orogeny (1.1–0.9 Ga) caused by the collision of Amazonian and Laurentia. Echos of this collision are also discernable in the adjacent Amazonian basement as large shear faults, folding and low-grade metamorphism of Mesoproterozoic sandstone sequences, thermal mineral age resetting and minor alkaline magmatism.
Salomon B. Kroonenberg

Early Paleozoic Tectono-Sedimentary History


Chapter 4. Ordovician Orogeny and Jurassic Low-Lying Orogen in the Santander Massif, Northern Andes (Colombia)

The metamorphic crystalline core of the Santander Massif recorded an early Paleozoic peak metamorphism that reached the granulite facies with temperatures above the wet pelite solidus and an overprinting Jurassic low-pressure metamorphism. The early Paleozoic metamorphism occurred during the Ordovician and produced greenschist to amphibolite facies rocks (Silgará Schist) in the outer and upper parts of the orogen and migmatitic granulite facies rocks (Bucaramanga Gneiss and Berlín Orthogneiss) as observed in the deepest exhumed parts of the orogen. The location of the highest recorded metamorphic PT conditions and the Sn+1 foliation geometry hints at a dome-like structure. The overprinting Jurassic low-pressure metamorphism affected middle to late Paleozoic sedimentary sequences and is related to a N-S Triassic-Jurassic magmatic belt of a low-lying orogen. The plutonic belt is composed mainly of granites and tonalites with a range in ages from 172 to 210 Ma and is interpreted to belong to a low-lying orogen (low-lying Triassic-Jurassic magmatic arc). Present structures in the massif imprint a geometry characterized by converging faults toward the core of the massif giving the appearance of compressional horsts similar to the known back thrust and shortcut thrust geometry. The most important structural features are the Bucaramanga fault toward the west and the Pamplona-Cubogón-Mercedes system toward the east; additionally, there are numerous structures with contrasting cinematic behavior. Some of those faults have been interpreted to represent reactivated and inverted normal faults. It is still unclear if these reactivated faults operated during the Triassic-Jurassic as the boundaries of extensional basins.
Carlos A. Zuluaga, Julian A. Lopez

Major Tectono-Magmatic Events


Chapter 5. Spatial-Temporal Migration of Granitoid Magmatism and the Phanerozoic Tectono-Magmatic Evolution of the Colombian Andes

Plutonic and hypabyssal porphyritic granitoids (and their volcanic equivalents) are important constituents of the composite geological record of the Colombian Andes, not only from a volumetric standpoint but more so as products of the complex Phanerozoic tectono-magmatic evolution of the region. Based upon U-Pb (zircon) age data circa 1995–2017, six principle periods of Phanerozoic granitoid magmatism have been identified, including early Paleozoic (ca. 485–439 Ma), Carboniferous (ca. 333–310 Ma), Permo-Triassic (ca. 289–225 Ma), latest Triassic-Jurassic (ca. 210–146 Ma), late Cretaceous to Eocene (ca. 100–42 Ma) and latest Oligocene to Mio-Pliocene (ca. 23–1.2 Ma). Mio-Pliocene granitoids of this last period, located within the physiographic Central Cordillera, are essentially coaxial with the Pleistocene to Recent Colombian (Northern Andean) volcanic arc. Major, trace and REE lithogeochemical data for Colombian granitoids are interpreted to reflect mantle vs. crustal magma source regions and variations in petrogenetic processes, including magmatic differentiation, partial melting, crustal anatexis/assimilation and magma mixing. Supported by Sr-Nd, Pb and Hf isotope analyses and regional geological and geophysical constraints, the lithogeochemical and isotopic compositions of Colombian granitoids are interpreted within the wide range of settings which characterize Phanerozoic tectonic evolution of the Northern Andean region. Mantle- and crustal-derived granitoids associated with subduction-related arcs, collision-type orogeny and post-orogenic collapse, regional taphrogenesis, back-arc extension, oceanic rifting and crustal anatexis related to slab delamination, asthenospheric upwelling and crustal underplating are all potentially represented. The analytical resolution of combined U-Pb (zircon), lithogeochemical and isotope data permits a detailed analysis of the temporal vs. spatial migration and petrogenetic variation of granitoid magmatism during the Phanerozoic. Major granitoid suites have herein been integrated into pre-Northern Andean, proto-Northern Andean and Northern Andean orogenic phases of Colombian tectonic evolution.
Hildebrando Leal-Mejía, Robert P. Shaw, Joan Carles Melgarejo i Draper

Chapter 6. Phanerozoic Metallogeny in the Colombian Andes: A Tectono-magmatic Analysis in Space and Time

The Colombian Andes are a highly fertile although little documented metallogenic province. Time-space analysis has identified numerous metallotects containing a wide variety of mineral deposits, framed within five broad metallogenic epochs, defined by important changes in the Phanerozoic tectonic and magmatic evolution of the region. Mineral deposits of both syngenetic and epigenetic origins range from the products of orthomagmatic cumulate segregation and those related to hydrothermal processes associated with oceanic and continental rifting and subduction-related volcanism/magmatism to accumulations related to uplift, basin development, chemical sedimentation and the amagmatic migration of mineral-rich brines. Important secondary and residual deposits are related to the complex weathering and erosion history of the Northern Andean region. Significant deposits and mineral districts were formed in the peri-cratonic or intra-oceanic realm and are allochthonous to the Colombian cordilleras, a result of the complex Meso-Cenozoic accretionary history of the region. Numerous metal deposits and mineral districts are described in detail, and the sympathetic relationship between metal occurrences in the Colombian Andes and the tectonic development of the region as a whole is demonstrated.
Despite the wide range of observed tectonic settings and deposit types, the Colombian Andes are highlighted as a Au-rich province. The close temporal and spatial affinity between hypogene Au mineralization of numerous styles and mantle-derived, metaluminous, tholeiitic and calc-alkaline (magnesian, calcic through alkali-calcic) plutonic and hypabyssal porphyritic granitoids (and their coeval volcanic equivalents), of Carboniferous, Jurassic, mid-late Cretaceous, Paleocene, Eocene, latest Oligocene, Miocene, Pliocene and even Recent age, is documented. Beyond tectono-magmatic setting of mineralization sensu lato, the nature, composition and tectonic architecture of the basement complex(es) which host individual granitoid suites and their associated mineral occurrences provided important controls upon the localization of mineral districts.
Robert P. Shaw, Hildebrando Leal-Mejía, Joan Carles Melgarejo i Draper

Chapter 7. Paleogene Magmatism of the Maracaibo Block and Its Tectonic Significance

One of the main northern South American geological conundrums has been to establish the tectonic relationship between Caribbean and South American plates during Mesozoic and Cenozoic times. Based on the petrogenetic interpretation of magmatic bodies within the Maracaibo block, we suggest an interplay between subduction and overthrusting tectonics in the northern part of South America during the Cenozoic. Our data show that the subduction of the Caribbean Plate beneath the South American Plate started around 65 million years ago, as is evidenced by the presence of trondhjemitic intrusions in the Santa Marta Province. Then, after a ca. 5-million-year magmatic gap, the evolution of this subduction system allowed the formation of a magmatic arc represented by the calc-alkaline Santa Marta Batholith (~56–49 Ma) and Parashi Pluton (51–47 Ma). For the interval between 50 and 25 million years, our data and compiled data point to a reduction in the tectonic activity, which is supported by relatively slow rates of cooling and uplifting in the Maracaibo block. Finally, for the period since the early Miocene, the reported uplift data, subsidence rates, and stratigraphic discordances indicate a differential uplift of the Maracaibo block, decreasing from the northwestern tip (Sierra Nevada de Santa Marta) toward the southeast (Merida Andes) and suggesting that this tectonic “reactivation” is the result of dominant overthrusting tectonics.
José F. Duque-Trujillo, Teresa Orozco-Esquivel, Carlos Javier Sánchez, Andrés L. Cárdenas-Rozo

Chapter 8. Late Cenozoic to Modern-Day Volcanism in the Northern Andes: A Geochronological, Petrographical, and Geochemical Review

The Northern Andean Block is the result of complex tectonic interaction between the Farallon-Nazca, South American, and Caribbean Plates. Abundant late Cenozoic volcanism (and associated hypabyssal porphyritic plutonism), beginning in the mid- to late Miocene, is the result of subduction-related mantle-derived magmatic activity, superimposed upon a compositionally varied and structurally complex basement during the late stages of the Northern Andean orogeny. Tectonic consolidation and subduction of the segmented Nazca Plate during the late Miocene-Pliocene led to conformation of the modern-day Colombian segment of the Northern Andean Volcanic Zone. The Colombian arc segment represents the northernmost expression of subduction-related volcanism within South America’s Andean Cordillera.
M. I. Marín-Cerón, H. Leal-Mejía, M. Bernet, J. Mesa-García

The Northern Andean Orogen


Chapter 9. Diagnostic Structural Features of NW South America: Structural Cross Sections Based Upon Detailed Field Transects

This chapter illustrates the structural architecture of the Colombian Andes, highlighting the geometric and temporal relationships between lithologic units, faulting, and folding, as derived from field transects across key areas of the complex Colombian Cordilleran system. The summary presented herein, permits a better understanding of the tectonic, physiographic evolution and temporal genetic linkages within the Northern Andes. It is primarily a visual tool, intended to aid in the interpretation of segments of the Colombian Andes where insufficent geological data is available and hence, in the construction of structural models. The chapter consists of selected cross-sections constructed from actual field data and supported whether in seismic interpretation or well data. The field data was acquired during structural and stratigraphic surveys produced for the petroleum, coal and mineral industry, as well as for academic purposes. Most of the sections are balanced or at least admissible. The quality of the presented sections is supported on the coherence among detailed lithologic mapping, lateral facies changes, thickness variations of the lithostratigraphic units, and strict biostratigraphic control.
Sections belonging to six regional transects are presented in the printed format. Whilst, an extended digital appendix includes 15 additional more specific structural case studies (Fig. 9.1).
The following regional transects are portrayed in printed format:
Guajira Allochthon
Maracaibo block
Eastern Cordillera
Central Cordillera
Western Cordillera
Chocó indenter
The following detailed sections are appended in digital format:
Northern Eastern Cordillera, Chinácota Graben.
Northern Eastern Cordillera, Tamá Strike-slip tectonics.
Middle Magdalena Valley, La Salina-Infantas.
Eastern Cordillera, Central Sector.
Central Cordillera, Ibagué-Calarcá.
Western Cordillera, Bolívar Ultramafic Zoned Complex.
Upper Magdalena Valley, Ortega.
Upper Magdalena Valley, Pechúi.
Upper Magdalena Valley, San Antonio.
Eastern Cordillera, Western Foothills (Colombia, Huila).
Upper Magdalena Valley, Upar.
Upper Magdalena Valley, El Pensil-La Plata.
Upper Magdalena Valley, Iskana.
Putumayo, San Juan Norte.
Northern Eastern Cordillera - Rio Nevado Canyon.
Fabio Colmenares, Laura Román García, Johan M. Sánchez, Juan C. Ramirez

Chapter 10. Cretaceous Stratigraphy and Paleo-Facies Maps of Northwestern South America

This paper presents 13 stratigraphic cross sections and 12 paleo-facies maps, spanning the Cretaceous, and summarizes the Cretaceous geological history surrounding northwestern South America during this period. The work outlines a regional sequence stratigraphic framework for the Cretaceous, evolving within the context of the complex geological history and interaction of at least three tectonic plates. Cretaceous rocks, including local uppermost Jurassic and Paleocene deposits, form a mega-sequence bounded by regional unconformities that are locally angular. On a broad scale, Cretaceous rocks represent a major transgressive-regressive cycle with the maximum flooding surface close to the Cenomanian-Turonian boundary (MFS 8), corresponding to the maximum Cretaceous, and even Mesozoic, eustatic level. Superimposed on this large-scale trend are several smaller transgressive-regressive cycles, suggesting an oscillating relative tectono-eustatic level. These minor cycles correspond to the several proposed stratigraphic sequences.Cretaceous sedimentary history can be summarized in four episodes: (1) Berriasian to Early Aptian: Sedimentation was restricted to rapidly subsiding extensional basins where great thickness of sediment accumulated. Sedimentation started in continental environments followed by a marine transgression. Marine shelves developed with carbonate- dominated sedimentation in Venezuela and northeastern Colombia, and mud-dominated sedimentation in Colombia, while in Peru sands and muds were deposited in shallow marine to deltaic environments. During the Aptian, a tectonically induced unconformity resulted from the closure and accretion of the Quebradagrande oceanic margin basin to western Colombia and Ecuador, or alternatively from the change from active rifting to regional thermal subsidence. (2) Late Aptian to Cenomanian: Regional thermal subsidence resulted in an increase of in the area of marine sedimentation via the coalescence of isolated basins into a regional basin extending along the continental margin from Venezuela to Peru. Marine shelf sedimentation was mud- dominated in Venezuela and Colombia, and carbonate-dominated in Peru. (3) Cenomanian to Santonian: During the latest Cenomanian-Early Turonian, sea level reached its maximum. Sedimentation was controlled by eustatic changes. Coincident with maximum Cretaceous flooding, anoxic events favored accumulation of organic matter at the sea bottom resulting in the best petroleum source rocks in northern South America. From Venezuela to Ecuador, pelagic shale and pelagic fine-grained limestone sedimentation prevailed. During the Coniacian-Santonian in Venezuela and Colombia, marine upwelling favored development of siliceous plankton and chert deposition. In Peru, marine shelf sedimentation was mud-dominated. (4) Campanian to Early Paleocene: Marine regression and a general shallowing of sedimentary environments occurred throughout northwestern South America, coeval with the appearance of compressional deformation events, which started earlier in Peru. During the Late Campanian, initial collision of the Caribbean Plate with northern Colombia generated a tectonically induced unconformity extending into western Venezuela. During the Late Maastrichtian and Paleocene, regional marine regression resulted in continental sedimentation extending from Venezuela to Ecuador. In Venezuela, the prevailing passive margin changed to an active margin with obduction of oceanic terranes of Caribbean affinity during the Maastrichtian and Paleocene. In Colombia, Campanian and Maastrichtian collision of the Caribbean Plate resulted in accretion of oceanic fragments to the continental margin and generated uplift of the Central Cordillera and its northern prolongation in the Lower Magdalena Valley (Plato-San Jorge area) and the Sierra Nevada de Santa Marta. Uplift of the Cordillera Real in Ecuador and the sub-Andean zone including the western part of the Oriente basin also occurred. Campanian uplift ofthe Peruvian Andes provided a source of detrital sediments that accumulated as continental and alluvial fan deposits in active synclines. During the Paleocene, most of the basins began to compartmentalize due to active deformation.
Luis Fernando Sarmiento-Rojas

Chapter 11. Morphotectonic and Orogenic Development of the Northern Andes of Colombia: A Low-Temperature Thermochronology Perspective

Landscapes in mountain belts evolve through complex feedback mechanisms between internal and external processes. Modern orogenic belts, such as the Andes, are the result of millions of years of continuing internal and external processes. Therefore, mountain ranges are rich repositories of geomorphic and tectonic information. Established techniques in low temperature thermochronology (LTTC), e.g., fission-track and (U-Th)/He dating, present novel opportunities to quantitatively explore key morphotectonic processes in the upper crust, e.g., the cooling of rocks as they move toward the Earth’s surface during exhumation, via erosion, normal faulting, and/or crustal thinning. We address the Late Mesozoic-Cenozoic morphotectonic and orogenic history of the Northern Andes of Colombia using detailed compilations and analysis of existing LTTC datasets, in an effort to define the spatial distribution, timing, and magnitude of the main orogenic phases in the region, while providing an up-to-date morphotectonic picture of the Northern Andes.
Sergio A. Restrepo-Moreno, David A. Foster, Matthias Bernet, Kyoungwon Min, Santiago Noriega

Chapter 12. The Romeral Shear Zone

The Romeral shear zone marks the geological boundary between the physiographic Central and Western cordilleras of the Colombian Andes. It demarcates and encompasses the main locus of deformation associated with the amalgamation and geological-structural evolution of the Northern Andean region during the Meso-Cenozoic, although as an ancient plate boundary, its origins may be traced into the Late Paleozoic. Today, Romeral corresponds to a km-scale shear zone containing poly-deformed, structurally juxtaposed fragments and slivers of a wide range of rock types, of varying ages and diverse origins, including metaigneous and metasedimentary blocks of the disjointed and reworked paleo-autochthon, fragments of pericratonic and possibly exotic oceanic margin, and late, autochthonous siliciclastic and volcanic sequences, each reflecting distinct development stages in the complex plate dynamics of the Northern Andean paleo-margin.
César Vinasco

Continental Uplift-Drift


Chapter 13. Exhumation-Denudation History of the Maracaibo Block, Northwestern South America: Insights from Thermochronology

The Maracaibo block forms a distinct continental fragment in northwestern South America lying between the Oca-El Pilar fault (north) and the Santa Marta-Bucaramanga fault (southwest). Bounding this continental block are the Sierra Nevada de Santa Marta, Perijá, Mérida, and Macizo de Santander mountain belts. These belts were formed by complex geodynamic interactions between the Caribbean Plate, the Panamá Arc, and the South American Plate, which resulted in the reactivation of major preexisting structures or inherited discontinuities. In this study we summarize published 40Ar/39Ar, fission-track, and (U-Th)/He data. The data organization takes into account the movement of different plates in time and space, major present-day regional faults, geophysical data, and precipitation patterns permitting the identification of different tectonic blocks with contrasting cooling and exhumation histories. Unraveling the cooling history of the individual blocks leads to an improved understanding of the control of preexisting faults and regional Caribbean geodynamics on the evolution of northwestern South America.
Mauricio A. Bermúdez, Matthias Bernet, Barry P. Kohn, Stephanie Brichau

Active Oceanic — Continental Collision


Chapter 14. The Geology of the Panama-Chocó Arc

The Panama-Chocó Arc is a composite volcano-plutonic island arc of Late Cretaceous to Miocene age developed on ocean crust of the Caribbean large igneous province (CLIP) on the western or trailing edge of the Caribbean Plate. An early arc of Late Cretaceous to Eocene age developed by northerly or north-easterly subduction of the Farallon Plate to form the volcano-plutonic rocks of the Chagres, Mamoní, San Blas, Atrato and Mandé Mountains. Arc shutdown in the middle Eocene was coincident with a change from compressional to extensional tectonics, with graben development in the fore-arc to form the Chuqunaque-Tuira-Atrato Basins; the opening of the Panama Canal Basin in a radial rift basin; and block rotations and displacements. This extension and arc break-up may be explained by steepening of the subducting Farallon Plate by slab rollback and ultimately break-off, and/or initial oblique collision of the eastern part of the Panama-Chocó Arc with South America in the Istmina area as a result of consumption of the proto-Caribbean Plate beneath South America. Following the break-up of the Farallon Plate at 25–23 Ma (late Oligocene), a short-lived later arc, related to the NE-dipping subduction of the Nazca Plate, was formed to the south of the early arc and fore-arc basins in the Majé-Baudó Mountains and the Pearl Islands. Oblique collision of the Chocó Block of Colombia was complete by about the Early Miocene. Panama started to collide against South America in the Middle Miocene, a process which is still ongoing. The Nazca Plate convergence with Panama changed to left-lateral strike-slip, resulting in the cessation of subduction and arc shutdown, formation of the east Panama deformed belt by left-lateral transpression, basin closure and uplift of the isthmus to create the land bridge with South America.
Stewart D. Redwood

Holocene — Anthropocene


Chapter 15. Sediment Transfers from the Andes of Colombia during the Anthropocene

This chapter reviews data, models, and analyses on Anthropocene-impacted sediment fluxes in the Andes of Colombia and provides examples on how direct human alteration has increased sediment flux during the last decades. Firstly, it describes the context of the northern Andes in terms of sediment production within the whole Andes Cordillera. Secondly, it presents a summary of major land cover changes witnessed in the region from 8000 years ago to the beginning of large-scale land transformation that occurred in Colombia during the last three decades and analyzes major human-induced drivers of change. Also, trends in sediment load during the 1980–2010 period are documented. Finally, it compares modern and prehuman conditions of sediment flux by using some applied models in global and Colombian rivers.
An inventory of per capita anthropogenic land cover change (ALCC) from 8 ka to AD 2000 for the Andes of Colombia reveals that a nearly pristine environment existed until 3 ka. Two thousand years later, by AD 1, ALCC only slightly increases. From AD 1500 to AD 1600, the ALCC scenarios show a decrease in anthropogenic land use in the Andes, as the indigenous populations of the Americas succumbed to disease and war brought by European explorers and colonists. The collapse of large precontact populations with advanced agriculture, which were especially concentrated in Mesoamerica and the Andes, led to high amounts of land abandonment. The low levels of ALCC shown at AD 1500 are almost entirely abandoned 100 years after conquest. By AD 1687, anthropogenic land use in the Andes accelerated with the spread of colonies and nations founded by Europeans. The Americas only start to result in substantial amounts of ALCC emissions during the last centuries.
Further studies on historical patterns and drivers of landscape change in Colombia since 1500 confirm that land conversion in the Andes started five centuries ago. The transformed area in the Andean region rose from 15 M ha in 1500 to 42 M ha in 2000. During the last two centuries, the annual rate of forest-transformed area increased two orders of magnitude, from 4330 ha y−1 in 1800 to 171,190 ha y−1 in 2000. By the year 2000, 80% of the natural vegetation in the Andes was cleared, with 20% remaining as scattered remnants. An assumed value of 30% was cleared in preconquest agricultural landscapes (before 1500), increasing to 80% in 2000. Demographic impacts of colonization and the introduction of cattle were major drivers of change.
Findings of land use and sediment load trends indicate that the extent of erosion within the Andes of Colombia has severely increased over the last 30 years. For example, the last decade has been a period of increased pulses in sediment transport and rates of deforestation as seen by the statistical significant trends in load and by a marked increase of 241% in forest clearance. As a whole, the Andean drainage basins have witnessed an increase in erosion rates of 33%, from 550 t km−2 y−1 before 2000 to 710 t km−2 y−1 for the 2000–2010 period. Levels of sediment transport are one order of magnitude higher in modern times than during prehuman conditions. The differences between prehuman and modern sediment load in South American rivers were more pronounced for the Magdalena River, with a difference ranging between −100 and −150 Mt. y−1. Thus, during pristine conditions and according to the observed total load of the Magdalena, 184 Mt. y−1, the Magdalena could have had an annual sediment load between 34 and 84 Mt. y−1 during prehuman times. Further results indicate that 35% of the sediment load in the Colombian Andes is due to deforestation; 1690 Mt. of sediments were produced due to forest clearance over the last three decades. Much of the river catchments (79%) are under severe erosional conditions due in part to the clearance of more than 80% natural forest during the last 500 years.
Juan D. Restrepo

Chapter 16. The Historical, Geomorphological Evolution of the Colombian Littoral Zones (Eighteenth Century to Present)

The complex geological framework of Colombia is reflected on its Caribbean and Pacific coasts by the highly contrasting nature of their littoral types, ranging from low-relief deltaic barrier islands and mangrove swamps to steep-rocky reliefs cut by plunging cliffs and wide erosional shore platforms. Relative sea-level changes during the Quaternary and the Holocene are evidenced by morphological features of ancient coastline positions, including emerged marine terraces with coral reefs, cliffs, stacks, and raised beach ridges deposits.
An overview of the historical evolution of the Colombian littorals since the end of the eighteenth century evidences a high morphological instability indicated by coastline changes of hundreds of meters and corresponding land losses or gains of tens of km2. These evolutions reflect noticeable variations in the littoral’s sediment budgets, much of them triggered or greatly influenced by human actions. Along the 1700 km-length, micro-tidal Caribbean shores, critical areas are found between the Magdalena delta and the Urabá Gulf, a developed, highly tectonic coastal fringe influenced by mud diapirism and by man-induced changes on its hydrological and sedimentological regimes. Along the meso-macro tidal, 1300 km-length, less populated and engineered Pacific coast (but highly intervened by deforestation and mining), most critical cases are shown by the breaching of its major barrier islands, due to natural factors including coseismic subsidence, tsunamis, and positive sea-level anomalies during El Niño events.
Iván D. Correa, Cristina I. Pereira


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