The Amazonian rainforest is arguably the most species-rich terrestrial ecosystem in the world, yet the timing of the origin and evolutionary causes of this diversity are a matter of debate. We review the geologic and phylogenetic evidence from Amazonia and compare it with uplift records from the Andes. This uplift and its effect on regional climate fundamentally changed the Amazonian landscape by reconfiguring drainage patterns and creating a vast influx of sediments into the basin. On this “Andean” substrate, a region-wide edaphic mosaic developed that became extremely rich in species, particularly in Western Amazonia. We show that Andean uplift was crucial for the evolution of Amazonian landscapes and ecosystems, and that current biodiversity patterns are rooted deep in the pre-Quaternary.

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Amazonia Through Time: Andean Uplift, Climate Change, Landscape Evolution, and Biodiversity

NewdatafromNeogenestratainnorthernSouthAmericasuggestthatMiocenetectonisminthenortheasternAndeswasresponsible for the genesis of the Amazon River and changes in the drainage patterns of other major rivers such as the Magdalena and the Orinoco. Here we present a new model for the paleogeographic evolution of northern South America during the Miocene. In the early Miocene, a large part of the drainage of northwest Amazonia was directed northward along the paleo‐Orinoco river system to a deltainLakeMaracaibo.UpliftoftheEasternCordillerainthelate middle Miocene caused thefirst development of the Amazon River; however, no connection with the Atlantic was established, and the Amazon fed the paleo‐Orinoco river system, which drained toward the Caribbean. Substantial Andean uplift in the late Miocene resultedinmajorchangesinpaleogeography:theOrinocochangedits course, the Amazon established a connection to the Atlantic, causing the drowning of carbonate platforms, and the Amazon-Caribbeanconnectionwasclosed.Thusthedrainageandpaleogeography ofnorthernSouthAmericaintheMiocenewerestronglycontrolled by tectonic movements in the northeastern Andes.

Andean tectonics as a cause for changing drainage patterns in Miocene northern South America

Geological evolution of the Caribbean region; A plate-tectonic perspective

Spreading along the Cocos-Nazca plate boundary since the breakup of the Farallon plate in the Miocene has resulted in the formation of the Panama basin and a complex interaction of plates in and near northwestern South America. Current plate boundaries have been defined, and segments of subducted lithosphere identified through selection of hypocentral locations of earthquakes, considering only well-located events, and through focal mechanism determinations. The existence of relict plate boundaries, bathymetric features, and the Panamanian isthmus has affected the subduction process of the Nazca plate beneath South America and determined the present-day configuration of the subducting lithospheric plate. There is no single triple junction separating the Caribbean, South American, and Nazca plates. Instead, the Panamanian isthmus and surrounding areas are accommodating east-west compression (and a lesser degree of north-south compression) along a series of thrust faults striking NW to NE, and the Andean ranges of Ecuador, Colombia, and Venezeula are moving as a block NNE relative to the rest of the South American plates, along a system of faults following the front of the Eastern Cordillera. The subducted portions of the Panama basin and old Farallon plate have become segmented into three pieces recognized in this study. From north to south, they are (1) a ‘Bucaramanga’ segment continuous with the Caribbean seafloor northwest of Colombia, (2) a ‘Cauca’ segment continuous with oceanic crust (Nazca plate) currently being subducted beneath South America at the Colombia-Ecuador trench, and (3) an ‘Ecuador’ segment at the northern end of the subducted lithospheric plate which is dipping at a small angle to the east beneath northern Peru. The segmentation of the subducted plate can be explained by the buoyancy of bathymetric features which have been partially subducted.

Subduction of the Eastern Panama Basin and seismotectonics of northwestern South America

A detailed model for the evolution of the Gulf of Mexico, the Bahamas and the Proto-Caribbean is built within the framework provided by a detailed initial Alleghenian (western Pangean) reconstruction and an accurate subsequent relative-motion history between North America and Gondwana (northern Africa and South America). The Alleghenian reconstruction closes all pre-Jurassic oceans; accounts for Jurassic attenuation of continental crust by restoring that attenuation to original prerift continental thicknesses; incorporates an improved Equatorial Atlantic fit between northern Brazil and the Guinea margin of Africa; quantitatively removes changes in shape of northern South America due to Late Cretaceous and Cenozoic accretion and internal deformation; includes pre-Mesozoic continental crust presently underlying the western Bahamas and southern Florida; and correlates Late Paleozoic geology of Yucatan with its neighboring continental masses. Extension occurred within the Gulf of Mexico from Late Triassic to earliest Cretaceous time, but seafloor spreading was delayed until the Late Callovian. This divided a single Gulf-wide salt basin into the Louann and Campeche salt provinces. The Yucatan block progressively rotated about 43 degrees counterclockwise away from the Texas-Louisiana margin around a pole in northern Florida. The Tamaulipas-Golden Lane-Chiapas fault zone of eastern Mexico is interpreted as the remains of an initially intracontinental transform system along which Yucatan migrated. Attenuated continental crust beneath southern Florida and the western Bahamas, termed here the Florida Straits block, migrated approximately 300 km out of the eastern Gulf, approximately along Central Atlantic flow lines. These rotations are consistent with recently suggested magnetic anomaly trends in the Gulf of Mexico (Shepherd et al., 1982; S. Hall, personal communication, 1984). The Proto-Caribbean formed synchronously by a fan-like rotation of Yucatan away from Venezuela.

Alleghenian reconstruction and subsequent evolution of the Gulf of Mexico, Bahamas, and Proto-Caribbean

Mesozoic-pleistocene fission-track ages on rocks of the venezuelan andes and their tectonic implications

The P/T gradient or “baric type” of low-grade metamorphic terranes can be characterized on the basis of cumulative frequency curves of the lattice parameter b
0 of dioctahedral micas (Sassi and Scolari 1974), which essentially reflects celadonite content and increases with pressure. The method is here applied to illite/muscovite of sub-greenschist (“incipient” metamorphism) and low-greenschist facies terranes from the marginal zones of the Swedish Caledonides, Swiss Alps and Venezuelan Andes, where the grade of metamorphism was determined on the basis of illite “crystallinity”. Complications in the determinations of b
0 arising from (a) shifts in the spacing of the apparent 060 diffraction peaks of the illites due to the presence of inter-stratified expandable layers, and (b) persistence of more “crystalline” clastic micas are pointed out. In contrast to the earlier-reported decrease of b
0 with progressive metamorphism at higher grades, b
0 tends to increase with grade during incipient metamorphism: it is markedly lower in the “diagenetic” and low-grade anchimetamorphic grades in the Cambro-Silurian of the Caledonides of Jamtland, western Sweden (zone A), and the Lower Tertiary of the Helvetic zone of the Swiss Alps, than in the higher grade anchizone and “epizone” of the former terrane. Mean b
0 values for the intermediate and highest (“epizone”) grades of the Swedish Caledonides are respectively 9.030 and 9.037 A compared to the mean value of 9.035 A for the medium-high pressure, Barrovian-type, terrane of Otago, N.Z. Mean b
0 of 9.005 A for the mainly epizonal slates of the Venezuelan Andes lies between those for the low-pressure terranes of Bosost (∼ 8.992 A), and the low-medium pressure terrane of northern New Hampshire (∼9.010 A). These baric estimates agree well with those for the metamorphic facies series at higher grade produced by the same events. Cumulative b
0 curves are concluded to be useful for the characterization of P/T gradients of incipient metamorphism, particularly in the higher grade part of the anchizone and the “epizone”.

Use of the lattice parameter b 0 of dioctahedral illite/muscovite for the characterization of P/T gradients of incipient metamorphism

[1] The Venezuelan Andes formed by complex geodynamic interaction between the Caribbean Plate, the Panama Arc, the South American Plate and the continental Maracaibo block. We study the spatial and temporal patterns of exhumation across the Venezuelan Andes using 47 new apatite fission track (AFT) ages as well as topographic analyses. This approach permits the identification of at least seven tectonic blocks (Escalante, Cerro Azul, Trujillo, Caparo, Sierra Nevada, Sierra La Culata and El Carmen blocks) with contrasting exhumation and cooling histories. The Sierra Nevada, Sierra La Culata and El Carmen blocks, located in the central part of the Venezuelan Andes and separated by the Bocono fault system, cooled rapidly but diachronously during the late Miocene–Pliocene. Major surface uplift and exhumation occurred in the Sierra Nevada block since before 8 Ma. A second phase of uplift and exhumation affected the El Carmen and Sierra La Culata blocks to the north of the Bocono fault during the late Miocene-Pliocene. The highest topography and steepest relief of the belt coincides with these blocks. The Caparo and Trujillo blocks, located at the northeastern and southwestern ends of the orogen, cooled more slowly from the Oligocene to the late Miocene. These blocks are characterized by significantly lower mean elevations and slightly lower mean slopes than the central blocks. Unraveling the cooling history of the individual blocks is important to better understand the control of preexisting faults and regional Caribbean geodynamics on the evolution of the Venezuelan Andes. Our data indicate a strong control of major preexisting fault zones on exhumation patterns and temporal correlation between phases of rapid exhumation in different blocks with major tectonic events (e.g., collision of the Panama arc; rotation of the Maracaibo block).

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2009TC002635

Spatial and temporal patterns of exhumation across the Venezuelan Andes: Implications for Cenozoic Caribbean geodynamics

In terms of topography, the northernmost extensions of the Andes branch into long fingerlike ranges separated by low-lying sediment-filled basins. Geologic definition of the northern Andes is a far more complex problem. For many, the term “Andes” has the connotation of Tertiary block uplifts or Germano-type orogeny, in contrast to the orogenic model associated with island arcs. It is common practice, therefore, to regard the Southern Caribbean Mountains, i.e., the coastal ranges of northern Venezuela and Trinidad, as having affinities with the Caribbean Island Arc, whereas the Merida ranges are classed as Andean. There are others such as Gansser (1973) who include all ranges on the continental mainland as Andean and consider the Caribbean Island Arc to begin at the southernmost of the Lesser Antilles. On the gross scale of this report, the two kinds of orogenic belt are closely associated in space: With allowance for major lateral offsets, one may claim geologic continuity from the lesser Antilles into the northern ranges of Trinidad-Venezuela and thence into the Guajira Peninsula and the northwestern apex of the Santa Marta block continuing into the Cordillera Central (cf. Alvarez, 1971). It has been an arbitrary decision on my part to exclude from discussion here the northern ranges of Trinidad-Venezuela and the Guajira Peninsula. For convenience, the southern limit of the region under discussion has been set at the latitude of Bogota (4°40’ N).

The Northern Termination of the Andes

Two rocks of the Tinaco Complex (one here so postulated on lithologic grounds) give zircon ages of 49 ± 6 m.y. and 42.7 ± 5.3 m.y. (mean of two ages). Eleven samples of Pena de Mora gneiss (Caracas Group) and Choroni-Tovar "granite" (gneiss) give zircon ages that cluster closely about a mean of 19.7 ± 2.1 m.y. The bimodal zircon ages are explained by a speculative model involving obduction of the Tinaco Complex over the Caracas Group followed by isostatic rebound after southward passage of the Villa de Cura klippe, which set the older ages. In turn, further block uplift during eastward translation of the Caribbean relative to the South American plate led to the setting of the younger group of zircon ages. A single sphene age of 126 ± 15 m.y. on Choroni "granite" (gneiss) is best viewed as a partially annealed remnant of a Paleozoic(?) clock in Sebastopol gneiss component of the "granite." One apatite separate from Tinaco Complex trondhjemite yields an age of 6.1 ± 1.3 m.y., reflecting a phase of uplift also prominent in the circum-Maracaibo Basin ranges to the west.

Reginald Shagam

Papers

Mesozoic-pleistocene fission-track ages on rocks of the venezuelan andes and their tectonic implications

Use of the lattice parameter b 0 of dioctahedral illite/muscovite for the characterization of P/T gradients of incipient metamorphism

Spatial and temporal patterns of exhumation across the Venezuelan Andes: Implications for Cenozoic Caribbean geodynamics

The Northern Termination of the Andes

Results and preliminary implications of sixteen fission-track ages from rocks of the western Caribbean Mountains, Venezuela.