DT - DOCUMENT TYPE: Serial
BL - BIB LEVEL: Analytic
MC - MAP COORDINATES: LAT: N010000; N013000; LONG: W0770000; W0780000.
NN - ANNOTATION: With GSA Data Repository Item 9626.
IL - ILLUSTRATION: Refs: 18; illus. incl. sect., sketch map.
RF - REFERENCE SOURCE: GeoRef, Copyright 2000, American Geological Institute. Reference includes data supplied by the Geological Society of America, Boulder, CO, United States
IS - ISSN: 0091-7613
CO - CODEN: GLGYBA
AN - ACCESSION NUMBER: 1996-042464
UD - UPDATE CODE: 199614
Registro 4625 de 5614 - GeoRef Disc 4: 1993-1996
TI - TITLE: Neogene ecology of the Salto de Tequendama site (2475 m altitude, Cordillera Oriental, Colombia); the paleobotanical record of montane and lowland forests.
AU - AUTHORS: Wijninga-Vincent-M
AF - AUTHOR AFFILIATION: University of Amsterdam, Department of Palynology, Amsterdam, Netherlands
SO - SOURCE: Review of Palaeobotany and Palynology. 92; 1-2, Pages 97-156. 1996.
PB - PUBLISHER: Elsevier. Amsterdam, Netherlands. 1996.
CP - COUNTRY OF PUBLICATION: Netherlands
PY - PUBLICATION YEAR: 1996
LA - LANGUAGE: English
AB - ABSTRACT: A paleobotanical and palynological study of Neogene fluvial sediments of sections Salto de Tequendama I and II, located in the area of the high plain of Bogota (Cordillera Oriental, Colombia) at 2475 m altitude was carried out. Several other sections of Miocene and Pliocene age were analysed for microfossils and macrofossils and evidence for the uplift of the Cordillera Oriental of Colombia was evaluated. Using modern vegetation zonation, with caution, as a reference, the fossil assemblages are interpreted and the elevation of the site during intervals of the Neogene is inferred. The pollen assemblages of sections Salto de Tequendama I and II include taxa such as Mauritia, Iriartea, Humiriaceae, Amanoa, Virola, Ceiba, indicating a lowland environment. These taxa are presently found on the alluvial plains in lowland areas, e.g. Amazonia. The pollen assemblage of section Salto de Tequendama I contains, in addition to lowland taxa, also montane taxa (e.g. Podocarpus, Clethra, Symplocos, Compositae, Ericaceae), suggesting presence of mountains in the region. Macrofossils representing mainly Humiriaceae in section I emphasize the allochthonous character of the plant assemblage. The peaty flood basin deposits of section II show fossil spectra indicative of swamp forest, dominated by Mauritia. The dominance of Cyperaceae and Cyclanthaceae seeds supports the conclusion that the plant assemblages of section II are autochthonous. Biostratigraphical evaluation suggests a middle Miocene age for the sediments of the sections Salto de Tequendama I and II, although an early Pliocene age cannot be ruled out. Paleovegetation charateristics suggest a paleoelevation below 700 m, compared to the present elevation of the site at 2475 m. This difference may be explained in terms of climatic change, and tectonic uplift. However, warming during the Miocene and Pliocene accounts at most for 3 degrees C, corresponding to a shift of vegetation belts of c. 500 m. The remaining difference in elevation of 1300 m is an approximation for the minimal uplift of the Cordillera Oriental during the middle Miocene and Pliocene. Plant macrofossils, mainly fruits and seeds, and pollen types new to the study area are described and illustrated.
DE - DESCRIPTORS: altitude-; Andes-; Cenozoic-; Colombia-; Eastern-Cordillera; ecology-; forests-; lithofacies-; microfossils-; Neogene-; paleoecology-; palynomorphs-; Salto-de-Tequendama; South-America; Tertiary-
CC - CATEGORY CODES: 09-Paleobotany
DT - DOCUMENT TYPE: Serial
BL - BIB LEVEL: Analytic
IL - ILLUSTRATION: Refs: 100; illus. incl. sect., 15 plates, 3 tables, sketch map.
RF - REFERENCE SOURCE: GeoRef, Copyright 2000, American Geological Institute.
IS - ISSN: 0034-6667
CO - CODEN: RPPYAX
AN - ACCESSION NUMBER: 1996-044038
UD - UPDATE CODE: 199615
Registro 4626 de 5614 - GeoRef Disc 4: 1993-1996
TI - TITLE: A Pliocene Podocarpus forest mire from the area of the high plain of Bogota (Cordillera Oriental, Colombia).
AU - AUTHORS: Wijninga-Vincent-M
AF - AUTHOR AFFILIATION: University of Amsterdam, Department of Palynology and Paleo/Actuo-ecology, Amsterdam, Netherlands
SO - SOURCE: Review of Palaeobotany and Palynology. 92; 1-2, Pages 157-205. 1996.
PB - PUBLISHER: Elsevier. Amsterdam, Netherlands. 1996.
CP - COUNTRY OF PUBLICATION: Netherlands
PY - PUBLICATION YEAR: 1996
LA - LANGUAGE: English
AB - ABSTRACT: Pollen and macrofossil assemblages in the sediments of the Facatativa 13 section (2750 m altitude, Cordillera Oriental, Colombia) document vegetation, and environmental conditions of the high plain of Bogota during the middle Pliocene. Modern analogs of these Pliocene vegetations do not exist, because of immigration of plant taxa and evolution of ecosystems; cautious use of the modern vegetation zonation as a reference allows inference of the altitude of sediment deposition. Pollen and macrofossil analysis of organic-rich deposits of section Facatativa 13 from the area of the high plain of Bogota showed that upper subandean (upper lower montane) to lower Andean (lower upper montane) climatic conditions prevailed. The most important taxa of the regional forest were Myrsine, Alchornea, Melastomataceae, Podocarpus, Hedyosmum and Ilex. The local vegetation consisted of a Podocarpus forest mire, associated with Melastomataceae and ferns. An abrupt change in lithology marks the disappearance of the forest mire and the subsequent development of a lacustrine depositional environment. Macrofossils indicate that during the early development of the lake herbaceous swamp taxa were dominant. The sediments of section Facatativa 13, fission-track dated at 3.7+ or -0.5 Ma, belong to Biozone II of the Neogene sediment sequence in the area of the high plain of Bogota. Prevailing conditions correspond to a paleoaltitude of approximately 2000 m, suggesting that uplift of the area had continued after 3.7 Ma. Accounting for the global Pliocene temperature range, with an amplitude of + or -3 degrees C, fossil assemblages are indicative of an altitudinal position between 1500 and 2500 m elevation during sedimentation. However, in the late Pliocene the Andean forest line was probably at a considerable lower elevation than at present as a result of Andean forest taxa ecologically unadapted to previous and ongoing tectonic uplift. Consequently, the maximum altitudinal range of the Andean forest taxa was less than at present and the paleoaltitude might be overestimated. Pollen, seeds, fruits, and wood fragments, new for the study area, are described and illustrated.
DE - DESCRIPTORS: Andes-; Bogota-Colombia; Cenozoic-; Colombia-; Eastern-Cordillera; forests-; fossil-wood; highlands-; microfossils-; miospores-; Neogene-; palynomorphs-; Pliocene-; pollen-; seeds-; South-America; Tertiary-; vegetation-
CC - CATEGORY CODES: 09-Paleobotany
DT - DOCUMENT TYPE: Serial
BL - BIB LEVEL: Analytic
MC - MAP COORDINATES: LAT: N043800; N043800; LONG: W0740500; W0740500.
IL - ILLUSTRATION: Refs: 88; illus. incl. 2 tables, 16 plates.
RF - REFERENCE SOURCE: GeoRef, Copyright 2000, American Geological Institute.
IS - ISSN: 0034-6667
CO - CODEN: RPPYAX
AN - ACCESSION NUMBER: 1996-044039
UD - UPDATE CODE: 199615
Registro 4627 de 5614 - GeoRef Disc 4: 1993-1996
TI - TITLE: A preliminary paleomagnetic pole for Mid-Cretaceous rocks from Tobago; further evidence for large clockwise rotations in the Caribbean-South American plate boundary zone.
AU - AUTHORS: Burmester-Russell-F; Beck-Myrl-E Jr.; Speed-Robert-C; Snoke-Arthur-W
AF - AUTHOR AFFILIATION: Western Washington University, Department of Geology, Bellingham, WA, United States
SO - SOURCE: Earth and Planetary Science Letters. 139; 1-2, Pages 79-90. 1996.
PB - PUBLISHER: Elsevier. Amsterdam, Netherlands. 1996.
CP - COUNTRY OF PUBLICATION: Netherlands
PY - PUBLICATION YEAR: 1996
LA - LANGUAGE: English
AB - ABSTRACT: The island of Tobago occupies the eastern end of the central (igneous) belt of the Caribbean-South American plate boundary zone. Volcaniclastic sediment of the Albian ( approximately 100 Ma) Tobago Volcanic Group and dikes of similar age within it were sampled in two homoclinal sections with different attitudes. The mean of virtual geomagnetic poles for 12 sites (25.4 degrees N, 24.1 degrees E, A (sub 95) = 4.2 degrees ) is well defined, pre-tilting and apparently reliable, yet is far removed from a similar age reference pole for South America. Five other paleomagnetic studies of Cretaceous rocks from widely separated localities farther west in the plate boundary zone yield pole positions that are remarkably similar to the Tobago pole. Poles obtained from the Guajira Peninsula of Colombia, the islands of Aruba and Bonaire, and the Caribbean Mountains of Venezuela are among those that agree with the Tobago result. The paleolatitudes for study areas within the plate boundary zone are consistent with an origin on or near South America, yet the poles throughout the zone are rotated roughly 90 degrees . Dextral relative motion between the Caribbean and South American plates was probably responsible for the rotation.
DE - DESCRIPTORS: Albian-; Antilles-; Caribbean-Plate; Caribbean-region; Cretaceous-; dikes-; diorites-; igneous-rocks; intrusions-; Lesser-Antilles; Lower-Cretaceous; Mesozoic-; Middle-Cretaceous; paleomagnetism-; plate-boundaries; plate-rotation; plate-tectonics; plutonic-rocks; pole-positions; sedimentary-rocks; South-American-Plate; Tobago-; Tobago-Intrusive-Complex; Tobago-Volcanic-Group; Trinidad-and-Tobago; volcanic-rocks; West-Indies
CC - CATEGORY CODES: 18-Solid-earth-geophysics; 12-Stratigraphy
DT - DOCUMENT TYPE: Serial
BL - BIB LEVEL: Analytic
MC - MAP COORDINATES: LAT: N111500; N111500; LONG: W0604000; W0604000.
IL - ILLUSTRATION: Refs: 31; illus. incl. 3 tables, geol. sketch map.
RF - REFERENCE SOURCE: GeoRef, Copyright 2000, American Geological Institute. Reference includes data from CAPCAS, Elsevier Scientific Publishers, Amsterdam, Netherlands
IS - ISSN: 0012-821X
CO - CODEN: EPSLA2
AN - ACCESSION NUMBER: 1996-046729
UD - UPDATE CODE: 199616
Registro 4628 de 5614 - GeoRef Disc 4: 1993-1996
TI - TITLE: Chevron hunting Llanos giant in Colombia.
AU - AUTHORS: Anonymous
SO - SOURCE: Oil and Gas Journal. 94; 19, Pages 50. 1996.
PB - PUBLISHER: PennWell. Tulsa, OK, United States. 1996.
CP - COUNTRY OF PUBLICATION: United-States
PY - PUBLICATION YEAR: 1996
LA - LANGUAGE: English
DE - DESCRIPTORS: Colombia-; giant-fields; Llanos-; oil-and-gas-fields; petroleum-; petroleum-exploration; Rio-Blanco-Block; South-America
CC - CATEGORY CODES: 29A-Economic-geology,-geology-of-energy-sources
DT - DOCUMENT TYPE: Serial
BL - BIB LEVEL: Analytic
IL - ILLUSTRATION: sketch map.
RF - REFERENCE SOURCE: GeoRef, Copyright 2000, American Geological Institute.
IS - ISSN: 0030-1388
CO - CODEN: OIGJAV
AN - ACCESSION NUMBER: 1996-047167
UD - UPDATE CODE: 199616
Registro 4629 de 5614 - GeoRef Disc 4: 1993-1996
TI - TITLE: Palynology and paleobotany of the early Pliocene section Rio Frio 17 (Cordillera Oriental, Colombia); biostratigraphical and chronostratigraphical implications.
AU - AUTHORS: Wijninga-Vincent-M
AF - AUTHOR AFFILIATION: University of Amsterdam, Department of Palynology and Paleo/Actuo-Ecology, Amsterdam, Netherlands
SO - SOURCE: Review of Palaeobotany and Palynology. 92; 3-4, Pages 329-350. 1996.
PB - PUBLISHER: Elsevier. Amsterdam, Netherlands. 1996.
CP - COUNTRY OF PUBLICATION: Netherlands
PY - PUBLICATION YEAR: 1996
LA - LANGUAGE: English
AB - ABSTRACT: Organic-rich sediments of section Rio Frio 17 (3165 m altitude, Cordillera Oriental, Colombia) were analyzed for pollen and plant macrofossils. Time control is based on fission-track dating of zircon from an intercalated tephra with an age of 5.3+ or -1.0 Ma. Pollen and macrofossil spectra of several outcrops and cores, including section Rio Frio 17, reveal gradually cooler depositional environments during the Neogene. Obvious differences between modern and Pliocene Andean vegetation belts are taken into account. The sequence of outcrops reflects the final uplift of the Cordillera Oriental. Pollen and macrofossils of section Rio Frio 17 suggest that lower subandean (lower part of lower montane belt) to tropical lowland conditions prevailed in the area during the early Pliocene: sediment deposition occurred apparently at c. 1000 m elevation. If Pliocene average temperatures were comparable to present-day values with an amplitude of + or -3 degrees C, an altitudinal shift of 500 m maximum is suggested. Hence sedimentation is estimated to have occurred at 1500 m elevation maximally, based on the fossil plants and the present-day ecological requirements of their extant relatives. The remaining difference in elevation is attributed to tectonic uplift by at least 1700 m. The macrofossil evidence and the presence of Hedyosmum pollen suggest that the sediments of section Rio Frio 17 should be placed in Biozone II, instead of Biozone I of the biostratigraphical zonation for the high plain of Bogota as suggested by Helmens and Kuhry (1990). The arrival of Hedyosmum in the pollen record and the final uplift of the high plain of Bogota is now estimated at c. 5.3+ or -1.0 Ma. The age of the sediments of sections Salto de Tequendama I and II (Biozone I), estimated as early Pliocene by Van der Hammen et al. (1973), is earlier than that date. Selected plant macrofossils, such as seeds and fruits, are described and illustrated.
DE - DESCRIPTORS: Andes-; biostratigraphy-; Cenozoic-; chronostratigraphy-; Colombia-; developing-countries; Eastern-Cordillera; lower-Pliocene; microfossils-; Neogene-; palynomorphs-; Pliocene-; pollen-diagrams; South-America; Tertiary-
CC - CATEGORY CODES: 12-Stratigraphy
DT - DOCUMENT TYPE: Serial
BL - BIB LEVEL: Analytic
IL - ILLUSTRATION: Refs: 52; illus. incl. sect., 4 plates, 1 table, sketch map.
RF - REFERENCE SOURCE: GeoRef, Copyright 2000, American Geological Institute. Reference includes data from CAPCAS, Elsevier Scientific Publishers, Amsterdam, Netherlands
IS - ISSN: 0034-6667
CO - CODEN: RPPYAX
AN - ACCESSION NUMBER: 1996-051738
UD - UPDATE CODE: 199617
Registro 4630 de 5614 - GeoRef Disc 4: 1993-1996
TI - TITLE: Plateaux ancient and modern; geochemical and sedimentological perspectives on Archaean oceanic magmatism.
AU - AUTHORS: Kent-R-W; Hardarson-B-S; Saunders-A-D; Storey-M
AF - AUTHOR AFFILIATION: University of Edinburgh, Department of Geology and Geophysics, Grant Institute, Edinburgh, United Kingdom
BK - BOOK TITLE: In: Mafic magmatism through time.
BA - BOOK AUTHORS: Ludden-J-N (editor); Arndt-N-T (editor); Francis-D (editor)
SO - SOURCE: Lithos. 37; 2-3, Pages 129-142. 1996.
PB - PUBLISHER: Elsevier. Amsterdam, International. 1996.
CP - COUNTRY OF PUBLICATION: International
PY - PUBLICATION YEAR: 1996
CN - CONFERENCE INFORMATION: Symposium on Evolution of mafic magmatism through time. St. Malo, France. May 9-13, 1994.
LA - LANGUAGE: English
AB - ABSTRACT: Unequivocal examples of oceanic plateaux older than about 2.1 Ga have yet to be identified from the geological record. The most likely explanation for this is the partial dismemberment of ancient plateaux at convergent plate margins, and their subsequent juxtaposition in accretionary complexes with arc volcanic, sedimentary and plutonic rocks. A review of Cretaceous plateaux in the eastern Indian Ocean suggests that certain geochemical-isotopic criteria (e.g. positive Nb anomalies relative to primitive mantle) employed by petrologists to identify modern oceanic plateau lavas are of little practical use in distinguishing ancient plateau lavas from arc and volcanic rifted margin basalts. The extreme chemical and isotopic heterogeneity of Indian Ocean plateaux, together with large variations in area and volume, suggest that these edifices represent one extreme of a spectrum of oceanic plateau compositions. The other extreme, represented by Iceland and Ontong Java, is characterised by relatively homogeneous melt compositions, reflecting steady-state melting conditions and the absence of a continental lithosphere contaminant to plateau magmas. Crustal thickness and compositional estimates for Archaean oceanic plateaux using the McKenzie-Bickle method give a mean thickness of approximately 43 km, and mean MgO content of approximately 19 wt.%. Archaean plateaux were thus compositionally distinct from surrounding ocean floor (basaltic komatiite?), and notably more magnesian than plateaux such as Iceland (mean for Tertiary basalts = 6.3 wt.% MgO) and Ontong Java (mean for core samples = 6.9 wt.% MgO). By analogy with Cretaceous-Tertiary ultramafic complexes in western Colombia, the deeper portions of these plateaux may have consisted of noritic rocks, underlain by lherzolite, pyroxenite, gabbronorite and dunite. The general absence of such rocks in Archaean terrains suggests that these portions of plateaux are only rarely preserved. The search for remnants of ancient oceanic plateaux has identified examples of Archaean submarine lavas in the Canadian Shield (> or =2.7 Ga: southern Abitibi belt, Superior Province) and Kaapvaal craton of southern Africa (3.5-3.3 Ga: Barberton and Pietersberg belts). Chemical and isotopic data suggest that komatiite-tholeiite units from these areas were derived by partial melting of a plume or asthenospheric mantle source, but do not distinguish adequately the tectonic environment (rifted continental margin, ocean floor, oceanic plateau) in which these rocks were erupted. However, the uplift histories of these putative plateau fragments, as recorded in sediments bounding and intercalated with the komatiite-basalt sequences, appear to be broadly comparable to those of the best-documented Phanerozoic oceanic plateaux. Although further stratigraphical investigations of presumed plateaux (ancient and modern) are required to test this hypothesis, we believe that the sedimentary record offers the best evidence yet for the formation of oceanic plateaux as far back as the Mid-Archaean ( approximately 3.5 Ga).
DE - DESCRIPTORS: Abitibi-Belt; Africa-; alkaline-earth-metals; Archean-; basalts-; Canadian-Shield; crust-; East-Indian-Ocean; evolution-; flood-basalts; geochemistry-; igneous-rocks; Indian-Ocean; isotope-ratios; isotopes-; Kaapvaal-Craton; lead-; magmas-; melts-; metals-; niobium-; North-America; oceanic-crust; partial-melting; Pb-206-Pb-204; plateaus-; plumes-; Precambrian-; preservation-; radioactive-isotopes; sedimentary-rocks; Southern-Africa; Sr-87-Sr-86; stable-isotopes; strontium-; Superior-Province; volcanic-rocks
CC - CATEGORY CODES: 05A-Igneous-and-metamorphic-petrology; 02D-Isotope-geochemistry
DT - DOCUMENT TYPE: Serial; Conference-Document
BL - BIB LEVEL: Analytic
MC - MAP COORDINATES: LAT: S600000; N020000; LONG: E1200000; E0600000.
IL - ILLUSTRATION: Refs: 65; illus. incl. sect., 1 table, sketch maps.
RF - REFERENCE SOURCE: GeoRef, Copyright 2000, American Geological Institute. Reference includes data from CAPCAS, Elsevier Scientific Publishers, Amsterdam, Netherlands
IS - ISSN: 0024-4937
CO - CODEN: LITHAN
AN - ACCESSION NUMBER: 1996-052554
UD - UPDATE CODE: 199617
Registro 4631 de 5614 - GeoRef Disc 4: 1993-1996
TI - TITLE: The petrogenesis of Gorgona komatiites, picrites and basalts: new field, petrographic and geochemical constraints.
AU - AUTHORS: Kerr-A-C; Marriner-G-F; Arndt-N-T; Tarney-J; Nivia-A; Saunders-A-D; Duncan-R-A
AF - AUTHOR AFFILIATION: University of Leicester, Department of Geology, Leicester, United Kingdom
BK - BOOK TITLE: In: Mafic magmatism through time.
BA - BOOK AUTHORS: Ludden-J-N (editor); Arndt-N-T (editor); Francis-D (editor)
SO - SOURCE: Lithos. 37; 2-3, Pages 245-260. 1996.
PB - PUBLISHER: Elsevier. Amsterdam, International. 1996.
CP - COUNTRY OF PUBLICATION: International
PY - PUBLICATION YEAR: 1996
CN - CONFERENCE INFORMATION: Symposium on Evolution of mafic magmatism through time. St. Malo, France. May 9-13, 1994.
LA - LANGUAGE: English
AB - ABSTRACT: Gorgona Island, Colombia is remarkable not only because it contains the only Phanerozoic komatiites, but also because it has mafic to ultramafic lavas with a wide range of compositions, from moderately enriched to extremely depleted (relative to Bulk Earth). The komatiite flows are, in many respects similar to Archaean komatiites; they formed from MgO-rich (18%) liquids and have upper spinifex zones and lower cumulate zones. The cumulate zones of Archaean komatiites contain many solid grains, in contrast more than 90% of the olivine in the Gorgona cumulates is highly skeletal. This combined with the fact that the Gorgona cumulate zones are thinner than those in Archaean komatiites, suggests that the komatiite magma became strongly superheated en route to the surface. The komatiites have trace element contents intermediate between those of the basalts and the ultramafic tuffs. Some basalts have isotope compositions indicative of long-term enrichment in incompatible elements, whereas other basalts and ultramafic volcanics have isotopic signatures that imply corresponding depletion. It is apparent that the plume source region of the Gorgona magmas was markedly heterogeneous, with at least two source components contributing to the observed variation in composition. This heterogeneity may have resulted from the incorporation of different components into the plume source, or it may be the result of complex melting and melt extraction processes during the ascent of a heterogeneous plume. Despite earlier suggestions that there may have been a significant age gap between depleted komatiite and basalt flows and the enriched basalts, new (super 40) Ar- (super 39) Ar dating of basalts and gabbros are more consistent with all being generated at 87 Ma during formation of the Caribbean/Colombian plateau, possibly at the Galapagos hotspot.
DE - DESCRIPTORS: absolute-age; Ar-Ar; basalts-; Colombia-; Cretaceous-; cumulates-; dates-; field-studies; genesis-; geochemistry-; Gorgona-igneous-complex; Gorgona-Island; igneous-rocks; komatiite-; magmas-; Mesozoic-; petrography-; picrite-; plate-tectonics; plumes-; plutonic-rocks; South-America; trace-elements; ultramafics-; volcanic-rocks
CC - CATEGORY CODES: 02C-Geochemistry-of-rocks,-soils,-and-sediments; 05A-Igneous-and-metamorphic-petrology
DT - DOCUMENT TYPE: Serial; Conference-Document
BL - BIB LEVEL: Analytic
MC - MAP COORDINATES: LAT: N023000; N033000; LONG: W0780000; W0800000.
IL - ILLUSTRATION: Refs: 39; illus. incl. sect., 1 plate, 2 tables, geol. sketch map.
RF - REFERENCE SOURCE: GeoRef, Copyright 2000, American Geological Institute. Reference includes data from CAPCAS, Elsevier Scientific Publishers, Amsterdam, Netherlands
IS - ISSN: 0024-4937
CO - CODEN: LITHAN
AN - ACCESSION NUMBER: 1996-052560
UD - UPDATE CODE: 199617
Registro 4632 de 5614 - GeoRef Disc 4: 1993-1996
TI - TITLE: The changing course of the Orinoco River during the Neogene: a review.
AU - AUTHORS: Diaz-de-Gamero-Maria-L
AF - AUTHOR AFFILIATION: Universidad Central de Venezuela, Caracas, Venezuela
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