No. Registros Solicitud 1 5614 colombia

DE - DESCRIPTORS: aggradation-; Albian-; Andean-Orogeny; carbonate-rocks; Colombia-; Cretaceous-; cycles-; depositional-environment; eastern-Ecuador; Ecuador-; fluvial-environment; frequency-; limestone-; Lower-Cretaceous; Maranon-Basin; marine-environment; Mesozoic-; northeastern-Peru; Oriente-Basin; passive-margins; Peru-; plate-tectonics; progradation-; Putumayo-Basin; sea-level-changes; sedimentary-rocks; sequence-stratigraphy; shelf-environment; South-America; southeastern-Colombia; stratigraphic-boundary; terrestrial-environment; transgression-; Vivian-Formation

CC - CATEGORY CODES: 12-Stratigraphy

DT - DOCUMENT TYPE: Abstract; Serial; Conference-Document

BL - BIB LEVEL: Analytic

RF - REFERENCE SOURCE: GeoRef, Copyright 2000, American Geological Institute. Reference includes data supplied by American Association of Petroleum Geologists, Tulsa, OK, United States

IS - ISSN: 0149-1423

CO - CODEN: AABUD2

AN - ACCESSION NUMBER: 1996-072231

UD - UPDATE CODE: 199622

Registro 4671 de 5614 - GeoRef Disc 4: 1993-1996

TI - TITLE: Identifying structural styles in Colombia.

AU - AUTHORS: Wilson-Wayne-P; van-Nieuwenhuise-R-E; Steuer-Mark-R; Ojeda-German

AF - AUTHOR AFFILIATION: Amoco, Houston, TX, United States

BK - BOOK TITLE: In: AAPG international conference and exhibition; abstracts.

BA - BOOK AUTHORS: Anonymous

SO - SOURCE: AAPG Bulletin. 80; 8, Pages 1345-1346. 1996.

PB - PUBLISHER: American Association of Petroleum Geologists. Tulsa, OK, United States. 1996.

CP - COUNTRY OF PUBLICATION: United-States

PY - PUBLICATION YEAR: 1996

CN - CONFERENCE INFORMATION: AAPG international conference and exhibition. Caracas, Venezuela. Sept. 8-11, 1996.

LA - LANGUAGE: English

AB - ABSTRACT: Much of our understanding of the earth is from the study of surface geology and seismic, but many surface structures are responses to deformation which occurred below sedimentary layers. The practice within the petroleum industry is to use top-down processes of analyzing the surface to understand the subsurface, and observed surface structural styles tend to influence seismic interpretations. Yet many conditions which influenced the structural styles seen at the surface are different at depth. Since seismic is a time representation of the earth, many interpretation pitfalls may exist within areas of complex geology. Also, its reliability decreases with depth and with increasing geologic complexity. Forward modeling and pre-stack depth migration technologies are used to provide true depth images of the seismic data. Even with these advances in seismic imaging technology, the interpreter needs to incorporate additional data into the interpretation. Accurate structural identification requires the interpreter to integrate seismic with surface geology, remote sensing, gravity, magnetic data, geochemistry, fault-plane solutions from earthquakes, and regional tectonic studies. Incorporating these types of data into the interpretation will help us learn how basement is involved in the deformation of overlying sediments. A study of the Eastern Cordillera of Colombia shows the deformation to be dominantly transpressional in style. Euler deconvolution of the aeromagnetic data shows a highly fractured basement, steep fault lineaments, en echelon structures, and complex fault patterns, all of which would be typical of wrench-type deformation. Available surface geology, regional studies, earthquake data, and forward modeling support this interpretation.

DE - DESCRIPTORS: Andes-; basement-tectonics; Colombia-; deformation-; direct-problem; earthquakes-; Eastern-Cordillera; faults-; geochemistry-; geophysical-methods; geophysical-surveys; gravity-methods; interpretation-; lineaments-; magnetic-methods; patterns-; petroleum-; remote-sensing; seismic-methods; seismic-migration; seismotectonics-; South-America; surveys-; tectonics-; transpression-

CC - CATEGORY CODES: 29A-Economic-geology,-geology-of-energy-sources; 20-Applied-geophysics

DT - DOCUMENT TYPE: Abstract; Serial; Conference-Document

BL - BIB LEVEL: Analytic

RF - REFERENCE SOURCE: GeoRef, Copyright 2000, American Geological Institute. Reference includes data supplied by American Association of Petroleum Geologists, Tulsa, OK, United States

IS - ISSN: 0149-1423

CO - CODEN: AABUD2

AN - ACCESSION NUMBER: 1996-072248

UD - UPDATE CODE: 199622

Registro 4672 de 5614 - GeoRef Disc 4: 1993-1996

TI - TITLE: Detailed lithostratigraphy and age determinations of La Luna Formation in two sections of SW Tachira State (Venezuela).

AU - AUTHORS: Yoris-F-G; Ostos-M; Boujana-M; Perez-J; Booth-G; Packer-S; Galea-F; Lander-R

AF - AUTHOR AFFILIATION: EIG Litos, Caracas, Venezuela

BK - BOOK TITLE: In: AAPG international conference and exhibition; abstracts.

BA - BOOK AUTHORS: Anonymous

SO - SOURCE: AAPG Bulletin. 80; 8, Pages 1346. 1996.

PB - PUBLISHER: American Association of Petroleum Geologists. Tulsa, OK, United States. 1996.

CP - COUNTRY OF PUBLICATION: United-States

PY - PUBLICATION YEAR: 1996

CN - CONFERENCE INFORMATION: AAPG international conference and exhibition. Caracas, Venezuela. Sept. 8-11, 1996.

LA - LANGUAGE: English

AB - ABSTRACT: The La Luna Formation crops out almost completely at Las Delicias Bramon road, near the Colombia-Venezuela border, and at La Ortiza creek near San Cristobal, capital city of Tachira State. The distance between these two sections is close to 35 km, and we have found similar thicknesses in both of them: 192 m (Las Delicias) and 188 m (La Ortiza). The lower contacts with the Capacho Formation seem to be concordant in mesoscopic scale but we do not discard some condensation. The upper contacts in both sections are transitional with the black shales of Colon Formation, increasing slowly the proportion of fine clastic sediments and diminishing the proportion of chert and siliceous mudstones; we cannot correlate the Tres Esquinas Member with any specific phosphatic bed or interval; the presence of primary structures with SW migration trend of bedforms and paleocurrent indicators along the cherty beds (Ftanita del Tachira Member, close to 97 m thick at both sections) and upper-transitional interval to Colon Formation, reveals that neither the "cherts" nor the phosphatic/glauconitic beds are all deposited in "quiet" environment and that any conclusion about the possibility of "slow rate" deposition environments need still more sedimentological, geochemical and biostratigraphic support. The general age for the La Luna Formation is Late Cenomanian to Campanian (Las Delicias) and Coniacian to early Maastrichtian(?) (La Ortiza).

DE - DESCRIPTORS: bedforms-; black-shale; Campanian-; Capacho-Formation; Cenomanian-; chemically-precipitated-rocks; chert-; clastic-rocks; clastic-sediments; Colon-Formation; Coniacian-; Cretaceous-; Ftanita-del-Tachira-Member; La-Luna-Formation; La-Ortiza-Creek; lithostratigraphy-; Maestrichtian-; Mesozoic-; migration-; outcrops-; paleocurrents-; San-Cristobal-Venezuela; sedimentary-rocks; sedimentation-; sedimentation-rates; sediments-; Senonian-; siliceous-composition; South-America; Tachira-Venezuela; thickness-; Tres-Esquinas-Member; Upper-Cretaceous; Venezuela-

CC - CATEGORY CODES: 12-Stratigraphy

DT - DOCUMENT TYPE: Abstract; Serial; Conference-Document

BL - BIB LEVEL: Analytic

RF - REFERENCE SOURCE: GeoRef, Copyright 2000, American Geological Institute. Reference includes data supplied by American Association of Petroleum Geologists, Tulsa, OK, United States

IS - ISSN: 0149-1423

CO - CODEN: AABUD2

AN - ACCESSION NUMBER: 1996-072250

UD - UPDATE CODE: 199622

Registro 4673 de 5614 - GeoRef Disc 4: 1993-1996

TI - TITLE: Hydrocarbon systems in the Southwest Maracaibo Basin, Colombia.

AU - AUTHORS: Yurewicz-Donald-A; Advocate-David-M; Sequeira-Jose-J; McDermott-Vince-J; Young-Raymond-H; Wellman-Paul-C; Hernandez-Edgar

AF - AUTHOR AFFILIATION: Exxon Exploration Company, Houston, TX, United States

BK - BOOK TITLE: In: AAPG international conference and exhibition; abstracts.

BA - BOOK AUTHORS: Anonymous

SO - SOURCE: AAPG Bulletin. 80; 8, Pages 1346-1347. 1996.

PB - PUBLISHER: American Association of Petroleum Geologists. Tulsa, OK, United States. 1996.

CP - COUNTRY OF PUBLICATION: United-States

PY - PUBLICATION YEAR: 1996

CN - CONFERENCE INFORMATION: AAPG international conference and exhibition. Caracas, Venezuela. Sept. 8-11, 1996.

LA - LANGUAGE: English

AB - ABSTRACT: Multiple hydrocarbon systems are recognized in the Colombian portion of the Maracaibo Basin (Catatumbo subbasin). Hydrocarbons, trapped in wrench controlled, faulted anticlines, were generated from two different source horizons, in two distinct source kitchens, and migrated along different pathways into Cretaceous and Tertiary reservoirs. Cretaceous reservoirs are shallow-marine sandstones and limestones characterized by low matrix porosity and permeability. They are separated from Tertiary reservoirs by a thick shale seal that limited cross-stratal migration. Tertiary reservoirs are fluvial-deltaic sandstones with good to excellent porosities and permeabilities. Geochemical data suggest the presence of two oil families. Family 1 oils were sourced locally from Cretaceous marine shales and limestones and account for most of the oil in Tertiary and Cretaceous reservoirs. Family 2 oils are only present in Tertiary reservoirs in the southern part of the subbasin, and are interpreted to be sourced from Paleocene terrestrial shales and coals. Two distinct migration systems operated to fill Catatumbo traps. Family I oils migrated from local Cretaceous source beds along fractures and faults that developed concurrently with trap formation. Family 2 oils were sourced from outside the Catatumbo subbasin. Maturation data and burial history modelling indicate that Paleocene rocks are immature in the Catatumbo subbasin. Maturation levels increase westward into the Maracaibo Basin and along the axis of the North Andean foredeep. The proximity of Rio Zulia Field to the North Andean foredeep, and lack of Tertiary-sourced oils in other Catatumbo fields suggest that the North Andean foredeep is the primary source for these oils.

DE - DESCRIPTORS: Andes-; anticlines-; carbonate-rocks; Catatumbo-Subbasin; Cenozoic-; clastic-rocks; coal-; Colombia-; Cretaceous-; deltaic-environment; evolution-; faults-; fluvial-environment; folds-; fractures-; genesis-; geochemistry-; limestone-; Maracaibo-Basin; marine-environment; matrix-; maturity-; Mesozoic-; migration-; organic-residues; permeability-; petroleum-; porosity-; reservoir-rocks; sandstone-; sedimentary-rocks; shale-; shallow-water-environment; source-rocks; South-America; structural-traps; terrestrial-environment; Tertiary-; traps-; Venezuela-; wrench-faults

CC - CATEGORY CODES: 29A-Economic-geology,-geology-of-energy-sources

DT - DOCUMENT TYPE: Abstract; Serial; Conference-Document

BL - BIB LEVEL: Analytic

RF - REFERENCE SOURCE: GeoRef, Copyright 2000, American Geological Institute. Reference includes data supplied by American Association of Petroleum Geologists, Tulsa, OK, United States

IS - ISSN: 0149-1423

CO - CODEN: AABUD2

AN - ACCESSION NUMBER: 1996-072252

UD - UPDATE CODE: 199622

Registro 4674 de 5614 - GeoRef Disc 4: 1993-1996

TI - TITLE: The oil and gas potential of southern Bolivia; contributions from a dual source rock system.

AU - AUTHORS: Hartshorn-Kelly-G

AF - AUTHOR AFFILIATION: Chevron Petroleum Company of Colombia, Santafe de Bogota, Colombia

BK - BOOK TITLE: In: AAPG international conference and exhibition; abstracts.

BA - BOOK AUTHORS: Anonymous

SO - SOURCE: AAPG Bulletin. 80; 8, Pages 1299-1300. 1996.

PB - PUBLISHER: American Association of Petroleum Geologists. Tulsa, OK, United States. 1996.

CP - COUNTRY OF PUBLICATION: United-States

PY - PUBLICATION YEAR: 1996

CN - CONFERENCE INFORMATION: AAPG international conference and exhibition. Caracas, Venezuela. Sept. 8-11, 1996.

LA - LANGUAGE: English

AB - ABSTRACT: The southern Sub-Andean and Chaco basins of Bolivia produce oil, gas and condensate from reservoirs ranging from Devonian to Tertiary in age. Geochemical evidence points to contributions from two Paleozoic source rocks: the Devonian Los Monos Formation and the Silurian Kirusillas Formation Rock-eval pyrolysis, biomarker data, microscopic kerogen analysis, and burial history modeling are used to assess the quality, distribution, and maturity of both source rock systems. The geochemical results are then integrated with the structural model for the area in order to determine the most likely pathways for migration of oil and gas in the thrust belt and its foreland. Geochemical analysis and modeling show that the primary source rock, shales of the Devonian Los Monos Formation, entered the oil window during the initial phase of thrusting in the sub-Andean belt. This provides ideal timing for oil accumulation in younger reservoirs of the thrust belt. The secondary source rock, although richer, consumed most of its oil generating capacity prior to the development of the thrust related structures. Depending on burial depth and location, however, the Silurian source still contributes gas, and some oil to traps in the region.

DE - DESCRIPTORS: Andes-; biomarkers-; Bolivia-; Chaco-Basin; clastic-rocks; condensates-; Devonian-; evolution-; faults-; genesis-; geochemistry-; kerogen-; Kirusillas-Formation; Los-Monos-Formation; maturity-; migration-; models-; natural-gas; organic-compounds; organic-materials; Paleozoic-; petroleum-; petroleum-accumulation; possibilities-; pyrolysis-; reservoir-rocks; Rock-Eval; sedimentary-rocks; shale-; Silurian-; source-rocks; South-America; southern-Bolivia; structural-traps; thrust-faults; traps-

CC - CATEGORY CODES: 29A-Economic-geology,-geology-of-energy-sources

DT - DOCUMENT TYPE: Abstract; Serial; Conference-Document

BL - BIB LEVEL: Analytic

RF - REFERENCE SOURCE: GeoRef, Copyright 2000, American Geological Institute. Reference includes data supplied by American Association of Petroleum Geologists, Tulsa, OK, United States

IS - ISSN: 0149-1423

CO - CODEN: AABUD2

AN - ACCESSION NUMBER: 1996-072261

UD - UPDATE CODE: 199622

Registro 4675 de 5614 - GeoRef Disc 4: 1993-1996

TI - TITLE: Low porosity/ high permeability, deeply-buried reservoirs of the Cusiana Field, Llanos foothills, eastern Colombia; controls on reservoir quality.

AU - AUTHORS: Pulham-Andrew-J; Warren-Edward; Naar-Joaquin

AF - AUTHOR AFFILIATION: University of Colorado, Boulder, CO, United States

BK - BOOK TITLE: In: AAPG international conference and exhibition; abstracts.

BA - BOOK AUTHORS: Anonymous

SO - SOURCE: AAPG Bulletin. 80; 8, Pages 1326. 1996.

PB - PUBLISHER: American Association of Petroleum Geologists. Tulsa, OK, United States. 1996.

CP - COUNTRY OF PUBLICATION: United-States

PY - PUBLICATION YEAR: 1996

CN - CONFERENCE INFORMATION: AAPG international conference and exhibition. Caracas, Venezuela. Sept. 8-11, 1996.

LA - LANGUAGE: English

AB - ABSTRACT: The Cusiana Field is a thrust-related anticline located on the eastern edge of the Eastern Cordillera of the Colombian Andes. It comprises three clastic reservoirs: lower Tertiary Mirador and Barco Formations and the Santonian-Campanian Guadalupe Formation. Sandstone porosity is generally low, averaging approximately 8% in the Mirador and Barco; and approximately 15% in the Guadalupe. Despite such low porosities, permeabilities are excellent and can exceed 1000mD. Detailed petrographic, sedimentological and biostratigraphic analyses have been used to identify the controls and distribution of porosity within the Cusiana Field. The majority of the reservoir sandstones in Cusiana are near pure quartz arenites cemented by blocky, euhedral quartz overgrowths. Other cement phases, including kaolinite, are minor. The low porosity values throughout the reservoirs can be simply explained by compactional loss and relatively hot cementation by quartz during deep burial (>20,000 feet) The exception to the pure quartz arenites are zones in the Guadalupe reservoir that contain significant quantities (up to 20%) of detrital phosphate. These phosphatic sandstones lack the blocky quartz cements, contain pore lining microcrystalline quartz cement, minor calcite and clays (kaolinite and chlorite). They also have the best porosities (up to 22%). There is a direct relationship between presence and quantity of phosphate in the Guadalupe reservoir and increased reservoir quality. The Cusiana reservoirs provide a good case study of porosity evolution in deeply buried, quartz-rich sandstones and the contrasts that can occur when a non-quartz component to the sandstones is introduced.

DE - DESCRIPTORS: Andes-; anticlines-; arenite-; Barco-Formation; biostratigraphy-; Campanian-; cement-; cementation-; Cenozoic-; clastic-rocks; Colombia-; controls-; Cretaceous-; Cusiana-Field; diagenesis-; eastern-Colombia; Eastern-Cordillera; Eocene-; faults-; folds-; Guadalupe-Formation; Llanos-; lower-Tertiary; Mesozoic-; Mirador-Formation; oil-and-gas-fields; Paleogene-; permeability-; petrography-; petroleum-; porosity-; quartz-arenite; reservoir-rocks; sandstone-; Santonian-; sedimentary-rocks; Senonian-; South-America; structural-traps; Tertiary-; thrust-faults; traps-; Upper-Cretaceous

CC - CATEGORY CODES: 29A-Economic-geology,-geology-of-energy-sources

DT - DOCUMENT TYPE: Abstract; Serial; Conference-Document

BL - BIB LEVEL: Analytic

RF - REFERENCE SOURCE: GeoRef, Copyright 2000, American Geological Institute. Reference includes data supplied by American Association of Petroleum Geologists, Tulsa, OK, United States

IS - ISSN: 0149-1423

CO - CODEN: AABUD2

AN - ACCESSION NUMBER: 1996-072267

UD - UPDATE CODE: 199622

Registro 4676 de 5614 - GeoRef Disc 4: 1993-1996

TI - TITLE: The Garzon Fault; active southwestern boundary of the Caribbean Plate in Colombia.

AU - AUTHORS: Chorowicz-J; Chotin-P; Guillande-R

AF - AUTHOR AFFILIATION: Univ. Pierre et Marie Curie, Lab. Geomorph.-Geol. Struct. Teledetection, URA 1759, Paris, France

BK - BOOK TITLE: In: Fractals in geoscience.

BA - BOOK AUTHORS: Kruhl-H (editor); Kuempel-H-J (editor)

SO - SOURCE: Geologische Rundschau. 85; 1, Pages 172-179. 1996.

PB - PUBLISHER: Springer International. Berlin, Federal Republic of Germany. 1996.

CP - COUNTRY OF PUBLICATION: Federal-Republic-of-Germany

PY - PUBLICATION YEAR: 1996

CN - CONFERENCE INFORMATION: Second international conference on Fractals and dynamic systems in geoscience. Gelnhausen, Federal Republic of Germany. April 1995.

LA - LANGUAGE: English

DE - DESCRIPTORS: active-margins; Algeciras-Basin; Andes-; basins-; Caribbean-Plate; Caribbean-region; Cenozoic-; Colombia-; deformation-; faults-; fracture-zones; Garzon-Fault; geodynamics-; image-analysis; plate-tectonics; Quaternary-; remote-sensing; satellite-methods; scale-models; sedimentary-basins; shear-; South-America; SPOT-

CC - CATEGORY CODES: 16-Structural-geology

DT - DOCUMENT TYPE: Serial; Conference-Document

BL - BIB LEVEL: Analytic

IL - ILLUSTRATION: Refs: 25; illus. incl. geol. sketch maps.

RF - REFERENCE SOURCE: GeoRef, Copyright 2000, American Geological Institute. Reference includes data from Geoline, Bundesanstalt fur Geowissenschaften und Rohstoffe, Hanover, Germany

IS - ISSN: 0016-7835

CO - CODEN: GERUA3

AN - ACCESSION NUMBER: 1996-073116

UD - UPDATE CODE: 199622

Registro 4677 de 5614 - GeoRef Disc 4: 1993-1996

TI - TITLE: Presence of stratigraphic traps in the back arc basins of the southern shelf of Cuba.

AU - AUTHORS: Rodriguez-Rodobaldo; Dominguez-Rene; Touset-Sonia

AF - AUTHOR AFFILIATION: Geophisical Enterprise, Havana, Cuba

BK - BOOK TITLE: In: AAPG Gulf Coast Association of Geological Societies meeting; abstracts.

BA - BOOK AUTHORS: Anonymous

SO - SOURCE: AAPG Bulletin. 80; 9, Pages 1511-1512. 1996.

PB - PUBLISHER: American Association of Petroleum Geologists. Tulsa, OK, United States. 1996.

CP - COUNTRY OF PUBLICATION: United-States

PY - PUBLICATION YEAR: 1996

CN - CONFERENCE INFORMATION: AAPG Gulf Coast Association of Geological Societies. San Antonio, TX, United States. Oct. 2-4, 1996.

LA - LANGUAGE: English

AB - ABSTRACT: For the last ten years the southern shelf of Cuba has been the object of seismic investigations, mainly in the Ana Maria and Guacanayabo areas. More than 4000 km of seismic lines with 3000 % had been shot. These seismic surveys had confirmed the following geological events: 1. Presence of backarc extensional basins as a result of the ocean-ocean subduction. These basins started to form since Middle Cretaceous; 2. Presence of sedimentary sequences which change in thickness between 3.0-7.0 km; 3. Predominance of the extensional regime since Middle Cretaceous with subsidence, accommodation and extending of the sediments; 4. Development of stratigraphic traps, mainly associated with reef facies and slope fans of Late Cretaeous-early Tertiary. These traps can reach some hundred square kilometers. They have very clear dynamic expression in the seismic section and usually form anomaly zones. Over these seismic anomalies some reverberation can be observed which could be related to hydrocarbon flows. The depth of the traps changes between 1.5-3.5 km. More than thirty of them have been localized. 5. Probably a wrench tectonic interested these basins since Middle Eocene; 6. In some wells has been found oil and gas seeps as well as seal sequences; 7. According to their origin and evolution they can be similar to the great oil basins of the Venezuela and Colombia.

DE - DESCRIPTORS: Antilles-; back-arc-basins; basins-; Caribbean-region; Cenozoic-; continental-shelf; Cretaceous-; crust-; Cuba-; evolution-; extension-tectonics; faults-; gas-seeps; geophysical-methods; geophysical-surveys; Greater-Antilles; lithofacies-; lower-Tertiary; Mesozoic-; Middle-Cretaceous; migration-; oceanic-crust; oil-seeps; petroleum-; plate-tectonics; reefs-; seismic-anomalies; seismic-methods; southern-Cuba; stratigraphic-traps; subduction-; subsidence-; surveys-; tectonics-; Tertiary-; thickness-; traps-; Upper-Cretaceous; West-Indies; wrench-faults

CC - CATEGORY CODES: 29A-Economic-geology,-geology-of-energy-sources

DT - DOCUMENT TYPE: Abstract; Serial; Conference-Document

BL - BIB LEVEL: Analytic

RF - REFERENCE SOURCE: GeoRef, Copyright 2000, American Geological Institute. Reference includes data supplied by American Association of Petroleum Geologists, Tulsa, OK, United States

IS - ISSN: 0149-1423

CO - CODEN: AABUD2

AN - ACCESSION NUMBER: 1996-073612

UD - UPDATE CODE: 199622

Registro 4678 de 5614 - GeoRef Disc 4: 1993-1996

TI - TITLE: Regional patterns of well drained upland soil differentiation in the middle Caqueta Basin of Colombian Amazonia.

AU - AUTHORS: Lips-Johanna-M; Duivenvoorden-Joost-F

AF - AUTHOR AFFILIATION: University of Amsterdam, Landscape and Environmental Research Group, Amsterdam, Netherlands

SO - SOURCE: Geoderma. 72; 3-4, Pages 219-257. 1996.

PB - PUBLISHER: Elsevier. Amsterdam, Netherlands. 1996.

CP - COUNTRY OF PUBLICATION: Netherlands

PY - PUBLICATION YEAR: 1996

LA - LANGUAGE: English

AB - ABSTRACT: As part of a land-ecological survey of the middle Caqueta basin in Colombian Amazonia, a total of 41 well drained upland soil profiles under primary rain forest was studied. Two soil groups were recognised on the basis of principal components analysis (PCA). Soils pertaining to the first group cover about 45-60% of the well drained uplands and classify as Alisols and Acrisols. They are characterised by fine textured, reddish B horizons, and are low in exchangeable bases, but high in exchangeable Al. Furthermore, they contain relatively high total nutrient reserves. Soils pertaining to the second group cover about 35-50% of the well drained uplands and classify as Acrisols and Ferralsols. These soils are characterised by medium textured, yellowish B horizons within 100 cm depth, are low in exchangeable bases and Al, and show very low total nutrient reserves. The soils of the Ali-Acrisol group are mostly developed in Andean-origin deposits of the low terraces of the Caqueta River and the Tertiary Pebas formation. The soils of the Acri-Ferralsol group are mostly developed on shield-derived medium to coarse textured Tertiary deposits and are also found on Palaeozoic sandstone outcrops. The differences between the soils of the two groups are, therefore, principally related to variation in the parent materials and reflect the principal geological structure of the middle Caqueta area. A similar kind of well drained upland soil differentiation is found in the Colombian Amazon area as a whole, including footslope areas near the Andes, and probably also in adjacent parts of Peru and Brazil. The presence of the soils of the Acri-Ferralsol group in the middle Caqueta area and in NW Amazonia is in conflict with general statements that well drained upland soils in upper Amazonia would be less weathered than those from central or eastern Amazonia. The reddish or yellowish colour of the B horizon within a depth of 100 cm provides a practical field characteristic to distinguish the two groups of soils. The colour of the B horizons seems mainly related to dynamics of the soil organic matter. In sandy profiles of the soils from the Acri-Ferralsol group a slight degree of podzolisation may occur in the topsoil. Current international soil classification systems do not adequately separate the two well drained upland soil groups in the middle Caqueta area, because total nutrient reserves are not sufficiently incorporated and too much emphasis is laid on the presence of a clay increase.