No. Registros Solicitud 1 5614 colombia

IS - ISSN: 0370-3908

CO - CODEN: RCCFAO

AN - ACCESSION NUMBER: 2004-003159

UD - UPDATE CODE: 200401

Registro 235 de 5614 - GeoRef : 2002-2004/12

TI - TITLE: Regiones de mayor riesgo volcanico de America del Sur

Translated Title: Regions of greater volcanic risk in South America.

AU - AUTHORS: Gonzalez-Ferran-O

AF - AUTHOR AFFILIATION: Universidad de Chile, Departamento de Geologia y Geofisica, CHL, Chile

BK - BOOK TITLE: In: Simposio sobre el peligro y riesgo sismico y volcanico en America del Sur--Symposium on Seismic and volcanic hazard and risk in South America.

BA - BOOK AUTHORS: Giesecke-M-Alberto (editor)

SO - SOURCE: Earthquake Mitigation Program in the Andean Region (Project SISRA). 14; Pages 421-432. 1985.

PB - PUBLISHER: CERESIS (Centro Regional de Sismologia para America del Sur). Lima, Peru. 1985.

CP - COUNTRY OF PUBLICATION: Peru

PY - PUBLICATION YEAR: 1985

CN - CONFERENCE INFORMATION: Simposio sobre el peligro y riesgo sismico y volcanico en America del Sur. San Juan, Argentina. Sept. 24-28, 1984.

LA - LANGUAGE: Spanish

LS - LANGUAGE OF SUMMARY: English

AB - ABSTRACT: Holocenic volcanism in South America is located along some 3680 kilometers, distributed in three important segments or belts on the occidental andean side of the continental American plate and are closely linked to the dynamic subduction processes of the Nazca Plate. These segments are: A. the northern Colombia-Ecuadorean chain, about 680 kilometers long; B. the Central Andes chain in Chile and Peru, about 1360 Km. long and C. The Meridional chain of Central and South Chile, some 1440 Km long. 128 active volcanoes have been identified in these chains, with a total of 514 eruptions recorded since year 1500, which number represents only 9.5% of the active volcanoes and total eruptions which have occurred historically throughout the world. The Colombia-Ecuadorean chain, with 12 active volcanoes concentrates 35.5% of the eruptions, with an explosive index which reaches 65.5% of the total activity, equal to or greater than 3, which has occurred along the subduction zone of the Nazca Plate. This is followed by the Central and South Chile chain, where the eruptive activity generated by 19 volcanos, in the last 100 years, is 52.5% with an explosive index of 31.5%. Almost 50% of the values indicated correspond to specific eruptive regions such as Reventador, Cotopaxi, Quizapu, Llaima, Villarrica and Hudson, making these the regions of greatest volcanic hazard. Considering the high density of population and of human activity which has developed around these regions, they can be considered the areas of the highest volcanic risk in South America.

DE - DESCRIPTORS: Andes-; Antofagasta-Chile; Cenozoic-; chemical-composition; Chile-; Colombia-; Cotopaxi-; earthquakes-; Ecuador-; eruptions-; explosive-eruptions; Galeras-; geologic-hazards; Holocene-; Hudson-; igneous-rocks; island-arcs; Lascar-; Llaima-; mineral-composition; Nazca-Plate; Peru-; plate-tectonics; pyroclastics-; Quaternary-; Quizapu-; Reventador-; risk-assessment; Sangay-; seismicity-; South-America; statistical-analysis; subduction-zones; tectonics-; Villarrica-; volcanic-earthquakes; volcanic-risk; volcanic-rocks; volcanism-; volcanoes-

CC - CATEGORY CODES: 22-Environmental-geology; 24-Quaternary-geology

DT - DOCUMENT TYPE: Serial; Conference-Document

BL - BIB LEVEL: Analytic

MC - MAP COORDINATES: LAT: S020000; N060000; LONG: W0750000; W0800000.

LAT: S240000; S160000; LONG: W0670000; W0720000.

LAT: S430000; S310000; LONG: W0690000; W0720000.

IL - ILLUSTRATION: Refs: 11; illus. incl. 5 tables, geol. sketch map.

RF - REFERENCE SOURCE: GeoRef, Copyright 2004, American Geological Institute.

CO - CODEN: #06339

AN - ACCESSION NUMBER: 2004-003052

UD - UPDATE CODE: 200401

Registro 236 de 5614 - GeoRef : 2002-2004/12

TI - TITLE: Sismos y riesgo sismico en Colombia

Translated Title: Earthquakes and seismic risk in Colombia.

AU - AUTHORS: Sarria-Molina-Alberto

AF - AUTHOR AFFILIATION: Universidad de Los Andes, Ingenieria Civil, Bogota, Colombia

BK - BOOK TITLE: In: Simposio sobre el peligro y riesgo sismico y volcanico en America del Sur--Symposium on Seismic and volcanic hazard and risk in South America.

BA - BOOK AUTHORS: Giesecke-M-Alberto (editor)

SO - SOURCE: Earthquake Mitigation Program in the Andean Region (Project SISRA). 14; Pages 330-371. 1985.

PB - PUBLISHER: CERESIS (Centro Regional de Sismologia para America del Sur). Lima, Peru. 1985.

CP - COUNTRY OF PUBLICATION: Peru

PY - PUBLICATION YEAR: 1985

CN - CONFERENCE INFORMATION: Simposio sobre el peligro y riesgo sismico y volcanico en America del Sur. San Juan, Argentina. Sept. 24-28, 1984.

LA - LANGUAGE: Spanish

LS - LANGUAGE OF SUMMARY: English

AB - ABSTRACT: The Presidential Decree of June 7, 1984, makes it obligatory to use the Earthquake Resistant Building Code in Colombia. This paper summarizes some of the background work that led to the Code, the limitations of the Code and necessary future work. Project SISRA provided a good deal of the reference information consulted in preparing the Seismic Zoning map of Colombia. Thus, in Colombia, the results of Project SISRA have been of immediate value and have been put to good use. The part of the Code that deals with the seismicity covers both historic and instrumental. Seismogenic sources refers to zones or volumes of the lithosphere where destructive earthquakes have originated. The section dealing with normalization presents some basic aspects; it is the norm for earthquake resistant design. The parts that deals with instrumentation shows the precarious distribution of instruments, both teleseismic and accelerographs. The paper concludes with some specific recommendations.

DE - DESCRIPTORS: accelerometers-; Andes-; Benioff-zone; buildings-; cartography-; catalogs-; Colombia-; compression-; construction-; deformation-; earthquakes-; epicenters-; faults-; focus-; geologic-hazards; instruments-; legislation-; magnitude-; mapping-; movement-; Nazca-Plate; nomenclature-; Northern-Andes; plate-tectonics; risk-assessment; segmentation-; seismic-intensity; seismic-networks; seismic-risk; seismic-zoning; seismicity-; seismology-; seismotectonics-; South-America; spatial-distribution; statistical-analysis; subduction-zones; systems-; tectonics-

CC - CATEGORY CODES: 19-Seismology; 22-Environmental-geology

DT - DOCUMENT TYPE: Serial; Conference-Document

BL - BIB LEVEL: Analytic

MC - MAP COORDINATES: LAT: N010000; N080000; LONG: W0740000; W0780000.

IL - ILLUSTRATION: Refs: 13; illus. incl. geol. sketch maps.

RF - REFERENCE SOURCE: GeoRef, Copyright 2004, American Geological Institute.

CO - CODEN: #06339

AN - ACCESSION NUMBER: 2004-003048

UD - UPDATE CODE: 200401

Registro 237 de 5614 - GeoRef : 2002-2004/12

TI - TITLE: Segmentacion volcano-tectonica de los Andes septentrionales

Translated Title: Volcano-tectonic segmentation of the Northern Andes.

AU - AUTHORS: Hall-Minard-L; Wood-Charles-A

AF - AUTHOR AFFILIATION: Escuela Politecnica Nacional, Instituto Geofisico, Quito, Ecuador

BK - BOOK TITLE: In: Simposio sobre el peligro y riesgo sismico y volcanico en America del Sur--Symposium on Seismic and volcanic hazard and risk in South America.

BA - BOOK AUTHORS: Giesecke-M-Alberto (editor)

SO - SOURCE: Earthquake Mitigation Program in the Andean Region (Project SISRA). 14; Pages 270-283. 1985.

PB - PUBLISHER: CERESIS (Centro Regional de Sismologia para America del Sur). Lima, Peru. 1985.

CP - COUNTRY OF PUBLICATION: Peru

PY - PUBLICATION YEAR: 1985

CN - CONFERENCE INFORMATION: Simposio sobre el peligro y riesgo sismico y volcanico en America del Sur. San Juan, Argentina. Sept. 24-28, 1984.

LA - LANGUAGE: Spanish

LS - LANGUAGE OF SUMMARY: English

AB - ABSTRACT: On the basis of information obtained from Landsat images, published geologic and geophysical data and on field work, a model is presented for the volcano-tectonic segmentation of the northern Andes. The model is based on the concept given by Carr (1973), in the which the distribution of the volcanoes in an arc reflects the fundamental fractures of the continental crust controlled by tearing or other structures of the subducted plate. Therefore, the structural characteristics in the oceanic plate as well as in the shifted continental plate greatly influence the superficial geology. Seven principal boundaries are recognized which divide the northern Andes in segments each approximately 125 km long. From north to south the boundaries cross the volcanic arc at latitudes 5.4 degrees N, 4.4 degrees N, 3.0 degrees N, 2.3 degrees N, 1.2 degrees N and 0.2 degrees N. These boundaries have bearings NW-SE, parallel to the inclination of the subducted plate and not parallel to the East of Convergence. The boundary of the most Southerly segment (0.7 degrees S) has a bearing NE-SW which is parallel to the northeastern inclination of the subduction zone. The surface of the Nazca plate is relatively flat and smooth between latitudes 7 degrees N and 1 degrees N to the East on the continent there is a simple line of stratovolcanoes with lava of restricted composition. Between latitudes 1 degrees N and 2 degrees S the great submarine Cordillera Carnegie is being subducted, 300 km wide and 3 km high. Related with this subduction it is noted that the trench reaches its minimum depth, the coast is uplifted, the Andes reach greater heights and the volcanism is widely distributed and is of diverse composition. Between latitudes 2 degrees S and 4 degrees S the Nazca plate is cut by three great fractures with bearing NE-SW. The most southerly boundary proposed here is aligned with those fractures. It is proposed that the area between these fractures constitutes a small plate which, once subducted, becomes anomalous with the Benioff zone identified by Pennington (1981).

DE - DESCRIPTORS: Andes-; basement-; Benioff-zone; Cenozoic-; Central-Cordillera; Colombia-; deformation-; depth-; earthquakes-; Eastern-Cordillera; Ecuador-; faults-; focus-; geomorphology-; geophysical-methods; geophysical-surveys; gravity-methods; igneous-rocks; island-arcs; Landsat-; Mesozoic-; Nazca-Plate; Northern-Andes; Paleozoic-; plate-collision; plate-tectonics; Quaternary-; remote-sensing; satellite-methods; segmentation-; seismicity-; South-America; subduction-zones; surveys-; tectonics-; volcanic-rocks; volcanism-; volcanoes-; Western-Cordillera

CC - CATEGORY CODES: 16-Structural-geology

DT - DOCUMENT TYPE: Serial; Conference-Document

BL - BIB LEVEL: Analytic

MC - MAP COORDINATES: LAT: S030000; N053000; LONG: W0750000; W0800000.

IL - ILLUSTRATION: Refs: 39; geol. sketch map.

RF - REFERENCE SOURCE: GeoRef, Copyright 2004, American Geological Institute.

CO - CODEN: #06339

AN - ACCESSION NUMBER: 2004-003043

UD - UPDATE CODE: 200401

Registro 238 de 5614 - GeoRef : 2002-2004/12

TI - TITLE: Catalogs of hypocenters and intensities for South America.

AU - AUTHORS: Askew-Bonny; Algermissen-S-T

AF - AUTHOR AFFILIATION: U. S. Geological Survey, USA, United States

BK - BOOK TITLE: In: Simposio sobre el peligro y riesgo sismico y volcanico en America del Sur--Symposium on Seismic and volcanic hazard and risk in South America.

BA - BOOK AUTHORS: Giesecke-M-Alberto (editor)

SO - SOURCE: Earthquake Mitigation Program in the Andean Region (Project SISRA). 14; Pages 137-170. 1985.

PB - PUBLISHER: CERESIS (Centro Regional de Sismologia para America del Sur). Lima, Peru. 1985.

RP - RESEARCH PROGRAM: USGSOP (Non-USGS publications with USGS authors)

CP - COUNTRY OF PUBLICATION: Peru

PY - PUBLICATION YEAR: 1985

CN - CONFERENCE INFORMATION: Simposio sobre el peligro y riesgo sismico y volcanico en America del Sur. San Juan, Argentina. Sept. 24-28, 1984.

LA - LANGUAGE: English

LS - LANGUAGE OF SUMMARY: Spanish

AB - ABSTRACT: The primary purpose of the compilation of the hypocenter and intensity catalog for South America is to obtain and present in a uniform format all of the historical and instrumental information which exists concerning earthquakes in each of the countries. The catalogs have been prepared on the basis of those prepared by each country for this project. The greater part of the material presented in the national catalogs represents many years of work of dedicated researches in each of the participating countries. Furthermore, much use has been made of the material collected by Project SISAN, which was a compilation of seismic data pertaining to Colombia, Ecuador, Bolivia and Peru. The hypocenters and the intensities have been classified by countries and include Argentina, Bolivia, Brasil, Chile, Colombia, Ecuador, Peru, Trinidad and Tobago, and Venezuela.

DE - DESCRIPTORS: Bolivia-; catalogs-; causes-; Colombia-; data-bases; deep-focus-earthquakes; earthquakes-; Ecuador-; focus-; geologic-hazards; information-management; magnitude-; Peru-; risk-assessment; seismic-intensity; seismic-risk; seismicity-; shallow-focus-earthquakes; South-America; tectonics-

CC - CATEGORY CODES: 19-Seismology

DT - DOCUMENT TYPE: Serial; Conference-Document

BL - BIB LEVEL: Analytic

NN - ANNOTATION: Includes appendices.

IL - ILLUSTRATION: Refs: 65

RF - REFERENCE SOURCE: GeoRef, Copyright 2004, American Geological Institute.

CO - CODEN: #06339

AN - ACCESSION NUMBER: 2004-003035

UD - UPDATE CODE: 200401

Registro 239 de 5614 - GeoRef : 2002-2004/12

TI - TITLE: Pollen-based biome reconstructions for Latin America; applications at a range of spatial and temporal scales.

AU - AUTHORS: Marchant-Robert; Behling-Hermann; Cleef-Antoine; Harrison-Sandy-P; Hooghiemstra-Henry; Markgraf-Vera; Ledru-Marie-Pierre; Lozano-Garcia-Socorro

AF - AUTHOR AFFILIATION: Trinity College, Department of Botany, Dublin, Ireland

BK - BOOK TITLE: In: XVI INQUA congress; shaping the Earth; a Quaternary perspective.

BA - BOOK AUTHORS: Anonymous

SO - SOURCE: Congress of the International Union for Quaternary Research. 16; Pages 122-123. 2003.

PB - PUBLISHER: [International Union for Quaternary Research], International. 2003.

CP - COUNTRY OF PUBLICATION: International

PY - PUBLICATION YEAR: 2003

CN - CONFERENCE INFORMATION: XVI INQUA congress; shaping the Earth; a Quaternary perspective. Reno, NV, United States. July 23-30, 2003.

LA - LANGUAGE: English

AB - ABSTRACT: The biomisation method is used to reconstruct vegetation from fossil pollen data across Latin American at 6000 and 18000 radiocarbon years before present (yr BP), we then focus in on Colombia at a higher temporal resolution. Tests using modern pollen from core top, surface samples, pollen traps and moss polsters were able to broadly reproduce vegetation distribution as reflected in a map of potential natural vegetation. The calibration between the pollen-based reconstruction and the potential vegetation makes it possible to reconstruct vegetation at past periods, and determine patterns of change relative to the present. Mismatches between the pollen-based vegetation reconstruction and the potential vegetation results from forcing factors such as human impact, methodological artefacts and mechanisms of pollen transport and representivity of the parent vegetation. At a Latin American scale, the main differences between the modern and the 6000 yr BP reconstruction is a transition to biomes characteristic of a slightly drier climate. At 18,000 yr BP the pattern of vegetation change is more pronounced and is characterised by a range of biomes where tropical dry forest, tropical seasonal forest and cool grass / shrub are common, these describing a generally cool and dry environment. By focusing our analysis on Colombia, which is prominent in Latin America due to the high quality and quantify of pollen-based environmental records stemming form some 50 years of palaeoecological study, it is possible to increase the temporal and spatial resolution, while retaining more information from the analysis that has to be discarded at the broader scale. Results are presented from the Holocene where the increasing importance attributed to human activity is documented initially in the lowlands and then at higher altitudes. This spatial and temporal zoom allows a discussion about differential response of the vegetation to Late Quaternary environmental change and a greater understanding on the forcing factors behind changing vegetation patterns than attainable at a continental scale. This abstract is coauthored with Latin American Pollen Database members, Latin American Pollen Database, http://www.ngdc.noaa.gov/paleo/lapd.html.

DE - DESCRIPTORS: biomes-; Cenozoic-; Colombia-; Latin-America; microfossils-; miospores-; paleoclimatology-; paleoecology-; paleoenvironment-; palynomorphs-; pollen-; Quaternary-; reconstruction-; South-America; spatial-distribution; temporal-distribution; upper-Quaternary; vegetation-

CC - CATEGORY CODES: 24-Quaternary-geology

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

BL - BIB LEVEL: Analytic

RF - REFERENCE SOURCE: GeoRef, Copyright 2004, American Geological Institute. Reference includes data from Desert Research Institute, Reno, NV, United States

CO - CODEN: #01587

UR - URL: (Full text) http://www.inqua2003.dri.edu/inqua03_abstracts_p101-124.pdf

AN - ACCESSION NUMBER: 2004-002741

UD - UPDATE CODE: 200401

XURL - URLs, etc : URL; URL-ITEM (UR)

Registro 240 de 5614 - GeoRef : 2002-2004/12

BK - BOOK TITLE: Materiales de construccion en la Sabana de Bogota

Translated Title: Construction materials in the Sabana de Bogota.

BA - BOOK AUTHORS: Gonzalez-O-Leopoldo; Cardenas-John-Fernan; Parrado-L-Guillermo

SO - SOURCE: Publicaciones Geologicas Especiales del INGEOMINAS. 23; 2001.

PB - PUBLISHER: Instituto Nacional de Investigaciones Geologico-Mineras (INGEOMINAS). Bogota, Colombia. Pages: 112. 2001.

CP - COUNTRY OF PUBLICATION: Colombia

PY - PUBLICATION YEAR: 2001

LA - LANGUAGE: Spanish

DE - DESCRIPTORS: beneficiation-; Bogota-Colombia; chronostratigraphy-; clays-; Colombia-; construction-materials; economics-; environmental-management; granulometry-; gravel-deposits; impact-statements; lithostratigraphy-; mineral-composition; mining-; mining-geology; nomenclature-; physical-properties; production-; quarries-; regional-; reserves-; Sabana-de-Bogota; sandstone-deposits; sediments-; South-America; stratigraphic-columns; stratigraphic-units

CC - CATEGORY CODES: 28A-Economic-geology,-geology-of-nonmetal-deposits

DT - DOCUMENT TYPE: Serial

BL - BIB LEVEL: Monograph

MC - MAP COORDINATES: LAT: N030000; N050000; LONG: W0720000; W0740000.

IL - ILLUSTRATION: Refs: 93; illus. incl. strat. col., 13 tables, geol. sketch map.

RF - REFERENCE SOURCE: GeoRef, Copyright 2004, American Geological Institute.

IS - ISSN: 0120-078X

CO - CODEN: #54756

AN - ACCESSION NUMBER: 2004-002674

UD - UPDATE CODE: 200401

Registro 241 de 5614 - GeoRef : 2002-2004/12

BK - BOOK TITLE: Sismicidad historica y analisis macrosismico de Bucaramanga

Translated Title: Historical seismicity and macroseismic analysis of Bucaramanga.

BA - BOOK AUTHORS: de-Jesus-Elkin; Hurtado-Salcedo

SO - SOURCE: Boletin Geologico - Ingeominas. 40; 1, 2002.

PB - PUBLISHER: Instituto Nacional de Investigaciones Geologico-Mineras (INGEOMINAS). Bogota, Colombia. Pages: 180. 2002.

CP - COUNTRY OF PUBLICATION: Colombia

PY - PUBLICATION YEAR: 2002

LA - LANGUAGE: Spanish

DE - DESCRIPTORS: attenuation-; Bucaramanga-Colombia; cartography-; Colombia-; deformation-; depth-; earthquakes-; epicenters-; faults-; focus-; history-; information-management; magnitude-; mathematical-methods; plate-tectonics; Santander-Colombia; seismic-zoning; seismicity-; seismology-; South-America; statistical-analysis

CC - CATEGORY CODES: 19-Seismology

DT - DOCUMENT TYPE: Serial

BL - BIB LEVEL: Monograph

MC - MAP COORDINATES: LAT: N060000; N080000; LONG: W0720000; W0740000.

NN - ANNOTATION: Includes appendices.

IL - ILLUSTRATION: Refs: 58; illus. incl. 9 tables, geol. sketch maps.

RF - REFERENCE SOURCE: GeoRef, Copyright 2004, American Geological Institute.

IS - ISSN: 0120-1425

CO - CODEN: #54470

AN - ACCESSION NUMBER: 2004-002673

UD - UPDATE CODE: 200401

Registro 242 de 5614 - GeoRef : 2002-2004/12

TI - TITLE: Maastrichtian-Danian dinoflagellate cyst biostratigraphy and biogeography from two equatorial sections in Colombia and Venezuela.

AU - AUTHORS: Yepes-Oscar

AF - AUTHOR AFFILIATION: Texas A&M University, Department of Geology and Geophysics, College Station, TX, United States

SO - SOURCE: Palynology. 25; Pages 217-249. 2001.

PB - PUBLISHER: American Association of Stratigraphic Palynologists. Dallas, TX, United States. 2001.

CP - COUNTRY OF PUBLICATION: United-States

PY - PUBLICATION YEAR: 2001

LA - LANGUAGE: English

AB - ABSTRACT: Two outcrop sections from the Maastrichtian Colon and Mito Juan Formations were analyzed for dinoflagellate cyst biostratigraphy. Samples from the Rio Molino section (Cesar-Rancheria Basin, Colombia) represent a subset of samples from the 240 m-thick hemipelagic limestones and calcareous mudstones reported in Martinez's (1989) foraminiferal study. The upper Campanian, lower Maastrichtian and uppermost Maastrichtian intervals were identified in this section based on some significant dinocyst biostratigraphic events, which are in agreement with planktonic foraminiferal data. In ascending stratigraphic order these events include the lowest occurrence (LO) of Areoligera spp., LO of Senegalinium spp., highest occurrence (HO) of Arichodinium castanea, HO of Xenascus ceratioides, LO of Cerodinium diebelii, LO of Trithyrodinium evittii, HO of Odontochitina operculata, LO of Phelodinium tricuspe, HO of Palaeohystrichophora infusorioides, LO of Glaphyrocysta perforata, LO of Disphaerogena carposphaeropsis and LO of Manumiella seelandica. Relative higher abundance of terrestrial-derived organic matter in the upper Colon Formation is consistent with a marine regression and consequent shallowing of depositional environments at the end of the Cretaceous in northwestern South America. The Rio Loro section (Merida Andes, western Venezuela) includes 980 m of Maastrichtian, open marine, marginal marine and deltaic siliciclastic and calcareous sediments. The occurrence of Phelodinium tricuspe and Paleocystodinium australinum below the highest occurrence of Hystrichodinium sp. and Odontochitina sp. indicates that the base of the studied interval in this section is early Maastrichtian in age. The K/T boundary in the Rio Loro section is placed within a 11.5 m-unexposed interval, which is above the lowest occurrence of G. perforata and just below the lowest occurrence of the Danian marker, Damassadinium californicum. Very high sedimentation rates during the K/T transition in northern Colombia and western Venezuela may have produced one of the most expanded K/T Boundary sections reported in the literature. Spiniferites-Achomosphaera Group and peridinioid cysts dominate most of the dinoflagellate cyst assemblage in both sections. The peridinioid assemblage reported here is assigned to the tropical to subtropical Malloy suite of Lentin and Williams (1980).

DE - DESCRIPTORS: assemblages-; biogeography-; biostratigraphy-; Cenozoic-; Colombia-; Colon-Formation; Cretaceous-; Danian-; depositional-environment; Dinoflagellata-; floral-list; K-T-boundary; lithostratigraphy-; lower-Paleocene; Maestrichtian-; Mesozoic-; microfossils-; Mito-Juan-Formation; morphology-; Paleocene-; Paleogene-; palynomorphs-; Senonian-; South-America; stratigraphic-boundary; Tertiary-; Upper-Cretaceous; Venezuela-