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The AAPG/Datapages Combined Publications Database

AAPG Bulletin


Volume: 22 (1938)

Issue: 8. (August)

First Page: 1101

Last Page: 1106

Title: Second Venezuelan Geological Congress, San Cristobal, April 1-7, 1938: Abstracts: GEOLOGICAL NOTES

Author(s): H. D. Hedberg (2)


The Second Venezuelan Geological Congress was held in the city of San Cristobal, State of Tachira, Venezuela, on April 1-7, 1938. This congress was organized by the Servicio Tecnico de Geologia y Mineria, a division of the Ministerio de Fomento of the Venezuelan Government, and was attended by 84 persons of whom the majority were geologists and petroleum engineers from Venezuela, Trinidad, and Colombia. Fifteen papers on the geology of Trinidad and Venezuela were presented and several days were spent in field excursions to points of geological interest in the State of Tachira and adjoining areas.

The city of San Cristobal, situated in the foothills of the Andes in the southwestern corner of the republic at an elevation of 2,900 feet, proved an excellent site for the Congress. Formal meetings were held in the beautiful new Salon de Lectura, the opening of which coincided with the Congress. Three or four full-day field excursions were interspersed with the regular sessions at which papers were presented and discussed. These excursions were ably led by L. Kehrer of the Caribbean Petroleum Company, whose experience in the geology of this region made these trips especially worth while.

A particularly interesting feature connected with the Congress was the trip over the Trans-Andean highway from Caracas to San Cristobal by means of which the majority of those attending the Congress arrived at the meeting place. This 685-mile trip over an excellent mountain road reaching altitudes of more than 13,000 feet was completely organized by the members of the Servicio and was made in a fleet of 25 cars, trucks, and trailers. Comfortable overnight camps were established for the party along the way near Barquisimeto, Valera, and Lagunillas. Four days were spent in making the trip in order to allow opportunities for enjoying the magnificent Andean scenery and for studying and collecting in important geological localities.

Members of the American Association of Petroleum Geologists,

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of whom 22 were present, take this opportunity of expressing their gratitude and appreciation to Nestor Luis Perez, Ministro de Fomento, and to the members of the Servicio Tecnico de Geologia y Mineria: Guillermo Zuloaga (secretary), S. E. Aguerrevere, Manuel Tello, V. M. Lopez, and Carlos Freeman, and to many others who contributed to the success of this Congress. The whole affair was handled in the inimitable manner which characterized last year's Congress in Caracas. While on the trip from Caracas to San Cristobal and throughout the stay at San Cristobal, those attending the Congress were the guests of the Venezuelan Government and nothing was spared in providing for their comfort and convenience.

Papers (and discussions) will be published shortly in special volumes in both Spanish and English. These, as well as the volumes containing the papers presented at last year's Congress in Caracas, may be obtained from the Servicio Tecnico de Mineria y Geologia, Ministerio de Fomento, Caracas.

At the close of the meetings, on behalf of the geologists from Trinidad, H. Kugler of the Trinidad Leaseholds, Ltd., presented to those attending the San Cristobal Congress an invitation to a geological convention in Trinidad, which will be held in March or April, 1939.


The following abstracts of papers presented at the Second Venezuelan Geological Congress have been obtained through the cooperation of the Servicio Tecnico de Geologia y Mineria.

GERTH, H. (Professor of Paleontology, Geological Institute, University of Amsterdam): Outlines of the Geological History of the South American Cordillera.

The author especially points out the great difference between the main part of the Cordillera with a principally meridional direction and the two ends of this chain, at the northern and southern extremities of the continent, which tend to a more nearly equatorial direction. In the former part we have to do with the border of an old continent, faulted down during older Mesozoic time and then flooded by numerous transgressions of the Pacific Ocean. At the end of the Mesozoic era this part of the Cordillera was raised up by block faulting accompanied by enormous magmatic activity--intrusive as well as effusive. Folding is of secondary character and prevails only in the eastern ranges.

In contrast, the northern and southern parts of the Cordillera were high regions during older Mesozoic times, permitting only insignificant marine sedimentation during this time. But in the Lower Cretaceous these parts of the continent began to sink and a big series of Cretaceous and older Tertiary sediments were deposited there. These sediments were strongly folded during Tertiary time without magmatic activity in any way comparable to that of the meridional part of the Cordillera but the sediments were partly changed

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by dynamic metamorphism unknown in the main part of the Cordillera. In this respect these northern and southern parts of the Cordillera with more nearly equatorial trends are more similar to the mountains of the Alpine system. (Author's abstract.)

TOMALIN, W. G. C. (Caribbean Petroleum Company, Maracaibo): Stratigraphy of Cretaceous Formations in the Neighborhood of the Rio Carache Valley, State of Trujillo.

A topographical map (scale, 1:50,000) showing localities is submitted together with a schematic cross section along the Trans-Andean Highway where it follows the Carache Valley. The Cretaceous formations discussed comprise the Colon shale (Upper Cretaceous), La Luna-Cogollo (Middle Cretaceous), and the Tomon (Lower Cretaceous), Thicknesses of 500, 400, and 800 meters respectively have been measured. A columnar section extending from the overlying Misoa-Trujillo formation to the unconformable contact of the Cretaceous with the Mucuchachi formation is also given. Paleontological determinations by Mr. Rainwater are summarized. The occurrence of Orbitolina concava (Lamarck) var. texana (Roemer) is reported from limestone beds near the base of the Tomon and the relationship with the Glen R se formation of Texas is discussed. (Author's abstract.)

KUNDIG, E. (Royal Dutch Shell, The Hague): The Pre-Cretaceous Rocks of the Central Venezuelan Andes with Some Remarks about the Tectonics.

The author discusses the petrology of pre-Cretaceous rocks in the central Venezuelan Andes. It is particularly concerned with the metamorphic and igneous rocks of supposed early Paleozoic age and the La Quinta (Red-bed) formation. A type section is designated for the La Quinta formation and new evidence (based on fossil fish remains) is presented for its Jurassic age.

KEHRER, L. (Caribbean Petroleum Company, Maracaibo): Some Observations on the Stratigraphy of the States of Tachira and Merida in Southwestern Venezuela.

This paper treats of the stratigraphy of the states of Tachira and Merida. The section includes sediments of Miocene, Eocene, Cretaceous, Jurassic, Permo-Carboniferous, Devonian?, and Ordovician ages. Fossil lists are given for several of the formations.

MANGER, G. E. (Mene Grande Oil Company, Maracaibo): Notes on the Stratigraphy of the Younger Tertiary Formations of the District of Bolivar, State of Zulia, Venezuela.

This paper discusses the younger Tertiary formations of the Bolivar Coastal Fields (La Rosa, Lagunillas, La Villa, La Puerta, Onia, and El Milagro formations). It deals principally with the zonation of the La Rosa and Lagunillas formations, the lateral intergradation of these two formations, and the direction of marine incursion in the Tia Juana field. Due to the non-marine character of the section above the La Rosa formation, conclusions on correlation are based largely on lithology and mineralogy. Stratigraphic relations between the several formations are discussed. (Author's abstract.)

DOUGLAS, J. G. (Mene Grande Oil Company, Maracaibo): Fresh-Water Resources of the Bolivar Coastal Fields.

The increasing need for an adequate drinking water supply and for fresh water suitable for boiler use has stimulated petroleum companies to make

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efforts to find such a supply in the vicinity of their camps. A brief lithologic description of the formations which carry fresh water sands is presented and the results of important tests for fresh water are taken up individually. The assistance obtained from electrical logs taken in numerous oil wells is demonstrated and chemical analyses are presented in chart form, grouped according to the formation in which the aquifers are found.

HOFFMEISTER, W. S. (Lago Petroleum Corporation, Maracaibo): Aspect and Zonation of the Molluscan Fauna in the La Rosa and Lagunillas Formations, Bolivar Coastal Fields, Venezuela.

The La Rosa formation can be separated according to macrofaunal content into a lower division, Cadulus zone, and an upper division, Microdrillia zone. On foraminiferal evidence the writer divided this later zone into a lower horizon, Bolivina sub-zone, and an upper horizon, Cibicides sub-zone. The aspect of the La Rosa fauna points to a tropical sea of shallow or moderate depth. The close affinity of the La Rosa fauna to the classic Lower or Middle Miocene faunas of the Caribbean region testifies for a Miocene age, preferably Lower Miocene.

A thin shallow marine fossil horizon known as the Lithophaga zone is found near the middle of the Lagunillas formation. Because of its wide lateral extent and the ease of recognition the Lithophaga zone is a valuable marker throughout most of the length of the Bolivar coastal fields. A Lower to Middle Miocene age has been assigned to the Lagunillas formation.

The author correlates the La Rosa formation with the upper Agua Clara formation of Falcon and the Lagunillas formation with the Cerro Pelado formation of the State of Falcon. (Author's abstract.)

GONZALEZ DE JUANA, C. (Ministerio de Obras Publicas, Caracas): Contributions to the Geology of the Zulia-Falcon Basin.

It has been determined by field observations and by actual drilling that the Oligocene formations, San Luis and Agua Clara, gradually thin from south to north and disappear along an east-northeast west-southwest line extending from the Isthmus of Paraguana to Maracaibo. Therefore, the existence of an Oligocene dry land in the northern part of northwestern Venezuela bordering the "Falconian channel" is reasonably certain. During Lower or Middle Miocene time the sinking of this dry land reversed the sedimentary conditions at the time of the great La Puerta unconformity. Since that time the shore line has been approximately parallel to the present one. (Author's abstract.)

DALLMUS, K. F. (Standard Oil Company of Venezuela, Caripito): Geology of El Valle de Guanape Area, District of Bruzual, Anzoategui.

The area lies in northwestern Anzoategui and northeastern Guarico. Under the heading of geography the author discusses physiography, drainage, vegetation, and population. The geological part of the paper deals principally with the stratigraphy of the Santa Ines formation (Miocene) and the Carapita formation (Oligocene-Miocene). It touches more briefly on Eocene sediments (Merecure formation?) and on Cretaceous sediments and pre-Cretaceous (?) metamorphics. The major structural feature of the area is a series of thrust faults of great horizontal displacement by which the metamorphics have been pushed over the Cretaceous and the Cretaceous and Eocene in turn over the Oligo-Miocene.

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AGUERREVERE, S. E., and LOPEZ, V. M. (Servicio Tecnico de Mineria y Geologia, Ministerio de Fomento, Caracas): The Geology of the Island Gran Roque and Its Phosphatic Deposits.

Gran Roque is situated at the extreme north of the archipelago Los Roques and lies about 144 kilometers N. 10° E. from the seaport of La Guaira, Venezuela. The island is composed chiefly of a body of gabbro and diabase which has been intruded by pegmatite dikes and apophyses of granodiorite. From the local geology no age criteria can be established. The commercial phosphate deposits of the island are the result of a partial replacement of the gabbro effected by the chemically active part of the guano on greatly sheared zones within the gabbro. (Author's abstract.)

KNECHTEL, M. M. (U. S. Geological Survey, Washington): Pre-Cretaceous Rocks in the State of Barinas, Venezuela.

The author discusses the paper on the geology of the Barinas area which was presented by A. N. Mackenzie at last year's congress in Caracas and gives additional data on the pre-Cretaceous rocks of this area.

REGAN, J. H. (Standard Oil Company of Venezuela): Notes on the Quiriquire field.

This is a compilation of written work by A. J. Freie on the stratigraphy and theory of oil accumulation in the Quiriquire field of eastern Venezuela. It also presents a summary of the history, present development, and structure of the field. (Author's abstract.)

KUGLER, H. (Trinidad Leasholds, Ltd., Trinidad, B.W.I.): Geology of Soldado Rock between Venezuela and Trinidad.

The author reviews the history of the geological investigation of this island which has been of so much importance with regard to the stratigraphy of the Caribbean region. He then presents the results of his own most recent work (an earlier paper by the author was published in 1923) accompanied by a detailed geologic map (scale, 1:500) and several cross sections. Paleontologic work which is now being carried out in both America and Europe on detailed collections from this island confirms the presence of Paleocene rocks unconformably overlain by Upper Eocene sediments. Thus far, however, the previously postulated unconformity within the Upper Eocene has not been definitely proved. The author gives an interpretation of the interesting tectonic and sedimentary structures shown on the isl nd. The paper is dedicated to the memory of Carlotta J. Maury, a pioneer worker on the paleontology of this island, who died in January of this year.

HUTCHISON, A. G. (United British Oilfields of Trinidad, Point Fortin, Trinidad): Notes on the Cretaceous of Trinidad.

This paper furnishes a tentative correlation of certain Trinidad beds, principally from the Northern and Central Ranges, with the eastern Venezuelan Cretaceous succession as described by Hollis D. Hedberg for the Rio Querecual section. The age of many shales could be inferred from that of the associated fossiliferous limestones if the author's views were accepted that these limestones were lenses indigenous to the formation and not derived blocks. (Author's abstract.)

JOHNSON, G. D. (Standard Oil Company of Venezuela, Caripito): Some Alteration Products in Miocene Clays of Guarico.

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Abundant gypsum in carbonaceous clays is shown to be entirely secondary--derived from limestone and pyrite. Cemented clay-pebble beds ("pudding stones") appear to occur in the Miocene section and are seen forming at present in the beds of intermittent streams. (Author's abstract.)

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(2) Mene Grande Oil Company, Apartado 35.

Copyright 1997 American Association of Petroleum Geologists

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