Del Orinoco Research Articles

Models of deposition of loess and loessoids in the upper quaternary of South America

Climatic changes occurred in South America during the Quaternary provoked deflation and deposition of large masses of silt, which formed loess and loessoid units of regional extension in several areas of the continent. An analysis of the most important Late Pleistocene and Holocene loess and loess-like deposits resulted in the identification of five types of transport and deposition of wind-blown silt. They are: 1. 1) Pampa type — Winds derived from the Patagonian ice field during the LGM transported to the NE silt and fine sand formed by frost action in the Cordillera, forming a large sand sea and a loess belt behind it. 2. 2) Chaco type — During the LGM, minor temporary streams transported frost-originated silt from the Cordillera to the low-lands in south Bolivia and NW Argentina. Dry tropical north winds deflated the sediment to the south, forming a valley-and-plain loess deposit. 3. 3) Originated in subtropical anticyclones — During the Upper Holocene, a stational anticyclonic center produced semiarid climatic conditions and dry winds in the Argentine plains and surrounding regions, eroding the Pleistocene loess and sedimenting a thin loess carpet and several sand fields over an area of 1,600,000 km 2. 4. 4) Originated in trade-winds — In the Llanos del Orinoco (Colombia and Venezuela) the NE trade winds deposited a sand and loess mantle during the dry late Pleistocene. Sediments came from the Guayana Shield and from the coastal plain. 5. 5) Volcanic loessoids — Several loess-like sediment sheets, composed of partially altered volcanic ash, cover the Interandean Valley in north Ecuador.

Francisco Antonio Zea: periodista, botánico y político

This work analyzes the journalistic facet of Francisco Antonio Zea, whose first article, «Avisos de Hebephilo», was published in 1791 in the Papel Periódico de la ciudad de Santa Fé de Bogotá. His interest for the press shows at his stage of student in the National Institute of France, but won't be up to 1803, at his return to Madrid, when he proves his talent for the organization and journalistic administration on The Mercury and on the Gazette de Madrid. Later on, being manager of the Royal Botanical Garden of Madrid, he shares the management of the Semanario de Agricultura y Artes, and, finally, in 1818 establishes and directs the Venezuelan Correo del Orinoco.

Depositional Environments and Invasion Profiling in Heavy Oil Sands, Eastern Venezuela: A Case Study: ABSTRACT

A comprehensive study of a single well for INTEVEP and Meneven in the Faja Petrolifera del Orinoco--an extensive (570 × 140 km, 350 × 90 mi) east-west trending heavying oil belt located immediately north of the Orinoco River, eastern Venezuela--resulted in an interpretation of an invasion profile dependent on depositional environments. The data base was derived from: (1) 400 ft (121 m) of whole core (67% recovery) and 124 sidewall cores taken from the 1,500-1,900 ft (457-579 m) interval of the upper Tertiary Oficina Formation, which, in this area, overlies the Precambrian metamorphosed igneous basement. (2) A logging suite of 22 conventional, experimental, and prototype wireline logs. In this area, the Oficina Formation is a complex series of stacked, heavy oil-saturated, sand-dominant, fluvially-transported, unconsolidated sediments overlain by lignite- and mud-dominant backswamp and estuarine sediments. Bedding, mineralogy, lithology, and paleontology define fluvial-channel fills, channel-lag deposits, crevasse splays, overbank levees, swamps, estuarine lagoons, and estuarine-channel fills in a delta-plain environment. Reservoir geometry and facies analyses suggest that several short, wide, deep-channeled, meandering rivers flowed generally northward across a tropical-subtropical plain of low relief carrying the bulk of the sediment in bedload traction (channel fills) and a smaller fraction in density suspension (crevasse splays). A unique logging suite permitted the measurement of invasion in this heavy-oil environment. The invasion of the mud filtrate was measured at varying depths of investigation using, from shallowest to deepest depths: (1) gamma ray spectrometry log, (2) microspherically focused log, (3) nuclear magnetism free fluid index, and (4) deep Laterolog. In addition, water trapped in the fine-grained sands was characterized by comparing the porosity from the electromagnetic propagation log to the free fluid index from the nuclear magnetism log. Identification of the depositional facies coupled with these log responses produced an innovative interpretation of the invasion profile. From an oil-bearing gross interval of 262 ft (80 m) 9 sand units were defined according to their primary and secondary (steam processing) production capability. End_of_Article - Last_Page 516------------