AB - ABSTRACT: Distributions of freshwater hydraulic heads have been, and continue to be, used in the representation and analysis of groundwater flow, including the flow of variable-properties formation water in deep sloping aquifers. Because of variations in pressure, temperature and salinity, the flow of formation waters in sedimentary basins is driven by potential forces resulting from pressure and elevation (topography) differences, by buoyancy resulting from density differences, and by osmosis caused by temperature and concentration gradients. Because of variations in both fluid and rock properties, it is not possible to define a flow potential to be used in representing and analysing the flow. Neither is there a force potential from which a flow-driving force can be derived, and which could be used in flow representation and analysis. Even if osmotic effects are neglected, buoyancy still plays a role which in certain cases may be important. In horizontal or near-horizontal aquifers, the lateral flow of variable-density water is correctly represented by freshwater potentiometric surfaces, and the vertical flow may be analysed using "environmental" hydraulic-head distributions. However, the flow of formation waters in sedimentary basins is mostly along bedding in confined sloping aquifers. In this case, short of calculating and representing either the velocity or the impelling force distribution, freshwater hydraulic heads remain the only tool available for representing and analysing the flow. By neglecting buoyancy, errors in flow strength and direction are introduced, which become significant if a dimensionless driving force ratio exceeds a threshold value estimated to be around 0.5. The review of representation and analysis methods for the flow of variable-properties formation water in deep sloping aquifers is illustrated with two case studies from the Alberta and Llanos sedimentary basins.
RF - REFERENCE SOURCE: GeoRef, Copyright 2000, American Geological Institute.
IS - ISSN: 0072-1077
IB - ISBN: 0-8237-2295-0
CO - CODEN: GSAPAZ
AN - ACCESSION NUMBER: 1995-028236
UD - UPDATE CODE: 199510
Registro 4788 de 5614 - GeoRef Disc 4: 1993-1996
TI - TITLE: Andean tectonics as a cause for changing drainage patterns in Miocene northern South America.
AU - AUTHORS: Hoorn-Carina; Guerrero-Javier; Sarmiento-Gustavo-A; Lorente-Maria-A
AF - AUTHOR AFFILIATION: Hugo de Vries-Laboratorium, Amsterdam, Netherlands
SO - SOURCE: Geology (Boulder). 23; 3, Pages 237-240. 1995.
PB - PUBLISHER: Geological Society of America (GSA). Boulder, CO, United States. 1995.
CP - COUNTRY OF PUBLICATION: United-States
PY - PUBLICATION YEAR: 1995
LA - LANGUAGE: English
AB - ABSTRACT: New data from Neogene strata in northern South America suggest that Miocene tectonism in the northeastern Andes was responsible for the genesis of the Amazon River and changes in the drainage patterns of other major rivers such as the Magdalena and the Orinoco. Here we present a new model for the paleogeographic evolution of northern South America during the Miocene. In the early Miocene, a large part of the drainage of northwest Amazonia was directed northward along the paleo-Orinoco river system to a delta in Lake Maracaibo. Uplift of the Eastern Cordillera in the late middle Miocene caused the first development of the Amazon River; however, no connection with the Atlantic was established, and the Amazon fed the paleo-Orinoco river system, which drained toward the Caribbean. Substantial Andean uplift in the late Miocene resulted in major changes in paleogeography: the Orinoco changed its course, the Amazon established a connection to the Atlantic, causing the drowning of carbonate platforms, and the Amazon-Caribbean connection was closed. Thus the drainage and paleogeography of northern South America in the Miocene were strongly controlled by tectonic movements in the northeastern Andes.