--> Abstract: Structural Inversion: Occurrence, Mechanics, and Implications for Petroleum Exploration, by James D. Lowell; #90985 (1994).
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Abstract: Previous HitStructuralNext Hit Previous HitInversionNext Hit: Occurrence, Mechanics, and Implications for Petroleum Exploration

James D. Lowell

Previous HitStructuralNext Hit Previous HitinversionNext Hit, defined as the uplift of previously extended, subsiding regions by later contraction, has been recognized on every continent that has been explored for petroleum. The process can occur at the large scale of deformation in orogenic belts, but this presentation focuses on Previous HitinversionNext Hit affecting sedimentary basins and their associated structures. Previous HitInversionNext Hit was probably first described and is widespread in northwestern Europe, including the North Sea; subsequent work has revealed its importance in southeast Asia, Australia and New Zealand, north Africa, and South America. Recognition in North America has lagged, probably because occurrences apparently are not as numerous as in the aforementioned areas, but the mid-continent rift and the Uinta Mountains of northeastern Utah are good examples of basin Previous HitinversionNext Hit.

Typically, rift and sag basins can be later inverted. Mainly by reactivation of older normal faults, Previous HitinversionNext Hit selects rift basins where, in pure shear, weakening because of necking or thinning of lithosphere has occurred, and where, in simple shear, mechanical detachment surfaces are available for subsequent movement. Sag basins can apparently be inverted in the absence of reactivated normal faults, as in the southern altiplano of Bolivia and offshore Sabah, Borneo. Basins can be inverted by dominant strike slip with some convergent component, e.g., offshore northeast Brazil, and by almost direct compression, e.g., Atlas Mountains, Morocco. Usually, however, Previous HitinversionNext Hit is caused by a combination of compression and strike slip (transpression) because the azimuth of maximum principal compressional stress to the direction of original basin trend vectors into an oblique-slip component. This is illustrated in Salta Province of northern Argentina where compression derived from Andean deformation is resolved obliquely against an older rift basin in the foreland nearby. Apparently, compressive forces can be stored for great distances backward from the lead edge of an underthrusted foreland plate to invert rather remote regions and basins that are carried m that plate; this may be a significant part of the mechanism for basin Previous HitinversionNext Hit in northwest Europe and the southern North Sea as that foreland region underthrusted along the Alpine system. With respect to the mechanics of Previous HitstructuralNext Hit Previous HitinversionNext Hit, the process has been successfully modeled in both clay and sandbox experiments.

Previous HitStructuralNext Hit Previous HitinversionNext Hit has important implications for petroleum exploration. Areas of Previous HitinversionNext Hit frequently have tighter porosity for a potential reservoir and faster seismic velocity for a particular stratigraphic interval than would be expected for their present depth of burial. Burial history curves characteristically have an upward inflection at the time of Previous HitinversionNext Hit, which can affect the hydrocarbon maturation process. Some source rocks may be overmature for present burial depths. In some presently shallow basins, however, maturation would not have occurred had not source rocks once been buried more deeply. Previous HitInversionNext Hit can cause remigration eft hydrocarbons. Finally, Previous HitinversionTop can create the trapping structures.

AAPG Search and Discovery Article #90985©1994-1995 AAPG Distinguished Lecture