Fractures, convection and underpressure: hydrogeology on the southern margin of the Piceance basin, west-central Colorado, USA | Fractures, convection et sous-pressions: Hydrogéologie sur la bordure sud du bassin de Piceance, centre-ouest du Colorado, USA Fracturas, convección y subpresiones: Hidrogeología en el margen sur de la Cuenca del Piceance, Colorado centro oeste, EE UU 裂隙、对流和低压 : 美国科罗拉多州中西部Piceance盆地南缘的水文地质 Fracturas, convecção e subpressão: Hidrogeologia da margem sul da bacia Piceance, centro-oeste do Colorado, EUA
2009
Lazear, GregoryD.
Grand Mesa is an erosional remnant on the southern margin of the Piceance basin (Colorado, USA) that appears to host topographically driven groundwater flow in low permeability strata via a pervasive network of vertical extensional fractures. The vertical fractures cut more than 1 km of clay-rich lithology ranging in age from Upper Cretaceous through Eocene, and likely formed from horizontal dilation, cooling, and erosional unloading associated with 2.8 km of regional uplift and 1.5 km of incision by the Gunnison and Colorado rivers. The vertical fractures create anisotropy in which vertical permeability exceeds horizontal permeability. This enhances vertical flow and depth of penetration of groundwater, favors local flow regimes over regional flow, and results in groundwater temperatures that are elevated by up to 10°C over mean surface temperatures at the location of springs. The uplift and cooling that formed the fractures may also have produced domains of abnormally underpressured pore fluids and natural gas within blocks of low permeability bedrock bounded by the fractures. Pore pressures inside these blocks may be in disequilibrium with the groundwater flow system due to ongoing stress release, and the long time scales required for pressure equilibration in the low permeability strata.
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