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首页> 外文期刊>Journal of structural geology >Structural and petrophysical evolution of extensional fault zones in low-porosity,poorly lithified sandstones of the Barreiras Formation, NE Brazil
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Structural and petrophysical evolution of extensional fault zones in low-porosity,poorly lithified sandstones of the Barreiras Formation, NE Brazil

机译：巴西东北部Barreiras组低孔隙度，弱石化砂岩伸展断裂带的结构和岩石物理演化

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摘要

We describe the structural and petrophysical evolution of extensional fault zones developed in low porosity, poorly lithified, quartz-dominated sandstones from the Mio-Pliocene continental Barreiras Formation, NE Brazil. We studied eight fault zones developed as sands were lithified. Fault displacement ranges from a few centimetres to ~50 m. A diagnostic feature of the studied fault zones is the lack of deformation bands, which typically develop in high porosity sand(stone)s. Structural and microstructural analyses, grain size and shape analyses, porosity and pore size analyses, and laboratory and in situ permeability measurements show relationships between deformation processes and hydrologic properties. Undeformed rocks are very poorly sorted, medium- to fine-grained, clay-rich sandstones with an average intergranular porosity of about 3%. Sandstones in damage zones record non-destructive dilatant granular flow and formation of opening-mode intergranular extensional fractures, which increase porosity, pore connectivity and permeability. Deformation in fault cores evolved from paniculate flow to compactional cataclastic flow, with progressive grain size reduction increasing the amount of silt- and clay-size fractions. Porosity was dramatically reduced to an average value of 0.2% and permeability is generally lower than the related protoliths. All this evidence highlights a conduit/barrier behaviour of the studied fault zones, which significantly differs from the sealing behaviour of deformation band fault zones commonly observed in high-porosity sandstones.
机译：我们描述了巴西东北部Mio-上新世大陆Barreiras组中低孔隙度，低石化，石英为主的砂岩中发育的伸展断裂带的结构和岩石物理演化。我们研究了随着砂岩化而形成的八个断层带。断层位移范围从几厘米到约50 m。研究断层带的诊断特征是缺乏变形带，变形带通常出现在高孔隙度的砂岩中。结构和微观结构分析，晶粒尺寸和形状分析，孔隙度和孔径分析以及实验室和原位渗透率测量显示了变形过程与水文性质之间的关系。未变形的岩石分类很差，中等至细粒度，富含粘土的砂岩，平均粒间孔隙度约为3％。损伤区的砂岩记录了非破坏性的膨胀性粒状流，并形成了开孔型粒间扩展性裂缝，从而增加了孔隙度，孔隙连通性和渗透性。断层岩心中的变形从粒状流演化为压实碎裂流，随着粒度的逐渐减小，增加了粉砂和黏土尺寸碎屑的数量。孔隙率显着降低至平均值的0.2％，渗透率通常低于相关的原石。所有这些证据都突出显示了研究断层带的导管/屏障行为，这与高孔隙度砂岩中通常观察到的变形带断层带的封闭行为有很大不同。

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