Evidence for temporally changing mechanical stratigraphy and effects on joint-network architecture
Evidence for temporally changing mechanical stratigraphy and effects on joint-network architecture
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DOI：
10.1130/g20930.1
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发表时间：
2005-02
期刊：
影响因子：
5.8
通讯作者：
J. Shackleton;M. Cooke;A. Sussman
中科院分区：
文献类型：
--
作者：
J. Shackleton;M. Cooke;A. Sussman
以往对沉积岩节理的研究表明，节理网络阿尔奇受力学地层学的控制，力学地层学的描述是（1）地层单元的厚度和刚度，（2）层间界面的性质。使用节理模式来推断岩层之间的刚度对比是复杂的，因为岩层的材料性质可能在压裂事件之间发生变化。在西班牙比利牛斯山脉的奥利亚纳背斜中，在同一生长地层层中观察到早期含层节理组和不同取向的晚期贯通节理组，这可能反映了力学性质的变化（即，通过成岩作用）。使用一个施密特锤，我们评估的刚度对比度之间的个别单位，并表明，目前的对比度是不够大，以终止关节接口。这一结果与以下解释相一致：晚期贯通节理形成于与现今条件相似的地层中，早期含层节理形成于层间刚度对比明显大于现今的地层中。例如，不同粒度的层之间的差异成岩作用速率将产生随时间变化的机械地层学。我们认为，机械地层学的变化可能在其他地层剖面中以前没有被认识到，这些变化影响了节理网络阿尔奇和随后的流体流动路径。
Previous studies of jointing in sedimentary rocks have shown that joint-network archi- tecture is controlled by mechanical stratigraphy, which is described by (1) the thickness and rigidity of stratigraphic units and (2) the nature of interfaces between beds. Using joint pattern to infer rigidity contrast between beds is complicated by the possibility that material properties of the beds may change between fracturing events. Observation of both an early bed-contained joint set and a differently oriented late throughgoing joint set in the same beds of growth strata in the Oliana anticline in the Spanish Pyrenees may reflect changing mechanical properties (i.e., via diagenesis) during the folding process. Using a Schmidt hammer, we assess the rigidity contrast between the individual units and show that the present-day contrast is not great enough to terminate joints at interfaces. This result is consistent with an interpretation that the late-stage throughgoing joints formed in strata with conditions similar to those of the present day and that the early bed-contained joints formed when the rigidity contrast between beds was significantly greater than that of the present day. For example, differential diagenesis rates between layers of differing grain size would produce temporally changing mechanical stratigraphy. We propose that changes in mechanical stratigraphy may have previously been unrec- ognized in other stratigraphic sections and that these changes affect joint-network archi- tecture and subsequent fluid-flow pathways.