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首页> 外文期刊>Facies >Diagenesis makes the impossible come true: intersecting beds in calcareous turbidites
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Diagenesis makes the impossible come true: intersecting beds in calcareous turbidites

机译：成岩作用使不可能变为现实：钙质浊质中的相交床

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Constructing a time-frame of the past is fundamental for any geological interpretation, and the recognition of orbital cycles preserved in the stratigraphic record has revolutionized our understanding of the global timescale, especially for the Cenozoic. In the past decades, astrochronological and cyclostratigraphic approaches based on Milankovitch cycles have become a widely used tool for precisely dating stratigraphic boundaries by calibrating sedimentary units with astronomically tuned time-scales. In many cases, strikingly rhythmic limestone-marl alternations are used for such approaches. Astrochronological approaches as a basic principle rely on the fundamental assumption that such rhythmites reflect fluctuating environmental conditions caused by variations in incident solar radiation such as changes in sea level, temperature, or weathering. Nevertheless, in many cases, the crucial question as to whether such rhythmites represent primary cycles or are purely of diagenetic origin has never been positively decided. In those cases, stratigraphic dating with this method is left unreliable. Here, the ability of diagenesis to produce rhythmic bedding lacking any relation to primary sedimentary signals is demonstrated. The Miocene succession discussed here shows two cemented sets of beds with different inclinations, one parallel to the sedimentary layering, the other, coeval, but in an oblique direction. These two sets merge and do not show distinct boundaries, thus indicating synchronous cementation. It is interpreted that minor early synsedimentary tectonic stress introduced an oblique anisotropy. During early differential diagenesis, this dual anisotropy influenced the geometry of the cemented layers, giving the impression of intersecting layers.
机译：构造过去的时间框架对于任何地质解释都是至关重要的，地层记录中保存的轨道周期的认识彻底改变了我们对全球时间尺度的理解，尤其是对于新生代。在过去的几十年中，基于Milankovitch旋回的天文学和旋回地层学方法已经成为一种广泛使用的工具，它可以通过用天文调整的时标校准沉积单元来精确地定地层边界。在许多情况下，这种方法使用了有节奏的石灰石-泥灰岩交替。占星学方法作为基本原理，依赖于这样的基本假设：这些节律反映了由入射太阳辐射的变化（例如海平面，温度或天气变化）引起的波动的环境条件。然而，在许多情况下，关于这类节律是否代表初级周期或纯粹是成岩作用的关键问题从未得到肯定的决定。在那些情况下，用这种方法进行地层测年是不可靠的。在此，证明了成岩作用产生与基本沉积信号没有任何关系的有节奏的地层的能力。这里讨论的中新世演替显示了两组胶合床，它们具有不同的倾斜度，一组平行于沉积层，另一组平行，但同时成倾斜方向。这两个集合合并并且没有显示明显的边界，因此表明同步胶结。据解释，较小的早期沉积沉积构造应力引入了倾斜各向异性。在早期的成岩作用中，这种双重各向异性影响了胶结层的几何形状，给人以相交层的印象。

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