Chalks originate as Cretaceous to Recent pelagic or hemipelagic calcareous ooze, which indurate via burial diagenesis to chalk and limestone. Because they accumulate in pelagic settings with high environmental continuity, chalks may form thick formations and even groups. For this reason, and because chalks have a simple mineralogy (low magnesium calcite, silica and clays), they are ideal for the study of diagenetic processes including the depth‐related decrease of porosity. It is the aim of this study to illustrate how the evaluation of in situ elastic strain can help in understanding these processes including the interplay between stress‐controlled diagenetic processes and processes furthered by thermal energy. Petrophysical core and well data can be used for analyses of how porosity reduction via pore collapse and pressure dissolution is related to in situ elastic strain. The data in question are: depth, density of overburden, pore pressure, ultrasonic P‐wave velocity and dry density/porosity. The analysis reveals that the transition from ooze to chalk is associated with high elastic strain and consequent pressure dissolution at calcite–particle contacts causing contact cementation. The transition from chalk to limestone is also associated with high elastic strain, especially at clay–calcite interphases causing development of stylolites via pressure dissolution, and consequent pore‐filling cementation. Following each transformation the elastic strain drops rapidly. The observation of this diagenesis‐related pattern in elastic strain of the sedimentary rock is novel and should not only be helpful in understanding the porosity development in sedimentary basins, but also add basic scientific insight.

中文翻译：

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白垩中的孔隙度–弹性应变和塑性应变的作用

粉笔起源于白垩纪，是最近的中上层或半中层钙质软泥，通过埋藏成岩作用硬化成白垩和石灰石。由于它们在具有高环境连续性的远洋环境中积聚，因此白垩可能会形成较厚的地层甚至群。因此，由于白垩具有简单的矿物学特征（低方解石镁，二氧化硅和粘土），因此是研究成岩过程（包括与深度相关的孔隙度降低）的理想之选。本研究的目的是说明如何对原位进行评估。弹性应变可以帮助理解这些过程，包括应力控制的成岩过程与热能推动的过程之间的相互作用。岩石物理岩心和井数据可用于分析通过孔隙塌陷和压力溶解引起的孔隙度降低与原位之间的关系弹性应变。所涉及的数据是：深度，覆盖层密度，孔隙压力，超声波纵波速度和干密度/孔隙度。分析表明，从渗流到白垩的转变与高弹性应变和方解石-颗粒接触处的压力溶解导致接触胶结有关。从白垩到石灰石的转变也与高弹性应变有关，特别是在粘土-方解石相间，通过压力溶解导致斜长石的发展，并因此导致充填胶结。每次变形后，弹性应变迅速下降。这种与成岩作用有关的沉积岩弹性应变模式的观测是新颖的，不仅有助于了解沉积盆地的孔隙度发展，而且还可以提供基本的科学见解。