This study presents the first analysis of the anisotropy of magnetic susceptibility (AMS) coupled with anisotropy of P-wave velocity (APV) in sedimentary rocks from a passive continental margin. In the Otway Ranges, Australia, the Lower Cretaceous sediments deposited during a period of subsidence and structural quiescence display triaxial-magnetic fabrics typical of extensional deformation. The extensional interpretation from AMS is also supported by the orientation of the pore fabric measured using APV.

The inferred extensional azimuths from both AMS and APV analyses are in good agreement with axes for renewed Late Cretaceous rifting and the continental break up of Gondwana, a period of structural evolution characterised by abnormally-high levels of paleostress in the Otway Basin. Predicated on this we introduce the concept of layer parallel stretching (LPSt), a process that describes pore-scale structuring representative of the first phase of extensional deformation during periods of intense tectonic extension, in this case the LPSt was oriented NE-SW. These extensional structural fabrics in the Otway Basin were preserved during NE-SW oriented basin inversion, a process that involved reactivation of the local detachment, the partitioning of strain, and low levels of coupling between the basement and the cover. The results highlight the applicability of AMS and APV for characterising rock anisotropy in sedimentary basins at continental margins and have distinct outcomes with respect to the structural framework of the study area in the Otway Ranges.

本研究首次分析了被动大陆边缘沉积岩中磁化率 (AMS) 的各向异性和 P 波速度 (APV) 的各向异性。在澳大利亚奥特韦山脉，下白垩纪沉积物在沉降和结构静止时期沉积，显示出典型的拉伸变形的三轴磁性织物。使用 APV 测量的孔隙结构的方向也支持 AMS 的拉伸解释。

从 AMS 和 APV 分析推断的伸展方位角与更新的晚白垩世裂谷和冈瓦纳大陆分裂的轴非常吻合，冈瓦纳是一个以奥特韦盆地异常高水平古应力为特征的构造演化时期。在此基础上，我们引入了层平行拉伸 (LPSt) 的概念，该过程描述了在强烈构造拉伸期间代表拉伸变形第一阶段的孔隙尺度结构，在这种情况下，LPSt 取向为 NE-SW。Otway 盆地中的这些伸展结构结构在 NE-SW 定向盆地反转过程中得以保留，这一过程涉及局部拆离的重新激活、应变的分配以及基底和覆盖层之间的低水平耦合。