Chronology of post-Messinian faulting along the Levant continental margin and its implications for salt tectonics
Chronology of post-Messinian faulting along the Levant continental margin and its implications for salt tectonics
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DOI：
10.1016/j.marpetgeo.2019.05.032
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发表时间：
2019-02
影响因子：
4.2
通讯作者：
Y. Elfassi;Zohar Gvirtzman;O. Katz;E. Aharonov
中科院分区：
文献类型：
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作者：
Y. Elfassi;Zohar Gvirtzman;O. Katz;E. Aharonov
在以色列海岸以西15-30 公里处的黎凡特大陆斜坡上，发现了许多表现出薄皮盐构造的正断层。以往的研究估计，这一断裂活动始于晚上新世至早更新世，这使得活动断裂的总持续时间存在约50%的不确定性。这项研究的目的是改进断裂开始的测年，并重建随时间变化的位移速率。为了提高测年分辨率，我们使用2D和3D地震资料，结合测井和岩屑，结合生物和地震地层学数据，将以色列近海的上新世(5.33-2.6 Ma)、格拉西亚(2.6-1.8 Ma)、卡拉布里亚-爱奥尼亚(1.8-0.35 Ma)和爱奥纪-全新世(<；0.35 Ma)划分为4个沉积单元。在此基础上，我们测量了老层位的位移，重建了沿断层的位移历史，确定了向生长断层增厚的同构造沉积单元。我们的分析表明，上新世(2.7My)断裂活动较少。在格拉西亚(持续时间0.8My)断层活动达到顶峰的同时，也出现了巨大的滑坡。在过去的1.8My，断裂和滑塌都减少了，但它们今天仍然活跃。观察到断裂的开始明显早于陆架边缘到现在的位置，这表明差异加载可能不是启动以色列近海盐构造的第一个触发因素。格拉西亚地区强烈的断裂和滑塌的组合被解释为区域内陆隆起和盆地沉降导致的盆地向倾斜的结果。然而，不能排除断层作用和滑塌作用之间的正反馈。目前海底的沉积速率与平均位移速率相似，甚至快于平均位移速率，因此在目前海底存在断层疤痕，显然表明断裂活动是由突然的地震破裂主导的，而不是持续的蠕动。因此，考虑到约50 m/My的沉积速率，1 m高的断层陡坎应大致年轻于约20 Ky。
Numerous normal faults, expressing thin-skinned salt tectonics, are detected along the Levant continental slope, 15–30 km west of the Israeli coast. Previous studies estimated that this faulting initiated during Late Pliocene to Early Pleistocene, which leaves an uncertainty of about 50% in the total duration of active faulting. The purpose of this study is to improve the dating of the onset of faulting, and to reconstruct displacement rates with time. This will allow better understanding of salt tectonics as well as better assessment of geohazards.To increase dating resolution, we use 2D and 3D seismic material integrated with well logs and cuttings to combine bio- and seismo-stratigraphic data and to divide the Plio-Quaternary section offshore Israel to 4 depositional units: Pliocene (5.33–2.6 Ma); Gelasian (2.6–1.8 Ma); Calabrian-Ionian (1.8–0.35 Ma); and Ionian-Holocene (<0.35 Ma). Then, we measure displacement of dated horizons, reconstruct displacement history along faults, and identify syn-tectonic depositional units that thicken towards growth faults.Our analysis shows that during the Pliocene (duration of 2.7 my) faulting activity was minor. In the Gelasian (duration of 0.8 my) faulting activity peaked alongside huge slumping. In the past 1.8 my, faulting and slumping had both decreased, but they are still active today.The observation that the onset of faulting significantly predates the progradation of the shelf edge to its present location indicates that differential loading was probably not the first trigger that initiated salt tectonics offshore Israel. The association of intense faulting and slumping in the Gelasian is interpreted as a result of basinwards tilting due to regional inland uplift and basin subsidence. Yet positive feedback between faulting and slumping cannot be ruled out.The presence of fault scars on the present seafloor, where current sedimentation rate is similar and even faster than the average displacement rate, apparently indicates that faulting is dominated by sudden seismic ruptures rather than by continued creeping. Hence, considering sedimentation rate of about 50 m/my, a 1 m high fault scarp should be roughly younger than about 20 ky.