Sedimentary features and processes in the Nazaré and Setúbal submarine canyons, west Iberian margin
Sedimentary features and processes in the Nazaré and Setúbal submarine canyons, west Iberian margin
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DOI：
10.1016/j.margeo.2007.12.006
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发表时间：
2008-04
期刊：
影响因子：
2.9
通讯作者：
R. G. Arzola;R. Wynn;G. Lastras;D. Masson;P. Weaver
中科院分区：
文献类型：
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作者：
R. G. Arzola;R. Wynn;G. Lastras;D. Masson;P. Weaver
这里我们介绍了伊比利亚西部纳扎雷和塞特巴尔峡谷的第一个完整的侧扫声纳数据集的一部分，这些数据集与多波束测深、浅层地震剖面和峡谷内目标的精确活塞取心相结合，被用来描述这些深海环境的沉积动力学。结果表明，纳扎雷和塞图巴尔峡谷是非常复杂的环境。它们显示了一系列沉积特征和过程，反映了下坡峡谷几何形状的变化，以及从侵蚀近端到更具沉积性的远端剖面的过渡。这两个峡谷的近(上)段的特点是有一个深深切割的、狭窄的V形水沟，两侧是小峡谷和梯田。这一地段发生了许多小型和局部的峡谷内山体滑坡和岩崩，这些都是由陡峭的地形预先规定的不稳定过程引发的。层叠的薄层、细粒浊积岩序列局部出现在峡谷内的阶地上，并被解释为小体积的结果，可能是河流洪水产生的浑浊流似乎没有到达较低的峡谷。在纳扎雷峡谷，这些浊积岩与丰富的煤化有机碎片共生。纳扎雷峡谷上部的一部分在全新世一直是一个明显的沉积中心，与增强的星云样层活动有关的非常高的沉积速率。更大的斜坡破坏来自于陆架断裂和峡谷头，是偶尔释放大量泥沙的结果，很可能与地震活动有关。这些断层迅速演变成大体积、高能量、富含沙子的浑浊水流，冲刷整个峡谷，并主要沉积在较低的峡谷和远处的深海平原。这种幕式的浊流活动导致两个峡谷的远(下)U型底部沉积物分布高度不均匀，具有丰富的侵蚀冲刷和沉积波等沉积床形态。我们的结果突出了主要峡谷系统内沉积过程的复杂相互作用，并对有效描述油气藏、准确的地质灾害空间和时间预测以及峡谷环境中海底生态系统的分布具有潜在的意义。
Here we present part of the first complete sidescan sonar dataset of the Nazaré and Setúbal Canyons, west Iberian margin, which, in combination with multibeam bathymetry, shallow seismic profiles and precise piston coring of intra-canyon targets, are used to characterise the sedimentary dynamics of these deep-sea settings. The results show that Nazaré and Setúbal Canyons are highly complex environments. They display a range of sedimentary features and processes that reflect changes in downslope canyon geometry and a transition from erosive proximal to more depositional distal sections. The proximal (upper) sections of both canyons are characterised by a deeply incised, narrow, V-shaped thalweg, flanked by small gullies and terraces. Numerous small and localised intra-canyon landslides and rock avalanches occur in this section, triggered by instability processes that are preconditioned by the steep topography. Sequences of stacked thin-bedded, fine-grained turbidites occur locally on intra-canyon terraces, and are interpreted to be the result of small-volume, possibly river flood-generated turbidity currents that do not appear to reach the lower canyon. In Nazaré Canyon these turbidites are associated with abundant coalified organic fragments. Part of the upper section in Nazaré Canyon has acted as an apparent depocenter through the Holocene, with very high sedimentation rates related to enhanced nepheloid layer activity. Much larger slope failures are sourced from the shelf break and canyon head and are the result of occasional releases of large volumes of sediment, likely related to earthquake activity. These failures rapidly evolve into large-volume, high-energy, sand-rich turbidity currents that flush the entire canyon and dominantly deposit in the lower canyon and distal abyssal plains. This episodic turbidity current activity results in highly heterogeneous sediment distribution across the distal (lower) U-shaped floor of both canyons, with abundant erosional scours and depositional bedforms such as sediment waves. Our results highlight the complex interplay of sedimentary processes operating within major canyon systems, and have potential implications for efficient characterisation of hydrocarbon reservoirs, accurate spatial and temporal prediction of geohazards, and the distribution of benthic ecosystems in canyon environments.