Shelfal sediment transport by an undercurrent forces turbidity-current activity during high sea level along the Chile continental margin
Shelfal sediment transport by an undercurrent forces turbidity-current activity during high sea level along the Chile continental margin
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DOI：
10.1130/g37594.1
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发表时间：
2016-04-01
期刊：
影响因子：
5.8
通讯作者：
Strecker, Manfred R.
中科院分区：
文献类型：
--
作者：
Bernhardt, Anne;Hebbeln, Dierk;Strecker, Manfred R.
陆源沉积物供给、海洋搬运和沉积过程沿着构造活动边缘是将浊积岩序列解码为气候和地震强迫的潜在档案的关键。层序地层学模型预测粗粒沉积物主要在海平面下降和低水位期间输送到深海站点。海侵和高位期间的海洋硅质沉积被归因于陆源和海洋汇之间的持续连接，由狭窄的货架促进。为了解释全新世高位浊积岩沉积的控制，我们分析了12个沉积岩芯的空间离散，同时代浊积岩系统沿着智利边缘（29度-40度S）不断变化的气候和地貌特征，但统一的海平面变化。从智利中北部斜坡内盆地（南纬29度-33度）近海一个狭窄到不存在的大陆架的沉积物岩心记录了全新世由于冰后期干旱化而关闭的浊流沉积。相比之下，在智利中南部（36度-40度S）离岸一个广泛的大陆架记录频繁的浊流沉积在高位条件的核心网站。两个核心站点与比奥比奥河-峡谷系统相连，直接从河口接收沉积物。然而，斜坡内盆地并不通过峡谷与河流系统相连，而是产生更高的浊积岩频率。高沉积物供应与宽陆架和向陆架边缘移动沉积物的暗流相结合，似乎控制了全新世浊流沉积和分布。大陆架暗流可能在沉积物横向迁移和向深海供应方面发挥重要作用，需要在沉积物质量平衡中加以考虑。
Terrigenous sediment supply, marine transport, and depositional processes along tectonically active margins are key to decoding turbidite successions as potential archives of climatic and seismic forcings. Sequence stratigraphic models predict coarse-grained sediment delivery to deep-marine sites mainly during sea-level fall and lowstand. Marine siliciclastic deposition during transgressions and highstands has been attributed to sustained connectivity between terrigenous sources and marine sinks facilitated by narrow shelves. To decipher the controls on Holocene highstand turbidite deposition, we analyzed 12 sediment cores from spatially discrete, coeval turbidite systems along the Chile margin (29 degrees-40 degrees S) with changing climatic and geomorphic characteristics but uniform changes in sea level. Sediment cores from intraslope basins in north-central Chile (29 degrees-33 degrees S) offshore a narrow to absent shelf record a shut-off of turbidite deposition during the Holocene due to postglacial aridification. In contrast, core sites in south-central Chile (36 degrees-40 degrees S) offshore a wide shelf record frequent turbidite deposition during highstand conditions. Two core sites are linked to the Biobio river-canyon system and receive sediment directly from the river mouth. However, intraslope basins are not connected via canyons to fluvial systems but yield even higher turbidite frequencies. High sediment supply combined with a wide shelf and an undercurrent moving sediment toward the shelf edge appear to control Holocene turbidite sedimentation and distribution. Shelf undercurrents may play an important role in lateral sediment transport and supply to the deep sea and need to be accounted for in sediment-mass balances.