Volume and recurrence of submarine-fan-building turbidity currents
Volume and recurrence of submarine-fan-building turbidity currents
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DOI：
10.1002/dep2.42
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发表时间：
2018-12-01
影响因子：
2.4
通讯作者：
Covault, Jacob A.
中科院分区：
文献类型：
--
作者：
Jobe, Zane R.;Howes, Nick;Covault, Jacob A.
海底扇是地球表面过程和变化的档案，记录了塑造它们的浊流的相关信息。浊流的流量和重现周期对于地质灾害评估、源 - 汇建模以及油气藏表征具有重要意义。然而，这些动态过程受到的约束较差。本研究综合了四个第四纪海底扇的数据，以重建形成这些海底扇的浊流的流量和重现周期。计算得出的事件流量在四个数量级（10⁵到10⁹立方米）之间变化，而重现间隔变化较小，为50到650年。计算得出的浊流事件流量大小似乎与斜坡位置和盆地封闭性有关。斜坡内扇沉积物的事件流量较小（约10⁶立方米），而封闭盆地扇沉积物的事件流量非常大（10⁸到10⁹立方米）。非封闭的坡底环境中的沉积物具有中间值（10⁷到10⁸立方米）。斜坡内环境中的沉积物绕过以及封闭盆地中的水流截留可能是造成这些差异的原因。事件重现周期和盆地封闭性之间似乎没有明显的关系。事件流量和源区特征之间存在弱的比例关系，但河流和/或斜坡内转移区的沉积物储存可能使这些关系变得复杂。这里介绍的方法和结果也被应用于重建南非坦夸卡鲁盆地古代海底扇沉积物的沉积时间。海底扇建造浊流的流量和重现周期在海底峡谷和水道所测值（10³年）之间形成中间值，这表明源自海底峡谷的小而频繁的水流在到达扇体之前往往就消失了，而罕见且非常大的水流大多绕过扇体，将沉积物沉积在深海平原上。沿着海底沉积物搬运系统对流量和重现周期的这种划分，为更好地约束地质灾害、油气资源以及地层记录的完整性提供了有价值的见解。
Submarine fans are archives of Earth-surface processes and change, recording information about the turbidity currents that construct and sculpt them. The volume and recurrence of turbidity currents are of great interest for geohazard assessment, source-to-sink modelling, and hydrocarbon reservoir characterization. Yet, such dynamics are poorly constrained. This study integrates data from four Quaternary submarine fans to reconstruct the volume and recurrence of the formative turbidity currents. Calculated event volumes vary over four orders of magnitude (10(5) to 10(9) m(3)), whereas recurrence intervals vary less, from 50 to 650 years. The calculated turbidity-current-event volume magnitudes appear to be related to slope position and basin confinement. Intraslope-fan deposits have small event volumes (ca 10(6) m(3)) while ponded-fan deposits have very large event volumes (10(8) to 10(9) m(3)). Deposits in non-ponded, base-of-slope environments have intermediate values (10(7) to 10(8) m(3)). Sediment bypass in intraslope settings and flow trapping in ponded basins likely account for these differences. There seems to be no clear relationship between event recurrence and basin confinement. Weak scaling exists between event volume and source-area characteristics, but sediment storage in fluvial and/or intraslope transfer zones likely complicates these relationships. The methodology and results presented here are also applied to reconstruct the time of deposition of ancient submarine-fan deposits of the Tanqua Karoo basin, South Africa. The volume and recurrence of submarine-fan-building turbidity currents form intermediate values between values measured in submarine canyons and channels (10(3) years), indicating that small, frequent flows originating in submarine canyons often die out prior to reaching the fan, while rare and very large flows mostly bypass the fan and deposit sediment on the abyssal plain. This partitioning of flow volume and recurrence along the submarine sediment-routing system provides valuable insights for better constraining geohazards, hydrocarbon resources and the completeness of the stratigraphic record.