Temporal Scales of Mass Wasting Sedimentation across the Mississippi River Delta Front Delineated by 210Pb/137Cs Geochronology

IF 2.7 3区地球科学 Q1 ENGINEERING, MARINE

Journal of Marine Science and Engineering Pub Date : 2024-09-13 DOI:10.3390/jmse12091644

Jeffrey Duxbury, Samuel J. Bentley, Kehui Xu, Navid H. Jafari

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Abstract

The Mississippi River Delta Front (MRDF) is a subaqueous apron of rapidly deposited and weakly consolidated sediment extending from the subaerial portions of the Birdsfoot Delta of the Mississippi River, long characterized by mass-wasting sediment transport. Four (4) depositional environments dominate regionally (an undisturbed topset apron, mudflow gully, mudflow lobe, and prodelta), centering around mudflow distribution initiated by a variety of factors (hurricanes, storms, and fluid pressure). To better understand the spatiotemporal scales of the events as well as the controlling processes, eight cores (5.8–8.0 m long) taken offshore from the South Pass (SP) and the Southwest Pass (SWP) were analyzed for gamma density, grain size, sediment fabric (X-radiography), and geochronology (210Pb/137Cs radionuclides). Previous work has focused on the deposition of individual passes and has been restricted to <3 m core penetration, limiting its geochronologic completeness. Building on other recent studies, within the mudflow gully and lobe cores, the homogeneous stepped profiles of 210Pb activities and the corresponding decreased gamma density indicate the presence of gravity-driven mass failures. 210Pb/137Cs indicates that gully sedimentary sediment accumulation since 1953 is greater than 580 cm (sediment accumulation rate [SAR] of 12.8 cm/y) in the southwest pass site, and a lower SAR of the South Pass gully sites (2.6 cm/y). This study shows that (1) recent dated mudflow deposits are identifiable in both the SWP and SP; (2) SWP mudflows have return periods of 10.7 y, six times more frequent than at the SP (66.7 y); (3) 210Pb inventories display higher levels in the SWP area, with the highest focusing factors in proximal/gully sedimentation, and (4) submarine landslides in both study areas remain important for sediment transport despite the differences in sediment delivery and discharge source proximity.

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通过 210Pb/137Cs 地球年代学划分密西西比河三角洲前沿大规模流失沉积的时间尺度

密西西比河三角洲前沿（MRDF）是一个由快速沉积和弱固结沉积物组成的水下地坪，从密西西比河鸟脚三角洲的地表下部分延伸出来，长期以来以大规模浪费性沉积物搬运为特征。该地区主要有四（4）种沉积环境（未受扰动的顶部沉积坪、泥流沟、泥流叶和原生三角洲），其中心是由各种因素（飓风、风暴和流体压力）引发的泥流分布。为了更好地了解这些事件的时空尺度以及控制过程，对从南口（South Pass，SP）和西南口（Southwest Pass，SWP）近海采集的 8 个岩芯（5.8-8.0 米长）进行了伽马密度、粒度、沉积物结构（X 射线）和地质年代（210Pb/137Cs 放射性核素）分析。以前的研究主要集中于单个岩层的沉积，岩芯穿透深度仅限于 <3 米，这限制了其地质年代的完整性。在其他最新研究的基础上，在泥流沟和岩叶岩芯中，210Pb 放射性活度的均匀阶梯状分布以及相应的伽马密度下降表明存在重力驱动的大规模崩塌。210Pb/137Cs表明，自1953年以来，西南山口地点的沟谷沉积物堆积大于580厘米（沉积物堆积速率[SAR]为12.8厘米/年），南山口沟谷地点的沉积物堆积速率较低（2.6厘米/年）。这项研究表明：(1) 西南坳口和南坳口均可识别近期的泥石流沉积；(2) 西南坳口泥石流的回归周期为 10.7 年，是南坳口（66.7 年）的六倍；(3) 210Pb 库存显示西南坳口地区的水平较高，近距离/沟谷沉积的聚焦因子最高；(4) 尽管沉积物输送和排放源的近距离不同，但两个研究区域的海底滑坡对沉积物输送仍然很重要。

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来源期刊

Journal of Marine Science and Engineering Engineering-Ocean Engineering

CiteScore

4.40

自引率

20.70%

发文量

1640

审稿时长

18.09 days

期刊介绍： Journal of Marine Science and Engineering (JMSE; ISSN 2077-1312) is an international, peer-reviewed open access journal which provides an advanced forum for studies related to marine science and engineering. It publishes reviews, research papers and communications. Our aim is to encourage scientists to publish their experimental and theoretical results in as much detail as possible. There is no restriction on the length of the papers. The full experimental details must be provided so that the results can be reproduced. Electronic files and software regarding the full details of the calculation or experimental procedure, if unable to be published in a normal way, can be deposited as supplementary electronic material.