Particle sorting during sediment redistribution processes and the effect on 230Th‐normalized mass accumulation rates
Particle sorting during sediment redistribution processes and the effect on 230Th‐normalized mass accumulation rates
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沉积物重新分布过程中的颗粒分选及其对 230Th 归一化质量积累率的影响
DOI：
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发表时间：
2014
期刊：
影响因子：
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通讯作者：
R. Ibrahim
中科院分区：
文献类型：
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作者：
F. Marcantonio;M. Lyle;R. Ibrahim
确定质量累积率 (MAR) 的第 230Th 方法假设海底沉积物重新分布过程中几乎不发生分馏。我们检查了巴拿马盆地科科斯和卡内基岭配对风选和集中地点的第 230 个放射性碳测年多岩沉积物清单。放射性碳衍生的沙子 MAR 很可能代表底部流传输不良的颗粒的垂直降雨，在每个配对地点都相似，但使用 230Th 归一化则不同。 230Th 归一化 MAR 在重点站点大约低 60%，并且可能低估了垂直 MAR，而对于筛选站点则相反。我们假设，尺寸分馏最常发生在较低的水流速度下，导致粗颗粒被留下，而主要是富含 230Th 的细颗粒被向下坡输送。 230Th 归一化非常适合记录经历了沉积物重新分布的区域中的细粒（碎屑和蛋白石）通量，但不适用于粗粒（碳酸盐）通量。
The 230Th method of determining mass accumulation rates (MARs) assumes that little to no fractionation occurs during sediment redistribution processes at the seafloor. We examine 230Th inventories in radiocarbon‐dated multicore sediments from paired winnowed and focused sites at Cocos and Carnegie Ridges, Panama Basin. Radiocarbon‐derived sand MARs, which likely represent the vertical rain of particles poorly transported by bottom currents, are similar at each of the paired sites but are different using 230Th normalization. 230Th‐normalized MARs are about 60% lower at focused sites and likely underestimate vertical MARs, while the reverse is true for winnowed sites. We hypothesize that size fractionation occurs most frequently at lower current velocities, resulting in the coarse fraction being left behind and primarily the fine 230Th‐rich grains being transported downslope. 230Th‐normalization works well for recording fine‐grained (detrital and opal), but not coarse‐grained (carbonate), fluxes in regions that have undergone sediment redistribution.