Holocene geochronology of a continentalshelf mudbelt off southwestern Africa
Holocene geochronology of a continentalshelf mudbelt off southwestern Africa
复制标题
非洲西南部大陆架泥带的全新世地质年代学
DOI：
--
复制
发表时间：
2002
期刊：
影响因子：
--
通讯作者：
R. Dingle
中科院分区：
文献类型：
--
作者：
M. Meadows;J. Rogers;J. Lee;M. Bateman;R. Dingle
介绍了南部非洲西海岸内大陆架泥带沉积物的全新世岩石地层学和地质年代学。根据对七个大型重力岩心、大量抓斗样品和两个振动岩心的研究，确定了泥带的两个独特部分。北方部分与橙子河前三角洲有关，主要是富含粘土的层状沉积物，而纳马夸兰附近的南部部分与更均匀的泥有关。AMS放射性碳年龄的31个样本从这些核心是有问题的，由于缺乏预期的现代物质在沉积-海洋界面和许多年龄逆转和不一致的一些核心。可能的机制，以解释明显的异常古老的表面和近地表样品的建议。最有可能的解释似乎在于沉积物恢复问题的组合，从水柱内的颗粒有机碳的周期性损失，可能的遗迹沉积物的采样，最有可能的是，14 C耗尽的陆源有机物质的沉积物的合并。年龄逆转是特别明显的层状沉积物，夹带的“老”碳从这些沉积物的陆源提供了最吝啬的解释。稳定的碳同位素分析和一个单一的发光年龄支持的论点，放射性碳测年不一致的结果是陆地输入的碳，这是非同期的实际沉积时间。因此，在研究陆源物质的近海堆积时，海洋来源的有机组分可能是一种更可靠的放射性碳年代学测量方法。
The Holocene lithostratigraphy and geochronology of sediments on an inner continental-shelf mudbelt off the west coast of southern Africa is presented. Based on a study of seven large gravity cores, numerous grab samples and two vibracores, two distinctive sections of the mudbelt have been identi” ed. The northern section is associated with the Orange River prodelta, and is dominated by laminated clay-rich sediments, while the southern section off Namaqualand is associated with more homogeneous muds. AMS radiocarbon ages of 31 samples from these cores are problematic due to the absence of expected modern material at the sedimentocean interface and numerous age reversals and inconsistencies in some of the cores. Possible mechanisms to explain the apparently anomalously old surface and near-surface samples are suggested. Most likely expla nations appear to lie in a combination of sediment-retrieval problems, the periodic loss of ” ne particulate organic carbon from within the water column, the sampling of possible relic sediments and, most likely of all, the incorporation into the sediments of 14C-depleted terrigenous organic matter. The age reversals are especially evident in the laminated sediments, and the entrainment of ‘old’ carbon from the terrestrial source of these sediments is offered as the most parsimonious explanation. Stable carbon isotope analyses and a single lumi nescence age support the contention that radiocarbon date inconsistencies are a consequence of terrestrial inputs of carbon which is non-contemporaneous with the actual time of sedimentation. In studies of offshore accumulations of terrigenous material, the marine-derived organic fraction may therefore prove a more reliable measure of radiocarbon chronology.