ABSTRACT

Sedimentological and rock magnetic analysis was performed on 67 turbidite samples recovered from Lithostratigraphic units I–III at IODP Site U1520 with the aim to characterise the sedimentary processes and post-depositional diagenesis within a Quaternary sequence in the Hikurangi Trough, New Zealand. Lithostratigraphic Unit I was rapidly emplaced with frequent turbidite deposition with high sedimentation rate (∼1.9 m/kyr). In contrast, in units II–III, the turbidites were finer grained and more thinly bedded, and were deposited at less than half the deposition rate of Unit I. The turbidites were classified into three clusters based on the magnetic properties. Clusters 1 and 2 are characterised by a high coercivity and SIRM/χ, but low to moderate B_cr/B_c. The recognition of gyroremanent magnetisation acquisition in their clusters indicates the diagenetic sulfidization. Cluster 3 was represented by low coercivity and SIRM/χ, but high B_cr/B_c, indicating lack of sulfidization. Restricted occurrence of Cluster 3 in Unit I may be ascribed to the high sedimentation rate, which prevents sulfidization at the sulfate–methane transition zone. Degree of sulfidization might be related with sedimentary features of turbidites in the trough, such as grain size, bed thickness and depositional rate.

摘要

对从 IODP Site U1520 的岩石地层单元 I-III 回收的 67 个浊积岩样品进行了沉积学和岩石磁力分析，旨在表征新西兰 Hikurangi 槽第四纪序列内的沉积过程和沉积后成岩作用。岩石地层单元 I 迅速就位，浊积岩沉积频繁，沉降速率高（~1.9 m/kyr）。相比之下，在单元 II-III 中，浊积岩粒度更细，层状更薄，沉积速率不到单元 I 的一半。基于磁性将浊积岩分为三个簇。簇 1 和 2 的特征是高矫顽力和 SIRM/χ，但 B _cr /B _{c低到中等}. 在它们的簇中识别出回旋剩余磁化强度表明了成岩硫化作用。簇 3 以低矫顽力和 SIRM/χ 为代表，但 B _cr /B _c高，表明缺乏硫化作用。第一单元中簇 3 的出现受限可能归因于高沉降速率，这阻止了硫酸盐 - 甲烷过渡带的硫化。硫化程度可能与槽内浊积岩的沉积特征有关，如粒度、床层厚度和沉积速率。