Bulk mineralogy of Cretaceous to Quaternary sediments from the Kerguelen Plateau

Carbonate-free portions of Upper Cretaceous to Holocene sediment samples from the Kerguelen Plateau in the southern Indian Ocean were investigated by X-ray diffraction. Downhole variations in the content of opal-A, opal-CT, quartz, feldspar, barite, and clinoptilolite were studied at Site 737 on the northern Kerguelen Plateau and at Sites 744 and 738 on the southern Kerguelen Plateau. The variation of these components reflects temporal changes in the depositional history of the Kerguelen Plateau as well as major differences in the sedimentary evolution between the northern plateau and the southern plateau.
Carbonate is the dominant component in the pelagic sediments on the Kerguelen Plateau. In addition, biogenic opal sedimentation plays an important role throughout most of the sequence. A major increase in opal accumulation is documented at all sites in late Miocene time, which is in accordance with the well-known increase in silica productivity probably caused by a major cooling step. Because of its position near the Polar Frontal Zone, sediments from Site 737 show a more extensive opal deposition than at Sites 744 and 738. An earlier productivity pulse is documented at Site 744 on the southern plateau within the early Oligocene, following the initial phase of intense East Antarctic glaciation. This cooling event resulted in higher amounts of ice-rafted terrigenous quartz and, to a lesser extent, feldspar. With the exception of the Site 744 sediments, opal deposition in Paleogene and older sediments can be reconstructed only from the diagenetic transformation products of opal-CT and probably clinoptilolite. In contrast to the southern sequence, on the northern Kerguelen Plateau higher amounts of clinoptilolite and no opal-CT were found. These major differences in the diagenetic environments may be due to extensive volcanism in the northern area. The volcanic influence at Site 737 is well recorded by the higher feldspar content and higher amounts of volcanic glass shards.

本研究通过X射线衍射（X-ray diffraction）分析了南印度洋凯尔盖朗海台（Kerguelen Plateau）白垩纪晚期至全新世的无碳酸盐组分沉积物样品。针对凯尔盖朗海台北部737站位，以及南部744、738站位，我们对其井下沉积物中蛋白石-A（opal-A）、蛋白石-CT（opal-CT）、石英（quartz）、长石（feldspar）、重晶石（barite）及斜发沸石（clinoptilolite）的含量垂向变化开展了研究。上述组分的含量变化，既反映了凯尔盖朗海台沉积演化历史的时间尺度变化，也体现了南北海台沉积演化过程中的显著差异。

凯尔盖朗海台的远洋沉积物以碳酸盐为主要组分，此外，生物成因蛋白石沉积在绝大多数沉积层序中均发挥着重要作用。晚中新世时期，所有站位的蛋白石堆积量均出现显著增加，这与已知的硅质生产力跃升现象一致，该跃升大概率由一次大规模降温事件引发。由于737站位紧邻极锋带（Polar Frontal Zone），其沉积物中的蛋白石沉积规模显著大于744与738站位。在东南极大规模冰川作用初期之后的早渐新世时期，南部海台的744站位出现了一次早期的生产力峰值事件。此次降温事件导致冰筏陆源石英的输入量显著升高，长石的输入量也有小幅提升。除744站位沉积物外，古近纪及更古老沉积物中的蛋白石沉积特征，仅能通过蛋白石-CT与斜发沸石的成岩转化产物进行反演。与南部沉积序列不同，凯尔盖朗海台北部发现了更高含量的斜发沸石，且未检测到蛋白石-CT。这种成岩环境的显著差异，可能与北部区域广泛发育的火山活动有关。737站位较高的长石含量与火山玻璃碎屑丰度，清晰记录了该区域受到的火山影响。