Clay and bulk mineralogy of ODP sites 119-745 and 119-746 from the Southern Ocean

The sediments recovered at ODP Sites 745 and 746 in the Australian-Antarctic Basin are characterized by cyclic facies changes between clayey diatom oozes and diatomaceous clays ranging in age from late Miocene (about 10 Ma) to Quaternary.
The gravel and terrigenous sand content of the sediments is used as an indicator of the intensity of ice rafting through time. Maxima are recorded at 8.7-7.9, 6.6-6.0, 5.0-4.4, and 4.0-3.2 Ma. The maxima in more recent times are much less pronounced and occur at 2.4-1.6 and 1.4-1.0 Ma. All sand- and gravel-sized terrigenous sediment particles are of gneissic or granitic origin and originated from the East Antarctic continent. The maxima of ice rafting recorded at Sites 745 and 746 do not appear to represent local phenomena. Rather they document major advances and decays of the Antarctic ice shelves and glaciers and therefore represent events of great importance for the reconstruction of the paleoceanography of the Southern Ocean and the glacial history of Antarctica. In general, ice rafting was pronounced in the late Miocene and early Pliocene epochs, which are characterized by repeated ice advances and retreats. Ice rafting was less intensive during the late Pliocene to Quaternary time period, when ice shelves remained relative stable.
The clay minerals indicate the fluctuating influence of different source areas on the delivery of fine-grained terrigenous sediment components. Part of this material may have been delivered from the Permian Amery Formation or from equivalents of this formation.

澳大利亚-南极盆地内大洋钻探计划（Ocean Drilling Program, ODP）745与746站位所获取的沉积物，以晚中新世（约10 Ma）至第四纪时期黏土质硅藻软泥与硅藻黏土之间的周期性岩相变化为典型特征。沉积物中的砾石与陆源砂含量被用作冰筏搬运强度随时间变化的指示指标，其峰值分别出现在8.7~7.9 Ma、6.6~6.0 Ma、5.0~4.4 Ma及4.0~3.2 Ma时段；较晚近时期的峰值则相对平缓，对应2.4~1.6 Ma与1.4~1.0 Ma区间。所有砂级与砾级陆源沉积物颗粒均为片麻岩或花岗岩成因，物质源自东南极大陆。745与746站位记录的冰筏搬运峰值并非局地现象，反而揭示了南极冰架与冰川的大规模进退过程，因此对于重建南大洋古海洋学演化历史与南极冰川演化史具有重要意义。总体而言，冰筏搬运作用在晚中新世与上新世早期更为显著，该时期存在频繁的冰进与冰退事件；而上新世晚期至第四纪时段，冰架相对稳定，冰筏搬运强度随之大幅减弱。黏土矿物特征表明，不同物源区对细粒陆源沉积物组分供给的影响存在周期性波动，其中部分细粒物质可能源自二叠系阿梅里组（Permian Amery Formation）或该组的同期地层。