Grain size analysis of sediment core CRP-3 from the Ross Sea, Antarctica

Grain-size analyses by sieve and Sedigraph are presented for 115 samples of core from CRP-3, 12 km off the coast of south Victoria Land. The data provide a useful check on visual core descriptions. The geographic setting for the strata sampled, some 790 m of early Oligocene nearshore marine sediments with a persistent glacial influence, is reviewed, and sediment textures interpreted in that context. Sand textures from the CRP-3 samples in the lower part of the core suggest that deposition was initially primarily wave-dominated, but that at times the influence of the waves was over-ridden by episodes of rapid sedimentation. Sedimentary cycles, recognised in the visual description of the core above 485 mbsf, show an increasing proportion of mudstone in the middle of each cycle above 330 mbsf that is interpreted to record periodic sedimentation in deeper water. Sandstone textures in the lower and upper parts of each cycle are interpreted to record departure from and return to shoreface deposition with changes in sea level. Mudstone textures above 176 mbsf indicate sedimentation below wave base. Many of the textures in both sand and mud samples show the coarse 'tail' characteristic of ice-rafted debris, but others do not, indicating ice-free periods. Many sandstones below c. 200 mbsf have virtually no silt, but significant amounts of clay (6 to 17%) that is thought to be of post-depositional origin.

本文呈现了采自南维多利亚海岸外12公里处CRP-3岩芯的115份样品的筛析法与Sedigraph法粒度分析结果。该数据集可为岩芯目视编录提供有效的校验依据。研究梳理了所采样地层的地理背景：该地层为一套厚度约790米的渐新世早期近岸海相沉积物，持续受冰川作用影响，并结合该背景对沉积物组构进行了解译。岩芯下部CRP-3样品的砂质组构特征表明，沉积初期主要受波浪作用主导，但部分时段快速沉积事件会抵消波浪作用的影响。在海底以下485米（mbsf）以上的岩芯目视编录中识别出的沉积旋回显示，海底以下330米（mbsf）以上的每个旋回中部，泥岩占比逐渐升高，该特征被解译为记录了周期性深水沉积过程。每个旋回上下部的砂岩组构特征，被解译为记录了随海平面变化而发生的近岸沉积环境脱离与恢复过程。海底以下176米（mbsf）以上的泥岩组构特征表明沉积物沉积于浪基面之下。多数砂质与泥质样品的组构特征均表现出冰筏碎屑（ice-rafted debris）特有的粗尾段分布特征，但部分样品并不具备该特征，指示了无冰期的存在。海底以下约200米（mbsf）以上的多数砂岩几乎不含粉砂，但含有占比达6%至17%的黏土组分，该组分被认为是沉积后期成因的。