Calcium carbonate concentrations in Miocene and Pliocene sediments of ODP Hole 120-751A

Detailed records of % calcium carbonate and calcium carbonate mass accumulation rate (MAR) for Site 751, located on the Southern Kerguelen Plateau, are presented. The shallow-water site contains a Neogene section with well-preserved carbonate sediments. These sediments record variations in the oceanography of the Antarctic surface waters. Carbonate sedimentation patterns reflect changing modes of biogenic sedimentation in the Miocene and Pliocene Antarctic Ocean.
Drilling at Site 751 recovered 166 m of early Miocene to Pleistocene siliceous and calcareous biogenic oozes. Three hiatuses, however, were detected: one between 14.8 and 12 Ma, another between 8.9 and 6.7 Ma, and a third between 5.08 and 5.36 Ma. Sedimentation rates were about 20 m/m.y. throughout the Miocene and <10 m/m.y. during the Pliocene and Pleistocene.
Key events in the depositional history are as follows: (1) a dramatic decrease in carbonate content, from 75% to near 0%, near the Miocene/Pliocene boundary; and (2) minima in % carbonate occur at 16.7, 16.3, 12.2, 11.7, and 9.8 Ma. The % carbonate record shows variability about a mean of ~70% and then a sharp drop near the Miocene/Pliocene boundary. The carbonate MAR record, however, exhibits a series of steplike changes throughout the Miocene. The terminal Miocene event in the carbonate MAR record is not as dramatic as in the % carbonate record, as carbonate MARs had already decreased to about 15% of their middle Miocene values.

本文呈现了位于南凯尔盖朗高原的751站位的碳酸钙百分含量与碳酸钙质量堆积速率（mass accumulation rate, MAR）的详细记录。该浅水站位发育保存完好的碳酸盐沉积物组成的新近纪地层，其所蕴含的沉积记录揭示了南极表层海水的海洋学演化过程。碳酸盐沉积模式反映了中新世与上新世南极海域生物沉积作用的演化特征。
751站位的钻探作业获取了166米的早中新世至更新世硅质、钙质生物软泥沉积序列。本次钻探共识别出三处沉积间断：分别位于14.8~12 Ma、8.9~6.7 Ma以及5.08~5.36 Ma地层区间。整个中新世的沉积速率约为20米/百万年（m/m.y.），而上新世与更新世的沉积速率则低于10米/百万年。
该沉积演化历史中的关键事件如下：（1）在中新世/上新世交界附近，碳酸钙含量从75%骤降至接近0%；（2）碳酸钙百分含量的低值出现于16.7 Ma、16.3 Ma、12.2 Ma、11.7 Ma与9.8 Ma时段。碳酸钙百分含量记录整体围绕约70%的平均值波动，随后在中新世/上新世交界附近出现急剧下降。然而，碳酸钙质量堆积速率（MAR）记录在整个中新世期间呈现出一系列阶梯式变化。中新世末期的碳酸钙MAR变化事件并不如百分含量记录那般剧烈，因为此时碳酸钙MAR值已降至中新世中期数值的约15%。