Accumulation rates, carbon composition and Eocene carbonate compensation depths of ODP Sites 199-1218 and 199-1219

CaCO3, Corg, and biogenic SiO2 were measured in Eocene equatorial Pacific sediments from Sites 1218 and 1219, and bulk oxygen and carbon isotopes were measured on selected intervals from Site 1219. These data delineate a series of CaCO3 events that first appeared at ~48 Ma and continued to the Eocene/Oligocene boundary. Each event lasted 1-2 m.y. and is separated from the next by a low CaCO3 interval of a similar time span. The largest of these carbonate accumulation events (CAE-3) is in Magnetochron 18. It began at ~42.2 Ma, lasted until ~40.3 Ma, and was marked by higher than average productivity. The end of CAE-3 was abrupt and was associated with a large-scale carbon transfer to the oceans prior to warming of high-latitude regions. Changes in carbonate compensation depth associated with CAE excursions were small in the early part of the middle Eocene but increased to as much as 800 m by the late middle Eocene before decreasing into the late Eocene. Oxygen isotope data indicate that the carbonate events are associated with cooling conditions and may mark small glaciations in the Eocene.

本数据集针对1218和1219站位的始新世（Eocene）赤道太平洋沉积物，测定了其中碳酸钙（CaCO3）、有机碳（Corg）与生物成因二氧化硅（biogenic SiO2）的含量；并对1219站位的选定层位开展了全岩氧、碳同位素分析。这些数据刻画了一系列最早出现于约48 Ma、延续至始新世/渐新世（Oligocene）边界的碳酸钙事件。每一事件持续时长为1至2百万年，相邻事件之间以时长相近的低碳酸钙含量层段相分隔。其中规模最大的碳酸盐堆积事件（carbonate accumulation events, CAE-3）位于磁极性带（Magnetochron）18内，其起始时间约为42.2 Ma，终止于约40.3 Ma，该事件伴随高于平均水平的生物生产力。CAE-3的终结过程较为突兀，且与高纬度地区升温前发生的大规模碳向海洋的输送过程相关联。与CAE偏移相关的碳酸盐补偿深度（carbonate compensation depth）变化在中始新世早期幅度较小，至中始新世晚期增至最高约800米，随后在晚始新世阶段逐渐降低。氧同位素数据表明，上述碳酸钙事件与降温环境相关联，或可代表始新世时期的小型冰期事件。