Oligocene to early Miocene benthic foraminifera in the eastern Equatorial Pacific@en

We investigated Oligocene and early Miocene benthic foraminiferal faunas (> 105 µm in size) from Ocean Drilling Program (Leg 199) Site 1218 (4826 m water depth and ~3300 to ~4000 m paleo-water depth) and Site 1219 (5063 m water depth and ~4200 to ~4400 m paleo-water depth) to understand the response of abyssal benthic foraminifera to mid-Oligocene glacial events in the eastern Equatorial Pacific Ocean. Two principal factor assemblages were recognized. The Factor 1 assemblage (common Nuttallides umbonifer) is related to either an influx of the Southern Component Water (SCW), possibly carbonate undersaturated, or a decrease in seasonality of the food supply from the surface ocean. The Factor 2 assemblage is characterized by typical deep-sea taxa living under variable trophic conditions, possibly with a seasonal component in food supply. The occurrence of abyssal benthic foraminifera faunas during the mid-Oligocene depends on either the effect of SCW or the seasonality of food resources. The Factor 1 assemblage was most common near 76Ol-C11r, 73Ol-C10rn and 67Ol-C9n (ca. 30.2, 29.1 and 26.8 Ma respectively by Pälike et al. (2006, doi:10.1126/science.1133822)). This indicates that the effect of SCW increased or the seasonal input of food from the surface ocean to benthic environments was weakened close to these glacial events. In contrast, the huge export flux of small biogenic carbonate particles close to these glacial events might be responsible for carbonate-rich sediments buffering carbonate undersaturation. Changes in deep-water masses or the periodicity of food supply from the surface ocean and variation in surface carbonate production affected by orbital forcing had an impact on the mid-Oligocene faunas of abyssal benthic foraminifera around the intervals of glacial events in the eastern Equatorial Pacific Ocean. The Factor 1 assemblage decreased sharply at ? 30 Ma (29.8 Ma by Pälike et al. (2006), 30.0 Ma by CK95) and returned to dominance after ? 29 Ma (28.6 Ma by Pälike et al. (2006), 28.8 Ma by CK95). It is likely that the effect of SCW (possibly carbonate undersaturated) has intensified since the late Oligocene. The faunal transition of benthic foraminifera in the eastern Equatorial Pacific Ocean at ~29 Ma might be attributable to the influence of Northern Component Water (NCW) input to the Southern Ocean and the subsequent formation of SCW at about that time.我们针对大洋钻探计划（Ocean Drilling Program，ODP）第199航次1218站位（水深4826米，古水深约3300~4000米）与1219站位（水深5063米，古水深约4200~4400米）的粒径大于105微米的渐新世与早中新世底栖有孔虫化石组合开展研究，旨在揭示东赤道太平洋深渊底栖有孔虫对渐新世中期冰川事件的响应规律。本研究识别出两类核心主因子组合：第一因子组合以常见的*Nuttallides umbonifer*为特征，其形成与南源水团（Southern Component Water，SCW）输入（可能伴随碳酸盐不饱和环境）或表层海洋食物供给的季节周期性减弱相关；第二因子组合以多变营养条件下栖息的典型深海类群为特征，其食物供给可能存在季节性组分。渐新世中期深渊底栖有孔虫组合的出现与否，取决于南源水团的影响或表层食物资源的季节变化特征。第一因子组合在76Ol-C11r、73Ol-C10rn与67Ol-C9n地层区间最为发育，据Pälike等人2006年研究（doi:10.1126/science.1133822），上述区间对应年龄分别约为30.2、29.1与26.8 Ma。这表明在上述冰川事件附近，南源水团的影响增强，或表层海洋向底栖环境输送食物的季节性输入减弱。与之相对，临近这些冰川事件期间小型生物成因碳酸盐颗粒的巨量输出通量，可能造就了富碳酸盐沉积物，从而缓冲了碳酸盐不饱和环境。深水团块的变化、表层海洋食物供给的周期性波动，以及受轨道强迫调控的表层碳酸盐生产变化，均对东赤道太平洋冰川事件区间内的渐新世中期深渊底栖有孔虫组合产生了显著影响。第一因子组合在~30 Ma处急剧减少，据Pälike等人2006年研究其对应年龄为29.8 Ma，CK95研究则认为该节点年龄为30.0 Ma；该组合在~29 Ma后重新占据优势，据Pälike等人2006年研究其对应年龄为28.6 Ma，CK95研究则认为该节点年龄为28.8 Ma。自渐新世晚期以来，南源水团（可能处于碳酸盐不饱和状态）的影响大概率有所增强。东赤道太平洋约29 Ma处的底栖有孔虫群落更替，可能与当时北源水团（Northern Component Water，NCW）输入南大洋并随后形成南源水团的过程相关。