Paleoenvironmental reconstruction of Challenger Mound initiation in the Porcupine Seabight, NE Atlantic
Paleoenvironmental reconstruction of Challenger Mound initiation in the Porcupine Seabight, NE Atlantic
复制标题
大西洋东北部豪猪湾挑战者丘启动的古环境重建
DOI：
10.1016/j.margeo.2010.10.019
复制
发表时间：
2011
期刊：
影响因子：
2.9
通讯作者：
IODP Expedition 307 Scientific Party
中科院分区：
文献类型：
--
作者：
Raddatz;Rüggeberg;Margreth;W.-Chr;IODP Expedition 307 Scientific Party
东北大西洋冷水珊瑚碳酸盐土丘形成和早期发育的古环境是目前国际研究的一个重点。综合大洋钻探计划（IODP）第307次考察在豪猪湾（爱尔兰西南部）钻取了155米高的挑战者丘，目的是首次调查一个巨大碳酸盐丘底部的沉积物。在这项研究中，我们专注于高分辨率的12米的沉积物从网站1317包括土墩基地。丘体的形成和启动阶段与2.7Ma左右北方半球冰川的加强相吻合。进一步碳酸盐丘的发展似乎强烈依赖于在上新世-更新世边界的古海洋和气候条件的快速变化，特别是特征和中间水团，地中海外流水（MOW），东北大西洋水（ENAW）和南部组成水（SCW）的影响的相互作用所造成的。本研究基于成熟的代用指标，如δ 18 O和δ 13 C的浮游生物（Globigerina bulloides）和底栖有孔虫（Fontbotia wuellerstorfi，Discanomalina coronata，Lobatula lobatula，Lobatula anastritica和Planulina ariminensis）以及粒度参数，以确定古环境和古生态环境有利于最初的珊瑚殖民的丘。底栖有孔虫种的稳定氧碳同位素记录表明，L。lobatula为古环境重建提供了可靠的同位素特征。特别是L. lobatula表明，最初的土丘生长开始于冰川模式，δ 18 O值有适度的偏移。D. coronata与其他底栖物种相比有很大的偏移。这种偏移可能与生命效应有关。根据有孔虫测试的δ 18 O，使用标准公式计算的底层水温在7至11°C之间，与已知的有利于冷水珊瑚生长和发育的温度范围一致。底层电流运输中间水团南部起源（地中海和比斯开湾）增强2.6Ma支持第一珊瑚定居点与INHG。底质δ 13 C和可分选的粉砂记录表明，早更新世水动力机制的特征是与中等深度MOW或其被SCW取代的垂直运动相关的较弱的水流强度。在这些缓慢的阶段后，增强MOW流再次占主导地位，并导致更强的电流强度和最有可能的沉积物侵蚀的挑战者丘。侵蚀与早期成岩（氧化）过程相结合覆盖了沉积层，如溶解的珊瑚骨骼、Ca含量和沉积物密度的增加、最小δ 13 C同位素值以及石膏和黄铁矿的出现所示，这意味着对原始和叠加的地球化学信号进行了仔细的评估。我们的结论是，挑战者丘的发展已经受到短期变化的水团从南部起源和可能的侵蚀事件的晚更新世设置。
The understanding of the paleoenvironment during initiation and early development of deep cold-water coral carbonate mounds in the NE Atlantic is currently a focus of international research. The Integrated Ocean Drilling Program (IODP) Expedition 307 drilled the 155m high Challenger Mound in the Porcupine Seabight (SW off Ireland) in order to investigate for the first time sediments from the base of a giant carbonate mound. In this study we focus in high resolution on 12m of sediments from Site 1317 encompassing the mound base. The mound initiation and start-up phase coincide with the intensification of the Northern Hemisphere Glaciation (INHG) at around 2.7Ma. Further carbonate mound development seems to be strongly dependent on rapid changes in paleoceanographic and climatic conditions at the Pliocene–Pleistocene boundary, especially characterized and caused by the interaction of intermediate water masses, the Mediterranean Outflow Water (MOW), the Eastern North Atlantic Water (ENAW) and the influence of Southern Component Water (SCW). This study is based on well-established proxies such as δ18O and δ13C of planktonic (Globigerina bulloides) and benthic foraminifera (Fontbotia wuellerstorfi, Discanomalina coronata, Lobatula lobatula, Lobatula antarctica, and Planulina ariminensis) as well as grain size parameters to identify the paleoenvironmental and paleoecological setting favourable for the initial coral colonization on the mound. Stable oxygen and carbon isotope records of benthic foraminiferal species indicate that L. lobatula provides a reliable isotopic signature for paleoenvironmental reconstructions. In particular, δ18O values of L. lobatula indicate that initial mound growth started in a glacial mode with moderate excursions in δ18O values. Carbon isotope values of D. coronata are significantly offset compared to other epibenthic species. This offset may be related to vital effects. Bottom water temperatures, calculated using standard equations based on δ18O of foraminiferal tests, range between 7 and 11°C, consistent with the known temperature range conducive for cold-water coral growth and development. Bottom currents transporting intermediate water masses of southern origin (Mediterranean and Bay of Biscay) enhanced at 2.6Ma supporting first coral settlements with the INHG. The benthic δ13C and the sortable silt records indicate that the early Pleistocene hydrodynamic regime was characterized by weaker current intensities associated with vertical movements of MOW or its replacement by SCW at intermediate depth. After these sluggish phases enhanced MOW flow dominated again and led to stronger current intensities and most probably sediment erosion on Challenger Mound. Erosion in combination with early diagenetic (oxidation) processes overprinted the sediment layers as indicated by dissolved coral skeletons, the increase in Ca-content and sediment density, minimum δ13Cplanktonicvalues, as well as the occurrence of gypsum and pyrite, implying a careful evaluation of original and overprinted geochemical signals. We conclude that the Challenger Mound development was already influenced by short-term variability of water masses from southern origin and possible erosional events comparable to the late Pleistocene setting.
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