Cyclic anoxia and organic rich carbonate sediments within a drowned carbonate platform linked to Antarctic ice volume changes: Late Oligocene-early Miocene Maldives-猫眼课题宝

DOI：

10.1016/j.epsl.2019.05.019

发表时间：

2019-09

期刊：

Earth and Planetary Science Letters

影响因子：

5.3

通讯作者：

中科院分区：

地球科学1区

文献类型：

作者：

P. Swart;C. Blättler;M. Nakakuni;G. Mackenzie;C. Betzler;G. Eberli;J. Reolid;M. Alonso-García;A. Slagle;J. Wright;D. Kroon;J. Reijmer;A. L. Hui Mee;J. Young;C. Alvarez‐Zarikian;O. Bialik;J. Guo;Sebastian Haffen;S. Horozal;M. Inoue;L. Jovane;L. Lanci;J. Laya;T. Lüdmann;B. Nagender Nath;K. Niino;L. Petruny;S. Pratiwi;X. Su;C. Sloss;Z. Yao

本文报道了国际海洋发现计划（IODP）第359次考察期间在马尔代夫群岛钻探的U1466和U1468站点新发现的晚渐新世和早中新世（1024.9 ~ 1020 Ma）厚层层序（1000 m）富有机质沉积物（腐泥）和远洋（贫有机质）碳酸盐的互层产出。这种情况是不寻常的，因为该序列位于环礁间盆地内周围洋底以上1 000米以上，与任何已知的全球海洋事件无关。在较暗的地层中，总有机物含量高达35%，而夹层碳酸盐的浓度低于0.1%。缺氧沃茨的微量元素特征，如Mo、V、Cr、U和Pb，与有机碳浓度呈正相关。氮同位素数据显示，没有证据表明，高的总有机碳的间隔与上升流驱动的生产力提高。相反，高有机碳与缺氧的间隔有关。我们认为，与南极冰量变化有关的海平面波动限制了与开阔洋的交换，导致环礁间盆地的底部沃茨周期性地缺氧。渐新世末期的台地结构，加上全球海平面的高水位，为轨道驱动的海平面变化创造了条件，产生了腐泥的循环沉积。所提出的机制可以作为一个类似的碳酸盐岩台地设置内的其他发生的有机碳丰富的沉积物。

This paper reports on the newly discovered occurrence of thick sequences (∼100 m) of Late Oligocene and Early Miocene (∼24.9 to ∼20 Ma) interbedded organic-rich sediments (sapropels) and pelagic (organic poor) carbonates at Sites U1466 and U1468 drilled in the Maldives archipelago during the International Ocean Discovery Program (IODP) Expedition 359. This occurrence is unusual in that this sequence is located > 1000 m above the surrounding ocean floor within an inter-atoll basin and not linked to any known global oceanic events. Total organic content reaches as high as 35% in the darker layers, while the interbedded carbonates have concentrations of less than 0.1%. Trace elements characteristic of anoxic waters, such as Mo, V, Cr, U, and Pb, correlate positively with concentrations of organic carbon. Nitrogen isotopic data show no evidence that the intervals of high total organic carbon are related to enhanced productivity driven by upwelling. Instead, high organic carbon is associated with intervals of anoxia. We propose that sea-level fluctuations linked to changes in Antarctic ice volume restricted exchange with the open ocean causing bottom waters of the inter-atoll basin to become anoxic periodically. The architecture of the platform at the end of the Oligocene, combined with the global sea-level highstand, set the stage for orbitally-driven sea-level changes producing cyclic deposition of sapropels. The proposed mechanism may serve as an analogue for other occurrences of organic carbon-rich sediments within carbonate platform settings.

Cyclic anoxia and organic rich carbonate sediments within a drowned carbonate platform linked to Antarctic ice volume changes: Late Oligocene-early Miocene Maldives

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