The enigma of rare Quaternary oolites in the Indian and Pacific Oceans: A result of global oceanographic physicochemical conditions or a sampling bias?
The enigma of rare Quaternary oolites in the Indian and Pacific Oceans: A result of global oceanographic physicochemical conditions or a sampling bias?
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DOI：
10.1016/j.quascirev.2018.09.028
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发表时间：
2018-11-15
影响因子：
4
通讯作者：
Bogus, K.
中科院分区：
文献类型：
--
作者：
Gallagher, S. J.;Reuning, L.;Bogus, K.
海洋鲕粒是浅海海水碳酸盐饱和度状态的标志性指示物，其形成传统上被归因于物理化学过程。印度 - 太平洋地区作为一个没有鲕粒岩的区域而引人注目，特别是在第四纪期间：这就是“鲕粒之谜”。在此，我们展示了国际大洋发现计划（综合大洋钻探计划356航次）在澳大利亚西部近海近期钻探的结果，该结果表明鲕粒层在距今73万年的更新世地层中很常见。由于存在长期受潮汐影响的平顶热带台地，这些台地适合在高水位期和海平面较低时期的数百到数千年间间歇性地形成鲕粒，从而形成了大量的“鲕粒工厂”。这项工作表明，海洋鲕粒在印度 - 太平洋地区可能实际上比之前所报道的更为常见。在更新世冰期，全球海洋碱度过去较高，并且与间冰期和全新世相比，印度 - 太平洋地区的大陆气候通常更为干旱。因此，冰期期间与较高碱度条件相关的干旱加剧促进了相邻热带碳酸盐台地上的鲕粒沉淀，特别是在干旱的澳大利亚近海。这些因素的共同作用表明，通过对印度 - 太平洋地区具有更新世长期存在的平坦碳酸盐陆架进行进一步钻探，可能会发现更多的“鲕粒工厂”。然而，澳大利亚以外的印度 - 太平洋第四纪鲕粒出现情况很罕见，这表明西北陆架可能是这种非骨骼沉淀的独特记录。对全新世之前鲕粒出现情况的岩石学和地球化学的进一步研究将为其起源以及生物、物理化学和其他因素在其形成过程中的相对作用提供见解。（C）2018爱思唯尔有限公司。保留所有权利。
Marine ooids are iconic indicators of shallow seawater carbonate saturation state, and their formation has traditionally been ascribed to physicochemical processes. The Indo-Pacific stands out as a region devoid of oolites, particularly during the Quaternary: the "ooid enigma". Here we present results from recent coring by the International Ocean Discovery Program (IODP Expedition 356) off west Australia that shows that ooid horizons are common in Pleistocene strata up to 730,000 years old. Extensive "ooid factories" were created due to the presence of long-lived tidally influenced flat topped tropical platforms suitable for intermittent ooid accretion over hundreds to thousands of years during highstands and times of lower sea level. This work suggests marine ooids may actually be more common in Indo-Pacific than previously reported. Past global ocean alkalinity was elevated during Pleistocene glacial periods and continental climate was generally more arid in the Indo-Pacific region compared to interglacials and the Holocene. Therefore, increased aridity associated with higher alkalinity conditions during the glacials facilitated ooid precipitation on adjacent tropical carbonate platforms particularly offshore from arid Australia. This confluence of factors suggests that more "ooid factories" may be encountered by further coring Indo-Pacific regions with Pleistocene flat long-lived carbonate shelves. However, Indo-Pacific Quaternary ooid occurrences outside Australia are rare, suggesting that the Northwest Shelf may be a unique archive of this non-skeletal precipitate. Further investigations into the petrography and geochemistry of pre-Holocene ooid occurrences will provide insights into their origin and the relative role of biotic, physicochemical and other factors in their formation. (C) 2018 Elsevier Ltd. All rights reserved.