Miocene methane-derived carbonates from southwestern Washington, USA and a model for silicification at seeps
Miocene methane-derived carbonates from southwestern Washington, USA and a model for silicification at seeps
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DOI：
10.1111/j.1502-3931.2011.00280.x
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发表时间：
2012-04-01
期刊：
影响因子：
1.5
通讯作者：
Peckmann, Joern
中科院分区：
文献类型：
--
作者：
Kuechler, Rony R.;Birgel, Daniel;Peckmann, Joern
含有硅化化石的奇异石灰岩块，封闭在早中新世阿斯托里亚组的深水海洋硅质碎屑沉积物中，沿着美国华盛顿州西南部的哥伦比亚河北岸暴露。对来自四个地点的样品进行了研究，以澄清这些石灰岩矿床的起源和成岩作用。经过生物扰动和改造的石灰岩含有类似于现代和新生代深水甲烷渗漏的动物群。共生序列由五个阶段组成：（1）泥晶和微晶石； (2)纤维状、带状和葡萄状文石胶结物，部分被二氧化硅替代或重结晶为方解石； (3)黄色方解石； (4)石英取代碳酸盐相和石英胶结物； (5)等量方解石晶石和伪晶石。黄铁矿层经常分隔不同的碳酸盐相和生成物，表明腐蚀时期。负d 13 C碳酸盐值低至)37.6&V-PDB揭示了甲烷衍生碳的吸收。在其他情况下，d 13 C碳酸盐值高达7.1&表明残留的、富含13 C的碳库受到产甲烷作用的影响。脂质生物标志物包括 13 C-耗尽、古细菌 2,6,10,15,19-五甲基二十烷 (PMI; d 13 C:) 128&)、十字花烷和植烷，以及各种异碳链和反异碳链，最有可能源自硫酸盐还原细菌。生物标志物清单证明，大部分碳酸盐是由于硫酸盐依赖性甲烷厌氧氧化而形成的。化石和早期成岩碳酸盐胶结物的硅化以及石英胶结物的沉淀——在含有丰富硅藻或放射虫的沉积物中的其他甲烷渗漏灰岩中也观察到，是由于甲烷厌氧氧化导致碱度增加而导致二氧化硅骨架溶解的结果。一旦甲烷的厌氧氧化停止，pH值再次下降并且二氧化硅相会沉淀。
Exotic limestone masses with silicified fossils, enclosed within deep- water marine siliciclastic sediments of the Early to Middle Miocene Astoria Formation, are exposed along the north shore of the Columbia River in southwestern Washington, USA. Samples from four localities were studied to clarify the origin and diagenesis of these limestone deposits. The bioturbated and reworked limestones contain a faunal assemblage resembling that of modern and Cenozoic deep- water methane- seeps. Five phases make up the paragenetic sequence: (1) micrite and microspar; (2) fibrous, banded and botryoidal aragonite cement, partially replaced by silica or recrystallized to calcite; (3) yellow calcite; (4) quartz replacing carbonate phases and quartz cement; and (5) equant calcite spar and pseudospar. Layers of pyrite frequently separate different carbonate phases and generations, indicating periods of corrosion. Negative d 13 Ccarbonate values as low as) 37.6& V- PDB reveal an uptake of methane- derived carbon. In other cases, d 13 Ccarbonate values as high as 7.1& point to a residual, 13 C- enriched carbon pool affected by methanogenesis. Lipid biomarkers include 13 C- depleted, archaeal 2,6,10,15,19- pentamethylicosane (PMI; d 13 C:) 128&), crocetane and phytane, as well as various iso- and anteiso- carbon chains, most likely derived from sulphate- reducing bacteria. The biomarker inventory proves that the majority of the carbonates formed as a consequence of sulphate- dependent anaerobic oxidation of methane. Silicification of fossils and early diagenetic carbonate cements as well as the precipitation of quartz cement - also observed in other methane- seep limestones enclosed in sediments with abundant diatoms or radiolarians is a consequence of a preceding increase of alkalinity due to anaerobic oxidation of methane, inducing the dissolution of silica skeletons. Once anaerobic oxidation of methane has ceased, the pH drops again and silica phases can precipitate.