Stable isotope analysis and biomarkers of carbonates from the Columbia River in southwestern Washington, USA

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. […]

美国华盛顿州西南部哥伦比亚河北岸，暴露于早至中中新世的阿斯托里亚层深水海洋硅质碎屑沉积之中，独特的石灰岩堆积体，其中含有硅化石化石，经过生物扰动和再加工，其动物群组合与现代及新生代深海甲烷渗漏相类似。通过对四个地点的样本进行研究，以阐明这些石灰岩沉积物的起源和成岩作用。这些生物扰动和再加工的石灰岩包含的生物群落与现生及新生代深海甲烷渗漏的生物群落相似。成岩序列由五个阶段组成：（1）微晶及微细晶；（2）纤维状、带状及葡萄状方解石胶结物，部分被石英取代或重结晶为方解石；（3）黄色方解石；（4）石英取代碳酸盐阶段及石英胶结物；（5）等轴方解石细晶及假晶。黄铁矿层频繁地分隔不同的碳酸盐阶段和世代，指示了腐蚀期。