Department of Earth Sciences, University of New Brunswick, Fredericton, New Brunswick, Canada.
Planetary and Space Science Centre, University of New Brunswick, Fredericton, New Brunswick, Canada.
Geobiology. 2018 Nov;16(6):610-627. doi: 10.1111/gbi.12310. Epub 2018 Aug 13.
Microscopic globular structures have been observed in some beds of oil shale from eastern Utah. These beds comprise carbonate-dominated mud that is interlaminated with variably thick and continuous organic-rich layers. Collectively they are enriched in phosphorus, REEs, and actinides. The beds are considered of lacustrine origin and assigned to the Eocene Green River Formation. The globules themselves are of microcrystalline carbonate fluorapatite (μCFA), often contain concentric internal structures, and usually group together in clusters of up to 80, possibly more. Detailed SEM and microprobe analyses have revealed tungsten (W) to be almost exclusively associated with the globular clusters found within the more organic-rich laminae, often at concentrations of over 200 ppm, two orders of magnitude above shale standards. The globular structures are present in freshly cut sections where they occasionally grade into a μCFA matrix cement. This, together with the draping of the clusters by stringers of organic matter that would have accumulated in the Eocene lake, confirms that the structures are not a contaminant. The limited range of sizes and globular shapes is consistent with the morphology of coccoidal bacteria: Concentric internal structures may represent remnants of the nucleoid and cell wall. Paired concentric structures may indicate cell division (reproduction) processes were occurring until mineralization. The phosphate mineralization itself may have been promoted by release of phosphate from the stressed cells, bringing porewaters to supersaturation, or by the cells acting as nucleation sites. The recording of trace amounts of W almost exclusively in globular clusters preserved in the most organic-rich stringers (anoxia prone) further suggests facultative use of W-enzymes in a microbial metabolism. Combined, their context, morphology, and indication of biogenic process are strong evidence that the structures are fossilized (phosphatized) microbes, possibly sulfate-reducing bacteria, or methanogenic archaea.
在犹他州东部的一些油页岩层中观察到了微观球状结构。这些层由碳酸盐占主导的泥岩组成，与厚度不同且连续的富有机层互层。它们总体上富含磷、稀土元素和锕系元素。这些层被认为是湖泊成因的，属于始新世绿河组。这些球本身是微晶氟磷灰石（μCFA），通常含有同心内部结构，并且通常聚集在一起形成多达 80 个的簇，可能更多。详细的 SEM 和微探针分析表明，钨（W）几乎完全与在更富有机层内发现的球状簇相关联，其浓度通常超过 200ppm，比页岩标准高出两个数量级。这些球状结构存在于新切割的部分中，在那里它们偶尔会变成μCFA 基质胶结物。这与簇被有机物条纹包裹在一起的情况一起，这些有机物条纹会在始新世湖中积累，证实这些结构不是污染物。大小和球状形状的有限范围与球菌状细菌的形态一致：同心内部结构可能代表核区和细胞壁的残余物。成对的同心结构可能表明细胞分裂（繁殖）过程在矿化之前一直在发生。磷酸盐矿化本身可能是由于应激细胞释放磷酸盐，使孔隙水过饱和，或者由于细胞充当成核位点而促进的。痕量 W 几乎仅在保存在最富有机条纹中的球状簇中记录（缺氧倾向）进一步表明，在微生物代谢中，W-酶可能具有兼性用途。总的来说，它们的上下文、形态和生物过程的指示是强烈的证据，表明这些结构是已矿化（磷酸化）的微生物，可能是硫酸盐还原菌或产甲烷古菌。
