Electron microprobe results of clay minerals from samples of the Frankenwald and the Thüringer Wald

Late Devonian (Frasnian) pillow basalts from the Frankenwald and Thüringer Wald within the Saxothuringian zone in Germany were found to contain abundant putative biogenic filaments, indicating that the volcanic rocks once harbored microbial life. The mineralized filaments are found in calcite-filled amygdules (former vesicles), where they started to form on internal surfaces of vesicles after seawater ingress. The filaments postdate an early fibrous carbonate cement but predate later equant calcite spar, revealing syngenetic formation. A biogenic origin of filaments is indicated by their size and morphology resembling modern microorganisms, their independence of crystal faces and cleavage plans, complex branching patterns, and internal segmentation. The filamentous microorganisms represent cryptoendoliths that lived in structural cavities of the basalt. They became preserved upon microbial clay authigenesis similar to the encrustation of modern prokaryotes in iron-rich environments. Filaments consist of clay minerals with the endmember composition berthierine-chamosite and illite-glauconite. Based on the discovery of fossilized filamentous microorganisms in Late Devonian pillow basalts of the Saxothurigian zone that are similar to filaments previously found in Middle Devonian pillow basalts of the Rhenohercynian zone, it is apparent that cryptoendolithic life was more widespread than previously recognized. Structural cavities within seafloor basalt may thus represent a common, perhaps universal niche for life in the oceanic crust.

在德国萨克森-图林根带（Saxothuringian zone）内的弗兰肯瓦尔德（Frankenwald）与图林根林山（Thüringer Wald）地区产出的晚泥盆世（弗拉斯期）枕状玄武岩中，发现了大量推定的生物成因丝状体，表明这类火山岩曾栖息过微生物生命。这些矿化丝状体赋存于充填方解石的杏仁体（原气孔）中，其形成始于海水侵入后气孔的内表面。丝状体的形成时间晚于早期纤维状碳酸盐胶结物，但早于后期等轴方解石石晶，显示其为同生形成。丝状体的生物成因依据包括：其尺寸与形态酷似现代微生物、不受晶面和解理面的约束、具有复杂的分枝形态以及内部分节结构。这类丝状微生物属于隐内生微生物（cryptoendoliths），曾栖息于玄武岩的构造空腔中。它们通过类似富铁环境中现代原核生物结壳作用的自生黏土微生物成岩过程得以保存。丝状体由黏土矿物组成，端元成分包括贝得石-鲕绿泥石（berthierine-chamosite）以及伊利石-海绿石（illite-glauconite）。基于萨克森-图林根带晚泥盆世枕状玄武岩中化石丝状微生物的发现——其与此前在莱茵海西带（Rhenohercynian zone）中泥盆世枕状玄武岩内发现的丝状体极为相似——可以明确，隐内生生命的分布范围比此前认知的更为广泛。因此，海底玄武岩内的构造空腔或许代表了洋壳中一种普遍存在、甚至可能是普适性的生命生境。