The Paleoproterozoic (1.7 Ga [billion years ago]) metasedimentary rocks of the Mount Barren Group in southwestern Australia contain burrows indistinguishable from ichnogenera Thalassinoides, Ophiomorpha, Teichichnus, and Taenidium, known from firmgrounds and softgrounds. The metamorphic fabric in the host rock is largely retained, and because the most resilient rocks in the sequence, the metaquartzites, are too hard for animal burrowing, the trace fossils have been interpreted as predating the last metamorphic event in the region. Since this event is dated at 1.2 Ga, this would bestow advanced animals an anomalously early age. We have studied the field relationships, petrographic fabric, and geochronology of the rocks and demonstrate that the burrowing took place during an Eocene transgression over a weathered regolith. At this time, the metaquartzites of the inundated surface had been weathered to friable sandstones or loose sands (arenized), allowing for animal burrowing. Subsequent to this event, there was a resilicification of the quartzites, filling the pore space with syntaxial quartz cement forming silcretes. Where the sand grains had not been dislocated during weathering, the metamorphic fabric was seemingly restored, and the rocks again assumed the appearance of hard metaquartzites impenetrable to animal burrowing.

澳大利亚西南部巴伦山群的古元古代（1.7 Ga [十亿年前]）变沉积岩包含与ichnogenera Thalassinoides、Ophiomorpha、Teichichnus和Taenidium无法区分的洞穴，从坚固地和软地中得知。主岩中的变质结构大部分被保留，并且由于序列中最具弹性的岩石变石英岩对于动物挖洞来说太硬，因此痕迹化石被解释为早于该地区最后一次变质事件。由于该事件的日期为 1.2 Ga，这将赋予高级动物异常早的年龄。我们研究了岩石的场关系、岩相结构和地质年代学，并证明了洞穴是在始新世海侵期间风化的风化层上发生的。此时，被淹没表面的偏石英岩已经风化成易碎的砂岩或松散的砂（矿化），允许动物挖洞。在这一事件之后，石英岩发生了再硅化，用形成硅质的合成石英胶结物填充孔隙空间。在风化过程中沙粒没有错位的地方，变质组织似乎恢复了，岩石再次呈现出动物洞穴无法穿透的坚硬偏石英岩的外观。