Possible animal-body fossils in pre-Marinoan limestones from South Australia
Possible animal-body fossils in pre-Marinoan limestones from South Australia
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DOI：
10.1038/ngeo934
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发表时间：
2010-09-01
影响因子：
18.3
通讯作者：
Simons, Frederik J.
中科院分区：
文献类型：
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作者：
Maloof, Adam C.;Rose, Catherine V.;Simons, Frederik J.
新元古代被斯图亚特期（约7.1亿年前）和马里诺期（约6.35亿年前）的冰期所打断。在南澳大利亚，冰川作用留下的岩石被一系列沉积在热带纬度的石灰石和页岩隔开。在这里，我们描述了来自特里佐纳组的毫米到厘米尺度的化石，它早于马里诺冰期。这些弱钙化的化石以砧状、叉骨状、环状和穿孔板状出现，并被包裹在叠层石灰岩中。Trezona组化石比已知最古老的这种尺寸的钙化化石早9000万年，并且不能与周围的方解石基质分开，也不能用传统的基于x射线的层析扫描方法成像。相反，我们通过连续研磨和扫描每个样本，以50.8 μ m的分辨率来追踪单个化石的横截面。根据这些图像，我们构建了化石的三维数字模型。我们的重建显示了一群不对称的椭球形生物，它们的内部管道网络导致化石表面出现圆形孔。我们认为，如果这些化石被确定为海绵级后生动物，那么这些礁栖化石的几个特征就能得到最好的解释。
The Neoproterozoic era was punctuated by the Sturtian (about 710 million years ago) and Marinoan (about 635 million years ago) intervals of glaciation. In South Australia, the rocks left behind by the glaciations are separated by a succession of limestones and shales, which were deposited at tropical latitudes. Here we describe millimetre- to centimetre-scale fossils from the Trezona Formation, which pre-dates the Marinoan glaciation. These weakly calcified fossils occur as anvil, wishbone, ring and perforated slab shapes and are contained within stromatolitic limestones. The Trezona Formation fossils pre-date the oldest known calcified fossils of this size by 90 million years, and cannot be separated from the surrounding calcite matrix or imaged by traditional X-ray-based tomographic scanning methods. Instead, we have traced cross-sections of individual fossils by serially grinding and scanning each sample at a resolution of 50.8 mu m. From these images we constructed three-dimensional digital models of the fossils. Our reconstructions show a population of ellipsoidal organisms without symmetry and with a network of interior canals that lead to circular apertures on the fossil surface. We suggest that several characteristics of these reef-dwelling fossils are best explained if the fossils are identified as sponge-grade metazoans.