Department of Earth & Planetary Sciences, Yale University, New Haven, Connecticut, USA.
Instituto de Ciencias de la Ingeniería, Universidad de O'Higgins, Rancagua, Chile.
Geobiology. 2024 Jul-Aug;22(4):e12615. doi: 10.1111/gbi.12615.
The earliest evidence of complex macroscopic life on Earth is preserved in Ediacaran-aged siliciclastic deposits as three-dimensional casts and molds, known as Ediacara-style preservation. The mechanisms that led to this extraordinary preservation of soft-bodied organisms in fine- to medium-grained sandstones have been extensively debated. Ediacara-style fossilization is recorded in a variety of sedimentary facies characterized by clean quartzose sandstones (as in the eponymous Ediacara Member) as well as less compositionally mature, clay-rich sandstones and heterolithic siliciclastic deposits. To investigate this preservational process, we conducted experiments using different mineral substrates (quartzose sand, kaolinite, and iron oxides), a variety of soft-bodied organisms (microalgae, cyanobacteria, marine invertebrates), and a range of estimates for Ediacaran seawater dissolved silica (DSi) levels (0.5-2.0 mM). These experiments collectively yielded extensive amorphous silica and authigenic clay coatings on the surfaces of organisms and in intergranular pore spaces surrounding organic substrates. This was accompanied by a progressive drawdown of the DSi concentration of the experimental solutions. These results provide evidence that soft tissues can be rapidly preserved by silicate minerals precipitated under variable substrate compositions and a wide range of predicted scenarios for Ediacaran seawater DSi concentrations. These observations suggest plausible mechanisms explaining how interactions between sediments, organic substrates, and seawater DSi played a significant role in the fossilization of the first complex ecosystems on Earth.
地球上最早的复杂宏观生命证据保存在埃迪卡拉纪的硅质碎屑沉积物中，这些沉积物以三维铸型和模具的形式存在，被称为埃迪卡拉式保存。导致这种非凡的软躯体生物在细至中粒砂岩中得以保存的机制已经被广泛讨论。埃迪卡拉式化石化记录在各种沉积相中，这些沉积相的特征是纯净的石英砂岩（如同名的埃迪卡拉成员）以及成分不太成熟、富含粘土的砂岩和异质硅质碎屑沉积物。为了研究这种保存过程，我们使用不同的矿物基质（石英砂、高岭石和氧化铁）、各种软躯体生物（微藻、蓝藻、海洋无脊椎动物）以及一系列估计的埃迪卡拉纪海水溶解硅（DSi）水平（0.5-2.0mM）进行了实验。这些实验共同在生物体表面和有机基质周围的颗粒间孔隙中产生了广泛的无定形硅和自生粘土涂层。同时，实验溶液中的 DSi 浓度也逐渐降低。这些结果提供了证据表明，在不同基质组成和广泛预测的埃迪卡拉纪海水 DSi 浓度情景下，硅酸盐矿物的沉淀可以迅速保存软组织。这些观察结果表明了合理的机制，解释了沉积物、有机基质和海水 DSi 之间的相互作用如何在地球上第一个复杂生态系统的化石形成中发挥了重要作用。
