Data from: Taphonomy of the Ediacaran fossil Pteridinium simplex preserved three-dimensionally in mass flow deposits, Nama Group, Namibia

Ediacara-type fossils are found in a diverse array of preservational styles, implying that multiple taphonomic mechanisms might have been responsible for their preservational expression. For many Ediacara fossils, the “death mask” model has been invoked as the primary taphonomic pathway. The key to this preservational regime is the replication or sealing of sediments around the degrading organisms by microbially induced precipitation of authigenic pyrite, leading toward fossil preservation along bedding planes. Nama-style preservation, on the other hand, captures Ediacaran organisms as molds and three-dimensional casts within coarse-grained mass flow beds, and has been previously regarded as showing little or no evidence of a microbial preservational influence. To further understand these two seemingly distinct taphonomic pathways, we investigated the three-dimensionally preserved Ediacaran fossil Pteridinium simplex from mass flow deposits of the upper Kliphoek Member, Dabis Formation, Kuibis Subgroup, southern Namibia. Our analysis, using a combination of petrographic and micro-analytical methods, shows that Pteridinium simplex vanes are replicated with minor pyrite, but are most often represented by open voids that can be filled with secondary carbonate material; clay minerals are also found in association with the vanes, but their origin remains unresolved. The scarcity of pyrite and the development of voids are likely related to oxidative weathering and it is possible that microbial activities and authigenic pyrite may have contributed to the preservation of Pteridinium simplex; however, any microbes growing on P. simplex vanes within mass flow deposits were unlikely to have formed thick mats as envisioned in the death mask model. Differential weathering of replicating minerals and precipitation of secondary minerals greatly facilitate fossil collection and morphological characterization by allowing Pteridinium simplex vanes to be parted from the massive hosting sandstone.

埃迪卡拉型化石（Ediacara-type fossils）以多样的保存样式被发现，这暗示多种埋藏学（taphonomic）机制可能共同塑造了其化石保存特征。针对多数埃迪卡拉化石，“死亡面具”模型（death mask model）被视为主要的埋藏学途径。该保存机制的核心在于，微生物诱导的自生黄铁矿（authigenic pyrite）沉淀，在降解中的生物体周围形成沉积物的包覆或胶结，从而使得化石沿层面（bedding planes）得以保存。而纳马型保存（Nama-style preservation）则将埃迪卡拉纪生物以铸模和三维铸型的形式保存在粗粒块流沉积层（coarse-grained mass flow beds）中，此前该保存类型被认为几乎或完全不存在微生物保存作用的证据。为进一步理解这两种看似迥异的埋藏学途径，我们对产自纳米比亚南部库伊比斯亚群（Kuibis Subgroup）达比斯组（Dabis Formation）上部克利霍克段（Kliphoek Member）块流沉积中的三维保存埃迪卡拉纪化石简单翼形盘（Pteridinium simplex）开展了研究。我们结合岩石学（petrographic）与微分析方法开展的分析显示，简单翼形盘的翼片虽有少量黄铁矿包覆，但多数情况下以开放孔隙的形式产出，孔隙可被次生碳酸盐（secondary carbonate）矿物充填；翼片周边还伴生有黏土矿物，但其成因尚未明确。黄铁矿的稀缺性与孔隙的形成可能与氧化风化（oxidative weathering）作用相关，且微生物活动与自生黄铁矿或许也曾助力简单翼形盘的化石保存；但在块流沉积中生长于P. simplex翼片上的微生物，大概率并未形成“死亡面具”模型所设想的厚层生物膜。包覆矿物的差异风化（differential weathering）与次生矿物的沉淀，使得简单翼形盘的翼片可从巨厚的赋存砂岩（hosting sandstone）中剥离，极大地便利了化石采集与形态学表征。