Palaeozoic hypercalcified sponges were ubiquitous Ordovician—Devonian reef builders but, despite their rich fossil record, their original skeletal mineralogy and microstructure remain poorly understood. This study provides the first application of electron backscatter diffraction (EBSD) to analyse skeletal structure of Silurian and Devonian stromatoporoids. The two Silurian and two Devonian stromatoporoid taxa selected are typical of stromatoporoids in showing poor preservation. A reference sample of an exceptionally well-preserved hypercalcified chaetetid sponge from the Carboniferous Buckhorn Asphalt Quarry (a fossil lagerstätte renowned for its preservation of skeletal microstructures) contains evidence that its skeleton comprised distinct bundles of single-crystal fibres, similar to modern hypercalcifying sponges. Similar bundles of crystal fibres are proposed here as the original microstructure of stromatoporoids, and acted as precursors to the coarse fibrous calcitic overprinting recrystallisation that is orientated normal to the growth layers, seen in all stromatoporoids viewed in cross-polarised light. The studied stromatoporoids show pronounced microporosity and micro-dolomite inclusions which are circumstantial evidence of an original composition of high-Mg calcite (HMC). We propose that the evidence of fibrous structures might be linked to inclusions of hydrated amorphous calcium carbonate (ACC·H 2 O) in the skeleton at the time of early diagenesis, as occurs in modern calcified sponges. The possible HMC skeletal composition of Palaeozoic stromatoporoids supports earlier views that the mineral composition of hypercalcifying reef builders is linked to Phanerozoic oscillations in the ratio of Mg:Ca, expressed as aragonite-calcite seas; stromatoporoids thrived in times of calcite-seas.

中文翻译：

---

使用电子背散射衍射 (EBSD) 分析古生代层孔虫和毛囊虫；对原始矿物学和微观结构的影响

古生代高钙化海绵是无处不在的奥陶纪-泥盆纪珊瑚礁建造者，但尽管有丰富的化石记录，但对其原始骨骼矿物学和微观结构仍知之甚少。这项研究首次应用电子背散射衍射 (EBSD) 来分析志留纪和泥盆纪层孔虫的骨骼结构。选择的两个志留纪和两个泥盆纪层孔虫类群是典型的层孔虫类，显示出较差的保存。来自石炭纪巴克霍恩沥青采石场（一种以保存骨骼微结构而闻名的拉格施塔特化石）的保存异常完好的高钙化毛毛虫海绵的参考样本包含证据表明其骨架由不同的单晶纤维束组成，类似于现代高钙化海绵。类似的晶体纤维束在这里被提议作为层孔体的原始微观结构，并作为粗纤维方解石叠印重结晶的前体，其方向垂直于生长层，在交叉偏振光下观察的所有层孔体中都可以看到。所研究的层孔体显示出明显的微孔和微白云石包裹体，这是高镁方解石 (HMC) 原始成分的间接证据。我们提出，纤维结构的证据可能与早期成岩作用时骨架中的水合无定形碳酸钙 (ACC·H 2 O) 包裹体有关，如现代钙化海绵中发生的那样。古生代层孔体可能的 HMC 骨骼组成支持早期的观点，即高钙化礁体的矿物组成与显生宙 Mg:Ca 比率的振荡有关，以文石-方解石海表示；层孔虫在方解石海时代繁衍生息。