Palaeozoic stromatoporoid futures: A discussion of their taxonomy, mineralogy and applications in palaeoecology and palaeoenvironmental analysis
Palaeozoic stromatoporoid futures: A discussion of their taxonomy, mineralogy and applications in palaeoecology and palaeoenvironmental analysis
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古生代层孔类未来：对其分类学、矿物学及其在古生态学和古环境分析中的应用的讨论
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发表时间：
2013
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通讯作者：
Wang Yuan
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作者：
S. Kershaw;Liu Min;Wang Yuan
摘要 古生代层孔类是中奥陶世至晚泥盆世生物礁及相关相中常见的钙化海绵。分类学工作众所周知，但由于基于钙质骨骼与针状体（古生代层孔类动物几乎完全缺乏）的分类方案之间的冲突而存在争议；然而，钙质骨骼的较低级别分类（属级别）被认为可以可靠地应用于古生物学研究。层孔类生态学的知识还很薄弱，因此只有少数志留纪和泥盆纪的案例研究提供了全面的信息。因此，尽管层孔虫可能能够处理它们最常出现的细粒沉积物，但尚未全面了解层孔虫对环境条件的反应。许多层孔虫属仅具有某些生长形式，因此未来重点关注在生态研究中使用低级分类学，通过高分辨率研究中的综合采样，可能会建立层孔虫与其环境之间的关系。层孔类生物中的共生生物和生长带是此类工作中具有巨大潜力的方面。对层孔类动物的矿物学仍然知之甚少。无论它们的表面保存状态如何（从明显保存完好到钙质骨骼特征完全丧失），所有层孔类生物实际上都已基本上重结晶。它们经历了一种特殊的成岩作用，所有层孔类的钙质骨架和廊道胶结物都被垂直于生长层状排列的不规则细长方解石晶体覆盖，在交叉偏振光下最清晰可见。层孔菌与软体动物壳共生，软体动物壳总是完全重结晶或溶解（以内部和外部模具的形式存在）；这种差异意味着，虽然软体动物在化石记录中的代表性可能不足，但层状类动物却不然，这为古生态学研究其组合提供了信心。层孔类缺乏可轻易将其归类为文石或低镁方解石的特征；它们可能是高镁方解石，但证据是间接的。它们独特的成岩结构也对关于层孔类与文石/方解石海概念之间关系的争论产生了影响，这需要更多的工作。
Abstract Palaeozoic stromatoporoids are calcified sponges common between Middle Ordovician and Late Devonian times in reefs and related facies. Taxonomic work is well known, but controversial because of conflict between classification schemes based on the calcareous skeleton versus spicules (which are almost completely lacking in Palaeozoic stromatoporoids); however, lower-level taxonomy (at genus-level) of the calcareous skeleton is considered reliable to be applied in palaeobiological study. Knowledge of stromatoporoid ecology is poorly developed, such that comprehensive information is available for only a few case studies, in some Silurian and Devonian examples. Thus an overall understanding of stromatoporoid responses to environmental conditions has not yet been achieved, although stromatoporoids were likely able to deal with fine-grained sediment where they mostly occur. Many stromatoporoid genera have only certain growth forms, so future focus on the use of low-level taxonomy in ecological studies, by comprehensive sampling in high-resolution studies, may establish the relationships between stromatoporoids and their environments. Intergrown organisms and growth banding in stromatoporoids are aspects that have great potential in such work. Mineralogy of stromatoporoids remains poorly understood. Regardless of their apparent state of preservation (ranging from apparently well-preserved to complete loss of calcareous skeleton features) all stromatoporoids are in fact substantially recrystallized. They underwent a peculiar diagenesis, whereby the calcareous skeleton and gallery cements of all stromatoporoids are overprinted by irregular elongated calcite crystals arranged normal to the growth laminations, most clearly visible in cross-polarized light. Stromatoporoids co-occur with mollusc shells that are always either fully recrystallized or dissolved (present as internal and external moulds); this difference means that while molluscs are likely under-represented in the fossil record, stromatoproids are not, providing confidence for palaeoecological work on their assemblages. Stromatoporoids lack characters which would readily classify them as being originally aragonite or low-Mg calcite; they may have been high-Mg calcite but the evidence is circumstantial. Their peculiar diagenetic fabric also has implications for the debate about the relationship between stromatoporoids and the concept of aragonite/calcite seas, which requires more work.