由于保存状态等因素, 很多笔石标本的始端发育型式和微观形态尚未被完全认识。立体或半立体保存的笔石实体标本, 以原始状态保存了笔石的大部分微细构造, 是研究笔石化石的最佳材料。然而, 这种保存状态在世界范围内都很罕见, 且分离困难。这些立体的标本可以通过特定的溶解方法分离出来, 但经常因破损和碎裂, 导致很多重要的笔石标本无法正常获取。本文介绍一种用发烟硝酸提高孤立笔石获取率和完整度的化石酸处理方法。该方法以黑色泥岩样品为处理对象, 并适用于从其他类似岩性样品获取孤立标本。通过选样品、放样品、酸处理、除杂质等流程, 本研究成功在溶液中分离出孤立笔石标本, 并使用发烟硝酸对标本进行改性, 有效避免了易断裂标本在处理过程中(带离溶液、转移容器和微观试验分析)发生碎裂, 从而显著提高了孤立标本的获取率和完整性。获得保存精美的孤立实体标本,在此基础上使用双束电镜对其开展微纳结构实验分析, 开展对背曲笔石属(Campograptus)的新探索。微纳结构实验分析展现了背曲笔石属的胞管新形态细节、体壁微纳结构以及内部空隙分布。首次观察到胞管口部具有半圆形、唇片状的口檐(thecal apertural lobe), 并发现了胞管的口部侧上方发育成对的、粗短的口刺(thecal apertural spine)。首次在胎管内壁上发现外皮条带(cortical bandages)。通过微纳结构研究首次证实了“胎索”结构存在于背曲笔石属的胎管中, 为笔石分类、系统发育及页岩油气生储潜力等研究提供了重要依据。

Due to their preservation modes, the proximal development and micromorphology of graptolites are not fully known. Three-dimensional or partially three-dimensional specimens of graptolites, preserving most of the microstructures in their original states, are the perfect materials for graptolite study. However, these modes of preservation are rare and it is difficult to isolate specimens from the matrices. These three-dimensionally preserved specimens can be isolated using specific dissolving techniques, but many of these isolated specimens cannot be used for further studies due to frequent breakages and fragmentations. Here we introduce an improved technique using fuming nitric acid to improve the acquisition rate and integrity of isolated graptolites. This technique applies to treating black mudstone samples and can be widely used to acquire isolated specimens from other samples with similar lithology. Through the procedure of sample selection and placement, acidic treatment, and residue removal, this technique uses fuming nitric acid to modify the flexibility of isolated graptolite specimens after they are chemically separated from the matrices in the solution. The introduction of fuming nitric acid to the procedure significantly enhances the flexibility and successfully reduces the fragmentations of those fragile specimens during their removal from the solutions and transfer to other containers, and mounting for stereo-microscopic or scanning electronic microscopic observations. Therefore, the improved technique significantly increases the acquisition rate and integrity of the isolated graptolite specimens. We have acquired exquisite, isolated specimens by using this improved technique. Based on these specimens, we observed their micro/nanostructures using FIB-SEM. The results reveal some new morphological features of the thecae, and some micro/nanostructures of the periderm, and the distribution of retained internal cavities of Campograptus. Semicircular, lip-shaped, thecal apertural lobes of Campograptus, typified by development of paired, stubby thecal apertural spines projecting disto-laterally from the thecal apertures, are observed for the first time. Cortical bandages are also discovered for the first time in the internal periderm of sicula. Our observation using FIB-SEM confirms that the poorly-known “virga” structure exists in the sicula of Campograptus. This observation provides an important clue for the taxonomy and phylogeny of graptolites, as well as the evaluation of the potential of the formation and entrapment of oil and gas in shale.