Improved graptolite isolation technique and micro/nanostructure analysis
Article
Figures
Metrics
Preview PDF
Reference
Related
Cited by
Materials
Abstract:
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.
