Extraction of calcareous dacryoconarid microfossils from limestones and mudrocks by surfactants paired with freeze-thaw processing.

Microfossils offer a wealth of paleoenvironmental information, but their extraction from consolidated material, especially ancient rocks, is time-consuming and often lacks systematic methodological development. This study examined the efficacy of repeated freeze-thaw processing paired with different surfactants (anionic, cationic, and detergent) on the extraction of fossils from the order Dacryoconarida, conically shaped calcareous microfossils that occur in diverse marine facies of the Devonian Period. A stepwise technique was developed involving saturation of rocks in either 18 Ω water or 25% NaCl, followed by freezing and then boiling in surfactant (Pinequat, Decon 90, or Calgon in Na 2 CO 3 solution). In comparison with saturation in NaCl solution, saturation in water generally had higher yields of disaggregated material and more intact fossils. All surfactants performed better at extraction compared to boiling in pure water. Across all lithologies examined, Na 2 CO 3 -buffered Calgon (sodium hexametaphosphate) disaggregated rock most efficiently, but Na 2 CO 3 solution alone generally had the highest yield of total and intact fossil specimens. Pinequat, a cationic surfactant, yielded more disaggregate for siliclastic samples compared to calcareous samples, but had lower fossil yield. Decon 90, an anionic surfactant, performed better at disaggregating limestones and had higher fossil extraction efficiency than Pinequat across all lithologies. Freeze-thaw processing pairing water saturation and 5% Na 2 CO 3 simmering is an effective treatment for the disaggregation of rocks to extract analytically viable amounts of dacryoconarids from fossiliferous samples. This pairing had greater fossil extraction potential than surfactants at the concentrations tested in this study and is recommended if the elemental composition of the target rocks is unconstrained. • For limestones, alkaline solutions and anionic surfactants extracted the most intact fossils. • Black shale was resistant to surfactants. Repeated water-based freeze-thaw processing was most effective for extraction. • For lithologies with high clay content Calgon and Na 2 CO 3 were most efficient at disaggregation. •.Calgon and Na 2 CO 3 have high disaggregating potential, but Calgon is more fragmentary to fossils than Na 2 CO Calgon and Na 2 CO 3 have high disaggregating potential, but Calgon is more fragmentary to fossils than Na 2 CO 3. • For arenaceous rocks, cationic surfactants may have a slightly higher disaggregation potential than anionic surfactants. [ABSTRACT FROM AUTHOR]