CHARACTERIZING RARE SPELEOTHEMS: RESUMING THE CONVERSATION ABOUT SHIELDS FORMATIONS

In solution caves there are different types of speleothems, among these we can find cave shields, also known as palettes. Shields are rare to find, this is why there is limited literature on the formation of them. In this study, we analyzed a piece of a shield (ECS) from Endless Caverns, located in the city of New Market, Virginia. Its dimensions are 22.3 cm in length, 23.1 cm in width, 15 cm in height, and 25.4 cm along its growth axis. For this specimen, we acquired subsamples with a resolution of 0.5 cm by micromilling following the growth axis through the concentric layers using a tungsten carbide drill bit. Currently with the subsampled material, several analyses are performed, including stable isotope chemistry to find existing trends of carbon and oxygen isotopes (climatic archive), Hendy’s test to detect the variation and equilibrium of stable isotope (C and O) through one layer, and U/Th dating to construct an age model.

Previous observations describe cave shield as a speleothem made up of two plates divided by a headline fracture, but when polishing and dissecting the sample, it was observed that the flowstone is not an accessory but is part of the lower part. Additional preliminary results the Scanning Electron Microscopy (SEM) revealed “boundary zones” where calcite crystals (<50 mm) alternate with crystals rich in silicon, as indicated by Energy Dispersive X-ray (EDX) analysis. This suggests an alternative genesis for shield speleothems, potentially involving clay sediments in cave environments. Additionally, sediments from Endless Caverns are being analyzed using X-Ray Fluorescence (XRF) to determine their elemental composition and compare them to the elements found in the shield. The finding from this research could enhance our understanding of how sediments dynamics in caves influence speleothem formation and make interpretation towards the rarity of shields.