This damned tephra problem

I hate to bore my usual readers with research problems but... I'm having a research problem.

I've been mulling over the slides from the Drangajökull outlet glacier core microtephras for some time now, but this week I've finally been able to focus on the problem (as I was microprobing other samples last week). Basically the microtephra from the peat core taken near the outlet glacier comes in three varieties: generally silicic, generally mafic, and then crazy microlite-studded bright orange. My samples from the archaeological peat core, and from the lake, which were cored about 5km away as the crow flies, have the first two -- and absolutely nothing like the third.

My first guess is that the orange colour is the result of some chemical leaching in the soil. I found a paper a few minutes ago that might tell me more about it but it's 11pm and my brain is fried so I'll check it in the morning.

The microlites are a more serious issue. They indicate that the microtephra has come from a source close by -- but the archaeological site is closer to any source volcanoes than this core. And if the tephra was transported by air, then it should have fallen in both places anyway. The presence of the glacier might create a rain shadow? Or something like that? Or meltwater pulses? I'm trying to come up with any reason why this might be the case. I need to come up with something convincing and interesting, however, because I'm giving a paper at the GSA on Halloween and part of it has to do with this research.

Blergh!