3.5 million year, Lake El'gygtgyn, core analysis

So I'm at page 386 of Climate Change Synthesis and learned about this meteor formed, lake, that has been collecting sediment in Siberia since it was formed. I'll have to go back to read the early reports but apparently this provides a credible record of ice free, Arctic periods:
http://www.geo.umass.edu/faculty/jbg/Mellesetalscience2012.pdf
http://www.geo.umass.edu/lake_e/SOM1222135s.pdf

Bob Wilson