1. That is one of my concerns about ice-core data ...
... it can "miss" periods of sudden heat ...
As you are only identifying very small layers in a small cross-section, there isn't
the scope to recognise a minor unconformity - only the gross changes - and as
these brief heating events will coincide across corresponding sites around the
globe, it will be taken as "the recognised reference pattern" rather than the tragic
anomaly that it is.
Compare this to the (geologically) short-term damage that modern humans
have done not only to the fossil record but to the geological stratifications
over large parts of the globe: unnatural extraction & transporation of an incredibly
wide range of materials (from finely distributed minerals to gross earth-shifting
operations), scouring of large areas of land & seabed, and the addition of layers
of long-term pollution.
Future geologists will look back and deduce that the extinction event was caused
by global tsunamis triggered by the catastrophic impact of a meteorite constisting
mainly of coal mixed with radioactive plastic.