And between that and the generally low levels of liquidity on this half-day holiday, markets turmoiled dramatically.

Before today, Brent had only fallen 10% or more on a single day in 14 occasions since the futures contract was launched more than three decades ago.

Stocks were crushed overnight with Small Caps leading the collapse (down over 5%) before the standard algo-driven ramp lifted everything into the US open. A big wave of selling hit the market then and continued accelerating back to the lows of the day into the European close.

So, finally, what happens next? Anyone looking for U.S. stocks to provide year-end fireworks is likely to be disappointed, if history is any guide. The S&P 500 Index's most recent move of more than 10% between Thanksgiving Day and the end of December occurred in 1991, according to data compiled by Bloomberg.