Bitcoin Cash started trading on GDAX at ~8:20 EST on 12/19/2017. The order book shows orders lining up buyers and seller at about $3300 but within minutes of opening it rocketed higher to $5000 and then even higher to $9500 on very light volume until GDAX essentially halted transaction again. Meanwhile the spread at other exchanges was extremely large with BCH still trading at $3300-$3450. Talk about arbitrage opportunities.
Clearly something is amiss at GDAX. They posted an update at ~8:24 EST:
|BCH on BitFinex is trading at a $6,000 discount to BCH on GDAX pictured below|
|BCH opens for trading on GDAX|
|GDAX BCH Status|