i have a diesel merit astra 1.7 td and its overheating?

my diesel 1.7 merit is overheating, just suddenly noticed the temp gauge nearly in the red. i removed the thermostat but its still the same. enigine has done 90k and when i remove the header tank cap, it violenltly bubbles and i could see a slight oiliness about the water. is it likely that my cylnder head gasket has blown. thanks in advance for solutions. kenny.