in fact, the term cark it is actually Hindi, and was picked up by the British during the Raj era. It was used prior to Australia's colonisation.
It stems from a Hindi word, like so many other english words such as bungalow, pajama, pakka, shampoo and a hundred others (books have been written on Hindi words coming into usage in english)
Back to cark.. it comes from the word Khak.. which means dirt, dust, etc. the word Khaki is also from the same root, meaning the colour of dust, or the colour of the dirt/mud, in Hindi.
So the term to 'cark it' derives from 'dust to dust, ashes to ashes' referring to death.. when we die, we return to dust.. therefore to cark it means to return to Khak...
thanks for the time