**This formed an obvious contrast and so sarcastic** - remove this sentence as it doesn't make any sense. 'Contrast' can be a noun or verb, so if you want to use the word you'd need to use it as a verb here: it contrasted with.... 'Sarcastic' is an adjective, meaning 'given to using irony in order to make fun of, or convey contempt', as so isn't the right word to use here. Someone needs to be sarcastic (to someone else), the contrast cannot be sarcastic. I think you mean to say 'ironic' perhaps (it was ironic: eg. 'ironic' means: the expression of one's meaning by using language that normally signifies the opposite.