I wouldn't call it wrong, but "the" lays stress on one particular marketing team. Saying "a marketing team" could mean any marketing team in the country/city/world/ etc. The marketing team refers to one specific team. The one you have in mind. I hope this helps.
Thanks for getting back to me. Sorry, the choice was between "The Marketing team" and "Marketing team", not "The Marketing team" and "A Marketing team."