RE:THE CRETACEOUS, HHMMM?
Brother it all depends on depth of source rock, you probably know from fractionating process what it takes to break down long carbon chain ---heavy oil --- HEAT. Shallower prospect suffee from this issue, unless they migrated from somewhere deep down below. At this point you cant make a blanket statement that all prospects close to shore are heavy oil. Alot depends on age of rock, how deep it is, and what the temperature and pressure its been cooking at