A 30-year-old man was involved in a head-on collision and was unconscious for two minutes prior to EMS arrival. Five minutes before arriving at the hospital, the paramedic notices clear fluid draining from the patient's nose. Having seen this before, the paramedic places a drop from the patient's nose onto a piece of gauze. The nurse is looking for a clinical finding that is called the halo's sign. What type of fracture does the paramedic suspect the patient has?