A bit of paleo for the enthusiasts. Nearly forty years ago, a Mexican fisherman named Rudesindo Cantarell noticed his shrimp nets kept on getting coated with sludge in Campeche Bay, off the Yucatan Peninsula. Turns out crude oil was bubbling up offshore. Today, the Cantarell oil fields are the second-largest producing in the world... and in rapid decline, but that's another story. The fields themselves are carbonate breccia -- pieces of rubbly limestone embedded in a natural cement -- several hundred feet thick, sealed by dolomite, a tougher chemical relative of limestone. Their formation dates from the Cretaceous-Tertiary boundary. When the dinosaurs became extinct. You got it: the dinosaur killer meteor impact at Chicxulub made Cantarell. To quote Grajales-Nishimura et al.:
On the basis of the unique stratigraphy and distribution of impact material within the calcareous breccia, the following sequence of events and products can be visualized as having taken place within few minutes or hours after the time of the impact: (1) carbonate platform collapse due to shaking, resulting in deposition of the lower breccia; (2) arrival of ballistic impact ejecta (ejecta layers with impact minerals); and (3) reworking and mixing of the ejecta layer with coarser material by one or more passages of the impact-generated tsunamis that were reflected back and forth across the Gulf of Mexico paleogeography.65 million BC, a real bad year to go to Cancún. Reference: Grajales-Nishimura et al., "Chicxulub impact: The origin of reservoir and seal facies in the southeastern Mexico oil fields", Geology; April 2000; v. 28; no. 4; p. 307–310.