The Bonarelli Event (a.k.a. OAE2) is a well-studied episode of "worldwide" ocean anoxic event at the Cenomanian-Turonian boundary (ca. 94 Ma). It is characterized by the presence of organic-rich marine sediments and a $\delta^{13}C$ shift. It is thought to have provoked a minor mass extinction and an increased atmospheric and oceanic temperature.  
What evidence do we have that the anoxia was indeed global?  
Is there really no known ocean basin with sediments spanning this time interval that doesn't show those characteristic black shales?