Ocean-wide stagnation episode in the late Cretaceous

Marine sediment location spread over a wide range of environments contain evidence of anoxic intervals dated early Late Cretaceous. In the north and south deep Atlantic deposition of anoxic layers followed a widespread sedimentary hiatus of Middle Cenomanian age. In the eastern-central parts of the Atlantic (Angola and Cape Verde basins) rythmic deposition of anoxic layers commenced in the Latermost Cenomanian and lasted as late as the Santonian. In the rest of the deep north Atlantic on the contrary anoxia duration was probably limited to the Cenomanian-Turonian boundary or thereabout. Late Cretaceous anoxic layer is not yet recorded south of the Walvis-Rio Grande Rises in the South Atlantic. In a number of locations in marginal and epicontinental seas in America, Africa and Europe previously related to the Tethys a few anoxic layers dated Cenomanian-Turonian are intercalated within thick oxic series. Coniacian to Santonian anoxic layers are limited to small areas in epeiric and marginal domains in the southern Alps, North Africa, Israel, North America (Santonian in the Western Interior) and (?) Australia all with no clear link with any ocean-wide event of early Senonian age. Rythmical alternation of oxic/anoxic layers helps to document the emplacement of sediment and disposition of anaerobic water masses. Development of anoxia at about the Cenomanian-Turonian boundary induced abnormal concentration of trace metals and a partial renewal of the marine fauna. To understand the relationship between a number of factors such as sea-level changes, climates, terrestrial influences, biogenic fertility, sedimentation rates, etc., is essential to explain of the very peculiar anoxic global event of early Late Cretaceous age.