Early Cretaceous »events« in the evolution of the eastern and western North Atlantic continental margins

At many North Atlantic continental margins, the early Neocomian is characterized by a major stratigraphic turning point from Late Jurassic-Berriasian carbonate bank/pelagic carbonate deposition to Valanginian-Barremian hemipelagic sedimentation with thick Wealden-type deltaic to deep-sea fan sequences. The stratigraphy and structure of the very old, starved passive margin of the Mazagan Plateau and adjacent steep escarpment off Morocco was studied during the French-German CYAMAZ deep diving campaign. The drowning of the Late Jurassic-early Berriasian carbonate platform was strongly influenced by a global late Berriasian sea level fall which was followed by a rapid late Valanginian sea level rise and/or by a major regional blockfaul ting event with accelerated subsidence rates. Upper Berriasian to (?) Hauterivian quartz-bearing bioclastic wackestones document the transition from the carbonate platform to the hemipelagic deposition on the drowned platform margin. Seawards, these deposits are correlated with a deep sea fan sequence. We discuss also an example from the Tarfaya Basin-Fuerteventura area further south. A 300 m thick succession of organic-rich claystone and sandstone turbidites (including m-thick debris flow units) of Hauterivian to Barremian age was an unexpected discovery at DSDP Site 603 off North Carolina (Leg 93). We discuss a tectonically confined fan model with laterally migrating channels, influenced by sea level fluctuations and varying terrigenous supply. During the Valanginian to Barremian time of high-standing (or rising) sea level, shelf construction (Wealden-type deltas) coincided with subdued, resedimentation-starved turbiditic system on the continental rise. Extensive unconsolidated sands, however, reflect sudden input of shelfal material into the basin during a mid-Aptian sea level lowstand (shelf destruction). The following global late Aptian transgression terminated the clastic fan deposition, raised the CCD and started the deposition of organic-rich shales.