Onset and demise of Cretaceous oceanic anoxic events: The coupling of surface and bottom oceanic processes in two pelagic basins of the western Tethys. (20th June 2016)

• Record Type: Journal Article
• Authors: Gambacorta, G.; Bersezio, R.; Weissert, H.; Erba, E.
• Is Part Of: Paleoceanography. Volume 31:Number 6(2016)
• Page Start: 732
• Page End: 757
• Publication Date: 2016-06-20
• Subjects: bottom currents -- surface water processes -- Cretaceous -- OAE 1d -- middle Cenomanian event -- OAE 2; Paleoceanography -- Periodicals; 551.46
• DOI: 10.1002/2015PA002922
• Languages: English
• ISSNs: 0883-8305

Abstract

Abstract: The upper Albian–lower Turonian pelagic successions of the Tethys record processes acting during the onset, core, and recovery from perturbed conditions across oceanic anoxic event (OAE) 1d, OAE 2, and the mid‐Cenomanian event I (MCE I) relative to intervening intervals. Five sections from Umbria‐Marche and Belluno Basins (Italy) were analyzed at high resolution to assess processes in surface and deep waters. Recurrent facies stacking patterns (SP) and their associations record periods of bottom current activity coupled with surface changes in trophic level. Climate changes appear to have been influential on deep circulation dynamics. Under greenhouse conditions, vigorous bottom currents were arguably induced by warm and dense saline deep waters originated on tropical shelves in the Tethys and/or proto‐Atlantic Ocean. Tractive facies postdating intermittent anoxia during OAE 1d and in the interval bracketed by MCE I and OAE 2 are indicative of feeble bottom currents, though capable of disrupting stratification and replenish deep water with oxygen. The major warming at the onset of OAE 2 might have enhanced the formation of warm salty waters, possibly producing local hiatuses at the base of the Bonarelli Level and winnowing at the seafloor. Hiatuses detected at the top of the Bonarelli Level possibly resulted from most effective bottom currents during the early Turonian thermal maximum. Times of minimal sediment displacement correlate with cooler climatic conditions and testify a different mechanism of deep water formation, as further suggested by a color change to reddish lithologies of the post‐OAE 1d and post‐OAE 2 intervals. Key Points: Recurrent facies stacking patterns are observed in upper Albian‐early Turonian pelagic sequences Coupled surface and bottom processes influenced onset and termination of intermittent and prolonged anoxia Climate changes were associated with salinity‐driven bottom currents redistributing and eroding sediments