Interaction between carbon cycle perturbations and marine calcareous organisms: the Aptian-Santonian evolution of the Northwestern Friuli Platform Margin (Southern Alps, NE Italy)

The dynamics of the carbonate sedimentary system have a fundamental role in the Earth’s climate changes as they exert a major influence on the global carbon cycle. The calcium carbonate production and preservation into the sediments significantly affect the ability of the oceans, the main carbon reservoir, to buffer the excess of atmospheric CO2. Carbonate production is strongly related to the evolution of marine benthic and planktonic organisms secreting carbonate shells: the evolutionary or ecological events affecting shallow-water marine calcareous organisms markedly influenced the architecture of the carbonate sedimentary system. The Cretaceous is a crucial interval of the Earth’s history being marked by significant changes in the global carbon cycle. This period is characterized by major paleoceanographic events testified by widespread deposition of organic-rich shales that are the sedimentary expression of Oceanic Anoxic Events (OAE). We present here the case-history of the Cretaceous Friuli carbonate platform margin (northwestern Italy) in order to identify the relationship between the global signal of the OAE and the evolution of the platform. No backstepping or drowning events of the platform margin are recorded at the OAEs 1a and 2. On the contrary, the main change in the margin geometry is observed in the uppermost Albian, probably close to the OAE 1d. The Cenomanian record in the Cellina section documents a transition from a rimmed platform margin, dominated by corals, green algae, benthic foraminifera, rudists (late Albian) to an open ramp environment (from Cenomanian to Santonian) with evidence of pelagic sedimentation. Because of the development over a previously rimmed platform as well as the occurrence of breccias and turbiditic structures on the slope, the ramp has been interpreted as a distally steepened ramp where the carbonate factory is dominated by microbial activity.