%0 Journal Article
%A Najarro, María
%A Rosales, Idoia
%A Martín Chivelet, Javier
%T Major palaeoenvironmental perturbation in an Early Aptian carbonate platform:Prelude of the Oceanic Anoxic Event 1a?
%D 2011
%@ 0037-0738
%U https://hdl.handle.net/20.500.14352/43673
%X The Early Aptian Oceanic Anoxic Event (OAE 1a) was characterized by intensified greenhouse climateconditions, widespread accumulation of organic deposits in open-marine settings, major perturbations in theC cycle and a generalized increase in terrestrial runoff. Sedimentological, diagenetic and chemostratigraphicanalyses of Lower Aptian platform carbonates from the North Cantabrian basin (N Spain) illustrate theregional impact and effects of those global conditions on shallow marine environments.The studied interval outlines four stages of platform evolution. Stage 1 (earliest Bedoulian) is defined by aninitial rapid marine transgression that led to deposition of shallow water oligotrophic photozoan skeletalassemblages, and by a later interval of subaerial exposure. Stage 2 (early Bedoulian) starts with a rapidtransgression followed by deposition of grainstones that yield heterozoan assemblages, more typical ofmesotrophic conditions, along with ferruginized oolites. Stage 3 (early Bedoulian) is defined by thedrowning of the carbonate platform and subsequent deposition of open-marine marls, which are thought torepresent the local expression of the OAE 1a. Finally, stage 4 shows the return of shallow water photozoancarbonate sedimentation. The carbonate O and C stable isotope records have revealed prominent negativeexcursions during deposition of the marly interval of the stage 3, which may be associated with theimportant global changes that occurred at the onset of the OAE 1a. The change in skeletal assemblages thatpreceded the isotopic excursions and the platform drowning documents conditions of environmental stresscaused by a combination of local and global factors. The global change, coupled with increased basinsubsidence, triggered the drowning of the platform by progressive reduction of the growth potential of thecarbonate factory.
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