HR: 0830h
AN: PP41B-0843    [PDF]
TI: Cretaceous Oceanic Anoxic Events and Radially Elongated Chambered Planktonic Foraminifera: Palaeoecological and Palaeoceanographic Implications
AU: * Venturati, A
EM: cron@info-net.it
AF: University of Ferrara, Istituto di Geologia, Urbino, 61029 Italy
AU: Coccioni, R
EM: cron@info-net.it
AF: University of Ferrara, Dipartimento di Scienze della Terra, Ferrara, 44100 Italy
AU: Luciani, V
EM: lcv@unife.it
AF: University of Ferrara, Istituto di Geologia, Urbino, 61029 Italy
AU: Luciani, V
EM: lcv@unife.it
AF: University of Ferrara, Dipartimento di Scienze della Terra, Ferrara, 44100 Italy
AB: Planktonic foraminifera with radially elongated chambers became a consistent component (up to 80%) of foraminiferal assemblages in coincidence with the deposition of the main prominent Cretaceous organic carbon-rich horizons. However, the exact ecological meaning of elongated chambered forms and related palaeoceanographic scenario are not definitively established. All this above moved us to investigate in greater detail on the elongated chambered planktonic foraminifera across the latest Hauterivian Faraoni Event, the late Early Aptian Selli Event (OAE1a) and the latest Cenomanian Bonarelli Event (OAE2) in different areas from the Mediterranean Tethys (Umbria-Marche Apennines as type area, Southern Alps, Gargano Promontory, Sicily, SE Spain, SE France). Our analysis, conducted both on washed residues and thin sections confirms that the radially elongated chambered forms preferred oxygen-depleted waters and provides the following main evidences: a) each events has its own peculiarities; b) there is not relationship between Corg accumulation and relative abundance of this foraminiferal group; c) the first radiation of elongated chambered morphotypes (i.e., P. eocretacea) remarkably just predates the Faraoni Event with the percentage of these forms not exceeding the 7%; d) the relative abundance of these forms across the Cretaceous anoxic events varies in the different studied areas, probably also controlled by the water depth. In particular, the development of radially elongated chambered forms across the Selli Event seems to be favoured in shallower settings; e) the three morphological categories established for the Early Cretaceous radially elongated chambered forms (sublavate to clavate chambers, pointed at the end chambers, bulbous terminations-bearing chambers) are present in the investigated areas in variable percentages. This evidence suggests that local environmental parameters influenced their distribution. Remarkably, the particularly elongated subclavate to clavate morphotypes (i. e., P. roblesae) appear almost restricted to the western Mediterranean Tethys; f) a possibile competition between radiolaria and leupoldinids across the Selli Event is reflected by their. distribution patterns showing evidence that the latter group became more abundant (up to 10%) when the former decrease in abundance or are absent. Conversely, the other subclavate to clavate forms do not seem to suffer the relative high abundance of radiolaria. All this above allow us to speculate that leupoldinids are the less eutrophic forms among the radially elongated chambered morphotypes proliferating under moderate degree of fertility; g) higher numbers of radially elongated chambered forms together with a more consistent distribution are recognized just after the Selli Event suggesting that this event played a fundamental role in the radiation of this planktonic foraminiferal group; h) the onset and end of the Bonarelli Event in deep-water settings is characterized by schackoinid assemblage-dominated (up to 80%). According to their morphological features, schackoinids appear more competitive than other radially elongated chambered forms in low-oxygen, eutrophic conditions; i) the remarkably higher percentages of radially elongate chambered forms across the Bonarelli Event may provide evidence that the intensity of the environmental perturbation related to the Cretaceous anoxic event was much stronger during this event and weaker during the Faraoni Event.
DE: 4267 Paleoceanography
DE: 4802 Anoxic environments
DE: 4805 Biogeochemical cycles (1615)
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2003 Fall Meeting