The mid-Cenomanian Event: the Prelude to the OAE 2

Details The mid-Cenomanian Event: the Prelude to the OAE 2 The mid-Cenomanian Event: the Prelude to the OAE 2

Dec 2001

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001agufmpp42a0495c&link_type=abstract

American Geophysical Union, Fall Meeting 2001, abstract #PP42A-0495

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3030 Micropaleontology

Scientific paper

Detailed bio- lithostratigraphic investigations of the Cenomanian pelagic limestones of the Scaglia Bianca Formation in the Umbria-Marche Basin, show that the Bonarelli Level, which is the regional sedimentary expression of the OAE 2, represents the climax of a ~2 myr-long cycle of black shale deposition starting in the middle Cenomanian within the planktic foraminiferal Rotalipora cushmani zone (Coccioni et al., 1992). This long-term cycle starts with a prominent short-term event, here named mid-Cenomanian Event (MCE), which is associated with several changes in the biotic and abiotic records. In particular, a comparison of the available chemo- litho-, and biostratigraphic data from the Umbria-Marche Basin, allows to recognise that the MCE is defined by: - a 0.7% positive shift in the carbon isotope values (Jenkins et al., 1994; Stoll & Schrag, 2000); - a reorganisation of planktic foraminiferal assemblages (Premoli Silva & Sliter, 1994, 1999); - a major change in benthic foraminifera (Coccioni et al. 1995); - a major turnover in the radiolarian assemblages (Erbacher et al., 1996). Moreover, the MCE is slightly (~400 kyr) preceeded by a short-term 0.5% negative excursion in the oxygen isotope record (Stoll & Schrag, 2000). The above mentioned changes in carbon and oxygen isotope values can be confidently correlated over different basins and oceans (Jenkins et al., 1994; Stoll & Schrag, 2000) and seems to occur in correspondence of a major sea level fall following the chronostratigraphy provided by Hardenbol et al. (1998). These lines of evidence concur to define the MCE as an outstanding event associated with large scale changes in the oceanic structure and paleoclimate. The MCE and the following cyclical deposition of organic-rich beds may serve as a good case-study to better understand differences and similarities between Mesozoic black shales and Cenozoic sapropels, and related paleoceanographic changes controlled by orbital climate cycles. References Coccioni, R., Galeotti, S., and Ragni, D., 1992, Litho- and biostratigraphy of the Scaglia Bianca Formation (Late Albian-Late Cenomanian) in the Umbria-Marche Apennines (Italy): 6th Annual Meeting of IGCP Project 262 (Tethyan Cretaceous platform correlation) - ``Cretaceous Facies in Orogenic Belts", Athens, 22-26 May 1992, p. 4. Coccioni, R., Galeotti, S., and Gravili, M., 1995, Latest Albian-early Turonian deep-water agglutinated foraminifera in the Bottaccione section (Gubbio, Italy) - Biostratigraphic and palaeoecology implications: Revista Española de Paleontologia, N?. Homenaje Al Dr. Guillermo Colom, p. 135-152. Erbacher, J., Thurow, J., and Little, R., 1996, Evolution patterns of radiolaria and organic matter variation: A new approach to identify sea-level changes in mid-Cretaceous pelagic environments: Geology, v. 24, p. 499-502. Jenkyns, H.C., Gale, A.S., and Corfield, R.M., 1994, Carbon and oxygen isotope stratigraphy of the English Chalk and Italian Scaglia and its paleoclimatic significance: Geological Magazine, v. 131, p. 1-34. Premoli Silva, I., and Sliter, W.V., 1994, Cretaceous planktonic foraminiferal biostratigraphy and evolutionary trends from the Bottaccione section, Gubbio, Italy: Palaeontographia Italica, v. 82, p. 1-89. Premoli Silva, I., and Sliter, W.V., 1994, Cretaceous paleoceanography: Evidence from planktonic foraminiferal evolution: Geological Society of America Special Paper 332, p. 301-328. Stoll, H.M., and Schrag, D.P., 2000, High-resolution stable isotope records from the Upper Cretaceous rocks of Italy and Spain: Glacial episodes in a greenhouse planet?: Geological Society of America Bulletin, v. 112, p. 308-319.

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