IASPEI - Picture Gallery

IUGG XXIV General Assembly July 2-13, 2007 Perugia, Italy
(S) - IASPEI - International Association of Seismology and Physics of the Earth's
Interior
JSS013 Poster presentation 2232
The Ypresian Lutetian boundary in the north of Tunisia, Biostratigraphy,
Climatic, Tectonic and Environmental Events
Dr. Karoui- Yaakoub Narjess
geology facult des sciences de bizerte
Moufida Ben M'barek-Jemai, Noureddine Ben Ayed
The stratigraphic study of the Ypresian-Lutetian interval in the north of Tunisia is based on the planctic
foraminifera distribution. Their analyses reveal that they are well preserved and very diversified and had
permitted us to precise the biozonation of the Ypresian-Lutetian boundary. So we had identified the
Morozovella aragonensis zone, the Acarinina pentacamerata zone and Globigerinatheka subconglobata
subconglobata zone. The simultaneous presence of the species Hantkenina nuttalli, H. dumblei,
Globigerinatheka mexicana mexicana and Morozovella lehneri indicates that there is a hiatus of the
Hantkenina nuttalli zone which is the first zone of early Lutetian. This hiatus doesnt exist in the center
of Tunisia where limit was complete (Ben Ismail & Bobier, 1996). In the north of Tunisia, the hiatus of
this zone would be linked to an active synsedimentary tectonics: the Eocene compression ( Ben Ayed,
1986) The systematic and statistic analyses of benthic foraminifera at the Ypresian/Lutetian transition
deposits, indicate that the benthic foraminifera are numerous, very diversified and are dominated by the
infaunal groups. We note the co-existence of both the Midway and the Velasco type faunas. The most
common Midwayan fauna species are: Cibicidoides alleni, C.succedens, Anomalinoides acuta, A.
midwayensis, Lenticulina midwayensis, Gavelinella dania The abundant Velascoan species are:
Nuttalides truempyi, Gavelinella rubiginosa, Gyroidinoides subangulatus, Gaudryina pyramidata The
mineralogical and geochemical analyses of marls indicate the abundance of the kaolinite and smecite
minerals, which indicate warm conditions. This warm climate is herited since the Paleocene/Eocene
boundary (Ben Ismail &Bobier, 1996; Bolle et al., 1999 ; Karoui-Yaakoub N., 1999; Thomas. E., J.C.
Zachos & T.J. Bralower, 2000) At the upper of the Ypresian, the smectie is more abundant than the
kaolinite with a pick 87%, this proves that the climate was warm with contrasted seasons: warm and
dried periods alternated with warm and humid periods. At the base of the Lutetian the kaolinite became
more abundant than the smectite, which indicate that the warm climate become more humid. In
conclusion, the increase of planctic ratio, the highly diversified benthic fauna, the co-existence of both
the Midway and Velasco type faunas and the abundance of the kaolinite and smectite minerals indicate
probably a bathyal to deeper warm environment with some seasonal fluctuations. References Ben Ayed,
N. (1986) - Evolution tectonique de lavant-pays de la chane alpine de Tunisie du dbut du Msozoque
lactuel. Thse de Doctorat es-Sciences, Universit Paris Sud Orsay. Edit. Office National Mines. Annales
des Mines et de Gologie, 32, dition du Service gologique de Tunisie, 1993, 286 p. Ben Ismail &Bobier,
1996 Etude biostratigraphique, palocologique et palobiogographique des sries eocnes (Yprsien-Luttien
basal) de Tunisie centrale. Gologie de lAfrique et de lAtlantique Sud, Actes Colloque Angers 1994, 563-
583, 4 fig., 3 tab., 4 pl. Bolle Bolle, M.P., T. Adatte, G. Keller, K. Von Salis & S. Burns (1999) - The
Paleocene-Eocene transition in southern Tethys (Tunisia): climatic and environmental fluctuations.
Bulletin de la Socit Gologique de France. 150 (5): 661-680. Karoui-Yaakoub N. (1999) - Le Palocne en
Tunisie septentrionale et centro-orientale: Systmatique, biostratigraphie des Foraminifres et
environnement de dpt. Thse de Doctorat, Universit de Tunis II, 357 pp. Thomas, E., J.C. Zachos & T.J.
Bralower (2000) - Deep-sea environments on a Warm Earth: Latest Paleocene-early Eocene. In: Huber,
B.T. et al. (Eds). Warm climates in Earth History, Cambridge University Press, Cambridge, 132-160.
Keywords: ypresian lutetian interval, environment deposition, tunisia