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 2251
Interpretation of mineralogic and geochimist results of clays from the
Ypresian/Lutetian boundary in the North of Tunisia and the
paleoenvironment reconstrution
Dr. Ben M'Barek Jema Moufida
Des Sciences de la Terre Facult des Sciences de Bizerte
Narjess Karoui Yaakoub, Noureddine Ben Ayed
The sejnen area is located at the border of north alpine zone in . It is caracterised by the presence of
the well developed Ypresien/Lutetian series which were composed of the clayey an calcareous series.
These formations present some lateral variations of the thikness on relation with the large
paleogeographic line of the Paleogene. The clayey assemblagewere largely dominated by the kaolinite
at the bottom and at the top of the lithostratigraphic series. At the middle the ratio of it the kaolinte
proportions increase. Indeed the illite presents the percentages little variable along all the series. Its
index of the cristallinity is high at the base and at top of the Ypresian/Lutetian boundary series. It
represents an average of 20% in the clayey mineralogic assemblage. The geochimic results show that
the clayey samples at the bottom and at the top of the series are more rich on CaO, MgO, en Fe2O3et
en K2O. The silica mineral (SiO2) and the alumine oxide (Al2O3) present a higher concentration at the
middle of the Ypresian/Lutetian boundary series. If we take into consideration the mineralogic content
and the geochimic results of the major elements indicated previously, we can propose an interpretation
of the paleoenvironment at the Ypresian/Lutetian boundary. So at this epoch, the kaolinite which is
prevailing at the bottom and at the top of the series give evidence the presence of the alteration factors
with a warm and humid climate. But the abundance of the smectite mineral at the middle of the series
suggest a high marin level so that the environment become deeper.
Keywords: mineralogy paleoenvironment, ypresian lutetian, illite kaolinite smectite