地球科学と気候変動ジャーナル

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Sedimentological, Mineralogical and Geochemical Analysis of the Hyperthermal Latest Danian Event across the Galuconitic Marker Bed (Central Tunisia)

Noura Kotti, Besma Mardassi, Jamel Ouali and Mariem Yangui

Field prospecting of the El-Haria Formation, which is Paleocene in age, leads to the discovery of the glauconitic marker bed in inner neritic to bathyal setting from Southern Tethyan realm. The recognition of this interval is based on lithological changes and an accurate stratigraphic proxy allows to distinguish of three main facies. The use of multivariate (cluster analysis and principal component analysis) and univariate (one-way Anova test) analysis confirm dissimilarities in composition between facies as testified by the significant differences. Sedimentological, geochemical and mineralogical analysis leads to assess paleo-environmental changes and to ascertain the variation of the lysocline and CCD across the glauconitic marker bed. Facies 1, particularly, rich in cobalt, sulfides and iron oxides reflects containment conditions affecting the surface and bottom water. These conditions lead to the extinction of the majority of benthic foraminifera and the disruption in planktonic foraminifers’ assemblage. In addition, the Facies 1 displays a brief shoaling of lysocline and CCD evidenced by the low calcite content, the bad preserved benthic foraminifera associated to the maximum fragmentation shells of planktonic foraminifera. In contrary, the rapid pattern of microfossil and the calcite recovery through the Facies 2 indicate suboxic to oxic conditions and a deepen lysocline and CCD. The cobalt lightly increases within the upper Facies, suggesting slightly oxygen deficient bottom water environment. The base of the glauconitic marker bed seems to be a lateral equivalent of the Latest Danian Event recorded throughout the Tethyan Realm (Spain and Egypt) and the Pacific Ocean.