Small benthic foraminiferal biostratigraphy and palaeoecology during the Campanian-Maastrichtian transition in north-western Tunisia

Authors : Abdellatif BEJAOUI, Ezzedine SAÏDI, Dalila ZAGHBIB-TURKI

Pages : 500-530

View : 16 | Download : 4

Publication Date : 0000-00-00

Article Type : Research Paper

Abstract :Campanian-Maastrichtian insert ignore into journalissuearticles values(C-M); sediments in the Kalâat Senan area insert ignore into journalissuearticles values(north-western Tunisia); include rich microfauna. Small benthic foraminifera insert ignore into journalissuearticles values(SBF); analysis at the Wadi Necham insert ignore into journalissuearticles values(ON); section reveals significant biostratigraphic and palaeoecological changes during the C-M transition. A progressive evolutionary trend within the Bolivinoides lineage allowed us to establish the late Campanian B. decoratus Interval Range Zone insert ignore into journalissuearticles values(IRZ); and two successive zones in the early Maastrichtian, namely the B. miliaris IRZ and the B. draco Total Range Zone insert ignore into journalissuearticles values(TRZ);, which span the standard planktonic foraminifera Gansserina gansseri IRZ. Foraminiferal semiquantitative data from the C-M transition interval at the studied section yield high values of planktonic/benthic insert ignore into journalissuearticles values(P/B); ratios insert ignore into journalissuearticles values(92%-98%); suggesting an upper to middle bathyal depositional palaeoenvironment. Assemblages of such a deep environment comprise diversified epibenthic and endobenthic taxa indicating major changes across and above the C-M transition. During the late Campanian insert ignore into journalissuearticles values(Bolivinoides decoratus Zone); endobenthic morphogroups dominate insert ignore into journalissuearticles values(71%); the assemblages as compared to epibenthic morphogroups, which reach 29%. In contrast, the abundance of epibenthic morphogroups increases to 40% just above the C/M boundary insert ignore into journalissuearticles values(Bolivinoides miliaris Zone); and suggests cooler and more oxygenated conditions on the sea floor. Epibenthic and endobenthic abundances fluctuate in opposite trends insert ignore into journalissuearticles values(40%-60%); throughout the early Maastrichtian insert ignore into journalissuearticles values(B. draco TRZ);. These variations are interpreted to reflect mesotrophic conditions intermittently interrupted by eutrophic shifts associated with the early Maastrichtian cooling event. The relative proportion of endobenthics increased insert ignore into journalissuearticles values(60%-80%); again towards the late Maastrichtian insert ignore into journalissuearticles values(upper part of the B. draco TRZ);, showing a particular increase in EnA morphogroups prevailing in the SBF assemblages. Moreover, test morphology analyses of SBF assemblages allowed us to distinguish six epibenthic insert ignore into journalissuearticles values(M1 to M6); and seven endobenthic insert ignore into journalissuearticles values(M7 to M13); morphogroups based on their mode of coiling. This classification reveals the flourishing of EpC M4 and M5 morphogroups during the early Maastrichtian due to more oxygenated conditions on the sea floor.
Keywords : Campanian Maastrichtian transition, small benthic foraminifera, morphogroups, palaeoecology, north western Tunisia