Abstract

The Bahloul Formation of Central Tunisia was deposited on the proximal part of the southern Tethyan platform. It recorded the global oceanic anoxic event (OAE 2) that occurred at the Cenomanian/Turonian boundary. The type section of the Wadi Bahloul comprises 29 m of sediment showing a regular repetition of an elementary depositional sequence including black, thinly-bedded limestones and bioturbated gray marls. These sedimentological fluctuations define two trophic states of the palaeoenvironment. The laminated black limestones are associated with eutrophic conditions in the water column above an anoxic basin, while oligotrophic and at least temporarily oxic conditions at the sediment/water interface prevailed during the deposition of the bioturbated grey marls. Each lithological cycle reflects short-term climatic fluctuations: arid conditions are associated with the deposition of the black laminated limestones, whereas the grey marls correspond to sub-humid conditions. These environmental changes are interpreted as being related to precession cycles of 20 ky. According to the number of precession cycles identified in the section of the type locality, the Bahloul Formation probably was deposited during one eccentricity cycle of 400 ky. This cyclostratigraphic interpretation, calibrated by biostratigraphy, constrains the duration of the anoxic event more precisely than radiometric ages which suggest a duration of 500+ or -400 ky.

First Page Preview

First page PDF preview
You do not currently have access to this article.