The regional Cenomanian-Turonian (C/T) structural framework of surface and subsurface coupled with subsidence data inferred from palegeographic and organic-rich C/T isopachs map, generated in this work, from several basins, wells and outcrops of Tunisia and eastern Algeria was investigated and provide constraints on the structural and sedimentary evolution of this part of the southern Tethyan margin during the C/T times. La réduction des zones emergées depuis la Cénomanien déduit de la carte paléogéographique est mis en évidence.L'évolution globale est également amplifiée par les mouvements diapirique du Trias créant des rim-synclines subsidents, où les faciès riches en matière organique ont prévalu.
In Tunisia, five Bahloul spaced sections, Bargou, Jerisa, Guern Halfaya, Kherij and Gafsa were analyzed for biostratigraphy (foraminifera and radiolarians) and major and trace elements. This high‐resolution biostratigraphic and chemostratigraphic integrated analyses for the Late Cenomanian‐Early Turonian Bahloul Formation provide new insight into the palaeoceanographic evolution of the southern Tethyan margin. Relative low abundance of related terrigenous Ti/Al and K/Al ratios and enrichment of some productivity proxies such as Ba, Cu, and Ni (organic matter related trace elements) suggests that the Bahloul, deposited during a relatively short period (0.5 Ma), was of relatively elevated primary productivity and minimal detrital input. While higher D* values concurrent with lower Ti/Al ratios are interpreted as caused by enhanced fluvial material contribution, due to more humid climate during the OAE‐2. Enhanced humidity triggered probably fluvial influxes, resulted in a sluggish water circulation and consequent anoxic/euxinic conditions favoring the preservation of organic matter at the bottom. Enrichments in redox‐sensitive trace metals U, V, and Mo in the Bahloul Formation deposits and redox indices, such as V/(V+Ni), U/Th, V/Cr, and Ni/Co, indicate that oxygen‐restricted conditions prevailed during the Late Cenomanian to earliest Turonian times and correlate well with relative abundances of some foraminiferal and radiolarian paleo‐environmental relevant indicators. High Baxs values and Uauth may indicate anoxic conditions at least at the water–sediment interface during the Bahloul Formation deposition and provide information about low to moderate sulfate‐reduction reactions.
Time series analysis has been performed for the first time on the Cenomanian-Turonian sequence in Central Tunisia in order to shed light on its Milankovitch-like cyclicity. This analysis was tested and applied on two foraminiferal species: the biserial Heterohelix, an oxygen minimum zone (OMZ) dweller, and the triserial Guembelitria, a eutrophic surface dweller. Average sedimentary rates and the duration of the second Oceanic Anoxic Event OAE-2 in each studied section were estimated. Alternatively, the fluctuations of these two opportunistic species can be related mainly to both precessional (23–19 ka) and eccentricity (414–106 ka) cyclicity suggesting that changes in surface water fertility were linked to the Milankovitch parameters.
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