Siliceous and organic-rich sedimentation during the Cenomanian–Turonian Oceanic Anoxic Event (OAE2) on the northern margin of Africa: an evidence from the Bargou area, Tunisia

Cretaceous oceanic anoxic events (OAEs) recorded in the northern margin of Africa as possible oil and gas shale potential in Tunisia: An overview

“…An ammonite biostratigraphic scheme for the Lower Cretaceous was previously used by Busnardo and Memmi (1972) and Memmi (1989). Foraminiferal and radiolarian biostratigraphic investigations have also dealt with black shale levels corresponding to the reviewed OAEs, as well as calpionellids and belemnites of the Lower Cretaceous sections (Memmi 1989;Maamouri et al 1994aMaamouri et al , 1994bSouquet et al 1997;Rami 1998;Soua et al 2006;Soua and Tribovillard 2007;Ben Fadhel et al 2010, 2012Soua 2011Soua , 2013bZaghbib-Turki and Soua 2013). The regional distribution maps of these organic-rich levels were carried out using various well data (depth, thickness, and gamma ray response).…”

“…In northwestern and central Tunisia, as well as in the Pelagian Province, Cretaceous diapiric movements in the Triassic played a major role locally in controlling organic-rich deposition (Perthuisot 1981;Souquet et al 1997;Vila et al 1998;Lüning et al 2004;Soua and Tribovillard 2007). These are characterized by a marked reduction in thickness and partly by the development of detrital horizons (microbreccia) such as in the area of Bargou (Soua 2013b). Complex diapiric vertical extrusions, possibly starting from the Aptian (and even before) through approximately the middle Eocene, were probably continuous but would have increased during periods of tectonic instability.…”

“…Well and outcrop data confirm these organic-rich provinces, and the exact boundaries have been clearly traced in earlier studies (Layeb 1990;Maamouri et al, 1994b;Saidi et al 1997;Soua and Tribovillard 2007;Soua et al 2009Soua et al , 2011bSoua 2011;Affouri et al 2013;Layeb et al 2013), especially north of the Gulf of Gabes domain ). Dealing with the Soua and Tribovillard (2007) model, the palaeogeographic setting suggests that distribution of the organic-rich facies represents the impingement of an OMZ onto the southern Tethyan margin and upwelling conditions where the organic-rich facies is associated with siliceous deposition (Soua 2013b). The Bahloul Formation is generally 10-30 m thick, with a maximum thickness of over 50 m recorded in northwestern Tunisia (Figure 21), and it consists generally of shale and limestone alternations.…”

“…Alternatively, the Bahloul was deposited during the UA18 radiolarian chronobizone, dominated by nassallarian, whereas the UA21 radiolarian chronobizone is dominated by spumellarian and radiolarian chronobiozones. The radiolarian assemblages recognized in the Bahloul Formation (Soua et al 2006;Soua 2013b) contain many species providing sufficient accurate biostratigraphical data such as Stichomitra, Pseudodictyomitra, and Rhopalosyringium genera, suggesting a latest Cenomanian to earliest Turonian age. The upper assemblage (UA21 Zone) seems to be early Turonian in age due to the existence of some ammonite species belonging to Watenoceras sp, which indicates the onset of the Turonian (Bengtson 1996).…”

Application of Facies Associations, Integrated Prediction Error Filter Analysis, and Chemostratigraphy to the Organic-Rich and Siliceous Cenomanian-Turonian Sequence, Bargou Area, Tunisia: Integrated Sequence Stratigraphic Analysis

“…No previous sequence stratigraphic framework has been taken yet on such siliceous deposition. The aims of this paper are: (1) to present a revised stratigraphic description of the siliceous and organic-rich upper Cenomanian-lower Turonian in central Tunisia using facies association; (2) to apply new tools to sequence stratigraphy which consist of integrated prediction error filter analysis (INPEFA) of spectral Gamma-ray data 2 Journal of Geological Research Table 1: Major and trace elements normalized to Al (after Soua [14]).…”