Increased terrigenous influx but no drowning: palaeoenvironmental evolution of the Tunisian carbonate platform margin during the Late Aptian

Abstract

During the Aptian, some carbonate platforms of the sub-tropical realm (for example, on the northern Tethys margin or in the Gulf of Mexico) were affected repeatedly by severe perturbations in the carbonate production factory and drowning, preferentially during global warming events such as the Early Aptian Oceanic Anoxic Event 1a and a prominent mid-Late Aptian warming interval. These platform growth crises have been explained mainly by strongly increased coastal runoff (for example, siliciclastics and nutrients) in combination with pronounced eustatic sea-level rises. In the last few years, increasing evidence suggests that carbonate platforms of lower latitudes were generally less or even not affected by environmental perturbations during these events. This raises the question as to the responsible factors that promoted platform growth or decline in different latitudinal areas. In this study, Upper Aptian (Middle Gargasian to Uppermost Clansayesian) inner-tropical carbonate ramp deposits of the Serdj Formation at Djebel Serdj, north-central Tunisia are studied in detail with regard to microfacies, lithology, biostratigraphy and chemostratigraphy. These data allow reconstruction of the palaeoenvironmental evolution of the Tunisian carbonate platform margin and investigation of its response to the prominent mid-Late Aptian warming interval. The unusually expanded, 600 m thick Serdj Formation consists of limestones, marlstones and siltstones, suggesting deposition within mid-ramp to inner-ramp palaeoenvironments. Deposits of the mid-Late Aptian are represented by quartz-rich platform carbonates and siltstones, probably resulting from increased coastal runoff on the Tunisian shelf as a response to global warming and accelerated water cycling. The siliciclastic input was accompanied by elevated nutrient levels as indicated by a partial decline in the abundance of oligotrophic biota and mass occurrences of orbitolines and green algae. Carbonate platform drowning during the mid-Late Aptian, as reported from the sub-tropical realm, has not been identified. A comparison with other tropical river-influenced platforms suggests that none of them drowned during the mid-Late Aptian. One important reason might be widespread arid to semi-arid climatic conditions within lower latitudes during that time, promoting platform growth due to comparably low nutrient runoff.

Analysis of Cretaceous (Aptian) strata in central Tunisia, using 2D seismic data and well logs

“…1B). Stratigraphic, sedimentologic and tectonic studies in this area have been undertaken since the beginning of the last century, and some of these studies have discussed the evolution of the sedimentary basins and the genesis of the ranges and associated structures (e.g., Pervinquière, 1903;Castany, 1954;Burollet, 1956;M'Rabet et al, 1979;Bismuth et al, 1981;Gargouri-Razgallah, 1983;Masse, 1984;Boltenhagen, 1985;Zargouni, 1985;Ouali et al, 1987;Abdallah 1989;Zouari et al, 1990Zouari et al, , 1999Boukadi, 1994;Negra, 1994;Abdallah et al, 1995Abdallah et al, , 2000Rabhi, 1999;Bédir et al, 2001; Bouaziz et al, 2002;Chaabani and Razgallah, 2006;Azaïez et al, 2007;Lazzez et al, 2008;Zouaghi, 2008;Gallala et al, 2009;Lehmann et al, 2009;Heldt et al, 2010). Other studies have shown that the Cretaceous strata in the central Atlas Mountains of Tunisia are organized into units and sequences (e.g., Tlatli, 1980;Bismuth et al, 1981;M'Rabet, 1981;Masse, 1984;Boltenhagen, 1985;Abdallah, 1989;Ben Youssef et al, 1989;Neri et al, 1991;Abdallah et al, 1995Abdallah et al, , 2000Chaabani, 1995;Sa...…”

“…16) with some reef buildings (M'Rabet et al, 1979;Tlatli, 1980;M'Rabet, 1981;Masse, 1984;Marie et al, 1984;Heldt et al, 2010).…”

Shallow water carbonate platforms (Late Aptian–Early Albian, Southern Apennines) in the context of supraregional to global changes: re-appraisal of palaeoecological events as reflectors of carbonate factory response

“…The "Orbitolina Level" therefore is one of the tie-points for the calibration of the upper Aptian biostratigraphy of central and southern Tethyan carbonate platforms (cf. Simmons et al, 2000;Bachmann and Hirsch, 2006;Chihaoui et al, 2010;Embry et al, 2010;Heldt et al, 2010;Vincent et al, 2010;Cherchi and Schroeder, 2012).…”

“…8) invites to link the "Orbitolina Level" with processes that affected the global carbon cycle during the lower Cretaceous (cf. Weissert and Lini, 1991;Takashima et al, 2007;Heldt et al, 2010). The "Orbitolina Level" of the middle Gargasian, in all likelihood, formed at the same time as part of the "Niveau Fallot" formed in a hemipelagic setting connected to the Tethyan Ocean, and probably to the Thalmann black shale event in California and a dark horizon on the Mazagan Plateau (DSDP Site 545; cf.…”

“…The Aptian-Albian was a time punctuated by biotic and environmental changes (e.g. Takashima et al, 2007;Hay, 2008;Huck et al, 2010;Donnadieu et al, 2011) that resulted in the drowning of many Tethyan carbonate platforms (Föllmi et al, 1994;Graziano, 1999Graziano, , 2000Heldt et al, 2010;Masse and Fenerci-Masse, 2011;Skelton and Gili, 2012). Increased geodynamic activity and massive injection of carbon dioxide in the ocean-atmosphere system accelerated the water cycle and increased weathering rates, thus threatening carbonateprecipitating organisms (e.g.…”