Geochemistry of early mesozoic basalts from Tunisia

Early Carnian anoxic event as recorded in the southern Tethyan margin, Tunisia: an overview

“…Macdonald et al 2003) stress the Late Triassic initiation of continental extension in isolated areas such as South America. Triassic evaporate-related basalts and tuffs (ophites) in Tunisia have been reported by Kurtz (1983), who considered them as tholeiitic continental basalts (according to their Ti-enrichment trend, K 2 O, Rb, and Sr contents) with slightly transitional alkaline character. He related these ophites to the widespread basaltic volcanism associated with the break-up of Pangea; since then, continental tholeiitic basaltic activity related to this episode has been reported from the Argana valley of the Moroccan western High Atlas (Beauchamp 1988;Aït Chayeb et al 1998;Tourani et al 1998) and in the Khemisset basin of the Moroccan Meseta (e.g.…”

“…For the western Tethys, terrigenous input has been suggested as the factor primarily responsible for the demise of carbonate platforms and reefal constructions in association with the increased salinity related to the continuing break-up of Pangea, extensional movements in some parts, as well as to the increased CO 2 emission related to the intense volcanic activity as inferred from the northwestern African margin (Tunisia, Morocco, Guinea, Mali, Mauritania) (Weigand and Ragland 1970;Biju-Duval et al 1977;Bertrand and Coffrant 1977;Laubscher and Bernoulli 1977;Manspeizer et al 1978;Bertrand et al 1982;Kurtz 1983). A monsoonal circulation system has been adopted by Parrish (1999) to explain the climatic model of the Carnian in the Tethyan realm associated with a rapid tectonic subsidence rate due to isostatic equilibrium (Garzanti 1999).…”

“…Note that this model compiles the regional structural framework (enhanced distensional movements) associated with the regional pluvial event (increased riverine influx, enhanced run-off, as well as high nutrition). In addition, probable increased humidity related to enhanced CO 2 -emission associated with tholeiitic volcanic activity (based partly on Kurtz 1983;Simms and Ruffell 1989;Barrett 1998;Lüning et al 2004;Brumsack 2006;Soua and Tribovillard 2007;Hornung et al 2007). …”

“…The increased humidity may be the consequence also of the enhanced CO 2 emission associated with the tholeiitic volcanic activity such as that recorded in northern and northcentral Tunisia in the Early to Late Triassic (e.g. Kurtz 1983).…”

“…Carnian sedimentation was influenced by monsoonal activity (Parrish 1999) at the same time as enhanced extension related to the break-up of Pangea (Golonka 2007). Enhanced volcanic activity (Kurtz 1983), which increased CO 2 emission into the atmosphere (Hornung et al 2007), is thought to be responsible for the well-known Carnian Pluvial Event (CPE), which was caused by enhanced rainfall and river run-off through the shelves as a consequence of the intensification of the hydrological cycle due to global warming (Hornung et al 2007). As a consequence of these tectonic and climatic changes, organic-rich black shale accumulation occurred in the Tethyan realm during the early Carnian.…”