Glauconitic-rich strata from Oligo-Miocene shallow-marine siliciclastic deposits of the northern margin of Africa (Tunis
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ORIGINAL PAPER
Glauconitic-rich strata from Oligo-Miocene shallow-marine siliciclastic deposits of the northern margin of Africa (Tunisia): geochemical approach for basin analysis Kamel Boukhalfa & Alessandro Amorosi & Mohamed Soussi & Kmar Ben Ismail-Lattrâche
Received: 2 October 2013 / Accepted: 16 January 2014 # Saudi Society for Geosciences 2014
Abstract Glauconitic minerals have long been appreciated as a reliable tool for sequence stratigraphic interpretation. A degree of maturity and occurrence of glauconite are closely related within a system tract context and substrate paleoenvironmental conditions. Within Oligo-Miocene shallow marine deposits of northern Tunisian outcrops, the glauconite occurs as thin (few centimeters) to moderate thick (1 m) clay and fine grain size sandstone horizons which are superbly exposed at many localities. Sedimentological investigations data indicate that these glaucony-bearing strata are deposited under shallow water shelfal and lagoonal siliciclastic depositional systems. Geochemical analysis from nine glaucony samples shows that Oligocene glaucony is invariably more evolved (K2O=6–8 %) than Miocene glaucony, which is typically slightly evolved (K2O=4–6 %). Vertical changes in glaucony maturity are consistent with sequence-stratigraphic interpretation, showing in general an upward increase in the transgressive systems tract. Maximum glaucony concentration is recorded corresponding to the maximum flooding surface/condensed section. Comparison of glaucony characteristics across different depositional systems at the same stratigraphic level shows a slight decrease in maturity and abundance from distal to proximal locations. This lateral tendency reflects more suitable conditions for glauconitization in open-marine environments than in shallow waters. Keywords Glaucony . Geochemical analysis . Oligocene . Miocene . Northern Tunisia K. Boukhalfa (*) : M. Soussi : K. B. Ismail-Lattrâche Département de Géologie, Faculté des Sciences de Tunis, Université de Tunis El Manar, 1062 Tunis, Tunisia e-mail: [email protected] A. Amorosi Dipartimento di Scienze della Terra e Geologico-Ambientali, University of Bologna, Via Zamboni 67, 40127 Bologna, Italy
Introduction Detailed analysis of literature on glaucony has shown the importance of a thorough investigation of glaucony characteristics as a reliable tool for basin analysis. Specifically, the glauconitic minerals have been extensively studied in terms of genetical models and depositional environments (Chafetz 1970, 1973, 1978; Siavochani et al. 1978; Odin and Matter 1981; Logvinenko 1982; King and Chafetz 1983; Odin 1985; Chafetz et al. 1986; Odin and Fullagar 1988; Odin and Morton 1988; Kelly and Webb 1999; Chafetz and Reid 2000; Pasquini et al. 2004; Ozgüner and Varol 2009; Hossain et al. 2011a, b; Banerjee et al. 2012a, b; Baioumy and Boulis 2012; Li et al. 2012), chronostratigraphy (Odin 1988; Morton and Long 1980; Keppens and Pasteels 1982; Odin 1982a, b, c; Grant et al. 1984; Craig et al. 1989; Clauer et al. 1992; Amorosi
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