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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 (KO = 6-8 %) than Miocene glaucony, which is typically slightly evolved (KO = 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. [ABSTRACT FROM AUTHOR]

Abstract: The new biostratigraphic, sedimentological and structural data confirm the allochthony of the Numidian flysch and suggest the existence, in northern Tunisia, of two different allochthonous units within the so-called Numidian flysch as well as several underlying small-scale Tellian tectonic units. The first unit, mainly composed of sandstones and then by “silexites” corresponds to the Kroumirie and Babbouch members, extends from Late Oligocene to Aquitanian. It rests tectonically on the unit predominantly composed of claystones with sandstones of the Zouza member which is of Early Oligocene to Aquitanian. The Zouza member, which is at least 1800m thick, extending from Oligocene to Early Miocene, should be considered, at least partly, coeval to the Kroumirie member considered in the classic stratigraphic scheme as the middle part of the flysch. In this study, we demonstrate also that the deposits of the Numidian flysch and those of the Tellian and Bejaoua group, outcropping to the south, do not belong to the same sedimentary system. Their current juxtaposition resulted from the thrusting of the Numidian flysch southwards during the inversion phase that accompanied the convergence of Africa and Europe. [Copyright &y& Elsevier]

The exceptionally glauconite-rich Miocene strata, superbly exposed throughout the front of the nappes zone of northern Tunisia, show marked contrast in Fe-silicate authigenesis within and outside foraminifera chambers. Glauconite forms by the alteration of fecal pellet, quartz, feldspar, volcaniclastic particles, feldspar, and quartz. X-ray diffraction patterns show the characteristic peaks of the 'evolved' variety glauconite. The glauconite contains high K 2 O and Al 2 O 3 and moderate to high Fe 2 O 3 (total). While chamosite occurs solely as infillings within bioclasts pores, containing high Fe 2 O 3 and Al 2 O 3. Each of the glauconitic intervals coincide with the peak rise of third order sea-level cycles during the Burdigalian-Langhian time. Glauconite occurs at the base of coarsening- and thickening-upward hemicycles consisting of shale and sandstone, recording a shallowing upward trend across offshore-shoreface settings. The glauconitic parasequences are correlated across the Tethyan margin. Within the Miocene succession of Tunisia, glauconite formed on shallow marine dysoxic bottom water condition charged with abundant cations. On the other hand, anoxic micro-environment within the bioclasts pore spaces, induced by the decomposition of organic matter, favored the fixation of Fe2+ into the crystal structure, forming chamosite. Contemporaneous volcanism in Algeria and surrounding areas, in response to the African-European plate convergence, appears to be the most significant sources of Fe and other cations necessary for green clay authigenesis. Therefore, the occurrence of glauconite in the Miocene succession of Tunisia, is influenced by the combination of eustacy and volcanism, the type of substrate dictating the ultimate composition of the authigenic Fe-silicates. • Authigenic Fe-silicates including glauconite and chamosite form abundantly in low-energy, offshore sediments of Miocene Bejaoua facies. • While glauconite forms by the alteration of pellets, quartz, feldspar and volcaniclastics, chamosite occupies exclusively the pores within bioclasts. [ABSTRACT FROM AUTHOR]

This paper presents an integrated study aiming to assess the stratigraphy, sedimentology and paleogeography of the marine and non-marine Tellian, Bejaoua and Fortuna Oligo-Miocene deposits of northern Tunisia. The fossiliferous strata, particularly the glauconite-rich facies, bounded by major unconformities, refine the stratigraphic framework and address the spatio-temporal relationship between marine and non-marine deposits. Three new updated paleogeographic maps for the Oligocene (30-27 Ma) and the Miocene (21-20 Ma and 15 Ma) epochs, outlining the major transgressive and regressive events and the relationships between the Tellian and Atlasic basins have been produced. The genesis and evolution of the Oligo-Miocene foreland sub-basins of the Tellian, the salt domes zone and the northern Atlas are reconstructed considering the geodynamic events that accompanied the African-Eurasian convergence, besides eustasy and climate. • The Oligo-Miocene siliciclastic succession of northern Tunisia has been revised based on ancient and new acquired biostratigraphic data. • New lithostratigraphic scheme outlines the spatio-temporal distribution of the continental and marine facies of the Tellian and Atlasic domains. • Transgressive events versus glauconitic events. [ABSTRACT FROM AUTHOR]

The Early Aptian organic-rich deep marine deposits of the upper Member of the M'Cherga Formation (Valanginian-Aptian) of northern Tunisia were studied based on a multidisciplinary approach including biostratigraphy, sedimentology and organic geochemistry. This study is based on the analysis of 128 samples collected from three sections (Oued Bazina, Djebba and Tel Ghozlene) selected from the salt dome zone (SDZ) and one section of Jebel Oust, situated westward of the Tunisian range. This work is supplemented by previous research undertaken on Oued Zarga and Jebel Ammar sections. Taxonomic analysis of previous and new data (ammonites and planktonic foraminifera) indicate that three informal lithological units rich in organic matter (U1, U2 and U3) are of Early Aptian age, covering both Blowiella blowi and Leupoldina cabri planktonic foraminiferal zones and indiscriminate Lowermost Aptian to the Deshayesites deshayesi – Dufrenoyia furcata ammonite Zones interval. The Rock-Eval analytical results indicate that the studied Early Aptian strata are relatively rich in total organic carbon (TOC) content with values reaching 4.6 % within the U3 (Leupoldina cabri biozone). The latter occurring in the different studied sections constitutes an important deepening phase related to a global sea-level rise testified by the development of well laminated platy limestones containing abundant ammonites and radiolaria. This unit (U3), covering Leupoldina cabri planktonic foraminiferal zone and Deshayesites deshayesi to Dufrenoyia furcata ammonite Zones interval records the Oceanic Anoxic Event -1a (OAE-1a). The palynofacies assemblages show that the organic matter is mainly represented by amorphous particles. The Tmax values ranging from 437 °C to 456 °C (Mean Tmax: 446 °C) and the measured vitrinite reflectance ranging from 0.79 to 1.03 %, indicate that most samples are early mature except for those of the Tel Ghozlene (TG) section which are within the peak oil-generation-window. Lateral facies and thickness variation, in addition to the organic matter distribution throughout the studied domains, strongly suggest the imprint of salt tectonics both on the sedimentological pattern and associated anoxia during the Aptian. Maturation of the organic-rich facies occurred during the Upper Cretaceous-Paleogene compressional phase and associated salt dome remobilization. Source rocks, developed in the Upper Member of the M'Cherga Formation, are attributed to the OAE1a Event and should be considered when reviewing the petroleum potential of conventional and unconventional resources in northern Tunisia. [Display omitted] • The sedimentary succession of the upper Member of M'Cherga Formation from northern Tunisia records organic-rich strata deposited in pelagic basin shedding light on the Early Aptian Oceanic Anoxic Event (OAE 1a). • The OAE-1a is characterized within the U3 (Early Aptian) covering Leupoldina cabri planktonic foraminiferal zone and Dashayesites deshayesi to Dufrenoyia furcata ammonite Zones interval. • Maximum preservation of organic matter is recorded in the SDZ particularly along the hanging wall of the tilted blocks as developed in the Tel Ghozlane area. [ABSTRACT FROM AUTHOR]