Radiolarian and Planktic Foraminifera Biostratigraphy of the Early Albian Organic Rich Beds of Fahdene Formation, Northern Tunisia
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Journal of Earth Science, Vol. 25, No. 1, p. 45–63, February 2014 ISSN 1674-487X Printed in China DOI: 10.1007/s12583-014-0399-5 Radiolarian and Planktic Foraminifera Biostratigraphy of the Early Albian Organic Rich Beds of Fahdene Formation, Northern Tunisia M Ben Fadhel* 1, 2, T Zouaghi2, A Amri2, M Ben Youssef 2 1. Département de Géologie, Faculté des Sciences de Gafsa-Campus Universitaire Sidi Ahmed Zarrouk–2112, Université de Gafsa, Tunisia 2. Département des Géoressources, CERTE–Technopole de Borj Cédria, PB 174 1164, Hammam E Chatt, Tunisia ABSTRACT: The lower part of Fahdene Formation outcropping in northeastern Tunisia is repre- sented by pelagic sequences and characterized by an important siliciclastic fraction that includes ra- diolarian and organic-rich beds of Allam Member. Litho-biostratigraphic analysis based on planktic foraminifera and radiolaria shows that deposition of organic-rich beds of Allam Member is confined to the Microhedbergella rischi Zone through the lower part of Ticinella primula Zone. Age diagnostic radiolaria recovered from these beds has been identified to constrain a direct age of black shale depo- sition. The assemblages can be correlated with the radiolarian biochronozone U.A.10–11 indicating an Early Albian to early Middle Albian in age. Radiolarian assemblages composed of species characteris- tic of U.A.10 biochronozone (A. montisserei, D. gracilis) are associated with radiolarian taxa belonging to Costata Zone (U.A.9 Pseudoeucyrtis hanni and Thanarla pseudodecora), which can be correlated with Dercourt Member in the Ionian Zone and Paquier level of the Vocontian Basin (southeast of France). Biostratigraphic and abundance curves analysis has demonstrated significant diversification of cryptocephalic Nassellaria and Archaeodictyomitrae, probably adapted to eutrophic conditions that characterized the Aptian-Albian transition. Ecological conditions may have governed the stratigraphic range of many cosmopolitan taxa (i.e., Pseudodictyomitrae lodogaensis) compared with stratigraphic distributions schemes reported from other domains. The timing of black shales deposition was dia- chronic due to local geodynamic conditions and upwelling currents distribution. The Allam black shales are correlative with the oceanic anoxic event OAE1b which is characterized by the widespread of supraregionnally organic-rich beds in the Mediterranean Tethys basins across the Aptian-Albian transition. KEY WORDS: northeastern Tunisia, Albian, Allam Member, black shale, radiolaria, planktic fo- raminifera. 1 INTRODUCTION and implications of orbital forcing (Heldt et al., 2010; Fiet et al., The Aptian-Albian transition is a “hinge” period during 2001). which subsequent sedimentation reflects global transgression Radiolarians were mostly used to calibrate the ophiolitic (Hardenbol et al., 1998) and orogenic events related to the “Aus- sutures age (O’Dogherty et al., 2006; Babazadeh and de Wever, trian” tectonic phase (Chihaoui et al., 2010; Dall’Agnolo, 2000). 2004; Beurrier et al., 1987), their occurrence in the Mediterra- Most debates center around its stratigraphic calibration and sev- nean pelagic sequences of Mid-Cretaceous age aroused the in- eral studies have discussed the ammonite biozonations (Chihaoui terest of micropaleontologists to use them as a biostratigraphic et al., 2010; Hancock, 2001; Kennedy et al., 2000), biological tool for large scale correlation and paleogeographic reconstruc- events on marine biota including phases of speciation and tions in addition to planktic foraminifera (O’Dogherty et al., planktic foraminifera turnover (Huber and Leckie, 2011) 2010, 2009; Danelian et al., 2007; Bak, 2004, 1999, 1995; Erba- cher, 1998; O’Dogherty, 1994). *Corresponding author: [email protected] The Early Albian pelagic sequences of western Tethyan © China University of Geosciences and Springer-Verlag Berlin margins include discrete organic-rich beds yielding diagnostic Heidelberg 2014 radiolarian microfauna (Danelian et al., 2007; Erbacher and Thurow, 1997). Previous biostratigraphic works on Aptian- Manuscript received July 23, 2012. Albian transition of north Central Tunisia focused on ostracods Manuscript accepted December 15, 2012. (Zghal et al., 1997; Khayati-Ammar, 1996; Bismuth et al., 1981), Ben Fadhel, M., Zouaghi, T., Amri, A., et al., 2014. Radiolarian and Planktic Foraminifera Biostratigraphy of the Early Albian Organic Rich Beds of Fahdene Formation, Northern Tunisia. Journal of Earth Science, 25(1): 45–63, doi:10.1007/s12583-014-0399-5 46 M Ben Fadhel, T Zouaghi, A Amri and M Ben Youssef ammonites (Chihaoui et al., 2010; Lehmann et al., 2009; Memmi, 2004). 1999) and planktic foraminifera (Ben Haj Ali, 2005). These au- The Cretaceous sedimentation was, under the control of thors have discussed the deposition age of Late Aptian Serj syn-sedimentary faults trending 140ºN–160ºN reflected by cha- and/or Hameima Formation and Early Albian Lower Fahdene otic and gravitational deposits (Saadi, 1991). Formation, and concluded that Lower to Middle Albian pelagic Early Cretaceous successions show northward, reduced successions are diachronic and affected by hiatuses. In addition, thickness and affected by hiatus and extreme condensations in some authors stated that Lower to Midlle Albian pelagic succes- Hammam Zriba (Saadi, 1990). The motion of a corridor trending sions of northeastern Tunisia can’t be differentiated due to poor north-south by 140ºN–160ºN faults has led to the fragmentation preservation of planktic foraminifera (Jauzein, 1967). of the seafloor in the lozenge-shaped basin (Saadi and Duee, So far, there are only few studies on Early Albian radiolaria. 1991). During the Valanginian–Barremian time span, these ba- The first dating attempts in the Tunisian realm using radiolarian sins were supplied by siliciclastic deposits while condensed se- assemblages were focused on Jurassic “radiolarites” of the Tuni- dimentation occupied uplifted horsts (Saadi et al., 1994; Biely et sian Ridge (Dorsale “Tunisienne”) (Boughdiri et al., 2007; Cor- al., 1973). dey et al., 2005). More recently, Ben Fadhel et al. (2010) and The Ragoubet Lahneche anticline (Fig. 1c) is located west- Soua et al. (2006) discussed the paleoenvironmental significance ward of Ain Slim Section, 20 km far from the Teboursouk Vil- respectively of Late Albian and Cenomanian-Turonian lage. The structure is a part of the Jebel Goraa structure, an radiolarian-rich beds of northern Tunisia. NE-SW roosted syncline. The NW flank is cross cut by a Triassic Here we present integrated biostratigraphic analysis of ra- lens separating the Neogene from Cretaceous successions. diolarian and planktic foraminiferal assemblages from Allam Southward, Aptian and Albian deposits outcropping in western Member in northern Tunisia outcropping in Jebel Garci, Ain border of Ragoubet Lahneche structure are pierced by the Triassic Slim and Jebel Ragoubet Lahnèche sections. salt extrusion. The faults bordering the western flank of Jebel The aim of this article is also to present: (1) new documen- Goraa structure are responsible for a normal downthrow of Cre- tation of radiolarian species extracted from organic-rich beds taceous successions which were overlain by quaternary alluvium which is the first attempt of Early Albian successions dating in of Oued Tessa and Arkou rivers (Hammami, 1999). northeastern Tunisia; (2) an integrated biostratigraphy using The first stratigraphic nomenclature of Fahdene Formation planktic foraminifera and radiolarian of organic-rich beds of Al- was proposed by Burollet (1956). That author subdivided the lam Member; (3) constraining the timing of black shales deposi- Fahdene Formation into five members: (1) The Lower Shale tion and correlation with equivalents black shales recorded in the Member, composed of dark shale and marls, including an Mediterranean Tethys basins. ammonite-rich horizon which Burollet et al. (1983) attributed it to the Latest Aptian; (2) the Allam Limestone Member, com- 2 GEOLOGICAL SETTING AND PREVIOUS WORKS posed of black massive limestone and dark shale attributed to the The studied sections are located in northeastern Tunisia, and Middle Albian; (3) the Middle Shale Member, which is com- belong to two different structural domains. The section of Ain posed of black shale and marl, attributed to the Late Albian; (4) Slim-Zebbas (Fig. 1a) is bordering the “salt-glacier” extrusion of the Mouelha Limestone Member, composed of black, laminated Bir Lafou (Ben Chelbi et al., 2006) located in Bir M’Cherga area and bituminous limestone bed of Late Albian age; (5) the Upper which belongs to the northeastern part of the Dome belt (Vila et Shale Member, composed of black shales embedding some marly al., 1996; Perthuisot, 1978). The area is characterized by intervals of Vraconian age (Uppermost Albian). NNE-SSW-trending anticlines dominated by the Triassic struc- Then Bismuth (1973) established a biostratigraphic frame- ture of Jebel Aouinet. It is bordered to the southeast by the Zag- work for the Aptian-Albian transition based on ostracod fauna. houan thrust and to the north by the prolongation of the “Té- Saadi (1991) discussed the biostratigraphic framework of Jebel boursouk suture” (Fig. 1). Garci Section based on planktic and benthic foraminifera as well The Triassic of Jebel Aouinet anticline consists of “Ger- as faunal content of reefal limestones of Serj Formation. She as- manic” facies (anhydrites, dolomites and cargneules) and shows signed the black shales of Lower Fahdène Formation to Early–