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– in its eastern slope, evaporites lenses, interstratified within Ap- Midlle Albian age and the hardground surface outlining the ree- tian to Early Albian shales (Ben Chelbi et al., 2006). fal limestone bed as an unconformity within the Aptian-Albian Early Cretaceous outcrops in Jebel Zebbas located northeast boundary. of Jebel Aouinet, consist of Barremian to Late Aptian pelagic Later, Robaszynski et al. (2008, 1994) proposed a detailed successions of gray clay and quartzite beds which yield Puzosia biostratigraphic and sedimentological analysis of the Fahdène getulina, Ptuchoceras laeve, Phylloceras winckleri ammonites Formation based on planktic foraminifera and ammonites and and belemnite fragments (Jauzein, 1967). The Albian sequences described the microfossil distribution within the Albian- consist of laminated limestone beds and organic-rich black marls Cenomanian boundary. including pyrite nodules (Talbi, 1991) More recently, biostratigraphic studies were focused mainly The Fadeloun-Garci-Mdeker structure (Fig. 1b) is com- on the lower part of Fahdene Formation which outlined the posed of three anticlines, trending north-south and is considered Aptian-Albian transition, based mainly on ammonite (Chihaoui as the northern prolongation of the N-S axis (Saadi, 1990). The et al., 2010; Memmi, 1999) or using planktic foraminifera for age anticlines are separated from the Atlas domain by the Zaghouan calibration of the “interstatified salt glaciers” outcropping in Ra- thrust, which its northeastern part becomes south-verging, com- goubet Lahnéche and Fej Lahdoum areas (Ghanmi et al., 2001; monly defined by the Chérichira-Kondar thrust (Khomsi et al., Vila et al., 1996, 1994).
Radiolarian and Planktic Foraminifera Biostratigraphy of the Early Albian Organic Rich Beds of Fahdene Formation 47
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lagoonal Santonian Figure 1. Structural Ne. Nefza; He. Hedil; Te. Tebarka. 2. Aptian reefal limestone; studied section. Albian; Maastrichtian
48 M Ben Fadhel, T Zouaghi, A Amri and M Ben Youssef
Studies on structural and geodynamic of Triassic salt bodies the marly intervals increase in thickness contrary to limestone outcropping in Bir M’Cherga area and cross cutting the Creta- beds. The microfauna content yields poor planktic foraminiferal ceous succession of Jebel Zebbas show that salt wall has an Ap- assemblages and radiolarian rich microfauna. tian age based on the presence of Planomalina cheniourensis Planktic foraminifera reappear on GA20 bed that yields (Ben Chelbi et al., 2006). The Late Aptian to Early Albian age of Hedbergella gorbachikae Longoria Microhedbergella prae- salt roof (80 m thickness) is estimated based on the presence of planispira Huber and Leckie and Microhedbergella pseudodel- an association of Hedbergella planispira Tappan, Vaginella rec- rioensis Huber and Leckie. The benthic foraminiferal assem- ta Reuss, Frondicularia filocuicta Reuss, Lenticulina turgidula blages consist of Osangularia schloenbachi (Reuss) and Valvu- Reuss, L. pulchella Reuss, Tristix concavata Reuss (Ben Chelbi lineria infracretacea Crespin. et al., 2006). Fractures related to a strike slip fault outlining the black Ben Chelbi et al. (2006) stated that normal microfaults, hales unit are onlapped by a marly interval and gray limestone cross cutting Clansayesian limestone beds and sealing Albian beds alternation (GA24–GA27). This unit is characterized by marls of Lower Shale Member, indicate an extensive tectonic highly abundant of benthic GA25 sample has provided benthic phase which is responsible for the tilting of the sedimentary foraminiferal assemblages composed of Fursenkoina viscida blocks. The time equivalent outcrops in Jebel Garci show olis- (Khan), Spirillina minima Schacko, Lenticulina sp., Nodosaria tostromes, burrowed surfaces, and condensed deposits as indica- sp., Ramulina aculaeta (D’Orbigny), Valvulinoides sp., Gav- tors of tectonic activity associated with marine sea-level fall elinella sp.. Planktic foraminifera are represented by M. prae- (Saadi et al., 1994; Saadi, 1991). planispira, (Gandolfi) and Microhedbergella pseudodelrioensis Huber and Leckie. 3 MATERIALS AND METHODS The organic-rich beds comprised between GA9 and GA23 A total of 48 samples of marl and limestone were collected have released a moderately to well-preserved and age- for biostratigraphic analysis. Organic-rich levels were sampled at diagnostic radiolarian species. relatively higher resolution (approximately every 50 cm). Soft Radiolarians appear with few discrete taxa within GA6 level. samples were crushed and soaked in hydrogen peroxide solution It provides an assemblage composed of Holocryptocanium barbui and then washed using standard techniques. Samples were sieved Dumitrica, Spongostichomitra elatica (Aliev), Pseudoeucyrtis sequentially using meshes of 500 mm-250 mm-125 mm-63 mm. hanni (Tan), Archeodictyomitra vulgaris Pessagno, Thanarla Each sieve was stained with methyl blue (10 g/L) to avoid con- brouweri (Tan), Stichomitra simplex (Smirnova and Aliev), An- tamination from previous samples. Specimens with good preser- gulobracchia portmanni Baumgartner, Thanarla pacifica Na- vation determined and picked under Wild Herbrugg light bin- kaseko and Nishimura. They become diversified and abundant ocular microscope. Abundance of radiolaria is expressed semi- within GA7. This latter provided an association of Dictyomitra aff. quantitatively by counting the total number of preserved speci- gracilis (Squinabol), Dictyomitra communis Squinabol, Ar- mens (per 1 g of sample). Planktic foraminifers and radiolarians chaeodictyomitra montisserei (Squinabol), Pseudodictyomitra were mounted on slide, using double-faced adhesive tape, coated lodogaensis Pessagno, Thanarla praeveneta Pessagno, Ar- with silver and photographed using JEOL JSM 5400 scanning chaeodictyomitra aff. A. vulgaris Pessagno, Hiscocapsa sp., Tha- electron microscope of the ETAP Research Center, Tunis. narla aff. pulchra (Squinabol), Spongostichomitra elatica (Aliev), Thanarla brouweri (Tan), Thanarla pseudodecora (Tan), Angu- 4 RESULTS lobracchia portmanni Baumgartner, Stichomitra simplex (Smir- 4.1 Jebel Garci Section nova and Aliev), Stichomitra communis Squinabol. The condensed section of Jebel Garci (Fig. 2) begins with GA15 sample provided Archaeodictyomitra montisserei orbitolinids-rich green to gray clay and discontinuous sandy li- (Squinabol), Holocryptocanium barbui Dumitrica Pseudodictyo- mestone beds alternations which are attributed to the Hameima mitra lodogaensis Pessagno, Stichomitra simplex (Smirnova and Formation. The clay intervals have also provided fragments of Aliev), Pseudoeucyrtis hanni (Tan), Diacanhocapsa sp., Hisco- rudist and bryozoans (GA1). The top is outlined by olistolites capsa grutterinki (Tan) Angulobracchia portmanni Baumgartner, deposits that gradually pass to a reefal limestone. The top is Stichomitra communis Squinabol, Pseudodictyomitra paronai capped by an oxidized hardground which is overlain by detrital (Aliev), Cryptamphorella conara (Foreman). quartz rich-marly interval that provided Hedbergella trocoidea GA18 provided Dictyomitra gracilis (Squinabol), Thanarla (Gandolfi), Microhedbergella pseudodelrioensis Huber and conica (Squinabol). Leckie, and Microhedbergella praeplanispira Huber and Leckie The upper part of black shales interval (G17–23), composed (GA6). by rhythmic bundles of limestone and marl beds, is characterized Upwards, the black gray marl interval (GA9–10) did not by a decrease of radiolarian abundance. The sample GA20 has re- provide well-preserved planktic foraminifera. Some small-sized leased a radiolarian assemblages composed of Thanarla brouweri planktic foraminifer species are identified associated with ben- (Tan), Spongostichomitra phalanga O’Dogherty, Pseudodictyo- thic foraminiferal assemblage composed by rare epistominids mitra paronai (Aliev), Dictyomitra communis Squinabol, Holoc- and Conorboides lamplughi (Sherlock) (GA10). ryptocanium barbui Dumitrica, Pseudodictyomitra lodogaensis The next successions (GA13–GA20) consist of centimeter- Pessagno, Dictyomitra gracilis (Squinabol), Archaeodictyomitra thick grey to dark laminated limestone bed and organic-rich montisserei (Squinabol), Spongostichomitra elatica (Aliev), black marls intervals. Upwards, the succession is rhythmic and Pseudodictyomitra paronai (Aliev).
Radiolarian and Planktic Foraminifera Biostratigraphy of the Early Albian Organic Rich Beds of Fahdene Formation 49
Ticinella primula Ticinella
Ticinella raynaudi Ticinella
Hebergella pseudodelrioensis Hebergella Microhedbergella praeplanispira Microhedbergella
eefal limestone; 4. sandy Hedbergella Gorbachikae Hedbergella
Planktic foraminifera Planktic Thanarla pseudodecora Thanarla
4 oi pelta Godia
hnraconica Thanarla
blsotsperspicuus Obeliscoites rhoitoir vulgaris Archeodictyomitra
3
7
hnrapraeveneta Thanarla
hnrapulchra Thanarla
suoitoir lodogaensis Pseudodictyomitra gf
gc Hiscocapsa grutterinki Hiscocapsa
2
6 blsotsvinassai Obeliscoites
iccpaasseni Hiscocapsa
Xitus spicularius Xitus
oclmcoronatum Torculum
Archaeodictyomitra montisserei Archaeodictyomitra 1
5
Stichomitra communis Stichomitra
suoitoir paronai Pseudodictyomitra
Pessagnobracchia rara Pessagnobracchia
atlopar maxima Dactyliosphaera
Cryptamphorella conara Cryptamphorella
Holocryptocanium barbui Holocryptocanium
pnotcoir elatica Spongostichomitra hnrabrouweri Thanarla
Thin bedded limestone; 2. thin laminated limestone; 3. r tcoir simplex Stichomitra
nuorchaportmannii Angulobracchia
oorpoaimtuberculatum Holocryptocanium
Radiolarian
suouytsapocrypha Pseudoeucyrtis
suouytshanni Pseudoeucyrtis
Stichomitra mediocris Stichomitra
Dictyomitra gracilis Dictyomitra ci Section. 1. Dictyomitra communis Dictyomitra
een to gray shale.
Hardground
5
40 30 20 10
0 m
biostratigraphy of Jebel Gar
GA17
GA6
GA18
GA3
GA16
GA8
GA 1
GA23 GA26 GA19
GA11 GA9 GA7
GA27
GA12 GA5
GA2
GA22 GA25 GA15 GA14 GA13
GA21 GA20
GA10
GA24
GA4
Leckie, 2011) Leckie,
irhdeglarischi Microhedbergella Undefined zone (Huber and (Huber zone Ticinella primula Ticinella
Planktic foraminifera Planktic
(O’Dogherty, 1994) (O’Dogherty,
biochronozone U.A.9-10 U.A.10-U.A.11
Radiolarian
Guex, 2002) Guex,
Costata
Romanus and (O’Dogherty
Radiolarian zone Radiolarian
ideshales Middle
Hameima Allam Member
i Albian Mid oe Albian Lower Stage pe Aptian Upper
limestone; 5. black shales; 6. marl (gc. light gray; gf. dark to gray); 7. gr Figure 2. Radiolarian and planktic foraminifer Figure
50 M Ben Fadhel, T Zouaghi, A Amri and M Ben Youssef
We identified well-preserved radiolarian population within marly interval (AS21), rich in detrital materials, provided GA24 beds composed of Pessagnobrachia rara (Squinabol), Sti- Ticinella roberti (Gandolfi), Ticinella primula Luterbacher and a chomitra communis Squinabol, Archaeodictyomitra montisserei benthic association composed of lenticulines, Spiroplectinata an- (Squinabol), Cryptamphorella conara (Foreman), Holocrypto- nectens (Parker and Jones), Gavelinella intermedia (Berthelin), canium barbui Dumitrica, Pseudodictyomitra lodogaensis Pessa- Laevidentalina communis (D’Orbigny). gno, Torculum coronatum (Squinabol), Xitus spicularius (Aliev), Obeliscoites vinassai (Squinabol), Hiscocapsa asseni (Tan), Tha- 4.3 Ragoubet Lahneche Section narla pulchra (Squinabol), Dictyomitra communis Squinabol, The section (Fig. 4) begins with chaotic Triassic evaporites Hiscocapsa grutterinki (Tan). and conglomerates which are overlain by dark greyish, slumped Marly interval of the top GA27 has released an assemblage marl interval (BLH0–BLH2, thickness: 2.50 m) showing of Holocryptocanium barbui Dumitrica, Stichomitra simplex centimeter-thick secant fractures and filled with calcite minerali- (Smirnova and Aliev), Pseudodictyomitra paronai (Aliev), and zation (BLH0–BLH2). The marl interval provided pyrite cubes, Dactyliosphaera maxima (Pessagno). tiny hedbergellids, mineralized skeletons of spherical radiolarian and some specimens of Microhedbergella praeplanispira Huber 4.2 Ain Slim Section and Leckie. The next successions (BLF2, BLF4–6) consist of 40 The Ain Slim Section, in vertically contact with Triassic m of grey to dark marl, passing upward into bituminous dark, evaporites (Fig. 3), begins with detrital and bipyramidal splintery and organic rich limestone beds of the Allam Member quartz-rich silty marls (AS1–6). They released diversified planktic (BLF3, BLF4 to 6). They yield relatively abundant planktic fo- foraminiferal assemblages composed of Globigerinelloides ferre- raminiferal microfauna with partially mineralized skeletons. Up- oloensis (Moullade), Globigerinelloides aptiensis Longoria, Hed- ward, the microfauna become rare, particularly within organic-rich bergella trocoidea (Gandolfi), Planomalina cheniourensis Sigal, beds. Clavihedbergella (Lilliputianella) bizonae (Chevalier). The ben- The interval comprised between BLH2 and BLH3 has pro- thic microfauna is composed of Lenticulina sp., Valvulineria sp., vided Microhedbergella praeplanispira Huber and Leckie, Mi- Gavelinella berthelini (Ten Dam). Upward, barite nodules-rich crohedbergella pseudodelrioensis Huber and Leckie, Ticinella marly interval has yielded Paraticinella eubejaouaensis (Randri- roberti (Gandolfi), Globigerinelloides maridalensis Bolli, Glo- anasolo and Anglada) and some tiny hedbergellids (AS7–AS10). bigerinelloides eaglefordensis (Moreman), Ticinella aff. yezoana We also identified sporadic occurrence of Saracenaria sp. (Takayanagi and Iwamoto). The first occurrence of Ticinella pri- and some spherical radiolarian fauna (AS10). mula Luterbacher is recorded within BLH3 bed, associated with The next intervals (AS11–AS14) consist of dark pyrite scarce ostracods. It also yields a moderately-preserved radiolarian nodules-rich marls and limestone beds that include stratiform bar- microfauna composed of Crolanium sp., Dactyliospharea maxima ite mineralizations. Planktic foraminifera are less diversified in (Pessagno), Obeliscoites perspicuous (Squinabol), Cavaspongia opposition to benthic foraminifera. They are poorly preserved sphaerica O’Dogherty, Stichomitra communis Squinabol. Sample within dark detrital quartz-rich marls (AS11–12–13) and are rep- from BLH8 has yield diversified microfauna of radiolarian and resented only by Microhedbergella pseudodelrioensis Huber and planktic foraminifera dominated by species of the genus Globig- Leckie, Hedbergella trocoidea (Gandolfi) and Microhedbergella erinelloide. The assemblage is composed by Globigerinelloides praeplanispira Huber and Leckie. bentonensis Morrow, Hedbergella sp. and Ticinella madecassiana AS11 sample provided an association of Globulina prisca Sigal. Reuss, Gavelinella baltica Brotzen, Gyroïdinoides sp., Lingu- Radiolarians are very abundant within organic-rich bed of logavelinella albiensis Malapris, Berthelina intermedia Allam Member. BLH8 sample has provided an assemblage com- (Berthelin). posed of Pessagnobrachia fabianii (Squinabol), Godia concava AS12 sample yields Osangularia schloenbachi (Reuss), (Li & Wu), Savaryella novalensis (Squinabol), Dactyliosphaera Berthelina sp., Gavelinella intermedia (Berthelin), Gavelinella acutispina Squinabol, Cavaspongia sphaerica O’Dogherty, Ho- ammonoïdes (Reuss), Lenticulina sp., Laevidentalina communis locryptocanium barbui Dumitrica, Stichomitra communis Squi- d’Orbigny. nabol, Savaryella quadra (Foreman), and Torculum coronatum The basal part of shaly limestones and pyritic nodules-rich (Squinabol). gray alternations (AS13) provided Lenticulina sp., Gavelinella The interval comprised between BLH9 and BLH11 (thick- intermedia (Berthelin), Ramulina aculatea Wright, Valvulineria ness: 11 m) correspond to grey marl and grey coarse-massive li- infracretacea Crespin, Gyroidinoïdes niditus (Reuss), Gavelinella mestone bed alternations. The radiolaria microfauna is rare. The ammonoïdes (Reuss) and Ticinella madecassiana Sigal. BLH11 has provided some specimens of Microhedbergella pra- AS16 beds underlying organic-rich laminated marl and lime- eplanispira Huber and Leckie Globigerinelloides bentonensis stone beds show the first occurrence of Ticinella roberti (Gan- Morrow. dolfi). Well-preserved species of benthic foraminifera were identi- fied such as Lenticulina munsteri (Roemer), Marginulina in- 5 DISCUSSION aequalis Reuss and Gavelinella sp. (AS17). 5.1 Biological Events and Biostratigraphic Attribution Stratigraphically upward, the abundance of benthic fo- The turbidic reefal and sandy limestone and green shales raminifera decreases whereas planktic foraminifera become alternations did not yield diagnostic planktic foraminifera micro- abundant (AS20). The first occurrence of Ticinella primula fauna. However, this interval could lithologically be correlated Luterbacher coincides with shaly limestone bed (AS18). The with the Hameima Formation in northeastern Tunisia of Upper
Radiolarian and Planktic Foraminifera Biostratigraphy of the Early Albian Organic Rich Beds of Fahdene Formation 51
Planktic foraminifera
Substage
Member
Planktic foraminifera Zone foraminifera Planktic (Huber and Leckie, 2011) Leckie, and (Huber
Micredbergella pseudodelrioensis Micredbergella Microhedbergella praeplanispira Microhedbergella
Hedbergella trocoïdea Hedbergella gorbachikae Hedbergella
Paraticinella eubejaouaensis Paraticinella
Ticinella primula Ticinella roberti Ticinella madecassiana Ticinella Globigerinelloides aptiensis Globigerinelloides sp., Globigerinelloides bizonae Clavihedbergella Globigerinelloides ferroloensis Globigerinelloides
AS21
Middle Albian AS20
Middle shales Middle
Ticinella primula Ticinella AS19 AS18 ox10 primula T. ox9 AS17 ox8 ox7 ox6 ox5 ox4 ox3 ox2 ox1 AS16 Allam AS15 AS14
Ticinella madecassiana Ticinella
AS13 Ti. madecassiana Ti.
Lower Albian AS12
100
AS11 Microhedbergella rischi Microhedbergella
Lower shales Lower AS10
Paraticinella
eubejaouaensis AS9 ------
Upper Aptian ------eubejaouaensis Para. ------AS8 ------AS7 ------
trocoïdea ------Hedbergella ------AS6 ------
G. aptiensis G.
Bir M’Cherga Bir ------AS5 ------Middle Aptian AS4 ------AS3 10 ------G. algerianus G. AS2 - - - - - AS1 ------0 m
Pl. cheniourensis Pl. 1234 gn
Trias gf gc 5 6 7 8 Figure 3. Planktic foraminifera biostratigraphy of Ain Slim Section. 1. Triassic; 2. thin bedded limestone; 3. green shale; 4. green to gray shale; 5. black shales; 6. shaly limestone; 7. barite concretions; 8. marls (gc. light gray; gf. dark to gray; gn. dark).
52 M Ben Fadhel, T Zouaghi, A Amri and M Ben Youssef
Radiolarian Planktic foraminifera
Bioevent
Age
Member
Formation
Radiolarian zone
aff.
Planktic foraminifera zone foraminifera Planktic (Huber and Leckie, 2011) Leckie, and (Huber
Radiolarian biochronozone Radiolarian (O’Dogherty, 1994) (O’Dogherty,
blh14*
Micro. praeplanispira Micro.
Crolanium sp. Crolanium fabianii Pessagnobracchia Dactyliosphaera maxima Dactyliosphaera concava Godia Obeliscoites perspicuus Obeliscoites novalensis Savaryella Cavaspongia sphaerica Cavaspongia acutispina Dactyliosphaera Stichomitra communis Stichomitra Crucella remanei Holocryptocanium barbui Holocryptocanium Stichomitra communis Stichomitra Savaryella quadra Savaryella Torculum coronatum Torculum
G. bentonensis G. Ticinella roberti Ticinella Ticinella raynaudi Ticinella Ticinella primula Ticinella
blh13* blh12*
Mic praeplanispira
blh11*
Marnes Moyennes blh10* blh9*
primula Romanus Middle Albian blh8*
Lower Fahdene Lower
U.A10-U.A11
blh7* blh6* blh5* blh4* blh3*
T. primula T.
Allam blh2* 10 blh1*
Costata
Lower Albian
Madecassiana blh0* 0 m Trias
Figure 4. Radiolarian and planktic foraminifer biostratigraphy of Ragoubet Lahneche Section. Legend see Figs. 2 and 3.
Gargasian to Clansayesian in age (Chihaoui, 2009). as Thanarla pseudodecora (Tan) and Pseudoeucyrtis hanni (Tan) It was not possible to find Paraticinella eubejaouaensis (Zyabrev, 2011; Michalik et al., 2008; Danelian et al., 2007; Er- (Randrianasolo and Anglada), a marker specie of the Aptian- bacher and Thurow, 1998; O’Dogherty, 1994). Thus, a Late Ap- Albian boundary (Bellier and Moullade, 2002; Bellier et al., 2000; tian age of these beds could not hitherto be ruled out. Silva and Sliter, 1999). According to Erbacher and Thurow (1998), the first occur- The next successions overlying the hardground surface have rence of Pseudodictyomitra lodogaensis Pessagno coincides with yielded abundant Microhedbergella praeplanispira Huber and the upper part of Globigerinelloides algerianus Zone. Its last oc- Leckie that indicates an Early Albian age (Moullade et al., 2002). currence coincides with the Aptian-Albian boundary and the first In addition, co-occurrence of Early Albian taxa such as Osangu- occurrence of Mita gracilis (=Dictyomitra gracilis). On the other laria schloenbachi (Reuss), Fursenkoina viscida (Khan) (Hol- side, this taxon is also recorded within Albian to Cenomanian bourn et al., 2001; Erbacher et al., 1998) respectively in GA20 deposits in the Atlantic domain, California and Pacific realms and GA25 beds, assign at least the upper part of the black shales (Palechek et al., 2010; Kariminia, 2006; Thurow, 1988). to the Early Albian (GA17 to GA23). Slaczka et al. (2009) described an assemblage containing In the following section, we used radiolarian calibration in Angulobracchia portmanni Baumgartner, Dictyomitra communis order to improve the resolution of biostratigraphic record. The (Squinabol), Hiscocapsa asseni (Tan), Pseudodictyomitra lo- assemblages recovered from black shale beds are discussed dogaensis Pessagno, Pseudoeucyrtis hanni (Tan), almost similar herein. to GA7 taxa. These authors attributed the assemblage to Costata Samples recovered from basal beds (GA2–GA6) show high Zone that is confined to U.A.6–9 biochronozones of Midlle to abundance of Pseudodictyomitra lodogaensis Pessagno and con- Late Aptian age (O’Dogherty, 1994). tain some Early Cretaceous taxa from Turbocapsula Zone such It is noteworthy to point to the coexistence of Albian species
Radiolarian and Planktic Foraminifera Biostratigraphy of the Early Albian Organic Rich Beds of Fahdene Formation 53 in all samples such as Dictyomitra montisserei Squinabol and (OX2–OX8) show an assemblage composed typically by Dictyomitra gracilis Squinabol with Aptian taxa particularly in Ticinella madecassiana and Micr. praeplanispira, associated GA7, GA15 and GA26. In this overall context, an assemblage with and benthic microfauna indicating an Early Albian age. recovered from Mid Cretaceous outcrops of northern Tethys The occurrence of Ticinella primula (AS18) is recorded 17 margins was described by Danelian et al. (2007), shows the m above the black shale beds (OX2–OX8). Upward, the series co-occurrence of Pseudodictyomitra lodogaensis Pessagno, Dic- are composed of fractured limestone beds and gray marl intervals tyomitra gracilis Squinabol Archaeodictyomitra aff. vulgaris (AS19–31) which are confined to the acme zone of T. roberti and Pessagno assigning it to the Early Albian U.A.10–11 biochrono- T. raynaudi and characterizing the upper part of primula Zone zone. Danelian et al. (2004) consider that an Early Albian age of (Sliter, 1989). Dercourt Member cannot be ruled out despite the presence of The Ragoubet Lahneche anticline was the subject of an in- pseudoeucyrtis cf. hanni (Tan) characteristic of U.A.9. These tegrated study using biostratigraphy and seismic reflection data in species are hitherto observed within an assemblage from GA15, order to explain the salt tectonic evolution in northern Tunisia associated with Archaeodictyomitra montisserei (Squinabol). (Vila et al., 2002). These authors have postulated that conglom- Kurilov and Vishnevskaya (2011) described an assemblage erate bed overlying the Triassic evaporites have a Middle Albian extracted from Early Cretaceous outcrops of Pacific domain that age based on the presence of Hedbergella planispira and Fa- does not differ from GA21. It contains Pseudodictyomitra lo- vusella washitensis. Then, Ben Haj Ali (2005) stated that marlous dogaensis Pessagno, Holocryptocanium barbui Dumitrica, Dic- bed in contact with Triassic evaporites has a Late Albian age tyomitra cf. montisserei Squinabol, Dictyomitra communis based on the presence of Hedbergella planispira, Biticinella (Squinabol) and Dictyomitra gracilis Squinabol indicating an breggiensis and Ticinella primula together with abundant radio- Early Albian age. larian microfauna. The samples GA26 have provided an assemblage charac- Slumped marly interval (BLH0-2) overlying Triassic eva- terized by high abundance of Hiscocapsa asseni (Tan) porites (Fig. 4) provided an abundant tiny Hedbergellids such as co-occurring with Dictyomitra gracilis Squinabol and Dictyomi- Microhedbergella praeplanispira Huber and Leckie. The first tra montisserei Squinabol. It lies with the U.A.10 biochronozone occurrence of Ticinella primula Luterbacher is recorded within of Romanus Zone (Danelian et al., 2004; O’Dogherty, 1994). BLH3 bed thus the organic-rich beds of Allam Member may out- Basal beds of Ain Slim Section, overlying Triassic evapo- line the late Early Albian. rites (AS1–AS6), have provided planktic foraminifera-rich as- The assemblage provided by the interval BLH3–BLH11 is semblages mainly composed of Globigerinelloides species (G. composed of Microhedbergella praeplanispira Huber and Leckie, ferreolensis, Globigerinelloides aptiensis (AS1), Clavihedber- Ticinella roberti (Gandolfi), Ticinella yezoana Takayanagi and gella (Lilliputianella) bizonae (Chevalier), Globigerinelloides Iwamoto Microhedbergella rischi Huber and Leckie, Microhed- aptiensis (Longoria) and Planomalina cheniourensis Sigal (AS3). bergella pseudodelrioensis Huber and Leckie, Ticinella primula These occurrences are confined to the upper part of algerianus Luterbacher, an association that is inferred to the Middle Albian. Zone, based on the lowest occurrence of Planomalina chenio- The assemblage recovered from BLH3 bed contains species urensis, which indicates a Middle Aptian age (Huber and Leckie, like Stichomitra communis Squinabol, Obeliscoites perspicuus 2011). (Squinabol) and Dactyliosphaera maxima (Pessagno) ascribed to The sample AS6 shows an assemblage composed of Hed- the Barremian–Middle Albian interval (Zyabrev, 2011; Danelian bergela trocoidea, Hedbergella excelsa, Hebergella gorbachikae et al., 2007; Zyabrev et al., 2003; Erbacher, 1998) together with and G. ferreolensis (AS6) which is confined to the Upper Aptian. Cavaspongia sphaerica O’Dogherty which are described in the Upward, the marly interval has yielded depauperate planktic fo- Late Albian–Turonian interval (Musavu-Moussavou and Danel- raminifera fauna. The samples AS9 and AS10 contain small ian, 2006; Yurtsever et al., 2003; Erbacher, 1998; O’Dogherty, well-preserved specimens of Paraticinella eubejaouaensis which 1994). is considered by many authors as a marker specie to identify the The BLH8 has provided an assemblage containing strictly Aptian-Albian boundary (Bellier and Moullade, 2002; Silva and Albian species together with Dactyliospharea acutispina Sliter, 1999; Sliter, 1989). (Squinabol). Following (Erba et al., 1999) the first occurrence of The next upper beds yield strongly impoverished plank- Dactyliosphaera acutispina (Squinabol) species is recorded tic faunas in opposition to a high abundance of benthic fo- within the Selli Livello black shales of Early Albian age. Bak raminifera (GA11), an event which was regarded as a timeline (1999) stated that first occurrence of Dactyliosphaera acutispina outlining the Aptian-Albian boundary (Ben Haj Ali, 2005) (Squinabol) is recorded within the upper part of Rotalipora The next dark marly interval (AS11–AS15) contains small ticinensis-Planomalina praebuxtorfi foraminiferal zone through R. nodules of pyrite, and yields Mic. praeplanispira, Micr. praedel- appenninica foraminiferal zone. Then, Kemkin (2009) described rioensis and benthic-rich assemblages composed of Globulina an assemblage from the Far East domain of Russia containing prisca Reuss, a cosmopolitan specie of Lower Cretaceous age Dactyliosphaera acutispina (Squinabol) together with Dac- associated with Osangularia schloenbachi (Reuss), Berthelina tyliosphaera maxima (Pessagno). He attributed the assemblage to intermedia (Berthelin) which indicates an Early Albian age the Middle–Late Albian. An assemblage containing this species is (Tyszka, 2006; Holbourn et al., 2001; Erbacher et al., 1998; also described within Late Albian black shales of northeastern Holbourn and Moullade, 1998). Tunisia (Ben Fadhel et al., 2010). The taxonomic and strati- Shaly limestones of Allam Member (AS14–16) which graphic range discrepancies of Dactyliospharea acutispina overlain by organic-rich thin laminated limestone beds (Squinabol) has been debated in Kemkin and Filippov (2010) who
54 M Ben Fadhel, T Zouaghi, A Amri and M Ben Youssef stated that range of the species is the Middle Albian–Early (Danelian et al., 2004; O’Dogherty, 1994). However, the first Cenomanian and not the Barremian. Taking into account the mi- occurrence of Ticinella primula planktic foraminifera is recorded crofauna content, we suppose that the organic-rich beds of Allam 24 m above GA17 bed. Thus, an Early Albian age for the lower Member lies with the upper part of U.A.10–U.A.11 biochrono- part of Romanus Zone cannot be ruled out. zones of Early to Middle Albian in age (O’Dogherty, 1994). In Ragoubet Lahneche Section, the top of Costata Zone We think that variation of stratigraphic ranges between Me- which is outlined by the first set of Allam black shales shows the diterranean Tethys and East Pacific domains may be influenced first occurrence of Ticinella primula planktic foraminifera. The by ecological and paleoceanographic conditions including water lower part of Romanus Zone which lies with the upper part of temperature and connections between domains during the Albian. Allam black shales is characterized by appearance of an abun- Studies on radiolarian biostratigraphy show that Early Al- dant Hagiastridae assemblage (i.e., Savaryella quadra and Sava- bian zonal schemes still not well established (Danelian et al., ryella novalensis). 2004; O’Dogherty, 1994). For example, O’Dogherty (1994) has assigned the Early–Middle Albian interval to the Mallanites ro- 5.2 Relationships between Radiolarian Abundance and manus Zone. Then, he modified the subdivision and assigned the Black Shales Deposition upper part of the Costata subzone to the Early Albian which the The abundance curves of Allam black shales show gradual top coincides with the upper part of Ticinella primula planktic increase of radiolarian abundance (Fig. 5) which could indicates foraminiferal zone (O’Dogherty and Guex, 2002). a rise of productivity rate. The continuous input of nutrients has Following the zonal schemes of (Erbacher and Thurow, created eutrophic environment associated with high rate of 1998, 1997), the first occurrence of Mita gracilis (=Dictyomitra planktic productivity. As consequences, significant quantity of gracilis) is recorded within the Hedbergella planispira Zone organic matter produced by the phytoplankton was degraded by (=Microhedbergella rischi Zone of Huber and Leckie, 2011) and the bacterial activity, thus minimizing the amount of oxygen and considered as a marker species of Aptian-Albian boundary. Fur- enhancing the widespread of anoxic conditions. thermore, these authors have assigned the base of Pseudodictyo- The decrease in Spumellaria abundance, subsequent to the mitra lodogaensis Zone to the upper half G. algerianus planktic abundance peak at GA10 bed (Fig. 5), indicates an unstable en- foraminifera zone of Late Aptian age which the top coincide the vironment with low rate of productivity. By consequence, op- FO (first occurrence) of Mita gracilis. However, it was stated portunistic species (mainly cryptocephalic Nassellaria, and some that Mita gracilis occurs much earlier in Hauterivian–Barremian Archaeodictyomitrae) adapted to low oxygen conditions in- successions of Umbria Marche Basin in Central Italy (Danelian creased in abundance. et al., 2007; Jud, 1994). Silva and Sliter (1999) suggest that low S/N (Spumellaria In their study about Mid Cretaceous black shales of Ionian vs. Nassellaria) ratio indicates a high productivity due to an im- domain, Danelian et al. (2007), Danelian (2008) stated an abun- portant input of nutrients in the surface sea-water and coupled dant diversified archaeodictyomitrae taxa within Lowermost Al- with intensified upwelling currents. However, the rise of S/N ra- bian successions. They postulated that last occurrence of Tha- tio could reflect in certain cases a low-oxygen environment (Go- narla brouweri (Tan) is recorded within Middle Albian U.A.11 rican et al., 2003; Kuhnt et al., 1986). biochronozone, equivalent to the planktic foraminifera T. pri- Such a tendency was observed GA10 and GA17 where S/N mula Zone. Nevertheless, it was demonstrated that stratigraphic ratio shows linear increase (Fig. 5). It can be explained by the range of Thanarla brouweri could reach the Cenomanian- widespread of strictly anoxic conditions following the exhaustion Turonian boundary, particularly within the lower part of Bon- of nutrient supply. If eutrophic conditions become increasingly arelli Horizon (Musavu-Moussavu et al., 2007). accentuated, the environment becomes hostile to bloom of Spu- Considering biotic changes across the Aptian-Albian boun- mellaria (Silva and Sliter, 1999). Other factors, such as the com- dary (Danelian, 2008) we think that constraining the age of black plexity of Spumellaria test structure, made their mobility difficult, shale beds based solely on radiolarian assemblages, may reveals which explains the dominance of Nassellaria in S/N ratio discrepancies because of similarities between archaeodictyomi- (O’Dogherty and Guex, 2002). trae morphospecies and mixing with strictly Aptian taxa. Studies on radiolarian paleoecology have demonstrated the We suggest that lower part of black shale intervals could be existence of relationship between radiolarian abundance and or- assigned to the upper part of Costata Zone based on the presence ganic matter content (de Wever and Baudin, 1996). Generally of Aptian taxa (i.e., Pseudoeucyrtis hanni, Thanarla pseudode- speaking, the organic-rich sedimentation was coeval with trans- cora). The lower part of this zone coincide with the first occur- gressive system tracts (TST) (Amèdro, 2008; O’Dogherty and rence of Microhedbergella praeplanispira planktic foraminifera. Guex, 2002; Arthur and Sageman 1994; Schlanger and Jenkyns, Whereas the top coincide with the last occurrence of Pseudoeu- 1976). Moreover, the vertical flux of nutrient-rich waters de- cyrtis hanni associated with a relative increase in abundance in- pends on oceanic circulation and intense upwelling currents crease of Archaedictyomitrae and Williriedellidae families. which occur during the transition from regressive to transgres- The Romanus Zone described in Jebel Garci show the sion episode (O’Dogherty and Guex, 2002). It was also shown dominance of high diversified nassellarian species. The assem- that radiolarian high abundance recorded from mid Cretaceous blage composed of Thanarla brouweri, Archaeodictyomitra organic-rich and biosiliceous beds indicates an environment montisserei, Thanarla conica may be attributed to the Middle characterized by high rate of productivity (Danelian, 2008; Albian Mallanites romanus Subzone (U.A.10–11 biochronozone) Silva and Sliter, 1999).
Radiolarian and Planktic Foraminifera Biostratigraphy of the Early Albian Organic Rich Beds of Fahdene Formation 55
0.110 (a) Ga17 (b) 200 Allam Member 0.100 Ga26 180 black shales 0.090 Ga23 160 Ga10 0.080 140 0.070 Ga25 120 0.065 0.060 100 Ga14 S/N 0.055 Ga16 0.050 Ga8 80 0.045 0.040 Ga19
Radiolarian abundance Radiolarian 60 0.035 Ga25 0.030 Allam Member Ga9 Ga20 40 Ga8 0.025 black shales Ga6 Sample 0.020 Ga6 Ga19 Ga23 Sample 20 Ga12 Ga21 Ga24 0.015 Ga5 Ga15Ga18 0.010 Ga10 Ga11 Ga13 Ga22 0.005 Ga17 10 15 20 25 30 35 40 45 50 55 60 10 15 20 25 30 35 40 45 50 55 60 Thickness (m) Thickness (m) Figure 5. (a) Radiolarian abundance within Allam Member black shales of Jebel Garci Section; (b) Spumellaria vs. Nassel- laria ratio (S/N) recorded from the Allam black shales in the Jebel Garci Section.
5.3 Age Correlation of Black Shale Beds Tajerouine area (northwestern Tunisia). The author attributed it Although Lower Albian didn’t provide well preserved to the Early Albian Hypacanthoplites buloti ammonite zone. Re- planktic foraminifera, radiolaria are thought to be a reliable bio- cently, Ben Fadhel et al. (2011) have proposed a biostratigraphic stratigraphic tool of large-scale correlation (Boughdiri et al., framework for Albian pelagic successions in Nebeur area. They 2007). The main target of this correlation (Fig. 6) is to compare ascribed the Upper Allam organic-rich beds to T. primula plank- the biological events as well as the Albian sedimentary record in tic foraminiferal zone. the Mediterranean Tethys basins. In this study, biostratigraphic results from northeastern Tu- The Jebel Garci Section shows the association of Aptian ra- nisia sections show that organic-rich beds precede the lowest diolarian assemblages (i.e., Pseudoeucyrtis hanni, Hiscocapsa occurrence of Ticinella primula (AS18) and 88 m above the sp., Thanarla pseudodecora) with Albian species that is men- highest occurrence of Paraticinella eubejaouaensis in Ain Slim tioned by Danelian et al. (2004) who suggested that an Early Al- Section. This could confirm the assessment of Huber and Leckie bian age attributed to Dercourt Member is not excluded. How- (2011) who stated that disappearance of Paraticinella eube- ever, we cannot with certainty assign the absolute age of these jaouaensis is recorded 52 m below the Paquier level in the Vo- black shales, since the Lower Albian radiolarian zonation was contian Basin. not identified in the nomenclature of O’Dogherty (1994). Large scale correlations show that timing of black shales These black shales can hitherto be attributed to the bio- deposition is diachronic between northern Mediterranean Tethys chronozone U.A.10 based on the co-occurrence of Dictyomitra margins and Tunisian domains. gracilis, Archaeodictyomitra montisserei and Hiscocapsa sp.. The diachronic beginning of Allam black shales deposition Toward the north-east, the age of Allam black shale is rather di- was controlled mostly by local geodynamic conditions and up- achronic. It outlines the Early–Middle Albian successions over- welling currents distribution in southwest and northeast basins on laying the Triassic evaporites. A late Middle Albian age cannot the one hand Tunisian and northern Tethys areas on the other (Ben be excluded on the basis of abundant Hagiastridae species (Sa- Fadhel et al., 2011). In fact, basin configuration of northern Tuni- varyella quadra and Savaryella novalensis). sia was the result of SW-NE extension tectonic regime and halo- Studies on radiolarian biostratigraphy in Atlantic domains kinetic dynamics recorded across the Aptian-Albian transition (Erbacher and Thurow, 1998) show that organic-rich beds occur (Rigane et al., 2010; Guiraud and Maurin, 1992; Boltenhagen, within Aptian-Albian transition which lies with the boundary 1985). This tectonic phase and the resulted restricted basins were between M. gracilis and P. lodogaensis zones. These two species coeval with the widespread of supraregionnally black shales of are abundant within the middle part of black shale set. It is note- Niveau Paquier which is considered as the record of the oceanic worthy that Pseudodictyomitrae lodogaensis records it last oc- anoxic event OAE1b (Danelian, 2008; Tsikos et al., 2004; Herrle currence in the Costata Zone. This species has’t been found nei- et al., 2003; Bréhéret, 1997; Bralower et al., 1993; Bréhéret et al., ther in Romanus Zone nor in Late Albian successions (Ben Fad- 1986). hel et al., 2010). Thus, we attribute an Early Albian to early Mid- Total organic carbon and Tmax vs. hydrogen index plots dle Albian to the Allam black shales. They can be correlated with analysis carried on Early Albian black shales of Allam Member the “Upper Shaly Siliceous” interval (Fig. 6) of Sopoti Section in has demonstrated a good to moderate potential source rock and southern Albania (Danelian et al., 2007). the organic matter is mainly terrigenous Type III (Ben Fadhel et Chihaoui (2009) has postulated through carbon isotope sig- al., 2011). Southward, the equivalent of Allam black shales nature, the presence of an equivalent of Paquier level (Herrle et (Lower Fahdene Formation) is represented by the Late Aptian– al., 2003; Bréhéret, 1988) between SA3 and SA4 sequence in Early Albian reefal limestones of Serj Formation which is
56 M Ben Fadhel, T Zouaghi, A Amri and M Ben Youssef
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Ragoubet Lahneche Ragoubet
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Tunisia with equivalent outcr Tunisia T. primula T.
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80
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Figure 6. Corr Figure
Last occurrence Last Ticinella bejaouaensis Ticinella
Jacob level Jacob
Kilian level Kilian
Paquier level Paquier
220 240 260 280 300
Vocontian Basin Vocontian SE France (Reichelt, 2005) (Reichelt, France SE
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Radiolarian and Planktic Foraminifera Biostratigraphy of the Early Albian Organic Rich Beds of Fahdene Formation 57 considered as a potential reservoir rock of hydrocarbons (Burollet, Carpathica, 50(1): 21–31 1988). Bak, M., 2004. Radiolarian Biostratigraphy of the Upper Cenomanian–Lower Turonian Deposits in the Subsilesian 6 CONCLUSION Nappe (Outer Western Carpathians). Geologica Carpathica, Radiolarian and planktic foraminifer biostratigraphic study 55(3): 239–250 of Lower Fahdene Formation has provided an age constraint of Bellier, J. P., Moullade, M., 2002. Lower Cretaceous Planktonic black shales embedded within the Allam Member. Radiolarian Foraminiferal Biostratigraphy of the Western North Atlantic assemblages analysis together with planktic foraminifera biologi- (ODP LEG 171B), and Taxonomic Clarification of Key In- cal events show that deposition of Allam Member black shales dex Species. Rev. de Micropal., 45(1): 9–26 lies with U.A.10–U.A.11 biochronozone and Microhedbergella Bellier, J. P., Moullade, M., Huber, B. T., 2000. Mid-Cretaceous rischi through the lowest part of Ticinella primula planktic fo- Planktic Foraminifers from Blake Nose: Revised Biostrati- raminiferal zone. However, an Earliest Albian age could not be graphic Framework. In: Norris, R. D., Kroon, D., Klaus, A., excluded on the basis of typical Aptian taxa. eds., Proceedings of the Ocean Drilling Program, Scientific The deposition of organic-rich beds in northern Tunisia is Results, 171B. Ocean Drilling Program, College Station, characterized by radiolarian bloom which reflects high productiv- Texas ity rates and eutrophic environment. As consequences, numerous Ben Chelbi, M., Melki, F., Zargouni, F., 2006. Mode of Salt Bodies Aptian taxa (i.e., pseudoeucyrtis hanni, Thanarla pseudodecora) Emplacement in Septentrional Atlas of Tunisia: Example of a disappeared and many taxa adapted to these conditions (i.e., Ar- Bir Afou Salt Body. Comptes Rendus Géosciences, 338(5): chaeodictyomitrae) are represented by various morphotypes. It is 349–358, doi:10.1016/j.crte.2006.02.009 noteworthy that ecological conditions may have governed the Ben Fadhel, M., Layeb, M., Ben Youssef, M., 2010. Upper Albian stratigraphic range of many cosmopolitan taxa (i.e., Pseudodic- Planktic Foraminifera and Radiolarian Biostratigraphy tyomitrae lodogaensis) compared with stratigraphic distributions (Nebeur-Northern Tunisia). Comptes Rendus Palevol, 9(3): schemes reported from other domains. 73–81 The large-scale correlation the black shales of Allam Mem- Ben Fadhel, M., Layeb, M., Hedfi, A., et al., 2011. Albian Oce- ber with sections reported from North Mediterranean Tethys mar- anic Anoxic Events in Northern Tunisia: Biostratigraphic and gins show that organic rich beds are correlable with Niveau Geochemical Insights. Cretaceous Research, 32(6): 685–699 Paquier of the Vocontian Basin and equivalent to the suprare- Ben Haj Ali, N., 2005. Les Foraminifères Planctoniques du gionnally distributed oceanic anoxic event OAE1b. Crétacé (Hauterivien à Turonien Inférieur) du Tunisie: Systématiques, Biozonations et Précisions Biostratigraphique: ACKNOWLEDGMENTS [Dissertation]. Université Tunis el Manar, Faculté des This work was supported by the «le Ministère de Sciences de Tunis, Tunis (in French) L’Enseignement Supérieur et de la Recherche Scientifique» and Beurrier, M., Bourdillon-De-Grissac, C., De Wever, P., et al., 1987. «Centre des recherches des technologies des eaux–CERTE». Drs. Biostratigraphie des Radiolarites Associées Aux Volcanites Moncef Saidi and Hedia Bessaies from ETAP Research Center Ophiolitiques de la Nappe de Samail (Sultanat d’Oman): gave all facilities needed for SEM photographs. We thank Prof. Conséquences Tectogénétiques. Comp. Ren. Acad. Sci., 304: Imen Khemiri for improving the English text. Authors are grateful 907–910 to Miroslava Smrečková from Comenius University, Bratislava, Biely, A., Memmi, L., Salaj, J., 1973. Le Crétacé Inferieur de la Slovakia for providing us with documentations and citations about Région d’Enfidaville. Decouverte d’Aptien Condense. Livr. Cretaceous radiolarians in Pacific domain. Comments provided Jub. M. Solignac, Ann. Min. Geol., 26: 169–l78 by an anonymous reviewer and the editor are gratefully acknowl- Bismuth, H., 1973. Réflexions Stratigraphiques Sur l’Albo-Aptien edged. Dans la Région des Djebels Douleb et Semmama et Son Environnement (Tunisie du Centre-Nord). Ann. Min. 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Radiolarian and Planktic Foraminifera Biostratigraphy of the Early Albian Organic Rich Beds of Fahdene Formation 61
Plate 1
1. Globigerinelloides ferreolensis (Moullade), 100 µm, AS3; 2. Microhedbergella rischi (Moullade), 100 µm, AS11; 3. Hedbergella excelsa Longoria, 50 µm, AS6; 4. Ticinella aff. yezoana? Takayanagi and Iwamoto, 50 µm, RAG 3; 5. Paraticinella eubejaouaensis Randrianasolo and Anglada, 50 µm, AS9. 6. Microhedbergella pseudodelrioensis Huber and Leckie, 50 µm, GA21; 7. Clavihedber- gella (Lilliputianella) bizonae (Chevalier), 100 µm, AS3; 8. Hedbergella planispira (Tappan), 100 µm, RAG8; 9. Globigerinelloides aptiensis (Longoria), 100 µm, AS3; 10. Planomalina cheniourensis Sigal, 100 µm, AS3; 11. Globigerinelloides bentonensis (Mor- row), 100 µm, AS13; 12. Ticinella aff. madecassiana SIGAL, 50 µm, AS13.
62 M Ben Fadhel, T Zouaghi, A Amri and M Ben Youssef
Plate 2
1. Dictyomitra cf. montisserei (Squinabol), 50 µm, GA8; 2. Pseudodictyomitra lodogaensis Pessagno, 50 µm, GA8; 3. Archaeodic- tyomitra cf. montisserei (Squinabol), 50 µm, GA21; 4. Hiscocapsa sp., 50 µm, GA9; 5. Archeodictyomitra sp., 50 µm GA8; 6. Dic- tyomitra cf. montisserei (Squinabol), 100 µm GA24; 7. Pseudoeucyrtis cf. hanni 100 µm, GA8; 8. Cryptamphorella conara (Fore- man), 50 µm, GA21; 9. Archaeodictyomitra cf. montisserei (Squinabol), 100 µm, GA21; 10. Thanarla cf. pseudodecora? (Tan), 50 µm, GA8; 11. Pseudodictyomitra lodogaensis Pessagno, 50 µm, GA21; 12. Pseudodictyomitra cf. lodogaensis Pessagno 200 µm, GA20.
Radiolarian and Planktic Foraminifera Biostratigraphy of the Early Albian Organic Rich Beds of Fahdene Formation 63
Plate 3
1. Stichomitra cf. communis Squinabol, 100 µm, GA25; 2. Pseudodictyomitra sp., 100 µm, GA25; 3. Stichocapsa sp., 100 μm, GA20; 4. Dactyliosphaera maxima (Pessagno), 100 µm, BLH3; 5. Distylocapsa cf. micropora (Squinabol), 100 µm, BLH8; 6. Holocrypto- canium barbui Dumitrica, 50 µm, BLH8; 7. Pessagnobrachia cf. rara (Squinabol) 100 µm, BLH8; 8. Cavaspongia sphaerica O’Dogherty, 100 µm, BLH3; 9. Dactyliosphaera maxima (Pessagno), 100 µm, BLH3; 10. Godia concava (Li & Wu), 100 µm, BLH8; 11. Cavaspongia sphaerica O’Dogherty, 50 µm, BLH8; 12. Savaryella cf. quadra (Foreman), 100 µm, BLH8; 13. Stichomitra cf. communis Squinabol, 100 µm, BLH8; 14. Godia cf. concava (Tumanda), 100 µm, BLH8.