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The lower and middle Berriasian in Central Tunisia: Integrated ammonite and calpionellid biostratigraphy of the Sidi Kralif Formation

The lower and middle Berriasian in Central Tunisia: Integrated ammonite and calpionellid... Maalaoui, K. and Zargouni, F. 2016. The lower and middle Berriasian in Central Tunisia: Integrated ammonite and calpionellid biostratigraphy of the Sidi Kralif Formation. Acta Geologica Polonica, 66 (1), 43­58. Warszawa. The lower and middle Berriasian sedimentary succession of the Sidi Kralif Formation has been a subject of biostratigraphic study in two key sections in Central Tunisia. Our contribution is an attempt to better define the basal Berriasian interval, between the Berriasella jacobi Zone and the Subthurmannia occitanica Zone. Zonal schemes are established using ammonites and calpionellids, and these permit correlation with other regions of Mediterranean Tethys and beyond. The use of biomarkers afforded by microfossil groups has allowed characterization and direct correlation with four widely accepted calpionellid sub-zones, namely Calpionella alpina, Remaniella, Calpionella elliptica and Tintinopsella longa. The two ammonite zones of Berriasella jacobi and of Subthurmannia occitanica are recognised on the basis of their index species. The parallel ammonite and calpionellid zonations are useful as a tool for correlation and calibration in time and space, thus allowing a better definition of a J/K boundary. The presence of four Berriasian calpionellid bioevents is recognised: (1) the `explosion' of Calpionella alpina, (2) the first occurrence of Remaniella, (3) the first occurrence of Calpionella elliptica and (4) the first occurrence of Tintinopsella longa. The last is here documented as coeval with the presence of Subthurmannia occitanica, which marks the lower/middle Berriasian boundary. Key words: Ammonite; Calpionellids; Berriasian; Bioevents; Biostratigraphy; Tunisia. INTRODUCTION In spite of intensive studies during recent decades, the formal definition of the Jurassic/Cretaceous boundary is still a problem, and it is the only Phanerozoic system boundary for which a GSSP has not been fixed (e.g., Remane 1991; Zakharov et al. 1996; Wimbledon 2008; Pessagno et al. 2009; Wimbledon et al. 2011; Wimbledon et al. 2014). There is a number of biological markers which may potentially be used as a marker for this boundary (Wimbledon et al. 2011), in an interval straddling the traditional base of the Berriasian Stage, the lower boundary of the Cretaceous. Successions across this critical interval, spanning the upper Tithonian and lower Berriasian, are known in Tunisia, in south-western Mediterranean Tethys. Many good sections are wellexposed in the central part of the country. The present paper provides a biostratigraphic report on the lower and middle Berriasian (Lower Cretaceous) succession of central Tunisia. Two sections, represen- 44 KAMEL MAALAOUI AND FOUAD ZARGOUNI Iberia Ita ly Africa Dj. Touila Ou Djebe Touati ed o Zer ud it Tall E J EB L EL h al K orsh if Dj. Bou Gobrine Dj. Guefaiat MN AR Ali Djeridi Dj. Nara Kef Khoudja Kef Krakrmat 1Km Kef el Hassine SK S i d Dj .Attaris Sebkhet el Bahira i f a l K h .667 .474 .645 .661 Kh el ar ro u ga O. Teba O. Nek h la J. Ti hala J . Sidi Khalif Neogene O.en Nakhla Key O. Dj. Akhouta Thrust fault Elevation Creek Gravel road Location o f studied sections Cenomanian to Paleocene Al la h Na s Dj. Faid Barremian (Boudinar Formation) Valanginian-Hauterrivian (Meloussi Formation) Upper Tithonian-Upper Berriasian: (Sidi kralif Formation) Jurassic dolomitic (Nara Formation) Triassic e Pi st de SF AX Text-fig. 1. Geological map of Central Tunisia (after Guiraud 1968, simplified) and location of the measured sections: SK - Sidi Kralif Section; N - Nara Section 45 BASAL CRETACEOUS BIOSTRATIGRAPHY IN TUNISIA Text-fig. 2. A ­ Panoramic view of the Jebel Sidi Khalif; B ­ The Nara section 46 KAMEL MAALAOUI AND FOUAD ZARGOUNI tative for the Sidi Khalif and Nara Hill ranges (Text-figs 1, 2) were selected. The Berriasian of these ranges is represented by marls, marly limestones and micritic limestones of the Sidi Kralif Formation (Burollet 1956). The formation is underlain by dolostones of the Nara Formation and overlain by the massive dolostone-sandstone of the Meloussi Formation. There is extensive bibliography on the geology of central Tunisia (e.g. Breistroffer 1937; Castany 1951; Arnould-Saget 1951; Burollet 1956; Bonnefous 1972; Guirand 1968; M'Rabet 1987). The biostratigraphy of the Sidi Kralif Formation was studied by Bismuth et al. (1967), Memmi (1967) and Busnardo et al. (1976, 1981). Bismuth et al. (1967) recognised four calpionellids zones in the Sidi Kralif Formation, although did not calibrate them to the ammonite zonation. Memmi (1967) recorded a succession of upper Tithonian and Berriasian ammonites in the Sidi Kralif Formation in the northern part of Jebel Nara and at Chaabet Attaris. Both calpionellid and ammonite assemblages were analysed by Busnardo et al. (1976, 1981). These authors characterized the Beriasella jacobi Zone; the Pseudosubplanites grandis Zone was difficult to define, but seemingly ammonites were seen as different compared to the B. jacobi Zone assemblage. In the Nara Range, they recognised a P. grandis Zone interval with calpionellids. The Subthurmannia occitanica Zone of the middle Berriasian was also characterized by calpionellids. The middle/upper Berriasian boundary could not be accurately determined because the fauna was found to be very rare. Both calpionellids and ammonites are critical in attempts to define the Jurassic­Cretaceous boundary (Wimbledon et al. 2011). Ammonites and calpionellids are treated in both sections studied herein, with the aim of calibration and correlation with other key sections in the Tethyan Realm: e.g., Msila area in the internal Prerif of Morocco (Benzaggagh et al. 2010); Le Chouet in SE France (Wimbledon et al. 2013); Puerto Escano in Spain (Pruner et al. 2010); Fiume Bosso in central Italy (Housa et al. 2004); Brodno in Western Carpathians, Slovakia (Housa et al.1999); Nutzhof in Austria (Lukeneder et al. 2010). All these sections have been discussed recently by Michalik and Rehakova (2011). for calpionellids. The calpionellids were studied in thin sections (25 in total) studied under an OLYMPUS BH2 transmitted light microscope, and photographed with Nikon COOLPIX L310 camera. All fossils described are stored in the collections of the Geological Survey of the National Office of Mines of Tunisia. GEOLOGICAL SETTING The study area is a part of the foreland of the Tunisian Maghrebide Chain, in the northernmost part of the structure known as the N-S Axis (Text-fig. 1), which limits the western part of the Sahel plains (Castany 1951; Burollet 1956). The axis is a N-S anticline that interferes locally with NE-SW folds (Castany 1951; Burollet 1956; Richert 1971; Ouali 2007). It is a major palaeogeographical limit that has been interpreted as having been a shoal at different times during the Mesozoic (Burollet 1956; M'Rabet 1987; Soussi et al. 2000). During late Jurassic to early Cretaceous times, Central Tunisia experienced continuous and regular sedimentation with a relatively slow subsidence in an infra-neritic depositional environment (Burollet, 1956). The evolution of the sedimentation of the Sidi Kralif Formation reflects the geological history of central Tunisia during J/K boundary times. Its lower part was deposited in relatively deep water with a marlylimestone sedimentation, whereas its upper part shows essentially clay sediments and indicates shallower waters. The decrease in depth is related to an increase in clastic sediments not compensated by subsidence, which explains the diachronism of this formation (Busnardo et al. 1981). In fact, central Tunisia was an external carbonate platform during the early Tithonian, except for the Chotts region (the salt-lake area) that corresponds to a littoral platform (Bonnefous 1972). During the late Tithonian, the first clay deposits arrived on this platform in a prodeltaic situation. In late Tithonian to mid Berriasian times the deposits prograded towards Jebel Meloussi and Jebel Bouhedma. Jebel Sidi Khalif and areas further north were still on an external carbonate platform with marly limestone sedimentation (Busnardo et al. 1981; M'Rabet 1987). MATERIAL AND METHODS Our detailed biostratigraphic survey has been on two sections: at Sidi Khalif (the type section of the Sidi Kralif Formation), and at Nara (Memmi 1967), localities which are c. 18 km apart. Both sections were collected for ammonites, and limestone beds were sampled AMMONITE AND CALPIONELLID RECORD IN THE STUDIED SECTIONS The Sidi Kralif Formation (Text-fig. 2) consists of clays and dark grey or black marls with a green or bluish patina, often fissile, with a number of limestone or sandstone beds (M'Rabet 1987). It has two informal 47 BASAL CRETACEOUS BIOSTRATIGRAPHY IN TUNISIA members (see Busnardo et al. 1976); (1) the lower composed of calcareous marls, with pyritic ammonites, belemnites, calpionellids, rare bivalves and brachiopods, and (2) the upper, composed of clays and marls, with numerous limestone beds, rich in bivalves, gastropods, brachiopods, echinoids, and ammonites, and rare calpionellids, limited to the lower beds. The lowest limestone beds are dolomitized, similarly as in the underlying Nara Formation. Nara section (Text-fig. 2B, 3A) (35°15'52.50"N, 9°41'47.07"E) The total thickness of the studied succession in the Nara section is 246 m. Both members of Busnardo et al. (1976) are recognised; the lower, beds N1­N18, and the upper, beds N19­N29. Ammonites (Text-fig. 3): The ammonite preservation is good except for the pyritized fossils. In beds N1­N18, ammonite taxa identified are dominated by adult forms of the genera Pseudosubplanites, Berriasella, Dalmasiceras, Fauriella, Jabronella and Subalpinites (Textfig. 5). Higher up in the succession the ammonites occur mostly in beds N19, N21, and in the two uppermost beds, N27 and N29. Calpionellids (Text-figs 3, 4). Calpionellids are represented up to bed N25. Four successive stratigraphically assemblages were recognized. Assemblage 1, in beds N3­N8, consists of Calpionella alpina, (Text-fig. 4.1­ 4.3) Tintinnopsella carpathica (Text-fig. 4.8, 4.9) and Crassicollaria parvula (Text-fig. 4.7). This assemblage is dominated by C. alpina (47%), variable morphologically, but with small sphaerical forms predominating. Assemblage 2, in beds N9­N12, is still dominated by C. alpina, but is characterised by first appearances of various species of the genus Remaniella. Assemblage 3, in beds N13­N18, is characterised by the appearance and continuous occurrence of Calpionella elliptica (12%) (Text-fig. 4.4­4.6), Lorenziella hungarica (4%) (Textfig. 4.17), and Remaniella colomi (1%) (Text-fig. 4.12), accompanied by species ranging up from below, C. alpina (57%), Cr. parvula (12%), T. carpathica (10%), Remaniella catalanoi (1%) (Text-fig. 4.16), Remaniella duranddelgai (2%) (Text-fig. 4.15) and Remaniella ferasini (1%) (Text-fig. 4.10, 4.11). Assemblage 4, in beds N19­N25, is characterised by the first appearance of Tintinnopsella longa (N19) (Text-fig. 4.19, 4.20) as well as an increased abundance of C. elliptica and a mass occurrence of a large variety T. carpathica. Sidi Khalif section (Text-fig. 3B) (35° 6'42.72"N, 9°40'36.70"E) The Berriasian of the Sidi Khalif section is c. 368 m thick. The succession is divided into two members; the lower, spanning beds SK2­SK42, and the upper, beds SK43­SK47. The lowermost part of the succession consists of alternating beds of marls and limestones of very irregular thickness. Ammonites (Text-figs 3, 6): In the lower beds, fossils are represented mainly by fragmentarily preserved, moderately small species of the genera Dalmasiceras, Jabronella, Berriasella and Pseudosubplanites. Higher in the succession (bed SK43), well-preserved representatives of the genera Subthurmannia and Mazenoticeras are common (Text-fig. 3). Calpionellids: Similarly as in Nara section, four successive calpionellid assemblages are recognised (Textfig. 4). Assemblage 1 (beds SK2­SK18) is dominated by C. alpina (58%) and Cr. parvula (36%); also noted was T. carpathica (6%). Calpionellid-rich Assemblage 2 (beds SK19­SK24) is characterised by the appearance of various species of the genus Remaniella (bed SK19) and the dominance of sphaerical forms of C. alpina (66%). Also noted were Cr. parvula (20%) and T. carpathica (7%). Assemblage 3 (beds SK25­SK42) is characterised by the appearance of C. elliptica (bed SK 25), which is accompanied by C. alpina (48%), C. parvula (10%), T. carpathica (6%), R. colomi (8%), R. catalanoi (2%), R. ferasini (1.5%), and R. duranddelgai (2.5%). In the upper part of the interval with Assemblage 3 there is an increase in abundance of small forms of C. Elliptica. Some of the Remaniella species are discontinuous through their range. Assemblage 4 (beds SK43­ SK47) is characterised by the appearance of T. longa (2%), although it is clearly dominated by C. elliptica (37%) and C. alpina (19%). Also noted were: Cr. parvula (8%), T. carpathica (16%), L. hungarica (6%), Remaniella cadischiana (6%) (Text-fig. 4.13, 4.14), R. catalanoi (3%) and Remaniella borzai (3%) (Text-fig. 4.18). BIOSTRATIGRAPHIC RESULTS Calpionellid biostratigraphy The Calpionella Zone, first defined by Allemann et al. (1971), was divided subsequently into the C. alpina and C. elliptica intervals by Catalano and Liguori (1971). Pop (1994) defined these two intervals as the Alpina and Elliptica Subzones, divided by a Remaniella Subzone (Remaniella ferasini Subzone of Pop 1994). The lower boundary of the C. alpina Subzone, taken as 48 KAMEL MAALAOUI AND FOUAD ZARGOUNI Text-fig. 3a. Geological log, biostratigraphy, and vertical ranges of ammonite and calpionellid species in the Nara section 49 BASAL CRETACEOUS BIOSTRATIGRAPHY IN TUNISIA Text-fig. 3b. Geological log, biostratigraphy, and vertical ranges of ammonite and calpionellid species in the Sidi Kralif section 50 KAMEL MAALAOUI AND FOUAD ZARGOUNI 51 BASAL CRETACEOUS BIOSTRATIGRAPHY IN TUNISIA the Tithonian / Berriasian boundary by Remane et al. (1986), is characterized by a change in the morphology of C. alpina, with an `explosion' of small spherical forms. The C. elliptica Subzone is marked by the first occurrence of the subzonal species. Pop (1994) distinguished a new Longa Subzone, named after Tintinnopsella longa Colom (1939), corresponding to the upper part of the Calpionella Zone. The calpionellid zonation used in this work is that established by Rehakova and Michalik (1997); Remane et al. (1986); Pop (1994, 1997) and Lakova and Petrova (2013) (Text-fig. 7). In this study, the preservation of calpionellid material from Nara and Sidi Khalif has been found to be generally good, and the fine and minute apertures of the loricas are well preserved, which facilitates their determination. In both the Nara section and the Sidi Khalif section the same calpionellid bioevents have been determined, The "acme" of small spherical forms of C. alpina,first appearance of the genus Remaniella, first occurrence of C. elliptica, and the last bioevent, the first appearance of index species T. longa. The events thus define and limit, respectively, the C. alpina, Remaniella, C. elliptica and T. longa subzones. Calpionella alpina Subzone The early Berriasian calpionellid association, i.e. Assemblage 1, is characterized by the species C. alpina, Cr. parvula, and T. carpathica. This composition is indicative of the C. alpina Subzone of the standard Calpionella Zone of the lower Berriasian, e.g., Remane et al. (1986) and Rehakova and Michalik (1997). This subzone has been recognized in North Africa by Boughdiri et al. (2006), and as sub-zone B1 of Ben Abdesselam-Mahdaoui et al. (2011) and Benzaggagh et al. (1995, 2012). Remaniella Subzone The Assemblage 2 association is typified by the first appearance of Remaniella with variable percentages of C. alpina and Cr. parvula. This association characterizes the Remaniella Subzone and corresponds to the upper part of B zone of Remane (1963, 1971). Ac- cording to Oloriz et al. (1995), Pop (1994, 1996), Andreini et al. (2007) and Lakova and Petrova (2013), it correlates to the Remaniella ferasini Subzone (see Rehakova and Michalik 1997). Calpionella elliptica Subzone This subzone was created by Catalano and Liguori (1971) and redefined by Pop (1974). Its base is marked by the first occurrence of C. elliptica associated with C. alpina, Cr. parvula, T. carpathica, L. hungarica, R. ferasini, R. colomi, and R. duranddelgai. The subzone was recognised elsewhere by Pop (1994­1997) and Grun and Blau (1997). Tintinnopsella longa Subzone The T. longa Subzone was originally defined by Pop (1974), the first occurrence of the eponymous species marking its base. The calpionellids of our assemblage 4 are T. longa, C. alpina, C. elliptica, R. borzai, R. duranddelgai, R. catalanoi, R. ferasini and T. carpathica, which is similar to the association found by Pop (1974). A palaeobiogeographical study on this bioevent (Pop 1994) showed its distribution in western Tethys in the Southern Carpathians (Pop 1974, 1986), Western Carpathians (Vasicek et al. 1994; Borza and Michalik 1986), SE France (Le Hégarat and Remane 1968; Charollais et al. 1981), Southern Alps (Channell and Grandesso 1987), Sicily (Catalano and Liguori 1971), Subbetic area (Alleman et al. 1975), and westwards to Cuba (Pop 1976). Ammonite biostratigraphy The reference ammonite biostratigraphic scale used here is the Tethyan ammonite zonation of the Berriasian following Tavera (1985) and Hoedemaeker et al. (1990) (Text-fig. 7). Berriasella jacobi Zone The ammonite species from the lower part of the two studied sections (Nara, beds N1­N18; Sidi Khalif, beds SK2-SK42) are from the Berriasella jacobi and Pseu- Text-fig. 4. Photomicrographs of calpionellids in thin sections from the Nara and Sidi Kralif sections. 1-3 ­ Calpionella alpina Lorenz, Lower Berriasian, Calpionella Zone, Alpina Subzone, sample SK17. 4-6 ­ Calpionella elliptica Cadisch, Middle Berriasian, Calpionella Zone, Longa Subzone, sample N21. 7 ­ Crassicollaria parvula Remane, Lower Berriasian, Calpionella zone, Remaniella Subzone, sample SK21. 8, 9 ­ Tintinnopsella carpathica Murgeanui & Filipescu, Middle Berriasian, Calpionella Zone, Alpina Subzone, sample N19. 10, 11 ­ Remaniella ferasini Catalano, Lower Berriasian Calpionella Zone, Elliptica Subzone, sample N17, 12 ­ Remaniella colomi Pop, Lower Berriasian, Calpionella Zone, Remaniella Subzone, sample SK21. 13, 14 ­ Remaniella cadischiana Colm, Middle Berriasian, Calpionella Zone, Remaniella Subzone, sample N21. 15 ­ Remaniella duranddelgai Pop, Lower Berriasian, Calpionella Zone, Remaniella Subzone, sample N9. 16 ­ Remaniella catalnoi Pop, Middle Berriasian, Calpionella Zone, Remaniella Subzone, sample N23. 17 ­ Lorenziella hungarica Knauer and Nagy, Middle Berriasian, Calpionella Zone, Longa Subzone, sample SK43. 18 ­ Remaniella borzai Pop, Lower Berriasian, Calpionella Zone, Remaniella Subzone, sample SK25. 19, 20 ­ Tintinnopsella longa Colom, Middle Berriasian, Calpionella Zone, Longa Subzone sample SK 43, N25 52 KAMEL MAALAOUI AND FOUAD ZARGOUNI Text-fig. 5. Selected ammonites from the studied sections: 1a, b ­ Pseudosubplanites grandis Mazenot; sample SK29: Pseudosubplanites grandis Subzone, Pseudosubplanites euxinus Zone, Lower Berriasian. 2 ­ Fauriella sp.gr. shipkovensis Nikolov and Mandov; sample N15: Grandis Subzone, Euxinus Zone, Lower Berriasian. 3 ­ Mazenetoceras curelence Kilian; sample SK43; Subthurmannia occitanica Zone, Middle Berriasian. 4 ­ Jabronella sp.; sample SK43 : Subthurmannia occitanica Zone, Middle Berriasian 53 BASAL CRETACEOUS BIOSTRATIGRAPHY IN TUNISIA Text-fig. 6. Selected ammonites from the studied sections. 5 ­ Subthurmannia occitanica Pictet; 5 ­ sample N2; 6 ­ sample SK43; Subthurmannia occitanica Zone, Middle Berriasian. 7 ­ Pseudosubplanites grandis Mazenot; sample N15, Pseudosubplanites grandis Subzone, Pseudosubplanites euxinus Zone, Lower Berriasian. 8 ­ Malbosiceras sp., sample N23; Subthurmannia occitanica Zone, Middle Berriasian 54 KAMEL MAALAOUI AND FOUAD ZARGOUNI dosubplanites grandis zones sensu Le Hégarat (1973). Hoedemaeker (1982) included them as subzones in a Pseudosubplanites euxinus Zone. Tavera (1985) proposed expanding the B. jacobi Subzone to be equivalent to the Pseudosubplanites euxinus Zone, This proposal which was accepted by the Working Group on Lower Cretaceous Cephalopods (1992; Hoedemaeker and Company 1993, and others e.g., Reboulet and Klein 2009; Reboulet et al. 2014). In the present paper, we follow the ammonite biozonation of Hoedemaeker et al. (1990) in discussing zonal calibration between ammonites and calpionellids. The B. jacobi Zone is characterized in the Nara section by the following ammonite association: Pseudosubplanites euxinus, P. lorioli (bed N3), B. (B.) oppeli (N5), Dalmasiceras sp. and Berriasella (B.) subcallisto (N7), and Pseudosubplanites sp. (N13). The assemblage at Sidi Khalif section includes Dalmasiceras subloevis, Jabronella sp. (Text-fig. 5.4) and B. (Picteticeras) chomeracensis. This association could be indicative of the B. jacobi Zone sensu Le Hégarat (1973) considering the association of the genera Delphinella, Dalmasiceras and Berriasella low in this zone in other regions (Wimbledon et al. 2013; Donze et al. 1975 in northern Tunisia, Memmi 1967, Busnardo et al. 1976 in Central of Tunisia, Memmi 1989). In the succeeding Nara beds we have been able to identify Ps. grandis (Text-fig. 5.1a, b) and Fauriella sp. ex gr. shipkovensis (bed N 15) (Text-fig. 5.2), Jabronella sp. and Subalpinites aff. mediterraneus (N17), and at Sidi Khalif Ps. grandis and Pseudosubplanites berriasensis (bed SK 29), whereas bed SK 37 contains Pseudosubplanites sp. and Jabronella aff. isaris. In this association the Gran- dis Zone sensu Le Hégarat (1973) is well represented by the index species Ps. grandis (Mazenot), as in the associations recorded by Memmi (1967) and Busnardo et al. (1976) in Central Tunisia. Subthurmannia occitanica Zone In the Nara section, we find an assemblage containing Tirnovella subalpinites (bed N19), Fauriella rarefurcata (bed N19), Fauriella floquinensis (bed 21), Subthurmannia occitanica (Bed N23) and Malbosiceras sp. (bed N25) (Text-fig. 6.8), Mazenoticeras aff. malbosiforme (Bed N27), Malbosiceras rouvillei and Jabronella paquieri (Bed N29). In the Sidi Khalif section, we collected Pseudosubplanites lorioli, S. occitanica (Text-fig. 6.5, 6.6) (bed Sk43), Mazenoticeras curelence (SK 43) (Text-fig. 5.3), and Jabronella sp. This association could be the equivalent of the Occitanica Zone (sensu Le Hégarat), correlated with the association of Memmi (1967); Enay and Geyssant (1975); Cecca et al. (1989); Wimbledon et al. (2011, 2013). DISCUSSION This work proposes a revised stratigraphy for the Lower to Middle Berriasian in Central Tunisia based on ammonites and calpionellids. The boundaries of the biostratigraphic units in this scheme fit well with those of the subdivisions of many other key Tethyan sections. The bases of our sections (Bed N1 in the Nara section and Beds SK1­SK5 at Sidi Khalif) do not allow us (because of unsuitable dolomitic lithologies) to rec- Text-fig. 7. Correlation of ammonite and calpionellid zonations for the upper Tithonian and lower-middle Berriasian, and major calpionellid bio-events (after Lakova and Petrova 2013) 55 BASAL CRETACEOUS BIOSTRATIGRAPHY IN TUNISIA ognize the top of Crassicollaria Zone (calpionellids) or the top of Durangites Zone (ammonites). However, comparing our C. alpina Subzone or C. jacobi Subzone (sensu Le Hégarat 1973) assemblages with those in other sections, one can conclude that the J/K boundary, i.e. the base of Berriasian approximately coincides with this lithological change from dolostones to micritic limestones, or is rather lower, within the dolomites of Nara Formation, since indications of lower laying Crassicollaria Zone and Durangites Zone are absent. The quantitative analysis of calpionellids shows major variations in their abundance and composition, and the well-marked first occurrences of species allow the delimitation of the C. alpina and Remaniella subzones, represented by the first appearance of the genus Remaniella in bed N9 (Nara) and in bed SK 17 (Sidi Khalif). It is worth noting that the ammonite fauna crosses this level with no change. In bed N13 and bed SK 25, we see the same phenomena, with variations detectable in the calpionellids species (first appearance of C. elliptica). In fact, none of the ammonite zonal boundaries corresponds to any calpionellid boundary. The only exception is the first appearance of T. longa coinciding in the studied sections (bed N19 and bed SK43) with the presence of the ammonite Subthurmannia occitanica. These two coeval events mark clearly the lower/middle Berriasian boundary. cult because of the unfavourable lithological nature of the base of both studied sections. Acknowledgements The authors would particularly like to thank Luccia Memmi and Noureddine Ben Ayed for their valuable insights and suggestions. We also thank W.A.P. Wimbledon, Iskra Lakova, Luc Bulot and Ireneusz Walaszczyk for their useful comments. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Acta Geologica Polonica de Gruyter

The lower and middle Berriasian in Central Tunisia: Integrated ammonite and calpionellid biostratigraphy of the Sidi Kralif Formation

Acta Geologica Polonica , Volume 66 (1) – Mar 1, 2016

The lower and middle Berriasian in Central Tunisia: Integrated ammonite and calpionellid biostratigraphy of the Sidi Kralif Formation


Maalaoui, K. and Zargouni, F. 2016. The lower and middle Berriasian in Central Tunisia: Integrated ammonite and calpionellid biostratigraphy of the Sidi Kralif Formation. Acta Geologica Polonica, 66 (1), 43­58. Warszawa. The lower and middle Berriasian sedimentary succession of the Sidi Kralif Formation has been a subject of biostratigraphic study in two key sections in Central Tunisia. Our contribution is an attempt to better define the basal Berriasian interval, between the Berriasella jacobi Zone and the Subthurmannia occitanica Zone. Zonal schemes are established using ammonites and calpionellids, and these permit correlation with other regions of Mediterranean Tethys and beyond. The use of biomarkers afforded by microfossil groups has allowed characterization and direct correlation with four widely accepted calpionellid sub-zones, namely Calpionella alpina, Remaniella, Calpionella elliptica and Tintinopsella longa. The two ammonite zones of Berriasella jacobi and of Subthurmannia occitanica are recognised on the basis of their index species. The parallel ammonite and calpionellid zonations are useful as a tool for correlation and calibration in time and space, thus allowing a better definition of a J/K boundary. The presence of four Berriasian calpionellid bioevents is recognised: (1) the `explosion' of Calpionella alpina, (2) the first occurrence of Remaniella, (3) the first occurrence of Calpionella elliptica and (4) the first occurrence of Tintinopsella longa. The last is here documented as coeval with the presence of Subthurmannia occitanica, which marks the lower/middle Berriasian boundary. Key words: Ammonite; Calpionellids; Berriasian; Bioevents; Biostratigraphy; Tunisia. INTRODUCTION In spite of intensive studies during recent decades, the formal definition of the Jurassic/Cretaceous boundary is still a problem, and it is the only Phanerozoic system boundary for which a GSSP has not been fixed (e.g., Remane 1991; Zakharov et al. 1996; Wimbledon 2008; Pessagno et al. 2009; Wimbledon et al. 2011; Wimbledon et al. 2014). There is a number of biological markers which may potentially be used as a marker for this boundary (Wimbledon et al. 2011), in an interval straddling the traditional base of the Berriasian Stage, the lower boundary of the Cretaceous. Successions across this critical interval, spanning the upper Tithonian and lower Berriasian, are known in Tunisia, in south-western Mediterranean Tethys. Many good sections are wellexposed in the central part of the country. The present paper provides a biostratigraphic report on the lower and middle Berriasian (Lower Cretaceous) succession of central Tunisia. Two sections, represen- 44 KAMEL MAALAOUI AND FOUAD ZARGOUNI Iberia Ita ly Africa Dj. Touila Ou Djebe Touati ed o Zer ud it Tall E J EB L EL h al K orsh if Dj. Bou Gobrine Dj. Guefaiat MN AR Ali Djeridi Dj. Nara Kef Khoudja Kef Krakrmat 1Km Kef el Hassine SK S i d Dj .Attaris Sebkhet el Bahira i f a l K h .667 .474 .645 .661 Kh el ar ro u ga O. Teba O. Nek h la J. Ti hala J . Sidi Khalif Neogene O.en Nakhla Key O. Dj. Akhouta Thrust fault Elevation Creek Gravel road Location o f studied sections Cenomanian to Paleocene Al la h Na s Dj. Faid Barremian (Boudinar Formation) Valanginian-Hauterrivian (Meloussi Formation) Upper Tithonian-Upper Berriasian: (Sidi kralif Formation) Jurassic dolomitic (Nara Formation) Triassic e Pi st de SF AX Text-fig. 1. Geological map of Central Tunisia (after Guiraud 1968, simplified) and location of the measured sections: SK - Sidi Kralif Section; N - Nara Section 45 BASAL CRETACEOUS BIOSTRATIGRAPHY IN TUNISIA Text-fig. 2. A ­ Panoramic view of the Jebel Sidi Khalif; B ­ The Nara section 46 KAMEL MAALAOUI AND FOUAD ZARGOUNI tative for the Sidi Khalif and Nara Hill ranges (Text-figs 1, 2) were selected. The Berriasian of these ranges is represented by marls, marly limestones and micritic limestones of the Sidi Kralif Formation (Burollet 1956). The formation is underlain by dolostones of the Nara Formation and overlain by the massive dolostone-sandstone of the Meloussi Formation. There is extensive bibliography on the geology of central Tunisia (e.g. Breistroffer 1937; Castany 1951; Arnould-Saget 1951; Burollet 1956; Bonnefous 1972; Guirand 1968; M'Rabet 1987). The biostratigraphy of the Sidi Kralif Formation was studied by Bismuth et al. (1967), Memmi (1967) and Busnardo et al. (1976, 1981). Bismuth et al. (1967) recognised four calpionellids zones in the Sidi Kralif Formation, although did not calibrate them to the ammonite zonation. Memmi (1967) recorded a succession of upper Tithonian and Berriasian ammonites in the Sidi Kralif Formation in the northern part of Jebel Nara and at Chaabet Attaris. Both calpionellid and ammonite assemblages were analysed by Busnardo et al. (1976, 1981). These authors characterized the Beriasella jacobi Zone; the Pseudosubplanites grandis Zone was difficult to define, but seemingly ammonites were seen as different compared to the B. jacobi Zone assemblage. In the Nara Range, they recognised a P. grandis Zone interval with calpionellids. The Subthurmannia occitanica Zone of the middle Berriasian was also characterized by calpionellids. The middle/upper Berriasian boundary could not be accurately determined because the fauna was found to be very rare. Both calpionellids and ammonites are critical in attempts to define the Jurassic­Cretaceous boundary (Wimbledon et al. 2011). Ammonites and calpionellids are treated in both sections studied herein, with the aim of calibration and correlation with other key sections in the Tethyan Realm: e.g., Msila area in the internal Prerif of Morocco (Benzaggagh et al. 2010); Le Chouet in SE France (Wimbledon et al. 2013); Puerto Escano in Spain (Pruner et al. 2010); Fiume Bosso in central Italy (Housa et al. 2004); Brodno in Western Carpathians, Slovakia (Housa et al.1999); Nutzhof in Austria (Lukeneder et al. 2010). All these sections have been discussed recently by Michalik and Rehakova (2011). for calpionellids. The calpionellids were studied in thin sections (25 in total) studied under an OLYMPUS BH2 transmitted light microscope, and photographed with Nikon COOLPIX L310 camera. All fossils described are stored in the collections of the Geological Survey of the National Office of Mines of Tunisia. GEOLOGICAL SETTING The study area is a part of the foreland of the Tunisian Maghrebide Chain, in the northernmost part of the structure known as the N-S Axis (Text-fig. 1), which limits the western part of the Sahel plains (Castany 1951; Burollet 1956). The axis is a N-S anticline that interferes locally with NE-SW folds (Castany 1951; Burollet 1956; Richert 1971; Ouali 2007). It is a major palaeogeographical limit that has been interpreted as having been a shoal at different times during the Mesozoic (Burollet 1956; M'Rabet 1987; Soussi et al. 2000). During late Jurassic to early Cretaceous times, Central Tunisia experienced continuous and regular sedimentation with a relatively slow subsidence in an infra-neritic depositional environment (Burollet, 1956). The evolution of the sedimentation of the Sidi Kralif Formation reflects the geological history of central Tunisia during J/K boundary times. Its lower part was deposited in relatively deep water with a marlylimestone sedimentation, whereas its upper part shows essentially clay sediments and indicates shallower waters. The decrease in depth is related to an increase in clastic sediments not compensated by subsidence, which explains the diachronism of this formation (Busnardo et al. 1981). In fact, central Tunisia was an external carbonate platform during the early Tithonian, except for the Chotts region (the salt-lake area) that corresponds to a littoral platform (Bonnefous 1972). During the late Tithonian, the first clay deposits arrived on this platform in a prodeltaic situation. In late Tithonian to mid Berriasian times the deposits prograded towards Jebel Meloussi and Jebel Bouhedma. Jebel Sidi Khalif and areas further north were still on an external carbonate platform with marly limestone sedimentation (Busnardo et al. 1981; M'Rabet 1987). MATERIAL AND METHODS Our detailed biostratigraphic survey has been on two sections: at Sidi Khalif (the type section of the Sidi Kralif Formation), and at Nara (Memmi 1967), localities which are c. 18 km apart. Both sections were collected for ammonites, and limestone beds were sampled AMMONITE AND CALPIONELLID RECORD IN THE STUDIED SECTIONS The Sidi Kralif Formation (Text-fig. 2) consists of clays and dark grey or black marls with a green or bluish patina, often fissile, with a number of limestone or sandstone beds (M'Rabet 1987). It has two informal 47 BASAL CRETACEOUS BIOSTRATIGRAPHY IN TUNISIA members (see Busnardo et al. 1976); (1) the lower composed of calcareous marls, with pyritic ammonites, belemnites, calpionellids, rare bivalves and brachiopods, and (2) the upper, composed of clays and marls, with numerous limestone beds, rich in bivalves, gastropods, brachiopods, echinoids, and ammonites, and rare calpionellids, limited to the lower beds. The lowest limestone beds are dolomitized, similarly as in the underlying Nara Formation. Nara section (Text-fig. 2B, 3A) (35°15'52.50"N, 9°41'47.07"E) The total thickness of the studied succession in the Nara section is 246 m. Both members of Busnardo et al. (1976) are recognised; the lower, beds N1­N18, and the upper, beds N19­N29. Ammonites (Text-fig. 3): The ammonite preservation is good except for the pyritized fossils. In beds N1­N18, ammonite taxa identified are dominated by adult forms of the genera Pseudosubplanites, Berriasella, Dalmasiceras, Fauriella, Jabronella and Subalpinites (Textfig. 5). Higher up in the succession the ammonites occur mostly in beds N19, N21, and in the two uppermost beds, N27 and N29. Calpionellids (Text-figs 3, 4). Calpionellids are represented up to bed N25. Four successive stratigraphically assemblages were recognized. Assemblage 1, in beds N3­N8, consists of Calpionella alpina, (Text-fig. 4.1­ 4.3) Tintinnopsella carpathica (Text-fig. 4.8, 4.9) and Crassicollaria parvula (Text-fig. 4.7). This assemblage is dominated by C. alpina (47%), variable morphologically, but with small sphaerical forms predominating. Assemblage 2, in beds N9­N12, is still dominated by C. alpina, but is characterised by first appearances of various species of the genus Remaniella. Assemblage 3, in beds N13­N18, is characterised by the appearance and continuous occurrence of Calpionella elliptica (12%) (Text-fig. 4.4­4.6), Lorenziella hungarica (4%) (Textfig. 4.17), and Remaniella colomi (1%) (Text-fig. 4.12), accompanied by species ranging up from below, C. alpina (57%), Cr. parvula (12%), T. carpathica (10%), Remaniella catalanoi (1%) (Text-fig. 4.16), Remaniella duranddelgai (2%) (Text-fig. 4.15) and Remaniella ferasini (1%) (Text-fig. 4.10, 4.11). Assemblage 4, in beds N19­N25, is characterised by the first appearance of Tintinnopsella longa (N19) (Text-fig. 4.19, 4.20) as well as an increased abundance of C. elliptica and a mass occurrence of a large variety T. carpathica. Sidi Khalif section (Text-fig. 3B) (35° 6'42.72"N, 9°40'36.70"E) The Berriasian of the Sidi Khalif section is c. 368 m thick. The succession is divided into two members; the lower, spanning beds SK2­SK42, and the upper, beds SK43­SK47. The lowermost part of the succession consists of alternating beds of marls and limestones of very irregular thickness. Ammonites (Text-figs 3, 6): In the lower beds, fossils are represented mainly by fragmentarily preserved, moderately small species of the genera Dalmasiceras, Jabronella, Berriasella and Pseudosubplanites. Higher in the succession (bed SK43), well-preserved representatives of the genera Subthurmannia and Mazenoticeras are common (Text-fig. 3). Calpionellids: Similarly as in Nara section, four successive calpionellid assemblages are recognised (Textfig. 4). Assemblage 1 (beds SK2­SK18) is dominated by C. alpina (58%) and Cr. parvula (36%); also noted was T. carpathica (6%). Calpionellid-rich Assemblage 2 (beds SK19­SK24) is characterised by the appearance of various species of the genus Remaniella (bed SK19) and the dominance of sphaerical forms of C. alpina (66%). Also noted were Cr. parvula (20%) and T. carpathica (7%). Assemblage 3 (beds SK25­SK42) is characterised by the appearance of C. elliptica (bed SK 25), which is accompanied by C. alpina (48%), C. parvula (10%), T. carpathica (6%), R. colomi (8%), R. catalanoi (2%), R. ferasini (1.5%), and R. duranddelgai (2.5%). In the upper part of the interval with Assemblage 3 there is an increase in abundance of small forms of C. Elliptica. Some of the Remaniella species are discontinuous through their range. Assemblage 4 (beds SK43­ SK47) is characterised by the appearance of T. longa (2%), although it is clearly dominated by C. elliptica (37%) and C. alpina (19%). Also noted were: Cr. parvula (8%), T. carpathica (16%), L. hungarica (6%), Remaniella cadischiana (6%) (Text-fig. 4.13, 4.14), R. catalanoi (3%) and Remaniella borzai (3%) (Text-fig. 4.18). BIOSTRATIGRAPHIC RESULTS Calpionellid biostratigraphy The Calpionella Zone, first defined by Allemann et al. (1971), was divided subsequently into the C. alpina and C. elliptica intervals by Catalano and Liguori (1971). Pop (1994) defined these two intervals as the Alpina and Elliptica Subzones, divided by a Remaniella Subzone (Remaniella ferasini Subzone of Pop 1994). The lower boundary of the C. alpina Subzone, taken as 48 KAMEL MAALAOUI AND FOUAD ZARGOUNI Text-fig. 3a. Geological log, biostratigraphy, and vertical ranges of ammonite and calpionellid species in the Nara section 49 BASAL CRETACEOUS BIOSTRATIGRAPHY IN TUNISIA Text-fig. 3b. Geological log, biostratigraphy, and vertical ranges of ammonite and calpionellid species in the Sidi Kralif section 50 KAMEL MAALAOUI AND FOUAD ZARGOUNI 51 BASAL CRETACEOUS BIOSTRATIGRAPHY IN TUNISIA the Tithonian / Berriasian boundary by Remane et al. (1986), is characterized by a change in the morphology of C. alpina, with an `explosion' of small spherical forms. The C. elliptica Subzone is marked by the first occurrence of the subzonal species. Pop (1994) distinguished a new Longa Subzone, named after Tintinnopsella longa Colom (1939), corresponding to the upper part of the Calpionella Zone. The calpionellid zonation used in this work is that established by Rehakova and Michalik (1997); Remane et al. (1986); Pop (1994, 1997) and Lakova and Petrova (2013) (Text-fig. 7). In this study, the preservation of calpionellid material from Nara and Sidi Khalif has been found to be generally good, and the fine and minute apertures of the loricas are well preserved, which facilitates their determination. In both the Nara section and the Sidi Khalif section the same calpionellid bioevents have been determined, The "acme" of small spherical forms of C. alpina,first appearance of the genus Remaniella, first occurrence of C. elliptica, and the last bioevent, the first appearance of index species T. longa. The events thus define and limit, respectively, the C. alpina, Remaniella, C. elliptica and T. longa subzones. Calpionella alpina Subzone The early Berriasian calpionellid association, i.e. Assemblage 1, is characterized by the species C. alpina, Cr. parvula, and T. carpathica. This composition is indicative of the C. alpina Subzone of the standard Calpionella Zone of the lower Berriasian, e.g., Remane et al. (1986) and Rehakova and Michalik (1997). This subzone has been recognized in North Africa by Boughdiri et al. (2006), and as sub-zone B1 of Ben Abdesselam-Mahdaoui et al. (2011) and Benzaggagh et al. (1995, 2012). Remaniella Subzone The Assemblage 2 association is typified by the first appearance of Remaniella with variable percentages of C. alpina and Cr. parvula. This association characterizes the Remaniella Subzone and corresponds to the upper part of B zone of Remane (1963, 1971). Ac- cording to Oloriz et al. (1995), Pop (1994, 1996), Andreini et al. (2007) and Lakova and Petrova (2013), it correlates to the Remaniella ferasini Subzone (see Rehakova and Michalik 1997). Calpionella elliptica Subzone This subzone was created by Catalano and Liguori (1971) and redefined by Pop (1974). Its base is marked by the first occurrence of C. elliptica associated with C. alpina, Cr. parvula, T. carpathica, L. hungarica, R. ferasini, R. colomi, and R. duranddelgai. The subzone was recognised elsewhere by Pop (1994­1997) and Grun and Blau (1997). Tintinnopsella longa Subzone The T. longa Subzone was originally defined by Pop (1974), the first occurrence of the eponymous species marking its base. The calpionellids of our assemblage 4 are T. longa, C. alpina, C. elliptica, R. borzai, R. duranddelgai, R. catalanoi, R. ferasini and T. carpathica, which is similar to the association found by Pop (1974). A palaeobiogeographical study on this bioevent (Pop 1994) showed its distribution in western Tethys in the Southern Carpathians (Pop 1974, 1986), Western Carpathians (Vasicek et al. 1994; Borza and Michalik 1986), SE France (Le Hégarat and Remane 1968; Charollais et al. 1981), Southern Alps (Channell and Grandesso 1987), Sicily (Catalano and Liguori 1971), Subbetic area (Alleman et al. 1975), and westwards to Cuba (Pop 1976). Ammonite biostratigraphy The reference ammonite biostratigraphic scale used here is the Tethyan ammonite zonation of the Berriasian following Tavera (1985) and Hoedemaeker et al. (1990) (Text-fig. 7). Berriasella jacobi Zone The ammonite species from the lower part of the two studied sections (Nara, beds N1­N18; Sidi Khalif, beds SK2-SK42) are from the Berriasella jacobi and Pseu- Text-fig. 4. Photomicrographs of calpionellids in thin sections from the Nara and Sidi Kralif sections. 1-3 ­ Calpionella alpina Lorenz, Lower Berriasian, Calpionella Zone, Alpina Subzone, sample SK17. 4-6 ­ Calpionella elliptica Cadisch, Middle Berriasian, Calpionella Zone, Longa Subzone, sample N21. 7 ­ Crassicollaria parvula Remane, Lower Berriasian, Calpionella zone, Remaniella Subzone, sample SK21. 8, 9 ­ Tintinnopsella carpathica Murgeanui & Filipescu, Middle Berriasian, Calpionella Zone, Alpina Subzone, sample N19. 10, 11 ­ Remaniella ferasini Catalano, Lower Berriasian Calpionella Zone, Elliptica Subzone, sample N17, 12 ­ Remaniella colomi Pop, Lower Berriasian, Calpionella Zone, Remaniella Subzone, sample SK21. 13, 14 ­ Remaniella cadischiana Colm, Middle Berriasian, Calpionella Zone, Remaniella Subzone, sample N21. 15 ­ Remaniella duranddelgai Pop, Lower Berriasian, Calpionella Zone, Remaniella Subzone, sample N9. 16 ­ Remaniella catalnoi Pop, Middle Berriasian, Calpionella Zone, Remaniella Subzone, sample N23. 17 ­ Lorenziella hungarica Knauer and Nagy, Middle Berriasian, Calpionella Zone, Longa Subzone, sample SK43. 18 ­ Remaniella borzai Pop, Lower Berriasian, Calpionella Zone, Remaniella Subzone, sample SK25. 19, 20 ­ Tintinnopsella longa Colom, Middle Berriasian, Calpionella Zone, Longa Subzone sample SK 43, N25 52 KAMEL MAALAOUI AND FOUAD ZARGOUNI Text-fig. 5. Selected ammonites from the studied sections: 1a, b ­ Pseudosubplanites grandis Mazenot; sample SK29: Pseudosubplanites grandis Subzone, Pseudosubplanites euxinus Zone, Lower Berriasian. 2 ­ Fauriella sp.gr. shipkovensis Nikolov and Mandov; sample N15: Grandis Subzone, Euxinus Zone, Lower Berriasian. 3 ­ Mazenetoceras curelence Kilian; sample SK43; Subthurmannia occitanica Zone, Middle Berriasian. 4 ­ Jabronella sp.; sample SK43 : Subthurmannia occitanica Zone, Middle Berriasian 53 BASAL CRETACEOUS BIOSTRATIGRAPHY IN TUNISIA Text-fig. 6. Selected ammonites from the studied sections. 5 ­ Subthurmannia occitanica Pictet; 5 ­ sample N2; 6 ­ sample SK43; Subthurmannia occitanica Zone, Middle Berriasian. 7 ­ Pseudosubplanites grandis Mazenot; sample N15, Pseudosubplanites grandis Subzone, Pseudosubplanites euxinus Zone, Lower Berriasian. 8 ­ Malbosiceras sp., sample N23; Subthurmannia occitanica Zone, Middle Berriasian 54 KAMEL MAALAOUI AND FOUAD ZARGOUNI dosubplanites grandis zones sensu Le Hégarat (1973). Hoedemaeker (1982) included them as subzones in a Pseudosubplanites euxinus Zone. Tavera (1985) proposed expanding the B. jacobi Subzone to be equivalent to the Pseudosubplanites euxinus Zone, This proposal which was accepted by the Working Group on Lower Cretaceous Cephalopods (1992; Hoedemaeker and Company 1993, and others e.g., Reboulet and Klein 2009; Reboulet et al. 2014). In the present paper, we follow the ammonite biozonation of Hoedemaeker et al. (1990) in discussing zonal calibration between ammonites and calpionellids. The B. jacobi Zone is characterized in the Nara section by the following ammonite association: Pseudosubplanites euxinus, P. lorioli (bed N3), B. (B.) oppeli (N5), Dalmasiceras sp. and Berriasella (B.) subcallisto (N7), and Pseudosubplanites sp. (N13). The assemblage at Sidi Khalif section includes Dalmasiceras subloevis, Jabronella sp. (Text-fig. 5.4) and B. (Picteticeras) chomeracensis. This association could be indicative of the B. jacobi Zone sensu Le Hégarat (1973) considering the association of the genera Delphinella, Dalmasiceras and Berriasella low in this zone in other regions (Wimbledon et al. 2013; Donze et al. 1975 in northern Tunisia, Memmi 1967, Busnardo et al. 1976 in Central of Tunisia, Memmi 1989). In the succeeding Nara beds we have been able to identify Ps. grandis (Text-fig. 5.1a, b) and Fauriella sp. ex gr. shipkovensis (bed N 15) (Text-fig. 5.2), Jabronella sp. and Subalpinites aff. mediterraneus (N17), and at Sidi Khalif Ps. grandis and Pseudosubplanites berriasensis (bed SK 29), whereas bed SK 37 contains Pseudosubplanites sp. and Jabronella aff. isaris. In this association the Gran- dis Zone sensu Le Hégarat (1973) is well represented by the index species Ps. grandis (Mazenot), as in the associations recorded by Memmi (1967) and Busnardo et al. (1976) in Central Tunisia. Subthurmannia occitanica Zone In the Nara section, we find an assemblage containing Tirnovella subalpinites (bed N19), Fauriella rarefurcata (bed N19), Fauriella floquinensis (bed 21), Subthurmannia occitanica (Bed N23) and Malbosiceras sp. (bed N25) (Text-fig. 6.8), Mazenoticeras aff. malbosiforme (Bed N27), Malbosiceras rouvillei and Jabronella paquieri (Bed N29). In the Sidi Khalif section, we collected Pseudosubplanites lorioli, S. occitanica (Text-fig. 6.5, 6.6) (bed Sk43), Mazenoticeras curelence (SK 43) (Text-fig. 5.3), and Jabronella sp. This association could be the equivalent of the Occitanica Zone (sensu Le Hégarat), correlated with the association of Memmi (1967); Enay and Geyssant (1975); Cecca et al. (1989); Wimbledon et al. (2011, 2013). DISCUSSION This work proposes a revised stratigraphy for the Lower to Middle Berriasian in Central Tunisia based on ammonites and calpionellids. The boundaries of the biostratigraphic units in this scheme fit well with those of the subdivisions of many other key Tethyan sections. The bases of our sections (Bed N1 in the Nara section and Beds SK1­SK5 at Sidi Khalif) do not allow us (because of unsuitable dolomitic lithologies) to rec- Text-fig. 7. Correlation of ammonite and calpionellid zonations for the upper Tithonian and lower-middle Berriasian, and major calpionellid bio-events (after Lakova and Petrova 2013) 55 BASAL CRETACEOUS BIOSTRATIGRAPHY IN TUNISIA ognize the top of Crassicollaria Zone (calpionellids) or the top of Durangites Zone (ammonites). However, comparing our C. alpina Subzone or C. jacobi Subzone (sensu Le Hégarat 1973) assemblages with those in other sections, one can conclude that the J/K boundary, i.e. the base of Berriasian approximately coincides with this lithological change from dolostones to micritic limestones, or is rather lower, within the dolomites of Nara Formation, since indications of lower laying Crassicollaria Zone and Durangites Zone are absent. The quantitative analysis of calpionellids shows major variations in their abundance and composition, and the well-marked first occurrences of species allow the delimitation of the C. alpina and Remaniella subzones, represented by the first appearance of the genus Remaniella in bed N9 (Nara) and in bed SK 17 (Sidi Khalif). It is worth noting that the ammonite fauna crosses this level with no change. In bed N13 and bed SK 25, we see the same phenomena, with variations detectable in the calpionellids species (first appearance of C. elliptica). In fact, none of the ammonite zonal boundaries corresponds to any calpionellid boundary. The only exception is the first appearance of T. longa coinciding in the studied sections (bed N19 and bed SK43) with the presence of the ammonite Subthurmannia occitanica. These two coeval events mark clearly the lower/middle Berriasian boundary. cult because of the unfavourable lithological nature of the base of both studied sections. Acknowledgements The authors would particularly like to thank Luccia Memmi and Noureddine Ben Ayed for their valuable insights and suggestions. We also thank W.A.P. Wimbledon, Iskra Lakova, Luc Bulot and Ireneusz Walaszczyk for their useful comments.
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de Gruyter
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Abstract

Maalaoui, K. and Zargouni, F. 2016. The lower and middle Berriasian in Central Tunisia: Integrated ammonite and calpionellid biostratigraphy of the Sidi Kralif Formation. Acta Geologica Polonica, 66 (1), 43­58. Warszawa. The lower and middle Berriasian sedimentary succession of the Sidi Kralif Formation has been a subject of biostratigraphic study in two key sections in Central Tunisia. Our contribution is an attempt to better define the basal Berriasian interval, between the Berriasella jacobi Zone and the Subthurmannia occitanica Zone. Zonal schemes are established using ammonites and calpionellids, and these permit correlation with other regions of Mediterranean Tethys and beyond. The use of biomarkers afforded by microfossil groups has allowed characterization and direct correlation with four widely accepted calpionellid sub-zones, namely Calpionella alpina, Remaniella, Calpionella elliptica and Tintinopsella longa. The two ammonite zones of Berriasella jacobi and of Subthurmannia occitanica are recognised on the basis of their index species. The parallel ammonite and calpionellid zonations are useful as a tool for correlation and calibration in time and space, thus allowing a better definition of a J/K boundary. The presence of four Berriasian calpionellid bioevents is recognised: (1) the `explosion' of Calpionella alpina, (2) the first occurrence of Remaniella, (3) the first occurrence of Calpionella elliptica and (4) the first occurrence of Tintinopsella longa. The last is here documented as coeval with the presence of Subthurmannia occitanica, which marks the lower/middle Berriasian boundary. Key words: Ammonite; Calpionellids; Berriasian; Bioevents; Biostratigraphy; Tunisia. INTRODUCTION In spite of intensive studies during recent decades, the formal definition of the Jurassic/Cretaceous boundary is still a problem, and it is the only Phanerozoic system boundary for which a GSSP has not been fixed (e.g., Remane 1991; Zakharov et al. 1996; Wimbledon 2008; Pessagno et al. 2009; Wimbledon et al. 2011; Wimbledon et al. 2014). There is a number of biological markers which may potentially be used as a marker for this boundary (Wimbledon et al. 2011), in an interval straddling the traditional base of the Berriasian Stage, the lower boundary of the Cretaceous. Successions across this critical interval, spanning the upper Tithonian and lower Berriasian, are known in Tunisia, in south-western Mediterranean Tethys. Many good sections are wellexposed in the central part of the country. The present paper provides a biostratigraphic report on the lower and middle Berriasian (Lower Cretaceous) succession of central Tunisia. Two sections, represen- 44 KAMEL MAALAOUI AND FOUAD ZARGOUNI Iberia Ita ly Africa Dj. Touila Ou Djebe Touati ed o Zer ud it Tall E J EB L EL h al K orsh if Dj. Bou Gobrine Dj. Guefaiat MN AR Ali Djeridi Dj. Nara Kef Khoudja Kef Krakrmat 1Km Kef el Hassine SK S i d Dj .Attaris Sebkhet el Bahira i f a l K h .667 .474 .645 .661 Kh el ar ro u ga O. Teba O. Nek h la J. Ti hala J . Sidi Khalif Neogene O.en Nakhla Key O. Dj. Akhouta Thrust fault Elevation Creek Gravel road Location o f studied sections Cenomanian to Paleocene Al la h Na s Dj. Faid Barremian (Boudinar Formation) Valanginian-Hauterrivian (Meloussi Formation) Upper Tithonian-Upper Berriasian: (Sidi kralif Formation) Jurassic dolomitic (Nara Formation) Triassic e Pi st de SF AX Text-fig. 1. Geological map of Central Tunisia (after Guiraud 1968, simplified) and location of the measured sections: SK - Sidi Kralif Section; N - Nara Section 45 BASAL CRETACEOUS BIOSTRATIGRAPHY IN TUNISIA Text-fig. 2. A ­ Panoramic view of the Jebel Sidi Khalif; B ­ The Nara section 46 KAMEL MAALAOUI AND FOUAD ZARGOUNI tative for the Sidi Khalif and Nara Hill ranges (Text-figs 1, 2) were selected. The Berriasian of these ranges is represented by marls, marly limestones and micritic limestones of the Sidi Kralif Formation (Burollet 1956). The formation is underlain by dolostones of the Nara Formation and overlain by the massive dolostone-sandstone of the Meloussi Formation. There is extensive bibliography on the geology of central Tunisia (e.g. Breistroffer 1937; Castany 1951; Arnould-Saget 1951; Burollet 1956; Bonnefous 1972; Guirand 1968; M'Rabet 1987). The biostratigraphy of the Sidi Kralif Formation was studied by Bismuth et al. (1967), Memmi (1967) and Busnardo et al. (1976, 1981). Bismuth et al. (1967) recognised four calpionellids zones in the Sidi Kralif Formation, although did not calibrate them to the ammonite zonation. Memmi (1967) recorded a succession of upper Tithonian and Berriasian ammonites in the Sidi Kralif Formation in the northern part of Jebel Nara and at Chaabet Attaris. Both calpionellid and ammonite assemblages were analysed by Busnardo et al. (1976, 1981). These authors characterized the Beriasella jacobi Zone; the Pseudosubplanites grandis Zone was difficult to define, but seemingly ammonites were seen as different compared to the B. jacobi Zone assemblage. In the Nara Range, they recognised a P. grandis Zone interval with calpionellids. The Subthurmannia occitanica Zone of the middle Berriasian was also characterized by calpionellids. The middle/upper Berriasian boundary could not be accurately determined because the fauna was found to be very rare. Both calpionellids and ammonites are critical in attempts to define the Jurassic­Cretaceous boundary (Wimbledon et al. 2011). Ammonites and calpionellids are treated in both sections studied herein, with the aim of calibration and correlation with other key sections in the Tethyan Realm: e.g., Msila area in the internal Prerif of Morocco (Benzaggagh et al. 2010); Le Chouet in SE France (Wimbledon et al. 2013); Puerto Escano in Spain (Pruner et al. 2010); Fiume Bosso in central Italy (Housa et al. 2004); Brodno in Western Carpathians, Slovakia (Housa et al.1999); Nutzhof in Austria (Lukeneder et al. 2010). All these sections have been discussed recently by Michalik and Rehakova (2011). for calpionellids. The calpionellids were studied in thin sections (25 in total) studied under an OLYMPUS BH2 transmitted light microscope, and photographed with Nikon COOLPIX L310 camera. All fossils described are stored in the collections of the Geological Survey of the National Office of Mines of Tunisia. GEOLOGICAL SETTING The study area is a part of the foreland of the Tunisian Maghrebide Chain, in the northernmost part of the structure known as the N-S Axis (Text-fig. 1), which limits the western part of the Sahel plains (Castany 1951; Burollet 1956). The axis is a N-S anticline that interferes locally with NE-SW folds (Castany 1951; Burollet 1956; Richert 1971; Ouali 2007). It is a major palaeogeographical limit that has been interpreted as having been a shoal at different times during the Mesozoic (Burollet 1956; M'Rabet 1987; Soussi et al. 2000). During late Jurassic to early Cretaceous times, Central Tunisia experienced continuous and regular sedimentation with a relatively slow subsidence in an infra-neritic depositional environment (Burollet, 1956). The evolution of the sedimentation of the Sidi Kralif Formation reflects the geological history of central Tunisia during J/K boundary times. Its lower part was deposited in relatively deep water with a marlylimestone sedimentation, whereas its upper part shows essentially clay sediments and indicates shallower waters. The decrease in depth is related to an increase in clastic sediments not compensated by subsidence, which explains the diachronism of this formation (Busnardo et al. 1981). In fact, central Tunisia was an external carbonate platform during the early Tithonian, except for the Chotts region (the salt-lake area) that corresponds to a littoral platform (Bonnefous 1972). During the late Tithonian, the first clay deposits arrived on this platform in a prodeltaic situation. In late Tithonian to mid Berriasian times the deposits prograded towards Jebel Meloussi and Jebel Bouhedma. Jebel Sidi Khalif and areas further north were still on an external carbonate platform with marly limestone sedimentation (Busnardo et al. 1981; M'Rabet 1987). MATERIAL AND METHODS Our detailed biostratigraphic survey has been on two sections: at Sidi Khalif (the type section of the Sidi Kralif Formation), and at Nara (Memmi 1967), localities which are c. 18 km apart. Both sections were collected for ammonites, and limestone beds were sampled AMMONITE AND CALPIONELLID RECORD IN THE STUDIED SECTIONS The Sidi Kralif Formation (Text-fig. 2) consists of clays and dark grey or black marls with a green or bluish patina, often fissile, with a number of limestone or sandstone beds (M'Rabet 1987). It has two informal 47 BASAL CRETACEOUS BIOSTRATIGRAPHY IN TUNISIA members (see Busnardo et al. 1976); (1) the lower composed of calcareous marls, with pyritic ammonites, belemnites, calpionellids, rare bivalves and brachiopods, and (2) the upper, composed of clays and marls, with numerous limestone beds, rich in bivalves, gastropods, brachiopods, echinoids, and ammonites, and rare calpionellids, limited to the lower beds. The lowest limestone beds are dolomitized, similarly as in the underlying Nara Formation. Nara section (Text-fig. 2B, 3A) (35°15'52.50"N, 9°41'47.07"E) The total thickness of the studied succession in the Nara section is 246 m. Both members of Busnardo et al. (1976) are recognised; the lower, beds N1­N18, and the upper, beds N19­N29. Ammonites (Text-fig. 3): The ammonite preservation is good except for the pyritized fossils. In beds N1­N18, ammonite taxa identified are dominated by adult forms of the genera Pseudosubplanites, Berriasella, Dalmasiceras, Fauriella, Jabronella and Subalpinites (Textfig. 5). Higher up in the succession the ammonites occur mostly in beds N19, N21, and in the two uppermost beds, N27 and N29. Calpionellids (Text-figs 3, 4). Calpionellids are represented up to bed N25. Four successive stratigraphically assemblages were recognized. Assemblage 1, in beds N3­N8, consists of Calpionella alpina, (Text-fig. 4.1­ 4.3) Tintinnopsella carpathica (Text-fig. 4.8, 4.9) and Crassicollaria parvula (Text-fig. 4.7). This assemblage is dominated by C. alpina (47%), variable morphologically, but with small sphaerical forms predominating. Assemblage 2, in beds N9­N12, is still dominated by C. alpina, but is characterised by first appearances of various species of the genus Remaniella. Assemblage 3, in beds N13­N18, is characterised by the appearance and continuous occurrence of Calpionella elliptica (12%) (Text-fig. 4.4­4.6), Lorenziella hungarica (4%) (Textfig. 4.17), and Remaniella colomi (1%) (Text-fig. 4.12), accompanied by species ranging up from below, C. alpina (57%), Cr. parvula (12%), T. carpathica (10%), Remaniella catalanoi (1%) (Text-fig. 4.16), Remaniella duranddelgai (2%) (Text-fig. 4.15) and Remaniella ferasini (1%) (Text-fig. 4.10, 4.11). Assemblage 4, in beds N19­N25, is characterised by the first appearance of Tintinnopsella longa (N19) (Text-fig. 4.19, 4.20) as well as an increased abundance of C. elliptica and a mass occurrence of a large variety T. carpathica. Sidi Khalif section (Text-fig. 3B) (35° 6'42.72"N, 9°40'36.70"E) The Berriasian of the Sidi Khalif section is c. 368 m thick. The succession is divided into two members; the lower, spanning beds SK2­SK42, and the upper, beds SK43­SK47. The lowermost part of the succession consists of alternating beds of marls and limestones of very irregular thickness. Ammonites (Text-figs 3, 6): In the lower beds, fossils are represented mainly by fragmentarily preserved, moderately small species of the genera Dalmasiceras, Jabronella, Berriasella and Pseudosubplanites. Higher in the succession (bed SK43), well-preserved representatives of the genera Subthurmannia and Mazenoticeras are common (Text-fig. 3). Calpionellids: Similarly as in Nara section, four successive calpionellid assemblages are recognised (Textfig. 4). Assemblage 1 (beds SK2­SK18) is dominated by C. alpina (58%) and Cr. parvula (36%); also noted was T. carpathica (6%). Calpionellid-rich Assemblage 2 (beds SK19­SK24) is characterised by the appearance of various species of the genus Remaniella (bed SK19) and the dominance of sphaerical forms of C. alpina (66%). Also noted were Cr. parvula (20%) and T. carpathica (7%). Assemblage 3 (beds SK25­SK42) is characterised by the appearance of C. elliptica (bed SK 25), which is accompanied by C. alpina (48%), C. parvula (10%), T. carpathica (6%), R. colomi (8%), R. catalanoi (2%), R. ferasini (1.5%), and R. duranddelgai (2.5%). In the upper part of the interval with Assemblage 3 there is an increase in abundance of small forms of C. Elliptica. Some of the Remaniella species are discontinuous through their range. Assemblage 4 (beds SK43­ SK47) is characterised by the appearance of T. longa (2%), although it is clearly dominated by C. elliptica (37%) and C. alpina (19%). Also noted were: Cr. parvula (8%), T. carpathica (16%), L. hungarica (6%), Remaniella cadischiana (6%) (Text-fig. 4.13, 4.14), R. catalanoi (3%) and Remaniella borzai (3%) (Text-fig. 4.18). BIOSTRATIGRAPHIC RESULTS Calpionellid biostratigraphy The Calpionella Zone, first defined by Allemann et al. (1971), was divided subsequently into the C. alpina and C. elliptica intervals by Catalano and Liguori (1971). Pop (1994) defined these two intervals as the Alpina and Elliptica Subzones, divided by a Remaniella Subzone (Remaniella ferasini Subzone of Pop 1994). The lower boundary of the C. alpina Subzone, taken as 48 KAMEL MAALAOUI AND FOUAD ZARGOUNI Text-fig. 3a. Geological log, biostratigraphy, and vertical ranges of ammonite and calpionellid species in the Nara section 49 BASAL CRETACEOUS BIOSTRATIGRAPHY IN TUNISIA Text-fig. 3b. Geological log, biostratigraphy, and vertical ranges of ammonite and calpionellid species in the Sidi Kralif section 50 KAMEL MAALAOUI AND FOUAD ZARGOUNI 51 BASAL CRETACEOUS BIOSTRATIGRAPHY IN TUNISIA the Tithonian / Berriasian boundary by Remane et al. (1986), is characterized by a change in the morphology of C. alpina, with an `explosion' of small spherical forms. The C. elliptica Subzone is marked by the first occurrence of the subzonal species. Pop (1994) distinguished a new Longa Subzone, named after Tintinnopsella longa Colom (1939), corresponding to the upper part of the Calpionella Zone. The calpionellid zonation used in this work is that established by Rehakova and Michalik (1997); Remane et al. (1986); Pop (1994, 1997) and Lakova and Petrova (2013) (Text-fig. 7). In this study, the preservation of calpionellid material from Nara and Sidi Khalif has been found to be generally good, and the fine and minute apertures of the loricas are well preserved, which facilitates their determination. In both the Nara section and the Sidi Khalif section the same calpionellid bioevents have been determined, The "acme" of small spherical forms of C. alpina,first appearance of the genus Remaniella, first occurrence of C. elliptica, and the last bioevent, the first appearance of index species T. longa. The events thus define and limit, respectively, the C. alpina, Remaniella, C. elliptica and T. longa subzones. Calpionella alpina Subzone The early Berriasian calpionellid association, i.e. Assemblage 1, is characterized by the species C. alpina, Cr. parvula, and T. carpathica. This composition is indicative of the C. alpina Subzone of the standard Calpionella Zone of the lower Berriasian, e.g., Remane et al. (1986) and Rehakova and Michalik (1997). This subzone has been recognized in North Africa by Boughdiri et al. (2006), and as sub-zone B1 of Ben Abdesselam-Mahdaoui et al. (2011) and Benzaggagh et al. (1995, 2012). Remaniella Subzone The Assemblage 2 association is typified by the first appearance of Remaniella with variable percentages of C. alpina and Cr. parvula. This association characterizes the Remaniella Subzone and corresponds to the upper part of B zone of Remane (1963, 1971). Ac- cording to Oloriz et al. (1995), Pop (1994, 1996), Andreini et al. (2007) and Lakova and Petrova (2013), it correlates to the Remaniella ferasini Subzone (see Rehakova and Michalik 1997). Calpionella elliptica Subzone This subzone was created by Catalano and Liguori (1971) and redefined by Pop (1974). Its base is marked by the first occurrence of C. elliptica associated with C. alpina, Cr. parvula, T. carpathica, L. hungarica, R. ferasini, R. colomi, and R. duranddelgai. The subzone was recognised elsewhere by Pop (1994­1997) and Grun and Blau (1997). Tintinnopsella longa Subzone The T. longa Subzone was originally defined by Pop (1974), the first occurrence of the eponymous species marking its base. The calpionellids of our assemblage 4 are T. longa, C. alpina, C. elliptica, R. borzai, R. duranddelgai, R. catalanoi, R. ferasini and T. carpathica, which is similar to the association found by Pop (1974). A palaeobiogeographical study on this bioevent (Pop 1994) showed its distribution in western Tethys in the Southern Carpathians (Pop 1974, 1986), Western Carpathians (Vasicek et al. 1994; Borza and Michalik 1986), SE France (Le Hégarat and Remane 1968; Charollais et al. 1981), Southern Alps (Channell and Grandesso 1987), Sicily (Catalano and Liguori 1971), Subbetic area (Alleman et al. 1975), and westwards to Cuba (Pop 1976). Ammonite biostratigraphy The reference ammonite biostratigraphic scale used here is the Tethyan ammonite zonation of the Berriasian following Tavera (1985) and Hoedemaeker et al. (1990) (Text-fig. 7). Berriasella jacobi Zone The ammonite species from the lower part of the two studied sections (Nara, beds N1­N18; Sidi Khalif, beds SK2-SK42) are from the Berriasella jacobi and Pseu- Text-fig. 4. Photomicrographs of calpionellids in thin sections from the Nara and Sidi Kralif sections. 1-3 ­ Calpionella alpina Lorenz, Lower Berriasian, Calpionella Zone, Alpina Subzone, sample SK17. 4-6 ­ Calpionella elliptica Cadisch, Middle Berriasian, Calpionella Zone, Longa Subzone, sample N21. 7 ­ Crassicollaria parvula Remane, Lower Berriasian, Calpionella zone, Remaniella Subzone, sample SK21. 8, 9 ­ Tintinnopsella carpathica Murgeanui & Filipescu, Middle Berriasian, Calpionella Zone, Alpina Subzone, sample N19. 10, 11 ­ Remaniella ferasini Catalano, Lower Berriasian Calpionella Zone, Elliptica Subzone, sample N17, 12 ­ Remaniella colomi Pop, Lower Berriasian, Calpionella Zone, Remaniella Subzone, sample SK21. 13, 14 ­ Remaniella cadischiana Colm, Middle Berriasian, Calpionella Zone, Remaniella Subzone, sample N21. 15 ­ Remaniella duranddelgai Pop, Lower Berriasian, Calpionella Zone, Remaniella Subzone, sample N9. 16 ­ Remaniella catalnoi Pop, Middle Berriasian, Calpionella Zone, Remaniella Subzone, sample N23. 17 ­ Lorenziella hungarica Knauer and Nagy, Middle Berriasian, Calpionella Zone, Longa Subzone, sample SK43. 18 ­ Remaniella borzai Pop, Lower Berriasian, Calpionella Zone, Remaniella Subzone, sample SK25. 19, 20 ­ Tintinnopsella longa Colom, Middle Berriasian, Calpionella Zone, Longa Subzone sample SK 43, N25 52 KAMEL MAALAOUI AND FOUAD ZARGOUNI Text-fig. 5. Selected ammonites from the studied sections: 1a, b ­ Pseudosubplanites grandis Mazenot; sample SK29: Pseudosubplanites grandis Subzone, Pseudosubplanites euxinus Zone, Lower Berriasian. 2 ­ Fauriella sp.gr. shipkovensis Nikolov and Mandov; sample N15: Grandis Subzone, Euxinus Zone, Lower Berriasian. 3 ­ Mazenetoceras curelence Kilian; sample SK43; Subthurmannia occitanica Zone, Middle Berriasian. 4 ­ Jabronella sp.; sample SK43 : Subthurmannia occitanica Zone, Middle Berriasian 53 BASAL CRETACEOUS BIOSTRATIGRAPHY IN TUNISIA Text-fig. 6. Selected ammonites from the studied sections. 5 ­ Subthurmannia occitanica Pictet; 5 ­ sample N2; 6 ­ sample SK43; Subthurmannia occitanica Zone, Middle Berriasian. 7 ­ Pseudosubplanites grandis Mazenot; sample N15, Pseudosubplanites grandis Subzone, Pseudosubplanites euxinus Zone, Lower Berriasian. 8 ­ Malbosiceras sp., sample N23; Subthurmannia occitanica Zone, Middle Berriasian 54 KAMEL MAALAOUI AND FOUAD ZARGOUNI dosubplanites grandis zones sensu Le Hégarat (1973). Hoedemaeker (1982) included them as subzones in a Pseudosubplanites euxinus Zone. Tavera (1985) proposed expanding the B. jacobi Subzone to be equivalent to the Pseudosubplanites euxinus Zone, This proposal which was accepted by the Working Group on Lower Cretaceous Cephalopods (1992; Hoedemaeker and Company 1993, and others e.g., Reboulet and Klein 2009; Reboulet et al. 2014). In the present paper, we follow the ammonite biozonation of Hoedemaeker et al. (1990) in discussing zonal calibration between ammonites and calpionellids. The B. jacobi Zone is characterized in the Nara section by the following ammonite association: Pseudosubplanites euxinus, P. lorioli (bed N3), B. (B.) oppeli (N5), Dalmasiceras sp. and Berriasella (B.) subcallisto (N7), and Pseudosubplanites sp. (N13). The assemblage at Sidi Khalif section includes Dalmasiceras subloevis, Jabronella sp. (Text-fig. 5.4) and B. (Picteticeras) chomeracensis. This association could be indicative of the B. jacobi Zone sensu Le Hégarat (1973) considering the association of the genera Delphinella, Dalmasiceras and Berriasella low in this zone in other regions (Wimbledon et al. 2013; Donze et al. 1975 in northern Tunisia, Memmi 1967, Busnardo et al. 1976 in Central of Tunisia, Memmi 1989). In the succeeding Nara beds we have been able to identify Ps. grandis (Text-fig. 5.1a, b) and Fauriella sp. ex gr. shipkovensis (bed N 15) (Text-fig. 5.2), Jabronella sp. and Subalpinites aff. mediterraneus (N17), and at Sidi Khalif Ps. grandis and Pseudosubplanites berriasensis (bed SK 29), whereas bed SK 37 contains Pseudosubplanites sp. and Jabronella aff. isaris. In this association the Gran- dis Zone sensu Le Hégarat (1973) is well represented by the index species Ps. grandis (Mazenot), as in the associations recorded by Memmi (1967) and Busnardo et al. (1976) in Central Tunisia. Subthurmannia occitanica Zone In the Nara section, we find an assemblage containing Tirnovella subalpinites (bed N19), Fauriella rarefurcata (bed N19), Fauriella floquinensis (bed 21), Subthurmannia occitanica (Bed N23) and Malbosiceras sp. (bed N25) (Text-fig. 6.8), Mazenoticeras aff. malbosiforme (Bed N27), Malbosiceras rouvillei and Jabronella paquieri (Bed N29). In the Sidi Khalif section, we collected Pseudosubplanites lorioli, S. occitanica (Text-fig. 6.5, 6.6) (bed Sk43), Mazenoticeras curelence (SK 43) (Text-fig. 5.3), and Jabronella sp. This association could be the equivalent of the Occitanica Zone (sensu Le Hégarat), correlated with the association of Memmi (1967); Enay and Geyssant (1975); Cecca et al. (1989); Wimbledon et al. (2011, 2013). DISCUSSION This work proposes a revised stratigraphy for the Lower to Middle Berriasian in Central Tunisia based on ammonites and calpionellids. The boundaries of the biostratigraphic units in this scheme fit well with those of the subdivisions of many other key Tethyan sections. The bases of our sections (Bed N1 in the Nara section and Beds SK1­SK5 at Sidi Khalif) do not allow us (because of unsuitable dolomitic lithologies) to rec- Text-fig. 7. Correlation of ammonite and calpionellid zonations for the upper Tithonian and lower-middle Berriasian, and major calpionellid bio-events (after Lakova and Petrova 2013) 55 BASAL CRETACEOUS BIOSTRATIGRAPHY IN TUNISIA ognize the top of Crassicollaria Zone (calpionellids) or the top of Durangites Zone (ammonites). However, comparing our C. alpina Subzone or C. jacobi Subzone (sensu Le Hégarat 1973) assemblages with those in other sections, one can conclude that the J/K boundary, i.e. the base of Berriasian approximately coincides with this lithological change from dolostones to micritic limestones, or is rather lower, within the dolomites of Nara Formation, since indications of lower laying Crassicollaria Zone and Durangites Zone are absent. The quantitative analysis of calpionellids shows major variations in their abundance and composition, and the well-marked first occurrences of species allow the delimitation of the C. alpina and Remaniella subzones, represented by the first appearance of the genus Remaniella in bed N9 (Nara) and in bed SK 17 (Sidi Khalif). It is worth noting that the ammonite fauna crosses this level with no change. In bed N13 and bed SK 25, we see the same phenomena, with variations detectable in the calpionellids species (first appearance of C. elliptica). In fact, none of the ammonite zonal boundaries corresponds to any calpionellid boundary. The only exception is the first appearance of T. longa coinciding in the studied sections (bed N19 and bed SK43) with the presence of the ammonite Subthurmannia occitanica. These two coeval events mark clearly the lower/middle Berriasian boundary. cult because of the unfavourable lithological nature of the base of both studied sections. Acknowledgements The authors would particularly like to thank Luccia Memmi and Noureddine Ben Ayed for their valuable insights and suggestions. We also thank W.A.P. Wimbledon, Iskra Lakova, Luc Bulot and Ireneusz Walaszczyk for their useful comments.

Journal

Acta Geologica Polonicade Gruyter

Published: Mar 1, 2016

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