sea-level changes and sedimentary response across the barremian

ACTA PALAEONTOLOGICA ROMANIAE V. 9 (2), P. 33-46

SEA-LEVEL CHANGES AND SEDIMENTARY RESPONSE ACROSS THE BARREMIANEARLY APTIAN IN PĂDUREA CRAIULUI MOUNTAINS, ROMANIA Călin Bruchental1, Ioan I. Bucur1, Ioan Cociuba2 & Anca M. Hebriştean1 Abstract Sedimentary and biostratigraphic studies of the Lower Cretaceous deposits in the northern part of the Pădurea Craiului Mountains (northwest Romania) revealed facies development interpreted as controlled by sea-level changes across Barremian-Early Aptian stages. Two sedimentary sequences were distinguished in the three sections of the Blid Formation: (1) Gorge Entrance Section, (2) Canton CFR Section and (3) Tunnel Section. A sea level drop is evidenced in the first two parts of the sections by frequent subaerial exposure surfaces including incipient paleosoil formation within a peritidal dominated carbonate succession. The upper part of all the sections starts with a transgression marked by abundant sponge spicules and cherty limestone in the deepest section. This transgression corresponds basically to the facies with abundant Palorbitolina lenticularis which appears in all sections. The three studied sections were correlated using microfacies criteria and microfossils. The age of the sections was established on orbitolinid foraminifera: Paracoskinolina? jourdanensis, Pfenderina globosa (Upper Hauterivian-Lower Baremian) occurring at the base of the sections and Preorbitolina cormyi (Early Aptian in the Tethyan realm), occurring in the middle-upper part of the Canton CFR section. Keywords: Barremian, Early Aptian, Sea-level changes, Paleosoil, Transgression, Orbitolinids

INTRODUCTION Lower Cretaceous shallow water deposits are well known along the Tethys margins in the Alps, south-eastern France (Provence), the Pyrenees, Adriatic/Dinaric region and the Western Carpathians (Masse, 1976; Peybernès, 1976; Arnaud-Vanneau, 1980; Husinec & Jeleska, 2006; Michalik et al., 2008). The sea-level changes or to some extent sequence stratigraphy of Lower Cretaceous involving the Barremian-Aptian stages are known from many papers (Arnaud-Vanneau & Arnaud, 1990; ArnaudVanneau et al. 2005; Masse, 1993; Jacquin et al., 1998; Hoedemaeker, 1998; Bernaus et al., 2002; Sandulli & Raspini, 2004; Haq & Al Qahtani, 2005; Husinec & Jeleska, 2006; Masse & Fenerci-Masse, 2011). Palaeoenvironment significance of Palorbitolina lenticularis or orbitolinids in general was also discussed in several papers (Arnaud-Vanneau, 1975; Masse, 1976; Villas et al. 1995, Masse & Fenerci-Masse, 2011). Shallow water carbonates are sensitive to climatic variations as well as to high-frequency sea-level changes and form the basis for recognizing sedimentary cycles and sequence stratigraphy (Flügel, 2004). They are also important palaeobathymetric indicators. The pre-Aptian cycles are mostly aggradational, and relate to high rates of sediment supply together with changing rates of accommodation space (Jaquin et al., 1998). The Cretaceous deposits from Pădurea Craiului have been intensively studied (Kräutner, 1941; Răileanu, 1956; Patrulius, 1956, 1961; Istocescu, 1970; Bordea & Istocescu 1970). Many microfacies and micropalaeontological studies concerning the Lower Cretceous limestone were published starting with Dragastan 1966, 1967; Dragastan et al., 1988, Dragastan & Ciobanu 2002; followed by Bucur 1981a, 1981b, 1985, 1995, 2000, Bucur et al., 2010, Bucur et al., 2012, Cociuba 1995, 1999, 2000, Daoud et al., 2004, Lazăr et al., 2012. Nevertheless, the Lower Cretaceous between the localities of Vadu Crişului and Şuncuiuș are poorly

known. In this area, these deposits are well exposed along the Crişul Repede Valley (Fig. 1).

Fig. 1 Location of the studied area within the Romanian territory, and location of the sampled sections in the northern part of Pădurea Craiului Mountains.

This paper focuses on the Blid Formation (Coposeni Member sensu Cociuba, 2000). Our aim is to define the main depositional environments based on paleontological and sedimentological features, show the short term sealevel changes across Barremian-Early Aptian stages, interpret their paleoenvironment significance, and 33

________________________________ Babeş-Bolyai University, Department of Geology and Center for Integrated Geological Studies, Str. M. Kogălniceanu nr. 1, 400084 Cluj-Napoca, Romania, [email protected]; [email protected]; [email protected] 2 Geological Institute of Romania, Cluj-Napoca Branch, 400379 Cluj-Napoca, Romania, [email protected] 1

Călin Bruchental, Ioan I. Bucur, Ioan Cociuba & Anca M. Hebriştean

provide new biostratigraphic data. Three sections namely Gorge Entrance Section, Canton CFR Section and Tunnel Section were studied and more than 250 samples were collected from which around 300 thin sections were made and analyzed. The vertical sample spacing was often less than 1m, but there were also few gaps with no outcrops. A 10 m spacing sample interval was kept along the Crişul Repede Valley to check for the lateral continuity of the facies and for mapping purposes. All the sections were described in the field including the lithology-sedimentary structures, bedding thickness and surface as well as geometric relationship between facies. GEOLOGICAL FRAMEWORK The Pădurea Craiului Mountains are located in the northwestern part of Romania (Fig. 1). Geologically they belong to the Northern Apuseni Mountains, part of the Tisza Mega-Unit (Csontos & Vörös, 2004; Schmid et al., 2008). TheTisza Mega-Unit was separated from the European continent during the Middle Jurassic, in connection with the opening of the eastern part of the Alpine Tethys (Schmid et al., 2008). Some facies of the post rift sediments (post Middle-Jurassic) show Adriatic affinities (Vörös, 1977, 1993, Lupu, 1984). This indicates that Tisza block became part of the Adriatic palaeogeographic realm (Schmid et al., 2008). The Tisza Mega-Unit was not affected by the Early Cretaceous orogenic activity (Schmid et al., 2008), until mid Cretaceous times when parts of the Transylvanian Tethys closed (Sandulescu, 1984). However, nappes emplacement was a more continuous process and at least the Codru Nappe System started moving since Barremian (Balintoni, 2001; Csontos & Vörös, 2004). The closure of the Transylvanian Tethys results in collision between Tisza and Dacia mega-units and the formation of the Tisza-Dacia microplate (Csontos & Vörös, 2004; Schmid et al., 2008). The outcome of the Cretaceous movements was a nappe stack in the Northern Apuseni Mountains with the Bihor Unit or the Bihor Nappe System at the base followed by Codru Nappe System, and in the upper position Biharia Nappe System (Ianovici et al., 1976; Balintoni, 1994). Patches of Senonian sediments have a post-tectonic character. The studied sections in Pădurea Craiului belong to the Bihor Unit. Its Mesozoic succession includes Triassic, Jurassic and Cretaceous deposits. The Lower Cretaceous succession (Fig. 2) in Pădurea Craiului is a matter of contradictory interpretations, due to difficulties in observing continuous sections (Bucur et al., 2012). The studied sections represent the (1) Blid Formation (Dragastan et al. 1986, 1988). This formation is made up of two members (Cociuba 1999, 2000): 1a) Dobresti Member is composed of limestones with bauxite rocks in the base or it is directly overlying the Upper Jurassic limestones. The deposits show a lacustrine character at the base and then gradually change to brackish and to a normal marine one. Algae and foraminifera from these limestones point to the Valanginian-? Hauterivian age. 1b) Coposeni Member was previously known as “the lower limestone with pachyodonts" (Patrulius, in Ianovici 34

Fig. 2 Succession of the Lower Cretaceous deposits from Pădurea Craiului Mountais (from Bucur et al. 2012). 1 bauxite; 2 limestone; 3 breccias; 4 shale and marls; 5 conglomerate.

et al., 1976). Micropaleontological association contains Paracoskinolina?jourdanensis, Pfenderina globosa at its base, indicating the Upper Hauterivian-Lower Barremian. The upper limit was regarded as Upper Barremian (Cociuba, 2000 and reference therein) or Early Aptian (Dragastan et al., 1988) based on Palorbitolina lenticularis. This formation is followed by: (2) Ecleja Formation (Early Aptian-Patrulius et al. 1968) is a formation of silty marls to marly silts and includes an intercalation of bioclastic limestone (Valea Bobdei Member, Cociuba, 2000).

Sea-level changes and sedimentary response across the Barremian-Early Aptian in Pădurea Craiului Mountains, Romania

(3) Valea Măgurii Formation (Early Aptian-Cociuba 2000) previously known as “middle limestone with pachyodonts” ends with an unconformity. Both the Valea Bobdei Member and the Valea Măgurii Formation contain Palorbitolina lenticularis. (4) Vârciorog Formation (Late Aptian-Albian) (Cociuba 2000) is a succession of gray to black marls, marly and glauconitic sandstone, and gray to black nodular limestone with orbitolinids and rudists, discordantly covering the Valea Măgurii Formation. The presence of Mesorbitolina texana orbitolinid points to the Upper Aptian-Albian age. AGE CONSTRAINTS The micropalaeontological assemblage indentified in the whole succession from Vadu Crisului includes both algae and foraminifers. The foraminifers (Fig. 3) are represented by Paracoskinolina? jourdanensis (Foury & Moullade), Paracoskinolina maynci (Chevalier), Pfenderina globosa Foury, Nezazatinella sp., Bellorusiella sp., Vercorsella sp., Nautiloculina sp., Pseudolituonella sp., Glomospira urgoniana ArnaudVanneau, Paleodictyoconus sp., Novalesia sp., Orbitolinopsis sp., Orbitolinopsis buccifer ArnaudVanneau & Thieuloy, Neotrocholina sp., Coscinophragma sp., Palorbitolina lenticularis (Blumenbach), Preorbitolina cormyi Schroeder, Sabaudia minuta (Hofker), Sabaudia auruncensis Chiocchini & Di Napoli Alliata. The algae assemblage (Fig. 4) consists of Salpingoporella sp., Clypeina sp., Salpingoporella cf. hasi Conrad, Radoičić & Rey, Salpingoporella muehlbergii (Lorenz), Salpingoporella melitae Radoičić, Salpingoporella genevensis (Conrad), Salpingoporella urladanasi Conrad, Peybernes & Radoičić, Salpingoporella biokovensis Sokač & Velić, Salpingoporella heraldica Sokač, Cylindroporella ivanovici (Sokač), Clypeina solkani Conrad & Radoičić, Falsolikanella danilovae (Radoičić), “Halimeda” misiki Schlagintweit, Dragastan & Gawlick, Juraella sp., Thaumatoporella sp. Rivulariacian-like cyanobacteria are very frequent in the first two parts of the sections, whilst Lithocodium aggregatum Elliot appears in the facies with Palorbitolina lenticularis. Bacinellid structures were occasionally observed and they are associated most often with Lithocodium. From the above mentioned species important age indicators are: Paracoskinolina? jourdanensis, Pfenderina globosa (Upper Hauterivian to Lower Barremian) found only at the base of the Tunnel Section and a few samples taken along the Crişul Repede Valley, and Palorbitolina lenticularis (Late BarremianBedoulian) appearing in the third part of all the sections, except for the Canton CFR Section, the longest section, where P. lenticularis appears since the middle part. Dragastan et al. (1988) considered the Blid Formation from Pădurea Craiului as including the Lower Aptian substage but without unequivocal proofs, hence its upper limit was considered Upper Barremian by other researchers (Cociuba, 2000 and reference therein). In the facies with Palorbitolina lenticularis of Canton CFR

Section species of Preorbitolina cormyi was recognized for the first time in the Blid Formation. This species has its first occurrence (FO) in the Early Aptian (ArnaudVanneau et al., 1998; Schroeder et al., 2010), and therefore it represents a compelling evidence for regarding the upper limit of the Blid Formation in the Early Aptian. MICROFACIES ANALYSIS All sampled sections (Fig. 5) are relatively well exposed along the Crişul Repede Valley between Vadu Crişului and Şuncuiuş localities. The microfacies types (MFT) were separated based on depositional texture, grain size and grain composition. Early diagenetic characteristics with environmental significance were also considered. The following microfacies types were distinguished: MFT1. Fenestral nonlaminated / laminated mudstone / wackestone. Biota is of reduced diversity and is represented by foraminifera (miliolids, textulariids, and occasionally cuneolinids) ostracods, gastropods, and rivulariacean-like cyanobacteria. Lamination, when present, is supposed to be of microbial nature (Fig. 8c). Desiccation cracks were sparsely observed (Fig. 6b) This MFT type is quite frequent in the first part of all the sections, and occasionally in the middle part. Because these fenestral fabrics frequently underlie short early exposure surfaces, cavities often form geopetal structure with vadose microsparitic silt (sensu Dunham 1969). MFT 2. Peloidal intraclastic packstone/grainstone. The grains consist almost entirely of peloids and micritic intraclasts or micritised cyanobacteria. Most peloids are probably fine micritic intraclasts. They are well to moderately sorted and most of them are moderatelly to well rounded. Rivularia-like cyanobacteria, miliolids, textulariids, green algae, rudist fragments and gastropods occur occasionally and could be locally important (Fig. 8e). Keystone vugs are common feature, occasionally with vadose silt infilling. This microfacies often alternates with fenestral laminated mudstone/wackestone, the limit between them being a discontinuity surface (probably firmground) which could be the result of erosion or partial lithification. The grains above the discontinuity surface commonly show micritic envelopes. MFT 3. Charophycean algal wackestone. Algal fragments are represented by gyrogonites (Fig. 6 d, f) and fragments of thallus internodes. It occurs at the end of the first part in the Tunnel Section and inside the first part of the Canton CFR Section. We identified this MFT in a few samples taken along the Crişul Repede Gorge as well. This means it has also an important lateral extent, and it could help to correlate the sections studied. This microfacies is associated with thin layers (up to 10 cm) of mottled, brecciated limestone with red clay matrix. MFT 4. Ostracods wackestone (Fig. 8d). This MFT type occurs at several levels within the lower and middle part of the sections. Apart from ostracods, rare foraminifers can be found occasionally. As in the two previous mentioned MFT mottled micrite and geopetal structures sometimes with vadose microsparitic silt are common. MFT 5. Wackestone with green algae (Fig. 4a, 4b, 4c, 4d, 4f are from this MFT). 35


Fig. 3 Orbitolinid foraminifers. a Paracoskinolina? jourdanensis (Foury & Moullade), sample 458. b Paracoskinolina maynci (Chevalier), sample 664. c, d Palorbitolina lenticularis (Blumenbach), samples 678, 536. e - h Preorbitolina cormyi Schroeder, samples 678, 685, 678, 679. Scale bar is 0.25mm. 36


Fig. 4 Calcareous algae. a Salpingoporella muehlbergii (Lorenz), sample 214. b Salpingoporella urladanasi Conrad, Peybernes & Radoičić, sample 490. c Salpingoporella genevensis (Conrad), sample 667. d Salpingoporella hasi Conrad, Radoičić & Rey, sample 208. e Salpingoporella melitae Radoičić, sample 477. f ?Salpingoporella biokovensis Sokač & Velić, sample 224. g “Halimeda” misiki Schlagintweit, Dragastan & Gawlick, sample 504. h Salpingoporella heraldica Sokač, sample 226. Scale bar is 0.25 mm (a-f, h); 0.50 mm (g). 37


Fig. 5 Stratigraphic sections of Barremian-Lower Aptian deposits from Vadu Crişului area.

Besides algae, small benthic foraminifera are common. The most abundant green algae are represented by dasycladaleans Salpingoporella sp., S. cf. hasi, S. muehlbergii, S. melitae, Clypeina sp. This MFT is common in the middle part of Gorge Entrance Section and Tunnel Section and in the lower part of Canton CFR Section. MFT 6. Bioclastic packstone/grainstone. Bioclasts are represented by (a) benthic foraminifera, rare green algae and rudists’ debris. These deposits show evidence of intense reworking and probably formed high energy internal shoals, but overall they are very weakly represented. In other cases (b) bioclasts are represented by echinoderm debris, foraminifera (Orbitolinopsis sp., Palorbitolina lenticularis, textulariids, Lenticulina sp.), Lithocodium sp. (occasionally associated with bacinellid38

like structures), bryozoans, corals and microbial structures. These deposits were heaped up by waves and could have formed weak external shoals. They were noticed only in the Tunnel section. MFT 7. Wackestone/packstone with orbitolinids and echinoderm debris (Fig. 8f). These deposits are common in the middle part of Canton CFR Section and in the upper part of the other two sections. The fauna is of low diversity; beside orbitolinids there are rare textulariids, sponge spicules and Lenticulina. Trocholinid foraminifera are locally abundant in the Gorge Entrance Section and Canton CFR Section. This MFT is dominant in the facies with Palorbitolina lenticularis. MFT 8. Wackestone/packstone with abundant sponge spicules (Fig. 7g, h). Echinoderm fragments are locally abundant. This MFT type is encountered in the third part of the Tunnel Section. In the field, these deposits overlie


Fig. 6 Microfacies. a Microbreccia with iron oxides filling the voids (Sample 699 taken from a discontinuity surface at the base of Canton CFR section). b Desiccation cracks, sample 225. c, e Wackestone with Microcodium, sample 493. d, f Fenestrate wackestone with charophyte girogonites, samples 471, 470. g, h Cavities filled with sparry calcite surrounded by irregular laminae (7) occasionally with breccia like features (8), formed probably in pedogenetic conditions, sample 502. Scale bar is 0.50 mm (a, b, d, g, h); 0.25mm (c, e, f). 39


Fig. 7 a-d Microcodium aggregates. The aggregates have the typical morphology of Microcodium consisting of a layer of individual, elongate, pyramidal or prismatic calcareous crystals (Košir, 2004). In d the aggregates are developed close to a root trace (r). e Microfacies with Microcodium (black arrows). Cracks originating probably from roots (r) as well as micritic nodular laminated structure (?calcrete) (n) can be noticed. f Laminated, probably rhizogenic calcrete crust. Note similarity with calcrete crust illustrated by Kabanov et al. (2010: Fig.8C).

2-3 m of covered surface (no outcrops). Throughout the limestone with sponge spicules nodular cherts are very common. Two levels of bedded chert were also recognized. DIAGENETIC OVERPRINT The studied sediments were affected by early marine and meteoric diagenetic processes. A clear distinction is 40

difficult to make between them. Marine diagenesis is represented by micritic envelopes around grains and micritised grains. Occasionally thin isopachous fringes of bladed or fibrous cements border the grains or pore spaces between grains. Peloidal microcrystalline cement appears locally, filling the center of the voids. Borings on shell fragments (usually rudists) are quite common. Vadose diagenesis is represented by thin isopachous rims around grains and meniscus cement (Fig. 8b).


Fig. 8 Microfacies. a Dolomitised/ferruginised mudstone surrounded by microbial crusts, sample 199. b Intraclastic peloidal grainstone ('beach rock'-with fibrous cement surrounding the grains and meniscus cement), sample 202. c Fenestral laminated mudstone/microbial bindstone, sample 500. d Accumulation of ostracods in a fenestrated wackestone, sample 199. e Peloidal bioclastic grainstone, sample 492. f Wackestone/packestone with Palorbitolina, sample 679. g Wackestone with sponge spicules, sample 688. h Wackestone with abundant sponge spicules and echinoderm debris, sample 517. Scale bar is 0.50mm. 41


The remaining pore spaces are usually filled with blocky calcite cement. Crystal silt is found sometimes inside dissolution cavities of subtidal deposits (wackestone rich in dasycladaleans and benthic foraminifers). The upper parts of the cavities are usually filled with sparitic calcite. Rarely, dolomitisation/feruginisation processes are present superimposed on the ostracodes wackestone (Fig. 8a). Very thin layers of mottled, brecciated grayish limestone with red clay matrix are present at several levels in the lower part of the sections (Fig 6a). They are associated with charophycean algal wackestone when the latter is present. The nodular aspect is probably due to desiccation and subsequent formation of planar to curved fissures (Freytet 1973, Alonso-Zarza 2003). In the middle part of the Tunnel section within peritidal deposits diagenetic processes went further resulting in incipient paleosoil horizons. Microcodium (Fig. 6 c, e, 7 a-e) was clearly recognized in one sample. Microcodium presumably represents intracellular calcification of roots (Wright et al., 1988, Alonso-Zarza, 2003, Flügel, 2004). Cavities filled with sparite calcite and bordered by laminae with irregular thickness (Fig. 6g, 7f), have probably a pedogenic origin, possibly related with root activity (Tucker, 2003). They were observed at several levels. In the Tunnel section silica for the chert nodules is probably derived from the siliceous sponge spicules as it is associated only with the limestone with abundant sponge spicules. Occasionally arguments for deep burial diagenesis were observed. Stylolites, dissolution seams and other pressure solution structures are present but not abundant. In rare cases breakage and distortion of grains due to physical compaction were noticed.

common microfacies are wackestone with green algae (MFT 5) and bioclastic packestone/grainstone (MFT 6a). Outer shelf deposits dominate the upper part of the sections. They are represented by wackestone of MFT 7, MFT 8, or MFT 6b. As in other parts of the Tethys Palorbitolina lenticularis is associated with muddy environments being indicative of warm waters and relatively shallow environments (Vilas et al., 1995). In the area of our study different forms were encountered: high conical shapes in shallow waters, short and very flat ones which apparently lived in a deeper environment or gigantic forms of a few millimeters but their assignment to Palorbitolina is uncertain. As a rule, the average beds thickness inside peritidal deposits is thinner than in the facies with Palorbitolina lenticularis. In the Tunnel sections during the main transgression wackestone/packestone with abundant sponge spicules (MFT 8) are dominant. Bioclastic packstone/grainstone of MFT 6b could have formed external shoals but it is unlikely they were effective barriers against wave energy. This and the lack of framebuilders lead us to presume a slight change in morphology of the carbonate shelf during the dominance of the facies with Palorbitolina, as noted in other parts of the Tethys (Vilas et al., 1995, Masse and Fenerci-Masse 2011). The flat-topped shelf became closer to a ramp type. Pomar (2001) argue that oligophotic producing biota like large foraminifera generate distally steepened ramp. The change of shelf morphology has not occur before, because sediments specific to carbonate ramps are lacking in the first to parts of the sections (for instance ooids are lacking almost completely or when present they are only superficial). Carbonate ramps form during the drowning of shelves or during the early stages of platform formation (Flügel, 2004).

SEDIMENTARY ENVIRONMENT

SEA-LEVEL CHANGES

The Lower Cretaceous deposits from Vadu Crisului (Blid Formation-Coposeni Member) can be assigned to inner, middle, and outer shelf environments (Fig. 9). Inner shelf deposits are represented by fenestral laminated mudstone/wackestone (MFT 1), peloidal intraclastic packstone/grainstone (MFT 2), charophycean algal wackestone (MFT 3), ostracod-bearing wackestone (MFT 4), and occasionally wakestone with green algae (MFT 5). Fenestral carbonates which are often finely laminated formed extensive tidal flats. Abundant charophyte remains testify for supratidal ponds and lakes. These charophyte remains were associated with breccias and red clay suggesting intermittent exposure of the inner platform. More than that, in the Tunnel section Microcodium and other specific soil features appear at several levels being an unambiguous proof of incipient paleosoil formation (Flügel, 2004; Schlager, 2005). The inner shelf deposits are dominant in the first two parts of the Gorge Entrance Section and Tunnel Section but only in the first part of Canton CFR Section, being characterized by shallowing-up peritidal deposits, capped sometimes by red clay. Middle shelf deposits are weakly represented, and are difficult to separate from the inner shelf ones. Most

In all three sections analyzed two large scale depositional trends could be recognized. (1) In the first part in all the three sections the sediment production kept pace with created accommodation space. The sediments are shallow water deposits, from shallow subtidal, intertidal to supratidal settings. The overall trend in these deposits is progradational to aggradational. Early exposure surfaces are quite frequent and are usually short lasting. In the middle part of the Tunnel section incipient paleosoil started to develop. This incipient paleosoil is stratigraphically above Paracoskinolina? jourdanensis but bellow the facies with Palorbitolina lenticularis. They were later covered by shallow water deposits. (2) The upper part of the sections shows a transgressive trend, being more obvious in the “Tunnel Section”. Sedimentary transgressive sequence starts with wackestone with large orbitolinids (Palorbitolina lenticularis - the most abundant one, and Preorbitolina cormyi) and echinoderm debris. In the Tunnel Section this MFT is followed by wackestone/packestone with very abundant sponge spicules. They start to decrease in importance towards the top of the section, and the wackestone/packestone with abundant orbitolinids takes its place showing a decrease in water depth. The Gorge

42


Fig. 9 Schematic representation of the distribution of the palaeoenvironments from Vadu Crişului area across Barremian-Early Aptian. The same legend as in Fig. 5.

Entrance section and the Tunnel section end with a slight shallowing upward trend. In the longest section, which is Canton CFR, the relative water depth is fluctuating on the last 50 m. After a shallowing trend which corresponds with the end of the other two sections, it ends with a deepening trend. The onset of the facies with Palorbitolina lenticularis marks the incipient drowning of the shallow carbonate platform. In the Gorge Entrance Section and Canton CFR Section this incipient drowning event is not that well marked, but there is a clear evidence of the change from shallow water facies to deeper ones. Common criteria used by marine geologists and biologist to distinguish between "shallow" and "deep" water environment are the shelf-break and the lower boundary of the well-illuminated zone (Flugel, 2004). Today the shelf break lies at an average depth of 150 m, being the result of the last 2 million years climate conditions, and the deposits it is made of. It was suggested that the shelf break was around 30 m depth before the extensive Cenomanian transgression as it is today off the coast of southern Florida (Hay & Southam, 1977, Hay, 2008). This involve that the interaction between shelf environments and open-ocean environments are very sensitive to sea-level changes (Hay, 2008). The negative excursion on δ13 C curve constructed by Papp et al. (2013) could be the result of the exposure of the inner platform and incipient paleosoil formation revealed by this study inside Blid Formation. This depletion in δ13 C can be the result of fresh water runoff, evaporation, cementation under meteoric condition and paleosoil formation (Patterson & Walter, 1994).

DISCUSSIONS The deposits analyzed are part of the so called "Urgonian facies". This facies started to develop in Pădurea Craiului Mountains at least from the Lower Barremian. The incipient paleosoil or abundant charophyte remains show the emersion of part of the platform and in consequence they are good candidates for sequence boundaries. Unfortunately parts of the outcrops are covered or discontinuous throughout Pădurea Craiului Mountains which make difficult the separation of depositional sequences. The relatively poor biostratigraphic control make correlation of the exposure surfaces with other studies from the Tethys speculative. The Late Barremian drowning event was also reported from the Provence region in France (Masse & FenerciMasse 2011) and to some extent in Turkey (Masse et al. 2009) and the South Carpathians (Barragán & Melinte, 2006). As depositional sequence boundary can be difficult to recognize in outcrops, cores and logs it was suggested that maximum flooding surface is a better marker and should be taken as possible sequence boundary (Galloway, 1989). The maximum flooding surface is recognized on seismic reflection sections as the reflector with the most landward penetration and is commonly associated with the deepest water or condensed section which make it observable in logs, cores and outcrops (Allen & Allen, 2005 and reference therein). In this respect the maximum flooding surface can be a useful tool in correlation (Masse & Fenerci Masse, 2011). 43


CONCLUSIONS The Barremian-Early Aptian deposits from the northern part of Pădurea Craiului have been analyzed from a sedimentological and biostratigraphic point of view. The analysis of the Barremian-Early Aptian deposits from the northern part of the Pădurea Craiului Mountains revealed eight main microfacies types belonging to a shallow water carbonate shelf or, possibly a carbonate ramp during the facies with abundant Palorbitolina lenticularis. The lower part of the sections is made of peritidal carbonate deposits that formed extended tidal flats with frequent ephemeral exposures surfaces. The presence of Microcodium and other pedogenic features evidence the relative fall in sea-level during Barremian. The upper part indicates a deepening event. The facies with Palorbitolina lenticularis mark the beginning of this transgression (in Canton CFR Section occur from the middle part) that led to the incipient drowning of the platform and to the installation of the Aptian conditions. During the main transgression a short-term deposition of limestones with abundant sponge spicules and cherts occur in the Tunnel Sections. The presence of Preorbitolina cormyi in the upper part of the studied sections is a strong argument for the Early Aptian age of their upper limit. Preorbitolina cormyi occurs just a few meters (2-3 m) above the FO of the Palorbitolina lenticularis. This suggests that the FO of Palorbitolina lenticularis in the Pădurea Craiului Mountains is very close to the Barremian-Aptian boundary. ACKNOWLEDGEMENTS We thank the two reviewers, Boguslaw Kolodziej and Emanoil Săsăran for their remarks which contributed to the improvement of the paper. We also thank Carles Martin Closas (Barcelona) for the enlightening discussions and information related to charophytes and Microcodium. REFERENCES Allen, P. A. & Allen, J. R., 2005. Basin Analysis: Principles and Applications. Blackwell Publishing, Oxford, 549 pp. Alonso-Zarza, A. M., 2003. Palaeoenviromental significance of palustrine carbonates and calcretes in the geological record. Earth Science Reviews, 60: 261-298. Arnaud-Vanneau, A., 1975. Reflexion sur le mode vie de certains Orbitolines du synclinal d'Autrans (Vercors septentrional). Geologie Alpine, 44: 25-48. Arnaud-Vanneau, A., 1980. Micropaléontologie, paléoécologie et sédimentologie d’une plate-forme carbonatée de la marge passive de la Téthys. Géologie Alpine, Mémoire 11, 874 pp. Arnaud-Vanneau, A., Arnaud, H., 1990. Hauterivian to Lower Aptian carbonate shelf sedimentation and sequence stratigraphy in the Jura and Northern Subalpine chains (southeastern France and Swiss 44

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