Palynological Characterization of a Transgressive Episode Intransitional Deposits in the Cretaceous Aren and Tremp Formations (South-Central Pyrenees, Spain)

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Palynological characterization of a transgressive episode intransitional deposits in the Cretaceous Aren and Tremp formations (South-Central Pyrenees, Spain)

Article in Neues Jahrbuch für Geologie und Paläontologie - Abhandlungen · January 2012 DOI: 10.1127/0077-7749/2012/0291

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Angelica Torices Maria Teresa Fernández-Marrón Universidad de La Rioja (Spain) Complutense University of Madrid

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Palynological characterization of a transgressive episode in transitional deposits in the Cretaceous Aren and Tremp formations (south-central Pyrenees, Spain)

Angélica Torices, María-Teresa Fernández-Marrón, Fernando Fonollá, and Nieves López-Martínez

With 6 figures

Nieves Lopez-Martinez initiated this study and was its driving force up to her premature death. The co-authors dedicate this paper to her memory.

Torices, A., Fernández-Marrón, M.-T., Fonollá, F. & López-Martínez, N. (2012): Palynological characterization of a transgressive episode in transitional deposits in the Cretaceous Aren and Tremp formations (south-central Pyrenees, Spain). – N. Jb. Geol. Paläont. Abh., 266: 159–172; Stuttgart.

Abstract: The overall marine regression leading to the infilling of the Cretaceous Pyrenean basin was punctuated by transgressive episodes. These events produced a complex architecture in the interfingering deposits in the marine Aren and continental Tremp formations in south-central Pyr- enees. The Vicari section is useful for studying the lateral change between these marine-continental deposits bearing fossil vertebrates and pollen. In this section, palynological changes reveal in detail transgressive and regressive events in the lower part of the continental Tremp Formation, which could not be detected otherwise by non-correlated lithological changes. A rapid regression is documented through the contact between the lower Aren and Tremp deposits: in-situ dinosaur egg clutches and other vertebrate remains are preserved with terrestrial palynomorphs indicating warm humid palaeoclimatic conditions (tree ferns, cycads, etc.). Furthermore, palynological content, rich in marine phytoplankton, reveals a transgressive episode in the upper grey marls in the Tremp Formation.

Key words: Upper Cretaceous, South-central Pyrenees, vertebrates, palynology, marine transgression.

1. Introduction aeoenvironments along the Cretaceous-Tertiary transition by means of sequence stratigraphy, biostratig- South-Pyrenean Upper Cretaceous deposits contain raphy and magnetostratigraphy on correlated marine abundant biotic (foraminifera, molluscs, vertebrates and continental formations (Salas Marls, Aren Sand- and plants) and sedimentary indicators to document stone and Tremp red beds) (Déramont et al. 1993; in detail the palaeoenvironment and palaeoclimatic Vicens et al. 1999, 2001, 2004; Ardèvol et al. 2000; changes registered in the ancient coastlines of the López-Martínez et al. 2001; Díaz Molina et al. 2007; Pyrenean Cretaceous basin during its last infilling epi- Oms et al. 2007). sodes. These deposits allow an accurate chronologi- The South Pyrenean Central Unit is one of the larg- cal framework of environmental and climatic changes est Pyrenean tectonic structures formed by detached to be established in both marine and continental pal- cover of the Pyrenean Orogen and contains the thickest

Fig. 1. Geological map of the Pyrenees and the Tremp syncline, with the location of the Vicari section and its detailed geological map: 1 – offshore marls and 2 – shoreface sandstones from the Aren Fm lower unit; 3 – transgressive calcarenites from the Aren Fm upper unit; 4 – Tremp Fm grey marls; 5 – Tremp Fm red lutites; 6 – covered. E – dinosaur eggs and eggshells; R – rudists belonging to the H. castroi horizon; W-C-E mark the position of the stratigraphic logs in Fig. 3.

succession of transitional marine-continental depos- be clearly observed. The marine-continental transition its within the Cretaceous-Tertiary transition. On the in this area is indicated by the micro- and macrover- northern flank of the Tremp Syncline, the sedimentary tebrates preserved at several localities (Buscalioni et succession has been extensively studied due to its ex- al. 1986; López-Martínez et al. 1996; Torices 2003). ceptional outcrops, which enable the documentation of The objective of this paper is to present a new overall marine regression since the Late Cretaceous. palynological record from the lower part of the Tremp Several of these works outline the complex interfinger- Formation, documenting the presence of marine paly- ing relations between the two main lithostratigraphic nomorphs in these red beds. These data allow us to in- units, namely, the Aren and Tremp formations, record- fer a previously undetected transgressive episode and ing the end of the Cretaceous marine basin in this area the palaeoenvironmental and palaeoclimatic changes (Nagtegaal et al. 1983; Diaz Molina 1987; Mutti & that took place at the end of the marine Cretaceous Sgavetti 1987; Déramont et al. 1993; Ardèvol et al. basin in the South-Central Pyrenees. 2000; Guillaume et al. 2008). The Vicari section, in the northern flank of the 2. Geological setting Tremp Syncline, is an east-west oriented outcrop where the interfingering architecture between marine The Tremp Syncline, where the Vicari section is locat- Aren sandstones and continental Tremp red beds can ed, is a major east-west oriented structure in the cen- Palynological characterization of a transgressive episode in transitional deposits 161

Fig. 2. Correlation chart between the uppermost Cretaceous and lowermost Tertiary marine (blue-clear)and continental (red-dull) deposits in southern Pyrenees, including the location of three main rudist horizons and the Vicari section. K/T – Cretaceous-Tertiary boundary; MPU – Mid-Paleocene unconformity; P/E – Paleocene-Eocene boundary. S1/S2 sequence boundary; data from Robador 2005; Vicens et al. 2001, 2004, and Oms et al. 2007; dating of the upper rudist horizon B. chapperi has been modified according to magnetostratigraphic data (see text; Oms & Canudo 2004; Pereda-Suberbiola et al. 2009).

tral part of the South-Pyrenean Central Unit (Séguret numerous existing publications and summarized in 1972; Fig. 1). The Tremp Syncline forms part of the Fig. 2. Marine Aren Fm is exclusively present in Cen- Montsec Unit and is bounded to the north by the Abel- tral Pyrenees, while continental Tremp Fm extends la-Boixols Anticline, which forms part of the Boixols along central and eastern Pyrenees. Both formations Unit (Ardèvol et al. 2000). change laterally to distal marine deposits in the west- The Vicari section is a 400 m-wide area, where a ern area of the South Pyrenean Central Unit and all N-S oriented ravine cuts across the contact between along western Pyrenees, where the Marboré Fm con- the marine Aren Formation and the non-marine Tremp stitutes a lithological unit analogous to Aren Fm (Ar- Formation. These formations have been described in dèvol et al. 2000; Robador 2005; Oms et al. 2007). 162 A. Torices et al.

Fig. 3. Correlation panel along an E-W transect in the Vicari section. The location of vertebrate fossil localities and palynological samples is indicated in the stratigraphic logs.

In south-central Pyrenees, time-transgressive clas- er, the stratigraphic correlation and dating previously tic deposits in the Aren Fm (calcarenites and hybrid proposed need to be modified on the basis of further arenites) prograde north-westwards (basinwards) over magnetostratigraphic data from the intermediate Riba- the Salas offshore marls, while the lower part of the gorzana section (Oms & Canudo 2004; Pereda-Suber- Tremp Fm (grey marls limestone from unit 1 and red biola et al. 2009). According to these data, the age of clastics from unit 2) prograde from south and east the Vicari section also includes the Maastrichtian (Fig. (landwards) over the Aren Fm (Diaz Molina 1987; 2). Eichenseer 1988; Ardèvol et al. 2000; Díaz Molina The Vicari section represents just one of several et al. 2007). The Aren Fm ends below the Cretaceous- episodes in which Aren shoreface deposits overlie Tertiary boundary, when the upper part of the unit 2 coastal Tremp red beds as both formations prograde of the Tremp Fm to the west it changes to the ma- north-westwards (Díaz Molina 1987; Ardèvol et al. rine Laspún Fm (Campo section) and expands across 2000). south-central Pyrenees (López-Martínez et al. 2006; Fig. 2). 3. Stratigraphy The age of these formations in the Vicari section was dated as Late Campanian through lateral corre- Vicari is a good example of the way the Aren and lation of rudist horizons to basinal deposits bearing Tremp formations change laterally relative to one an- planktonic foraminifera in a more north-western loca- other. In this area, the lower part of the Tremp Forma- tion (Campo section in the Esera Valley, see Fig. 1; tion appears sandwiched between two units of the Aren Ardèvol et al. 2000; Vicens et al. 2001, 2004). Howev- Formation. This relationship is shown in the east-west Palynological characterization of a transgressive episode in transitional deposits 163 cross-section shown in Fig. 3, where five logs – named tion (Level 1 in Fig. 3) is composed by 0.40 m of dark E, C and W1-3 – are correlated along a nearly continu- fossiliferous marls, rich in organic matter, in which ous 400 m-long transect. A more general stratigraphic microvertebrate remains (fish scales, teeth of fish, view of the interfingering relationships between the theropod dinosaurs and crocodiles, eggshell frag- two formations is presented in Fig. 2. ments) were found after sediment washing and pick- ing (Vicari 4 microvertebrate site). This level mainly Aren Fm, lower unit: The base of the stratigraphic appears in the easternmost area of the section (log E in logs is located over a thick clastic succession in the Fig. 3) and also contains the V-0 palynological sample. Aren Formation (lower unit) and is composed of clean, The second level (Level 2) is composed of grey mature, mixed carbonate-cemented shoreface-to-near- marls with two intercalated compact levels of nodular shore arenites with rudists belonging to the H. castroi marly limestones. This level is present in the whole horizon and grey offshore marls with inoceramids (see area but both its thickness and aspect are strikingly detailed map in Fig. 1). The top of the lower unit of the variable. It is 6 m thick in its easternmost section, Aren Formation is composed of middle-grained hybrid quickly becoming around 20 m thick in the central log arenites modified by reddish-ochre mottling and iron of the section and thinning out westwards. The two crusts containing abundant dinosaur eggshell frag- nodular levels can be correlated westwards across the ments and in situ egg clutches. These features clearly cross section, clearly showing their edaphic origin document the emergence and aerial exposure of the through their enrichment with root casts and pedog- top of the upper unit of the Aren Sandstone, similar enetic features in its western area. The lowermost cal- to the more ancient egg-bearing Aren deposits in the careous palaeosoil pinches out between the W1 and eastern Bastus sites, which formed beach ridges colo- W2 logs and changes laterally to a cemented body of nized by nesting dinosaurs (Sanz et al. 1995; López- the Aren Sandstone in the western W1, W2 and W3 Martínez 2000; Díaz Molina et al. 2007). The iron- logs, while the uppermost palaeosoil sits directly on stained top of the lower unit of the Aren Formation top of this Aren Fm body and finally disappears within is immediately overlaid by the marls and clays of the the Aren Sandstone in more westward settings. The lower part of the continental Tremp Formation, where cemented sandstone body appears in log W1 interca- the new palynological succession was sampled. These lated between two palaeosoils, pinches out eastwards continental sediments are overlaid by a new Aren For- and changes laterally westwards to the main Aren Fm mation marine unit (upper unit). lower unit, which occupies a higher stratigraphic position in the westernmost logs. Fig. 4 shows a field view Tremp Formation: Tremp Fm deposits in the Vicari of this lateral facies change between both formations section, around 40 m thick, represent just a thin por- at these levels. tion of the Tremp Fm, which reaches over 900 m thick- The aspect and thickness of the third level (Level ness in the whole Tremp Syncline and extend to Early 3) is much more continuous along the whole section. Eocene in age. Tremp Fm deposits generally thicken It is composed of 8.40 m of purple marls. This purple south-eastwards and thin out north-westwards (Vicens marly level has an intercalated reddish sandstone level et al. 2001; López-Martínez et al. 2006). In the local (0.40-1 m-thick), with hummocky stratification. Vicari succession, the Tremp Fm lower part thins out The fourth level (Level 4) shows 2.80 m of white westwards and continues with a much reduced thick- soft limestone forming a powder similar to wheat flour. ness for more than 7 km north-westwards of this area. It is present in the eastern and western areas, and also In the Vicari section, the succession of the Tremp probably in the central part, although invisibly, since it Fm lower part changes notably from east to west. is covered by debris in most of the outcrop. Tremp Fm deposits in the Vicari section have a par- ticular architecture, forming a local furrow or lens- Aren Formation, upper unit: Tremp Formation soft shaped geometry (Fig. 3). This is apparently due to sediments are capped by a well-cemented calcarenitic a lateral facies change complicated by some synsedi- deposit in the Aren Fm upper unit (Figs. 1, 3), formed mentary normal faults visible in the contact between by marine calcarenites and sandy limestones showing the Aren and Tremp Fms. These faults appear lined by wackestone-packstone texture and wavy cross stratifi- iron crusts and have a different orientation (E80) from cation. These sediments contain foraminifera (miliol- the younger dextral fault network (E110). ids and other uni- and biserial benthic foraminifera), The first level of the Tremp Fm in the Vicari sec- mollusc fragments (gastropods), algae and peloids. In 164 A. Torices et al.

Fig. 4. Field view of the western Vicari area (log W2), showing the lateral change between Tremp Fm soft deposits on the left, with the two indurate paleosoil levels, and the cemented Aren Sandstone on the right, connected to a thin sandstone body intercalated within the Tremp Fm. Palynological characterization of a transgressive episode in transitional deposits 165 its lower part, a thin level of coarse quartzose sands ours may be due to different draining conditions in the with plant remains, about 10 cm thick, can be observed lagoon. The grey colour in the lower marls indicates a in the westernmost Vicari logs (Fig. 3), which may higher content of organic material and deficient drain- represent a transgressive lag deposit previous to the ing, while the purple colour in the upper marls indi- widespread deposition of shelf calcarenite deposits. cates better drainage, lower content of organic matter Unlike the top surface of the Aren Fm lower unit, and oscillating water-table conditions (Kraus 2001). the top surface of the shelf deposits of calcarenites apparently shows no exhumation or modification signs: 5. Vertebrate samples the Tremp Fm upper part (units 2-4), with marls, red claystones and sandstones, directly overlies the Aren Aside from the egg clutches and eggshell fragments Fm upper unit. This unit reaches about 10 m thickness preserved in the top surface of the Aren Fm lower unit in the Vicari area (not represented in the logs) and in the Vicari section, there are two main vertebrate- pinches out about 500 m eastwards from the Vicari bearing levels in Tremp Fm deposits: one composed section, disappearing into the covered Tremp Fm soft of microvertebrate remains (Vicari 4, V-0 in palyno- sediments (Fig. 1). logical samples) and another composed of macrore- mains (Els Nerets, V-2B palynological sample). Tremp 4. Interpretation Fm vertebrate fossils (bones, scales, teeth, eggshells) were only recorded in the grey level. Remains of Different sedimentological interpretations of the Aren fishes, crocodiles Acynodon ( , Allodaposuchus prec- and Tremp Fms have been proposed, ranging from lit- edens), unidentified turtles, titanosaurid sauropods, toral (Diaz-Molina et al. 2007) to fluvio-deltaic A( r- ornithopods (Hadrosauridae indet., Iguanodontidae devol et al. 2000) and to alluvial settings, because indet.) and theropods (Coelurosauria indet., cf. Rich- some previous research has shown that the concentra- ardoestesia indet.) have been found in these two sites, tion of dinosaur egg clutches and eggshell fragments (Buscalioni et al. 1986; 2001; Casanovas et al. 1987, is greater in alluvial deposits (Escuer et al. 2003; Van 1988; Brinkmann 1988; Pereda 1999; Canudo & Itterbeeck et al. 2004). We favour alternate interpre- Ruiz-Omeñaca 2003; Royo-Torres & Canudo 2003; tations of a barrier island and lagoon system to explain Torices et al. 2004; Torices 2007). All these remains the formation of these deposits (Nagtegaal et al. 1983; indicate a diverse and rich vertebrate fauna mainly Díaz Molina 1987; Díaz Molina et al. 2007). Accord- composed of various terrestrial dinosaurs, probably ing to this model, the Aren Sandstone was formed inhabitants of the coastal plain and barrier islands, and by shelf currents along longitudinal marine shelves by some non-marine or coastal fishes and crocodiles which formed barrier islands in coastal settings, while which are likely to have inhabited the lagoonal setting Tremp Fm deposits were formed in marginal-marine and distributary channels. These vertebrates lived in and coastal lagoons settings, protected from waves by landscapes with rich vegetation, based on the presence those swells. The palaeosoils, crust and iron nodules of sediments rich in organic matter and palaeosoil de- observed on top of the Aren Sandstone correspond to velopment, as well as from the palynological record alteration processes due to the emersion and subaeri- described below. al exposure of the sands forming barrier islands and beaches, while the grey and purple marls in the lower 6. Palynological samples part of the Tremp Formation represent the backbarrier lagoonal deposits in the coastal plain. Nine samples belonging to the Tremp Fm deposits Tremp Fm lagoonal sediments thin out both north- from the Vicari area were studied to determine the and westwards (basinwards), which correspond to the palynological assemblages and palaeoenvironmental regional progradation directions of continental depos- evolution of this succession. Six of them correspond its over marine deposits (Nagtegaal et al. 1983; Diaz to the grey level, one to the boundary with the pur- Molina 1987). In the Vicari section, as well as in other ple level, and two of them from the purple marls. The outcrops, the marls in the lower part of the Tremp Fm whole sample comprises 179 identified taxa, including are divided into two different coloured levels: A) a 96 types of fern and moss spores, 33 types of gym- lower level of grey marls (levels 1 and 2) with interca- nosperm pollen, 14 angiosperm types, 16 cyst types lated palaeosoils, and B) an upper level of purple marls from Zygnemataceae algae, 17 types of dinoflagellate with intercalated thin sandstones. These different col- cysts and 3 types of prasinophyte algae (Figs. 5, 6). 166 A. Torices et al.

Fig. 5. 1 – Cyathidites australis Couper, V-0; 2 – Matonisporites equiexinus Couper, V-0; 3 – Cicatricosisporites sp., V-2; 4 – Biretisporites potoniaei Delcourt & Sprumont, V-1b; 5 – Leiotriletes dorogensis Kedves, V-2; 6 – Leiotriletes adriennis (Pot & Gell.) Krutzsch, V-1; 7 – Gabonisporis vigourouxii Boltenhagen, V-1; 8 – Acanthotriletes sp. V-0; 9 – Retitriletes austroclavatidites (Cookson) Doring et al. , V-0; 10 – Zlivisporis sp., V-2; 11 – Echinatisporis cycloides Krutzsch, V-0; 12 –Ischyosporites scaberis Cookson & Dettman, V-2b; 13 – Verrucatosporites alienus (Pot.) Thomson & Pflug, V-1b; 14 – Laevigatosporites sp., V-0; 15 – Echinatisporis longechinus Krutzsch, V-1; 16 – Cycadopites carpen- teri (Delcourt & Sprumont) Singh, V-4b; 17 – Polyplicate pollen aff. Ephedripites sp., V-1b; 18 – Pityosporites sp., V-3; 19 – Pinuspollenites ruginosa (Stanley) Oltz, V-2b; 20 – Araucariacites australis Cookson, V-0; 21 – Ovoidites cyclus Krutzsch, V-0; 22 – Ovoidites parvus (Cookson & Dettman) Nakoman, V-0; 23 – Ovoidites ligneolus (Pot.) Potonié, V-0; 24 – Ovoidites sp., V-1; 25 – Subtriporopollenites cf. constans Pflug, V-0; 26 – Subtriporopollenites cf. constans Pflug, V-5b; 27 – Oedogonium cretaceum Zippi, V-3; 28-30 – Algal cysts of dinoflagellates, V-3; 31 – Foraminiferal test lining, V-3. –Scale bar 50 μm. Palynological characterization of a transgressive episode in transitional deposits 167

Fig. 6. Palynological diagrams (abundance on the left and diversity on the right) of the successive samples of the Tremp Fm, lower part, in the Vicari section and relative curve of the transgressive and regressive cycles based on palynological content and sedimentological data.

Additionally, there are non-plant microfossils includ- to Juglandaceae (Subtriporopollenites), Ulmaceae ing foraminfera, scolecodonts, and fungi. (Rugulitriporites), Compositae (Compositoipollenites) Sample V-0 is the lowest palynological sample lo- and others. Palm pollen and Normapolles (Papillopol- cated in Level 1, immediately above the contact be- lis) have also been identified although at much lower tween the Aren and Tremp Fms, and corresponds to frequency than in the La Posa section, which is geo- the Vicari 4 site with microvertebrate remains (see graphically near Vicari and similar in stratigraphic above). V-0 is very rich in palynomorphs: abundant position (De Porta et al. 1985). gymnosperm grains (43% of total sample) mainly cor- Some zygospore cysts are also present, although responding to Cycadales/Ginkgoales (i.e., thermophil- they are less abundant than in V-0. Ovoidites ligneo- ous flora components). Spores reach 28% of total iden- lus (Pot.) Potonié is the predominant taxon, attributed tified microfossils, showing considerable taxonomic to Zygnematacea algae and very similar to the extant diversity (54% of identified taxa in the sample).Laevi- genus Spyrogira (Batten et al. 1994). gatosporites is the predominant genus. Abundant (26 The abundance of pteridophyte spores in these %) zygospores of fresh or brackish water algae (Ovoid- assemblages suggests the presence of humid forests ites and Schizosporis) also appear (Fig. 6). and biotopes with hydrophilic components (Schrank Samples V-1, V-1b, V-2 and V-3 come from Level 2 1994). The high amount of Cycadales/Ginkgoales in the Tremp Fm deposits, in the upper part of the grey pollen grains and the abundance of large and heavily- level. Sample V-2B corresponds to the Els Nerets mac- ornamented fern spores, typical of undergrowth, sug- rovertebrate site. Spore-pollen composition is similar gest humid and warm, non-marine environments for in samples V-1, V-1B, V-2 and V-2B although 1B and these samples. The abundance of Cyathidites spp. and 2B are poorer and the last sample shows a decrease of the presence of Concavissimisporites spp. suggest wet spores and an increase of conifer pollen. Spores from conditions within humid environments (Mahmoud & ferns (mainly Schizaeaceae, Cyatheaceae, and Polypo- Moawad 2002). The great diversity and large number diaceae) and lycophyta are dominant. Non-saccate pol- of recovered palynomorphs suggests this area was len conifers are very abundant, attributed to Araucari- heavily vegetated. acites sp., reaching up to 33% of total pollen grains. The V-3 sample, near the top of the grey level, Angiosperm pollen grains are scarce in all levels, ex- clearly differs from the other palynological samples. cept in the lowermost V-1 sample. They correspond It is rich in palynomorphs, but has a lower diversity 168 A. Torices et al. than the previous samples. Inaperturate and bisac- complement each other, allowing us to complete a rela- cate conifer pollens represent 25%, of the assemblage tive curve of transgressive-regressive events through and Cycadals/Gynkgoales are less than 5%; pterido- this succession. phyte spores are scarce (below 2%) and aquatic paly- Lithologically, the Tremp Fm can be differentiated nomorphs are predominant, mainly from freshwater into lower grey marls (V-0 to V-3) and upper purple algae (30%, Ovoidites, Oedogonium, Schizosporis) marls (V-4 and V-5). The upper part of the Aren Fm marine algae (12%, Tasmanites, Leiosphaeridia) and overlaps. Dinoflagellate cysts (30%) (Figs. 5-6). Remains of In terms of transgressive-regressive trends, a sedi- foraminifera internal chambers were also found. The ment-based interpretation of the complete Vicari suc- large amount of anemophilous pollen, planktonic ma- cession suggests two episodes: rine algae and dinoflagellate cysts in this sample and 1) A general regression starting at the top of the the scarce number of spores suggest that the beds con- lower Aren unit, gradually increasing along the Tremp cerned were deposited in a marginal marine environ- Fm grey marls and reaching its maximum peak at the ment (Li et al. 2008). Tremp Fm purple marls. Above the marine sample V-3, sample V-3B (lo- 2) A transgressive trend, starting from the base of cated in the contact between the grey and purple the white limestone (Tremp Fm) up to the clastic lag levels) and samples V-4B and V-5B (from the purple deposit, reaching its maximum peak at the Aren Fm marls) have few palynomorphs and contain no marine upper unit. microfossils, unlike sample V-3. These spore-pollen However, these lithological differences do not cor- assemblages also preserve Cycadales/Ginkgoales. relate with the palynological content. This fact has Particularly, sample V-4B shows the lowest diversity similarly been observed in the palynological study of the whole section: nearly all grains, except some across the Cretaceous-Tertiary boundary in North gymnosperm-attributed grains, correspond to Zyg- America (Bercovici et al. 2009). nemataceae zygospores, mainly of Lecaniella. These Palynological content indicates that the interpreta- algae are similar to recent Debarya and Zygnemopsis tion based on lithological data only must be modified, green algae. separating the Tremp Formation into three parts rather than two: the lower part of the grey marls (samples V-0 7. Discussion to V-2B), the upper part of the grey marls (sample V-3) and the purple marls (samples V-3B, V-4B and V-5B). The abundance and diversity of the palynological com- Fig. 6 summarizes the pollen profile, according to the position in the Vicari samples is dominated by fern modified guidelines established by Lister & Batten and moss spores, reaching around 60% of the com- (1988). These data allow a relative curve of transgres- ponents in 5 out of the 9 samples. This composition sive and regressive episodes to be built, drawn at the and diversity is similar across most Pyrenean samples right-hand side of Fig. 6. from different sections of the non-marine Tremp Fm According to these data, transgressive-regressive and other examples from the Campanian-Maastrich- trends can be separated in four episodes: tian of the Pyrenees (Fernández-Marrón et al. 2004a; 1) A regressive episode is supported by the con- López-Martínez et al. 2006). tent of V-0 to V-2B samples. These samples show high In the Pyrenean region, a decrease in plant diversity abundance and diversity of large autochthonous pteri- around the Early Maastrichtian has not been observed, dophyte and briophyte spores, indicating a clear ter- in contrast with other Old World regions (Stets et al. restrial origin and proximity of the plant producers. 1996; Markevitch et al. 2000). This is in contrast with the dominance of aquatic ele- The palaeontological content in the Vicari section ments in middle and upper palynological assemblages. provides important new information for interpreting Significantly, vertebrates are only present in the lower the changing palaeoenvironmental and palaeoclimatic part of the grey marls (Vicari 4 = V-0 and Els Nerets = conditions during the Campanian-Maastrichtian tran- V-2B). Therefore, the Tremp Fm lowermost part, close sition in the south-central Pyrenees. The differences to the contact with the beach ridges marine deposits observed in the composition of the palynological as- of the Aren Fm, contains the most diverse fossils from semblages do not correlate with the lithological dif- terrestrial environments, indicating a very rapid major ferences observed in the Tremp Fm succession. There- regressive event. fore, both sedimentological and palaeontological data 2) A transgressive episode can be inferred due Palynological characterization of a transgressive episode in transitional deposits 169 to the palynological content of V-3 sample from the arid climatic conditions. However, another interpreta- upper part of the grey level that shows a significant tion is also possible and even likely within the context change in composition. It is dominated by remains of of the upper samples in the Vicari section: Zygospore planktonic organisms from saline waters (dinoflagel- cysts are among the most resistant palynomorphs to late, prasinophyte cysts, and microforaminifera). This oxidizing conditions (Zippi 1998), since they are cov- sample is significant due to its high number of grains. ered by a thick chemically resistant wall of extremely Pteridophyte spores suffer a significant decrease and durable material (Head 1992). When they are domi- pollen of Cycadales/Gynkgoales a moderate decline, nant in otherwise very poor samples such as sample while dinocysts, zygospore algae and bisaccate pol- V-4B, their abundance may be attributed to taphonom- len of conifers increase. This composition represents a ic factors such as the increased oxidizing conditions in previously undetected transgressive episode, recorded these purple levels, which might have destroyed other well below the shelf deposits of calcarenites from the less resistant palynological grains. Oxidation proc- Aren Fm upper unit (Fernández-Marrón et al. 2004b). esses prevent the preservation of organic remains and The relative increase of bisaccate pollen observed widely affect the preservation of sporopollenin, which in this sample can be related to its distal position, undergoes intense degradation due to the action of at- where only aerial conifer pollen reached the area. mospheric oxygen (Batten 1996, 1999; Martin Clo- Conifers are also very resistant to aridity saline condi- sas & Gomez 2004). This selective alteration would tions in marginal marine environments (Prauss 2001). explain, in this and some other cases, palynological 3) A new regressive episode is documented by the samples containing abundant zygospore cysts within palynological composition of the upper samples from oxidizing palaeoenvironments. the oxidized purple level (V-3B, V-4B and V-5B). In spite of their poor content, these samples indicate more 8. Conclusions proximal conditions than the previous V-3 sample. 4) The last episode of this succession corresponds The Vicari palynoflora is closer to the Maastrichtian to the main transgression event represented by the shelf Gondwanan samples (e.g. El Kef, Méon 1991) than to deposits of calcarenites in the Aren Fm upper unit. the Campanian-Maastrichtian ones from North Euro- Most Vicari samples show a noticeable ratio of pean subprovince (Batten & Li Wenden 1987) (e.g. zygospore cysts attributed to fresh-or brackish Zygne- Gulpen and Maastricht Fms., Kedves & Herngreen mataceae algae, an unusual component in Tremp Fm 1980; Herngreen et al. 1986, 1998). The African (north palynological associations which had not been recov- Gondwanan) and Pyrenean palynological assemblages ered in other previous palaeobotanical studies on the share the abundance of Cycadopites and Monosul- Pyrenean upper Cretaceous-lower Tertiary deposits cites, the presence of Gabonisporis, and the rarity of yet (Médus 1970a, b, 1972; Médus et al. 1992; Mayr Normapolles, in contrast to the North-European ones. et al. 1999; Fernández-Marrón et al. 2004a,;López- The Vicari section studied here allows the observa- Martínez et al. 1999, 2006) even from the rich sam- tion in detail of the lateral change between the marine ples of La Posa (De Porta et al. 1985) and Coll de Aren Fm and the lower part of the continental Tremp Nargó (Ashraf & Erben 1986; Upper Campanian, Fm. This succession based on lithology and palaeonto- lower unit 1, Tremp-Fm). However, Head 1992 warns logical content (vertebrates and palynomorphs) is here about difficulties in the identification of these remains, interpreted in terms of transgressive-regressive cycles which can be easily overlooked when they are scarce. and palaeoenvironmental conditions. In any case, their abundance along the whole succes- The palynological composition of Vicari deposits sion in the Vicari section is notable. thus shows a clear and unexpected palaeoenvironmen- The high number of Zygnemataceae cysts in the tal evolution along the deposition of the lower Tremp Vicari Section in otherwise very poor palynological Fm. Instead of a gradual regressive trend as suggested assemblages, needs further explanation. These fresh- by the lithology alone, the palynological composition water algae are usually associated with a wide range shows a quick regression at the very beginning of the of other taxa from warm and wet environments such Tremp deposits (which contain abundant terrestrial as Cycadaceae and ferns. The presence of only zy- plants and vertebrates) followed by a dramatic trans- gospores has been interpreted as the result of droughts gression near the top of the lower grey level and then, affecting the freshwater lakes where these algae might finally, another regression with different oxidizing have proliferated (Zippi 1998), thus suggesting semi- conditions before the major transgression represented 170 A. Torices et al. by the overlying Aren Fm upper unit. These results J.V. (1986): An Eusuchian Crocodile from the Upper have implications for regional studies on sequence Cretaceous of Spain (Vilamitjana, province of Lleida). – stratigraphy and for global correlations of transgres- Journal of Vertebrate Paleontology, 6: 209-214. Buscalioni, A.D., Ortega, F., Weishampel, D.B. & Jianu, sive and regressive cycles. C.M. (2001): A revision of the crocodyliform Alloda- posuchus precedens from the Upper Cretaceous of the Hateg Basin, Romania. Its relevance in the phylogeny Acknowledgements of Eusuchia. – Journal of Vertebrate Paleontology, 21 (1): 74-86. Funds were provided by projects CGL 2006-04646 and Canudo, J.I. & Ruiz-Omeñaca, J.I. (2003): Los restos direc- CGL 2009-09000 (Spanish Ministry of Education and Sci- tos de dinosaurios terópodos (Excluyendo Aves) en Es- ence and the Ministry of Science and Innovation) and Re- paña. – In: Pérez-Lorente, F. (Ed.): Dinosaurios y otros search Group no. 910161, Registro geológico de períodos reptiles mesozoicos de España. – Instituto de Estudios críticos: factores paleoclimáticos y paleoambientales (Uni- Riojanos, 26: 347-373. versidad Complutense de Madrid, Autonomous Community Casanovas, M.L., Santafé, J.V., Sanz, J.L. & Buscalioni, of Madrid, Spain). We acknowledge the help of many field A.D. (1987): Arcosaurios (Crocodilia, Dinosauria) del geologists, particularly E. Vicens (Universidad Autonoma Cretácico superior de la Conca de Tremp (Lleida, Spain). de Barcelona), L. Ardèvol (Geoplay, Tremp), O. Kälin, M. – In: Sanz, J.L. (Ed.): Geología y Paleontología (Arco- Díaz-Molina, M. I. Benito (UCM), A. Robador (IGME) saurios) de los yacimientos de Galve (Teruel, Cretácico and M. Soler Sempere. Authors thank Günter Schweigert, inferior) y Tremp (Lérida, Cretácico superior). – Estu- an anonymous reviewer for comments and suggestions, and dios Geologicos, Vol. extr., 95-110. 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