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1. Introduction
The evolution of Iberia during the Upper Permian and Mesozoic can be divided into three rift cycles and post-rift stages. The rift cycle corresponding to the Late Permian–Triassic, mainly affected the eastern part of the Iberian plate giving rise to basins that were filled with sediments attributed to the Germanic facies during the late Permian and Triassic times [Ramos et al. 1996, Salas and Casas 1993, Salas et al. 2001].
In Iberia, the Triassic stratigraphic record can be subdivided into the three parts, from the base to the top: Buntsandstein facies (continental clastic sediments and red beds), Muschelkalk facies (marine carbonates, evaporites and red beds) and Keuper facies (tidal and sabkha deposits) [Calvet et al. 1990, Virgili et al. 1983].
In the Triassic Catalan basin, the Muschelkalk facies (Anisian to Ladinian) is constituted by two marine carbonate sequences with an interstratified evaporite-siliciclastic unit. The second carbonate sequence was recently subdivided into two Transgressive–Regressive sequences corresponding to two fault-block, microbial-dominated carbonate ramps separated by a marked correlative conformity formed in association with a regional sea-level fall [Mercedes-Martín et al. 2013, 2014a]. Ammonites, bivalves and palynomorphs have been previously used to constrain the age of these platforms particularly in open marine, deep ramp settings where these organisms are better preserved in organic-rich sediments [Calvet et al. 1990]. However, refined biostratigraphic surveys are needed to: (i) shed light on the age of the correlative conformity which leads to a significant paleogeographic reorganisation of the depocentres of eastern Iberia [Mercedes-Martín et al. 2014b], and (ii) identify the Ladinian–Carnian transition in marine sediments. Palynological assemblages can help to temporally constrain the age of these carbonate-shale sequences since palynomorphs are easily well-preserved in organic-rich facies and their remains are abundant in the study area.
1.1. Background
There are previous palynological studies that analyse different assemblages in the Catalan Coastal Ranges. Following the chronostratigraphic order, we have the following data.
For the Lower Muschelkalk facies, in Figaró-Montmany area (Barcelona), Solé de Porta et al. [1987] studied a palynological assemblage which was dated as middle Anisian. This assemblage contains Alisporites grauvogeli, cf. Latosaccus latus, Microcachryidites doubingeri, Microcachryidites fastidioides, Platysaccus reticutatus, Striatoabieites aytugii, Sulcatisporites cf. reticulatus, Triadispora aurea, Triadispora crassa, Triadispora falcata, Triadispora plicata, Voltziaceaesporites heteromorpha, Alisporites sp., Aratrisporites sp., Cyclotriletes sp., Punctatisporites sp., Sulcatisporites sp., Triadispora sp., and unidentified bisaccates.
For the Lower Muschelkalk–Middle Muschelkalk Calvet and Marzo [1994] suggested an Upper Anisian age, using a palynological assemblage identified in El Figaro (Barcelona): Alisporites grauvogeli, Lunatisporites acutus, Microcachryidites doubingeri, Praecirculina granifer, Striatoabieites aytugii, Stellatopollenites thiergartii ( = Hexasaccites muelleri), Cycadopites sp., Cyclotriletes sp., and Triadispora sp.
In the base of the Middle Muschelkalk Solé de Porta et al. [1987] studied an outcrop in La Riba (Tarragona). This outcrop consists of dark shales, dating by this author as Upper Anisian according to the following palynological assemblage: Alisporites grauvogeli, Cyclotriletes cf. granulatus, Cyclotriletes cf. oligogranifer, Cyclotriletes triassicus, Kuglerina meieri, Lunatisporites acutus, Microcachryidites doubingeri, Microcachryidites fastidioides, Praecirculina granifer, Striatoabieites aytugii, Stellatopollenites thiergartii ( = Hexasaccites muelleri), Triadispora aurea, Triadispora crassa, Triadispora falcata, Triadispora plicata, Triadispora staplinii, Triadispora suspecta, Alisporites sp., Cycadopites sp., Cyclotriletes sp., Lunatisporites sp., Punctatisporites sp., Sulcatisporites sp., and Triadispora sp.
Also, Diez [2000] analysed the base of the Middle Muschelkalk in the outcrop of “El Figaro”, characterised by an organic-rich interval. This palynological assemblage is constituted by the following species: Alisporites cf. grauvogeli, Heliosaccusdimorphus, Lunatisporites cf. acutus, Ovalipollis cf. ovalis, Parasaccites cf. korbeensis, Punctatisporitesfungosus, Triadispora epigona, Triadispora falcata, Triadispora staplinii, Verrucosisporitesremyanus, cf. Alisporites, Alisporites sp., Aratrisporites sp., Calamospora sp., cf. Illinites, Microreticulatisporites sp., and Platysaccus sp. Despite the high palynological diversity, this assemblage did not provide detailed chronostratigraphic information.
The palynological content of the Middle Muschelkalk of the Catalan Basin was studied by Visscher [1967] in Pradell (Tarragona) giving an assemblage of poor chronostratigraphic value: Alisporites grauvogeli, Angustisulcitesklausii, Voltziaceaesporitesheteromorpha, and Triadispora sp.
Subsequently, Calvet and Marzo [1994] studied the upper part of the Middle Muschelkalk succession in La Riba (Tarragona) suggesting a Ladinian age on the basis of the following assemblage: Duplicisporites granulatus, Duplicisporites scurrilis ( = Paracirculina scurrilis), Ovalipollis ovalis, Praecirculina granifer, Staurosaccites quadrifidus, and Triadispora sp.
Finally, for the Upper Muschelkalk, Solé de Porta et al. [1987] studied the microflora of Capafons Unit, in Capafons (Tarragona) which raised a Ladinian microflora constituted by the speciments: Camerosporites secatus, Duplicisporites granulatus, Duplicisporites scurrilis ( = Paracirculinascurrilis), Microcachryidites doubingeri, Microcachryidites fastidioides, Ovalipollis ovalis, Praecirculina granifer, Rimaesporites potonei, Striatoabieites aytugii, Triadispora aurea, Triadispora crassa, Triadispora falcata, Triadispora plicata, Triadispora suspecta, Platysaccus sp., Triadispora sp., and Verrucosisporites sp. Also, Calvet and Marzo [1994] studied two palynological assemblages from Rojals and Rasquera Units. The Rojals Unit was recognised at the top of Rojals Unit from la Riera de Sant Jaume (Barcelona) and contains Camerosporites secatus, Duplicisporites scurrilis ( = Paracirculina scurrilis), Ovalipollis cultus, Ovalipollis ovalis, Praecirculina granifer, Triadispora crassa, Alisporites sp., Calamospora sp., and Triadispora sp. The Rasquera Unit was recognised from marly sediments sampled in Rasquera (Tarragona) yielding Camerosporites secatus, Praecirculina granifer, Ovalipollis ovalis, Staurosaccites quadrifidus, Triadispora crassa, Platysaccus sp., and Triadispora sp. An Upper Ladinian age was suggested for both units [Calvet and Marzo 1994].
Unfortunately, the mentioned previous studies other than that the work of Diez [2000], lack accurate representation of the listed palynomorphs, so a critical motivation of our work was to study similar stratigraphic units in the Catalan Basin to obtain new appropriated data. This study aims at characterising new palynological assemblage from two outcrops located in the surroundings of Falset and Rasquera (Tarragona, Spain), contributing to better constrain the age of the Upper Muschelkalk facies of the Catalan Basin.
2. Geological setting
The study area is located in the Catalan Coastal Ranges, which developed by inversion of the Mesozoic rifts during the Palaeogene [Salas et al. 2001]. The Triassic materials of the Catalan Coastal Ranges are widely distributed in an area about 300 km long and 200 km wide showing a NE-SW orientation. During the Triassic, the basin opened towards the SE into the Neotethys Sea, with shallow depocentres located towards the western and northern parts of the Spanish Meseta [Calvet et al. 1990].
During the Permian to Middle Triassic times, Iberia experienced the development of graben systems that were closely related to the rapid propagation of the northern Europe-Greenland Sea rift to the south and the propagation of the Neotethys Sea to the west. The late Permian and Mesozoic evolution of Iberia can be divided into four major rift cycles and post-rift stages [Ramos et al. 1996, Salas and Casas 1993, Salas et al. 2001]. The first of these cycles (late Permian-Triassic rift cycle of Salas and Casas [1993]) broadly affected the eastern part of the Iberian plate (including the Triassic Catalan Basin). This cycle was divided into several syn-rift and post-rift phases [Vargas et al. 2009] providing evidence that the Triassic of Iberia was marked by generalised pulses of rapid syn-rift subsidence which influenced the deposition of extensive carbonate ramps [Mercedes-Martín et al. 2013, 2014a, Tucker et al. 1993].
These Triassic graben systems were filled with sediments attributed to Germanic facies during the late Permian and Triassic allowing a tripartite facies subdivision of such deposits. The lower part is made up of continental Buntsandstein siliciclastics and red beds, the middle part is composed of marine Muschelkalk limestones, evaporites and red beds, and the upper part consisting of tidal, sabkha and evaporite deposits of the Keuper facies [Virgili et al. 1983].
In the Catalan Basin, the Muschelkalk facies (Anisian to Ladinian, Middle Triassic) consist of two marine carbonate units separated by a siliciclastic-evaporite unit. The second carbonate unit (Upper Muschelkalk) records paleogeographical thickness variations between the shallowest carbonate deposits, located in the Gaià domain, and the deeper carbonate-shale deposits, located in the Baix Ebre-Priorat domain [Calvet et al. 1987, Calvet and Tucker 1988] (Figure 1). The outcrops studied in this work belongs to the Baix Ebre-Priorat domain.
Geographical and geological location of the study area.
The Ladinian sedimentary record of the Triassic Catalan Basin has been recently divided into two transgressive–regressive (T-R) sequences by [Mercedes-Martín et al. 2014a]. The two T-R sequences represent examples of carbonate ramps, with low-gradient depositional angles and clearly recognised lateral relationships of facies belts. The depositional model for the T-R Sequence 1 corresponds to a microbial-dominated fault-block carbonate ramp. The T-R Sequence 1 (early Ladinian) contains widespread microbial carbonate deposits: stromatolites in the inner ramp (up to 10 m thick) and thrombolytic biostromes and mounds in the middle ramp (up to 70 m thick). However, the T-R Sequence 2 (late Ladinian) is made up of oolitic stromatolites in the inner ramp, and internal shoals and sheltered lagoons in the middle-outer ramp [Mercedes-Martín et al. 2013, 2014a,b].
Both T-R sequences are bounded by a prominent correlative conformity associated with incised-valley erosional features and collapse breccia fillings. The correlative conformity was interpreted as formed by a significant sea-level drop of at least 50 m [Mercedes-Martín et al. 2013, 2014a]. The deep-water expression of such surface is the correlative conformity, which was recognised in the Rasquera section (Figure 2).
Depositional profile and sequence stratigraphic interpretation of the Upper Muschelkalk rocks in the Catalan Basin (Baix Ebre-Priorat domain). Note the location of the studied sections (Rasquera and Falset) and the lithological units of Calvet et al. [1987]. The black dotted line represents the correlative conformity (see text for more details).
2.1. Stratigraphy of the Baix Ebre-Priorat domain
From a lithostratigraphic perspective, the Upper Muschelkalk is constituted by different units in the Baix Ebre-Priorat domain (Figure 2). Calvet et al. [1987] and Calvet and Tucker [1988] recognised five units, which from base to top are: (1) the Rojals Unit, (2) the Benifallet Unit, (3) the Rasquera Unit, (4) the Tivissa Unit, and (5) the Capafons Unit. Collectively, the sedimentary sections studied in this work (Falset and Rasquera, Figures 2, 3) contain the lithological units 1 to 4 which have been placed in the stratigraphic sequence framework provided by Mercedes-Martín et al. [2013].
Stratigraphic sections studied (Rasquera and Falset) displaying the main lithological, sequence stratigraphical, and paleontologic characteristics (modified from Mercedes-Martín et al. [2014a]).
Rojals Unit. It is made up to 14 m thick carbonate succession sharply lying on top of the Middle Muschelkalk siliciclastic-evaporitic deposits. Rojals Unit is composed of several alternating facies: grey massive bioturbated mudstone; grey laminated mudstone-wackestone with mud-cracks and evaporitic moulds; grey wackestone with ripple lamination; white oolitic grainstone showing ripple, herringbone, planar, and wavy laminations; planar to domal stromatolites with occasional flat-pebble intraclasts and bivalve fragments [Calvet et al. 1987]. The Rojals Unit represents the Transgressive Systems Tract of the T-R sequence 1 of [Mercedes-Martín et al. 2013] dated as early Ladinian. This unit is outcropping in Rasquera section (Figures 2, 3).
Benifallet Unit. It is composed by up to 20 m of a carbonate succession sharply lying on top of the Rojals Unit. Benifallet Unit is constituted by an array of facies: grey to greenish skeletal mudstone to wackestone with echinoid and bivalve allochems; massive to bioturbated mudstone to wackestone with occasional ripple and herringbone lamination; marly to shaley dolostones with evidence of bioturbation and bivalve fauna. A change from the Rojals Unit (shallow water stromatolitic facies) to Benifallet Unit (deeper water burrowed mudstone to wackestone) was identified as the Maximum Flooding Zone of the T-R sequence 1. Thus, Benifallet Unit was interpreted to be the lower portion of the Regressive Systems Tract of the T-R sequence 1 of Mercedes-Martín et al. [2013], and it was dated as early Ladinian. This unit is outcropping in Rasquera section (Figures 2, 3).
Rasquera Unit. It is made up of at least 40 m of a carbonate-marly succession sharply lying on top of the Benifallet Unit. Rasquera Unit is characterised by a wide range of lithofacies including alternation of grey skeletal mudstone-wackestone (with bivalves as Daonella, brachiopods, peloids, foraminifera and ostracods) with dark marls/shales forming nodular and continuous beds; grey bioturbated mudstone-wackestone with bivalves arranged in massive to nodular layers; wackestone-packstone with echinoids, foraminifera, peloids, and brachiopods organised in massive beds exhibiting cross-bedded laminations. Rasquera Unit was interpreted to be the upper portion of the Regressive Systems Tract of the T-R sequence 1 of Mercedes-Martín et al. [2013], and it was dated as late Ladinian on the basis of ammonoids (Prothachyceras steinmann, P. hispanicum, Hungarites pradoi) and conodonts (Metapolygnathus mungoensis, Pseudofurnishius murcianus) [Calvet et al. 1987, Calvet and Tucker 1988]. However, a early Ladinian age was determined by Mercedes-Martín et al. [2013] by the stratigraphic relationships and lateral facies distributions. This unit is outcropping in Rasquera section (Figures 2, 3).
Tivissa Unit. It is composed of at least 42 m-thick of a coarse-grained carbonate succession alternating with shale/marl-rich intervals. The base of this unit is characterised by an iron-rich hardground containing abundant ammonite fauna. This unit is made up of the following facies: bioturbated marlstone-shale; marlstone with thin-bedded bioturbated limestones; thick-bedded and massive mudstone and wackestone; bioclastic packstone-grainstone with ooids, echinoids, peloids and molluscs with evidence of ripple and planar laminations, and silica o iron nodules. This unit is interpreted as the Transgressive Systems Tract of the T-R sequence 2 [Mercedes-Martín et al. 2013] which is bounded by a composite stratigraphic surface (correlative conformity and transgressive surface). The Tivissa Unit was dated as late Ladinian by ammonite fauna (Hungarites pradoi, Protrachyceras hispanicum, P. ibericum, P. batalleri, and P. vilanovae), and conodonts (Metapolygnathus mungoensis, Pseudofurnishius murcianus) [Calvet and Tucker 1988, Calvet et al. 1987]. This unit is cropping out both in Rasquera and Falset sections (Figures 2, 3).
3. Materials and methods
In this paper, we have studied two stratigraphic sections close to Falset and Rasquera, in the province of Tarragona (Spain).
In the Rasquera Section (40° 59′ 41.40′′ N, 0° 34′ 6.12′′ E) four samples were collected in marly levels. Sample CRQ-1 and CRQ-2 were collected below the correlative conformity (see Figure 3), while samples CRQ-3 and CRQ-4 were collected above. In the Falset section (41° 9′ 2.66′′ N, 0° 51′ 35.30′′ E) five samples were sampled (FL2-1 to FL2-5) above the correlative conformity. All the samples contained palynomorphs. Due to the positive results of the marly levels, two new complementary samples were subsequently collected in the Falset section (FL2-0 and FL2-6) in limestone levels. Both samples were negative in both marine and continental palynomorphs.
Palynological samples were processed using HCl-HF-HCl attack techniques as described by Wood et al. [1996] in the palynological Laboratory of Geosciences Department at the University of Vigo. A dispersing agent was added to facilitate filtering and sieving at 10 μm. The palynological slides were studied under a Leica DM 2000 LED, and the photomicrographs were taken with a Leica ICC50 W camera using ×1000 magnification.
The slides are stored in the palynological Laboratory of Geosciences Department at the University of Vigo.
4. Results
Two palynological assemblages were considered (Supplementary Table 1), and a synthetic assemblage is shown in Figure 4. The isolated and complete assemblages of each section are shown in the Supplementary data.
Synthesis of the palynomorphs found in the Falset and Rasquera sections. (1) Calamospora sp., (2) Calamospora tener, (3) Deltoidospora sp., (4) Concavisporites sp., (5) Retusotriletes sp., (6) Camarozonosporites laevigatus, (7) Chasmatosporites sp., (8) Ephedripites sp., (9) Praecirculina granifer, (10) Paracirculina scurrilis, (11) Paracirculina tenebrosa, (12) Patinasporites densus, (13) Duplicisporites granulatus, (14) Camerosporites secatus, (15) Aratrisporites granulatus, (16) Palaeospongisporis europaeus, (17) Maculatasporites sp., (18) Verrucosisporites sp., (19) Alisporites sp., (20) Triadispora falcata, (21) Triadispora plicata, (22) Triadispora crassa, (23) Triadispora staplinii, (24) Triadispora epigona, (25) Triadispora suspecta, (26) Ellipsovelatisporites rugosus, (27) Platysaccus papilionis, (28) Microcachryiditesfastidioides, (29) Microcachryidites doubingeri, (30) Chordasporites sp., (31) Striatoabieites aytugii, (32) Lunatisporites noviaulensis, (33) Lunatisporites acutus, (34) Cymatiosphaera sp., (35) Staurosaccites quadrifidus, (36) Ovalipollis pseudoalatus, (37) Ovalipollis cultus, (38) Ovalipollis ovalis, (39) Tasmanites sp., (40) foraminiferal test lining.
The samples CRQ-1 to CRQ-4 in the Rasquera section contain: Aratrisporites granulatus (Klaus 1960) Playford and Dettmann 1965, Calamospora tener (Leschik) Mädler 1964, Camerosporites secatus Leschik 1956, Duplicisporites granulatus (Leschik) Scheuring 1970, Ellipsovelatisporites rugosus Scheuring 1970, Lunatisporites noviaulensis (Leschik 1956) de Jersey 1979, Microcachryidites doubingeri Klaus 1964, Microcachryidites fastidioides Klaus 1964, Ovalipollis cultus Scheuring 1970, Ovalipollis ovalis (Krutzsch 1955) Scheuring 1970, Ovalipollispseudoalatus (Thiergart) Schuurman 1976, Palaeospongisporis europaeus Schulz 1965, Paracirculina tenebrosa Scheuring 1970, Patinasporitesdensus Leschik 1955, Platysaccus papilionis Potonié and Klaus 1954, Praecirculina granifer (Leschik) Klaus 1960, Striatoabieites aytugii (Visscher) Scheuring 1970, Triadispora crassa Klaus 1964, Triadispora epigona Klaus 1964, Triadispora falcata Klaus 1964, Triadispora plicata Klaus 1964, Triadispora staplinii (Jansonius) Klaus 1964, Triadispora suspecta Scheuring 1970, Chordasporites sp., Concavisporites sp., Deltoidospora sp., Maculatasporites sp., Microcachryidites sp., Paracirculina sp., Retusotriletes sp., Triadispora sp., Verrucosisporites sp., Cymatiosphaera sp., Tasmanites sp., and foraminiferal test lining.
The samples FL2-1 to FL2-5 in the Falset section contain: Aratrisporites granulatus (Klaus 1960) Playford and Dettmann 1965, Calamospora tener (Leschik) Mädler 1964, Camarozonosporites laevigatus Schulz 1967, Camerosporites secatus Leschik 1956, Duplicisporites granulatus (Leschik) Scheuring 1970, Lunatisporites acutus Leschik 1956, Microcachryidites doubingeri Klaus 1964, Microcachryidites fastidioides Klaus 1964, Ovalipolliscultus Scheuring 1970, Ovalipollis pseudoalatus (Thiergart) Schuurman 1976, Paracirculina scurrilis Scheuring 1970, Paracirculina tenebrosa Scheuring 1970, Patinasporites densus (Leschik) Scheuring 1970, Platysaccus papilionis Potonié and Klaus 1954, Praecirculina granifer (Leschik) Klaus 1960, Staurosaccites quadrifidus Dolvy 1976, Striatoabieites aytugii (Visscher) Scheuring 1970, Triadisporacrassa Klaus 1964, Triadispora epigona Klaus 1964, Triadispora falcata Klaus 1964, Triadispora suspecta Scheuring 1970, Alisporites sp., Calamospora sp., Chasmatosporites sp., Concavisporites sp., Ephedripites sp., Maculatasporites sp., Microcachryidites sp., Retusotriletes sp., Triadispora sp. and Verrucosisporites sp. We also identified Tasmanites sp. and foraminiferal test lining.
5. Discussion
5.1. Age assessment
The First Appearance Datum (FAD) of Camerosporites secatus is documented in the early Fassanian (early Ladinian) of alpine Domaine of Europe [Roghi 1995, Stockar et al. 2012, Van Der Eem 1983, Visscher and Brugman 1981], and the FAD of Duplicisporites granulatus raises a middle Fassanian age in central and northwestern Europe [Kürschner and Herngreen 2010]. By the other hand, the bisaccate pollen grains like Lunatisporites noviaulensis, Microcachryidites doubingeri, and Microcachryidites fastidioides are characteristic of the Early-Middle Triassic and rarely appear in early Carnian assemblages (e.g. [Doubinger and Bühmann 1981], in Germany; [Doubinger and Adloff 1983], in the Mediterranean area; [Orłowska-Zwolińska 1983, 1985], in Poland; [Eshet 1990], in Israel; [Kürschner and Herngreen 2010] in central and northwestern Europe). The Last Appearance Datum (LAD) of Protodiploxypinus fastidioides ( = Microcachryidites fastidioides) is reported in the middle Longobardian of central and northwestern Europe [Kürschner and Herngreen 2010].
Van Der Eem [1983] in Wester Dolomites (Italy), Scheuring [1970] in Solothurner Jura (Switzerland) and Kürschner and Herngreen [2010] in Central and northwestern of Europe placed the first appearance of Patinasporites densus to the base of the early Carnian. Cirili [2010] in the revision of the Upper Triassic materials in Central and Northwestern of Europe suggested for this taxon a Carnian–early Norian age. Scheuring [1970] in Solothurner Jura (Switzerland) linked the presence of Ellipsovelatisporites rugosus to Gipskeuper, with an late Ladinian–early Norian age.
The two assemblages correspond to the intervals between Camerosporites secatus–Enzonalasporites vigens/Enzonalasporites vigens – Patinasporites densus phases [Van Der Eem 1983], the Heliosaccus dimorphus/Porcellispora longdonensis Zones of Orłowska-Zwolińska [1983, 1985, 1988] amended by Herngreen [2005], zones GTr 11 and 12 in the palynostratigraphical subdivision of the Germanic Basin [Heunisch 1999], and the Heliosaccus dimorphus/Camerosporites secatus zones [Kürschner and Herngreen 2010].
The palynological assemblages studied in the Upper Muschelkalk of the Catalan Coastal Ranges are comparable with other assemblages recognised in the middle-upper part of Royuela Formation in Torrecilla and Arroyo de San Roman (Guadalajara, Spain; Ramos [1979]), the Upper Muschelkalk of Alcalá de la Selva and Barranco del Contador, Cañete Formation (Teruel, Spain; Arche et al. [1995]), the Upper Muschelkalk of Pantano de la Tranquera (Zaragoza, Spain. García-Royo et al. [1989]), and the assemblage SC-2 of Juncal et al. [2018] in the Paris Basin.
Thus, the palynomorph assemblages identified from Falset and Rasquera sections raise a Longobardian–Cordevolian age.
This palynological dating is consistent with the age provided by ammonite fauna and conodonts from Rasquera and Falset Units [Calvet and Tucker 1988, Calvet et al. 1987] and is coherent with previous biostratigraphical and sedimentological correlations between the Muschelkalk of the Catalan Basin and the Iberian Ranges [Diez et al. 2014].
5.2. Paleoenvironmental and paleoecological remarks
The lithostratigraphical data suggest deposition in the middle to outer carbonate ramp environments with a predominant increase in water depth towards Rasquera section, where marls and shaly marls are more abundant [Mercedes-Martín et al. 2013, 2014b]. Despite the marine character of the sediments, the overall palynological assemblage found in marly levels, present a clear dominance of continental palynomorphs. Notwithstanding, although scarce, some samples show the presence of authochtonous marine prasinophytes (Tasmanites and Cymatiosphaera), and foraminiferal test linings indicating that mixing of marine and continental associations occurred at least in the more proximal parts of the basin.
Moreover, as mentioned previously, the absence of palynomorphs in the sampled coarse-grained carbonate intervals could be due to deposition of these sediments in moderate to high energy and oxygenated environments which can encourage the rapid disintegration of the organic remains. The limited tissue preservation of the studied carbonates can also be attributed to the pervasive post-depositional dolomitisation that these rocks have suffered [Tucker and Marshall 2004]. Consequently, the taphonomic bias produced should be kept in mind when carrying out the approximate hinterland and coastal floral reconstruction. This same bias makes it impossible to make percentage variation graphs of palynomorphs to try to discern the paleoclimatic evolution of the study area.
Paleoenvironmental reconstruction based on palynomorphs assemblages.
The composition of the microfloras of the Falset and Rasquera assemblages reflects a flora dominated by xerophytic species whose pollen grains were transported by wind and water currents to the deposition zone. The presence of Triadispora spp. indicates an influx of hinterland elements also with saline mudflats [Brugman et al. 1994, Roghi et al. 2010]. In addition, the occurrence of Duplicisporites, Camerosporites, Paracirculina and Praecirculina (Circumpolles group) could represent a xerophytic coastal vegetation [Roghi et al. 2010] due to their Cheirolepidiaceae affinity [Roghi 2004, Scheuring 1970, 1978, Visscher et al. 1994, Zavialova and Roghi 2005]. Although the Cheirolepidiaceae could live in a wide variety of habitats, the presence of this group in the Falset and Rasquera assemblages could indicate a drier and/or saline influence [Kustatscher et al. 2018].
Although scarcer, the occurrence of spores could indicate the presence of hygrophytic vegetation. In addition, coastal, swamp and freshwater environments could have sourced different lycophytes (Aratrisporites) to marine settings. Small and larger ferns (e.g. Verrucosisporites, Deltoidospora and Concavisporites) are typically associated to more humid environments in the hinterland, while bryophytes (Maculatasporites), and horsetail specimens (Calamospora) could have been sourced from wetter areas and along a small river.
Based on the probable parent plant affinities of the palynological record (see Supplementary data) in combination with sedimentological data, we can propose an approximate paleoenvironmental reconstruction of the study area (Figure 5).
6. Conclusions
The palynological assemblages recognised from Rasquera and Falset Sections give a Longobardian–Cordevolian age.
Our data are in agreement with the marine previous biostratigraphycal data published, providing the most complete and recent figuration of the palynomorphs of the Catalan Basin. This refined calibration helps to constrain the age of the Upper Muschelkalk sediments themselves, and the overlying Keuper facies (Ladinian–Carnian) in the Catalan Coastal Ranges and the stratigraphical correlation whit the Iberian Ranges, and adjacent basins of the Tethys region.
Although taphonomic bias is important, the composition of the recovered oryctocoenosis makes it possible to sketch the composition of the continental flora in the source sedimentary area. However, the decrease in preservation due to the increase in the proportion of carbonates indicates that the bias makes impossible, as in most cases, the statistical use of the data in the deduction of paleoclimatic evolution.
Acknowledgements
The authors are grateful to the anonymous reviewers for helpful and constructive suggestions, and the editor Dr. Sylvie Bourquin for her valuable recommendations. This work was supported by projects CGL2014-52699P (Spanish Ministry of Economy) and GRC 2015/020 (Xunta de Galicia) and a Percy Sladen Memorial Fund Grant of the Linnean Society of London (RM-M).
Supplementary data
Supporting information for this article is available on the journal’s website under https://doi.org/10.5802/crgeos.8 or from the author.