New charophytes from the Upper Jurassic of the Lusitanian Basin (Portugal)

In the Lusitanian Basin (west-central Portugal), Upper Jurassic (Oxfordian) sediments were investigated in order to identify palaeontological assemblages of charophytes. Systematic studies were undertaken on specimens obtained from four field sections (Pedrógão, Vale de Ventos, Memória and Valverde). These studies revealed the presence of new forms of Porocharaceae (Porochara pedunculata n. sp) and of forms previously unknown in this region (Auerbachichara cf. saidakovskyi), as well as P. raskyae, P. minima, P. fusca, P. sulcata, P. kimmeridgensis, Aclistochara longiformis and Porochara sp. Comparison of the charophyte palaeofloras recognized in all of the studied sections has allowed the definition of three different assemblages which, coupled with other data, help to correlate these successions of Early (?) to Middle (Late?) Oxfordian age.

The aim of this paper is to present the systematic description of the charophyte species recognized in the Oxfordian deposits of the studied region (locally possibly uppermost Callovian), within a regional sedimentary and palaeoecological framework. The vertical distribution of the identified species in the studied successions is also presented.
The abundance of charophyte specimens and the well-known high intraspecific diversity of the gyrogonites led us to try a twofold approach, integrating both morphological analysis and comparative populational analysis (see below). The charophyte data, presented here, refer to four field sections in the Lusitanian Basin ( Fig. 1): Pedrógão (shoreline S of Figueira da Foz), Vale de Ventos, Valverde and Memória (all three at Serra dos Candeeiros, in the east of the basin).

GEOLOGICAL SETTING
The Lusitanian Basin, in West-Central Portugal (Fig. 1), is one of the marginal basins associated with the opening of the North Atlantic Ocean. While most of the basin fill is Jurassic in age, sediments from the Upper Triassic to the Upper Cretaceous are found, overlain by a cover of Tertiary sediments. The basin is bounded to the east by uplifted Hercynian basement and to the west (offshore) by small basement horsts. Two main episodes of extension and rifting are recorded in the basin: the first one, in the late Triassic, which only developed the early rift-stage and a later one, which gave rise to ocean opening, ranging from the Late Jurassic through the Early Cretaceous (Ribeiro et al., 1979;Wilson, 1988). The basin was subjected to tectonic inversion in the Tertiary and, consequently, a great part of its pre-, syn and post-rift sequences became exposed (Ribeiro et al., 1979;Wilson, 1988).
The Upper Jurassic deposits above the discontinuity are traditionally assigned to the Cabaços formation (though often quoted as a Formation, it is not formally described), which basically corresponds to the Cabaços Beds (sensu Choffat, 1893a,b, and followed by Ruget-Perrot (1961) and Ramalho (1971a,b)). These are also known as the Cabaços Limestones (e.g. Mouterde et al., 1979). The charophyte data presented here were obtained from marly levels within this formation (see below).
The Cabaços formation lacks good biostratigraphical markers, especially in its lower part. It unevenly overlies Middle Jurassic limestones ranging in age from the late Bathonian to the late (but not latest) Callovian. Over the whole of the basin, the lower (locally) to intermediate (mostly) part of the successions are typified by the presence of the dasycladacean alga Heteroporella lusitanica (Ramalho, 1970), which is attributed to the Middle Oxfordian in Portugal (Ramalho, 1970(Ramalho, , 1971a(Ramalho, ,b, 1981. This species was also found by Ramalho (1971b) in the Torres Vedras region (where the original descriptions of the unit by Choffat were made), in levels where a few ammonite records attributed to the Transversarium Zone have been recorded (cf. Ruget-Perrot, 1961;Ramalho, 1971a,b). In places, Middle Oxfordian or Upper Oxfordian ammonites are documented from levels well above those containing H. lusitanica (Ruget-Perrot, 1961;Mouterde et al., 1979;Rocha, 1996). It is also worth mentioning that the lituolid foraminiferids Alveosepta jaccardi (Schrodt) and/or Pseudocyclammina parvula Höttinger, 1967 (Middle Oxfordian to Kimmeridgian) always appear, all over the basin, in the more marine facies which succeed, or laterally replace, the transitional lagoonal facies with H. lusitanica (Ramalho, 1971a(Ramalho, , b, 1981Azerêdo et al., 2000Azerêdo et al., , 2002a.

BRIEF DESCRIPTION OF THE STUDIED SECTIONS
The studied sections ( Fig. 1) are representative of the typical eastern (Vale de Ventos, Memória, Valverde) and western (Pedrógão) Middle-Upper Jurassic transitional successions in the Lusitanian Basin. These successions are mostly composed of marls and limestones, and both thin sections and washed residues were used for petrographical and micropalaeontological studies. For the charophytes, of course, only the marly sediments were subjected to a detailed analysis and the studied levels are indicated in the logs of Figs 2 and 3.
+ The overlying levels up to P90 are dominated by fossiliferous and bioturbated limestones, with some marly interbeds and microbial laminites, frequently bounded by desiccation cracks. These levels are marked by the appearance and usually abundant occurrence of Heteroporella lusitanica, together with abundant ostracods, less frequent charophyte gyrogonites, some agglutinated foraminifera, serpulids, gastropods and bivalves. + From P91 upwards, massive and fossiliferous limestones and less common marly limestones are increasingly intercalated with microbial laminites, pedogenic conglomerates and evaporite relict levels. H. lusitanica becomes rarer towards its last occurrence at P106. The fossil content varies from moderately diverse assemblages of restricted marine influence (euryhaline and marine ostracods and molluscs, rare echinoids, Porostromata, several benthic foraminifera, namely Pseudocyclammina parvula, charophytes namely, P. kimmeridgensis (Mädler, 1952) Mädler, 1955, P. fusca?, a few acritarchs) to low-diversity or even monospecific assemblages of euryhaline ostracods (ostracodites, closely related to the microbial laminites or to the evaporites). The Pedrógão succession depositional environments are interpreted as having developed from an open marine setting (at the base) to fresh-brackish water and marginal-restricted marine settings, with fluctuating salinity and frequent subaerial exposure (Azerêdo et al., , 2000Azerêdo & Cabral, in press).

Vale de Ventos, Memória and Valverde
These field sections are located at Serra dos Candeeiros, a range of hills in the eastern zone of the Lusitanian Basin (Rio Maior-Alcobaça-Fátima region; see Fig. 1). The successions observed at these three locations are broadly similar and timeequivalent, as shown in Figure 3. A detailed field study of these sections was originally made by Azerêdo and Ramalho (unpublished), and later descriptions were presented by Azerêdo et al. (1998Azerêdo et al. ( , 2000Azerêdo et al. ( , 2002a. The Vale de Ventos and Valverde outcrops have also been particularly mentioned in relation to systematic studies of ostracods (Cabral et al., 1999b(Cabral et al., , 2001Colin et al., 2000;Cabral & Colin, 2002). The charophytes from Vale de Ventos are described in Pereira et al. (1998Pereira et al. ( , 1999 and Pereira (2002). A summarized description of the Vale de Ventos (SE of Alcobaça), Memória (SW of Fátima, to the north of Vale de Ventos) and Valverde (NW of Rio Maior, to the SE of previous ones) sections is given below.
These successions reflect evolution from shallow marine, lagoonal environment (Middle Jurassic), to continental and transitional settings (subaerial exposure, freshwater to brackish lacustrine, perilacustrine and restricted lagoon).

POPULATION ANALYSIS
All the charophyte samples were studied using a simple quantitative analysis with Microsoft Excel as a complement to the morphological description (for example, Feist & Grambast-Fessard, 1982). This analysis uses the morphometric parameters most widely accepted by several authors (e.g. Horn af Rantzien, 1959;Bonnet & Soulié-Märsche, 1971;Schudack, 1996a). The use of this analysis has proved to be very useful in separating different populations of charophytes, when using graphical plotting of the morphometric parameters (LPA LED or sphericity index (ISI) symmetry index (ANI)).
In Figure 4, four populations of various samples are plotted, showing elongated clouds that merge in restricted areas. These areas are evidence of populational variation that only strengthens this analysis, for which the highest number of gyrogonites as possible must be used (Soulié-Märsche & Joseph, 1991) to avoid erroneous classification of few samples, which can be located in mergence areas.
(Pl. Diagnosis. Medium-sized Porochara gyrogonite with an inverted pear shape, marked by a basal necking (larger at apical half), concave spiral cells (8-15, usually 12-13) and a pentagonal basal pore (about 40 µm in diameter); segmented basal plate, not visible from the outside. Major axis ranges from 392 to 882 µm, minor axis from 304 to 667 µm, apical pore about 100 to 130 µm and equatorial cells around 50-60 µm. ISI shows an elliptical gyrogonite (102-144) and ANI shows an asymmetrical shape with a larger apical half of 48, up to 60 in some samples. Remarks. These gyrogonites were previously described as Porochara jargaraensis Shaikin & Saidakovsky, 1976by Grambast-Fessard & Ramalho (1985. However, compared with Shaikin's (1976) original description and drawings, this new form clearly shows a basal neck that is not present in P. jargaraensis. The size and number of spiral cells of both species are similar, but P. pedunculata n. sp gyrogonites show stronger variation, different ISI values (more elliptical), the ANI indicates a larger apical half and the apical pore is smaller.
P. kimmeridgensis, P. westerbeckensis (Mädler, 1952) Mädler, 1955 or P. raskyae are clearly different in size, number of spiral cells and ratio indexes and none of these forms show the pedunculate character of P. pedunculata n. sp.

Diagnosis. Small
Porochara of concave spiral cells (8-12) and elliptical asymmetrical shape (larger at basal half) and with an apical pore of about 80-100 µm diameter.

Diagnosis.
Medium-sized charophyte gyrogonites usually with 9 to 10 concave to convex spiral cells of elliptical to spherical shape and symmetrical halves.
Remarks. These gyrogonites show a large variation in size and shape, and this has led some authors (for example Mojon, 1989b) to include P. kimmeridgensis and P. westerbeckensis within a single form. However, the forms found in the studied sections have more affinities with P. kimmeridgensis as regards the general shape (rounder) and average size.
Diagnosis. Small gyrogonite with 8-10 spiral cells (more common) of elliptical symmetrical shape, sometimes larger at apical half, with the major axis around 300 µm and the minor axis around 230 µm.
Remarks. Some of the samples are larger, but these must correspond to size variation within the species population.

Diagnosis.
Medium-sized gyrogonites with concave spiral cells (8-15 in some samples, but 11 is more common) and with an elliptical asymmetrical shape (larger at basal half).

Diagnosis.
Large-sized gyrogonites with 7 to 9 deep concave spiral cells, spherical to elliptical and mostly with symmetrical form. Apical pore is about 155 µm in diameter and ECD from 118 to 176 µm.
Gyrogonites are elliptical and are larger at the basal half. Basal pore is rarely seen.
Occurrence. Middle Oxfordian of Vale de Ventos (VV28?, VV30) and the Triassic of Ukraine (Kisielevsky, 1967;Saidakovsky, 1968). The Oxfordian age of the Portuguese locality extends the stratigraphical range of the genus Auerbachichara to the Upper Jurassic, as it was only previously known from the Triassic.
Remarks. These charophytes have larger dimensions than those described by Kisielevsky (1967), but are very similar to that author's description and drawings, mainly in respect of the apical spines. The larger size of the studied species of A. saidakovskyi, might represent an evolutionary character, which may be interpreted as related to migration and growth during the time period corresponding to the gap between the Ukrainian forms and those found in the Lusitanian Basin.
Diagnosis. Small gyrogonites of marked elliptical form, symmetrical to slightly larger at apical half, with 7-12, often 10, concave spiral cells. No basal plate could be observed.

ASSOCIATION WITH OTHER MICROFOSSILS AND ENVIRONMENTAL INTERPRETATION
The charophytes always occur associated with other microfossils, as mentioned above. Among these, the most commonly represented in these sections are the ostracods, which often form very rich assemblages. Foraminifera, dasycladaceans, palynomorphs and some osteological remains are also present. These microfossil assemblages, in particular the ostracods, allow the definition of associations with palaeoecological significance, mainly based on the Pedrógão and Vale de Ventos sections (Cabral et al., 1998(Cabral et al., , 1999aAzerêdo et al., 2000Azerêdo et al., , 2002aAzerêdo & Cabral, in press).
The charophyte associations (Fig. 5) have allowed the definition of three major units for the Late Callovian-Middle Oxfordian interval. For this interpretation, only the most common or more important forms were considered. Thus, Association 1, which is only observed in the western sections of the studied area, is characterized by the presence of Porochara pedunculata n. sp and Porochara sulcata, ranges from the Late Callovian to Early(?)-Middle Oxfordian, and defines a brackish to freshwater palaeoenvironment. Association 2 is characterized by Porochara pedunculata n. sp, P. raskyae and P. minima. Association 3 corresponds to levels with a greater marine influence and shows a change in the charophyte assemblages to one that is mainly composed of P. kimmeridgensis and P. fusca.
At Pedrógão and Vale de Ventos there is a difference in the palaeontological content, with the presence of P. kimmeridgensis only in the upper part of the section, together with Auerbachichara cf. saidakovskyi. The underlying beds at Pedrógão have Aclistochara cf. longiformis, which is usually associated with stronger freshwater conditions (Schudack, 1993).
The presence of P. pedunculata n. sp both in the west (at Pedrógão) and in the east (at Memória) reinforces the inferred spatial and temporal distribution of this species in the basin, allowing the correlation between the two sections and placing them at the Lower-Middle Oxfordian interval. The palaeoenvironmental interpretation for this part of the successions suggests brackish to freshwater-dominated conditions. The correlation with the European charophyte biozones (Riveline et al., 1996) is not completely defined, but the absence of the forms proposed for the closest time intervals (Porochara palmeri Feist & Grambast-Fessard, 1984) of Bathonian age and Clavatoraceae for Late Oxfordian) reinforces the Lower?-Middle Oxfordian age suggested for the studied sections.

CONCLUSIONS
The study of four uppermost Callovian to Oxfordian sections in the Lusitanian Basin (Pedrógão, Memória, Valverde and Vale de Ventos) has contributed to the detailed knowledge of the charophytes in this region and showed the presence of a new species, Porochara pedunculata n. sp, and the occurrence of a previously unknown form in this area, Auerbachichara cf.

saidakovskyi.
This study, coupled with studies on the facies types, ostracods, palynomorphs, foraminifera and dasycladaceans, has contributed to the definition of three zones for the Pedrógão section: Porochara sulcata and Porochara sp. (at the base), Porochara pedunculata n. sp, P. raskyae, P. minima and Aclistochara longiformis (mid-zone) and P. kimmeridgensis and P. fusca (top). This succession shows an environmental change from more marine-influenced facies at the base, to restricted lagoonal facies and then more marine influence towards the top. The forms Porochara raskyae, P. minimaare also present at the base of Vale de Ventos section and, at the top, P. fusca, P. kimmeridgensis, Auerbachichara cf. saidakovskyi and Porochara sp. occur. The Memória section is only comparable to the middle part of the Pedrógão section, as indicated by the occurrence of P. pedunculata and P. raskyae.
Auerbachichara cf. saidakovskyi was previously known from Caspian formations of Triassic age, described by Kisielevsky (1967). However, its presence in the Lusitanian Basin raises a problem on the dispersion and morphological evolution of this species. The Portuguese form is larger than the one described by Kisielevsky (1967) and the interval of time between the two occurrences is very long. Considering these facts, we may interpret the geographical distance of these occurrences as reflecting a migration of this form from eastern regions towards the west, allowing the species to grow, but conserving the distinctive apical crown character. The apparent absence of this form in intermediate regions may be simply related to the relative lack of knowledge of the charophyte floras of the Lower and Middle Jurassic formations of Europe.
This study used traditional systematics and comparative statistical analysis to help separating the new forms and to strengthen the classification of other specimens.