A palynological investigation of some Lower Kimmeridgian deposits from Spain

The present paper provides the first palynological data from two ammonite controlled sections from the Lower Kimmeridgian (Sutneria platynota Ammonite Zone) in Spain. The Segura de la Sierra sequence is located in the Betic Cordilleras and the Hontanar sequence is located in the Iberian Chain. The palynological assemblages, dominated by dinoflagellate cysts and sporomorphs, include taxa which are well known from other areas to be long-ranging throughout the major part of the Mesozoic. Most noteworthy is the presence of Cicatricosisporites spp. in the material investigated. The impact of this on the assumption that a strong diachronous south-north migration of this taxon existed during Middle and Late Jurassic times is discussed.


INTRODUCTION
Age assessments of Jurassic sedimentary rocks from the Iberian Peninsula have generally been based on faunal evidence, especially ammonites, although occasionally, due to the absence of palaeontological control, assessments have also been established on lithostratigraphical criteria. So far few Jurassic palynological records are available from this area. Most of these concern Portugal (Riley, 1974;Adloff et al., 1977;Adloff & Doubinger, 1978;Williams & Bujak, 1985;Davies, 1985;Van Erve & Mohr, in press) and little is known about the Jurassic microfloral development in Spain.
To increase the palynological information on the Jurassic of the Iberian Peninsula two Lower Kimmeridgian ammonite controlled sections from different structural units in Spain have been investigated: (1) the Segura de la Sierra section of the Betic Cordilleras and (2) the Hontanar section of the Iberian Chain (Fig. 1). In both sequences some samples were taken from ammonite bearing strata which have been assigned to the Sutneria platynota Ammonite Zone. This zone represents the earliest Kimmeridgian of the Tethyan realm and is generally assumed to be time-equivalent to the Pictonia-baylei -Ammonite Zone of ihe realm (Fig. 2).

THE SEGURA DE LA SIERRA SECTION
Location. The Segura de la Sierra section is Boreal located north-east of the village of Segura de la Sierra (province of Jaen) along the road to Siles (Lopez Garrido, 1971; Fig. 1). Geological setting. In the province of Jaen, the Prebetic Zone is one of the structural units of the Betic Cordilleras, the Alpine fold-belt of southern Spain (Hermes, 1978;Alvarado, 1980). Lopez Garrido (1971) recognized three distinct structural sub-units in this area which approximately correspond to palaeogeographical domaines: (1) Unit of Beas de Segura, (2) Unit of Sierra de Cazorla and (3) Unit of Sierra del Segura.
In the former two units only Jurassic deposits are present, whereas in the latter Cretaceous sediments are also encountered. The Segura de la Sierra section is part of the Unit of Sierra del Segura and represents predominantly shallow marine Jurassic-?Cretaceous deposits, uncomfortably overlain by the continental Cretaceous sediments of the so-called "Utrillas" (Lopez Garrido, 1971). Stratigraphy (Figure 3). No formal lithostratigraphical subdivision has been established in the Unit of Sierra del Segura. However, Lopez Garrido (1971) distinguished several lithological intervals, which, on the basis of their stratigraphical position or fossil content, have been recognized throughout the province of Jaen. The Jurassic-?Cretaceous intervals exposed in the Segura de la Sierra section can be briefly summarized in ascending order (Lopez Garrido, 1971):  Fig. 2). -the middle 27m are formed of marly limestones with marl intercalations. Ostracods, radiolarians, echinoderms and globochaetes have been recorded.the uppermost 13-15m comprise an alternation of marls, limestones and marly limestones. Ostracods, radiolarians, foraminifera and sponge spicules have been recorded. Interval 4: 35m of well-bedded grey dolomites. Although no fossils have been recorded, a Kimmeridgian age has been assigned to this unit on lithostratigraphical considerations. Interval 5: 1-3m of whitish coloured limestones. A few fragments of gastropods and charophytes have been observed.
Lithostratigraphical correlations with adjacent areas suggest this unit represents the Portlandian-?Neocomian.
This sequence is uncomformably overlain by Cretaceous green marls and white sands of the "Utrillas" of Interval 6 and the yellowish sandy dolomites of Interval 7.

THE HONTANAR SECTION
Location. The Hontanar section is located along the road Teruel-Cuenca (province of Teruel) between kilometer poles 185-186 (Viallard, 1973; Fig. 1). Geological setting. The section is part of the Sierra de Albaracin, one of the structural units of the Iberian Chain (Viallard, 1973). In this unit the Precambrian and Palaezoic Hercynian basement is covered by thick more or less complete sequences of Mesozoic and Palaeogene sediments. As a result of tectonics, major differences are apparent in the palaeogeographical configuration of the Jurassic and Cretaceous sedimentary basins. Stratigraphy (Figure 4). No formal lithostratigraphical subdivision of the Jurassic has been established in this area and the lithostratigraphy, as in the Segura de la Sierra, is discussed in terms of Liassic, Dogger and Malm. In the Hontanar section the Malm is exposed. The Callovian to Middle Oxfordian sequence is very condensed and the Lower Oxfordian seems to be missing. Within the Hontanar section 7 lithological units have been distinguished. These units will be briefly discussed in a ascending order (Viallard, 1973 Unit 6: 35m of fine sands and silty marls with intercalations of microcrystalline limestone beds. On the basis of the foraminifera taxa Alveosepta jaccardi (Schrodt) a Kimmeridgian age has been assigned. Unit 7: 70m of fine micaceous sands and silty m a r k Based on lithostratigraphical considerations a Late Kimmeridgian to Portlandian age has been assigned. The Malm sequence is uncomfortably overlain by Cretaceous (Albian) deposits which constitute argillaceous sands with quartz pebbles of the "Utrillas".

PALYNOLOGY
Sampling. Twelve samples from the two sections described were taken and prepared, using standard palynological techniques. Eight samples are from Interval 3 of the Segura de la Sierra section ( Figure 3); three samples from unit 3 and one sample from unit 4 of the Hontanar section ( Figure 4). From the Hontanar section only samples HON 01 and HON 03 provided palynological assemblages, whereas samples HON 02 and HON 04 proved to be barren.
The samples were collected during a field excursion of the Laboratory of Palaeobotany and Palynology of the Utrecht State University, The Netherlands, in the early spring of 1979. Annotated species list. The following taxa have been recognised in the palynological assemblages investigated. The taxonomical classification of the palynomorphs was mainly based on publications by Couper (1958), Burger (1966), ), Dorhofer (1979), Herngreen et al. (1980, Hunt (1985) and Thusu & Vigran (1985). For genera identification the Genera File of Jansonius & Hills (1976) was consulted. Therefore, no other papers are included in the reference list. Full references to the dinoflagellate cysts cited can be found in Lentin & Williams, 1985. Those taxa marked by an asterisk are further discussed in the systematics section.
Benson also suggests that the differentiation by the development of paracingular crests is variable, impossible to observe in highly compressed specimens and should not be used to seperate dinocysts at a generic level. Although agreeing that development of crests are highly variable and an undesirable characteristic for generic separation, it seems that his use of the presence of an apical paraplate, although being probably a unique morphological feature, for practical purposes is equally difficult to apply. This difficulty is highlighted in the Spanish material where the poor presentation makes the recognition of an apical paraplate impossible, whereas the crest morphology can readily be interpreted. Therefore the symmetry of the paracingular crests and the fine, long crestal spines places the morphotype recorded in Spain within the Dichadogonyaulax sellwoodii group sensu Woollam (1983, p.193 Figs. 1, 4. "Gonyaulacysta complex" sample SIE-08. The specimen figured is probably conspecific with Meristaulax angulosa (Gitmez, 1970) Sarjeant & Gocht in Sarjeant 1984, however the species was so rare that it has been recorded under the "Gonyaulacysta complex".  Fig. 11. Dingodinium tuberosum (Gitmez, 1970 Davey (1982). It seems likely however, that the presence or absence of a corona, linked to an indication of a stratigraphical element to this variability, would suggest two species are involved. Hence the forms recorded in Spain have not been assigned to C. membranoidea, although the poor quality of the material in Spain could not support the erection of a new species.
(Plate 11, Figs. 1, 4) Remarks. The term "Gonyaulacysta complex" was coined by Stover & Evitt (1978, p.271). Jan du ChCne, Masure et al. (1986 p.15) also adopted this term although incorporating several new genera, including Apteodinium and Meristaulax (which they synonymize with Cribroperidinium). The generally poor preservation of the Spanish material means that many dinocysts could not be positively identified. However, many could clearly be recognised as part of the "Gonyaulacysta complex" and probably are representatives of the genera Apteodinium, Cribroperidinium, and Meristaulau.

GENERAL COMPOSITION OF THE ASSEMBLAGES
The samples investigated yielded relatively moderate diversified but rather poorly preserved palynomorphs. The relative frequencies and distribution of the taxa recognised are presented on Figures 5 and 6. The plots were made within S.I.P.M., EPW36 with the Checklist programme of J. Phillips.
The sporomorph content of the Segura de la Sierra assemblages is generally dominated by Corollina spp. and Spheripollenites spp. All other sporomorph taxa are minor constituents although occasionally Concavisporites spp. can be present in higher proportions. Noteworthy is the persistent occurrence of Cicatricosisporites spp. Acantomorph acritarchs, dinoflagellate cysts forming part of the "Gonaulacysta complex", Sentusidinium cf. rioultii and Apteodinium cf. nuciforme are generally the most frequent microplankton constituents.
The sporomorph content of the Hontanar assemblages is dominated by Spheripollenites spp., All other sporomorph taxa are minor constituents although Corollina spp. and Exesipollenites tumulus may occur in higher proportions. It should be noted that due to the overall poor preservation some specimens referred to Exesipollenites tumulus may represent inner bodies of Corollina spp. (see also Riley, 1974;p.36). Cicatricosisporites spp. has been recorded in both assemblages. Microplankton is a minor constituent.
The major difference between the Segura de la Sierra and Hontanar assemblages is that the latter are less diversified and contain fewer microplankton. The Segura de la Sierra assemblages show a general decrease in diversity towards the higher part of Interval 3.

DISCUSSION
Sporomorphs. The majority of taxa which have been recognised from the sections investigated occur in both Tethyan and Boreal realms. Some of them range throughout the larger part of the Jurassic and Cretaceous of Northwest Europe, e.g. Deltoidospora spp., Cleicheniidites senonicus, Ischyosporites variegatus, Leptolepidites spp., Spheripollenites spp. Todisporites spp., Callialasporites spp., Corollina spp. and Taurucosporites segmentatus, while other taxa are known from the Upper Jurassic onwards, e.g. Cicatricosisporites spp., Concavissimisporites spp., Leptolepidites proxigranulatus and Trilobosporites spp. (e.g. Couper, 1958;Burger, 1966;Dorhofer, 1979;Herngreen et al., 1980, Hunt, 1985. Although the bulk of taxa are present in both Tethyan and Boreal areas, the composition of Middle to Late Jurassic assemblages from these areas are quite different. This difference has already been discussed by Thusu & Vigran (1985). Although these authors do not discuss coeval Early Kimmeridgian assemblages, the composition of the Spanish sporomorph fraction in broad terms resembles that of other Jurassic Tethyan assemblages from the Sahara and north-eastern Libya being dominated by Corollina spp. and Spheripollenites spp. with scarce bisaccate pollen grains. (see also Reyre, 1973;Riley, 1974;Thusu & Vigran, 1985;Van Erve & Mohr, in press.). Assemblages from the Boreal area however show a reverse combination (Thusu & Vigran, 1985).
Most noteworthy in the sporomorph content of the samples investivated is the presence of Cicatricosisporites spp. According to Dorhofer (1979, fig. 4), this taxon evolved and migrated from lower palaeolati-tudes (10 degrees) in the Callovian of North Africa towards the north. At a palaeolatitude of ca 20 degrees (= approx. Iberian peninsula) it would appear in the Oxfordian and at a palaeolatitude of ca 30 degrees (North-west Europe) its first appearance would be in the Upper Kimmeridgian. However, the palynological data available do not support this theory: (1) the presence of indigenous Cicatricosisporites spp. in the "Callovian" of North Africa is rather doubtful. The palynological data from North Africa used by Dorhofer (1979) is based on the work of Reyre (1973). This author used subsurface cutting material and reports the first (= bottom) appearance of Cicatricosisporites spp. at the base of his zone 5B of presumed Middle Callovian to Late Jurassic age. Reyre's Zone 5B a c c o m m o d a t e s " C a 11 o v o -0 xf o r d i a n -Kimmendgian" (litho-) stratigraphical unit and the age assessments of this unit has been based on both stratigraphical/palaeontological and palynological criteria. The Middle Callovian age for the base of this unit has been established by stratigraphical correlations with the Tazerdunet outcrop section. The major part of this outcrop section is dated Callovian-Oxfordian by means of ammonites, whereas its upper part probably represents the Kimmeridgian (Reyre, 1973). The Late Jurassic age of the top part of the "Callovo-Oxfordian-Kimmeridgian" unit is adopted on palynological criteria: the presence of Cicatricosisporites spp. and Trilobosporites spp. The lowermost appearance of very few specimens of Cicatricosisporites spp. in the "Callovo-Oxfordian-Kimmeridgian", definitely not caved from the overlying units, is only reported in the well DB-1, where this (litho-) unit of 160m thickness reaches surface. In the upper part of this unit Cicatricosisporites spp. has been recorded together with Trilobosporites spp. However, from Reyre's data it is not conclusive whether Cicatricosisporites spp. are present in the lower part of the "Callovo-Oxfordian-Kimmeridgian" unit in well DB-1, and if so, that they are indigenous and have not been caved from the upper part of this unit. In conclusion it can be stated that, at present no strong evidence is available for the first appearance of Cicatricosisporites spp. in the "Middle" Callovian.
(2) the presence of Cicatricosisporites spp. in the Sutneria platynota zone of earliest Kimmeridgian age from Spain is the oldest known occurrence from the Iberian peninsula (compare Van Erve & Mohr, in press.). (3) In Northwest Europe Cicatricosisporites spp. have been recorded from strata referred to the Rasenia cymodoce Zone , which represents the equivalent of the zone overlying the Sutneria plafynota Zone (Fig. 2).
From this it is obvious that the assumption of a strong diachronous migration of Cicatricosisporites spp. from lower to higher palaeolatitudes on the northern hemi-t h e sphere is speculative and not supported by palynologic-a1 data. Microplankton. Although Gitmez (1970) describes microplankton assemblages from the Pictonia baylei zone of North-west Europe, there are relatively few other publications discussing microplankton assemblages specifically from the earliest Kimmeridgian. Also in the Tethyan realm no records are available: in the Upper Bathonian-Tithonian interval described by Thusu & Vigran (1985) no marine Lower Kimmeridgian deposits have been recorded. However, the Lower Kimmeridgian interval is considered in several Upper Jurassic zonal schemes notably Fisher & Riley (1980) (Leptodinium egemenii subzone) and Woollam & Riding (1983) (Gj/Sc(c) subzone). In general the microplankton assemblages described from these publications are all fairly similar being dominated by species of the "Gonyaulacysta complex," normally with common G. jurassica, Hystrichogonyaulax cladophora, and species of Leptodinium. The assemblages also typically contain Sentusidinium spp. and with varying records of chorate dinocysts.
In some respects the assemblages recorded in Spain are similar to those mentioned above, particularly in the dominance of species of the "Gonyaulacysta complex". However G. jurassica, which is normally frequent in Northwest European Early Kimmeridgian assemblages, although present in Spain, is only recorded in low numbers and H. cladophora is not recorded at all.
The other apparently major difference is the presence of species of Dichadogonyaulax and Ctenidodinium with high parasutural ornament in the Spain material. Ctenidodinium chondrum Drugg 1978, which has low parasutural ornament, is the only published species of these genera from the Early Kimmeridgian. This apparent difference is probably a reflection of the lack of published data, since several forms, similar to those recorded in Spain, have been frequently noted to occur in borehole material from the Kimmeridgian of the North Sea (CFL pers. obs.).
Of palynostratigraphical interest is that both the publications on zonal schemes mentioned above note the last stratigraphical occurrence of Scriniodinium crystallinurn in the Pictonia baylei zone and significantly this form is also recorded in Spain. Equally Woollam & Riding (1983) note the first appearance of .Dingodinium tuberosum in the earliest Kimmeridgian Gj/sc(c) subzone, again a species recorded in Spain.  I 1  II  II  I 1  II  II  II  II  II  II  II  II  II   II  II A