Climate variations in the Boreal Triassic — Inferred from palynological records from the Barents Sea

Palaeogeography, Palaeoclimatology, Palaeoecology 290 (2010) 20–42

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Palaeogeography, Palaeoclimatology, Palaeoecology j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / p a l a e o

Climate variations in the Boreal Triassic — Inferred from palynological records from the Barents Sea Peter A. Hochuli a,⁎, Jorunn Os Vigran b a b

Palaeontological Institute and Museum, University Zürich, Karl Schmid Str. 4, CH-8006 Zürich, Switzerland Sintef Petroleum Research, NO-7465 Trondheim, Norway

a r t i c l e

i n f o

Article history: Received 23 January 2009 Received in revised form 5 August 2009 Accepted 26 August 2009 Available online 3 September 2009 Keywords: Triassic Palynology Palaeobotany Palaeoclimate Barents Sea

a b s t r a c t This paper presents palynological evidence from the late Early Triassic (late Smithian) to the Late Triassic (Rhaetian) of the Barents Sea area: A continuous palynological succession from an exploration well (7228/7-1A) in the Nordkapp Basin (SW Barents Sea) and palynological data from a series of shallow cores drilled at the Svalis Dome (Central Barents Sea) representing selected Triassic intervals. These fully marine sediments are independently dated by marine faunas. Both records show significant shifts in the distribution of the main floral elements. Changing ratios of spore-pollen taxa, grouped as hygrophytes versus xerophytes and spores versus pollen, reveal major changes of the floras within the studied interval. One distinct turnover coincides with the Smithian/ Spathian boundary where lycopsid and pteridophyte spores dominated assemblages change to pollen (pteridosperms and conifers) dominated assemblages. Lower Middle Triassic assemblages are again dominated by lycopsid spores while the assemblages from the upper part of the Middle Triassic and the lower part of the Late Triassic are characterised by dominance of coniferous pollen and show the decline of pteridosperms. In the latest Triassic fern spores are abundant and diverse. In contrast to the Middle Triassic the pollen assemblages are characterized by cycadophytes and Araucariacites. These distribution patterns are interpreted to reflect climatic changes. The presented results from Norwegian Boreal areas confirm the significant differences between quantitative distribution of specific taxa as well as diversity of major groups in plant assemblages from low and mid latitudes. The present survey opens new perspectives for more detailed comparisons and climatic interpretations of floras from the Triassic period, a time during which Mesozoic vegetation established. The major changes in the dominance of specific floral elements, especially the diversification and spreading of the conifers, can probably be related to climatic changes. © 2009 Elsevier B.V. All rights reserved.

1. Introduction The Triassic climate is generally known to be hot and arid, but little is known about the climatic variations in time and space (Scotese, 2000; Sellwood and Valdes, 2006 and references therein). The widespread occurrence of red beds and the lack of continuous fossil plant records have lead to the general belief that during the Triassic continents represented extremely hostile environments. However, the variable distribution of sediments (e.g. coal, evaporites) and changes in the palaeontological record suggest the existence of long and shorter term climatic variations (Scotese, 2000). Palynological data are generally considered good proxies for climatic conditions. Countless Cenozoic records have shown that the distribution of spore-pollen is a good proxy for climatic conditions (Traverse, 2007, and refs. therein). However, for this period palaeoenvironmental and palaeoclimatic requirements of most parent plants of spores and pollen are known, whereas for ⁎ Corresponding author. Tel.: +41 634 23 38; fax: +41 634 49 23. E-mail address: [email protected] (P.A. Hochuli). 0031-0182/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.palaeo.2009.08.013

Mesozoic and older material the botanical affiliation of spore-pollen is less secure or unknown. For the Triassic long and continuous palynological records are extremely rare and climatic interpretations based on palynological assemblages have rarely been applied. In boreal areas thick continuous successions of marine sediments containing rich spore-pollen assemblages represent the best possible archives and allow direct correlations of palynological records with the marine fauna and the corresponding time calibration. The palynological records from the central and south-western Barents Sea open the possibility to follow trends in the development of the floras through most of the Triassic, covering a time span of about 40 million years. In this paper we attempt to evaluate the palaeoclimatic significance of observed fluctuations in the distribution of spore-pollen in well 7228/7-1A and in the data from the shallow cores from the Svalis Dome area (7323/07-U-08, 06, 03, 04, 01, 07, 09, 10, 05, 02). The idea that specific sporomorph groups might provide useful palaeoclimatic and palaeogeographic information also for the Triassic has been put forward by several authors (e.g. Dolby and Balme, 1976; Visscher and Van Der Zwan, 1981). However, few Triassic records

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provide adequate data allowing interpretation of palaeoclimatic successions. Some authors (e.g. Brugman et al., 1994; Visscher et al., 1994) relate variations in the palynological successions essentially to variations in the depositional environments. Others consider variations in the sedimentary successions and in the floras, including palynological records, as palaeoclimatic signals (e.g. Simms and Ruffell, 1989, 1990; Simms et al., 1994; Scotese, 2000; Chumakov and Zharkov, 2003; Roghi, 2004; Galfetti et al., 2007; Bachmann and Kozur, 2004; Kozur and Bachmann, 2008; Preto et al., 2008). A multi-proxy approach including sedimentology, geochemistry (e.g. stable isotopes), palynology and palaeontology seems to provide the means to separate climatic and taphonomic effects (Galfetti et al., 2007; Hermann et al., 2008). These studies confirm the existence of distinct climatic shifts for the Triassic with implications for the evolution of terrestrial and marine biota. So far palynological studies of the Arctic including the Barents Sea area have focused on biostratigraphy. In this context the first comprehensive zonation of the Triassic of the Barents Sea area has been proposed by Hochuli et al. (1989). Based on detailed studies of shallow cores drilled in the Svalis Dome area a refined zonation of the Early and Middle Triassic interval has been proposed by Vigran et al. (1998). These cores were drilled with focus on specific boundaries and events (Mørk and Elvebakk, 1999). Thus the cored sections represent selected intervals covering important boundaries, and have been integrated within the regional geological history with seismic evidence (Riis et al., 2008). Most of this material is independently dated by marine fauna recovered from the cores. Studies of shorter intervals have been published for the lowermost Triassic (Mangerud 1994), the late Early and the Middle Triassic (Mørk et al., 1990; Mangerud and Rømuld, 1991). In other studies palynological evidence from this area has been used in the context of sequence stratigraphic interpretations (Van Veen et al., 1992; Mørk et al., 1992) or for stratigraphic schemes combining magnetostratigraphy, biostratigraphy and lithostratigraphy (Hounslow et al., 2007, 2008). Comparable Triassic records are missing from southern localities of Europe, but palynological data from selected intervals from Central and Southern Europe show clear differences in the composition of the assemblages. Some important floral elements of the Tethyan realm are extremely rare in the contemporaneous deposits of the study area. Other elements seem to have their main distribution in the Boreal realm. There are major differences in the distribution of the conifers, especially within the genera Ovalipollis, Protodiploxypinus and the families Cheirolepidaceae and Araucariaceae. There are also differences in the quantitative distribution and diversity of spores of lycopsids and ferns. 2. Geology The present records are based on work related to the exploration campaign of Statoil 2001 and to the stratigraphic drilling in the Nordkapp Basin, the south-western part of the Barents Sea (Fig. 1). The Late Palaeozoic Nordkapp Basin is a rift basin in the south-western Barents Sea where the sedimentary fill ranges from Carboniferous to Tertiary ages and the infill of the basin was strongly influenced by diapirism (Bugge et al., 2002). Due to Cenozoic uplift most of the younger sediments were later eroded. During the Triassic this basin was connected to a large embayment, opening towards Panthalassa in the northwest. Progradation of sediments from the land masses in the east and southeast filled the deep Early Triassic basin and it gradually changed into a paralic platform (Riis et al., 2008; Worsley, 2008). Well 7228/7-1A was drilled in the vicinity of a salt diaper and due to the uplift of the salt the Triassic sediments are steeply dipping towards NW. The main objective of this well was to test the hydrocarbon potential of Middle and Upper Triassic sandstones of the Snadd Formation. The well was drilled into the Early Triassic (Spathian) and good reservoir zones were penetrated and cored in the Klappmyss and Snadd formations. The lithostratigraphic subdivision of the studied section of well 7228/7-1A is plotted in Fig. 3. Additional information on this well may be obtained

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Fig. 1. Location of the studied sites.

from: http://www.npd.no/engelsk/cwi/pbl/en/well/all/4257.htm). The palynological record of the thick Triassic sequence of this well covers the essential part of the Triassic (late Early to Late Triassic). The monotonous lithological succession with predominating siltstones with a few sandy intervals suggests homogeneous marginal marine conditions throughout the more than 1000 m thick section. The palynological record of the thick late Early to Late Triassic sequence from a single site, apparently with minimal changes in the depositional environment, is ideally suited for palaeoclimatic considerations. The second record comprises high resolution data from shallow cores at the Svalis Dome (Vigran et al., 1998). The cores were obtained through a shallow drilling program focusing on stratigraphic boundaries but also on potential source and reservoir rocks of the Norwegian Shelf deposits (Mangerud and Rømuld, 1991; Vigran et al., 1998; Mørk and Elvebakk, 1999). The Svalis Dome is situated northwest of well 7228/7-1A, an area closer to the centre of the rift basin and representing more distal environments. During the Middle Triassic this area developed from a deep shelf, through prodelta to paralic environments (Riis et al., 2008). Most cores contain marine invertebrates that give independent dating of the palynological data presented by Vigran et al. (1998). For additional information on the drilling and images of the cores see: http://www.sintef.no/static/pe/ produkt/shadripro/corephotos/area_pages/svalis_dome.htm. 3. Materials and method Relatively dense sampling and detailed study of well 7228/7-1A led to a complete palynological record (Figs. 2–5). Ditch cuttings samples were routinely taken every 6 m and prepared and studied for palynology. In the cored interval the sample density is considerably higher. The record is based on the study of 243 samples (including 3 sidewall cores and 22 core samples). Although essentially based on ditch cuttings samples, this palynological record shows consistent distribution patterns of sporomorphs. The samples were prepared following the standard palynological procedure (Traverse, 2007) and sieved with 15 µm mesh sieve. For the quantitative analysis a minimum number of 200 palynomorphs was counted before searching the slides of each sample for additional rare taxa. The average number of taxa recorded per slide was 35 (min. 20./max. 53); a total of 190 sporepollen taxa were determined from this well. The preservation of the

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Fig. 2. Palynological record of well 7228/7-1A, biostratigraphic subdivision, quantitative distribution of main floral elements and H/X ratio. Based on these distribution patterns the section is subdivided into 20 floral phases (see also Figs. 3–5).

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palynomorphs varied from mediocre to good; with few exceptions the productivity of the samples was high. The present study deals with spore-pollen only. Dinoflagellate cysts — present in the uppermost part of the section — acritarchs, algal and fungal remains observed in all samples are excluded from the calculated percentages. These forms are generally rare, never reaching percentages over 5% of the total palynomorph counts. The Svalis Dome record is based on the study of 279 productive samples from 10 cores. For most samples recovery and preservation of palynomorphs was good or excellent. The plotted results (Figs. 6–10) are based on values calculated from the semi-quantitative data as published by Vigran et al. (1998). The results are plotted in the same way as the records of well 7228/7-1A (Figs. 2, 3). For simplicity empty columns (e.g. Circumpolles in Figs. 6, 7) are omitted. 4. Depositional environments For well 7228/7-1A the palynological evidence confirms the interpretation that the succession was deposited in a marginal marine environment. Marine influence is reflected by the occurrence of acritarchs and of dinoflagellate cysts. The record of the latter is restricted to the Late Triassic zone ASS-C, whereas acritarchs occur regularly from the base of the section to the top of the Ladinian but become rare in the Late Triassic. Prasinophycean algae (Cymatiosphaera, Tasmanites, and Dictyotidium) also of marine origin are regularly observed in the Anisian/Ladinian interval (ASS-G/H–ASS-I) and occur sporadically throughout the remaining part of the section. Remains of fresh- or brackish-water algae such as Botryococcus and Schizosporis are present throughout the studied section; however, they are more common in the youngest segment (Carnian to Rhaetian). The green algae Plaesiodictyon, which is also known to be common in brackish and freshwater environments, appears rarely in the Anisian interval (ASS-K); but it occurs regularly from the Anisian/ Ladinian (Ass-I) up to the late Carnian (Ass-C). Together with the continuous strong dominance of terrestrial organic matter the distribution of the above mentioned groups reflects marginal marine conditions for the entire section with a slight increase of marine influence in the Spathian/early Anisian segment (Klappmyss Formation) and in the Anisian/Ladinian interval (Kobbe Formation). The shallow cores of the Svalis Dome area contain abundant acritarchs and prasinophycean algae and some intervals are characterized by high TOC values and palynofacies dominated by kerogen of marine origin. A restricted, deep, mostly anoxic shelf environment has been attributed to the sediments of late Spathian and Anisian age (cores 7323/07-U-04, 01, 07, 09). The depositional environment of the Ladinian part of the section shows stronger terrestrial influence with increased sand influx. These samples yield comparatively low TOC values and the kerogen assemblages are dominated by terrestrial phytoclasts. Based on sedimentological evidence and palynofacies the depositional environment has been interpreted as a storm influenced open shelf (Vigran et al., 1998). Some differences recorded in the composition of spore-pollen assemblages of well 7228/7-1A and the shallow cores may be attributed to the marked differences in depositional environments (Riis et al., 2008, Fig. 10). 5. Biostratigraphy The palynostratigraphic breakdown of well 7228/7-1A is based on the comprehensive zonation published by Hochuli et al. (1989), which covers the entire Triassic of the Barents Sea area. The zones, originally designed to be used for exploration purposes, were essentially defined by first appearance datum (FADs) and last appearance datum (LADs) of spore-pollen, but also include typical events marked by abundances of certain species or groups of taxa. Definitions and calibrations of most of the Early and Middle Triassic zones were based on dated material from outcrop sections. But in parts of the Late Triassic, especially in the Norian

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and parts of the Carnian section, direct correlation of the corresponding zones was hampered by the lack of adequately calibrated material. A calibration was attempted by using independently dated ranges of spore-pollen from other areas (e.g. the Germanic Basin). Thus, the ages of these zones are loosely constrained. For the Early and Middle Triassic part of the succession additional information has been gained through the detailed study of the shallow cores of the Svalis Dome area (for details and references see Vigran et al., 1998). The stratigraphic interval covered by these cores (late Griesbachian and late Smithian to early Ladinian) was subdivided in 8 formally defined assemblage zones (Svalis-1–Svalis-8), all calibrated with marine fauna and tied to seismic reflectors (see below). 6. Floral elements The following chapter lists the spore-pollen groups, which are included in the distribution charts (Figs. 2–10) following the order given in Figs. 2 and 3. It also includes some details concerning their specific composition and their known or probable botanical affinity. Comments on the quantitative distribution of the groups within the study area are added together comparisons with other areas and possible palaeoclimatic implications. Useful information on the botanical affiliation and palaeoenvironmental requirements of fossil plants can be gained from sporomorphs found in situ. For the present study we refer to the compilations of in situ finds by Balme (1995) and Traverse (2007). 6.1. Cavate trilete spores (cf. Figs. 2, 4, 6–9) This diverse group includes the genera Densoisporites, Kraeuselisporites, Pechorosporites and Endosporites, all representing spores of lycopsids. Their distribution shows a particular pattern; they are abundant in the assemblages of the Early Triassic (Svalis-2–Svalis-4). In well 7228/7-1A they are also relatively common and quite diverse in the lower part of the studied section (phases 1–3). In the following phases 4–12 they are rare. Although with different specific composition they show an overall increasing abundance and diversity in the latest Triassic (e.g. phases 16–20). In the present context Densoisporites nejburgii is treated separately (see below). 6.2 Aratrisporites (cf. Figs. 2, 4, 6–9) Contrary to most Tethyan localities (Brugman, 1986) Aratrisporites is extremely abundant in some parts of the studied material. In well 7228/7-1A the highest abundance is in the Early Triassic and in the lower part of the Middle Triassic (phases 1–8), where it also shows its highest diversity. It is much rarer but consistently present in the interval of phases 10–14 and becomes rare in the late Carnian to Norian intervals (phases 15–17). However, it shows another peak in the Norian/Rhaetian interval (phase 18). The genus has been recovered in situ in Russian Early Triassic floras (Yaroshenko, 1988) and is attributed to the lycopsids (Pleuromeiaceae). Although attributed to the same group Aratrisporites and Densoisporites nejburgii show different stratigraphic and palaeogeographic distribution patterns. D. nejburgii is essentially restricted to the Early Triassic and has it main distribution area in the low latitudes. Aratrisporites, appearing in the Early Triassic, seems to have its main distribution and diversity in the Middle and Late Triassic of mid- and high latitudinal sites. In low latitudinal sites it seems to be more common in assemblages with other evidence for increased humidity (e.g. Raibl beds, cf. Hochuli and Frank, 2000). 6.3. Smooth trilete spores (Figs. 2, 6–9) Main components of this group are Annulispora, Calamospora, Concavisporites, Dictyophyllidites, and Punctatisporites. Most species can be related to ferns and are stratigraphically long ranging. Because

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of their peculiar distribution patterns the taxa Calamospora spp. (attributed to equisetopsids) and Concavisporites crassiexinus are plotted separately in Fig. 3.

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1998 suggests angiospermous affinity (Hochuli and Feist-Burkhardt, 2004). 6.9 Chasmatosporites (Figs. 3, 10)

6.4. Ornamented trilete spores (Figs. 2, 6–9) Most common members of this group, comprising ornamented spores of heterogeneous origin, are the representatives of the genera Cyclotriletes, Kyrtomisporis, Lycopodiacidites, Osmundacidites, Trachysporis and Verrucosisporites. It includes a high number of species; most of which are rare or occur only sporadically. As an exception Kyrtomisporis is abundant and shows a typical distribution pattern in the Late Triassic (Fig. 4). Lycopodiacidites and several megaspores are probably of lycopsid origin; Cyclotriletes, Osmundacidites and Verrucosisporites represent Filicales. The affiliation of some other genera like Trachysporis and Kyrtomisporis is uncertain; they probably also represent ferns. 6.5. Monolete spores (Figs. 2, 6, 8, 9) Included in this group are the genera Leschikisporis, Punctatosporites and Polypodiisporites affiliated with ferns. In the studied material Leschikisporis is by far the most abundant form and like Punctatosporites it possibly represents the Marattiales (Balme, 1995). The abundance peak of the monolete spores observed in the Carnian deposits of well 7228/7-1A (Fig. 2) has also been seen in other exploration wells and in shallow cores from the Barents Shelf (pers. observations). Hence, it is of at least regional significance. 6.6. Bryophytes/Ricciisporites (Figs. 2, 4, 6, 8, 9) The genera Stereisporites, Porcellispora, and as the most conspicuous taxon Ricciisporites are included in this group (Balme, 1995). The affinity of the latter genus, which we tentatively include with the bryophyte group, is ambiguous. Its original attribution to Ricciaceae (Marchantiales) by Lundblad (1954) has later been revoked (Lundblad, 1959). Due to the strong representation of this genus bryophytes are common in the uppermost part of the section (ASS-B and ASS-A). All the other taxa occur only sporadically. 6.7 Araucariacites (Figs. 2, 7–9) Araucariacites spp. represents the most common genus of this group, which also includes the genus Cerebropollenites (Cerebropollenites spp. and C. macroverrucosus). Araucariacites first appears in the early Anisian (Svalis-5) but becomes common only in the Late Triassic (ASS-F, phase 11). Cerebropollenites spp. are represented in the uppermost part of the section (ASS-B2, ASS-B and ASS-A). The mentioned genera are attributed to Araucariaceae (Balme, 1995). 6.8 Cycadopites/Chasmatosporites (Figs. 2, 6–9) This group of monosulcate pollen includes Cycadopites, Chasmatosporites, Eucommiidites, Retisulcites, Echinitosporites and Pretricolpipollenites. Some representatives, such as Cycadopites and Monosulcites, are regularly represented throughout the section. Echinitosporites iliacoides, Retisulcites perforatus, Retisulcites sp. 2 of Hochuli et al., 1989, and Retisulcites spp. show sporadic occurrences in late Anisian and Ladinian assemblages (Svalis-7 and Svalis-8). Most genera are attributed to gymnosperm groups like Cycadales, Bennettitales, and Ginkgoales (Balme, 1995). The biological attribution of Retisulcites is uncertain. The morphology of Retisulcites sp.1 and sp. 2 of Hochuli et al. (1989) and Retisulcites sp. A of Vigran et al.,

The genus Chasmatosporites is known to appear with rare occurrences in the Anisian (phase 9 and Svalis-7; cf. Figs. 3, 10); it probably was produced by the Cycadales (Balme, 1995). It occurs regularly in the lower part of the Carnian (phase 11) and becomes successively more frequent in the upper part of the Late Triassic (phase 15–20). 6.10 Densoisporites nejburgii (Figs. 2, 6–8) D. nejburgii has a wide palaeogeographic distribution and is common in Lower Triassic sections also of low latitudinal sites. For this reason this species is treated separately from the other cavate spores and has been attributed to the xerophytes (see below). In the studied material it occurs abundantly in the assemblages of Olenekian age and fades out during the lower part of the Anisian. In well 7228/7-1A it is restricted to phases 1–4. Spores determined as D. nejburgii have been found in situ in sporangia of various species of Pleuromeia, including P. sternbergii (Balme, 1995). 6.11 Taeniate bisaccate pollen (Figs. 2, 5–9) Pollen with a proximally striated body, Lunatisporites, Protohaploxypinus, Striatoabieites, Striatopodocarpites, Infernosporites, Tubantipollenites and Lueckisporites are included in this group. In the studied sections the group shows a characteristic distribution. It is abundant in the Early Triassic and lower part of the Middle Triassic. In well 7228/7-1A it is common during phases 1–4, becomes reduced in phase 5, shows another peak during phases 7–9 (late Anisian to early Ladinian), before fading out in the Carnian (phases 10 and 11). Above phase 11 these pollen occur sporadically (Fig. 5). Most genera of the group can be attributed to pteridosperms; some, like Lueckisporites, are related to conifers (Balme, 1995). 6.12 Circumpolles (Figs. 2, 5, 8, 9) In the studied material Circumpolles occur sporadically and is, in comparison to southern localities, poorly diversified (Brugman, 1986; Hochuli, 1998; Roghi, 2004; Buratti and Cirilli, 2007). Only rare specimens of the following genera have been observed in this study: Classopollis, Granuloperculatipollis and Duplicipollis, Partitisporites and Paracirculina. Some of the typical and common elements of Tethyan Middle and Late Triassic assemblages such as Camerosporites have been found only sporadically in the Barents Sea area and have not been observed in the present study. Pollen grains of the Circumpolles group are generally attributed to the conifer family Cheirolepidaceae (Scheuring, 1978; Zavialova and Roghi, 2005). 6.13 Monosaccate pollen (Figs. 2, 8, 9) Undetermined monosaccate pollen as well as the genera Dyupetalum and Cordaitina are essentially restricted to the lower part (preCarnian) of the studied sections. Cordaitina has been attributed to Cordaites (Balme, 1995). In this paper the monosaccate pollen are regarded as hygrophytic elements. The monosaccate taxa Patinasporites, Enzonalasporites and Vallasporites, which are common or abundant in Upper Triassic sediments of the Tethyan area, are probably related to conifers (Balme, 1995). Due to their palaeogeographic distribution they have to be considered xerophytic elements.

Fig. 3. Palynological record of well 7228/7-1A with quantitative distribution of the groups Calamospora, Kyrtomisporis, Concavisporites crassiexinus, Chasmatosporites, Triadispora/ Angustisulcites, Brachysaccus and Protodiploxypinus as well as the spore/pollen ratios.

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Fig. 4. Palynological record of well 7228/7-1A with the distribution of individual taxa of cavate trilete spores, Aratrisporites, Bryophytes and Kyrtomisporis.

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Fig. 5. Palynological record of well 7228/7-1A with the distribution of individual taxa of the following groups: taeniate bisaccate pollen, Protodiploxypinus, Ovalipollis/Illinites, Triadispora/Angustisulcites and Circumpolles.

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Fig. 6. Palynological record of shallow core 7323/07-U-08 and 06 (Svalis-2 and -3), biostratigraphic subdivision, quantitative distribution of main floral elements and H/X ratios.

In the present material they are extremely rare and are — together with the Early and Middle Triassic forms — considered as one group. 6.14 Non-taeniate bisaccate pollen (Figs. 2, 6–9) Indeterminate non-taeniate bisaccate pollen and common genera like Angustisulcites, Brachysaccus, Protodiploxypinus and Triadispora are included in this group. In well 7228/7-1A this group shows a distinct distribution pattern. The frequency steadily increases in the lower part of the section (phases 1–5), and above an interval with varying abundance (phases 6–8) becomes the dominant element of Ladinian and early Carnian assemblages (phases 9–11). In the younger assemblages (phases 12–20) percentages decrease essentially in favour of the various groups of spores. Most non-taeniate bisaccate pollen probably were produced by conifers (Balme, 1995; Scheuring, 1970, 1978; Traverse, 2007). In the Figs. 3, 5 and 10 the distribution of the above mentioned genera are treated as separate groups (see below).

genus Kuglerina. For well 7228/7-1A its record is shown separately in Fig. 3 and itemized as individual taxa in Fig. 5. The group appears in the Spathian (Svalis-3), reaches its maximum in the late Anisian and lower part of the Ladinian, and has frequent occurrences up to the lower part of the Carnian (phase 11). Above the Carnian pollen of this group are generally rare and disappear near the Triassic/Jurassic boundary. Based on morphological studies (Scheuring, 1970) and in situ occurrences (Balme, 1995) Triadispora has been attributed to conifers. 6.16 Brachysaccus group (Figs. 3, 10) The genus Brachysaccus represents an important element of the non-taeniate bisaccate pollen. It appears in the Anisian and occurs frequently in Ladinian and Carnian assemblages (Hochuli et al., 1989). In well 7228/7-1A representatives of this genus are most common during the phases 10 and 11 and 15. The genus Brachysaccus most probably represents the conifers.

6.15 Triadispora/Angustisulcites group (Figs. 3, 5, 10)

6.17 Protodiploxypinus group (Figs. 3, 5, 10)

The Triadispora/Angustisulcites group is considered part of the nontaeniate bisaccate pollen (see above). The group also includes the

The genus Protodiploxypinus shows a distinct distribution pattern. Its peak abundances characterise the assemblages from the upper

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Fig. 7. Palynological record of shallow core 7323/07-U-03 and -04 (Svalis-4 and 5) with biostratigraphic subdivision, quantitative distribution of main floral elements and H/X ratios.

Fig. 8. Palynological record of shallow core 7323/07-U-01 (Svalis-6) as well as 7323/07-U-07 and -09 (Svalis-7) with biostratigraphic subdivision, quantitative distribution of main floral elements and H/X ratios.

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Fig. 9. Palynological record of shallow core 7323/07-U-10, -05 and -02 (Svalis-8) with biostratigraphic subdivision, quantitative distribution of main floral elements and H/X ratios.

part of the Carnian (ASS-C, Hochuli et al., 1989), corresponding to phase 15. This feature has been observed in other exploration wells from the Barents Shelf (pers. observations). The genus is probably related to conifers (Scheuring, 1970; Traverse, 2007).

xerophytic elements. Representatives of this group are most likely of gnetalean origin.

6.18 Ovalipollis/Illinites group (Figs. 2, 5, 7–9)

The representatives of this group, Perinopollenites cf. elatoides, Sciadopityspollenites spp. and Inaperturopollenites spp., are extremely rare in the studied well. For this reason they are not listed separately, but are included as hygrophytic elements. These pollen types are produced by conifers.

The genera Ovalipollis, lllinites and Staurosaccites are treated separately from the bisaccate pollen. Illinites, first recorded in the late Spathian, is an important element in Middle Triassic assemblages; Ovalipollis and Staurosaccites have their main distribution in the Late Triassic. In well 7228/7-1A the group is rare in the lower part of the section (phases 1–5) and becomes common in the interval between the late Anisian and the lower part of the Ladinian (phases 6–9). Due to the abundance of Ovalipollis another frequency peak has been recorded in phase 14. The above mentioned genera are known to disappear in the latest Triassic. Pollen grains similar to Illinites occur in male cones of the conifer Aethophyllum (Balme, 1995). Considering their similar morphology the genera Ovalipollis and Staurosaccites are also regarded as being of coniferous origin (Scheuring, 1970). 6.19 Ephedripites group The taxa Ephedripites and Schizaeosporites worsleyi included in this group occur only sporadically in the studied intervals. For this reason they are not plotted separately, but they are included within the

6.20 Inaperturopollenites group

6.21 Hygro- and xerophytic elements (Figs. 2, 6–9) The above listed groups are classified according to their assumed ecological requirements as the two entities — hygrophytes and xerophytes. This classification, essentially following the concept of Visscher and Van Der Zwan (1981), regards all spores with the exception of Densoisporites nejburgii as hygrophytes. Among gymnosperm pollen the Cycadopites-Chasmatosporites and the Araucariacites group, as well as monosaccate pollen are attributed to the hygrophytes; all other pollen groups are classified as xerophytes. The spore/pollen (SP/P) ratios plotted on Figs. 3 and 10 reflect essentially the same trends as the hygrophyte/ xerophyte (H/X) ratios. Divergences are due to relatively strong representation of the above mentioned pollen groups, which are classified as hygrophytes. Consistent changes of these ratios are interpreted as climatic proxies, e.g. as changes in the humidity

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available to the parent plants. It should be noted that floral turnovers are not necessarily accompanied by changes in H/X ratios (cf. phase 14–18).

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frequency of Densoisporites nejburgii remains unchanged. Smooth trilete spores show a continuous increase. Compared to phase 2 H/X ratios are slightly reduced (0.5–0.6). Phase 3 and the following phase 4 cover the interval attributed to ASS-L (see below).

7. Floral successions 7.1.4. Phase 4 The quantitative palynological data from the exploration well 7228/7-1A and the shallow cores of the Svalis Dome area reflect a succession of floral assemblages that gives a unique overview of the distribution of Triassic floral elements of the Barents Sea area. 7.1. Well 7228/7-1A The ages of the Triassic sediments penetrated in this well range from late Spathian to Rhaetian. The palynological record is essentially based on the study of ditch cutting samples. Due to this fact the first appearance of groups or individual taxa may be biased by material caved from higher levels. However, there are no obvious indications for cavings. The consistent distribution of the main floral elements and the observed ranges of individual taxa essentially correspond to previously published data (Hochuli et al., 1989; Mørk et al., 1992; Vigran et al., 1998). The biostratigraphic breakdown is based on the zonation of Hochuli et al. (1989). The sedimentary succession and the palynological data suggest that the depositional environment was quite homogenous during the time of deposition. For this reason taphonomic bias of the assemblages is probably essentially constant. There is no evidence for major breaks in sedimentation. In order to facilitate the discussion of the palynological succession, it is subdivided into 20 distinct floral phases (1–20, cf. Figs. 2–5). 7.1.1. Phase 1 Interval: 2880.00–2833.65 m. This interval is characterized by the abundance and high diversity of taeniate bisaccate pollen and spores of the Aratrisporites group. Cavate trilete spores and among them Densoisporites nejburgii occur regularly. Non-taeniate bisaccate pollen show relatively low frequency. Trilete spores (smooth and ornamented) occur frequently. The pollen Taeniaesporites sp. U of Jansonius (1962), Lunatisporites novimundanus as well as spores like Uvaesporites cf. imperialis are restricted to this interval. The H/X ratios vary around 0.6. Phase 1 and 2 correspond to the interval assigned to late Spathian zone ASS-M. 7.1.2. Phase 2 Interval: 2826.0–2775.0 m. Phase 2 is marked by the dominance of spores. Most abundant are representatives of the Aratrisporites group. Taxa such as A. paenulatus, A. cf. banksii and A. “densispinatus” have their highest occurrence at the top of this interval. The cavate trilete spores are quite frequent, including several species of Densoisporites, namely D. playfordii, and the regularly occurring species Lundbladispora brevicula. Smooth trilete spores, especially Calamospora, show a slight increase. Compared to phase 1 the percentage of taeniate bisaccate pollen decreases significantly. A distinct feature of this phase is the onset of the continuous record of the Triadispora/Angustisulcites group. In this interval the H/X ratio reaches about 0.7.

Interval: 2724.0–2604.0 m. In this interval the cavate trilete spores including D. nejburgii occur only sporadically. The latter is consistently recorded up to the top of this phase. There is an increasing abundance of the Aratrisporites group and a high abundance of bisaccate pollen (taeniate and non-taeniate forms). Smooth trilete spores decrease. The H/X ratios remain within the same range as below. Phases 3 and 4 have been assigned to zone ASS-L. The LAD of D. nejburgii at the top of this interval is taken as evidence for the assignment to this zone. 7.1.5. Phase 5 Interval: 2598.0–2493.0 m. The highest abundance of the Aratrisporites group characterises this phase. From phase 5 to phase 10 cavate trilete spores are extremely rare. Taeniate and non-taeniate bisaccate pollen, show a distinct decrease; but among the latter the Triadispora/Angustisulcites group starts to increase. The onset of a continuous record of the Ovalipollis/Illinites group is another distinct feature. Due to the strong dominance of spores H/X ratios are high (>0.75). Phase 5 and the following phases 6 and 7 fall within the range of zone ASS-K. 7.1.6. Phase 6 Interval: 2487.0–2442.0 m. Phase 6 is characterized by a general decrease of the Aratrisporites group although it still dominates in a few samples. The strong increase of the non-taeniate bisaccate pollen, especially of the Triadispora/Angustisulcites group is a typical feature of this phase. The increased frequency of Illinites causes a first small peak of the Ovalipollis/Illinites group. The decreasing trend in the abundance of spores results in H/X ratios decreasing to about 0.5. 7.1.7. Phase 7 Interval: 2436.0–2385.0 m. The trends observed in the previous phase continue in phase 7, which is marked by a first peak of the nontaeniate bisaccate pollen, and among them by the rare but almost continuous record of Brachysaccus. Typical is also the first common occurrence (>10%) of Illinites. Spores are comparatively rare except for Aratrisporites, but also this group shows a distinct decrease. H/X ratios vary between 0.4 and 0.5. 7.1.8. Phase 8 Interval: 2379.0–2349.0 m. Phase 8 is marked by a renewed high abundance of Aratrisporites occurring together with a first peak of monolete spores (Leschikisporis spp.). Non-taeniate bisaccate pollen show a distinct decrease whereas the frequency of the taeniate forms remains unchanged. Reflecting the high abundance of spores the H/X ratios increase to around 0.6. Phase 8 is interpreted to fall within the lower part of zone ASS-I. 7.1.9. Phase 9

7.1.3. Phase 3 Interval: 2769.0–2730.0 m. An increase in the abundance of taeniate and non-taeniate bisaccate pollen marks phase 3. The Aratrisporites group is reduced but still represents a major part of the assemblages. The cavate trilete spores decrease during this phase, whereas the

Interval: 2343.0–2226.0 m. Phase 9 marks the onset of an interval (including phases 9–11), which is characterized by dominance of nontaeniate bisaccate pollen. Especially the groups Brachysaccus and Triadispora/Angustisulcites show a distinct increase. Representatives of the genus Protodiploxypinus occur quite frequently in the upper part

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of the interval. Noticeable is also the slight decrease of the Ovalipollis/ Illinites group. Aratrisporites decreases to low frequency values at the top of this interval. This decrease of spores and the strong dominance of bisaccate pollen result in average H/X ratios of about 0.25, the lowest values of the entire section. Phase 9 covers the transition between the late Anisian and the lower part of the Ladinian (ASS-I–ASS-G/H).

below. Aratrisporites shows a minor peak in the upper part of this interval. Although the composition of the assemblages change significantly compared to phase 13 the H/X ratios remain unchanged. The range of phase 14 coincides with the interval assigned zone ASS-D, which also is interpreted to fall within the middle part of the Carnian. 7.1.15. Phase 15

7.1.10. Phase 10 Interval: 2220.0–2118.0 m. Non-taeniate bisaccate pollen, including Brachysaccus as a common element, dominate the assemblages throughout this interval. Compared to phase 9 the frequencies of taeniate bisaccate pollen and of the Ovalipollis/Illinites group are strongly reduced. Araucariacites shows its first continuous record in this interval. A minor increase in the abundance of spores is reflected by the slightly increased H/X ratios. Phase 10 is interpreted to cover the transition between the highest Ladinian and the lowermost Carnian (ASS-G/H and basal part of ASS-F).

Interval: 1893.0–1770.0 m. The abundance of trilete spores is typical for the assemblages of phase 15. It is mostly due to the marked increase of Concavisporites crassiexinus and several species of the genus Kyrtomisporis. Typical is also the diversity and peak abundance of the genus Protodiploxypinus as well as the common occurrence of Araucariacites. Chasmatosporites is frequent throughout this interval. Compared to phase 14 H/X ratios remain essentially unchanged. The range of phase 15 coincides with zone ASS-C, which is interpreted as late Carnian in age. 7.1.16. Phase 16

7.1.11. Phase 11 Interval: 2112.0–2034.0 m. Non-taeniate bisaccates with common Brachysaccus and representatives of the Triadispora/Angustisulcites group largely dominate the assemblages of phase 11. Distinct features are the first peak of Araucariacites and the first rare but continuous record of the genus Chasmatosporites. Taeniate bisaccate pollen are rare and have their last continuous record in this phase. In the upper part of this interval there is a slight increase of trilete and monolete spores; accordingly the H/X ratios increase to values > 0.5. Phase 11 falls within zone ASS-F corresponding to an early Carnian age. 7.1.12. Phase 12 Interval: 2028.0–1989.0 m. The boundary between phases 11 and 12 is marked by a distinct change in the predominant floral elements, changing from conifer dominated to fern dominated assemblages. Phase 12 is characterized by the high abundance of monolete spores, essentially represented by the genus Leschikisporis. Smooth trilete spores, and to a minor degree also Aratrisporites, are more common. In this and in all following phases the taeniate bisaccate pollen occur only sporadically. Compared to phase 11 the frequency of nontaeniate bisaccate pollen drops considerably, and consequently there is a marked increase in H/X ratios, reaching about 0.8. Phase 12 covers the transition between ASS-F and ASS-E and it possibly still belongs in the early Carnian. 7.1.13. Phase 13 Interval: 1983.0–1956.0 m. The distinct increase of smooth trilete spores together with common monolete spores of phase 13 essentially represents a transitional stage between phases 12 and 14. A remarkable feature is the first frequent occurrence of the genus Protodiploxypinus. The increased representation of non-taeniate bisaccates causes a slight drop of H/X ratios to about 0.7. Phase 13 falls within ASS-E, which is interpreted to correspond to the middle part of the Carnian. 7.1.14. Phase 14 Interval: 1950.0–1899.0 m. The most characteristic feature of phase 14 is the common occurrence of Ovalipollis. Otherwise this interval is marked by a strong increase of smooth trilete spores with Calamospora as the most abundant form. Monolete spores are still quite common, but occur in markedly lower numbers than

Interval: 1767.0–1668.0 m. The consistently common occurrences of Chasmatosporites and Kyrtomisporis mark this interval. Compared to the high values in phase 15 there is a distinct decrease in the frequencies of Araucariacites and Protodiploxypinus. The percentage of non-taeniate bisaccate pollen, being high at the base of this interval drops to values below 20%, which is reflected in a slight increase of the H/X ratios. Together, phase 16 and 17 coincide with zone ASS-B2 that is considered to be of Norian age. 7.1.17. Phase 17 Interval: 1662.0–1611.0 m. Trilete spores are abundant throughout phase 17. Remarkable is the common occurrence of Kyrtomisporis and Concavisporites crassiexinus. Additionally a renewed increase of cavate trilete spores and of Aratrisporites are typical for the upper part of this interval. Percentages of non-taeniate bisaccate pollen decrease to low values. Average H/X ratios of > 0.8 for this phase and the following phase 18 represent the highest values of the studied section. 7.1.18. Phase 18 Interval: 1593.0–1554.0 m. Phase 18 is characterized by common occurrence of Concavisporites crassiexinus, Aratrisporites and cavate trilete spores. Bryophytes, and among them Ricciisporites, appear as a regular element of the assemblages. In contrast to that the frequency of Kyrtomisporis drops. The frequency of nontaeniate bisaccates varies but at comparatively low levels. The H/X ratios remain unchanged from phase 17 (> 0.8). Phase 18 coincides with zone ASS-B of indeterminate Rhaetian–Norian age. 7.1.19. Phase 19 Interval: 1547.0–1533.0 m. Phase 19 is marked by a distinct increase of non-taeniate bisaccate pollen and by a frequency drop of smooth trilete spores. Aratrisporites and monolete spores are also rare. Consequently the average H/X ratios also drop significantly. The differences in the composition of the assemblages of phase 19 and 20 can be used to subdivide zone ASS-A, which is interpreted to be of Rhaetian age. 7.1.20. Phase 20 Interval: 1524.0–1495.0 m. The composition of the assemblages is quite variable within this interval. The most distinctive feature is the

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pp. 33–36

Fig. 10. Palynological record of shallow core 7323/07-U-08 and -06 (Svalis-2 and 3), 7323/07-U-03 and 04 (Svalis-4 and 5), 7323/07-U-01 (Svalis-6), 7323/07-U-07 and -09 (Svalis-7), and 7323/07-U-10, -05 and -02 (Svalis-8) with quantitative distribution of the groups Calamospora, Chasmatosporites, Triadispora/Angustisulcites, Brachysaccus, and Protodiploxypinus as well as the spore/pollen ratios.

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abundance of bryophyte spores, namely Ricciisporites. Compared to the interval below non-taeniate bisaccate pollen are more abundant, although the groups Brachysaccus and Triadispora/Angustisulcites have not been observed. Reflecting the variable composition of the assemblages the H/X ratios vary between 0.6 and >0.8. 7.2. Svalis Dome — the shallow cores 7323/07-U-08, 06, 03, 04, 01, 07, 09, 10, 05, 02 The cores from the stratigraphic drilling at the Svalis Dome area represent selected intervals covering specific boundaries and events (Mørk and Elvebakk, 1999; Vigran et al., 1998). This paper discusses only the data representing the interval between the late Early Triassic (Smithian, Svalis-2) and the late Middle Triassic (Ladinian, Svalis-8), which cover a critical phase in the development of the Mesozoic floras. Within this interval the vegetation changes from the typical Early Triassic assemblages with high representation of pteridophytes (spores) to the gymnosperm (pollen) dominated assemblages as seen in the Middle Triassic. The palynological data document a major turnover, which can be related to eminent palaeoenvironmental changes in the marine and the terrestrial realm (Galfetti et al., 2007). A summary of the characteristics of the zones Svalis-2 to Svalis-8 is presented below. The records from assemblages Svalis-2 and -3 do not overlap with that of well 7228/7-1A. 7.2.1. Svalis-2/Svalis-3 (Figs. 6, 10) Sediments of late Smithian age have been recovered in core 7323/ 07-U-06 and -08. The palynological assemblages from this interval have been defined as zone Svalis-2 representing an Olenekian age. The zone is characterized by the common to abundant occurrence of Punctatisporites fungosus and Densoisporites playfordii as well as common D. nejburgii. Another distinguishing feature is the presence of Pechorosporites disertus and Rewanispora foveolata. Zone Svalis-2 is directly calibrated with the Wasatchites tardus ammonoid Zone. It is interpreted to coincide with the upper part of ASS-N (Vigran et al., 1998). The assemblages recovered from the sediments of core 7323/07-U03 have been defined as zone Svalis-3. The base of the zone is marked by the first common appearance of Pechorosporites disertus, Rewanispora foveolata and Acanthotriletes sp. F. The FAD of Cordaitina spp. and C. gunyalensis occurs within this zone and its top is defined by the LAD of the species P. disertus, D. playfordii, Reticulatisporites bunteri and Verrucosisporites remyanus. A most characteristic feature of this zone is the abundance of taeniate and non-taeniate bisaccate pollen. Based on the stratigraphic succession and palynological correlations an early Spathian age is attributed to zone Svalis-3. Its correlation with zone ASS-M has recently been confirmed based on magnetostratigraphic evidence (Hounslow et al., 2008). 7.2.2. Svalis-4/Svalis-5 (Figs. 7, 10) The transition from the late Olenekian (Spathian) to the Middle Triassic (early Anisian) is covered in core 7323/07-U-04. The palynological assemblages of the Spathian part of the section have been described as zone Svalis-4. This zone is characterized by the first stratigraphic occurrences of a number of spores, such as Jerseyaspora punctispinosa, Cyclotriletes pustulatus, C. oligogranifer, Verrucosisporites jenensis and the last consistent record of common D. nejburgii (Vigran et al., 1998). The assemblages are directly calibrated by the co-occurring late Spathian ammonoid fauna of the Keyserlingites subrobustus Zone. Svalis-4 covers the transition between the zones ASS-L and M (Hounslow et al., 2008). The assemblages from the upper part of core 7323/07-U-04, differentiated as zone Svalis-5, are characterized by the FADs of several typical species such as Accinctisporites circumdatus, Anapiculatisporites spiniger and Striatella seebergensis. The top of the zone is

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marked by the last consistent appearance of D. nejburgii and the LAD of the genus Pretricolpipollenites. Another typical feature of this zone is the regular occurrence of Jerseyaspora punctispinosa. The upper part of core 04 is directly calibrated with ammonoids attributed to the early Anisian Karangatites evolutus Zone. Zone Svalis-5 falls within the lower part of ASS-L (Vigran et al., 1998). 7.3. Svalis-6 (Figs. 8, 10) Zone Svalis-6 recovered from core 7323/07-U-01 is defined as the interval between the FAD of Aratrisporites macrocavatus and Triadispora plicata and the LADs of the spores Jerseyaspora punctispinosa. Aratrisporites parvispinosus and Kraeuselisporites punctatus. Densoisporites nejburgii has its LAD in the lower part of this zone. A feature differentiating zone Svalis-6 from the underlying zones is the abundance and the diversity of Triadispora and Striatoabieites. Svalis-6 co-appears with the ammonoids of the Anagymnotoceras varium zone of middle Anisian age. The zone covers the transition between the zones ASS-L and ASS-K (Vigran et al., 1998). 7.3.1. Svalis-7 (Figs. 8, 10) Assemblages from the cores 7323/07-U-07 and 09 have been attributed to zone Svalis-7. This zone is defined as the interval between the FAD of Protodiploxypinus decus, P. ornatus, and Chasmatosporites sp. A and Retisulcites perforatus and is restricted by the LAD of Kraeuselisporites apiculatus and Acanthotriletes sp. F. Other characteristic features are the abundance of Aratrisporites, taeniate bisaccate pollen (Lunatisporites spp., Striatoabieites spp.), and Illinites chitonoides. The interval co-appears with the fauna of the Frechites laqueatus ammonoid Zone of late Anisian age and falls within zone ASS-K (Vigran et al., 1998). 7.3.2. Svalis-8 (Figs. 9, 10) Zone Svalis-8 comprises the interval between the FAD of Ovalipollis pseudoalatus and Echinitosporites iliacoides and the LAD of Cordaitina gunyalensis and C. minor. The FAD of Triadispora verrucata falls within this zone. The zone is dated as early Ladinian by the occurrence of fauna of the Tsvetkovites varius ammonoid Zone. Its palynological content corresponds to ASS-I. 8. Correlation and comparisons 8.1. Correlation of the palynological records of 7228/7-1A and of the shallow cores from the Svalis Dome area (7372/03-U-01–10) The palynological record of the Svalis Dome area is originally based on semi-quantitative data that are presented in the same manner as those of well 7228/7-1A. The assemblages Svalis-2 and Svalis-3 have no correspondence in well 7228/7-1A (Fig. 5) but are characterized by several distinct changes. In the late Smithian interval (Svalis-2) cavate trilete spores, including Densoisporites nejburgii are abundant and appear together with mainly smooth trilete spores. The abundance of these forms decreases considerably between the late Smithian and the early Spathian (Svalis-3). In contrast to that the bisaccate pollen (taeniate and non-taeniate forms) occur in low frequencies in the late Smithian and increase abruptly at the boundary between the two zones. The patterns result in high hygrophytic/xerophytic ratios, mostly > 0.7 for the Smithian interval (Svalis-2) and values of < 0.5 in the early Spathian (Svalis-3), which have been interpreted as results of a distinct climatic change. These changes coincide with a massive turnover in global faunal distribution patterns as well as in values of stable isotopes (Galfetti et al., 2007 and discussion below). The interval covered by the zones Svalis-4 and Svalis-5 (Figs. 7, 10) is marked by a distinct change in the frequency of trilete cavate spores. This group, excluding Densoisporites nejburgii, is relatively

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frequent in the lower part of the section and becomes rare in its upper part. In the same interval D. nejburgii decreases from high abundances (>20%) to values of about 2%. Spores of the Aratrisporites group are consistently present, reaching average values of about 10%. Other spores are also common; the ornamented forms show a significant increase. Bisaccate pollen, especially taeniate forms, also increase significantly within the interval. Some of these trends can be traced in the interval covered by the phases 1 to 3 in well 7228/7-1A. Similar features are the drop of cavate spores, and the increase of bisaccate pollen and of smooth trilete spores. In both records the Ovalipollis/Illinites group appears within this interval. However, in the shallow cores there is no equivalence to the pronounced abundance of Aratrisporites and to the low representation of D. nejburgii as observed in well 7228/7-1A. The differences recognised may suggest that the deposits in well 7228/7-1A are of Anisian rather than Spathian age and render the proposed correlation ambiguous. Alternatively, these differences could be due to disparities in the depositional environment. In both records the H/X ratios are around 0.5. Within the interval of zone Svalis-6 the significant increase of the Aratrisporites group and the corresponding decrease of bisaccate pollen (taeniate and non-taeniate forms) marks a floral change. Cavate trilete spores are rare; D. nejburgii is consistently present in the lowermost samples but has not been observed above. Araucariacites appears within this zone. These changes account for a relatively low H/X index of <0.5 for the lower part of the section and around 0.6 at in the upper part. In well 7228/7-1A similar trends can be seen at the transition between phase 4 and 5 with a major increase of Aratrisporites, from about 40% in phase 4 to over 60% in phase 5, and a decrease of bisaccate pollen of similar magnitude. This is also true for the H/X ratios, increasing from about 0.4 to 0.6 in zone Svalis-6, compared to an increase from about 0.6 in phase 4 to 0.8 in phase 5 in well 7228/7-1A. Zone Svalis-7 is again characterized by a distinct drop in the abundance of spores whereas taeniate and non-taeniate bisaccate pollen show a strong increase. Among the latter the Triadispora/Angustisulcites group is quite common, and compared to the intervals below, Protodiploxypinus appears more frequently. The common occurrence of the Ovalipollis/Illinites group and the appearance of Chasmatosporites are other distinct features of this assemblage. The H/ X ratios drop from >0.5 in the lower part of zone Svalis-7 to values <0.3 in the upper part. A comparable shift occurs in well 7228/7-1A: values of about 0.6 in phase 8 drop to about 0.3 in phase 9. These trends suggest a late Anisian age for the lower part of phase 9. The early Ladinian assemblages (Svalis-8) are characterized by the dominance of non-taeniate bisaccate pollen. Among them Triadispora/Angustisulcites and Protodiploxypinus are quite common. The frequency of taeniate forms drops from common (10–20%) at the base of the interval to values below 10% in the upper part. Although showing highly variable percentages the Ovalipollis/Illinites group is generally common. Araucariacites is still rare, whereas Chasmatosporites reaches relatively high values in some samples. Compared to the interval below spores are more common, and with the appearance of monolete form and bryophytes, also more diverse. The relative abundance of spores leads the H/X ratio to reach average values of about 0.5. In well 7228/7-1A similar trends can be recognized in the upper part of phase 9 and at the transition to phase 10. Common features are the dominance of bisaccate pollen with the consistent, but reduced frequency of the taeniate forms, the common occurrence of the Ovalipollis/Illinites group, the rare occurrence of Araucariacites, low frequency of Aratrisporites and increasing representation of spores. However, the rather frequent occurrence of the Cycadopites/Chasmatosporites group and of cavate spores in zone Svalis-8 has no correspondence in well 7228/7-1A. H/X ratios in zone Svalis-8 are relatively high (0.5) compared to about 0.3 in phase 9 and 10 of well 7228/7-1A. The suggested correlation is compatible with the Ladinian age attributed to this interval in well 7228/7-1A.

8.2. Comparisons to Central and Southern European palynological records Early Triassic spore-pollen assemblages are generally considered to be poorly diversified and to be strongly dominated by lycopsid spores. This idea has been coined by the assemblages known from the Tethyan realm (Brugman, 1986; Visscher and Brugman, 1986; Looy et al., 1999). At least for some areas and for some parts of the Early Triassic this opinion has to be revised. Remarkably diverse assemblages have been described from the Permian/Triassic transition of the Boreal realm (Griesbachian) (Balme, 1979; Mangerud, 1994; Vigran et al., 1998; Hochuli et al., 2010) while the coeval records from low latitudes of the northern hemisphere are rare and poorly diversified. Late Early Triassic sections (Spathian) from Central and Southern Europe (Hungary, Poland, Germany, Italy) are dominated by spores of the Densoisporites nejburgii group. At the transition to the Middle Triassic these spores are successively replaced by conifer pollen like Voltziaceaepollenites and Jugasporites (Orlowska-Zwolinska, 1979; Brugman, 1986; Visscher and Brugman, 1986; Reitz, 1988; Looy et al., 1999). The patterns observed in the coeval sections of the Barents Sea area are also marked by high abundance of spores but differ from the above mentioned sites by their higher diversity, the strong representation of Aratrisporites, and by the higher abundance of taeniate and non-taeniate bisaccate pollen. Inferred from mostly semi-quantitative data from southern localities D. nejburgii seems to be less common in the Boreal realm. In Central and Southern Europe the lower part of the Middle Triassic is characterized by a strong dominance of conifer pollen, especially Triadispora and Angustisulcites, and common occurrence of taeniate bisaccate pollen (pteridosperms). Trilete spores (e.g. Punctatisporites, Cyclotriletes) are regularly represented (OrlowskaZwolinska, 1979; Brugman, 1986). The presence of typical elements such as Stellatopollis thiergartii or Staropollenites antonescui has never been satisfactorily proven for the Barents Sea area. In the material from well 7228/7-1A the approximately equivalent section (phase 3–4) is similarly characterized by an increase in non-taeniate bisaccate pollen but also by significantly increased percentages and diversity of spores (e.g. Aratrisporites). In records from Hungary and the Southern Alps one interval from the lower part of the late Anisian (Pelsonian, Balatonicus ammonoid zone) stands out by exceptionally high abundance of spores (Brugman, 1986). This pattern suggests a similarity with the spore dominated phase 5, which shows the highest abundance of Aratrisporites and the highest H/X ratios of the entire Middle Triassic. Late Anisian and early Ladinian assemblages of Central and Southern Europe are characterized by the dominance of taeniate and non-taeniate bisaccate pollen (e.g. Striatoabieites, Triadispora), and by the massive appearance of pollen of the Circumpolles group (e.g. Partitisporites and Camerosporites) (Brugman, 1986). The approximately coeval assemblages from the Barents Sea also contain common taeniate and non-taeniate bisaccate pollen, with the latter dominating the assemblages. In contrast to that Circumpolles appear only sporadically and in reduced diversity (cf. Figs. 2, 5, 8, 9). In a new calibrated record from the Southern Alps representing open marine conditions the late Anisian palynological assemblages are characterized by extremely high abundance of bisaccate pollen (taeniate and non-taeniate forms) and rare spores (Hochuli and Roghi, 2002). This results in H/X ratios approaching 0. In this record the Ladinian assemblages are characterized by the appearance of several representatives of the Circumpolles (e.g. Paracirculina, Duplicisporites) and of the Ovalipollis groups. During the Ladinian spores become slightly more common and increasingly diverse. However, compared to assemblages from northern localities the spores are still extremely rare. Thus, in the middle part of the Ladinian (Archelaus Zone) the H/X ratios reach about 0.1. Late Ladinian (lower Keuper) records from Poland (OrlowskaZwolinska, 1979) and Germany (Heunisch, 1986; Brugman et al.,

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1994) comprise assemblages with common occurrence of spores, including Aratrisporites, Calamospora, and monolete spores. According to our tentative correlations this interval corresponds to the interval between the upper part of phase 10 and the lower part of phase 11. In this part of the section the slight increase of the spore abundance coincides with the distinct decrease of taeniate bisaccate pollen and the first consistent occurrence of the Araucariacites group. Compared to Anisian assemblages Aratrisporites is relatively rare (around 10%). The trend of relatively reduced humidity inferred from the data of well 7228/7-1A cannot be followed in the above mentioned records from Central Europe. For the Late Triassic, namely for the Carnian and the Norian, Buratti and Cirilli (2007) postulate the existence of a large circum Mediterranean Province, which was characterized by the common occurrence of pollen of the Circumpolles group, with Camerosporites as one of the typical elements. The climatic conditions of the Carnian of the low- and mid-latitudinal belt have been interpreted as arid (Visscher and Van Der Zwan, 1981; Visscher et al., 1994; Buratti and Cirilli, 2007). However, new evidence shows that Carnian assemblages of the Alpine realm vary considerably (Hochuli and Frank, 2000; Roghi, 2004; Rigo et al., 2007). Approximately coeval assemblages in the Barents Sea area also provide evidence for distinct climatic variations during this time. Thus, interpreting climatic conditions of the Carnian interval requires a more precise stratigraphic resolution. Palynological successions from the Rhaetian are known for their relatively homogeneous composition over wide geographic areas. The records from Greenland (Pedersen and Lund, 1980) and from the Barents Sea (Hochuli et al., 1989) are closely comparable with those from Central Europe. The assemblages are characterised by strong fluctuations in SP/P ratios (Morbey 1975; Lund, 1977; Bonis et al., 2008). For NW Europe a spore spike has been postulated for the uppermost Rhaetian accompanying or heralding the extinction event of the Triassic/Jurassic boundary (Van De Schootbrugge et al., 2008). Distinct fluctuations in the spore/pollen ratios can also be observed in the record of well 7228/7-1A. However, the Rhaetian record of the studied material may be incomplete and the uppermost part of the Triassic seems to be missing as in most other parts of the Barents Sea area (pers. observations). 9. Climatic features of the Triassic The climate of the Triassic is regarded as one of an extreme “hothouse”. According to some authors it may have been one of the hottest times in Earth history (Scotese, 2000). One of the main characteristics of the Triassic climate seems to be the large arid equatorial belt extending over the major part of the great landmass of Pangea. Most models consider the climate of Pangea as extremely hot and dry (Péron et al., 2005; Sellwood and Valdes, 2006 and references therein). These models also infer a very narrow humid tropical belt over the central part of the Tethys. The polar areas were ice free. For Antarctica growth of forests with tall trees is documented by petrified trunks in the Queen Alexandra Range of the central Transantarctic Mountains (Taylor et al., 2000). These forests are interpreted as of early Middle Triassic age and grew at latitudes between 70 and 75°S. Growth ring data suggest a highly seasonal climate and light — not temperatures — has been considered as a limiting factor (Taylor et al., 2000). These authors conclude from palaeobotanical evidence that the climate during the Late Permian and the Middle Triassic was hospitable for the growth of diverse floras near the pole and that temperatures were much higher than predicted by the available physical models. Comparisons between Late Permian and Early Triassic palynological records from the Prince Charles Mountains (Antarctica) suggest that the Early Triassic climate was warmer and less seasonal (Lindström and McLoughlin, 2007). Based on palynological evidence Yaroshenko (1997) and Chumakov and Zharkov (2003)) estimated that the temperature increase between the Late Permian and the Early Triassic was particularly

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strong at high latitudes of the Northern Hemisphere. They conclude that in parts of North Siberia the climate became at least temperatewarm and humid during the earliest Triassic. From palaeobotanical evidence from the Early Triassic of Siberia these authors infer a warm temperate climate for areas north of 65°N. For the Olenekian the model of Péron et al. (2005) deduces mean annual surface temperatures between 0 and − 10 °C for continental areas of northern high latitudes (e.g. Siberia, >70°N) and mean annual precipitation of 1–2.5 mm/d. According to Ziegler et al. (1994) the Early Triassic palaeobotanical record of high northern latitude (up to 70°N) includes floras of warm temperate as well as cool temperate character, whereas records from the Middle and Late Triassic are strongly dominated by floras of warm temperate character. These authors interpret the changes as a result of continental motions rather than true global changes. According to the reconstruction of Worsley (2008) the study area of this paper moved from 50°N in the Middle Triassic to 55°N in the Late Triassic. Considering the flat temperature gradient the impact of this shift cannot account for the major changes in the composition of the floras. The plate movements are slow processes and the relatively fast shifts in the flora must have been induced by other factors (e.g. precipitations patterns). The palynological evidence for the high latitudes presented in this paper favours models with warm temperatures and minimal seasonality (Sellwood and Valdes, 2006; Chumakov and Zharkov, 2003). In the studied material the continuous strong representation of ferns, including families with affinities to extant tropical groups (e.g. Marattiales), provide supporting evidence for these models. Thus for the floras of mid latitudes, including the study area, temperatures were not the limiting factor. Accordingly the variations in the palynological assemblages must reflect vegetational patterns, which were essentially influenced by variations in precipitation. In Central Europe the late Ladinian palynological records (Orlowska-Zwolinska, 1979; Heunisch, 1986; Brugman et al., 1994) as well as the sedimentological evidence (Lettenkohle) suggest more humid conditions during the youngest Middle Triassic. This apparent contradiction with our results might be explained by a more pronounced seasonality in the area of the Germanic basin during this time. Based on the analysis of carbonates, the distribution of clastic sediments, and evaporites fluctuating climatic conditions have been interpreted for the Middle and Late Triassic of the Southern Alps (Mutti and Weissert, 1995). For the late Ladinian to early Carnian interval these authors assume seasonally increased rainfall and longer episodes of high precipitation. On the other hand mid to late Carnian and Norian sequences reflect considerably dryer conditions. According to these authors the assumed precipitation patterns are in line with a monsoonal climate. For low latitudes seasonality with the strongly decreased precipitation during summer might have been the controlling factor for the composition of the floras. The identification of episodes of high precipitation is in line with the interpretation of a “pluvial event” as recorded from the palynological data from Carnian deposits (see below). 10. Conclusions The composition of spore-pollen assemblages is considered to represent a proxy for past climatic conditions. In the Triassic changes in the distribution of sediments (e.g. coal, evaporites) and in the palaeontological record of the marine realm strongly suggest the existence of long and shorter term variations (e.g. Mutti and Weissert, 1995; Scotese, 2000; Brayard et al., 2005; Galfetti et al., 2007; Zakharov et al., 2008). In this paper we postulate that the observed consistent variations in the distribution of spore-pollen reflect climatic changes. Based on numerous samples with highly diverse spore-pollen assemblages the studied palynological sequences reflect considerable variations in the distribution of the major floral elements. Attributing the spore-pollen groups to hygrophytic or xerophytic elements, as

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described by Visscher and Van Der Zwan (1981), we recognise the sequence of changing ratios as a proxy for changes in the relative humidity available to the plants in the Barents Shelf area. The distinct change in the distribution of floral elements at the Smithian/Spathian boundary represents a major shift in the palynological records of the Early Triassic. It has been interpreted as a change from humid to drier conditions. The global significance of this event has been proven by a multiproxy approach (Galfetti et al., 2007; Hermann et al., 2008). The authors relate the palynological record to the coeval reorganization of paleobiogeographic distribution of ammonoids — changing from poorly diversified faunas with homogeneous distribution in the late Smithian to highly diversified assemblages reflecting major difference in latitudinal distribution during the early Spathian. Accepting ammonoids as temperaturesensitive organisms, changes in their global taxonomic diversity and paleobiogeographic patterns provide a proxy for changing SST gradients (Brayard et al., 2005). Thus, for the Smithian/Spathian boundary the above mentioned change in the distribution of ammonoids can be interpreted as cooling event. Global environmental changes at this boundary are also be substantiated by the prominent positive carbon isotope excursion known from Tethyan marine rocks (Ccarb), but also by an equivalent high paleolatitude Corg record from Spitsbergen (Galfetti et al., 2007). Other events related to this boundary include the major turnover in the distribution of conodonts, comprising a major extinction in the late Smithian followed by a great diversification in the early Spathian (Orchard, 2007; Goudemand et al., 2008). The cooling trend at the Smithian/Spathian boundary as inferred from the distribution of ammonoids can be used as an indication for the palaeoclimatic interpretation of the palynological assemblages. A cooling event would have resulted in different precipitation patterns and would have indirectly affected floral assemblages. Thus, for the area considered humid phases as indicated by high H/X ratios probably reflect warmer conditions. Applying this hypothesis, the warmest phases in the studied interval would be the late Smithian (Svalis-2), the middle part of the Anisian (Svalis-6, phase 5) and the entire post-early Carnian (phases 12–20). Beside the Smithian/Spathian boundary event a distinct climatic turnover is known as the “Carnian pluvial event”. This was first recognized based on changes in the sedimentary system (Simms and Ruffell, 1989). Later its existence has been confirmed by palynological evidence (Hochuli and Frank, 2000; Roghi, 2004; Rigo et al., 2007). Although not precisely calibrated, the Late Triassic record of the Barents Sea reveals a major change within the Carnian, showing an abrupt change from relatively dry conditions in the early Carnian (phase 10/11) to more humid conditions in the upper part of the Late Triassic (phases 12–20). Presently the relationship between the “Carnian pluvial event” and the turnover in the palynofloras in the Barents Sea area is unclear. However, increased humidity in the Late Triassic of the Boreal realm is supported by sedimentological evidence. Compared to the Early and Middle Triassic the Late Triassic sequences are characterized by widespread deposition of coal. Accordingly it can be inferred that during this time the low latitudinal arid zones were much narrower (Scotese, 2000). The present overview illustrating the evolution of the floras of the Boreal realm opens new perspectives for more detailed climatic interpretations of Triassic palynomorph assemblages. The continuous record in well 7228/7-1A allows recognizing three major intervals in the development of the floral succession. The first one corresponds to the interval covered by phases 1–6 and is characterised by the association of abundant spores (e.g. Aratrisporites), common taeniate bisaccate pollen and increasing percentages and diversity of nontaeniate bisaccate pollen. It ranges from the late Spathian to the middle part of the Anisian. The second interval (phases 7–11) is marked by the highest abundance of non-taeniate bisaccate pollen and strongly reduced hygrophytic elements. It corresponds to a late Anisian to early Carnian age. During this interval H/X ratios remain

consistently below 0.5. The third interval (phases 12–20) is again marked by the high representation of spores. Here, abundant trilete spores are associated with common non-taeniate bisaccate pollen and frequent Araucariacites as well as Chasmatosporites. Taeniate bisaccate pollen occur only sporadically. This interval ranges from the mid Carnian to the top of the Triassic. The comparison of the data from the Barents Sea area with those from the Alpine and Germanic realms reveals significant differences. Most obvious disparity appears in the latitudinal distribution of the Circumpolles group, or in distribution of the monosaccate conifer pollen such as Enzonalasporites, Vallasporites and Patinasporites. These groups are common or dominant in Late Triassic Tethyan plant assemblages (Buratti and Cirilli, 2007 and ref. therein) whereas they occur only sporadically in the material from the Boreal realm (Hochuli et al., 1989; Mørk et al., 1992). In contrast to that the abundance of groups like Protodiploxypinus and Araucariacites as well as the abundance and diversity of monolete and trilete spores (e.g. Kyrtomisporis) seem to be typical features of Boreal assemblages. According to our current knowledge a few forms of the genus Retisulcites (R. sp.1, R. sp. 2 of Hochuli et al., 1989, and Retisulcites sp. A of Vigran et al., 1998) might be restricted to the Boreal realm (Hochuli and Feist-Burkhardt, 2004) whereas some typical species like Stellatopollis thiergartii or Staropollenites antonescui are probably absent from Barents Sea area. In the light of these differences biostratigraphic correlations based on the distribution of single taxa over long distances and across climatic zones are of limited value. We assume that the observed differences in frequency patterns of specific taxa might also apply to their vertical distribution (e.g. differences in LADs and FADs of individual taxa). However, attempts to detect more subtle differences depend on well calibrated material from several areas. The palynological records presented in this paper cover the time interval during which the Mesozoic vegetation established. Major changes in the composition of the floras, namely the decline of lycopsids, the diversification and spreading of the conifers as well as the demise of pteridosperms appear to be related to climatic changes. Acknowledgements The authors gratefully acknowledge StatoilHydro ASA, Forus, Norway and Sintef Petroleum Research, Trondheim, Norway for the permission to publish this material. The original study of well 7228/7-1A was carried out in cooperation with APT (Applied Petroleum Technology) SA, Kjeller, Norway where the slides have been processed. We are indebted to H. Selnes and D.G. Bell for their help and cooperation during this study. We thank E. Kustatscher (Naturmuseum Südtirol, Bozen, Italy) for the encouragement to present and publish the paper. S. Lindström, as well as an anonymous reviewer, helped to improve the clarity of the manuscript. We also acknowledge the continuous help of our colleagues H. Bucher and E. Hermann (University Zürich) as well as A. Mørk and H. Weiss (Sintef Petroleum Research). References Bachmann, G.H., Kozur, H.W., 2004. The Germanic Triassic: correlations with the international chronostratigraphic scale, numerical ages and Milankovitch cyclicity. Hallesches Jahrbuch für Geowissenschaften 26, 17–62. Balme, B.E., 1979. Palynology of the Permian Triassic boundary bed at Kap Stosch, East Greenland. Meddelelser om Grønland 20 (no. 6), 1–37. Balme, B.E., 1995. Fossil in situ spores and pollen grain: an annotated catalogue. Review of Palaeobotany and Palynology 87 (2–4), 81–323. Bonis, N.R., Kürschner, W.M., Krystyn, L., 2008. Floral and palaeoenvironmental changes across the Triassic–Jurassic boundary interval. The Triassic climate. Workshop on Triassic palaeoclimatology. Abstract volume. Naturmuseum Südtirol, Bozen, p. 16. Brayard, A., Escarguel, G., Bucher, H., 2005. Latitudinal gradient of taxonomic richness: combined outcome of temperature and geographic mid-domains effects? Journal of Zoological Systematic and Evolutionary Research 43, 178–188. Brugman, W., 1986. A palynological characterization of the Upper Scythian and Anisian of the Transdanubian Central Range (Hungary) and the Vicentinian Alps (Italy). PhD thesis, State University of Utrecht, 95 pp.

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