Morphological and abundance variations in Homotryblium-cyst assemblages related to depositional environments; uppermost Oligocene–Lower Miocene, Jylland, Denmark

Palaeogeography, Palaeoclimatology, Palaeoecology 206 (2004) 41 – 58 www.elsevier.com/locate/palaeo

Morphological and abundance variations in Homotryblium-cyst assemblages related to depositional environments; uppermost Oligocene–Lower Miocene, Jylland, Denmark Karen Dybkjær * Geological Survey of Denmark and Greenland (GEUS), Øster Voldgade 10, DK-1350 Copenhagen K, Denmark Received 10 February 2003; received in revised form 17 December 2003; accepted 23 December 2003

Abstract Abundant occurrences of Homotryblium dinoflagellate cysts have been interpreted as reflecting deposition in near-shore, marginal marine areas, either in hypersaline or low-salinity environments. It has also been suggested that the process length of Homotryblium cysts is related to proximity to the coast. The present study provides new insights in the ecology of Homotryblium and adds important information about the use of the morphological variations of Homotryblium cysts for environmental reconstructions. It presents an example where Homotryblium cysts show high relative abundances in a low-salinity, partly restricted marine depositional environment. Four different species of Homotryblium were recorded. Homotryblium? additense is proposed as a new species. The regional palaeogeographic distribution of the four species: H.? additense, Homotryblium vallum, Homotryblium plectilum and Homotryblium tenuispinosum, shows a distinct depositional proximal – distal distribution pattern. H.? additense occurs only in a narrow stratigraphic interval in the most proximal part of the study area. H. vallum only occurs sporadically, mainly in the proximal parts of the study area. H. plectilum dominates the proximal areas while H. tenuispinosum dominates the more distal areas. Variations in abundance and cyst-type also seem to respond to systems tracts, sequence boundaries and flooding surfaces. The observed distributional patterns of Homotryblium species strongly indicate a response to the salinity of the depositional environment. It is further suggested that at least some of the recorded species of Homotryblium originated from the same motile dinoflagellate species, producing cysts of different morphology in response to variations in salinity, a phenomenon known from extant dinoflagellates. D 2004 Elsevier B.V. All rights reserved. Keywords: Denmark; Upper Oligocene – Lower Miocene; biostratigraphy; palynology; palaoeecology; dinoflagellate cysts; Homotryblium

1. Introduction The ecology of recent dinoflagellates has been studied since the 1970s and a general understanding

* Fax: +45-38142050. E-mail address: [email protected] (K. Dybkjær). 0031-0182/$ - see front matter D 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.palaeo.2003.12.021

of the influence of ecological factors on the distribution of recent cyst taxa seems to be established. Such studies have shown that water temperature, salinity, nutrient availability and watermass composition are the principle controlling parameters in the distribution of cysts (e.g. Williams, 1971; Wall and Dale, 1973; Wall et al., 1977; Harland, 1983; Dale, 1996; Matsuoka, 1999; Ellegaard, 2000; Marret and Zonneveld,

42

K. Dybkjær / Palaeogeography, Palaeoclimatology, Palaeoecology 206 (2004) 41–58

2003). Salinity and water temperature further seem to affect the morphology of the organic walled cysts (e.g. Wall and Dale, 1973; Nehring, 1994; Dale, 1996; Matthiessen and Brenner, 1996; Hallett, 1999; Ellegaard, 2000). In a recent study, Ellegaard et al. (2002) studied the morphological variations in cysts of Gonyaulax baltica in cultures grown at salinity levels from 5xto 55x. Cultures at each salinity level were grown at 12, 16, and 20 jC. The results showed

that the size of the central body decreased at higher temperatures and lower salinities. Furthermore, the process length varied with salinity. Cysts that formed at extreme salinity levels (low as well as high salinities) displayed lower average process length than cysts formed at intermediate salinity levels. In some cases, the cysts did not develop any processes at all. The ecological signals from the cyst-morphology of extinct dinoflagellate species are naturally much

Fig. 1. Study area and location of boreholes. The orientation of the palaeo-coastline and the location of the Ringkøbing-Fyn High is indicated.

K. Dybkjær / Palaeogeography, Palaeoclimatology, Palaeoecology 206 (2004) 41–58

more difficult to outline. However, this subject has also been studied since the 1970s (e.g. Williams and Bujak, 1977; Williams, 1977) and more intensively in the last decade (e.g. Brinkhuis et al., 1992; Stover and Hardenbol, 1993; Brinkhuis, 1994; Versteegh, 1994; Versteegh and Zonneveld, 1994; Zevenboom et al., 1994; Powell et al., 1996; de Verteuil and Norris, 1996; Jaramillo and Oboh-Ikuenobe, 1999; Van Mourik et al., 2001) in order to support the models for palaeo-depositional environments and to improve the geological models. The results of the latter kind of studies, as listed by Jaramillo and Oboh-Ikuenobe (1999) in Appendix A, show that the ecological signals from a specific organic walled dinoflagellate cyst (dinocyst) species or genus are a complex matter and cannot be established based upon a single or a few investigations. A number of very detailed basic studies, covering different well-studied depositional environments in different climatic zones, etc., are required to reach an overview of the ecological factors influencing the distribution of the species/genus in question. This paper presents data from a palynological study of a series of seven boreholes comprising the uppermost Oligocene –Lower Miocene succession in Jylland, Denmark (Fig. 1). The series of boreholes runs perpendicularly to the palaeo-coastline and thus give a rare opportunity to study the changes in the dinocyst assemblage within a proximal – distal transect of a thoroughly studied, marginal marine depositional setting, and to discuss the relations between the distribution pattern of the dinocysts and environmental factors. The variations in the overall dinocyst assemblage are presented in Dybkjær (in press). The present study focuses on the distribution of dinocysts referred to the genus Homotryblium.

2. Previous studies of the palaeo-ecology of Homotryblium Studies of the environmental preferences of motile Homotryblium cyst-producing dinoflagellates are not possible as the cyst-type does not appear in modern sediments, but became extinct in the Late Miocene (Hardenbol et al., 1998). However, it has been suggested that the modern dinoflagellate Pyrodinium bahamense is related to Homotryblium as P. baha-

43

mense produces cysts (Polysphaeridium zoharyi) which have strong morphological similarities to Homotryblium (Fensome et al., 1993; de Verteuil and Norris, 1996). P. bahamense is ‘‘a bloom-forming red tide species that lives in tropical to subtropical, shallow, semi-restricted embayments, estuaries and lagoons, having low, normal or high salinity’’ (de Verteuil and Norris, 1996). Studies of the occurrence of Homotryblium cysts in Eocene to Late Miocene successions have resulted in a number of interpretations. Based on the regional distribution of Homotryblium and on its possible relationship with Polysphaeridium (Hemicystodinium) zoharyi, Williams (1977, p. 1274) and Williams and Bujak (1977) suggested that the occurrence of Homotryblium is related to warmerwater conditions. Liengjarern et al. (1980) studied the Upper Eocene – Lower Oligocene of the Isle of Wight, UK. They found that Homotryblium plectilum dominated the dinocyst assemblage in a succession interpreted (on the basis of the ostracod assemblage) as being deposited in open sea conditions while Homotryblium pallidum (junior synonym of Homotryblium tenuispinosum) occurred commonly in a succession interpreted as being deposited in a low-salinity environment. The actual dominance of broken species of H. plectilum in the latter section was interpreted as being allochthonous. Islam (1984) stated (based on results from unpublished accounts) that Homotryblium species with longer processes reflect more open marine environments while those with shorter processes indicate brackish water, inner shelf and estuarine conditions. His own study of the Lower Eocene succession on the Isle of Sheppey confirmed this trend with the appearance and gradual increase in two successive regressive cycles first of Homotryblium ‘‘l.s.’’ (= with long spines) followed by the appearance of Homotryblium ‘‘s.s.’’ (= with short spines). Ko¨the (1990) studied Paleogene dinocyst assemblages in Northwest Germany. She tentatively suggested that abundance of Homotryblium, especially Homotryblium plectilum, indicate increased salinity. This suggestion was based on the absence of normal salinity indicators (foraminifers and nannofossils), the absence of brackish water indicators (ostracods) and of freshwater indicators (e.g. Pediastrum, ostracods), the

44

K. Dybkjær / Palaeogeography, Palaeoclimatology, Palaeoecology 206 (2004) 41–58

rare occurrence of the eco-groups indicating reduced salinity (Wetzeliellaceae and Deflandrea) and the presence of time-equivalent evaporite sediments in the Paris Basin and the Upper Rhine Embayment. Stover and Hardenbol (1993) studied the variations in abundance of a number of dinocyst ‘‘Eco-groups’’ in the Rupelian Boom Clay Formation (Belgium). Their Homotryblium+Thalassiphora eco-group comprised Homotryblium pallidum, Homotryblium plectilum, Homotryblium tenuispinosum, Homotryblium vallum and Thalassiphora pelagica. This group occurred frequently to commonly in the late highstand of the RU-1 sequence and slightly above the RU-2 sequence boundary, an interval representing the uppermost part of a coarsening upward-trend. Otherwise, the Homotryblium+Thalassiphora eco-group only occurred sporadically. Brinkhuis (1994) summarised the palaeoecology of Homotryblium as interpreted in former studies. He concluded that Homotryblium optima represent restricted marine to open marine inner neritic watermasses or the influence of the latter in hypersaline, subtropical– tropical settings. Assemblages with high relative frequencies of Homotryblium spp. may be linked to hypersaline lagoons (or their influence). The suggested relation to hypersaline lagoons was inferred based on the presumed relationship between Homotryblium spp. and Polysphaeridium zoharyi. The motile stage of the latter, Pyrodinium bahamense, had formerly been reported to occur predominantly in hypersaline waters (e.g. Bradford and Wall, 1984). However, according to Edwards and Andrle (1992), P. bahamense is euryhaline, and can occur abundantly in low salinity as well as high salinity waters. de Verteuil and Norris (1996) discussed the palaeoenvironmental preferences of selected ‘‘Homotryblium Complex’’ taxa (Pyrodinium/Polysphaeridium, Eocladopyxis and Homotryblium). They concluded that ‘‘Homotryblium Complex’’ species are pyrodinioid dinoflagellates, often occurring dominant in moderate to low-diversity dinocyst assemblages, typically in unstable coastal environments. This trend suggests an opportunistic, bloom-forming ecology. Directly or indirectly, salinity and concentrations of nutrients provide important controls on the local distribution and abundance of individuals within species. This group appears to reflect warm temperate to tropical palaeo-oceanographic provinces.

Pross and Schmiedl (2002) studied the distribution of dinocysts in the Rupelian of the Mainz Embayment. They found the highest relative abundances of Homotryblium tenuispinosum in the proximal to intermediate parts of the study area, in samples with reduced diversity. They interpreted dominance of H. tenuispinosum as reflecting relatively dry periods during which increased salinity conditions prevailed in the proximal to intermediate depositional settings.

3. Geological setting 3.1. Regional geology The northeastern limit of the North Sea Basin was located in the Danish area in Late Oligocene– Early Miocene times. The shoreline was oriented NNW – SSE; the orientation was possibly related to the orientation of the local structural element, the Ringkøbing-Fyn High (Fig. 1). The shoreline migrated significantly due to succeeding transgressions and regressions. Siliciclastic sediments were transported along the coastline and into the basin from the north and northeast by large rivers (e.g. Rasmussen, L.B., 1961; Rasmussen, E.S., 1948; in press; Clausen et al., 1999). The climate was humid, varying between cold temperate and subtropical (Sorgenfrei, 1958; Lotsch, 1968; Radwanski et al., 1975; Buchardt, 1978). The uppermost Oligocene – Miocene succession in Jylland has been subdivided into six sequences, A to F (Rasmussen, in press) (Fig. 2). The succession dealt with in the present study comprises sequences A to D. Lithostratigraphically, sequences A and B correspond to the Vejle Fjord Formation (Larsen and Dinesen, 1959). Sequence A corresponds to the Brejning Clay Member while sequence B comprises the deposits referred to as the Vejle Fjord Clay and Sand Members and the informal Hvidbjerg sand and Billund sand (Rasmussen, in press). The marine clay in the sequences C and D corresponds to the Arnum Formation (Sorgenfrei, 1958), while the intercalating, limnic to near-shore marine sand is referred to as the informal Bastrup sand (Rasmussen, in press) and the lower part of the Odderup Formation (Rasmussen, 1961), respectively. In the study area, the Ribe

K. Dybkjær / Palaeogeography, Palaeoclimatology, Palaeoecology 206 (2004) 41–58

45

Fig. 2. Lithostratigraphy of the uppermost Oligocene – Miocene succession in Denmark. From Rasmussen (in press).

Formation (Sorgenfrei, 1958) is represented only by a thin gravel layer, at the sequence boundary between sequences B and C. 3.2. Depositional environment of the study area The depositional environment of the study area was a marginal marine setting, including limnic deposits, back-barrier deposits, spit systems and fully marine inner shelf deposits (Friis et al., 1998; Rasmussen and Dybkjær, 1999, submitted for publication; Rasmussen, in press; Dybkjær, in press). The transgressive systems tract (TST) of sequence A (Fig. 3) was deposited in a fully marine environment. Changes in the foraminiferal assemblage, sedimentology and palynofacies all indicate a shallower and more near-shore setting for the highstand systems

tract (HST) (Larsen and Dinesen, 1959; Rasmussen and Dybkjær, submitted for publication). During deposition of sequence B, especially during deposition of the TST, the Ringkøbing-Fyn High probably acted as a structural barrier. In the areas north of the High (including the study area) fine grained, organic-rich sediments were deposited in a silled basin with very little marine influence (Larsen and Dinesen, 1959; Rasmussen and Dybkjær, submitted for publication). River-systems supplied freshwater, sediments and terrestrial organic particles to the study area from the north. The rising sea level (especially at the maximum flooding surface, MFS) resulted in partial flooding of the structural highs thus increasing the marine influence. The sediments of the HST were therefore generally deposited in an environment with more marine influence than the TST. In most proximal

46 K. Dybkjær / Palaeogeography, Palaeoclimatology, Palaeoecology 206 (2004) 41–58 Fig. 3. Correlation-panel showing the sequence stratigraphic subdivision (sequences A to E) and the environmental interpretation. Modified from Rasmussen (in press, Fig. 5).

K. Dybkjær / Palaeogeography, Palaeoclimatology, Palaeoecology 206 (2004) 41–58

Fig. 4. Distribution of Homotryblium species, where they dominate the dinocyst assemblage. Note that the sporadic occurrences of H. vallum is indicated with dots. 47

48

K. Dybkjær / Palaeogeography, Palaeoclimatology, Palaeoecology 206 (2004) 41–58

parts of the marine setting, represented by the Addit Mark and Klovborg boreholes, the environment was, however, continuously exposed to an influx of freshwater (Rasmussen and Dybkjær, submitted for publication; Dybkjær, in press). Geochemical parameters indicate brackish water conditions during deposition of the HST of sequence A and of sequence B (Rasmussen, 1995). Brackish water conditions were also reported by Dinesen (in Larsen and Dinesen, 1959) on the basis of the foraminiferal fauna. The high relative abundances of terrestrially derived organic matter (woody particles, spores and pollen) and of freshwater algae further indicate an influx of freshwater (Dybkjær, in press). The sequence boundary between the sequences B and C comprises a major unconformity (Dybkjær and Rasmussen, 2000; Dybkjær, in press). The marine clays of sequences C and D were generally deposited in a more open marine environment than sequence B (Rasmussen, in press; Dybkjær, in press). The sand intercalating sequence C/D and D/E, the Bastrup sand and the Odderup Formation, comprise limnic to nearshore marine progradational units (Rasmussen, in press). Based on dinocyst stratigraphy (Dybkjær, in press), sequence A can be referred to the latest Chattian, sequence B to the latest Chattian and/or early Aquitanian, sequence C to the early to mid-Burdigalian and sequence D to the mid-Burdigalian to Langhian.

4. Material and methods The seven boreholes supplying the material for the present study were drilled using the airlift method. Each sample thus represents an interval of 1 m. The preparation technique included dissolution of silicates with HF and HCl, oxygenation with HNO3, heavy liquid separation and sieving through 20-Am filters. The organic residue was mounted in glycerine jelly. The relative abundances of dinocyst species are based on counts of at least 200 specimens from each sample, wherever possible. The type material and the illustrated dinoflagellate cysts marked with MGUH numbers are stored in the type collection of the Geological Museum of the University of Copenhagen (Øster Voldgade 5– 7, DK-1350 Copenhagen K, Denmark).

5. Distribution Four species of Homotryblium were recorded; Homotryblium? additense, Homotryblium plectilum, Homotryblium tenuispinosum and Homotryblium vallum (Figs. 4 and 5). H. vallum was only recorded sporadically and its distribution is therefore shown using dots in Fig. 4 , and is not included in Fig. 5 . Each of the four species of Homotryblium seems to occur mainly within a well-defined regional palaeogeographic area and to be most abundant within specific stratigraphic intervals (Figs. 4 and 5). Homotryblium? additense has only been recorded in the most proximal part of the marine depositional system, in the Addit Mark borehole. Here, it occurs in the upper part of the HST in sequence B (in association with Homotryblium plectilum), and constitutes 13– 15% of the total dinocyst assemblage (Figs. 4 and 5). Homotryblium plectilum dominates the dinocyst assemblage in the most proximal parts of the marine depositional system (in the Addit Mark, Klovborg and partly in the St. Vorslunde boreholes) (Figs. 4 and 5). It is the only Homotryblium species present in sequence A, where it appears in the HST. In sequence B, it occurs commonly in the Addit Mark borehole, concurrent with H.? additense, and it dominates the dinocyst assemblage in the Klovborg borehole. In the St. Vorslunde borehole, H. plectilum dominates in the lower part of the TST but after a secondary flooding, within the TST, the relative abundance decreases and at the maximum flooding surface the abundance decreases further. In the boreholes further south, H. plectilum has only been recorded in low numbers within sequence B. In the most proximal areas, represented by the Addit Mark borehole, Homotryblium plectilum continues to dominate the dinocyst assemblage in sequence C and in the lower part of sequence D (due to very coarse lithology no samples were taken from the upper part of sequence D). In the Klovborg borehole, it dominates in sequence C, but occurs only very sporadically in sequence D. In the more distal areas, from the St. Vorslunde borehole and further south it has not been recorded above sequence B. Within the sequences, Homotryblium plectilum generally shows peak abundance in the uppermost HSTs, near the sequence boundaries, in the Addit Mark and Klovborg boreholes (Fig. 5).

K. Dybkjær / Palaeogeography, Palaeoclimatology, Palaeoecology 206 (2004) 41–58

Fig. 5. Relative abundances of Homotryblium species in the studied boreholes. Sequence stratigraphic subdivision is indicated.

49

50

K. Dybkjær / Palaeogeography, Palaeoclimatology, Palaeoecology 206 (2004) 41–58

Homotryblium tenuispinosum has not been recorded in sequence A. In sequence B, it is missing in the proximal parts of the study area (in the Addit Mark and Klovborg boreholes). In sequence B in the St. Vorslunde borehole, it shows a stepwise increase in abundance concurrent with the flooding surfaces and the decreasing abundance of Homotryblium plectilum. H. tenuispinosum dominates the dinocyst assemblage in the HST of sequence B in the St. Vorslunde borehole and in the boreholes further south, representing the distal parts of the HST (Figs. 4 and 5). It disappears abruptly at the sequence boundary between sequences B and C and occurs only sporadically in the sequences C and D. Homotryblium vallum, although occurring sporadically, shows a distinct pattern of distribution, occurring mainly in the proximal parts of the marine setting, in the HST of sequence A and in the lower part of the TST of sequence B.

6. Discussion 6.1. Relations between the distribution and relative abundance of Homotryblium-cysts and the depositional environment The present study is an example where Homotryblium-cysts dominated a generally sparse dinocyst assemblage in a restricted marine, low-salinity environment. The palaeogeographic and stratigraphic distribution of the four Homotryblium species (Figs. 4 and 5) strongly suggests a close relation to salinity. The restricted distribution of H.? additense may be related to extremely low salinities. The Addit Mark borehole, from where H.? additense was recorded, is located furthest to the north and thus consequently in the most proximal parts of the marine setting with the presumably highest freshwater influx (see the palaeogeographic maps of Rasmussen, in press, Fig. 9). Furthermore, the samples in which H.? additense occurs have a high relative abundance of the freshwater algae Botryococcus indicating a high influx of freshwater (Dybkjær, in press, Fig. 4). The distribution of Homotryblium plectilum (Figs. 4 and 5) shows a pattern that apparently reflects the variations in the marine/freshwater influence. It dom-

inates the dinocyst assemblages in the proximal parts of the marine setting, while it only occurs sporadically in the more distal areas. Furthermore, it shows a stepwise decreasing relative abundance in sequence B (in the St. Vorslunde borehole) concurrent with increasing marine influence at the flooding surfaces. The distribution of Homotryblium tenuispinosum, dominating in the distal parts of the study area during deposition of sequence B, suggests that this species is related to somewhat higher salinities than Homotryblium plectilum and H.? additense. This hypothesis is supported by the stepwise increase in relative abundance of H. tenuispinosum concurrent with the decrease in abundance of H. plectilum in St. Vorslunde, apparently related to the marine floodings. The sporadic occurrence of Homotryblium vallum, mainly in the proximal parts of the study area, indicates a relation to relatively low salinities. This is supported by the regular presence of H. vallum in the lower part of the TST of sequence B in the St. Vorslunde borehole, while it was not recorded in the succession deposited after the marine flooding within the TST or above the MFS (Fig. 4). The distributional patterns and the morphological similarities of the recorded Homotryblium species open the possibility that it was the same motile dinoflagellate species that produced (at least some of) the Homotryblium cyst species, forming cysts with processes of different length and shape depending on salinity. Variations in process-length related to salinity is a phenomenon known from recent dinoflagellates. In a study of the distribution of recent dinocysts in the Baltic Sea, Gundersen (1988; referred in Dale, 1996, p. 1261) found that Lingulodinium machaeophorum, Operculodinium centrocarpum and some small forms of Spiniferites showed proportionally increasing numbers of individuals with reduced length of processes as salinities decreased (e.g. >50% of specimens of Operculodinium centrocarpum showed markedly reduced processes at salinities < 7x; the major shift from ‘‘normal coastal/neritic’’ to low-salinity assemblages occurred at salinities < 10x). Corresponding observations of reduction in process length as a response to low salinities have been documented by, e.g., Wall and Dale (1973), Nehring (1994), Matthiessen and Brenner (1996), Ellegaard (2000), Mudie et al. (2001) and Ellegaard et al. (2002). The latter even found examples of cysts where the processes disap-

K. Dybkjær / Palaeogeography, Palaeoclimatology, Palaeoecology 206 (2004) 41–58

peared completely. Similar changes in cyst morphology were observed in dinoflagellate cultures exposed to high salinities (Ellegaard et al., 2002). It is not possible to evaluate the influence of nutrient availability. However, there is no evidence from either the present study or any previous studies (see previous section) that this factor should have had a major effect on the distribution of Homotryblium cysts. In addition, the water temperature does not seem to have had a major influence on the occurrence of Homotryblium-cysts in the studied succession. According to de Verteuil and Norris (1996), the ‘‘Homotrybblium Complex’’ ‘‘appears to reflect warm temperate to tropical palaeo-oceanographic provinces’’. The climate in Central Europe during deposition of sequences A and B was possibly warm temperate, while it may have been subtropical during deposition of sequence C (Lotsch, 1968, see Dybkjær, in press, Fig. 15). The seawater temperatures in the North Sea only varied slightly, increasing from about 9 to 13 jC from the uppermost Chattian – mid Burdigalian (25 – 18 Ma), studied here (Buchardt, 1978). The appearance of Homotryblium-cysts in the HST of sequence A, the abundant occurrence in sequence B and the abrupt decrease/disappearance from sequence B to C (in the distal areas) strongly suggest that the seawater temperature was of less importance relative to other environmental factors (e.g. salinity). 6.2. Stratigraphy The present study shows that Homotryblium plectilum and Homotryblium tenuispinosum both occur in the uppermost Oligocene to the Middle Miocene, from the uppermost Chattian (sequence A) to the Langhian (sequence D) in the Danish area (Fig. 2 and Dybkjær, in press). The last occurrence of Homotryblium plectilum was earlier reported from the upper Lower Miocene (upper Burdigalian) in the Norwegian Sea (Manum et al., 1989) and the northern hemisphere in general (Williams et al., 1993). In other studies from the Danish area, Homotryblium tenuispinosum has also been found abundantly in late Middle Miocene and Upper Miocene deposits (Stefan Piasecki, personal communication, 2002). The last occurrence of H. tenuispinosum is thus distinctly younger than the 23.67 Ma (earliest Aquita-

51

nian) suggested by Hardenbol et al. (1998, chart 3) for northwestern Europe, but is generally in accordance with the last occurrence of this species as indicated for the Mediterranean and North Atlantic areas (5.90 Ma, latest Messinian).

7. Conclusions – A new species, H.? additense n. sp., is proposed. – The dinocyst genus Homotryblium showed high relative abundances in a low-salinity setting in Denmark in the uppermost Oligocene and Lower Miocene. – Palaeogeographic and stratigraphic distributional patterns of four Homotryblium-cyst species probably reflect variations in salinity: H.? additense n.sp. was restricted to the most proximal part of the study area, to the HST of sequence B, possibly representing the area with the lowest salinities, Homotryblium plectilum and Homotryblium vallum occurred mainly in the proximal areas, while H. tenuispinosum dominated in the more distal parts of the study area. A stepwise change in dominance of H. plectilum to a dominance of H. tenuispinosum within sequence B is apparently related to the marine flooding surfaces, indicating that the latter reflects somewhat higher salinities than the former. – Some of the recorded Homotryblium-cyst species may have been produced by the same motile dinoflagellate species, producing cysts with different process-morphology as a response to variations in salinity. – The stratigraphic range of H. tenuispinosum should be prolonged to the late Miocene for northwestern Europe, in accordance with the range known from the Mediterranean and the North Atlantic.

Acknowledgements The author thanks the Danish counties, Vejle and Ribe, for providing the sample material and supporting the study economically. Yvonne Desezar prepared the samples in the laboratory and Eva Melskens made the figures. My colleagues at GEUS, Stefan Piasecki, Erik Skovbjerg Rasmussen, Emma Sheldon and Poul Schiøler are thanked for commenting early and later

52

K. Dybkjær / Palaeogeography, Palaeoclimatology, Palaeoecology 206 (2004) 41–58

drafts of the manuscript. The comments and constructive criticism from the referees Henk Brinkhuis and Gerard J.M. Versteegh are deeply acknowledged. The paper is published with the permission of the Geological Survey of Denmark and Greenland.

Appendix A . Taxonomy Genus Homotryblium Davey and Williams in Davey et al. (1966). H.? additense Dybkjær, sp. nov. (Plates 1, 1a –d, 2a,b and 2, 1a,b, 2a,b, 3a,b, 4a– d and 5a,b). Holotype: Addit Mark borehole, sample 155 –156 m, slide no. 5, England Finder coordinates P29-2, Plate 1, 1a– d. MGUH no. 26862. Paratype: Addit Mark borehole, sample 144 –145 m, slide no. 6, England Finder coordinates H38. Plate 1, 2a,b. MGUH no. 26863. Repository: Geological Museum of the University of Copenhagen, Denmark. Type locality: Addit Mark borehole (UTM coordinates: 6208748 north, 537941 East), Jylland, Denmark (in the samples 156, 148 and 145 m). Stratigraphic horizon: Vejle Fjord Formation, the Vejle Fjord Clay Member. Occurrence: At present, H.? additense is only known from the borehole Addit Mark, in Jylland, Denmark, in a very narrow stratigraphic interval (the HST of sequence B) referred to the uppermost Chattian and/or lower Aquitanian (uppermost Oligocene and/or lowermost Miocene) based on dinocyst stratigraphy (Dybkjær, in press). Etymology: The species name, additense means ‘‘coming from Addit’’ and refers to the village, Addit, in Jylland, Denmark. Diagnosis: H.? additense comprise skolochorate cysts with a epicystal archaeopyle. The body is spherical to subspherical. The processes are intratabular; the cingular processes are missing. The processes are polytubular, broadly cylindrical to tubiform and distally closed. The number of processes varies; processes are not always developed on the smaller paraplates. Description: Skolochorate cysts with an epicystal archaeopyle. The operculum presumably splits up

totally into single plates, as pieces of connected plates have not been found. However, single plates confidently referable to H.? additense were not found either. Accessory archaeopyle sutures at the archaeopyle margin indicate the cingular paraplates. The body is spherical to subspherical, bearing intratabular processes. The hypocyst is represented by a hemispherical body while definite remnants of the epicyst have not been found. The number of processes on the hypocyst varies from 6 to 9. The larger processes are broadly cylindrical and may narrow a little distally (e.g. Plate 1, 1a –d (the holotype), 3j– 5j, and Plate 2, 3a,b ). The smaller processes are slender, cylindrical or slightly tubiform (e.g. Plate 1, 1a– d; the holotype), 2j and 6j). The larger processes are polytubular, formed by fused tubules (two to nine tubules have been seen), the larger the process, the more tubules. Due to the polytubular structure, the processes show a flower-like pattern at the base, where they fuse with the central body. The processes are closed distally. The thin body wall consists of an endophragm and a periphragm, the latter giving rise to the processes. The wall is equal to or less than 1 Am thick. The surface is smooth or faintly micro-granulate. No wall-structure was observed. The tabulation of the epicyst is unknown. The hypocyst tabulation is indicated by the intratabular processes and by the presence of a sulcal tab. The cingular paraplates are not represented by processes, but the cingular plates, 1c – 6c have been identified by the suture of the archaeopyle (Plate 1, 1a). The number of processes varies from 6 to 9. Due to their position on the hypocyst in relation to the sulcal tap they are identified as 6 (2j –6j, 1I), 7 (2j– 6j, 1I, 1p), 8 (2j– 6j, 1I, 1p, ps) to 9 (1j –6j, 1I, 1p, ps). The post-cingular processes 3j, 4j and 5j are the largest, while 1j, 2j, 6j and the antapical 1I, 1p and ps processes are smaller, if present at all. Eight processes are present on the holotype. Dimensions: Holotype: Cyst body diameter: 38– 52 Am (slightly compressed); length of processes: 3j –5j: 22 Am, 2j and 6j: 18 Am; width of processes: 3j –5j: 20– 23 Am, 2j and 6j: 16 – 18 Am at base, narrowing to 10 Am at the middle, widening again to 12 Am distally. Paratype: Cyst body diameter: 43 Am; length of processes: 3j – 5j: 21 Am, 2j and 6j: 18 –20 Am, ps: 18 Am; width of processes: 3j– 5j: 12 – 18 Am, 2j and 6j: 10– 12 Am, ps: 10 Am.

K. Dybkjær / Palaeogeography, Palaeoclimatology, Palaeoecology 206 (2004) 41–58

53

Plate 1. All figures are with the same magnification indicated by the 20 Am bar. (1a – d) H.? additense n. sp., holotype. Addit Mark borehole, 155 – 156 m, slide 5, England Finder coordinates P29-2, MGUH 26862. (2a, b) H.? additense n. sp., paratype. Addit Mark borehole, 144 – 145 m, slide 6, England Finder coordinates H38, MGUH 26863. (3a, b) H. plectilum. Addit Mark borehole, 137 – 138 m, slide 5, England Finder coordinates Q36-3, MGUH 26864. (4a, b) H. tenuispinosum. Vandel Mark borehole, 199 – 200 m, slide 6, England Finder coordinates V29-1, MGUH 26865. (5a, b) H. vallum. St. Vorslunde borehole, 215 – 216 m, slide 6, England Finder coordinates E27-3/4, MGUH 26866.

54

K. Dybkjær / Palaeogeography, Palaeoclimatology, Palaeoecology 206 (2004) 41–58

K. Dybkjær / Palaeogeography, Palaeoclimatology, Palaeoecology 206 (2004) 41–58

Size range: Cyst body diameter: 36 (40) 44 Am; length of processes: 3j– 5j: 11 (17) 22 Am, 2j and 6j: 12 (17) 22 Am, antapical and parasulcal processes: 12 (17) 20 Am; width of processes: 3j –5j: 10 (16) 22 Am, 2j and 6j: 6 (10) 14 Am, antapical and parasulcal processes: 3 (10) 13 Am; (12 specimens). Discussion: It has been chosen questionably to refer Homotryblium? additense to the genus Homotryblium although the cysts referred to H.? additense lack cingular processes and have processes which are closed distally. The presence of cingular, distally open processes was part of the original diagnosis for the genus Homotryblium. However, the cysts of H.? additense otherwise compare closely with the diagnosis of Homotryblium, having an epicystal archaeopyle, intratabular, polytubular processes, and a tabulation that corresponds to that of Homotryblium. The combination of absent cingular processes and the presence of polytubular processes have not been described from any other genus with an epicystal archaeopyle. Homotryblium? additense has some characteristics similar to the genus Lithosphaeridium. These chorate cysts lack cingular processes, they have three apical processes, while the sulcal processes may be either absent or few. However, Lithosphaeridium has an apical archaeopyle in contrast to the epicystal archaeopyle of H.? additense and the processes are not polytubular. The informal species Hystrichokolpoma pseudooceanica and H. reducta proposed by Zevenboom and Santarelli in Zevenboom (1995) both have hollow, tubular processes and lack paracingular processes. However, they can be distinguished from the genus Homotryblium by possessing an apical archaeopyle. The processes of H.? additense resemble the processes of Homotryblium plectilum, Homotryblium floripes and Homotryblium vallum in being polytubular, intratabular and vary in size, according to their location on the cyst. However, the processes of H.? additense differ in being closed distally and in being cylindrical (e.g. Plate 2, 1a,b) or narrow a little

55

distally (e.g. Plate 2, 3a,b). The processes of H. plectilum, H. floripes and H. vallum are buccinate or tubiform or split up into separate tubules or few, fused tubules (e.g. Plate 1, 3a,b and 5a,b). The processes of Homotryblium tenuispinosum are not polytubular, they have a buccinate or tubiform shape and seccate process-tips (e.g. Plate 1, 4a,b). Homotryblium plectilum Drugg and Loeblich (1967) (Plate 1, 3a,b). According to Bujak et al. (1980, p. 64), H. floripes (Deflandre and Cookson, 1955) Stover (1975) is a taxonomic senior synonym to Homotryblium plectilum. However, Stover in Lentin and Williams (1985, p. 168) retained H. plectilum: ‘‘Stover (personal communication) has studied the holotype of Homotryblium floripes and believes H. plectilum is a distinct and separate species’’. According to Williams et al. (1993, p. 30), ‘‘the southern hemisphere form (Homotryblium floripes), in contrast to the typically northern hemisphere Homotryblium plectilum, has a distinctly granular body in which the periphragm is about twice as thick as the endophragm. To the best of our knowledge, H. floripes is a strictly southern hemisphere species.’’ With this knowledge, it has been chosen to use H. plectilum in the present study. Homotryblium tenuispinosum Davey and Williams (1966) (Plate 1, 4a,b). Taxonomic junior synonym: Homotryblium pallidum according to Edwards (1996, p. 989). Homotryblium vallum Stover (1977) (Plate 1, 5a,b). References Bradford, M.R., Wall, D.A., 1984. The distribution of Recent organic-walled dinoflagellate cysts in the Persian Gulf, Gulf of Oman, and northwestern Arabian Sea. Palaeontogra. Abt. B Pala¨ophytol. 192, 16 – 84.

Y Plate 2. All figures are with the same magnification indicated by the 20 Am bar. (1a, b) H.? additense n. sp. Addit Mark borehole, 144 – 145 m, slide 5, England Finder coordinates S22, MGUH 26867. (2a, b) H.? additense n. sp. Addit Mark borehole, 144 – 145 m, slide 6, England Finder coordinates H38, MGUH 26868. (3a, b) H.? additense n. sp. Addit Mark borehole, 155 – 156 m, slide 6, England Finder coordinates W43-3, MGUH 26869. (4a – d) H.? additense n. sp. Addit Mark borehole, 144 – 145 m, slide 6, England Finder coordinates F55-4, MGUH 26870. (5a, b) H.? additense n. sp. Addit Mark borehole, 155 – 156 m, slide 5, England Finder coordinates M53, MGUH 26871.

56

K. Dybkjær / Palaeogeography, Palaeoclimatology, Palaeoecology 206 (2004) 41–58

Brinkhuis, H., 1994. Late Eocene to Early Oligocene dinoflagellate cysts from the Priabonian type-area (Northeast Italy): biostratigraphy and paleoenvironmental interpretation. Palaeogeogr., Palaeoclimatol., Palaeoecol. 107, 121 – 163. Brinkhuis, H., Powell, A.J., Zevenboom, D., 1992. High-resolution dinoflagellate cyst stratigraphy of the Oligocene/Miocene transition interval in northwest and central Italy. In: Head, M.J., Wrenn, J.H. (Eds.), Neogene and Quaternary Dinoflagellate Cysts and Acritarchs. American Association of Stratigraphic Palynologists Foundation, Dallas, TX, pp. 219 – 258. Buchardt, B., 1978. Oxygen isotope palaeotemperatures from the North Sea Area. Nature 275, 121 – 123. Bujak, J.P., Downie, C., Eaton, G.L., Williams, G.L., 1980. Dinoflagellate cysts and acritarchs from the Eocene of southern England. Special Papers in Palaeontology 24, 100 pp. Clausen, O.R., Gregersen, U., Michelsen, O., Sørensen, J.C., 1999. Factors controlling the Cenozoic sequence development in the eastern parts of the North Sea. J. Geolog. Soc. (London) 156, 809 – 816. Dale, B., 1996. Chapter 31. Dinoflagellate cyst ecology: modelling and geological applications. In: Jansonius, J., McGregor, D.C. (Eds.), New Directions, Other Applications and Floral History. Palynology: Principles and Applications, vol. 3. American Association of Stratigraphic Palynologists Foundation, Salt Lake City, UT, pp. 1249 – 1275. Davey, R.J., Williams, G.L., 1966. The genus Hystrichosphaeridium and its allies. In: Davey, R.J., Downie, C., Sarjeant, W.A.S., Williams, G.L. (Eds.), Studies on Mesozoic and Cainozoic Dinoflagellate Cysts. Bulletin of the British Museum, Natural History. Geology, Suppl. 3, pp. 53 – 106. Davey, R.J., Downie, C., Sarjeant, W.A.S., Williams, G.L., 1966. Studies on Mesozoic and Cainozoic Dinoflagellate Cysts. Bul. Brit. Mus., Natural History. Geology, Suppl. 3. 248 pp. Deflandre, G., Cookson, I.B., 1955. Fossil microplankton from Australian Late Mesozoic and Tertiary sediments. Aust. J. Marine Freshwater Res. 6, 242 – 313. de Verteuil, L., Norris, G., 1996. Middle to upper Miocene Geonettia clineae, an opportunistic coastal embayment dinoflagellate of the Homotryblium complex. Micropaleontology 42, 263 – 284. Drugg, W.S., Loeblich Jr., A.R., 1967. Some Eocene and Oligocene phytoplankton from the Gulf Coast, USA. Tulane Stud. Geol. 5, 181 – 194. Dybkjær, K., Rasmussen, E.S., 2000. Palynological dating of the Oligocene – Miocene successions in the Lille Bælt area, Denmark. Bull. Geolog. Soc. Denmark 47, 87 – 103. Dybkjær, K., in press. Dinocyst stratigraphy and palynofacies studies used for refining a sequence stratigraphic model—uppermost Oligocene to Lower Miocene, Jylland, Denmark. Rev. Palaeobot. Palynol. Edwards, L.E., 1996. Chapter 25 A. Graphic correlation of the Marlboro Clay and Nanjemoy Formation (uppermost Paleocene and Lower Eocene) of Virginia and Maryland. In: Jansonius, J., McGregor, D.C. (Eds.), Palynology: Principles and Applications. American Association of Stratigraphic Palynologists Foundation, Dallas, TX, pp. 989 – 999.

Edwards, L.E., Andrle, V.A.S., 1992. Distribution of selected dinoflagellate cysts in modern marine sediments. In: Head, M.J., Wrenn, J.H. (Eds.), Neogene and Quaternary Dinoflagellate Cysts and Acritarchs. American Association of Stratigraphic Palynologists Foundation, Salt Lake City, UT, pp. 259 – 288. Ellegaard, M., 2000. Variations in dinoflagellate cysts morphology under conditions of changing salinity during the last 2000 years in the Limfjord, Denmark. Rev. Palaeobot. Palynol. 109, 65 – 81. Ellegaard, M., Lewis, J., Harding, I., 2002. Cyst – theca relationship, life cycle, and effects of temperature and salinity on the cyst morphology of Gonyaulax baltica sp. nov. (Dinophyceae) from the Baltic Sea area. J. Phycol. 38, 775 – 789. Fensome, R.A., Taylor, F.J.R., Norris, G., Sarjeant, W.A.S., Wharton, D.I., Williams, G.J., 1993. A classification of living and fossil dinoflagellates. Micropaleontology Special Publication 7, 351 pp. Friis, H., Mikkelsen, J., Sandersen, P., 1998. Depositional environment of the Vejle Fjord Formation of the Upper Oligocene – Lower Miocene of Denmark: a barrier island/ barrier-protected depositional complex. Sediment. Geol. 117, 221 – 244. Gundersen, N., 1988. A palynological investigation of dinoflagellate cysts along a lowering salinity gradient in recent sediments from the Baltic Sea region. Cand. scient. thesis, University of Oslo, Norway. 103 pp. Hallett, R.I., 1999. Consequences of Environmental Change on the Growth and Morphology of Lingulodinium polyedrum (Dinophyceae) in Culture. PhD thesis, University of Westminster, London. 145 pp. Hardenbol, J., Thierry, J., Farley, M.B., Jacquin, T., de Graciansky, P.-C., Vail, P.R., 1998. Mesozoic and Cenozoic sequence chronostratigraphic framework of European basins. In: De Graciansky, P.C., Hardenbol, J., Jacquin, Th., Vail, P.R. (Eds.), Mesozoic and Cenozoic Sequence Stratigraphy of European Basins. SEPM Special Publication, vol. 60, pp. 3 – 13. Harland, R., 1983. Distribution maps of recent dinoflagellate cysts in bottom sediments from the North Atlantic Ocean and adjacent seas. Palaeontology 26, 321 – 387. Islam, M.A., 1984. A study of early Eocene palaeoenvironments in the Isle of Sheppey as determined from microplankton assemblage composition. Terti. Res. 6, 11 – 21. Jaramillo, C.A., Oboh-Ikuenobe, F.E., 1999. Sequence stratigraphic interpretations from palynofacies, dinocyst and lithological data of Upper Eocene – Lower Oligocene strata in southern Mississippi and Alabama, U.S. Gulf Coast. Palaeogeogr., Palaeoclimatol., Palaeoecol. 145, 259 – 302. Ko¨the, A., 1990. Paleogene dinoflagellates from Northwest Germany. Geologische Jahrbuch, Reihe A 118, 111 pp. Larsen, G., Dinesen, A., 1959. Vejle Fjord Formationen ved Brejning. Sedimenterne og foraminiferfaunaen (Oligocæn – Miocæn). Danmarks Geologiske Undersøgelse: 2. Række 82, 114 pp. Lentin, J.K., Williams, G.L., 1985. Fossil dinoflagellates: index to genera and species, 1985 edition. Canadian Technical Report of Hydrography and Ocean Sciences 60, 451 pp.

K. Dybkjær / Palaeogeography, Palaeoclimatology, Palaeoecology 206 (2004) 41–58 Liengjarern, M., Costa, L., Downie, C., 1980. Dinoflagellate cysts from the Upper Eocene – Lower Oligocene of the Isle of Wight. Palaeontology 23, 475 – 499. Lotsch, D., 1968. Tertia¨r (Pala¨ogen und Neogen) Grundriss der geologie der Deutschen Demokratischen Republik: Band 1. Geologische Entwicklung des Gesamtgebietes. Akademie Verlag, Berlin, pp. 356 – 379. Manum, S., Boulter, M.C., Gunnarsdottir, H., Rangnes, K., Scholze, A., 1989. Eocene to Miocene palynology of the Norwegian Sea (ODP Leg 104). Eldolm, O., Thiede, J., Taylor, E., et al., (Eds.), Proceedings of the Ocean Drilling Program. Scientific Results, vol. 104, pp. 611 – 662. Marret, F., Zonneveld, K.A.F., 2003. Atlas of modern organicwalled dinoflagellate cyst distribution. Review of Palaeobotany and Palynology 125, 1 – 200. Matsuoka, K., 1999. Eutrophication recorded in dinoflagellate cyst assemblages—a case of Yokohama Port, Tokyo Bay, Japan. Science of the Total Environment 231, 17 – 35. Matthiessen, J., Brenner, W., 1996. Chlorococcalalgen und Dinoflagellaten-Zysten in rezenten Sedimenten des Greifswalder Boddens (Su¨dliche Ostsee). Senckenbergiana Maritima 27, 33 – 48. Mudie, P.J., Aksu, A.E., Yasar, D., 2001. Late Quaternary dinoflagellate cysts from the Black, Marmara and Aegean seas: variations in assemblages, morphology and paleosalinity. Marine Micropaleontology 43, 155 – 178. Nehring, S., 1994. Spatial distribution of dinoflagellate resting cysts in Recent sediments of Kiel Bight, Germany (Baltic Sea). Ophelia 39, 137 – 158. Powell, A.J., Brinkhuis, H., Bujak, J.P., 1996. Upper Paleocene – Lower Eocene dinoflagellate cyst sequence biostratigraphy of southeast England. In: Knox, R.W.O’B., Corfield, R., Dunay, R.E. (Eds.), Correlation of the Early Paleogene in Northwest Europe. Special Publication-Geological Society of London, vol. 101, pp. 145 – 183. Pross, J., Schmiedl, G., 2002. Early Oligocene dinoflagellate cysts from the Upper Rhine Graben (SW Germany): paleoenvironmental and paleoclimatic implications. Marine Micropaleontology 45, 1 – 24. Radwanski, A., Friis, H., Larsen, G., 1975. The Miocene HagenørBørup sequence at Lillebælt (Denmark): its biogenic structures and depositional environment. Bulletin of the Geological Society of Denmark 24, 229 – 260. Rasmussen, L.B., 1961. De Miocæne formationeri Danmark. Danmarks Geologiske Undersøgelse: 4. Række 5, 45 pp. Rasmussen, E.S., 1995. Mineralogy and geochemistry of the Vejle Fjord Formation. Bulletin of the Geological Society of Denmark 42, 53 – 62. Rasmussen, E.S., 1998. Detached lowstand deposits illustrated through seismic data, lithology and clay mineralogy: an example from the Lower Miocene of Denmark. In: Gradstein, F.M., Sandvik, K.O., Milton, N.J. (Eds.), Sequence Stratigraphy— Concepts and ApplicationsSpecial Publication-Norwegian Petroleum Society, NPF, vol. 8, pp. 413 – 421. Rasmussen, E.S., in press. Stratigraphy and depositional evolution of the uppermost Oligocene – Miocene succession in Denmark. Bulletin of the Geological Society of Denmark.

57

Rasmussen, E.S., Dybkjær, K., 1999. Excursion: Upper Oligocene – Lower Miocene storm and tidal dominated deposits at Lillebælt and Vejle Fjord. Rapport-Danmarks og Grønlands Geologiske Undersøgelse 52, 76 pp. Rasmussen, E.S.R., Dybkjær, K., submitted for publication. Sedimentology and sequence stratigraphy of upper Oligocene – lower Miocene deposits in East Jylland, Denmark: a storm and tidal dominated shallow marine environment. Sedimentology. Sorgenfrei, T., 1958. Molluscan assemblages from the marine middle Miocene of South Jutland and their environments. Danmarks Geologiske Undersøgelse. 2: Række 79, 503 pp. Stover, L.E., 1975. Observations on some Australian Eocene dinoflagellates. Geoscience and Man 11, 35 – 45. Stover, L.E., 1977. Oligocene and Early Miocene dinoflagellates from Atlantic Corehole 5/5B, Blake Plateau. Contributions Series-American Association of Stratigraphic Palynologists 5A, 66 – 89. Stover, L.E., Hardenbol, J., 1993. Dinoflagellates and depositional sequences in the Lower Oligocene (Rupelian) Boom Clay Formation, Belgium. Bulletin de la Socie´te´ belge de Ge´ologie 102, 5 – 77. Van Mourik, C.A., Brinkhuis, H., Williams, G.L., 2001. Mid- to Late Eocene organic-walled dinoflagellate cysts from ODP Leg 171B, offshore Florida. In: Kroon, D., Norris, R.D., Klaus, A. (Eds.), Western North Atlantic Palaeogene and Cretaceous Palaeoceanography. Special Publication-Geological Society of London, vol. 183, pp. 225 – 251. Versteegh, G.J.M., 1994. Recognition of cyclic and non-cyclic environmental changes in the Mediterranean Pliocene: a palynological approach. Marine Micropaleontology 23, 147 – 183. Versteegh, G.J.M., Zonneveld, K.A.F., 1994. Determination of (Palaeo-) ecological preferences of dinoflagellates by applying Detrended and Canonical Correspondence analysis to Late Pliocene dinoflagellate cyst assemblages of the south Italian Singa section. Review of Palaeobotany and Palynology 84, 181 – 199. Wall, D., Dale, B., 1973. Paleosalinity relationships of dinoflagellates in the Late Quaternary of the Black Sea—a summary. Geoscience and Man 7, 95 – 102. Wall, D., Dale, B., Lohmann, G.P., Smith, W.K., 1977. The environmental and climatic distribution of dinoflagellate cysts in modern marine sediments from regions in the north and south Atlantic oceans and adjacent seas. Marine Micropalaeontology 2, 121 – 200. Williams, D.B., 1971. The distribution of marine dinoflagellates in relation to physical and chemical conditions. In: Funnell, B.M., Riedel, W.R. (Eds.), The Micropalaeontology of Oceans. Cambridge Univ. Press, Cambridge, pp. 91 – 95. Williams, G.L., 1977. Dinoflagellate cysts, their classification, biostratigraphy and palaeoecology. Oceanic Micropaleontol. 2, 1231 – 1325. Williams, G.L., Bujak, J.P., 1977. Distribution patterns of some North Atlantic Cenozoic dinoflagellate cysts. Marine Micropaleontol. 2, 223 – 233. Williams, G.L., Stover, L.E., Kidson, E.J., 1993. Morphology and

58

K. Dybkjær / Palaeogeography, Palaeoclimatology, Palaeoecology 206 (2004) 41–58

stratigraphic ranges of selected Mesozoic – Cenozoic dinoflagellate taxa in the Northern Hemisphere. Geological Survey of Canada Paper 92 – 10, 137 pp. Zevenboom, D., 1995. Dinoflagellate cysts from the Mediterranean Late Oligocene and Miocene. PhD thesis, University of Utrecht, The Netherlands, 137 pp.

Zevenboom, D., Brinkhuis, H., Visscher, H., 1994. Dinoflagellate cysts palaeoenvironmental analysis of the Oligocene/Miocene transition in northwest and central Italy. Giorn. Geolog. ser. 3a (56/1), 155 – 169.