New Species of Organic-Walled Dinoflagellates and Acritarchs From

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New species of organic-walled dino¯agellates and acritarchs from the Upper Miocene Diest Formation, northern Belgium (southern North Sea Basin)

S. Louwye * Laboratory for Palaeontology, University Gent, Krijgslaan 281=S8, B-9000 Gent, Belgium Received 9 November 1998; revised version received 17 March 1999; accepted 16 April 1999

Abstract

A palynological investigation of the shallow marine Diest Formation (Upper Miocene) in northern Belgium has revealed the presence of ®ve previously undescribed dino¯agellate cyst species and one acritarch. A formal description and a preliminary assessment of the stratigraphical ranges of following species is given: Bitectatodinium? arborichiarum Louwye, sp. nov., Operculodinium antwerpensis Louwye, sp. nov., Batiacasphaera deheinzelinii Louwye, sp. nov., Cerebrocysta lagae Louwye, sp. nov., Barssidinium taxandrianum Louwye, sp. nov.andPalaeostomocystis globosa Louwye, sp. nov.  1999 Elsevier Science B.V. All rights reserved.

Keywords: dino¯agellate cysts; Upper Miocene; North Sea Basin; Belgium; stratigraphy

1. Introduction allowed interregional correlation with The Nether- lands (Breda Formation) and northern Germany (Sylt Recent palynological analysis of the Diest For- and Gram formations) and a relative dating of the se- mation has revealed the presence of moderately well quence (Louwye et al., in press). The present paper preserved dino¯agellate cyst associations (Louwye reports on previously undescribed dino¯agellate cyst and Laga, 1998). The occurrence of the formation is and acritarch species encountered from the Diest limited to northern Belgium: the Antwerp area, the Formation in four wells and one outcrop (Figs. 1 and Campine area and the area in between, the Antwerp 2). Campine (Fig. 1). The unit is largely decalci®ed, either by primary or by post-depositional decalci®- cation, and recovery of calcareous fossils is poor. As 2. Material a consequence, biostratigraphical data were scarce and the age assessment remained vague; only a Late 2.1. Stratigraphy Miocene age was proposed for the unit (see below). However, dino¯agellate cysts newly recovered from The Diest Formation was formally rede®ned by the Diest Formation in wells and outcrops have now De Meuter and Laga (1976) as a coarse-grained, glauconitic sandy unit, mainly decalci®ed, with occa- Ł Fax: C32-9-2644608; E-mail: [email protected] sional sandstone layers and clayey intercalations. The

6˚E Southern North Sea K Antwerpen The Netherlands Campine O R

Antwerpen G M

Campine 51˚N

Belgium

10 Km France

Fig. 1. Location of the wells (K D Kalmthout 6E110; O D Oostmalle 29E249; R D Retie 31W243; m D Mol 31W221; numbers refer to the archives of the Geological Survey of Belgium) and the outcrop at the PIDPA waterworks at Grobbendonk. Dashed line D southern limit of Neogene deposits in northern Belgium (modi®ed after Tavernier and De Heinzelin, 1963). coarse-grained sands are commonly referred to as the Formation and consists of ®ne-grained glauconitic `Diest Sands' in the literature. The sediments were de- sand. Laga and De Meuter (1972) described the posited along the extreme southern rim of the North planktonic and benthic foraminiferal assemblages of Sea Basin in a shallow marine environment (Vanden- this member. berghe et al., 1998). The complete invertebrate fauna, The Diest Formation rests unconformably on the mainly casts and internal moulds of molluscs, was Lower Miocene Berchem Formation and is covered studied by Glibert (1962) and, more recently, the or- unconformably by Lower Pliocene deposits: the Kat- ganic walled microplankton was studied by Louwye tendijk Formation in the western part of the study and Laga (1998) and Louwye et al. (in press). area and the Kasterlee Formation in the eastern part Two members, each with a restricted local distri- (Fig. 2). De Meuter and Laga (1976) have noted bution, are distinguished. The Deurne Sands Mem- a gradual transition of the Kattendijk Formation to ber (Glibert and De Heinzelin, 1955) occurs east the Kasterlee Formation. The lithostratigraphical in- of the city of Antwerp and is described as medium terpretation of the Upper Miocene sequence in the ®ne-grained glauconitic sand. From this member, studied wells is based on the archives of the Geo- planktonic foraminifers (De Meuter and Laga, 1970; logical Survey of Belgium and on own observations Hooyberghs and De Meuter, 1972), bryozoans (La- (Fig. 2). gaaij, 1952) and invertebrates (Glibert and De Heinzelin, 1955) were studied. This member is not 2.2. Age of the Diest Formation present in the studied wells and outcrop. The Dessel Sands Member (Laga and De Meuter, 1972) occurs The absence of calcareous microfossils and the in the Antwerp Campine area at the base of the Diest scarce presence of poorly preserved moulds and cast S. Louwye / Review of Palaeobotany and Palynology 107 (1999) 109±123 111

Altidtude (m) Altidtude deheinzelinii Batiacasphaera lagae Cerebrocysta Samples Depth m Depth Depth m Depth Lithostratigraphy Samples Lithostratigraphy globosa Palaeostomocystis Lithostratigraphy Samples Depth m Depth Lithostratigraphy Samples taxandrianum Barssidinium arborichiarum Bitectatodinium? Operculodinium antwerpenensis Operculodinium m Depth Lithostratigraphy Samples 30 30 80 30 5 40 40 40 90 4 50 50 50 100 3 60 60 60 110 PIDPA Outcrop 70 Grobbendonk 70 70 Kalmthout 80 6E110 80 80 90 90 90 Oostmalle 29E249 100 100 Kasterlee Formation 110 110 Kattendijk Formation 120 120 Diest Formation - Diest Sands 130 130 Diest Formation - Dessel Sands Member 140

Berchem Formation Retie 31W243 150 No core recovery Mol Sample 31W221

Fig. 2. Lithostratigraphy of the sequences, based on the archives of the Geological Survey of Belgium and own observations; position of the samples and distribution of the new species in the type localities. Depths refer to core top. Altitude (m) refers to TAW, the Belgian Ordnance Datum. of molluscs have long hindered an age assessment of Heinzelin, 1955) fauna had indicated a Late Miocene the decalci®ed coarse-grained sand of the Diest For- age also for the Deurne Sands. Hinsch (1988) places mation. Nothing more precise than a Late Miocene the molluscs from the Deurne Sands in mollusc Zone age for the Diest Sands could be advanced by Glibert BM21A of Late Miocene age. An evaluation of the (1962) based on a study of the invertebrates. The bry- benthic foraminiferal associations from the Deurne ozoan (Lagaaij, 1952) and molluscan (Glibert and De and Dessel sands members by Willems et al. (1988) 112 S. Louwye / Review of Palaeobotany and Palynology 107 (1999) 109±123 allows a correlation with Zone B9 (Late Miocene) Subclass PERIDINIPHYCIDAE Fensome et al., 1993 of the interregional biozonation for the Northwest Order GONYAULACALES Taylor, 1980 European Tertiary Basin (IGCP 124 Working Group, Suborder GONYAULACINEAE (Autonym) 1988). Hooyberghs and Moorkens (1988) correlate Family GONYAULACACEAE Lindemann, 1928 the planktonic foraminiferal associations from the Subfamily GONYAULACOIDEAE (Autonym) Deurne Sands Member, described by De Meuter and Laga (1970), with the NPF 15 Zone (Late Miocene) Genus Bitectatodinium Wilson, 1973 of Spiegler et al. (1988). This zone corresponds with the N16±17 Zone of Blow (1979). The scarce nanno- Bitectatodinium? arborichiarum Louwye, sp. nov. plankton data from the Diest Formation indicate an (Plate I, 1±8) age younger than Early Miocene for the Deurne 1994a cf. Habibacysta sp., Head, p. 210, pl. 6, ®gs. Sands (Verbeek et al., 1988) and a Late Miocene age 10±13. for the Diest and Deurne sands from the Antwerp ?1992 Filisphaera ®lifera Bujak, 1984 in RusbuÈlt area (Martini and MuÈller, 1973). The dinocyst asso- and Strauss, pl. 7, ®gs. 6±7. ciations have allowed the attribution of a Tortonian± Messinian age for the Diest and Dessel sands and Holotype: Slide Retie 125.5(3), England Finder ref- serve to highlight their strongly diachronous char- erence D51=1 (Plate I, 1±3). acter (Louwye and Laga, 1998; Louwye et al., in Repository: Collection of the `Institut Royal des press). During early Tortonian times the depocentre Sciences Naturelles' (Brussels), catalogue number was located in the Campine area and shifted to the IRScN b3655. area north of Antwerp during the late Tortonian± Type locality: Retie (Antwerp province, Belgium), Messinian. well no. 31W243 of the Geological Survey of Bel- gium, 125.5 m below core top. 2.3. Methods Type stratum: Diest Formation, Upper Miocene. Etymology: Named after the `Arborichae', occupants The position of the samples is given in Fig. 2. The of the Campine area during late Roman times. maceration of 50 g of sediment followed standard Diagnosis: Spherical, holocavate cyst with a solid techniques involving treatment with cold 20% HCl, endophragm densely covered with short, solid rods digestion for one or two days in HF (40% at 70ëC) which form a periphragm. The rods support a thin, followed by repeated hot baths (70±80ëC) of 20% hyaline and continuous ectophragm. A small apical HCl. The samples were rinsed to neutrality between protuberance formed by the endophragm is mostly each step. Finally, oxidation for 30 seconds in 90% present. Archeopyle type 2P, probably plates 200 and 00 HNO3 was applied, followed by repeated washing in 3 . The operculum is mostly free, occasionally ad- 10% KOH. No heavy liquid separation or ultrasonic herent, with separated opercular plates. treatment was applied. The residues were sieved on Description: The endophragm has a thickness of less a nylon screen with 20 µm mesh size, stained with than 0.4 µm. The length of the rods is uniform on methyl green, and mounted using glycerine jelly. an individual and the distribution is nontabular. The Photographs were taken with interference contrast average distance between adjacent rods varies from on NIKON Optiphot and ZEISS Axioplan-2 light ca.0.5to1.5µm. The rods are mostly simple, but microscopes and a JEOL 6400 SEM. proximal or distal bifurcation occurs occasionally. The thickness of the simple rods is ca. 0.25 µm and even over the greater part of the length. The 3. Taxonomy rods are proximally and distally slightly expanded. The smooth ectophragm is very thin and in trans- Division DINOFLAGELLATA (BuÈtschli, 1885) mitted light best visible at the margins of the cyst. Fensome et al., 1993 The archeopyle has well de®ned angles and is the Subdivision DINOKARYOTA Fensome et al., 1993 only expression of tabulation. Accessory archeopyle Class DINOPHYCEAE Pascher, 1914 sutures were observed on a few specimens. S. Louwye / Review of Palaeobotany and Palynology 107 (1999) 109±123 113

PLATE I

Bitectatodinium? arborichiarum Louwye, sp. nov. 1±3. Holotype, slide Retie 125.5(3), E.F. reference D51=1. 4, 5. Slightly differing foci on opercular plate. 1. High focus on archeopyle. ð1000. 6. Optical section, ambitus and wall ornamentation. 2. Optical section, wall and ambitus. ð800. 7, 8. Stub Retie 125.5(3). Scale bar 10 µm. 3. Low focus, wall structure and apical protrusion. ð1000. 7. Left dorsal view, overview and archeopyle. 4±6. Slide Retie 125.5(3), E.F. reference E54=3. ð1000. 8. Archeopyle margin and wall structure. 114 S. Louwye / Review of Palaeobotany and Palynology 107 (1999) 109±123

PLATE II S. Louwye / Review of Palaeobotany and Palynology 107 (1999) 109±123 115

Dimensions: Holotype: diameter cyst body, 40 µm; Occurrence: Upper Miocene (Diest Formation) of length of rods, 2 µm; height of apical boss, 1± northern Belgium (this study); Middle Miocene of 1.5 µm. Range: diameter cyst body, 33(39)49 µm; the Netherlands as cf. Habibacysta sp. in Head length of rods, 2(2.5)3 µm. Number of specimens (1994a). measured: 16. Comparison: Habibacysta tectata Head et al., 1989b Subfamily CRIBROPERIDINIOIDEAE Fensome et al., is most similar but differs by the distinctive precin- 1993 gular archeopyle formed by the loss of only plate 300, the discontinuous ectophragm and the smaller wall Genus Operculodinium Wall, 1967 thickness. `Headinium miocenicum' Zevenboom and Operculodinium antwerpensis Louwye, sp. nov. Santarelli (ms name) in Zevenboom, 1995 (Middle (Plate II, 1±9) to Upper Miocene, The Netherlands) appears to dif- fer by the 3P archeopyle, the larger size [39 (54) 60 1998 `Operculodinium pontis'? Zevenboom and µm] and hollow, higher [5 (6) 7 µm] rods. Bitecta- Santarelli (ms name) in Zevenboom, 1995, todinium raedwaldii Head, 1997 is characterised by Louwye and Laga, table 1. an ornamentation of distally fused pili with variable Holotype: Slide Kalmthout 82(1), England Finder length. At a ®rst glance, Filisphaera ®lifera auct. non reference J49=3 (Plate II, 1±6). Bujak, 1984 in RusbuÈlt and Strauss (1992) (Mid- Repository: Collection of the `Institut Royal des dle Miocene, Mecklenburg, Germany) resembles B.? Sciences Naturelles' (Brussels), catalogue number arborichiarum and may be conspeci®c. IRScN b3656. Remarks: The new species possesses characteris- Type locality: Kalmthout (Antwerp province, Bel- tics of the genus Bitectatodinium Wilson, 1973 but gium), well no. 6E110 of the Geological Survey of differs in its wall structure, hence the questioned as- Belgium, 82 m below core top. signment to this genus. The wall of Bitectatodinium Type stratum: Diest Formation, Upper Miocene. is characterised by a dense inner layer and a tectate Etymology: Named for the Antwerp province, Bel- spongy outer layer, according to Wilson, 1973. Head gium, in which the type locality Kalmthout is lo- (1994b) describes the wall structure of this genus as cated. having a luxuria comprising lamellar elements aris- Diagnosis: Small, proximochorate cyst with an el- ing from raised bases and subcircular in plan view. liptical to spherical ambitus. The endophragm is ornamented with granules or small, solid rods sup- porting a thin smooth and continuous periphragm. The periphragm forms short and solid, tapering pro- PLATE II cesses, distally blunt to minutely platformed and 1±9. Operculodinium antwerpensis Louwye, sp. nov. with hollow expanded bases. The processes are iso- = 1±6. Holotype, slide Kalmthout 82(1), E.F. reference J49 3. lated or proximally to medially joined. The distribu- 1±4. Slightly differing high foci on archeopyle margin and wall. ð800. tion of the processes is non-tabular. Large precingu- 00 5. Optical section, ambitus and processes. ð800. lar archeopyle, type P(3 ) with free operculum. 6. Slightly lower optical section, ambitus and processes. Description: The thickness of the cyst wall varies be- ð1000. tween 0.8 and 2.5 µm and consists of an endophragm = 7±9. Slide Kalmthout 82(1), E.F. reference M47 1. and hyaline periphragm. Both have a thickness of 7. High focus, wall and ambitus. ð1000. µ 8. Optical section, ambitus. ð800. less than 0.3 m and are separated by granules or 9. Low focus on wall structure. ð1000. solid rods. The length of the processes on a cyst 10±13. Batiacasphaera deheinzelinii Louwye, sp. nov. is usually uniform. The simple processes can prox- 10±12. Holotype, slide Retie 30.3(1), E.F. reference S46=2. imally be 2 to 5 times wider than distally which 10, 11. Slightly differing high foci on archeopyle and ornamen- gives the simple process the appearance of a steep, tation. ð850. 12. Optical section, ambitus and ornamentation. ð600. truncated pyramid. No alignment of the processes 13. Slide Retie 30.3(1), E.F. reference G49=1. was observed, the archeopyle is the only re¯ection of 13. High focus on archeopyle. ð700. a tabulation. 116 S. Louwye / Review of Palaeobotany and Palynology 107 (1999) 109±123

Dimensions: Holotype: length of central body, 36 body, 32(36)42 µm; width (equatorial) of central µm; width (equatorial) of central body, 34 µm; body, 29(34)39 µm; length of processes 2(5)8 µm. length of processes 5±7 µm. Range: length of central Number of specimens measured: 12.

PLATE III S. Louwye / Review of Palaeobotany and Palynology 107 (1999) 109±123 117

Comparison: The periphragm of Operculodinium te- Type locality: Retie (Antwerp province, Belgium), gillatum Head, 1997 is clearly reticulate to perforate, well no. 31W243 of the Geological Survey of Bel- while the periphragm of the new species is con- gium, 80.5 m below core top. tinuous. Furthermore, proximally to medially joined Type stratum: Diest Formation, Upper Miocene. processes are observed on every specimen of Op- Etymology: Named in honour of Jean de Heinzelin erculodinium antwerpensis, a feature apparently not for his stratigraphical studies of the Neogene from shared with Operculodinium tegillatum Head, 1997. northern Belgium. Operculodinium antwerpenis differs from all other Diagnosis: Small, autophragmal cyst with a spher- Operculodinium species by the architecture of the ical central body. The thin autophragm is densely bilayered wall and the presence of granules or small, covered with short, solid and acuminate hairs. solid rods between the wall layers. Archeopyle apical (type tA), principal archeopyle Occurrence: Upper Miocene (Diest Formation) of suture with low angularity, operculum free. northern Belgium (this study); Upper Miocene (Diest Description: The hyaline cyst wall has a thickness Formation) and Pliocene (Kattendijk and Lillo for- of less than 0.3 µm. The distribution of the solid mations) of northern Belgium as `Operculodinium hairs is nontabular and appears evenly spaced. The pontis'? Zevenboom and Santarelli (ms name) in average distance between the hairs is 1 µm. The Zevenboom (1995) and Louwye and Laga (1998). bases of the hairlike processes are slightly widened. No morphological variation of the simple, acuminate Suborder UNCERTAIN processes was noted. The archeopyle is generally Family UNCERTAIN the only indication of tabulation, although minute accessory archeopyle sutures between precingular Genus Batiacasphaera Drugg, 1970 plates have been observed on a few specimens. Dimensions: Holotype: diameter central body, 27 Batiacasphaera deheinzelinii Louwye, sp. nov. µm; length of hairs, up to 3.5 µm. Range: diameter (Plate II, 10±13; Plate III, 1±7) central body, 23(27)30 µm; length of hairs, 2±4.5 Holotype: Slide Retie 30.3(1), England Finder refer- µm. Number of specimens measured: 19. ence S46=2 (Plate II, 10±12). Comparison: This species differs from Batiacas- Repository: Collection of the `Institut Royal des phaera hirsuta Stover, 1977 in its much smaller size Sciences Naturelles' (Brussels), catalogue number (23±30 µm vs. 41±49 µm) and the less angular IRScN b3657. archeopyle, although the general appearance of the cyst and the distribution of the processes are much alike. Batiacasphaera? sp. 1 Head et al., 1989a from the Middle Miocene of Baf®n Bay could be conspe- PLATE III ci®c when considering the general appearance, size 1±7. Batiacasphaera deheinzelinii Louwye, sp. nov. and ornamentation. However, the archeopyle type of 1, 2. Stub Retie 30.3(4). 1. Detail of processes and wall. Scale bar 1 µm. Batiacasphaera? sp. 1 Head et al., 1989a is uncer- 2. Overview and process distribution. Scale bar 10 µm. tain. Batiacasphaera? sp. 1 Head et al., 1989a has 3, 4. Slide Retie 30.3(1), E.F. reference G58=3. ð1100. also been recorded from the mid-Pliocene of eastern 3. Optical section, ambitus and processes. England (as Batiacasphaera? sp. in Head, 1997). 4. Low focus on archeopyle margin. Occurrence: Upper Miocene (Diest Formation) of 5±7. Slide Mol 80.2(2), E.F. reference C48=1. ð700. 5. Optical section, ambitus and processes. northern Belgium (this study). 6, 7. Slightly differing low foci on archeopyle margin and wall. Genus Cerebrocysta Bujak, 1980 8±11. Cerebrocysta lagae Louwye, sp. nov. 8±11. Holotype, slide Mol 60.5(2), E.F. reference U52=4. Cerebrocysta lagae Louwye, sp. nov. (Plate III, 8± 8. High focus on ornamentation. ð2000. 11) 9, 10. Slightly differing high foci on archeopyle margin and ornamentation. ð700. Holotype: Slide Mol 60.5(2), England Finder refer- 11. Optical section, ambitus and ornamentation. ð700. ence U52=4 (Plate III, 8±11). 118 S. Louwye / Review of Palaeobotany and Palynology 107 (1999) 109±123

PLATE IV S. Louwye / Review of Palaeobotany and Palynology 107 (1999) 109±123 119

Repository: Collection of the `Institut Royal des cysta bartonensis Bujak, 1980 except for its larger Sciences Naturelles' (Brussels), catalogue number size. Cerebrocysta poulsenii De Verteuil and Norris, IRScN b3658. 1996 differs in having a less dense distribution of Type locality: Mol (Antwerp province, Belgium), larger septa. Cerebrocysta? namocensis Head et al., well no. 31W221 of the Geological Survey of Bel- 1989b is characterised by a network of low sinu- gium, 60.5 m below core top. ous ridges forming an irregular ®ne reticular pattern. Type stratum: Diest Formation, Upper Miocene. Cerebrocysta mediterranea Bif® and Manum, 1988 Etymology: Named in tribute to Pieter Laga for his differs by the larger size (60±80 µm) and the pres- contribution to the biostratigraphy and lithostratigra- ence of a well de®ned reticulum. phy of the Belgian Neogene. Occurrence: Upper Miocene (Diest Formation) of Diagnosis: Small, spherical proximate cyst with a northern Belgium (this study). smooth, thin autophragm ornamented with low, solid lamellae. In plan view, the lamellae are short and Order PERIDINIALES Haeckel, 1894 isolated or may connect for a short distance forming Suborder PERIDINIINEAE (Autonym) a fence-like pattern. Archeopyle type 1P, operculum Family CONGRUENTIDIACEAE Schiller, 1935 free. Subfamily CONGRUENTIDIOIDEAE (Autonym) Description: The autophragm is relatively thin (less than 0.5 µm) and smooth. A discrete scabrate au- Genus Barssidinium Lentin et al., 1994 tophragm was observed on a few specimens only. Barssidinium taxandrianum Louwye, sp. nov. The height and width (0.5 to 0.8 µm) of the lamel- (Plate IV, 1±6; Plate V, 1±2) lae on an individual are constant. Their base is not enlarged and they arise perpendicular to the cyst Holotype: Slide Grob. 1(1), England Finder refer- wall on well preserved specimens. The distribution ence L56=3 (Plate IV,4±6). of the lamellae appears regular with no indication of Repository: Collection of the `Institut Royal des a sulcus or a cingulum. The precingular archeopyle Sciences Naturelles' (Brussels), catalogue number is relatively large compared to the cyst diameter, the IRScN b3659. margins even or uneven and the angles well de®ned. Type locality: Outcrop at the PIDPA waterworks, The archeopyle is the only indication of a tabulation. altitude 5.15 m TAW, Grobbendonk, Antwerp Dimensions: Holotype: central body diameter, 26 province, Belgium. µm; height of lamellae, 2.5 µm. Range: central body Type stratum: Diest Formation, Upper Miocene. diameter, 24(25.5)27 µm; height of lamellae, 1.5 to Etymology: `Taxandria', name of the mythical king- 3 µm. Number of specimens measured: 6. dom in the Campine area. Comparison: Cerebrocysta bartonensis Bujak, 1980 Diagnosis: A dorsoventrally compressed, proximo- differs in having a much denser and more regu- chorate species with subcircular to rounded subquad- lar distribution of low crests and by the occasional rangular ambitus and hollow, acuminate and distally re¯ection of tabulation in the crest distribution. Cere- closed processes. Processes have internal annular brocysta magna Bujak, 1994 is identical to Cerebro- thickenings or septa. The distribution of the processes is nontabular and appears denser at the margin of the cyst. The tabulation is expressed only by a large, intercalary 2a archeopyle (hexa isodeltaform). PLATE IV Operculum free or adherent. Barssidinium taxandrianum Louwye, sp. nov. Description: The pigmented cyst wall is apparently 1±3. Slide Grob 1(2), E.F. reference Z36=4. made up of a laevigate autophragm only. The wall 1, 2. Slightly differing optical sections, ambitus and processes. often has an irregular, grooved appearance. A dis- ð750. crete scabrate or minutely granular ornamentation 3. high focus on wall and archeopyle margin. ð600. 4±6. Holotype, slide Grob 1(1), EF.F. reference L56=3. ð750. was observed on a few specimens. The thin pro- 4, 5. Slightly differing high foci, wall structure and processes. cesses are slightly widened at their base and they 6. Optical section, ambitus and processes. narrow rapidly at mid-length. The processes are 120 S. Louwye / Review of Palaeobotany and Palynology 107 (1999) 109±123 usually simple although a few processes on each Dimensions: Holotype: length, 70 µm; width, 70 µm; specimen bifurcate at mid length. A re-entrant an- length of processes, 5±8 µm. Range: central body gle on the opercular plate was observed on a few length 64(72)85 µm; central body width. 54(63)74 specimens. µm; minimum length of processes, 5(7)9 µm;

PLATE V S. Louwye / Review of Palaeobotany and Palynology 107 (1999) 109±123 121 maximum length of processes, 7(8)13 µm. Number the pylome. The operculum is always free and often of specimens measured: 11. collapsed into the cyst body. Comparison: This species differs from all other Description: The wall of the spherical cyst is thin Barssidinium species by its hollow, acuminate and (less than 0.8 µm). The two rims surrounding the py- distally closed processes. lome are mostly fully developed and are considered Occurrence: Upper Miocene (Diest Formation) of to be a characteristic feature. The distance between northern Belgium (this study). the rims varies from 1.5 to 4 µm. The ratio of diameter pylome=cyst body varies between 0.4 and Group ACRITARCHA 0.9. Dimensions: Holotype: diameter, 40 µm; diameter Genus Palaeostomocystis De¯andre, 1937 pylome, 24 µm. Range: diameter, 30 (36) 42 µm; diameter pylome, 12 (25) 38 µm. Number of speci- Palaeostomocystis globosa Louwye sp. nov.(PlateV, mens measured: 15. 3±7) Comparison: This species differs from all other 1998 Cyst D, Louwye and Laga, table 1. Palaeostomocystis species by the generally, large circular pylome encircled by two parallel rims. Holotype: Slide Oostmalle 88.8(1), England Finder Occurrence: Upper Miocene (Diest Formation) of reference W43=3 (Plate V,3±6). northern Belgium (this study); Upper Miocene of Repository: Collection of the `Institut Royal des northern Belgium as Cyst D in Louwye and Laga Sciences Naturelles' (Brussels), catalogue number (1998). IRScN b3660. Type locality: Oostmalle (Antwerp province, Bel- gium), well no. 29E249 of the Geological Society of Acknowledgements Belgium, 88.8 m below core top. Type stratum: Diest Formation, Upper Miocene. I am indebted to P. Laga (Geological Survey Etymology: Latin, globosus, spherical. of Belgium) for kindly providing the samples and Diagnosis: Medium-sized cyst with a spherical shape well data. Critical remarks and comments by M. and a smooth to scabrate central body. The central J. Head (University of Toronto) on some species body on well preserved specimens is loosely sur- are greatly acknowledged. This research was carried rounded by a ¯occulent covering. The thickness of out in the framework of research project 01105098 this ¯occulent covering varies, but is fairly constant (promoters: J. De Coninck and J. Verniers) of the on an individual (0.5 to 2 µm). A circular pylome is University of Gent. The linguistic remarks by M. always developed. Two low, parallel rims, which are Winsall (London, UK) are much appreciated and the only ornamentation of the cyst body, surround improved the manuscript considerably.

References PLATE V 1, 2. Barssidinium taxandrianum Louwye, sp. nov. Bif®, U., Manum, S.B., 1988. Late Eocene±Early Miocene di- 1, 2. Stub Grob 1(5). Scale bar 10 µm. no¯agellate cyst stratigraphy from the Marche region (Central 1. Ventral view, ambitus and process distribution. Italy). Boll. Soc. Paleontol. Ital. 27 (2), 163±212. 2. Focus on wall and processes. Blow, W.H., 1979. The Cainozoic Globigerinidae: A Study of 3±7. Palaeostomocystis globosa Louwye, sp. nov. the Morphology, Taxonomy, Evolutionary Relationships and 3±6. Holotype, slide Oostmallle 88.8(1), E.F. reference W43=3. the Stratigraphical Distribution of some Globigerinidae I±III. 3. High focus on wall. ð950. Brill, Leiden. 4. Optical section, rims surrounding pylome. ð950. Bujak, J.P., 1980. Dino¯agellate cysts and acritarchs from the 5. Low focus on pylome and parallel rims. ð630. Eocene Barton Beds. In: Bujak, J.P., Downie, C., Eaton, G.L., 6. Slightly higher focus on parallel rims. ð950. Williams, G.L. (Eds.), Dino¯agellate cysts from the Eocene of 7. Stub Mol 110(1). Scale bar 10 µm. southern England. Paleontol. Assoc. Spec. Pap. Palaeontol. 24, 7. Axial view, pylome and ¯occulent covering. 36±91. 122 S. Louwye / Review of Palaeobotany and Palynology 107 (1999) 109±123

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