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A Jurassic (Pliensbachian) flora from Bornholm, Denmark – a study
of a historic plant-fossil collection at Lund University, Sweden
KRISTINA MEHLQVIST
1
, VIVI VAJDA
1
and LINDA M. LARSSON
1
Mehlqvist, K., Vajda, V. & Larsson, L., 2009: A Jurassic (Pliensbachian) flora from Bornholm, Denmark – a study of a
historic plant-fossil collection at Lund University, Sweden. GFF, Vol. 131 (Pt. 1–2, June), pp. 137–146. Stockholm.
ISSN 1103-5897.
Abstract: A historic collection of plant fossils from the Baga
˚
Formation, Bornholm, Denmark registered
at the Lund University is reviewed and found to be dominated by ferns with subsidiary Ginkgoales,
Coniferales, Bennettitales and Equisitales. Ten genera are represented, of which six can be confidently
identified to species level. The Baga
˚
Formation flora is most similar in age to the flora of the Middle
Jurassic Mariedals Formation of Eriksdal, Ska
˚
ne, although there are important compositional differences
between these assemblages. The Baga
˚
flora is characteristic of the temperate (warm and humid) biome of
the Early–mid Jurassic. A historical investigation reveals that at least four scientists contributed material
to the collections. A palynological investigation made on samples from the leaf fossils reveals that the
macroflora was most probably collected from the Sorthat beds as the palynoflora corresponds to the
Pliensbachian Chasmatosporites Zone.
Keywords: Baga
˚
Formation, Bornholm, Jurassic, flora, climate, vegetation.
1
GeoBiosphere Science Centre, Lund University, So
¨
lvegatan 12, SE 223 62 Lund, Sweden.
vivi.vajda@geol.lu.se
Manuscript received 2 November 2008. Revised manuscript accepted 10 March 2009.
Introduction
Plant fossils have long been reported from exposures from the
Baga
˚
Formation along the western side of the Danish island of
Bornholm (Fig. 1). Plant fossils were particularly abundant in
the old clay pit at the Hasle tile factory until closure of the
operation and inundation of the pit. Many well-preserved plant
fossils were recovered from this site in the early 20
th
century and
a small collection (ca. 50 specimens) of these is available at the
Department of Geology. Lund University, Sweden. Some of the
plant fossils in the Lund collection were collected and described
by Mo
¨
ller (1902, 1903) but at least four other geologists have
contributed to the collection since 1881. Other studies of the
Baga
˚
Formation macroflora have been carried out by Bartholin
(1892– 1894), Hjort (1899), Florin (1958) and McElwain et al.
(2005).
The Baga
˚
macroflora has not been studied in detail for the
past 100 years and the collection held at the Lund University
has never been described. This study aims to document the
floristic composition of the collection, compare the flora to
coeval plant associations, assess the depositional environment
and palaeocli matic setting of the assemblages and outline the
historical context of the collectors. Since there are no records
indicating the precise position of the beds from which the plant
fossils were sourced, we further aim to date the macroflora by
palynostratigraphic analysis of sam ples taken from the same
blocks.
Geological setting
Bornholm constitutes a complex fault-bounded horst in the
Sorgenfrei–Tornquist Zone between the Danish Basin and the
Polish Trough (Koppelhus & Nielsen 1994). Crystalline
Precambrian rocks are exposed in the northeastern part
of Bornholm but in the southwestern and western part of the
island, Palaeozoic and Mesozoic sedimentary successions are
preserved overlying crystalline basement in a complex series of
downfaulted blocks (Gry & Flemming 1977; Gravesen et al.
1982). On the west coast two fault zones converge at the Rønne
Graben, which together with several smaller structural blocks on
the island probably experienced initial movement during the late
Carboniferous–early Perm ian (Koppelhus & Nielsen 1994).
Sedimentation continued episodically in the Røn ne Graben
through most of the Mesozoic.
Lower to Middle Jurassic sediments on Bornholm are bound
by unconformities. The Jurassic strata rest on either lower
Palaeozoic or Upper Triassic sediments, and they are in turn
overlain by unconsolidated Quaternary sediments (Koppelhus &
Nielsen 1994). During the early Hettangian, deepening of the
basin occurred leading to the formation of lacustrine
environments and deposition of carbonaceous clays. In these
sediments (Munkerup Member of the Rønne Formation), plant
fossils belonging to the Thaumatopteris flora are abundantly
preserved (Vajda & Wigforss-Lange 2009, this volume). In the
late Hettangian, lower delta plain/coastal plain environments
were represented in the area and carbonates, sand, sandy clay
and clay were deposited (Sose Bugt Member). A transgression
during the Sinemurian saw deposition of sands and clays in
tidally-influenced channels and coastal plains (Galgeløkke
Member). A further marine transgression in the early
Pliensbachian resulted in deposition of the 80 –140 m thick,
sandy and silty Hasle Formation in shelf and shoreface
environments (Koppelhus & Nielsen 1994) followed by a
regression in the late Pliensbachian which saw deposition of the
coal-bearing Baga
˚
Formation (Petersen 1993).
GFF
volume 131 (2009), pp. 137–146. Article
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Baga
˚
Formation
The Pliensbachian–lower Bathonian Sorthat and Baga
˚
for-
mations were originally both part of the Baga
˚
Formation as
defined by Gravesen et al. (1982), includi ng the Levka, Sorthat
and Baga
˚
beds. However, Michelsen et al. (2003) subdivided the
Baga
˚
Formation into the Sorthat Formation (Levka and Sorthat
beds) that had previously been called “Baga
˚
Fm lower”
(Koppelhus & Nielsen 1994), and the overlying Baga
˚
Formation
(Baga
˚
beds) that had previous been called “Baga
˚
Fm upper”.
The plant fossils studied herein were all collected before the
differentiation of the Sorthat and Baga
˚
formations and there is
no information accompanying the mater ial to be certain from
which part of the succession they derive. We therefore employ
the old stratigraphical terminology (Fig. 2).
The Sorthat beds have been estimated to be coeval with
the Levka beds since both ov erlie the Hasle Formation
(Koppelhus & Nielsen 1994). The Sorthat beds have been
estimated to reach a thickness of 200 m (Gry 1969) and these
beds have been exposed in the southernmost part of the clay pit
of the Hasle tile factory until relatively recently. A thorough
lithological and palynological study was presented by
Koppelhus & Nielsen (1994). The lithology of the Sorthat
beds consists of carbonaceous sandstones with coal beds and
rootlets deposited on a delta plain (Gravesen et al. 1982).
The Baga
˚
beds consist mainly of a series of relatively uniform
successions of grey lacustrine clay packages, up to 190 m thick,
capped by coaly clays and coals with rootlets, interbedded with
sands. The clays are typically white, yellowish or red-brown and
contain abundant well -preserved plant compressions. Plant
impressions are also abundant in some yellowish or reddish iron-
rich claystones (Mo
¨
ller 1902). The depositional environment has
been interpreted as a meandering river system within an overall
deltaic setting. Extensive peat-forming mires and lakes
developed on the floodplains adjacent to the sandy and gravely
channels (Koppelhus & Nielsen 1994). The best exposures of the
Baga
˚
beds were formerly in the clay pit of the Hasle tile factory
(Fig. 2) but this type section became inaccessible in the late
1990s after closure of the tile works and flooding of the clay pit.
However, small exposures are still present around the margin of
the pit, from which plant remains can be recovered. Exposures
are also accessible at the coastal section at Korsodde (Fig. 2),
which based on detailed palynological investigations have been
subdivided into six palynological zones encompassing late
Pliensbachian –early Bathonian (Koppelhus & Nielsen 1994).
Material and methods
Macroflora
A collection of ca. 50 specimens of plant fossils (referred to as
the Lund collection in this text) from the Baga
˚
Formation on
Bornholm was described and illustrated using standard
macrophotographic techniques with low-angle illumination
from the upper left. Cuticular analysis of the fossil leaves was
not attempted since the preserved organic matter is generally
thin and strongly degraded. Assessment of the palaeoclimate
was based broadly on the taxonomic composition of the
assemblage. To this end, the assemblage was compared with the
fossil collection from the same formations held at the Swedish
Museum of Natural History in Stockholm to evaluate any
collection bias.
The plant fossils were classified according to the scheme of
Meyen (1987) and emendments according to Smith et al. (2006).
Where the whole leaves have been preserved, the length and
width were measured and the length/width relationship
calculated. The whole length of the shoot is only given when
the whole shoot has been preserved.
Palynology
Palynological samples were prepared from the sediment
samples derived from four blocks that host macrofossil
specimens; the macrofossils were not damaged during sampling.
Fig. 1. Locality map of Bornholm with the distribution of Triassic–
Jurassic sediments indicated in green. Arrow indicates Baga
˚
quarry
locality. The main plant-bearing outcrops are indicated by circles at
Baga
˚
and Korsodde.
Fig. 2. Jurassic lithostratigraphic scheme for Bornholm and SE Ska
˚
ne.
138 Mehlqvist et al.: A Jurassic (Pliensbachian) flora from Bornholm GFF 131 (2009)
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The palynological samples were collecte d from the blocks
hosting the following leaf fossils: Eboracia lobifolia, Cladoph-
lebis nebbensis and Ginkgoites troedssonii. The samples were
processed at Global Geolab Ltd., Alberta, Canada, according to
the standard palynological procedures, first treated with dilute
hydrochloric acid to remove calcium carbonate, then macerated
by leaving the sample in hydrofluoric acid of a concentration of
75% overnight. The organic residue was collected on a 20 mm
mesh sieve and mounted in epoxy on strew slides. Three hundred
palynomorphs from each slide were counted. Palynological
slides and macerated residues are deposited at the GeoBiosphere
Science centre, Lund University, Sweden and illustrated pollen
and spores are registered by LO-numbers.
History
The Lund collection was gathere d between 1881 and 1946, from
Hasle Clay pit, Korsodde and Nebbeodde. The contributors were
all well known personalities linked to the Lund University and a
short summary of their geological achievements is outlined
below.
Hjalmar Mo
¨
ller (1866–1941) was a Swedish botanist and
geologist. His primary background was in botany and he
obtained his doctoral degree at the Lund University in 1903. In
his early career, he made research trips not only within the
nordic countries but also to remote places such as Java and
Burma, collecting exotic plants (Regne
´
ll 1992). However, he
also had a strong interest in geology and combined his dual
interests when in 1901–1903 he worked as a amanuensis at the
Swedish Museum of Natural History, Stockholm, with fossil
plants (Regne
´
ll 1992). It was during this time that Mo
¨
ller
collected fossil-plant material from the Jurassic Baga
˚
Formation
that was subsequently stored both at the Swedish Museum of
Natural History and at the Geological Department of Lund
University. He published two volumes based on that material:
Contribution to the fossil flora of Bornholm (in Swedish): 1.
Pteridophytes (1902), 2. Gymnosperms (1903). Mo
¨
ller also
studied the Jurassic floras in Fyledalen, Ska
˚
ne, resulting in a
publication in collaboration with Thore Gustaf Halle
1884–1964 (Mo
¨
ller & Halle 1913). In the following years he
worked as lecturer at several colleges of higher learning but from
1917 he obtained a full-time research position at the Swedish
Museum of Natural History. He contributed to the Lund
collection in 1901–1902.
Bernhard Lundgren (1843 –1897) was a Swedish palaeontol-
ogist born in Malmo
¨
, Ska
˚
ne. Lundgren began his geological
carrier as a student at the Lund University in 1860. In 1865 he
finished a thesis on the Maastrichtian –Danian chalk exposed in
the Limhamn quarry, near Malmo
¨
(Regne
´
ll 1992). He later
continued describing the fauna in these limestones but also the
fauna from the Campanian limestones in the northwestern part
of Ska
˚
ne, resulting in several publications. In 1880 he became a
professor of geology at the Lund University. He collected the
plant fossils of the Lund collection in 1876.
A.F. Carlson was a collaborator to Alfred Nathorst. Carlson
was a keen collector employed at one of the coal mines in Ska
˚
ne
and over 35 years he provided Nathorst with plant fossils
(Halle 1921). The fossil floras of Baga
˚
were collected by Carlsson
in 1881 and 1883. Nathorst named the Dipteridacean fern,
Dictyophyllum carlsonii Nathorst 1878b in honour of Carlson.
Seth Nilsson –Stenestro
¨
m was a geologist, active at the Lund
University. He wrote his thesis in 1940 on the Ordovician
sediments from the Fa
˚
gelsa
˚
ng valley in Ska
˚
ne. He was an active
member of the Lund Geological Fieldclub and became its
secretary in 1946 (Regne
´
ll 1992). The circumstances of his
collection of the Bornholm material remain unknown but the
material was collected in 1946, a time when the Soviet military
still maintained post-war control over the island of Bornholm.
Results
Ten plant genera were identified in the studied material, of
which six were determined to species level. Ferns dominate the
collection and are mostly represented by specimens attributable
to Eboracia. Only one genus of conifers is present. Other orders
represented are Ginkgoales, Bennettitales and Equisetales. Some
of the plant fossils from the Lund collection could not be
identified due to poor preservation.
Systematic Palaeobotany
Sphenophytes
Order Equisetales
Family Incertae Sedis
Genus Neocalamites Halle, 1908
Type species.– Neocalmites hoerensis Halle, 1908; Lower
Jurassic; Ska
˚
ne; Sweden.
Neocalmites sp.
Fig. 3A
Material. – Three incomplete axes.
Description. – The three incomplete axes are compressions in a
white claystone. The axes are ca. 80 mm long and 10 mm wide at
the nodes. The segments between the nodes are 20 mm long.
Ribs run longitudinally along the stems with an average of 12
ribs across the full width of the stem, each rib is 0.8 mm wide.
No leaves are preserved.
Remarks. – Segmented equisetalean axes from the Jurassic may
have borne foliage of various types (e.g. Schizoneura,
Equisetum, Phyllotheca) but in the absence of leaves such
axes are traditionally assigned to the morphotaxon Neocalmites.
Mo
¨
ller (1902) classified several equisetalean stems as Equisetum
sp. but like the presently studied material, they lack leaves or
reproductive structures, so definitive attribution to the
extant genus is not possible. Neocalamites has a long
(Mesozoic– Cenozoic) stratigraphic distribution hence its
biostratigraphic utility is limited. However, it may be a useful
palaeoenvironmental index. Based on analogies with
morphologically similar extant Equisetum species, it is
interpreted to represent a plant of consistently moist habitats
(e.g. marsh, lake margin or forest understorey) that typically
occurred in dense thickets.
Ferns
Order Osmundales
Family Osmundaceae (Martinov, 1820)
Genus Cladophlebis Seward, 1894.
Type species.–Cladophle bis alberts ii (Dunker) Brongniart
(1849); early Cretaceous, northern Germany.
GFF 131 (2009) Mehlqvist et al.: A Jurassic (Pliensbachian) flora from Bornholm 139
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C. nebbensis (Brongniart) Nathorst, 1876
Figs. 3H, I
Material. – Eight specimens.
Description. – Isolated pinnae are preserved as compressions
and impressions. Most specimens have lost their organic
material. The pinnules are oblong with entire or slightly dentate
margins and are attached by their full base. The pinnules are
arranged oppositely across the rachilla and are inserted at
45–608. The rachilla is 1 mm wide. Each pinnule has a
prominent and persistent midvein. The lateral veins are once-
forked. Pinnules are 11 (14) 17 mm long (10 specimens), 3 (4.5)
5 mm wide (10 specimens), with a L/W ratio of 3.17.
Remarks. – According to Mo
¨
ller (1902), Cladophlebis is one of
the most common ferns in the Baga
˚
Formation and he
identified several different species within this genus.
Cladophlebis is a very widespread and long-ranging genus in
the Mesozoic. Individual species potentially have some
biostratigraphic value but their use is hampered by
difficulties in consistently differentiating the many established
species. Of the species commonly reported from the Triassic–
Jurassic of southern Sweden, the Bornholm specimens appear
to match the features of C. nebbensis (Brongniart) Nathorst,
1876, especially in their rather large pinnules. Cladophlebis
svedbergii Johansson, 1922 from the Triassic– Jurassic of
Ska
˚
ne is also similar in the pinnule form and may be
synonymous with C. nebbensis.
Order Cyatheales
Family Dicksoniaceae (Schomburgk, 1848)
Genus Eboracia Thomas, 1911
Type species.–E. lobifolia (Phillips) Thomas, 1911; Jurassic;
Yorkshire, England.
E. lobifolia (Phillips) Thomas, 1911
Fig. 3B
Holotype. – See Thomas (1911, p. 388, figure on p. 387).
Material. – Twenty-eight specimens in the Lund collec tion.
Diagnosis. – See Thomas (1911).
Description. – The specimens are represented by isolated pinna
impressions ca. 40 mm long. The pinnules are attached by their
full base and are oppositely to subo ppositely arranged.
A prominent midvein can be distinguished on most specimens.
The pinnule margin is entire with a broadly rounded apex.
The pinnules are attached to the rachilla at angles of ca. 458.
Pinnules are 10 (11) 13 mm long (10 specimens), 4 (4.5) 5 mm
wide (10 specimens), with a L/W ratio of 2.41.
Remarks. – The specimens in the Lund collection are conspecific
with several specimens held at the Swedish Museum of Natural
History, which Mo
¨
ller (1902) assigned to Dicksonia lobifolia.
This species has a chequered taxonomic history having been
assigned to several genera by various workers. It is here assigned
to Eboracia based on its gross morphological similarities to
fertile fronds described from the middle Jurassic of Yorkshire
(Thomas 1911). E. lobifolia appears to represent the most
common fern, in the Baga
˚
Formation flora based on the
collections in both Lund and Stockholm.
Eboracia sp.
Fig. 3C
Material. – Fourteen specimens.
Description. – The specimens are represented by incomplete
fronds and occur as thin coalified films in a reddish-brown
claystone. The specimens have 25 mm long pinnae attached to a
prominent rachis but no complete fronds were encoun tered.
The pinnules are small, oblong and are inserted on the rachilla at
458. The rachillae in turn depart the rachis at 458. The pinnules
are oblong, nearly li near, with a broadly rounded apex.
The pinnules are attached by their full base and are oppositely
arranged. Each pinnule has an entire margin and a prominent
midvein. Pinnules are 3 (3.5) 5 mm long (10 specimens), 2 (2)
2 mm wide (10 specimens), with a L/W ratio of 1.85.
Remarks. – Specimens attributable to this genus fall into two
morphotypes and are here assigned to Eboracia lobifolia
and Eboracia sp. These species are preserved in different
lithologies: Eboracia lobifolia in a white clay as impressions
whereas Eboracia sp. is preserved as compressions in a red clay.
Eboracia sp. has considerably smaller pinnules than Eboracia
lobifolia. Although this may be a developmental difference, we
retain these forms as separate species until a larger population of
better preserved specimens becomes available.
Order Polypodiales
Family Dipteridaceae (Seward & Dale, 1901)
Genus Hausmannia Dunker, 1846
Type species.–Hausmannia dichotoma Dunker, 1846; Lower
Cretaceous; near Buckenburg, Hanover, Germany.
Hausmannia forchhammeri Bartholin, 1892
Fig. 3E
Holotype. – Table VII, Fig. 4 of Bartholin (1892), the specimens
are not numbered (selected here).
Material. – Fourteen incomplete speci mens.
Diagnosis. – See Bartholin (1892, p. 17).
Description. – The specimens are represented by incomplete
leaves that occur as coalified films in a reddish-brown mudstone.
The leaves are palmately lobed. The shape of the apex of each
lobe is pointed acute. The leaf base is cuneate. The veins are
easily distinguishable. The major veins are dichotomously
forked and run radially to the margin. From these major veins, a
complex reticulate array of smaller veins is given off dividing
the leaf into a fine meshwork. The major veins are separated by
about 5 mm for most of their leng th. Areolae between the
secondary veins are around 1 mm in diameter.
Remarks. – The collection contains only portions of these
leaves but their shape, texture and reticulate veins are
distinctive and permit ready assignment to H. forchhammeri.
H. forchhammeri occurs in considerable numbers in an
assemblage from the Baga
˚
Formation held in the collections
of the Swedish Museum of Natural History. Those specimens
are very well preserved and include complete leaves.
Additionally, several specimens attributable to Hausmannia
from Rhaetian to middle Jurassic strata of southern Sweden
(Stabbarp, Ho
¨
o
¨
r, Bjuv and Eriksdal localities) are held in the
140 Mehlqvist et al.: A Jurassic (Pliensbachian) flora from Bornholm GFF 131 (2009)
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collections of the Natural History Museum. Whilst the latter
have venation patterns broadly consistent with the Baga
˚
Formation specimen, they are all too fragmentary to be assigned
to an established species. The genus is long-ranging (from late
Triassic to late Cretaceous).
Genus Dictyophyllum Lindley & Hutton, 1834
Type species.–Dictyophyllum rugosum Lindley & Hutton,
1834; Jurassic; Yorkshire, England.
Dictyophyllum sp. cf. Dictyophyllum nilssonii (Brongniart)
Goeppert, 1846
Fig. 3D
Material. – Two specimens.
Description. – These fossils retain a thin coaly film of organic
matter. One incomplete pinnate frond measures 60£ 50 mm.
The rachis and midvein of each pinnule are very clear
(0.5 mm wide) and persistent, but the reticulate subsidiary
veins are indistinct. The pinnules are around 10 mm wide and
30 mm long with an entire margin; pinnule apices are pointed
acute. The pinnules are attached at a 908 to the rachis by their
full base and are alternately arranged. The lamina is
continuous between adjacent pinnules via a very narrow
flange flanking the rachis, thus making these leaves strictly
pinnatisect.
Remarks.–Dictyophyllum is a common Dipteridacean genus
of the mid-Mesozoic. About nine species have been recorded
from the Triassic–Jurassic of southern Sweden and
representatives of these are held in the Swedish Natural
History Museum. Of these, the single degraded specimen in the
Lund collection is closest to D. nilssonii (Brongniart) Goeppert,
1846 in its relatively large size and long pinnules that are
arranged at a high angle to the rachis. Of the several other
Dictyophyllum species reported from the Triassic–Jurassic of
southern Sweden, Dictyophyllum acutilobum (Braun) Schenk,
1867 and Dictyophyllum exile (Braun) Nathorst, 1906 have
proportionately shorter pinnules. D. carlsonii Nathorst, 1878b
and D. rugosum Lindley & Hutton, 1834 are distinguished by
their more completely fused pinnules. Dictyophyllu m muensteri
(Goeppert) Nathorst, 1878a and Dictyophyllum obsole tum
Nathorst, 1878b are separated from the studied material by
their shorter and/or rounded pinnules, whereas Dictyophyllum
spectabile Nathorst, 1906 is differentiated by its very long and
narrow pinnules.
Family Dicksoniaceae (Gaud.) (Schomburgk,
1848)
Genus Coniopteris Brongniart, 1849
Type species.–Coniopteris murrayana Brongniart, 1849.
Coniopteris hymenophylloides (Brongniart) Seward, 1900
Fig. 3F
Description. – The single specimen found in the Lund collection
is an incomplete frond fragment (compression) 40 mm long and
30 mm wide. The pinnules are small (, 4 mm long), attached by
their full base, and have slightly lobed margins.
Remarks.–Coniopteris is a common cosmopolitan Mesozoic
fern genus. Similar leaves from the Baga
˚
Fm were assigned
to the morphogenus Sphenopteris by Mo
¨
ller (1902) but
the available material is essentially identical to the pinnule
shape of the widespread Jurassic species Coniopteris
hymenophylloides.
Incertae Ordinis
Spiropteris Schimper, 1869
Type species.–Spiropteris miltoni (Brongniart) Schimper
(1869); age and location uncertain.
Spiropteris sp.
Fig. 3G
Material. – A single impression is present in the collection.
Description. – The circinnately coiled portion of this frond apex
is oval with major and minor diameters of 20 and 10 mm,
respectively. The rachis is 2– 3 mm wide.
Remarks.–Spiropteris was erected as a morphotaxon to include
distinctive fossil circinnately coiled frond tips (or “fiddle-
heads”) that could not be assigned to foliage-based genera
due to the absence of lamina features. Hence, Spiropteris
species have little stratigraphic or phylogenetic values. Mo
¨
llers
(1902, 1903) collection at the Swedish Museum of Natural
History contains several similar Spiropteris specimens of
variable size.
Seed Plants
Order Pinales
Family ?Cheirolepidiaceae (Takhtajan, 1963)
Genus Pagiophyllum Heer emend. Harris, 1979
Type species.–Pagiophyllum circinium (Saporta) Heer, 1881;
Upper Jurassic; Sierra de San Luiz, Portugal.
Pagiophyllum steenstrupi Bartholin, 1894
Fig. 3J
Material. – Five specimens.
Description. – The fossils consist of fragmentary axis
compressions with preserved leaves arranged in a loose spiral
(flattened on compressions). The leaves arch shortly above their
base; they have entire margins and pointed acute apices. Leaves
depart the stem at 20 –308 b efore sharply arching to 80 –908.
Leaf density is 10 per 20 mm along the stem. Leaves have a
prominent, persistent midvein. Whole shoots are 40 mm long.
Leaves are 5 (8) 10 mm long (10 specimens), 1 (2) 3 mm wide
(10 speci mens), with a L/W ratio of 3.85.
Remarks.–Pagiophyllum has short but relatively broad leaves
similar to several modern southern hemisphere conifers
(Townrow 1969; Harris 1979; Jansson et al. 2008a, 2008b).
Several Pagiophyllum species occur in Mo
¨
ller’s collection:
Pagiophyllum johnstrupi Bartholin, 1894 and P. steenstrupi
Bartholin, 1894, Pagiophyllum falcatum Bartholin, 1894,
Pagiophyllum peregrinum (Lindley & Hutton) Schenk emend.
Kendall, 1948, Pagiophyllum kurrii (Pomel) Schimper, 1872 and
these species were described by Mo
¨
ller (1902) as being very
GFF 131 (2009) Mehlqvist et al.: A Jurassic (Pliensbachian) flora from Bornholm 141
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142 Mehlqvist et al.: A Jurassic (Pliensbachian) flora from Bornholm GFF 131 (2009)
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abundant in the Baga
˚
Formation. The specimens available in the
Lund collection are most similar to P. johnstrupi and
P. steenstrupi, Bartholin 1894, but as these two species are
rather similar and the available material is not well preserved,
identification at species level is somewhat tentative. Assignment
to P. steenstrupi is preferred as this species is characterised by
relatively broad leaves inserted at high angles to the stem.
P. johnstrupi has slightly arched leaves at lower angles to the
stem. However, the latter may simply represent a morphological
variant of P. steenstrupi, since both taxa occur in the same
assemblage from the Baga
˚
Formation (Bartholin 1892 –1894)
and are commonly preserved close together. A more detailed
study of a larger collection is warranted to evaluate the
distinctiveness of these species. P. steenstrupi is interpreted to
represent one of the mid-storey or canopy components of the
vegetation. There is no evidence to suggest that the branches
were shed as regular units as, for example, in extant Taxodium or
Metasequoia, so the plant is interpreted to have been evergreen.
Pagiophyllum species are widespread in the Jurassic of Europe
(see for example, Harris 1979).
Order Ginkgoales
Family Ginkgoaceae Engler (In Engler &
Prantl, 1897)
Genus Ginkgoites Seward, 1919
Type species.–Ginkgoites obovata (Nathorst) Seward, 1919;
Upper Triassic (Rhaetian); Ska
˚
ne, Sweden.
Ginkgoites troedssonii Lundblad, 1959
Fig. 3K
Material. – Eight specimens.
Description. – The specimens are preserved as compressions in
both red and white clay. The leaves are fan shaped with multiple
deep dissections. Each lamina segment has an entire margin and
is 10 –15 mm wide and up to 100 mm long. The veins are
prominent, gently divergent, sparsely forked with densities of 10
veins per 10 mm across the apical part of each segment (ave rage
12 veins per segment). The petiole is not preserved in any of the
specimens.
Remarks. – Several Ginkgo species were reported by Mo
¨
ller
(1903). Around seven species assigned to either Ginkgo or
Ginkgoites have been reported from the Latest Triassic to
middle Jurassic strata of southern Sweden. Of these, the
specimens in the Lund collection are consistent with the
characters of G. troedssonii Lundblad, 1959, especially in their
relatively broad lamina segments with blunt or truncate apices.
The remaining six species from southern Sweden have shorter
and narrower lamina segments or, in the case of Ginkgo
obovata Nathorst, 1886, an almost undivided obovate lamina.
Ginkgoaleans are assumed to have been deciduous trees
and were more common in cooler (non-tropical) regions in the
middle Jurassic. Their presence in moderate numbers favours a
mid-latitude location for the Baga
˚
Formation flora.
Order Bennettitales Engler, 1892
Family Williamsoniaceae (Carruthers, 1870)
Genus Otozamites Braun emend. Watson & Sincock, 1992
Type species.–Otozamites (Zamites) brevifolius Braun, 1843;
Jurassic; Bayreuth, Germany (see Watson & Sincock (1992) for
discussion of typification).
Otozamites sp. cf. Otozamites mimetes Harris, 1949
Fig. 3L
Material. – Five specimens.
Description. – No complete leaves of Otozamites were identified
in this study and only the leaflets on one side of the rachis are
preserved in any one specimen. The leaflets have an
asymmetrical contracted base with a slight auricle on the
acroscopic side and are attached to the upper side of the rachis,
which is 1 mm wide. The specimens are preserved as
compressions and impressions in red clay. The leaflets are
oblong with a rounded apex and entire margin. The veins
are narrowly spaced with about 20 veins/pinnule; they are
gently divergent from the centre of the leaflet base to the margin.
Leaflets are separated by 1 mm from each other along the rachis,
departing the rachis at about 908. The preserved length of leaf:
50 mm; leaflets are 5 (7.5) 9 mm long (9 leaflets), 3 (3) 5 mm wide
(9 leaflets), with a L/W ratio of 1.95.
Remarks.–Mo
¨
ller’s collection in the Swedish Natural History
Museum contains several well-preserved Otozamites species
that are similar to the one described here. Only one species of
Otozamites has been thus far collected from the Triassic–
Jurassic strata of southern Sweden (specimens from the middle
Jurassic of Kurremo
¨
lla held in the Swedish Museum of Natural
History). The Ska
˚
ne specimen is designated Otozamites
bunburyanus Zigno, 1873 on the specimen’s label but this
material has never been formally described. It differs from the
Bornholm specimens in the Lund collection by its much
narrower leaflets. The specimen in the Lund collection is most
similar to O. mimetes Harris, 1949 from the middle Jurassic of
Yorkshire in its short, proportionately broad leaflets with
broadly rounded apices. Insufficient and incomplete material
prevents certain allocation to that species.
Palynology and dating
The samples yielded a well-preserved and entirely continental
palynoflora dominated by gymnosperm pollen grains, particu-
larly Chasmatosporites spp., Cerebropollenites macroverrucosus,
Fig. 3. Plant macrofossils from the Baga
˚
Formation (Middle Jurassic) of Bornholm. A. Neocalmites sp., a leafless sphenophyte axis. LO10508.
B. Eboracia lobifolia (Phillips) Thomas, 1911, detached fern pinna, LO10509. C. Eboracia sp., fern frond, LO10510. D. Dictyophyllum sp. cf.
D. nilssonii (Brongniart) Goeppert, 1846, a dipteridacean fern frond, LO10511. E. Hausmannia forchhammeri Bartholin, 1892, fragment of
fan-shaped dipteridacean fern frond, LO10512. F. Coniopteris hymenophylloides (Brongniart) Seward, 1900, fragmentary fern frond, LO10513.
G. Spiropteris sp., detached fern crozier, LO10514. H, I. Cladophlebis nebbensis (Brongniart) Nathorst, 1876, osmundaceous fern pinnae,
LO10515, LO10516. J. Pagiophyllum steenstrupi Bartholin, 1894, possible cheirolepidiacean conifer twig, LO10517. K. Ginkgoites troedssonii
Lundblad, 1959, matted and dissected ginkgoalean leaves, LO10518. L. Otozamites sp. cf. O. mimetes Harris, 1949, fragmentary bennettitalean
leaf, LO10519. Scale bars 10 mm.
R
GFF 131 (2009) Mehlqvist et al.: A Jurassic (Pliensbachian) flora from Bornholm 143
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Corollina torosus and Perinopollenites elatoides (Fig. 4).
Seed ferns are represented by bisaccate pollen grains of
Alisporites spp. The understorey vegetation of ferns is
represented by the spores Deltoidospora toralis, various species
of Baculatisporites spp. and isolated specimens of Striatella
seebergensis amongst others. This assemblage is typical for the
Chasmatosporites Zone, as defined by Koppelhus and Nielsen
(1994) indicative of a latest Pliensbachian age. Assemblages
ascribed to this zone have been described from the Sorthat beds
of the Hasle Clay pit. There, the Sorthat beds rest on the Hasle
Formation and are estimated to be around 200 m thick.
The exposure is no longer accessible but almost 60 m was
previously exposed in the pit. The palynological content broadly
matches the composition of the macroflora in terms of fern and
conifer abundance.
We have excluded the Baga
˚
beds as the source for the main
part of the macroflora since the palynoflora of Baga
˚
beds is
dominated by laevigate fern spores and lar ge quantities of
the gymnosperm pollen P. elatoides and the presence of the
Callialasporites spp. (Koppelhus & Nielsen 1994). Callialas-
porites is missing altogether in the presently studied assemblages
and Perinopollenites abundance is low. Additionally, ornamen-
ted spores occur in the Baga
˚
beds, such as Ischyosporites
variegatus, Sestrosporites pseudoalveolatus and Staplinisporites
caminus that are not present in the assemblages studied herein.
The assemblages from the Baga
˚
beds have been referred
to the Callialasporit es –Perinopollenites zone tentatively dated
to the Aalenian– Bathonian (Koppelhus & Nielsen 1994).
Discussion and comparison with other floras
Bartholin (1892 –1894) first described the plant fossils from the
Baga
˚
Formation and compared them to various early- to mid-
Mesozoic floras. He recognised a more diverse flora than
represented in the Lund assemblage and considered 25 species to
be characteristic of the Rha etian to Hettangian.
Mo
¨
ller (1902) identified 68 species from the Baga
˚
Formation and
suggested that of all the Ska
˚
ne assemblages, the Baga
˚
flora is most
similar to the Rhaeto–Liassic floras of Bjuv and argued that they
contained 19 species in common (Mo
¨
ller & Halle 1913). He also
noted similarities to the Rhaetian flora of Franken, Germany (with
19 species in common), and to the Rhaetian/Liassic floras of
Poland. These correlations were tentative given the relatively few
well-studied Mesozoic assemblages of northern Europe at that
time. The palynological investigation herein indicates that the
macroflora is of latest Pliensbachian age, a dating that also explains
the relative dissimilarity with the Bajocian fossil flora of Eriksdal,
Ska
˚
ne described by e.g. Tralau (1966). Only five genera in the
Lund collection (Baga
˚
Format ion) are represented in the
macrofloral assemblage from Eriksdal, so the floristic differences
may reflectcontrasting depositional settings and the younger age of
the Eriksdal flora.
Mo
¨
ller (1902, 1903) identified a surprisingly large number of
species (68) of which nearly 50% were ferns (mostly Dicksonia
and Cladophlebis species), represented in the spore assemblages
by Deltoidospora. Twenty-four species distributed in six genera
were identified as cycads/bennettitaleans (Mo
¨
ller 1902, 1903).
The pollen genus Chasmatosporites, so abundant in the
palynological assemblages of this study, may be linked to the
Cycadales/Bennettitales (Batten & Dutta 1997). Especially
prominent in Mo
¨
ller’s studies, in terms of its species richness (11
species), is the bennettite Otozamites, which contrasts with the
single known species assigned to this genus from the Triassic–
Jurassic of nearby Ska
˚
ne. These levels of diversity are atypical
of most mid-Mesozoic assemblages from northern Europe
suggesting considerable taxonomic duplication in the original
study. A thorough revision of all the assemblages from the Baga
˚
Formation is, therefore, justified to determine the full
composition and diversity of the flora and clarify its
biostratigraphic signature.
Although Mo
¨
ller (1902) described cycads from the Baga
˚
Formation none was found in the Lund collection. Given that
these are generally rare plants in coal-mire assemblages, their
absence is not unexpected in the comparatively small Lund
collection. The size of the presently studied collection (ca. 50
specimens) is probably not completely representative of the flora
that grew on Bornholm during the Jurassic period but it
complements the work of Mo
¨
ller. The floristic components
represented in the Swedish Natural History Museum and Lund
collections collectively provide a preliminary basis for
palaeoclimatic interpretation.
Palaeo-environment and climate interpretation
The Lund-material is dominated by ferns belonging to
Eboracia. At least four other genera of ferns are present,
which together with spheonphytes, suggests moist conditions
since these groups are dependent on water for their
reproduction and generally thrive in the understorey of
moist-climate forests. The miospore assemblages reveal a
flora of gymnosperms, ferns and some seed ferns consistent
with, but rather more diverse than, the macrofloral content.
This plant association also suggests a relatively warm, climate
based on the high diversity of ferns (Mo
¨
ller 1902) and the
presence of Dipteridaceae in particular. Dipteridaceae has a
tropical distribution in the modern flora. Although this family
was more extensively distributed in the Mesozoic, it appears to
have favoured generally warmer climates (Corsin & Waterlot
1979). According to Behrensmeyer et al. (1992) ferns
belonging to the families Osmundaceae, Matoniaceae and
Dipteridaceae were probably the dominant herbs in many
floras during this period.
The warm temperate/cold temperate biome boundary is typically
placed at 608 latitude and the warm temperate biome is centred at
408 under modern conditions (Willis & McElwain 2002).
Bornholm was situated at a latitude of 358N during deposition of
the Baga
˚
Formation sediments (Scotese 2003), which places
Bornholm firmly within the Jurassic warm temperature biome
(Rees et al. 2000). However, the presence of ginkgoaleans and the
absence of very large-leafed bennettites suggest the climate was
somewhat seasonal and not so warm as to be considered tropical or
megathermal.
Previous studies have interpreted the Baga
˚
Formation to have
been deposited in a meandering river system with well-
vegetated marshy flood plains (Petersen 1993). The coal
deposits in the formation attest to long periods of mire
development a nd support a humid climate interpretation
(Vakhrameev 1991; Vajda 2001).
The ferns and sphenophytes in the assemblage are interpreted to
have occupied the lowermost stratum in marsh and associated
moist-forest vegetation. Bennettites, such as Otozamites are
interpreted to have been mid-storey shrubs since there is no
evidence that this group ever developed a truly tall arborescent
habit. Conifers, such as Pagiophyllum, together with ginkgoaleans,
144 Mehlqvist et al.: A Jurassic (Pliensbachian) flora from Bornholm GFF 131 (2009)
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probably grew on better-drained sites and were the dominant mid-
to upper-storey plants.
These palaeoenvironmental interpretations of the Baga
˚
assemblages agree well with Vakhrameev’s (1991) vegetation-
community, type 1, which characterised swampy littoral or
intra-montane lowland areas and was dominated by moisture-
loving plants such as ferns and sphenophytes, and which is
commonly associated with coal-bearing deposits.
Conclusions
A historical collection of the Middle-Jurassic fossil plants from
sediments of the Baga
˚
-Sorthat formations, Bornholm, held at the
Geological Department, Lund University, Sweden, is dominated
by ferns, although Coniferales, Bennettitales, Ginkgoales and
Equisetales are also present. Ten fossil-plant genera were
identified, of which six could be identified to the species level.
The flora is interpreted as growing in a humid, warm temperate
biome. Although smaller and less diverse, the Lund collection
includes the same taxa identified during Mo
¨
ller’s (1902, 1903)
studies of the Baga
˚
Formation flora. The macroflora of the Lund
material has further been dated to the latest Pliensbachian
Chasmatosporites zone based on palynology. This age, together
with some possible variation in depositional environment, is likely
to explain the taxonomic differences evident with the Rhaetian–
Hettangian and Bajocian macrofloras of neighbouring Ska
˚
ne.
Fig. 4. Photomicrographs of selected taxa from sample R-2357-26/PTC collected at the Hasle Clay Pit, Bornholm. Magnifications £ 500
A. Deltoidospora toralis (Leschik) Lund, 1977, LO10520. B. Deltoidospora toralis (Leschik) Lund, 1977, LO10521. C. Apiculatisporites ovalis
(Nilsson) Norris, 1965, LO10522. D. Baculatisporites comaumensis (Cookson) Potonie
´
, 1970, LO10523. E. Striatella seebergensis (Nilsson) Filatoff &
Price, 1988, LO10524. F. Corollina torosa Cornet & Traverse, 1975, LO10525. G. Chasmatosporites elegans Nilsson, 1958, LO10526.
H. Chasmatosporites hians Nilsson, 1958, LO10527. I. Cerebropollenites macroverrucosus (Thiergart) Schultz, 1967, LO10528. J. Perinopollenities
elatoides Couper, 1958, LO10529. K. Monosulcites minimus Cookson, 1947, LO10530. L. Alisporites robustus Nilsson, 1958, LO10531.
GFF 131 (2009) Mehlqvist et al.: A Jurassic (Pliensbachian) flora from Bornholm 145
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Acknowledgements.–The authors would like to express their sincere gratitude to Prof.
Else Marie Friis for providing access to the fossil-plant collections at the Swedish Museum
of Natural History. Dr Stephen McLoughlin is acknowledged for the valuable comments on
the manuscript and help for identification of problematic macrofossil specimens. Ove
Johansson is thanked for the help with the collections at NRM and for providing general
information on the collections. Susan Turner is thanked for the additional comments. This is
a project within the Lund University Centre for Studies of Carbon Cycle and Climate
Interactions (LUCCI) and a contribution to IGCP 506: Marine/Non-marine Jurassic
correlation.
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