Dinosaur tracks in Lower Jurassic coastal plain sediments (Sose Bugt Member, Rønne Formation) on Bornholm, Denmark
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Dinosaur tracks in Lower Jurassic coastal plain sediments
(Sose Bugt Member, Rønne Formation) on Bornholm,
Denmark
GUNVER K. PEDERSEN, ANNE B. JOHANNESEN AND CONNIE
LARS B. CLEMMENSEN, JESPER MILAN,
LARSEN
Clemmensen, L.B., Milan, J., Pedersen, G.K., Johannesen, A.B. & Larsen, C. 2014:
Dinosaur tracks in Lower Jurassic coastal plain sediments (Sose Bugt Member, Rønne
Formation) on Bornholm, Denmark. Lethaia,Vol. 47, pp. 485–493.
Fluvial palaeochannels of coastal plain sediments of the Lower Jurassic Sose Bugt
Member of the Rønne Formation exposed in the coastal cliffs at Sose Bugt, Bornholm,
contain abundant dinosaur or other large vertebrate tracks in the form of deformation
structures exposed in vertical section. The tracks are represented by steep-walled, flat-
to-concave-bottomed depressions, with a raised ridge at each side. The tracks are filled
with laminated sediments, draping the contours of the bottom of the depression. Un-
derprints, stacked concave deformations beneath the prints, are present beneath each
track. Contemporary Upper Triassic – Lower Jurassic strata from southern Sweden
and Poland contain a diverse track fauna, supporting our interpretation. This is the
earliest evidence of dinosaur activity in Denmark. □ Bornholm, coastal plain, dinosaur
tracks, lake sediments, Lower Jurassic.
Lars B. Clemmensen [larsc@geo.ku.dk], Jesper Milan [jesperm@oesm.dk], Anne B. Joh-
annesen [jzb294@alumni.ku.dk], and Connie Larsen [gnk171@alumni.ku.dk], Depart-
ment for Geosciences and Natural Resource Managements, University of Copenhagen, Øster
Voldgade 10, DK-1350 Copenhagen K, Denmark; Jesper Milan [jesperm@oesm.dk],
Geomuseum Faxe/Østsjællands Museum, Østervej 2, DK-4640 Faxe, Denmark; Gunver
K. Pedersen [gkb@geus.dk], GEUS Geological Survey of Denmark and Greenland, Øster
Voldgade 10, DK-1350 Copenhagen K, Denmark; manuscript received on 12/04/2013;
manuscript accepted on 04/12/2013.
Outcrops of terrestrial Mesozoic sediments in Den- and jawbone fragments of actinopterygians, post-
mark are restricted to a few scattered exposures cranial remains of amphibians and primitive lizards,
along the southwest coast of the Baltic Island of small dromaeosaurid dinosaurs and perhaps bird
Bornholm (Fig. 1). Despite the very limited extent teeth, and a single tooth of a multi-tuberculate mam-
of the exposures, an increased interest and intensive mal (Lindgren et al. 2004, 2008; Rees et al. 2005;
field studies during the last decade have yielded evi- Schwarz-Wings et al. 2009). In contrast to the dimin-
dence of a relatively diverse fauna of terrestrial verte- utive body fossils, a trample ground with abundant
brates, from Middle Jurassic and Early Cretaceous cross-sections through large dinosaur tracks (up to
deposits (Fig. 2). 70 cm in length), and possible lungfish aestivation
To date, the earliest evidence of dinosaur activity burrows have been described from an adjacent expo-
comes from the Middle Jurassic Bag a Formation sure in the coastal cliff (Surlyk et al. 2008).
(Gravesen et al. 1982) (Fig. 2), exposed in the aban- The overlying Jydegaard Formation (Fig. 2),
doned Hasle Klinker Factory clay pit at Bag a, at the known from inland quarries, has yielded dromaeo-
coast between Hasle and Rønne. This pit has yielded saurian teeth, Dromaeosaurides bornholmensis and a
a diverse dinosaur ichnofauna comprising large and possible tooth crown from a juvenile sauropod
small tracks of sauropods, thyreophoreans and (Bonde & Christiansen 2003; Christiansen & Bonde
theropods but no body fossils (Milan & Bromley 2003), as well as fragments from carapaces of turtles,
2005; Milan 2011). teeth of the crocodile Pholidosaurus, and abundant
The lowermost Cretaceous Rabekke Formation, teeth and scales of the holostean fish Lepidotes and
exposed in a coastal cliff east of Arnager (Gravesen the freshwater shark Hybodus and some pycnodont
et al. 1982) (Fig. 2), has recently yielded remains of a jaws, small stem-teleosteans and coprolites (Noe-
rich fauna of micro-vertebrates including abundant Nygaard et al. 1987; Noe-Nygaard & Surlyk 1988;
crocodile teeth (Bernissartia sp., Theriosuches sp., and Rees 2001; Bonde 2004; Milan et al. 2012). For a
Goniopholis sp.), fragments of turtle carapaces, scales complete review of the Mesozoic vertebrate faunas,
DOI 10.1111/let.12073 © 2014 Lethaia Foundation. Published by John Wiley & Sons Ltd486 Clemmensen et al. LETHAIA 47 (2014)
A
B C
Fig. 1. A, geological map of Bornholm (map modified from Graversen 2009). Localities with dinosaur tracks are indicated with dots; the
locality at Sose Bugt with newly recognized dinosaur tracks is described in the article. B, detailed geological map of the Sose Bugt area. C,
location of Bornholm in a broader geographical context.
including the marine fauna of Bornholm, see Bonde found in the Late Cretaceous Asen locality in the
(2012). Kristianstad Basin (Lindgren et al. 2007) (Fig. 2). In
Early Jurassic environments similar to those on addition to the ichnofauna, a few dinosaurian verte-
Bornholm are known to have supported a rich dino- brae have been found in the same level as the tracks
saur fauna in nearby Scania, southern Sweden, from Billesholm coal mine (B€ olau 1954).
which was connected to Bornholm during most of During a recent field course, deformation struc-
the Mesozoic (Surlyk et al.1995; Michelsen et al. tures were observed in the Lower Jurassic Sose Bugt
2003). The Late Triassic – Early Jurassic H€ ogan€as Member of the Rønne Formation (Gravesen et al.
Formation has yielded tracks and trackways of the- 1982; Surlyk et al. 1995) at the type section in Sose
ropod and possible thyreophorean dinosaurs as well Bugt on the south coast of Bornholm (Fig. 1). The
as a few indeterminate skeletal remains (B€
olau 1952, deformation structures showed many of the charac-
1954; Pleijel 1975; Ahlberg & Siverson 1991; Gierlin- teristics known from vertebrate tracks emplaced in
ski & Ahlberg 1994; Milan & Gierlinski 2004), and soft sediment and exposed in cross-section (e.g.
remains of neoceratopsian dinosaurs have been Loope 1986; Allen 1997; Milan & Bromley 2006,LETHAIA 47 (2014) Dinosaur tracks in Denmark 487
System
Stage
Fennoscandian Border Zone Material and methods
Series NW Skåne SE Bornholm
U Jydegård Formation Six detailed sedimentological sections were mea-
Cretaceous
Valanginian
sured along a c. 50-m-long coastal cliff at Sose
Lower
L
Vita- Robbe-
U bäck dale Formation Bugt. Within these sections, we recognize eight sed-
Ryazanian
L Clay
Rabekke Formation
imentary units and correlate them across the profile
U Annero (Fig. 3). Continued coastal erosion ensures the
Volgian Fm
M Nytorp availability of good exposures, and the deformation
Annero Fm
L Sand
structures described here were seen after a year with
U
Upper
Kimmeridgian particularly severe erosion. However, landslides may
L Fyle-
dalen frequently cover large parts of the formation, mak-
U Clay
Oxfordian M ing it difficult to measure complete sedimentologi-
L cal logs. The deformation structures occur in four
U
Fortuna main levels; we here focus on deformation struc-
Callovian M
L
Marl tures 1–8 in the uppermost two levels (Fig. 3).
? ?
U Glass These structures were cleaned with hand-held
Mariedal Fm
Bathonian Sand
Jurassic
M scrapers and photographed. Based on photographs
Middle
L Vilhelmsfält Mb
Fm and field notes, simplified, interpretive sketches of
U Bagå Formation
Bajocian
Fug-
the deformation structures were produced. A few of
L
lunda the structures were dug out to reveal the plan-
Mb
Aalenian U surface geometry.
L ? ?
U
Ryde-
Toarcian M
L
bäck Sorthat Formation Geological setting
Mb
Rya Fm
Pliensbachian
U In the Early Jurassic, Bornholm and Scania in south-
L Katslösa Hasle Formation ern Sweden formed part of the NW–SE trending
Lower
Mb
Rønne Formation
U Pankarp Mb
Galge-
løkke Mb
Sorgenfrei–Tornquist Zone, which separates the
Sinemurian
L Döshult
Mb
Danish Basin from the Baltic Shield (Michelsen et al.
Sose Bugt Mb
Helsingborg
2003). The uppermost Triassic and lowermost Juras-
Höganäs Fm
Hettangian ?
Mb Munkerup Mb sic in Bornholm and Scania (Fig. 3) include non-
Bjuv Mb marine, coastal and shallow marine deposits referred
Höör
Sst.
Rhaetian to the Rønne, H€ ogan€as and Rya Formations (Surlyk
Triassic
Upper
Vallåkra Mb
et al. 1995; Nielsen 2003; Lindstr€ om & Erlstr€ om
Kågeröd
Kågeröd
Fm
Norian
Fm
Risebæk Mb 2006). On Bornholm, the Lower Jurassic Rønne For-
mation comprises lacustrine, floodplain or coastal
Marine mudstones and siltstones Unconformity plain, tidal and marine shoreface deposits of Hettan-
Shallow marine sandstones and Dinosaur skeleton remains gian to Sinemurian age (Gravesen et al. 1982; Surlyk
siltstones
Paralic and non-marine sandstones, Dinosaur tracks et al. 1995). These paralic deposits contain organic-
siltstones, mudstones and coals rich beds and plant material testifying to a warm
Hiatus and humid climate (Petersen et al. 2003).
Fig. 2. Stratigraphical scheme of Mesozoic units on Bornholm The sediments of the H€ ogan€as Formation are
and southern Scania (Sk ane), with indications of vertebrate ich- interpreted to have been deposited in lagoons,
no and body fossils. Stratigraphical scheme modified from swamps, lakes and floodplains. The formation con-
Michelsen et al. 2003.
tains two extensive coal beds, and numerous hori-
2008; Milan et al. 2006). This is the first record of zons enriched in comminuted plant debris. The
dinosaurs from the Lower Jurassic in Denmark. The spore–pollen flora in Scania includes bryophytes and
aim of this study is to describe the newly observed Equisetites, which usually thrive under wet and
deformation structures from the Lower Jurassic Sose humid conditions, and Taxodiacean, conifer pollen
Bugt Member of the Rønne Formation, to discuss the and fern spores are abundant. A majority of the ferns
possibility that they are dinosaur tracks and to put grew under moist and preferably rather warm condi-
them into context with the other Scandinavian finds tions (Lindstr€om & Erlstr€ om 2006).
of Lower Jurassic dinosaur tracks. We also describe The Lower Jurassic Sose Bugt Member of the
related sediments and interpret the depositional envi- Rønne Formation (Gravesen et al. 1982) is exposed
ronment in which the presumed dinosaurs lived. in the coastal cliff at Sose Bugt on the south coast of488 Clemmensen et al. LETHAIA 47 (2014)
m A C D E F
3.0 m m
3.0 8 4.0 m
2.0
7 t7
t1 t2
2.0
2.0 6 3.0 t3 t4 t5 t6 t8
1.0
B 5
m
2.0
3 4
1.0
1.0 2.0
t 2 0
Clay Silt Sand
1.0
t
0
Clay Silt Sand 1 0 1.0
Clay Silt Sand
0
Clay Silt Sand
0
Legend Clay Silt Sand
Coal Water escape structure Coal clasts Burrows
Structureless Lenticular bedding Tracks t Plant debris Bioturbation
Parallel lamination Faint parallel lamination Slump folds Roots Twigs Erosive surface
Fig. 3. Sedimentological logs (A–F) from the studied section of the Lower Jurassic Sose Bugt Member in the south-facing coastal cliff at
Sose Bugt on Bornholm. The logs show the lateral facies variations of lacustrine and fluvial deposits over a distance of c. 50 metres. Eight
sedimentary units (1–8) are distinguished. Sediment deformation structures, interpreted as dinosaur tracks, are located in unit 1, unit 2,
at the boundary between unit 6 and 7, and in the middle part of unit 7.
Bornholm (Fig. 1). The exposure comprises lacus- sequence 1 are divided into eight depositional units
trine, marine shoreface, coastal plain and incised (Fig. 3), which comprise the deformation structures
valley deposits. The repeated shifts between non- described here and interpreted as dinosaur tracks.
marine and marine depositional environments sug- Parasequences PS1–PS3 were interpreted as lacus-
gest that the palaeogeographical position of locality trine based on the abundance of roots and stems, the
was relatively close to the regional coastline. The very low content of pyrite in the coal bed and the
sequence stratigraphic interpretation indicates that absence of marine palynomorphs (Surlyk et al.
the Hettangian–Sinemurian mainly consists of 1995).
deposits belonging to transgressive systems tracts.
During periods with increasing rate of sea-level rise, Unit 1. – This lowermost unit is seen in logs A–D
the newly formed accommodation space was filled (Fig. 3) and shows considerable variation in sedi-
by coastal lake and lagoonal deposits. Only close to mentary characteristics. It is dominated by silt-
the time of maximum flooding was the paralic envi- streaked mud with very thin laminae or lenses of
ronment flooded by marine water (Surlyk et al. pale silt interbedded in dark grey clay. The original
1995). lamination is disturbed by pervasive penecontempo-
raneous deformation structures including folds, c.
5 cm high, and water escape structures. The base of
Sedimentary units
the unit is not exposed, and the top is locally trun-
The 24-m-thick succession of the Sose Bugt Member cated by an erosion surface overlain by silt and fine-
was divided into three sequences and 18 parase- grained sand of unit 2 (log C) or by a shallow, chan-
quences by Surlyk et al. (1995). In the present study, nelized sand bed (log A). Log D shows that unit 1
parasequences PS1, PS2 and basal part of PS3 of also includes 10- to 30-cm-thick layers of sand, someLETHAIA 47 (2014) Dinosaur tracks in Denmark 489
of them with soft sediment deformation structures by Arndorff (1992). The erosive surface separating
and water escape structures. Unit 1 is sharply or ero- units 2 and 3 is interpreted as a lacustrine transgres-
sively overlain by unit 2 and constitutes the lower sive surface.
part of PS1 of Surlyk et al. (1995).
The silt-streaked mudstone is interpreted as Unit 3. – This unit is seen at logs A–E. It is 10–
deposited at low energy in a body of standing water 40 cm thick and composed of horizontally lami-
(a lake) by settling from suspension (clay) and from nated, brown heterolithic sediment with a fairly high
dilute gravity currents (the planar to lensoid silt proportion of comminuted plant debris. The strata
streaks). The small folds suggest that the sedimen- are not penetrated by rootlets. The basal surface,
tary pile was subject to slumping, which may have which is erosive, is locally overlain by pockets of
generated the water escape structures. We suggest sand or intraformational clasts of coaly mudstone.
that the deformation structures below the channeli- Unit 3 is overlain by shallow lake deposits of unit 5
zed sand (log A) can be attributed to dinosaur tram- (logs A and B) and by channel deposits of unit 4
pling at the lake floor. The majority of the remaining (logs C–E).
soft sediment deformation structures are not suffi- Unit 3 is interpreted as recording episodic depo-
ciently distinct to be interpreted with certainty. The sitional events, possibly as overbank flooding. The
upper erosion surface is interpreted as a forced absence of rootlets suggests that the sediment was
regression due to a fall in lake level. deposited in a lake, and the scarcity of wave rip-
ples indicates that the water was deeper than wave
Unit 2. – This unit is present in logs A–E and base. If the lake was small, water depth may not
forms the upper part of PS1 of Surlyk et al. (1995). have been more than a few metres. Deposition
Unit 2 is dominantly silty with a small proportion from overbank flooding suggests the proximity of
of very fine-grained sand deposited as thin streaks a river.
or small lenses. Root traces increase in number
upwards in the unit, and comminuted plant debris Unit 4. – This unit is seen at logs C–E. It consists of
is common in the upper 5–10 cm. At log C, the fine- to medium-grained, low-angle cross-bedded
unit is a c. 1-m-thick, upward-coarsening succes- sand, which locally contains intraformational clasts
sion overlying two thin, normally graded sand beds of coaly mudstone. The lower boundary of unit 4 is
at the base of the unit. In log E, only the upper part erosive and locally truncates the upper part of unit 3
of unit 2 is exposed as a structureless, silty to very (Fig. 3). Unit 4 is interpreted as deposited in a
fine-grained sediment with numerous rootlets. The minor river channel.
unit is erosively truncated and overlain by unit 3
(Fig. 3). Unit 5. – This unit is seen at log A and C–E. It is
Unit 2 is thinner and more complex in log A, a 20- to 30-cm-thick unit of interbedded sand and
where it comprises a 20-cm-thick bed of structure- mud, in which the sand layers become thinner and
less silt with lenses of pale, fine-grained sand. It is more fine-grained upwards. The sand locally con-
cut by a small, channelized sand body with rare tains comminuted plant debris. The lower bound-
burrows and trough cross-bedding. This sand body ary is locally erosional, as seen where it truncates
outlines large deformation structures and is over- unit 4 in log E. The upper boundary is transitional
lain by structureless silt and a small channelized to unit 6.
sand body. Coal-rich lithologies form intraforma- Unit 5 is interpreted to record episodic deposition
tional clasts, and locally organic-rich sediment is of sand from sediment gravity flows in a lake in
preserved above a horizon of rootlets, which are which water depth increased with time. The bound-
seen in the top of unit 2 throughout the outcrop ary between units 5 and 6 thus reflects relatively deep
(Fig. 3). water and low-energy conditions. Unit 5 corre-
The coarsening upward succession of very fine- sponds to the lower part of PS2 of Surlyk et al.
grained silt and sand is interpreted as lake-fill depos- (1995).
its. The large deformation structures are interpreted
as dinosaur tracks, but as the sediment was fine- Unit 6. – This unit is seen in logs A, C, D and E
grained and water-logged, these footprints are much where it overlies unit 5 with a transitional boundary.
deformed. The extensive root horizon at top of unit Unit 6 forms an upward-coarsening succession rang-
2 suggests that the former lake deposits were subaer- ing from silt to very fine-grained sand, with a maxi-
ially exposed and overgrown. This is supported by mum thickness of c. 120 cm (log A). The sediment
palaeosol development in unit 2, where a sandy loam is structureless to weakly laminated with few thin
with illuviated iron sesquioxides has been described streaks of silt or very fine-grained sand. Upwards,490 Clemmensen et al. LETHAIA 47 (2014)
the content of sand increases gradually. Locally, a
Description of dinosaur tracks
large number of coalified wood (twigs and stems)
are found parallel to bedding planes (logs C, D and The exposed section at Sose Bugt contains four levels
E). A well-developed horizon of vertical roots, none with deformation structures interpreted as dinosaur
of which resemble tree roots, is seen in the upper c. tracks: unit 1 (log A), unit 2 (log A), the boundary
80 cm of unit 6 (log A). The density of roots between unit 6 and 7 (logs C, E and F) and unit 7
increases upwards. In contrast, the roots generally (log F) (Fig. 3). The best preserved dinosaur tracks
are lacking in unit 6 where this is truncated by unit 7 at the boundary between unit 6 and 7 are steep-
(logs C–F) and unit 6 is overlain by a thin coal bed, walled, concave-to-flat-bottomed depressions, with
unit 8, or truncated by channel deposits, unit 7. Unit a raised ridge at each side of the walls. Where visible,
6 corresponds to the upper part of PS2 of Surlyk the infillings are laminated, draping the contours of
et al. (1995). A series of conspicuous deformation the bottom of the depression. The seven track struc-
structures interpreted as dinosaur tracks are seen at tures in the main level between units 6 and 7 are clo-
the top of unit 6 (Fig. 3). These structures are sely spaced. Below each structure, a series of bowl-
described below in more detail. shaped deformation structures are present in the
Unit 6 is interpreted to record fairly steady pro- subjacent layers. These structures become succes-
gradation of the lake shoreline. Thin homogeneous sively shallower downwards. In the following, the
sand beds are interpreted as episodic infill probably three most informative structures will be described
from fluvial currents. The extensive root horizon at in detail.
top of unit 6 suggests that the former lake deposits
were subaerially exposed and overgrown and the Dinosaur track 4. – This structure from the main
roots indicate a fairly dense vegetation devoid of level at the boundary between unit 6 and unit 7 con-
trees. The subaerial exposure is supported by palaeo- sists of two adjacent flat-bottomed depressions, each
sol development in unit 6, where a silty to sandy about 20 cm wide, separated by a raised ridge. The
loam shows strong iron staining due to illuviation of shaft of the depressions is subvertical, and each side
sesquioxides (Arndorff 1992). of the depressions is bordered against the sediment
surface by a raised ridge. One of the depressions has
Unit 7. – This unit is seen in logs C–F and com- a steep-walled deep structure protruding 15 cm
prises trough cross-bedded sand, horizontally lami- down below the bottom of the depression (Fig. 4A,
nated sand and structureless sand bounded by B). Subsediment deformations are present below
erosional surfaces. The lowest of these separates hor- both main depressions. The structures are infilled
izontally bedded sand (unit 7, log E) from hetero- with layered sand containing scattered coal clasts;
lithic silt (unit 6). This facies is erosionally overlain the sand drapes and moulds the contours of the
by structureless or cross-bedded sand (logs C–F), depressions (Fig. 4A, B). The structure is overlain by
locally with a high content of coalified wood (log F). channel sand of unit 7.
The common occurrence of erosional surfaces, the
well-sorted and relatively coarse-grained sediment as Dinosaur track 7. – This structure from the upper-
well as the current generated structures indicate that most level in unit 7 is impressed into a layer of finely
unit 7 is the fill of a small fluvial stream. laminated mud, which drapes a cross-bedded chan-
nel deposit (Fig. 4C, D). The structure is 17 cm wide
Unit 8. – Unit 8 is a 10- to 15-cm-thick coal-rich and consists of a concave-bottomed depression in a
bed characterized by a high amount of inertinite mud layer, which has been compressed below the
(coal bed D in Surlyk et al. 1995). It is seen in all structure and displaced upwards in sharply defined
logs and is continuous through the outcrop. The raised ridges on each side. The shaft of the structure
coal petrography indicates that the bed formed has steep walls, and the whole structure is infilled
either from oxidation of a fragile herbaceous-like with structureless sand containing abundant rootlets
vegetation or as redeposition of a dessicated peat (Fig. 4C, D).
surface. The top 4 cm of the bed is almost entirely
allochtonous, and the bed represents a limnotelmatic Dinosaur track 3. – This structure from the main
facies (Surlyk et al. 1995). The organic material level at the boundary between unit 6 and unit 7 is
accumulated in fresh water in a relatively high- almost 40 cm wide and shows a remarkable set of
energy zone at low water depth (limnotelmatic deformation structures. The main structure is a flat-
facies). Units 7 and 8 form the basal part of PS3 in bottomed depression with sharply defined walls,
Surlyk et al. (1995). The formation of peat is inter- with a sharp ridge towards the surface it originates
preted as reflecting a rise in lake level. from (Fig. 4E, F). The upper part of the structureLETHAIA 47 (2014) Dinosaur tracks in Denmark 491
A B
C D
E F
Fig. 4. Cross-sections through deformation structures representing dinosaur tracks. A, dinosaur track 4 (log F). Double track structure
consisting of two flat-bottomed depressions. B, interpretative drawing of A with descriptive structures highlighted. C, dinosaur track 7
(log F). Track emplaced in a thin layer of laminated mud. D, interpretative drawing of C, illustrating the compaction of the clay layers
and the sideways displacement of the sediment into raised ridges. E, dinosaur track 3 (log E–F). Track with a prominent zone of
deformed and rotated sediment. F, interpretative drawing of E.
contains two tracks filled with structureless sand (Fig. 3). This is in agreement with Surlyk et al.
containing numerous coal clasts. Below these tracks (1995), who referred parasequences 1, 2 and the
is a mixed zone of subvertically rotated sediments basal part of parasequence 3 (our units 1–8) to a
similar to what can be found below vertebrate tracks lacustrine environment, because freshwater green
(Brown 1999; Graversen et al. 2007). The whole algae such as Botryococcus spp. are particularly abun-
structure is covered by channel sand of unit 7 dant in the coal bed (unit 8). No marine pal-
(Fig. 4E, F). ynomorphs have been recovered from these
sediments. The lacustrine successions are thin and
show lateral facies variations within the 50 m
Discussion distance from log A to log F. These observations
suggest that the lakes were small and shallow. The
Palaeoenvironment channel deposits observed in units 1, 2, 4 and 7 are
interpreted as small streams or creeks. The small
The sedimentological logs are divided into eight freshwater lakes and small streams may have formed
units, which are interpreted as mainly lacustrine492 Clemmensen et al. LETHAIA 47 (2014)
on a large coastal plain or a large delta plain. Overly- (B€olau 1952; Pleijel 1975; Ahlberg & Siverson 1991;
ing sediments in the Sose Bugt succession include a Gierlinski & Ahlberg 1994) and a single track of pre-
large channel and two levels of marine shoreface sumed thyreophorean affinity (Milan & Gierlinski
deposits separated by non-marine deposits (Surlyk 2004). The Upper Triassic and Lower Jurassic strata
et al. 1995). It is probable, that the freshwater lakes of the Holy Cross Mountains in Poland have a
were located fairly close to the shoreline as the lake diverse tetrapod ichnofauna with tracks of early
level changes are related to changes in relative sea mammals, small- to large-sized theropods, ornithis-
level (Surlyk et al. 1995). chians and sauropods (Gierlinski 1997, 1999; Gier-
linski et al. 2001, 2004).
The Swedish and Polish finds demonstrate that an
Dinosaur tracks abundant and diverse dinosaur fauna was present in
The morphology of the deformation structures here the region during the Late Triassic and Early Jurassic
interpreted as dinosaur tracks displays a remarkable times. This supports the dinosaurian interpretation
difference in degree of preservation and architecture, of the tracks from the Lower Jurassic at Sose Bugt.
from sharply defined to chaotic mingling of the sedi- The tracks from Sose Bugt thus fills a biogeographi-
ments, but most of them share a common morphol- cal gap between the Swedish and Polish track faunas.
ogy, with raised ridges around steep walls, concave
to flat bottoms and layered infilling. This morphol-
ogy is consistent with the morphology of vertebrate Conclusions
tracks exposed in cross-section (Loope 1986; Allen
1997; Milan et al. 2006). The presence of deforma- The lowermost part of the Lower Jurassic Sose Bugt
tions in the layers below the structures is consistent Member of the Rønne Formation is interpreted as
with the interpretation of the structures as vertebrate lacustrine and fluvial. At the exposure in Sose Bugt
tracks, as they are consistent with the morphology of on Bornholm, newly recognized deformation struc-
undertracks and other subsediment deformations tures exposed in cross-section at the base of small
formed below vertebrate tracks (Brown 1999; Man- fluvial palaeochannels are interpreted as dinosaur
ning 2004; Milan & Bromley 2006, 2008; Graversen tracks. This is consistent with abundant finds of con-
et al. 2007). Further, the structures are consistent temporary dinosaur tracks from both Sweden and
with dinosaur tracks exposed in cross-section, Poland, which were part of the same landmass dur-
described from the nearby Lower Cretaceous Rabe- ing the Lower Jurassic. This is the geologically earli-
kke Formation (Surlyk et al. 2008). One of the struc- est record of dinosaurs in Denmark.
tures was excavated by exposing the original bedding
Acknowledgements. – The fieldwork on Bornholm was sup-
plane in order to examine the three-dimensional ported by the Department for Geosciences and Natural Resource
morphology of the structure. It turned out to be Management, University of Copenhagen. Spencer G. Lucas and
subcircular in shape, which excludes the possibility an anonymous reviewer provided critical reviews that helped to
shape the focus of the paper.
that the structures are cut through small channels
and supports our interpretation that they are tracks
from vertebrates.
Dinosaur tracks 1–6 and 8 are located at the floor References
of a small shallow stream (unit 7) connected to the Ahlberg, A. & Siverson, M. 1991: Lower Jurassic dinosaur foot-
freshwater lake. Also dinosaur track 7 seen in the prints in Helsingborg, southern Sweden. Geologiska F€orenin-
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