Late Jurassic shallow-marine carbonate facies and

Late Jurassic shallow-marine carbonate facies and sequences (and dinosaur tracks) André Strasser1, Daniel Marty2, Wolfgang Hug2 1

Department of Geosciences, University of Fribourg, 1700 Fribourg (Switzerland) [email protected] 2 Paléontologie A16, Office de la culture, Hôtel des Halles, 2900 Porrentruy 2 (Switzerland) [email protected], [email protected]

CONTENTS Introduction Palaeogeographic setting, facies, and stratigraphy Methods Stop 1: Late Oxfordian and Kimmeridgian platform progradation at Péry-Reuchenette Stop 2: Late Oxfordian sequence- and cyclostratigraphy in the Gorges de Court Stop 3: Bedding surfaces at the tunnel entrance, Gorges de Court Stop 4: Coral carpets and ooid sandwave at Hautes-Roches Stop 5: Kimmeridgian Banné Marls close to Porrentruy Stop 6: Dinotec Porrentruy Stop 7: Kimmeridgian peritidal facies at Roche-de-Mars (Porrentruy) Stop 8: Oxfordian patchreefs at St. Ursanne Stop 9: Late Kimmeridgian to Tithonian facies and sequences at Noirvaux Discussion Conclusions References Short history of Porrentruy Short history of St. Ursanne

19th International Sedimentological Congress – Geneva – Field trip guidebook

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2 2 4 6 7 10 10 11 12 16 17 19 20 23 23 27 28

Introduction During the Late Jurassic, more precisely from the Middle Oxfordian to the Late Kimmerdigian, the mixed carbonate-siliciclastic platform on the northern margin of the Tethys ocean displayed a great variety of shallow-marine depositional environments: tidal flats, beaches, shallow lagoons, ooid dunes, and coral reefs. On this fieldtrip, the lateral and vertical variability of these environments will be illustrated in nine outcrops (Fig. 1). The interpretation is based on facies analysis coupled with high-resolution sequence stratigraphy and cyclostratigraphy, which allows for a detailed interpretation of the evolution of the sedimentary systems with a time resolution of a few ten-thousand years. The respective roles of sea-level and climatic changes as well as of differential subsidence will be discussed.

Basel

Switzerland

Porrentruy

5,6,7 8

Delémont

Ste-Ursanne

France

M

N

ou Jura nt ai ns

Geneva

4 2

Moutier

3

1 Biel

Neuchâtel

10 km

Bern

9 Ste-Croix

Fig. 1 Locations of the visited outcrops in the Swiss Jura. Inset: Jura Mountains in green.

Palaeogeographic setting, facies, and stratigraphy In Middle Oxfordian to Late Kimmerdigian times, a wide, carbonate-dominated shelf covered the realm of today‘s Jura Mountains (Fig. 2). It was structured by differential subsidence along faults inherited from older lineaments (Wetzel et al. 1993, Wetzel & Allia 2000). To the north, very shallow depositional environments predominated, whereas to the south deeper epicontinental basins developed. Siliciclastic material was furnished episodically by the erosion of crystalline massifs in the hinterland (Fig. 2). The study area was situated at a palaeolatitude estimated between 33° and 38°N (Barron et al. 1981, Dercourt et al. 1993, Smith et al. 1994). Lithostratigraphy and facies of the Oxfordian and Kimmerdigian in the Swiss Jura Mountains have been studied extensively by, e.g., Ziegler (1956), Ziegler (1962), Gygi (1969, 1992, 2000, 2012), and Bolliger & Burri (1970). The biostratigraphy based on ammonites was mainly established by Gygi (1995, 2000: including summary of earlier work). Gygi & Persoz (1986) used bio- and mineralostratigraphy to reconstruct the widely used scheme of platform-to-basin transition. A correlation with the French Jura was established by, e.g., Enay et al. (1988); a sequencestratigraphic interpretation has been proposed by Gygi et al. (1998). Selected intervals calibrated by high-resolution sequence stratigraphy and cyclostratigraphy have been analyzed in the PhD theses of Pittet (1996) who concentrated on Oxfordian facies and palaeoclimate, of Plunkett (1997) who studied the diagenetic history, of Dupraz (1999) who worked out the reef ecology, of Hug (2003) who focused on oncoid formation, and of Védrine (2007) who interpreted the sedimentology and palaeoecology in individual 20-kyr sequences during a large-scale transgression. The PhD work of 19th International Sedimentological Congress – Geneva – Field trip guidebook

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Stienne (2010) concerned palaeoecology and taphonomy of the carbonate-producing organisms. Colombié (2002) analysed the sedimentology, sequence- and cyclostratigraphy of the Kimmeridgian, Rameil (2005) studied the Late Kimmeridgian and Tithonian sections, Marty (2008) analyzed the Kimmeridgian dinosaur tracks and the corresponding tidal-flat environments, and Waite (2010) concentrated on nerineoid mass accumulations and palaeosols. The formation of platform and basin facies in space and time and their relationship to pre-existing structures was analyzed in detail by Allenbach (2001). Jank et al. (2006) presented a comprehensive view of Late Oxfordian to Kimmeridgian stratigraphy and palaeogeography. Based on these high-resolution studies, Strasser et al. (2012) discussed rates and synchronicity of the sedimentary processes on this platform. The terminology of formations and members used in this field guide and their biostratigraphic attribution follow Gygi (1995; Fig. 3). The major sequence boundaries are labeled according to Hardenbol et al. (1998), and the absolute ages are based on Gradstein et al. (1995).

Fenno-Scandian High Scottish Massif

LondonBrabant Massif

Franconian Platform

Lorraine Platform Armorican Massif

Lusitanian High

Rhenish Massif

Swabian Platform

Jura Platform

Paris Basin

Burgundy Platform Central Massif Aquitaine Basin

Bohemian Massif

lv He

etic

Ba

sin

Dauphinois Basin

Corbières-Provence Platform

N Tethys Basin

100 km

emerged lands

deep basin

deltaic, coastal and shallowmarine clastics

deep basin with oceanic crust

shallow-marine, mainly shales

oceanic ridge

carbonates and shales, mainly shallow-marine

present-day coastline

Fig. 2 Palaeogeographic setting of the Jura platform during the Oxfordian. Modified from Carpentier et al. (2006), based on Enay et al. (1980), Ziegler (1990), and Thierry et al. (2000).


3

Sequence boundaries

Lithostratigraphy (Swiss Jura)

Hybonotum

Ti 1

Twannbach Fm

Autissiodorensis

Kim 5

Upper Virgula Mb

Kim 4

Lower Virgula Mb Banné Mb

Kimmeridgian

Tithonian

Biostratigraphy Chronostrat. ammonite zones subzones

Eudoxus Acanthicum Divisum Hypselocyclum Platynota Planula

Galar Planula

Oxfordian

Hauffianum Bimammatum

Bimammatum Hypselum

Bifurcatus Transversarium Plicatilis

Grossouvrei Stenocycloides Rotoides / Schilli Luciaef. / Parandieri

Kim 3 Kim 2 Kim 1 Ox 8

Reuchenette Fm

Courgenay Fm

Porrentruy Mb La May Mb

Bure Mb Oolithe rousse Hauptmumienbank Mb

Ox 7 Ox 6

Vellerat Fm

Röschenz Mb

Vorbourg Mb

Ox 5

St. Ursanne Fm

Antecedens

Ox 4

Densiplicatum / Vertebr.

Ox 3

Liesberg Mb Bärschwil Fm

Verena Mb Laufen Mb

Holzfluh Mb

Steinebach Mb Balsthal Fm Effingen Mb Günsberg Wildegg Fm Mb Birmenstorf Mb Pichoux Fm (hiatus)

Birmenstorf Mb (condensed)

Fig. 3 Chronostratigraphy, biostratigraphy, and lithostratigraphy of the studied intervals. Litho- and biostratigraphic scheme after Gygi (1995, 2000), with circles indicating where biostratigraphically significant ammonites have been found. Sequence boundaries after Hardenbol et al. (1998) and Gygi et al. (1998).

Methods The sections presented here have been logged at cm-scale. Dense sampling guaranteed that even minor facies changes were detected. Thin-sections were prepared for the rock samples; marls were washed and the residue picked for microfossils. Under the optical microscope or the binocular, microfacies have been analysed using the Dunham (1962) classification and a semi-quantitative estimation of the abundance of rock constituents (Fig. 4). Special attention has been paid to sedimentary structures and to omission surfaces (Clari et al. 1995; Hillgärtner 1998), as well as to palaeosurfaces with dinosaur tracks. The sum of this sedimentological information is then used to interpret the depositional environments. For the sequence-stratigraphic interpretation of the facies evolution, the nomenclature of Vail et al. (1991) is applied. Vertical facies changes define deepening-shallowing depositional sequences, which are hierarchically stacked (example in Fig. 4). Elementary sequences are the smallest units where facies evolution indicates a cycle of environmental change, including sea-level change (Strasser et al. 1999). In some cases, there is no facies evolution discernable within a bed but marls or omission surfaces delimiting the bed suggest an environmental change (Strasser & Hillgärtner 1998). Commonly, 2 to 7 elementary sequences compose a small-scale sequence, which generally displays a deepening then shallowing trend and exhibits the relatively shallowest facies at its boundaries (Fig. 4). For example, birdseyes, microbial mats, penecontemporaneous dolomitization, and/or dinosaur tracks suggest tidal-flat environments, lithoclasts and black pebbles imply erosion of previously exposed and consolidated sediment (Strasser & Davaud 1983), and detrital quartz and plant fragments indicate input from the hinterland during low relative sea level. In some cases, however, no changes in water depth are implied but a change to more open-marine fauna and an increase in energy points to a transgressive event (e.g., at metre 13.8 in Fig. 4). There, a transgressive surface delimits the small-scale sequence rather than a sequence boundary sensu Vail et al. (1991). Four small-scale sequences make up a medium-scale sequence, which again displays a general deeping-shallowing trend of facies evolution and the relatively shallowest facies at its boundaries. Furthermore, the elementary sequences are thinner around the small-scale and medium19th International Sedimentological Congress – Geneva – Field trip guidebook

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scale sequence boundaries, which suggests reduced accommodation. Thick elementary sequences in the central parts of these sequences imply higher accommodation.

medium-scale sequences

Sequence interpretation small-scale sequences

Depositional environment

elementary sequences

black pebbles lithoclasts peloids grapestones oncoids ooids

Facies Texture

quartz dolomite iron

Field observations

Samples Metres

Constituents

ostracodes gastropods bivalves serpulids benthic foraminifera dasycladaceans sponge spicules echinoderms

The fact that most of the small-scale and medium-scale sequence boundaries can be followed over hundreds of kilometres points to an allocyclic control on sequence formation. However, also autocyclic processes (such as lateral migration of sediment bodies or reactivation of high-energy shoals) occurred and are recorded mainly on the level of the elementary sequences (Strasser 1991; Strasser & Védrine 2009; Hill et al. 2012).

?

TS SB

SB

restricted lagoon semi-restricted lagoon marsh intertidal flat restricted lagoon

?

4

15

open lagoon

TS sheltered lagoon

semi-restricted lagoon

3

10

muddy lagoon

MF


restricted lagoon semi-restricted lagoon

5

restricted lagoon

SB

? ?

2


SB

1

tidal channel restricted lagoon

TS

?

?

SB

marsh

SB

intertidal flat m M W P G

Facies Texture Sedimentary Structures birdseyes bioturbation microbial mat laminations

m M W P G

marls mudstone wackestone packstone grainstone

limestone with quartz limestone with dolomite peloids oncoids ooids lithoclasts black pebbles unidentified bioclasts echinoderms brachiopods

Relative abundance corals serpulids foraminifera green algae bivalves gastropods ostracodes plant fragments

present common

abundant very abundant

Sequence stratigraphy SB TS MF

sequence boundary (zone) transgressive surface maximum-flooding zone

Fig. 4 Example of detailed facies analysis of a part of the Kimmeridgian in the Péry-Reuchenette section. Based on this analysis, depositional environments, high-resolution sequence stratigraphy and cyclostratigraphy are interpreted (modified from Colombié 2002). For the medium-scale sequences, the grey areas indicate sequence-boundary respectively maximum-flooding zones.


5

Each section is first interpreted independently. Within the framework given by biostratigraphy and large-scale sequence stratigraphy (Fig. 3), the sections are then correlated on the level of small-scale and medium-scale depositional sequences. Correlation between platform sections and biostratigraphically well-dated basinal sections helps to constrain the stratigraphical framework (Strasser 2007). Some small- or medium-scale sequence boundaries defined in an isolated section may have to be reinterpreted and shifted by one or two elementary sequences in order to obtain a best-fit solution that satisfies the sedimentological observations as well as the general stratigraphic frame. In several cases it is not possible to attribute a small-scale or mediumscale sequence boundary to a specific bed surface: a sequence-boundary zone is then introduced, which covers the interval of relatively lowest accommodation (Montañez & Osleger 1993; Strasser et al. 1999). The same holds for maximum-flooding situations, where highest accommodation gain on the shallow platform is not always translated by a specific surface but by particularly thick beds and by the relatively most open-marine facies. All sections have been studied with the same detail as shown in Figure 4. Once the best-fit correlation of all sections is established, the small-scale sequences (which are the best defined ones in the studied sections) are counted between ammonite zone boundaries and large-scale sequence boundaries. These boundaries have been dated by Hardenbol et al. (1998) through interpolation between the ages of the stage boundaries proposed by Gradstein et al. (1995). When dividing the duration of an interval by the corresponding number of small-scale sequences, the average duration of one small-scale sequence can be estimated.

Stop 1: Late Oxfordian and Kimmeridgian platform progradation at PéryReuchenette The Oxfordian and Kimmeridgian deposits exposed in the large quarry of Péry-Reuchenette (coordinates 585.800/226.000) have been studied in detail by Pittet (1996), Allenbach (2001), Colombié (2002), and Hug (2003). During this fieldtrip, only a general overview will be given (Fig. 5). At the base of the quarry, ca. 5 m of dark grey clays of the Bärschwil Formation are overlain by about 35 m of grey micrites with marly partings belonging to the Pichoux Formation; they are capped by a hardground (SB Ox5). The overlying Effingen Member displays a general shallowingupward trend. The advancing platform is represented by patch reefs of the Günsberg Member. Upsection the reefs become denser and are finally overrun by oolites of the upper Günsberg Member. The major transgression at the base of the Hauptmumienbank and Steinebach members then allowed for enhanced carbonate production on the platform. It is marked by a distinct lithological change to lagoonal deposits. Abundant carbonate production on the platform resulted in a rapid progradation and a southward shift of the reef belt on the platform margin (Gygi & Persoz 1986). Despite of periodic sea-level falls creating sequence boundaries Ox7 and Ox8, the general transgressive trend continued, and massive ooid dunes dominated on the platform margin in the latest Oxfordian (Verena Member). During the Kimmeridgian, the platform margin still prograded towards the south, and thick-bedded, mainly lagoonal facies with peritidal caps developed in the platform interior (Reuchenette Formation).


6

N

S

Fig. 5 Simplified sketch of the Péry-Reuchenette quarry, looking east.

Stop 2: Late Oxfordian sequence- and cyclostratigraphy in the Gorges de Court On the southern flank of the Graitery anticline, northeast of the village of Court, the Late Oxfordian and the Kimmeridgian are well exposed (coordinates 592.920/232.970). Along a footpath running along the Birs river, the interval between the Oolithe rousse and Verena members can be observed (Fig. 6). This section has been studied in detail by Hug (2003). Based on the lithostratigraphic and biostratigraphic frame furnished by Gygi & Persoz (1986) and Gygi (1995, 2000), and on the detailed analyses of stacking pattern and facies evolution, a sequence-stratigraphic and cyclostratigraphic interpretation for the Gorges de Court is proposed (Fig. 7). This interpretation is consistent with the other sections studied (e.g., Péry-Reuchenette; Fig. 7). However, superposition of higher-frequency sea-level fluctuations on a long-term trend of sea-level change led to repetition of diagnostic surfaces, defining sequence-boundary zones (Montañez & Osleger 1993; Strasser et al. 1999). Relatively fastest rise of sea level either caused distinct maximum-flooding surfaces (which again may be repeated defining a maximum-flooding zone), or is recorded by the relatively deepest or most open-marine facies. Major transgressive surfaces generally correlate well from one section to another. Comparing the interpretation of the studied sections with the sequence stratigraphy of Hardenbol et al. (1998) established in European basins, sequence boundaries Ox6, Ox7, and Ox8 can easily be identified. On the other hand, maximum-flooding surfaces or intervals appear to be shifted by one or two small-scale sequences. This again may be due to superposition of several frequencies of sea-level fluctuations. Depending on the morphology of the platform and the basin, the relatively deepest, most marine, or condensed facies will thus not appear at exactly the same time in all locations, but within an interval related to the relatively fastest rise of long-term sea level. The numerical ages attributed by Hardenbol et al. (1998) to Ox6, Ox7, and Ox8 allow estimating the duration of the small- and medium-scale sequences identified in the studied outcrops, assuming that each sequence of a given order had the same duration: about 100 kyr for the smallscale sequences, and about 400 kyr for the medium-scale ones.


7

Field aspect

Sequence- and cyclostratigraphy

Facies samples

Verena M.

elementary

?

mediumscale

SB

La May Member

20 m

smallscale

MF

?

10

Hauptmumienbank Ool. rousse

? ?

SB

mMWP G F B

Fig. 6

Detailed sequence- and cyclostratigraphic interpretation of a part of the Gorges de Court section (legend in Fig. 4).


8

Fig. 7 Sequence-stratigraphic and cyclostratigraphic interpretations of the Court and Péry-Reuchenette sections and correlation with the sequences of Hardenbol et al. (1998). For legend refer to Figure 4. Ool.R. = Oolithe rousse. Court section based on Hug (2003), Péry-Reuchenette section on Pittet (1996) and Hug (2003).


9

Stop 3: Bedding surfaces at the tunnel entrance, Gorges de Court Thanks to the construction of the highway A16 tunnel through the Graitery anticline, the Kimmeridgian – Tithonian transition beds (including the nerineoid mass accumulation of the “Grenznerineenbank”) are well exposed above the southern tunnel entrance. Several bedding planes exhibit various types of sedimentary structures (different kinds of microbial mats, desiccation cracks, firmgrounds, and hardgrounds; Fig. 8). Also visible are some dinosaur (possibly sauropod) tracks in cross-sectional view and on some of the bedding planes (palaeosurfaces). However, so far no well-preserved dinosaur tracks or trackways have been reported from this locality. Another interesting feature is an empty karst cavity of Eocene or Miocene age.

Fig. 8 Desiccation cracks on palaeosurface initially covered with a microbial mat (left) and oyster-encrusted hardground (right) at Gorges de Court (photos: D. Marty)

Stop 4: Coral carpets and ooid sandwave at Hautes-Roches Along a forest path close to the hamlet of Hautes-Roches, the transgression of the Steinebach Member over the Günsberg Member is clearly visible (coordinates 594.950/238.250). The section has been studied in detail by Dupraz (1999) and Védrine (2007). Stienne (2010) analyzed the taphonomy of the lagoonal and reefal organisms. After the marly facies of a protected lagoon (Günsberg Member), three growth phases of coral carpets are found (Fig. 9). The corals show intense perforation by boring bivalves (Gastrochaenolites trace fossil) and are encrusted by microbialites. Reworking by storm waves produced coral rubble that again was coated by microbialites. After a sharp discontinuity (wave-cut terrace ?), ooids, echinoderms, and bivalves accumulated in a thin layer. Sedimentation was interrupted again before a large sandwave composed of ooids and bioclasts migrated over the site. Ooid bars dominate the outcrop for the next 4 meters. This clearly indicates that a transgression created accommodation and opened the sedimentary system to the high energy of tidal currents.


10

Fig. 9 Detail of the Hautes-Roches section (Stienne 2010). eHD: early highstand deposits; LHD: late highstand deposits; TD: transgressive deposits.

Stop 5: Kimmeridgian Banné Marls close to Porrentruy This new outcrop has been created in 2014 south of Porrentruy close to the type locality of the Banné Member and is open for the interested public to dig for fossils in the frame of the valorization project JURASSICA Museum (see also: jurassica.ch). The Banné Member of the Reuchenette Formation was defined by Gygi in 2000 (Fig. 3), and in older literature it is also known as “Marnes à Ptérocères“. It is a ca. 10 m thick interval of highly fossiliferous calcareous marls and marly limestones deposited in a shallow, internal lagoon. It is notably rich in marine invertebrates (mainly bivalves, gastropods, brachiopods). Between 2001 and 2007, the “Palaeontology A16”, a palaeontological survey project in charge of the documentation and safeguarding of palaeontological heritage prior to the construction of highway A16 (Transjurane), carried out systematic excavations in the Banné Member near Porrentruy. Based on 19th International Sedimentological Congress – Geneva – Field trip guidebook

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bulk sampling and detailed documentation of several successive beds of one square meter, species richness, abundance and commonness were used to characterize the vertical evolution of the invertebrate assemblages (Hicks 2006; Richardt 2006). Larger surfaces were also excavated in order to improve the completeness of the fossil record, recovering uncommon taxa (echinoids, ammonites, fishes, turtles, and crocodiles). A systematic sampling was performed for mineralogical and sedimentological analyses using X-ray diffraction and microfacies descriptions (Ayer et al. 2008). Jens Koppka studied the Banné Member in detail: The transgressional first phase is usually characterised by coarse grained, partially glauconitic marls, invertebrate lumachelles and grey, marly or micritic limestones situated above the distinct basal hardground frequently bored by Gastrochaenolites isp. The bivalve fauna at the base is less diverse than in the middle part of the member, but some rare species can be found only in these beds. The attachment areas of the small oyster Nanogyra nana frequently shows perfect imprints of the calcareous algae Goniolina geometrica, indicating the presence of algal meadows (Koppka in prep.). Rare corals and regular and irregular echinoids (Pygurus, Pseudocidaris Hemicidaris) together with debris of ophiourids imply fully marine conditions. The water depth might have ranged between 5 and 15 m. The middle part of the Banné Member is characterised by an intercalation of fossiliferous marly limestone horizons separated by soft marls and yields the highest diversity of bivalves with more than 70 species. The environment was fully marine, calm, and situated below the fair-weather wave base, at a water depth of 15 to 25 m. The majority of the bivalve fauna is preserved with both shells, even epibenthic taxa, which disarticulate easily under influence of currents. The diversity of epibenthic bivalves (Camptonectes, Chlamys, Eopecten, Ctenolima, Arcomytilus, Falcimytilus, Modiolus, Pinna, Gervillella, Costigervillia, Pteria, Isognomon, Mytiliceramus, Praeexogyra) is the highest in the whole member. Frequent are also large specimens of Trichites matheyi, usually encrusted on both valves by Actinostreon and Nanogyra nana and nearly always strongly bioeroded by grazing regular echinoids (Gnathichnus pentax) and penetrated by the burrowing bivalve Lithophaga. Endobenthic taxa such as Pholadomya protei, Ceratomya excentrica, Myopholas and Thracia become frequent, less deep burrowing bivalves such as Trigonia, Integricardium, Ceratomyopsis, Mesomiltha, Protocardia are common. The gastropod Harpagodes thirriae can be found in numerous specimens, in cases completely overgrown by Actionostreon gregareum. In the upper part, 2 m of yellowish-brown clays and marls seem to have been quickly deposited as bivalves are rare and less diverse, even though in the lower third of the clays several marine bivalves such as small Trichites and clusters of Actinostreon and Nanogyra nana can still be found. Water depth became shallower towards the top as proven by rizoliths that imply a former soil formation. Decompacted, the upper clays were more than 10 m thick and accommodation was probably quickly filled by an increased supply of eroded terrestrial sediment.

Stop 6: Dinotec Porrentruy Important dinosaur track discoveries were made along the course of the Transjurane highway A16. Between 2002 and 2011, the “Palaeontology A16” systematically excavated six large Late Kimmeridgian dinosaur tracksites near Porrentruy. Additionally, financed by the valorisation project JURASSICA Museum, a number of smaller tracksites within the city of Porrentruy have been excavated. On highway A16, 68 ichnoassemblages corresponding to a total surface of 17’917 m2 were excavated, revealing 13’900 tracks including 250 sauropod trackways and 387 trackways of tridactyl, bipedal dinosaurs (mostly theropods). All these ichnoassemblages were documented with standard ichnological methods (e.g., track outline drawings, measuring of trackway parameters), and also with 3D imaging technologies (laser-scanning, photogrammetry). The 19th International Sedimentological Congress – Geneva – Field trip guidebook

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systematic acquisition of such a wealth of track data can be considered as exemplary in the field of vertebrate ichnology, and the Jura Mountains have become one of the classical dinosaur track regions, notably for epicontinental carbonate platform deposits. All tracksites are today destroyed and/or covered by the highway. However, financed by the valorisation project JURASSICA Museum, an important tracksite called Dinotec was excavated in 2011 prior to the construction of the School of Engineering within the city of Porrentruy, and a part of this tracksite has been made accessible to the public in 2013 (Fig 10). Over a hundred in-situ tracks of sauropods and theropods can be observed beneath glass covers in the courtyard of the school. At night, horizontal lighting enhances the relief of the tracks, and additional state-of-the-art communication media including augmented reality complete this innovative exhibition. A detailed analysis and interpretation of the prints and trackways has been given by Marty (2008) and Marty et al. (2010). Examples of trackways and their interpretation in terms of locomotion are shown in Figure 11. The expression of the tracks and their preservation potential is strongly dependent on the substrate (Fig. 12; Marty et al. 2009).

Fig. 10 Dinotec at Porrentruy. Right: Megalosauripus-type tridactyl track of a large carnivor theropod dinosaur ('Allosaurus') (Photos A. Strasser).


13

14

= = = =

left pes left manus right pes right manus

left manus rotation [°]


[WAM/MW]- [WAP/PL]-ratio ratio [ ] [WAM/MW]-ratio

calculated pes trackway ratio [%] pes trackway gauge cf. Romano et al. (2007)

[WAP/PL]ratio [ ]

22,5

40,6

1m

1,46 37,0 medium-gauge

3,34

N

28,0

3,7

RP2

0,44

WAP=54,6 / WAM=68,1

37,5 20,4

right pes rotation [°]

right manus rotation [°]

LP2

RM2

RP3

RM3

RP4

RM4

RP5

RM5

0

LP3

38,4

6,2

1m

RP2

RM2

RP3

RM3 eroded

RP4

RM4

RP5

RM5

8,3 31,0

1,28

35,5 medium-gauge

3,37

0,38

WAP=50,0 / WAM=67,9

20,2

39,0

LM2

LM3

LP4

LM4

LP5

LM5

LP6

0

LP2

LM2

8,8 29,7

29,0

30,5

1m

N

RP2

RM2

RP3

RM3

RP4

2,30

27,3 wide-gauge

3,98

0,58

WAP=68,9 / WAM=76,2

19,1

30,0

LP3

LM3

LP4

LM4

LP5

RP5

RM5

C

LM6

B

pes-dominated to quadr.

S10 (3,9 km/h)

quadrupedal

S2 (4,6 km/h)

28,3 12,7

20,1

1m

no value no value

8,5

N

RP2

RM2

RP3

RP4

RP5

RP6

1,34

32,7 wide-gauge

no value no value

WAP=37,8 / WAM=no value

0

LP2

E173 ?LP3

LP4

LM4

LP5

LM5

LP6

E202 ?LM6

D

pes-dominated

S11 (3,4 km/h)

RP3

52,7

16,0

50 cm

LP4

LP3

RP4

RP5

LP6

72,5

22,1

RM4

RM5

RP6

1,31

33,0 wide-gauge

no value no value

WAP=25,7 / WAM=no value

11,8

19,6

0

LM3

LP5

LM6

LM4

E

pes-dominated

S12 (4,7 km/h)

N

width of the angulation pattern [cm] pes (WAP) / manus (WAM)

left pes rotation [°]

pes length (PL) [cm]

0

LP3

LM2

LM3

LP4

LM4

LP5

LM5

LP6

A

quadrupedal

S1 (3,6 km/h)

0

LP2

19,0

18,0

50 cm

RP1

RM1

RP2

RM2

RP3

RM3

RP4

RM4

RP5

20,0 32,0

1,22

34,7 wide-gauge

2,68

0,46

WAP=27,0 / WAM=39,2

14,6

22,1

LM2

LP3

LM3

LP4

LM4

E194

LP5

F

S13 (4,0 km/h)

pes-dominated to quadr.

N

manus width (MW) [cm]

calculated ratios and trackway gauge

mean track and trackway parameters

S1 & S2; S10 & S11; and S12 & 13 are drawn to approximately the same scale

S1 and S2 feature shallow tracks generally without displacement rims; S10-S13 deeper tracks mostly with displ. rims

S12 and S13 are parallel, located side by side, and are part of sauropod group 2 heading W

S10 and S11 are parallel, located side by side, and are part of sauropod group 1 heading N-NNE

LP LM RP RM

internal track outline or true track sensu stricto

external track outline or crest of the displacement rim

exterior limit of the displacement rim

Trackway outline drawings

trackway pattern

N

Trackway (speed)

124 – Chapter 5

Fig. 11 Chevenez—Combe Ronde tracksite, main track level. Outline drawings (not to scale) of representative parts of selected trackways and indication of some mean track and trackway parameters. Note that trackway S10 (C) has the widest gauge, which is confirmed by the pes trackway ratio and the [WAP/PL]-ratio. Note also the striking exterior position of the left manus tracks, and the interior position of the right manus tracks in trackway S1 (A) and in a similar way but less pronounced in S2 (B). Trackway S12 (E) with the smallest tracks features a striking lateral and exterior position of some manus tracks with regard to the pes, and the most pronounced manus outward rotation of all trackways. In trackway S13(F) the track E194 in front of LM4 is one of the best preserved manus tracks of the main track level. It is most probably a double imprint of the left manus, because an affiliation with the trackway S11, which is in close proximity but heading in an other direction, is unlikely (Marty 2008).

15

deep tracks

ts

° ° ° °


homogeneous track fills, trapping of coarse material

weathered tracks, levelled displ. rims

lack of (internal) overtracks

ts

intermediate (~20-60%) higher intertidal (mud)flat

arid

humid

ts

° modified true track ° brecciation below track ° homogeneous track fill

consolidated layer

° shallow true track ° brecciation below track ° homogeneous track fill

consolidated layer

ts

true track with displ. rims stack of undertracks stack of internal overtracks overtracks with broad & flat displ. rims

consolidated layer

° ° ° °

° true tracks with well-developed displ. rims ° stack of undertracks ° stack of overtracks with broad & flat displ. rims

ts

high (~>60%) supratidal flat / marsh

modified true tracks

undertracks and overtracks with broad & flat displ. rims

(stacks of) internal overtracks

true tracks on tracked surface, shallow true tracks

underprint with well-developed displ. rims stack of internal overtracks shallow overtrack without displ. rims homogeneous track fill

shallow overtracks without displ. rims

° ° ° °

consolidated layer

° underprint with well-developed displ. rims ° shallow overtrack without displ. rims ° homogeneous track fill

consolidated layer

ts

deep underprint with well-developed displ. rims displ. rims may be levelled lack of overtracks homogeneous track fill with trapping of coarser material

deep tracks, underprints, deep true tracks

° weathered track with levelled displ. rims ° homogeneous track fill with trapping of coarser material ° lack of overtracks

ts

° deep underprint with weakly-developed or without displ. rims ° homogeneous track fill with trapping of coarser material ° lack of overtracks

° deep track without displ. rims ° collapsed track ° homogeneous track fill

ts

low (~