CENOZOIC

RESEARCH

Fossil trunk conservation of “Beuchille“

The fossil tree trunks of the site DEL-BEU are unique paleontological objects regarding their preservation (70% of organic matter preserved, mostly lignine and maybe a part of proteins). Problems of conservation linked primarily to oxygene and phenomena of pyritisation make them particularly unstable (highly corrosive sulfuric acid production). The trunks of average size were treated with PEG (polyethylene glycol), then with the resin Epoxy and the results are convincing for instant.

On the other hand, for the largest tree found (Photo 1) at “Beuchille” (6x1m), this solution was not possible because of its dimensions (PEG penetration). A solution had to be found temporarly to avoid its degradation. This method consists of regular applications of bicarbonate of soda in order to neutralize the acidity temporarily and thus the disintegration of the trunk.

Photo 1: “Beuchille“ trunk.

In addition, contacts were established with Mr. Q. K. Tran of the laboratory Arc Nucleart of Grenoble, specialist in the fossil wood conservation, in order to find a method of suitable final safeguarding. His conservation study is almost ready, and treatment will begin, probably based on silicification methods.

Karst phenomena with gas emanations in Early Oligocene conglomerates: risks within a highway context (Jura, Switzerland).

During the construction of the A16 motorway, four cavities were discovered in the Early Oligocene carbonate conglomerates of the Jura mountains, Northwestern Switzerland (Photo 2). One cavity was particularly interesting because of its size and gas emanations. As this cavity was located at the edge of an acceleration lance of the motorway, there was a risk of subsidence/collapse and hence concern for the safety of personnel.

Photo 2: Karst of “L'Oiselier“.

The cave topography was established by the local speleology club using a laser distometer to measure the shape of the cavity conduits at discrete intervals. These points were then extrapolated to give a vertical and horizontal projection of the cave (Fig.1, Lapaire et al. 2006). Atmospheric pressure, temperature, humidity and radon were measured continuously, and periodic mesurements of CO2, O2, H2S, CO, CH4 and LIE (lower limit of explosivity) were undertaken. These analyses highlighted some anomalies, as a deficit in oxygen, concentrations of methane reaching at times the lower limit of explosivity recommended, temporary concentrations of CO2 below the average exposure limit values recommended, and high concentrations of radon (which are however not exceptional for a cave).

Although radon is normally produced by the degasification of percolation waters (Surbeck 1990, Von Gunten et al. 1996), the origin of the other gases was likely to be related to the chemical decomposition of old organic deposits (Permo-Carboniferous coal basins). And as this cave was located near a farm, the CO2 could also be associated with animal excrement percolating into the ground. Moreover it was considered that the gases measured in the caves could originate from two nearby public dumping grounds as the decomposition of domestic waste is known to produce carbon dioxide and methane.

Despite the scientific importance of this cave, the urgent economic necessity to progress the highway works led to the decision that it should be infilled. In order to allow the continuation of the measurements, gas monitoring tubes have been placed. A potential new study would give more information about the origin of the gases and could elucidate a general phenomenon of degasification from Permo-Carboniferous coal basins in Europe. New discoveries could improve our understanding of these geological structures, particularly in terms of their influence on underground water transfer.

Molasse, karsts and tectonics : an integrated approach of the relief evolution in the Northern Jura.

This study is currently in preparation, however preliminary results were already published by Becker & Braillard (2004) and Braillard (2006).

The Jura canton is particularly suited to reconstruct the relief of the Jura Mountains.

Numerous Cenozoïc formations (Molasse) are present throughout the investigated area. Their litho- and biostratigraphical data allow the chronological calibration of the various steps in relief evolution.

Moreover, this area is characterised by the presence of the Tabular Jura in the north (Ajoie) and the folded Jura in the south (Delémont Basin), which makes it particularly representative for the whole Jura mountain range.

From a more general structural point, the Ajoie region can be considered as a triple point: it constitutes 1) the east ending of the Rhine-Bresse Transfer Zone, 2) the southern limit of the Rhine Graben and 3) the most northern part of the Jura mountain range, which was the northern limit of the Molasse Basin during the Oligo-Miocene.

This exceptional geological setting was already of interest to many authors. Based on the knowledge of stratigraphy at that time, most of these previous authors explained the formation of the Jura relief as a three steps tectonic process:


1) An upper Cretaceous to lower Eocene gentle uplift, followed by a peneplanation.
2) An Oligocene rifting (Rhine Graben formation), which southern extension led to the formation of small grabens in the Ajoie Tabular Jura.
3) A classical Pliocene Jura folding.


According to new stratigraphical data, an alternative model for the formation of the Jura relief can be suggested. Here we integrate new data from the tectonic and karst (formation and fillings) to propose five phases (Fig.2):

1) An upper Eocene gentle uplift of both the tabular and folded Jura.
2) Oligocene grabens of the Ajoie area induced by the Rhine Graben formation.
3) A lower Miocene general uplift, responsible for a general sedimentary hiatus.
4) A Mio-Pliocene folding of the Jura mountain range.
5) An upper Pliocene to Pleistocene reactivation of basement faults (thick-skinned tectonic), which formed small en-échelon anticlines in the tabular Jura.

Current research should further refine this reconstruction of the Jura relief evolution, especially the integration of new karstic, litho- and biostratigraphical data.

Exceptionnal fossils

Photo 3: Rhinocerotidae sacrum (“Beuchille“).

Fig.3: Iberomeryx minor lower jaw (“Beuchille”) (modified from Becker & Lapaire 2004).

Fig.4: Upper molar of Anthracotherium sp.1 (“Beuchille“). © SAP 2004.

Rhinocerotoidea and clay minerals of the Jura Molasse: implications for paleoecology and paleoclimates

The Jura Molasse, in which most remains of the studied Rhinocerotoidea remains were found, constitutes a well preserved distal part of the Molasse Basin. This sedimentary series covered a major part of the Jura chain during the Oligocene and Miocene. Today, it is only sporadically found trapped in valleys or preserved in karst fillings. During the Oligo-Miocene period, the Jura region was considerably affected by hydrodynamic, tectonic and climatic changes as reflected by the marked variations of the heavy mineral spectra and the composition of the clay mineral assemblages (Becker 2003).

The taxonomy of the Rhinocerotoidea from the Oligo-Miocene of northern Switzerland is partially revised. A biostratigraphical and paleoecological interpretation of this group is proposed. Results show that trends in diversity and anatomy of the taxa are controlled by paleoenvironmental changes. The recorded mineralogical changes and the evolution of Rhinocerotoidea seem to be controlled by regional or global tectonic and/or climatic events (Fig.5 ; Becker 2003 and 2004).

During the Middle Eocene, only small and cursorial primitive forms of Rhinocerotoidea evolve in a partially open forested environment. During the Late Eocene, just before the “Grande Coupure”, none Rhinocerotoidea has been reported in Switzerland. The forests become more dense and the climatic conditions remain warm and wet.

The beginning of the Oligocene matches with the occurrence of the first true Rhinocerotidae and the reopening of the forested environments. The climate seems to deteriorate and become more arid. The Rupelian/Chattian boundary is marked by a tendency to cooling. Chattian Rhinocerotidae present weak, but perceptible predispositions to brachypody and hypsodonty. The climate continues to deteriorate and is marked by a crisis at the terminal Chattian as shown by the abrupt disappearance of palm trees and Taxodiaceae.

From the base of the Miocene, a renewal within the Rhinocerotidae is observed. The environmental conditions improve and offer a wide range of biotopes. At the “Proboscidean Datum” (Burdigalian/Langhian boundary), the Rhinocerotidae are strongly perturbed by Asian migrants, while again the climate changes in a more continental and arid way due to closure of the Tethys. During the Late Serravalian, a return to humid conditions is observed. The last recorded Miocene stratigraphic interval corresponds to the mammal zone MN9. Its lower limit is characterized by the “Hippotherium Datum”, which opens the migratory corridor of the Bering strait. New migrants from Asia and Africa renew the Rhinocerotidae. The environment remains forested and the relatively warm and wet climate of the Late Serravalian persists.

The macromammalian fauna of Rickenbach (Solothurn), Late Chattian, Swiss Molasse:
biostratigraphy, paleoecology and paleoclimate

This study is currently in preparation, however preliminary results were already published by (Emery et al. 2004, 2007).

The Rickenbach quarry is located in the canton of Solothurn close to Wangen (Swiss coordinates: 632200 / 242300). It belongs to the Lower Freshwater Molasse (USM) and more precisely to the “Aarwanger Molasse”. The site is dated by micromammals and has been chosen to be the reference locality for the MP29 international mammal zone (Late Chattian).

The first excavations going up in 1905 were carried out by Dr Stehlin, Dr Martin and J. Stuber (see Martin 1906 and the “Cadastre des gisements de mammifères fossiles” of Basle). The collections are stored mainly in the Museum of Basel, Solothurn and Olten. The goal of this work is to revise the material of the macromammals in order to reconstitute various ecological parameters such as the diversity, the weight, the size and the diet to propose hypothesis concerning the paleoecology and the paleoclimate.

The small mammal fauna (more than 15 taxa) have been already described in several publications and synthesized in Engesser & Mödden (1997).

The (re)discovery of the very rich collection (more than 2000 pieces) stored the Museum Olten allowed a revision of the ungulate list of Rickenbach. (according to the studies of Stehlin 1914; Brunet 1979; Michel 1983; Engesser & Mödden 1997; Becker 2003). The ungulate fauna can be preliminary assigned now to the following taxa: Ronzotherium romani, Rhinocerotidae sp. 1, Microbunodon minimum, Cephalogale sp.1, Cephalogale sp.2, Anthracotherium cf. magnum, Propalaeochoerus sp., Caenotherium sp.1, Caenotherium sp.2, Amphitragulus sp.

In a second phase, the detailed study of the Ronzothere of Rickenbach confirms its attribution to Ronzotherium romani and informs us about his ecology. The size of the species can be evaluated thanks to the astragalus. The weight is estimated according to the method of Legendre (1989) according to the surface of the m1. The slenderness ratio is interpreted with the index of slenderness ratio on MtIII.

We can deduce from the methods described above that Ronzotherium romani presents an anatomical type very close to Ronzotherium filholi to which it succeeds. Even if he was probably a browser, he presents however more grazing affinities and could show a better adaptation to drier environments. He compensates his light loss of mobility by a weak increase of his bodymass. He would be, just like Ronzotherium filholi, an inhabitant of the savannas living without predatory to his size.

This study confirms the general results of Becker (2003 and 2004) assuming open woodland in a semi-arid climate for this time period.

The discovery of a juvenile Diaceratherium lemanense (Rhinocerotidae) from the Aquitanian Molasse of Switzerland

A skull of a juvenile rhinocerotid from the Swiss locality of Eschenbach (Eastern Swiss Molasse Basin) has been reported and studied by Becker et al. (2006a). Computed tomography revealed the presence of the unerupted adult teeth P4 and M3 and facilitated their three dimensional virtual reconstruction. Typical morphological features of this skull (postglenoid and posttympanic apophyses in contact, deep nasal opening, very slight occipital elevation, molar lingual cingulum absent) (Fig.6) and the comparison with other European specimens, thanks to the virtually extracted adult teeth, ascribed the Eschenbach specimen to Diaceratherium lemanense (Pomel 1853).

The genus Diaceratherium is restricted to the western European basins, except the occurrence of a Diaceratherium cf. lamilloquense in the Upper Oligocene lignite deposits of Nong Ya Plong Tertiary Basin in Central Thailand (Marivaux et al. 2004). This specimen could be the first representative of the group, whereas the first occurrence in Europe is D. lamilloquense of Lamilloque (France), mammal zone MP29, at the beginning of a Late Oligocene regional climatic crisis (Berger 1990, 1992a; Becker 2003). During MN1 (Early Miocene), Diaceratherium shows a relatively high diversity, it is represented by three species (D. lemanense, D. asphaltense, D. tomerdingense) spreading from southwestern France to eastern Switzerland and southern Germany. D. lemanense probably ranges from MP30 (latest Oligocene) with D. aff. lemanense (Thezel, France) to the base of MN2 (D. lemanense of Montaigu-le-Blin, France) and appears as the dominating form during MN1. During MN2 Diaceratherium is still represented by three species (D. lemanense, D. aginense, D. cf. aurelianense). At this time, it shows its widest geographic repartition, spreading also into the Iberian Peninsula and northwestern Germany. Since MN3, only D. aurelianense persists, essentially in the Iberian Peninsula and in France, whereas the genus disappears in Germany in MN3 and in Switzerland in MN4. At the end of MN4 (latest Early Miocene), just after the Proboscidean event, Diaceratherium definitively disappears to be replaced in MN6 by the first true European Brachypotherium (Becker 2003).

Consequently, the reported Eschenbach specimen appears as a new biostratigraphical pinpoint within the “Granitische Molasse Formation”, upper part of the Lower Freshwater Molasse (USM) of the Eastern Molasse Basin of Switzerland, and clearly indicates an Early Miocene age for this new locality. Moreover, the Eschenbach specimen is the eastern most occurrence of D. lemanense, in agreement with the observed eastern paleobiogeographic extension of Diaceratherium in MN1 and at the base of MN2. Consequently the Diaceratherium species could shed light to the Oligocene-Miocene large mammal turnovers and climatic events.

Terrestrial palaeoecosystems of large mammals from the Early Oligocene to Early Miocene Switzerland

Numerous authors have studied the litho- and biostratigraphy of the small mammal localities within the Molasse basin in Switzerland, but none of them has recently focused their works on large mammal fossils, yet very valuable. These localities require an update because of the lack of biometrical and taxonomical data. Furthermore, some small mammal localities have not been studied at all for what concerns large mammals.

During the Palaeogene and the beginning of the Neogene, the global climate changes considerably. The Late Eocene is characterized by a tropical and humid climate, but an aridification of the environments defined by a seasonal contrast can be observed in the Early Rupelian (Oligocene). In the Late Rupelian, the increasing humidity becomes stable whilst temperatures decrease. In the Late Oligocene, the warm and wet conditions evolve to a warm and drier climate, and define the Oligocene/Miocene boundary.

All these changes influence the fauna and flora evolution. For example, large mammal body mass is bound to the general characteristics of the environments, and these evolutions can be observed particularly in the ungulate community: the climatic stresses of the Oligocene lead to changes in the diversity of the perissodactyls and artiodactyls. All around the world, the evolutionary trends of the ecological parameters of the Rhinocerotoidea show considerable changes. Furthermore, the European large mammal evolution in general records important structural modifications. According to the floral data, a renewal can be observed at the end of the Oligocene and at the beginning of the Miocene, characterizing the important climatic event of the Oligocene/Miocene boundary.

The main goal of this study is to characterize climates and environments during the Oligocene, as well as climatic and environmental changes at the end of the Oligocene, to analyse the faunal renewal across the Oligocene/Miocene boundary, and to define the importance of the biotic/abiotic events as well as the influences of the global parameters on local parameters. In order to quantify and qualify this event, a special focus will be set on decisive large mammal genera of the Oligocene and Early Miocene, and also on lineages present on both sides of the Oligocene/Miocene boundary (Fig.7, Becker et al. 2006b).

Then the different palaeoecologaical parameters will be calculated and compared with extant species, and biogeochemical analyses will also be performed on herbivorous mammal tooth enamel and on reptile remains, in order to bring complementary information for the estimation of the palaeotemperatures and for palaeoenvironmental reconstructions.

Transgression and regression of the UMM in the Swiss Jura mountains during the Palaeogene:
a palaeoecological model based on ostracods and X-Ray Diffraction on sediments

The marine deposits of the stratigraphical Group Septarienton (Paleogene), which crop out in several synclines of the Swiss Jura Mountains (Picot 2002, Becker 2003), have been subjected to detail sedimentological and palaeontological studies. Overall stratigraphical columns have been built for the synclines of Delémont and Laufen, and the Ajoie basin. Different fossil groups including foraminifers, ostracods, fishes, pollens and spores have been studied in terms of taxonomy, biostratigraphy and palaeoecology.

Palaeoenvironmental and palaeoclimatical reconstruction is based mainly on the studies of sedimentology, ostracods and X-Ray Diffraction on sediments. Different palaeoecological statistical tools like PCA and taxonomical indices (Clarke & Warwick 2001) are used on ostracods to observe the repartition and the evolution of the associations with the depositional environments. Theses studies lead to a better understanding of Paleogene palaeoenvironments and their evolution (Fig.8, Picot et al. 2006): the transgressive sequence is very abrupt and floods immediately the Mesozoic bedrock, leading to a coastal marine environment. The regressive sequence shows a progressive evolution from outer marine to brackish continental palaeoenvironments.

New biostratigraphical data allow, for the first time, the dating of the rhinish UMM transgression and regression in this area, corresponding to the stratigraphical nannofossil biozone NP22. Clay analyze shows an increase of the climate seasonality along the section. Heavy mineral study shows that the draining systems was constituted of different sources of materials, coming from the Scandinavian Shield, the Massif Central zone, and from the Vosges and the Black Forest areas, but without inputs from the Alpine zone. The transgression appears to be synchronous in the whole area whereas the regression is clearly diachronous. The regression shows that the shoreline moved westwards, suggesting a connection between the south of the Rhine Graben and the Bresse Graben.