Paul Bernier

Role of microbial mats in the fossilization of soft tissues

It has been speculated that microbial mats are an important agent in the fossilization of soft tissues, particularly when apatite (Ca 5 [CO 3 , PO 4 ] 3 [OH, F]) is involved. This has been tested by chemical analyses of the Jurassic limestones of Cerin, France, where phosphatized soft tissues are abundant and are associated with unequivocal microbial mats. The sedimentary distribution of P, K, and Fe following deposition was controlled by the presence of the mats. P concentrations in the mats may approach 2.5 times those elsewhere in the sediment. The highest P concentrations correlate with the occurrence of phosphatized soft tissues. This is the first analytical evidence to demonstrate a fundamental role for microbial mats in the preservation of soft-bodied fossils.

Cathodoluminescence of carbonate-cemented Holocene beachrock from the Togo coastline (West Africa): an approach to early diagenesis

Carbonate-cemented Holocene beachrock outcrops sporadically along more than 100 km of the Togo and Benin coasts. The sands are siliciclastic with subsidiary carbonate skeletal fragments and intraclasts. 14C radiometric dating indicates the sand deposits have formed within the last 5000 years. Beachrock has been indurated in phreatic environments undergoing, afterwards, several stages of burial and subaerial exposure. Cathodoluminescence (CL) proved a useful tool in unravelling the intricate cementation of this beachrock which can be subdivided into three stages. Firstly, magnesian calcite was precipitated in a marine-phreatic active zone. Very dull orange and very dull blue colours emitted in isopachous rims of needle-like crystals and peloidal micrite (CL1-fabric) reveal different Eh and pH precipitating conditions in this environment. Secondly, bright yellow-orange luminescing acicular and equant spar cement (CL2-fabric) is interpreted to have formed in a mixed-water phreatic zone. The third stage of cementation occurred dominantly in the landward part of the beachrock and accompanied neomorphism of the earlier marine cements. The resultant CL3-fabric, dull blue, medium orange luminescing equant spar is typical of continental fresh-water phreatic zones. The progression from marine to fresh-water pore fillings accompanied sand-bar progradation during a stable sea-level stage. Ultimately there was erosion stage of the sand-bar deposits which led to subaerial exposure and partial erosion of the beachrock. Recognition of the effects of repeated shoreline progradation during the early diagenesis of this Holocene beachrock indicates the potential value of diagenetic studies in aiding recognition of marine regressions and transgressions in the geological record.

A giant Upper Jurassic turtle revealed by its trackways

Exceptional fossilization of large tetrapod swimming traces occurs in the Cerin Lagerstatte (Jura Mountains, France). These trackways are imprinted in Jurassic (Late Kimmeridgian) lagoonal fine-grained limestones and are attributed to giant turtles, which swam with a simultaneous movement of their forelimbs like the modern ones. These turtles swam in very shallow waters close to land, perhaps near a nesting area. As a major consequence, these new ichnologic data place the origin of true large marine turtles during the Jurassic period and not during the Cretaceous period as previously considered on the basis of skeletal remains.

Coastal progradation and very early diagenesis of ultramafic sands as a result of rubble discharge from asbestos excavations (northern Corsica, western Mediterranean)

Abstract The western coast of Cape Corse in northern Corsica is a remarkable area by virtue of its geological, biological and landscape diversity. Asbestos extraction between 1948 and 1965 however at Canari Mine, has modified the natural rocky escarpments, cutting the mountain into steps and has altered the coastal and marine zones from Punta di Canella to Farinole. Albo harbour was filled with rubble discharging directly to the sea, and the coast prograded 400 m after 4 years between 1954 and 1958. Artificial shores of up to 300 m in width appeared at the bottom of existing steep cliffs over a distance of more than 5 km between 1948 and 1973. The Posidonia seagrass was buried by the introduction of debris. Since June 1965, the mine is closed and coastal modification results from material movement from north to south. As an exception, Campana beach appeared in the northern part of the discharge area in 1973. The sediment on Nonza beach already displays cemented slabs that attest to very early diagenesis. This particular environment of ultramafic sands and pebbles appear to have produced alkaline conditions and probably enhances carbonate precipitation.

Holocene shoreline variations in the Persian Gulf: Example of the Umm al-Qowayn lagoon (UAE)

Abstract The United Arab Emirate lagoons display several generations of successively settled coastal spits, the study of which allows reconstruction of the Holocene shoreline changes from the end of the last marine transgression. The very variable volume of sediment migrating along the coast attests climatic changes. On the other hand, vertical shoreline variations are documented by high sea level evidence around 6000, 4500, 3500 and 2500 BP. When compared with other areas on the Persian Gulf southern coast (Kuwait and Bahrain), such Holocene oscillations might be interpreted as tectonic in origin.

For a reinstatement of “lithographic”, a precise word to define a precise limestone

Abstract The modern classifications of carbonate rocks have brought a new approach to the different types of limestonesbased on their genesis in the depositional environment, the hydrodynamism, the morphology of the basin and its relationship with landmasses. Thus, limestones appear clearly in space and time as a result of different parameters coming together to give the characteristics of the observed rock. However, the term “mudstone” from Dunhams classification or “micrite” in Folks classification is not sufficiently precise to define very fine micrites for which the term “lithographic” is particularly appropriate. A definition of lithographic mudstone or micrite is proposed.

The underlying substrate ofthe Cerin Lithographic Limestones

Abstract The Cerin Lithographic Limestones do not cover a wide area. They correspond to numerous lagoon in-fillings of limited development, within a wide emerged area characterized by sandy (skeletal) limestones mainly of coral origin (Landaize Limestones). At the village of Cerin where an excavation for paleoecological studies is located, the sandy Landaize Limestones provide the lithographic limestone substrate. Their cementation is partly of supratidal and/or intertidal origin, but frequently shows phreatic freshwater features. Finally, microbial cements (bacteria or cyanobacteria) reflect a major process of lithification. The original substrate consisted of grainstones, the top of which was considerably eroded, producing uneven relief with steep slopes and even cliffs, sometimes reaching several metres in height. The erosion processes were probably mechanical in origin, but also biochemical (biokarst) and especially biological (bioerosion by grazing, boring and microbial erosion). Lime mud which produced the lithographic limestones filled the hollows between the substrate reliefs. Around areas where the uneven rocky substrate had steep gradients locally developed gravity flows occur. These are capped with microbial films which are affected by superficial slides showing more or less concentric or complex wavy structures. Locally, true slumps giving rolls and synsedimentary microfolds also occur.

Eichstätt and Cerin: Geochemical comparison and definition of two different plattenkalk types

Abstract Bed-by-bed analyses of a lateral set of profiles in the Eichstatt area, and of one profile of Cerin reveal some analogies and some differences. The analogies are: A.1) There appear three distinct lithofacies which differ in their contents of insolubles in 1 : 3 : 10 ratios. A.2) The 12 analyzed elements can be separated into 3 groups: a “clastic group” (Si, Al, K, Fe) with very similar trends in profile, caused by the detrital input of silicate minerals; a “semiclastic group” (Ti, Rb, Ba, P), which follows the clastic trend, but not quantitatively; and Mn, S, Sr (and Mg) which form the “diagenetic group” with special behaviour. The differences are: B.1) Cerin in general is purer than Eichstatt, but according to the correlation lines in 2-element-diagrams it has relatively less K and Al, more Si and Fe, and more Mg in the carbonate phase. B.2) For Eichstatt it can be suggested that the sediment was brought into the plattenkalk basin as a ready mixture of carbonate and non-carbonates. At Cerin the relation between thickness and contents of insolubles proves the “Seibold-rule”: dilution of insoluble input by in situ carbonate production. Cerin is a simple rhythmite, whereas Eichstatt is dominated by “undulations”. These features, and the differences described in B.2, are used as the basis for definition of “Plattenkalk C-type” and “E-type”.

Petrascula arabica nov. sp.nouvelle espèce d'algue dasycladacée du Bathonien d'Arabie saoudite

Resume La nouvelle espece, denommee Petrascula arabica nov. sp., correspond au plus ancien taxon du genre connu a ce jour. Parfaitement preservee, cette espece presente clairement les caracteres du genre Petrascula avec un ou deux ordres de ramification representes dans la tige, deux ordres developpes au collet et seulement le deuxieme ordre conserve dans la tete. Les organes reproducteurs ont pu etre observes et sont de type endospore.