Richard Ciszak

Pedogenic and Karstic Features at the Boundaries of Bathonian Depositional Sequences in the Grands Causses Area (Southern France): Stratigraphic Implications

ABSTRACT Several exposure surfaces (D1 to D6) underlain by paleosols, paleokarstic surfaces, and subsurface paleokarsts were identified in the Middle to Upper Bathonian Calcaires a Stipites and Dolomies II Formations in southern France. Two kinds of paleosols with different degrees of maturity were recognized: simple ferruginous crusts, capping very irregular bed surfaces, and a rooted horizon. The paleokarstic surfaces are marked by nodular horizons and paleocaves. On the Cevennes shoal, the paleokarsts discontinuities are associated with synsedimentary tectonic processes, which did not extend into the overlying Dolomies II Formation. Subsurface paleokarsts were observed in the Cirque du Bout du Monde (on the Cevennes shoal) within the Calcaires a Stipites Formation, just beneath surface D5. They are characterized by stronger brecciation of the beds. Most of the paleokarstic discontinuities described in this study correspond to the boundaries of four third-order depositional sequences, Bt 1 to Bt 4 (D1 at the base of Bt 1; D2, D3, D4, and D5 capping Bt 1, Bt 2, Bt 3, and Bt 4, respectively; D6 at the top of the Dolomies II Formation). D1, D2, and D3 paleokarsts are geographically limited to the Grands Causses Graben, whereas D4, D5, and D6 are present only on the Cevennes shoal. Geographic trends of paleokarsts confirm the transgressive trend of sequences Bt 3 and Bt 4, and of the overlying Dolomies II Formation towards the shoal. D6 paleokarstic features were also observed within the uppermost part of the Dolomies II Formation in the Horst de Saint-Bresson. The latter transgressive process provides evidence for subaerial exposure of this paleostructure during the latest Bathonian-Callovian interval, induced by tectonic uplifts.

Présence de Paléocène marin dans les Grands Causses (France)

Identification of Palaeocene marine sediments in the Grands Causses (France). In the Grands Causses, incised valleys, lapies, fissures and sinkholes inherited from successive polyphase karstifications were filled by Palaeocene marine sediments overall assigned to the P1c–P3 interval (Upper Danian–Lower Selandian). These sediments are distributed into three detritic facies, generated by extensional tectonics controlling karstic and erosional processes. Upper Cretaceous marine fossils known within these facies are interpreted as reworked from hypothetically pellicular deposits. The probable palaeogeographic connection with the Pyrenean Palaeocene ‘Breccia trough’ supposes the presence of a SE–NW ‘ria’ running across the continental areas of Lower Languedoc and draining towards the northwest the marine waters of the Palaeocene transgression as

Séquences de dépôt à l'articulation plate-forme urgonienne–bassin (intervalle Barrémien–Albien) dans le Prébalkan occidental (Bulgarie du Nord-Ouest)

Abstract In the western Fore-Balkan (northwest Bulgaria), the characterization of numerous depositional sequences within the Barremian–Albian interval allows us to reconstruct from southeast to northwest the successive palaeogeographies of this part of the north Tethyan margin: two carbonate (Urgonian) platforms flanking a central terrigenous basin during the Barremian; a single centrifugal terrigenous basin (Aptian) marked, along its axis, by an olistostrome and siliciclastic turbidites; a single Albian basin characterized by the stacking of glauconite-rich condensation sections and anoxic black marls.

Géométrie des formations et des séquences de dépôt éocrétacées (intervalle Hauterivien-Aptien) de Bulgarie nord-orientale

Abstract The study, in terms of sequence stratigraphy (with ammonite zone control), of numerous cross-sections of Lower Cretaceous (Hauterivian to Aptian) series cropping out along two transects A-B (Fore Balkan and southern part of the Moesian Platform) and C-D (northeastern part of the Moesian Platform) shows the eastwards extension of the North-Tethyan palaeogeographic pattern platform-basin-platform, previously established in central Bulgaria. However, the two boundaryplatforms are strongly assymetrical, this assymetry being revealed by the importance, to the south, of the relative lowstand prograding siliciclastic bodies (supplied by continental erosions linked to extensional tectonics) during the synrift phase (not marked to the north) and by the age, the facies (oolitic to the north, Urgonian to the south) and the number of the calcareous tongues interpreted as the transgressive systems tracts of backstepping depositional sequences, well-marked at the shelf/basin transition.

Enregistrement sédimentaire de la tectonique extensive et de l'eustatisme dans le Jurassique terminal et le Crétacé basal du Prébalkan central et oriental (Bulgarie)

Abstract The thick (2 000 m) siliciclastic-dominated synrifi series, which fills up most of the internal troughs of the Central Fore Balkan from Uppermost Tithonian to Valanginian, is subdivided into ten tectono- eustatic depositional sequences. The sequences consist of a coarse and voluminous low stand wedge (block complex, canyon-cone conglomerates, megaslumps, calcareous breccias, etc.) induced by extensional tectonics; and above, a pelite-dominated high stand wedge, of eustatic origin, which contains most of the zonal and subzonal Ammonites allowing datations and correlations. To the NE, towards the Moesian Platform, only the high stand wedges (with or without the transgressive system tracts) of the successive sequences overflow the troughs and become richer in carbonates to the top of the parasequences.