Découverte de la série basale du Cambrien et de son substratum dans les Rehamna Centraux, haut-fond au Cambrien (Meseta marocaine). Prémices de l'orogenèse hercynienne.

International audienc

Recifs et plates-formes carbonatees miocenes de Mediterranee Marseille, 3-6 mai 1994

SIGLEAvailable at INIST (FR), Document Supply Service, under shelf-number : YM 6627 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

Variations d'épaisseur du Cambrien moyen en Meseta marocaine occidentale: signification géodynamique des données de surface et de subsurface

International audienc

Cisaillement ductile synmétamorphe et déplacement tangentiel vers le SW dans les Rehamna (Maroc hercynien).

International audienc

Transect from near-to offshore in Devonian-Carboniferous Boundary sections of the stratotype area (Montagne Noire, Southern France)

International audienceThe Montagne Noire offers the unique opportunity to compare and potentially correlate distal basinal settings with contemporaneous near-shore carbonate deposits across the Devonian-Carboniferous Boundary that allow to build a virtual transect from shoreline to deep basin. Nearshore facies characterise the D-C Boundary stratotype and neighbouring sections at La Serre in the Cabrières klippen domain and offshore facies are present at the Col de Tribes and Puech de la Suque sections in the Mont Peyroux nappe domain. Both domains exhibit equivalents of the Hangenberg Black Shale (HBS). At La Serre, an initial regressive trend is indicated by the presence of oculated trilobites in the topmost pre-HBS Wocklumeria Limestones. Above the HBS level, regressive depositional conditions characterise oolitic deposits that comprise lithic erosional flows with an admixture of transported shallow-water biota. Maximum regression is recognised with the deposition of coarse breccias and local features of emergence prior to the first appearance of Protognathodus kockeli. The oolites are superseded by the transgression of outer shelf deposits. In the nappe domain, the HBS is intercalated in outer ramp nodular limestones, and it exhibits detrital elements pointing to its regressive nature. Thin-sections and X-ray analysis of the silty greyish to black shales, devoid of carbonates, reveal the presence of detrital quartz and muscovite grains that make up to 80 % of the whole rock as well as berlinite grains, a high temperature mineral. The allochthonous origin of the sand indicates erosion of distant emergent areas and emphasises the regressive nature of this level. Using the maximum and minimum amounts of quartz and muscovite (easily transportable), two minor regressive/transgressive cycles can be interpreted from Beds PS 89 to HJt1 (Fig. 1). The regressive trend culminates, then reverses when post-HBS carbonate sedimentation resumes. Protognathodus kockeli appears in the post HBS carbonates. Associated oculated trilobites indicate shallower bathymetric conditions than those of the pre-HBS Wocklumeria Limestones. Thereafter, replacement of sighted trilobites by blind ones and the protognathodid biofacies by facies dominated by siphonodellids indicate a deepening trend. The near-and offshore sites of the D-C transition permit correlation of short-term bathymetric fluctuations with faunal turnovers and entries of biostratigraphic markers. The D-C Boundary sections of the Montagne Noire emphasise the importance of the Hangenberg Event affecting marine biota in both near-and offshore domains. As in the Rhenish Slate Mountains and Carnic Alps for example, the biotic turnover is particularly marked in the outer shelf domain; it seems the same in the nearshore domain of La Serre, though the evidence is obscured by reworking processes during deposition of detrital input. As elsewhere, the Hangenberg Event in the Montagne Noire is characterised mainly by eustatic perturbations, notably regressive trends in the topmost Wocklumeria Limestones and during the HBS, followed up by a global transgression above. Among level-bottom biota with light receptors, trilobites are most sensitive to changing conditions in the degree of light penetration to their habitats. With the onset of the HBS regression they lost all lower-rank taxa (genera and species) and none of them survived the crisis

Triassic pelagic deposits of Timor: palaeogeographic and sea-level implications

In West Timer, Triassic deposits are found in the Parautochthonous Complex, as well as in the Allochthonous series of Sonnebait. A detailed biostratigraphic investigation integrating field observations and facies analysis, allowed the reconstruction of a synthetic lithostratigraphic succession for the Upper Triassic, a stratigraphic transition from Carnian shales to Upper Norian-Rhaetian limestones is also shown by this study. The fossil content predominantly originates from an open marine environment; lithostratigraphic Units A-E are dated on the basis of radiolaria and palynomorphs, and Unit H, on ammonites and conodonts. The presence of pelagic bioclasts, together with normal grading, horizontal laminations, and current ripples, is indicative of a distal slope to basin environment. The ammonite rich condensed limestone of Unit H was deposited on a `pelagic carbonate plateau' exposed to storms and currents. The organic facies have been used as criteria for biostratigraphy, palaeoenvironmental interpretation, and sequence stratigraphy. The palaeontological analysis of the Triassic succession of West Timer is based on the investigation of radiolaria and palynomorphs, in the marls and limestones of Units A-E, and also on ammonites and conodonts in the condensed limestone of Unit H. Units A and B are Carnian (Cordevolian) in age, based on the occurrence of the palynomorph Camerosporites secatus, associated with `Lueckisporites' cf. singhii, Vallasporites ignacii, Patinosporites densus and Partitisporites novimundanus. Unit C is considered as Norian, on the basis of a relatively high percentage of Gliscopollis meyeriana and Granuloperculatipollis rudis. Unit D contains significant palynomorphs and radiolaria; the organic facies, characterized by marine elements, is dominated by the Norian dinocysts Heibergella salebrosacea and Heibergella aculeata; the radiolaria confirm the Norian age. They range from the lowermost Norian to the lower Upper Norian. Unit E also contains radiolaria, associated in the upper part with the well-known marker of the Upper Norian, Monotis salinaria. For Unit E, the radiolaria attest to a Lower to Upper Norian age based on the occurrence of Capnodoce and abundant Capnuchosphaera; the upper part is Upper Norian to Rhaetian based on the presence of Livarella valida. Finally, the blocks of condensed limestone with ammonites and conodonts of Unit H allowed the reconstruction of a synthetic stratigraphic succession of Upper Carnian to Upper Norian age. Our stratigraphic data lead to the suggestion that the Allochthonous complex, classically interpreted as a tectonic melange of the accretionary prism of the island Arc of Banda. is a tectonically dismembered part of a Triassic lithostratigraphic succession. (C) 2000 Elsevier Science B.V. All rights reserved

Modèle 3D Terre-Mer et nouvelles données chronostratigraphiques sur le bassin Oligo-Miocène de Castelsardo, Sardaigne

International audienc

GAARLANDIA land-bridge vs lesser Antilles dispersal pathways – coupling subduc-tion dynamics and evolutionary processesin the Caribbean domain

International audienceThe purpose of the GAARAnti project is to unravel couplings between deep Earth dynamics and evolutionary processes through an innovative and original multi-disciplinary study combining Earth and Life sciences. This innovative approach will reconcile biological and geological clocks and timeframes through the combined use of radiochronological methods, biostratigraphy and phylogenetic inferences, to constrain the Cenozoic paleo-biogeography of the Antillean arc. The GAARAnti project will generate novel collaborative works between geologists/marine geophysicists and biologists/paleontologists and new results by constraining the pattern, timing, and dynamics of biodiversity in Lesser Antilles at the Cenozoic scale. This will in turn allow untangling biotic and geological constraints that forced such history. In the frame of the ongoing debate about the Tertiary origin of terrestrial organisms of the Greater Antilles, GAARAnti will focus on the role of subduction dynamics onto the evolution of emergent areas as a promoter or an antagonist of the terrestrial faunas dispersal. Although it is now widely admitted that most components of Antillean terrestrial communities originated from South and Central America, the mechanisms (dispersal vs vicariance) responsible for the observed evolution and its precise timing are still highly debated. Previous studies have mainly addressed this question through Earth sciences or Life sciences separately. We are confident and deeply believe that our innovative and original multi-disciplinary approach within the GAARAnti project will generate major advances in the knowledge of Cenozoic Antillean biodiversity dynamics