Coelobiontic communities in neptunian fissures of synsedimentary tectonic origin in Permian reef, southern Urals, Russia

Sedimentary dykes in the Permian reef complexes of the Russian platform are well preserved and important in providing information about reef growth, the reef biota and, particularly, cavity-dwelling organisms and sediment sources. Two main fissure assemblages are recognized with N80° and N170° (late Asselian-early Sakmarian) and N130°–140° and N60° (Sakmarian-Artinskian) orientations. These contemporaneous orthogonal dyke sets present orientations corresponding to the regional tectonic fabric and a tectonic origin for fracturing associated with the foreland basin development. The largest dykes record eight lithofacies and several stages of fracture opening. Stromatoids and centimetre-thick …

Influence of basement heterogeneity on the architecture of low subsidence rate Paleozoic intracratonic basins (Ahnet and Mouydir basins, Central Sahara)

Abstract. The Paleozoic intracratonic North African Platform is characterized by an association of arches (ridges, domes, swells or paleo-highs) and low subsidence rate syncline basins of different wavelengths (75–620 km). The structural framework of the platform results from the accretion of Archean and Proterozoic terranes during the Pan-African orogeny (750–580 Ma). The Ahnet and Mouydir basins are successively delimited from east to west by the Amguid El Biod, Arak-Foum Belrem, and Azzel Matti arches, bounded by inherited Precambrian sub-vertical fault systems which were repeatedly reactivated or inverted during the Paleozoic. Major unconformities are related to several tectonic events …

The Early-Cambrian Boho volcano of the El Graara massif, Morocco: Petrology, geodynamic setting and coeval sedimentation

15 pages; International audience; A major volcanic episode is recorded across the Neoproterozoic-Cambrian transition in the Moroccan Anti-Atlas. Several volcanic cones are still preserved in the El Graara massif, laterally correlatable with volcanic flows dated as Early Cambrian (U/Pb date of 534 ± 10 Ma). Volcanic ashes and flows are interbedded with the uppermost part of the Adoudou dolostones, whereas the best-preserved volcano (the Boho Jbel) is onlapped by the overlying Lie-de-vin strata. Available petro-geochemical data from the Boho volcano suggest an alkaline magmatism probably derived from low-grade melting of a garnet–lherzolite mantle source, followed by fractional crystallizatio…

Étude des traces de pas de vertébrés du Permien et du Trias d'Ardèche. Enjeux et perspectives.

Le département de l'Ardèche estremarquable car il offre un accès privilégié auxroches sédimentaires permiennes et triasiques danslesquelles abondent les traces de vertébrés fossiles.Une vingtaine de localités et plus de 1500empreintes de pas ont déjà été recensées le longd'une succession sédimentaire affleurant entrePrivas et Les Vans. Ce patrimoine ichnologique,reconnu internationalement, documente le passagede grands groupes de reptiles en terres ardéchoises,incluant essentiellement des représentants basauxde la lignée des crocodiles (pseudosuchiens) et de lalignée des oiseaux (dinosauriformes et dinosaures),ainsi que quelques membres de la lignée des lézards/serpents (lépidosauromorphes)…

Micro- to macro-scale internal structures, diagenesis and petrophysical evolution of injectite networks in the Vocontian Basin (France): implications for fluid flow.

27 pages; International audience; This study discusses the characteristics of two Lower Cretaceous injectite networks in the Vocontian Basin (SE France) using combined structural, sedimentary, diagenetic, and petrophysical analyses. Internal structures, at both the macro- and micro-scale, and diagenetic phases characterising these injectite networks have been described. Simultaneously, precementation porosity values were estimated and parameters controlling the geographical distributions of these values were analysed and statistically tested. All of the data were integrated so as to reconstruct the spatial evolution of the porosity from the time of injection to modern times through five maj…

Facies from Palaeozoic reefs and bioaccumulations.

341 pages

A diagenetic control on the Early Triassic Smithian-Spathian carbon isotopic excursions recorded in the marine settings of the Thaynes Group (Utah, USA)

17 pages; International audience; n the aftermath of the end-Permian mass extinction, Early Triassic sediments record some of the largest Phanerozoic carbon isotopic excursions. Among them, a global Smithian-negative carbonate carbon isotope excursion has been identified, followed by an abrupt increase across the Smithian–Spathian boundary (SSB; ~250.8 Myr ago). This chemostratigraphic evolution is associated with palaeontological evidence that indicate a major collapse of terrestrial and marine ecosystems during the Late Smithian. It is commonly assumed that Smithian and Spathian isotopic variations are intimately linked to major perturbations in the exogenic carbon reservoir. We present p…

Smithian shoreline migrations and depositional settings in Timpoweap Canyon (Early Triassic, Utah, USA).

AbstractIn Timpoweap Canyon near Hurricane (Utah, USA), spectacular outcrop conditions of Early Triassic rocks document the geometric relationships between a massive Smithian fenestral-microbial unit and underlying, lateral and overlying sedimentary units. This allows us to reconstruct the evolution of depositional environments and high-frequency relative sea-level fluctuations in the studied area. Depositional environments evolved from a coastal plain with continental deposits to peritidal settings with fenestral-microbial limestones, which are overlain by intertidal to shallow subtidal marine bioclastic limestones. This transgressive trend of a large-scale depositional sequence marks a lo…

Palaeozoic Reefs and Bioaccumulations: Climatic and Evolutionary Controls.

291 pages

Microbial deposits in the aftermath of the end-Permian mass extinction: A diverging case from the Mineral Mountains (Utah, USA)

40 pages; International audience; The Lower Triassic Mineral Mountains area (Utah, USA) preserves diversified Smithian and Spathian reefs and bioaccumulations that contain fenestral-microbialites and various benthic and pelagic organisms. Ecological and environmental changes during the Early Triassic are commonly assumed to be associated with numerous perturbations (productivity changes, acidifica-tion, redox changes, hypercapnia, eustatism and temperature changes) post-dating the Permian–Triassic mass extinction. New data acquired in the Mineral Mountains sediments provide evidence to decipher the relationships between depositional environments and the growth and distribution of microbial …

The end of the Messinian Salinity Crisis in the western Mediterranean: insights from the carbonate platforms of south-eastern Spain.

International audience; How the Messinian Salinity Crisis (MSC) ended is still a matter of intense debate. The Terminal Carbonate Complex (TCC) is a late Messinian carbonate platform system that recorded western Mediterranean hydrological changes from the final stages of evaporite deposition till the advent of Lago-Mare fresh- to brackish water conditions at the very end of Messinian times. A multidisciplinary study has been carried out in three localities in south-eastern Spain to reconstruct the history of TCC platforms and elucidate their significance in the MSC. Overall, this study provides evidence that the TCC formed following a regional 4th order water level rise and fall concomitant…

Fabric transitions from shell accumulations to reefs: an introduction with Palaeozoic examples

One unresolved conceptual problem in some Palaeozoic sedimentary strata is the boundary between the concepts of ‘shell concentration’ and ‘reef’. In fact, numerous bioclastic strata are transitional coquina–reef deposits, because either distinct frame-building skeletons are not commonly preserved in growth position, or skeletal remains are episodically encrusted by ‘stabilizer’ (reef-like) organisms, such as calcareous and problematic algae, encrusting microbes, bryozoans, foraminifers and sponges. The term ‘parabiostrome’, coined by Kershaw, can be used to describe some stratiform bioclastic deposits formed through the growth and destruction, by fair-weather wave and storm wave action, of …

Stratigraphic modelling of platform architecture and carbonate production: a Messinian case study (Sorbas Basin, SE Spain).

27 pages; International audience; The late Messinian mixed carbonate-siliciclastic platforms of the Sorbas Basin, known as the Terminal Carbonate Complex, record significant changes in carbonate production and geometry. Their facies and stratigraphic architecture result from complex interactions between base-level fluctuations, evaporite deformation/dissolution and detrital inputs. A 3D quantitative approach (with DIONISOS software) is used to explore the basin-scale platform architecture and to quantify the carbonate production of the Terminal Carbonate Complex. The modelling strategy consists in integrating detailed 2D field-based transects and modern carbonate system parameters (e.g. car…

Permian.

Pre-Hirnantian (latest Ordovician) benthic community assemblages: controls and replacements in a siliciclastic-dominated platform of the eastern Anti-Atlas, Morocco.

17 pages; International audience; Lower-middle Ashgill sedimentary strata from the Mediterranean region have recorded a key episode of temperate-to-cold water, carbonate productivity predating the onset of the Hirnantian glaciation. The latitudinal position of the Moroccan margin of North Gondwana during Ashgill should have been adequate for the recorded development of carbonate factories. However, carbonate productivity was neither homogeneous nor laterally persistent, as documented in the eastern Anti-Atlas. Whereas in the Erfoud area, the bryozoan-dominated limestones of the Ashgill Khabt-el-Hajar Formation indicate the intensive activity of carbonate factories, these were dramatically r…

New trepostomate bryozoans from the Upper Ordovician of Morocco and the temperature influence on zooid size

AbstractNew Upper Ordovician trepostomate bryozoans from the eastern Anti-Atlas of Morocco have been identified. They have been collected from the lower and intermediate units of the Khabt-el-Hajar Formation, late Katian in age, representing, respectively, bryozoan-pelmatozoan meadows with siliciclastic input, degraded by wave activity in a mid-ramp setting, and outer-ramp environments with marly substrates. Ten species of the generaCyphotrypa,Calloporella,Diplotrypa,Parvohallopora,Dekayia, andAostiporaare described. Of them, three species are new:Cyphotrypa regularisJiménez-Sánchez,Parvohallopora cystataJiménez-Sánchez, andAostipora elongataJiménez-Sánchez. Univariate statistical analyses …

Influence of basement heterogeneity on the architecture of low subsidence rate Paleozoic intracratonic basins (Reggane, Ahnet, Mouydir and Illizi basins, Hoggar Massif)

The Paleozoic intracratonic North African Platform is characterized by an association of arches (ridges, domes, swells, or paleo-highs) and low subsidence rate syncline basins of different wavelengths (75–620 km). The Reggane, Ahnet, Mouydir and Illizi basins are successively delimited from east to west by the Amguid El Biod, Arak-Foum Belrem, and Azzel Matti arches. Through the analysis of new unpublished geological data (i.e., satellite images, well logs, seismic lines), the deposits associated with these arches and syncline basins exhibit thickness variations and facies changes ranging from continental to marine environments. The arches are characterized by thin amalgamated deposi…

Structure and evolution of a Messinian mixed carbonate-siliciclastic platform: the role of evaporites (Sorbas Basin, South-east Spain).

36 pages; International audience; The Sorbas Member is a late Messinian complex sedimentary systemthat formed immediately following deposition of the Messinian evaporites in the Sorbas Basin (South-east Spain). This work describes the sequence architecture and facies organization of a continuous kilometre long, alluvial fan to open platform transect near the village of Cariatiz in the north-east of the basin. The postevaporitic Cariatiz platform was a mixed carbonate-siliciclastic system composed of four intermediate-frequency, fifth-order depositional sequences (Depositional Sequences 1 to 4) arranged in an overall prograding trend. The intense fracturing and brecciation of these deposits …

Contrôles locaux vs globaux sur les alternances carbonates-silicoclastiques dans le bassin de Lorca (Tortonien-Messinien, Espagne)

International audience

Subglacial to proglacial depositional environments in an Ordovician glacial tunnel valley, Alnif, Morocco

Abstract This paper presents the sedimentary analysis of an exceptional Ordovician glacial tunnel valley in the eastern part of the Anti-Atlas. The valley infill comprises two major glacial erosion surfaces (striated pavements) each overlain by a fining-upward glacial unit. These units are composed of five distinct facies associations, recording the evolution from subglacial to proglacial environments, and an additional sixth facies association, overtopping the tunnel valley infill, and associated with post-glacial environments. The tunnel valley infill also records a transitional environment between the subglacial and proglacial settings, which is compared with the Antarctic ice-sheet marg…

Effect of the Ordovician paleogeography on the (in)stability of the climate.

The Ordovician Period (485–443 Ma) is characterized by abundant evidence for continental-sized ice sheets. Modeling studies published so far require a sharp CO2 drawdown to initiate this glaciation. They mostly used non-dynamic slab mixed-layer ocean models. Here, we use a general circulation model with coupled components for ocean, atmosphere, and sea ice to examine the response of Ordovician climate to changes in CO2 and paleogeography. We conduct experiments for a wide range of CO2 (from 16 to 2 times the preindustrial atmospheric CO2 level (PAL)) and for two continental configurations (at 470 and at 450 Ma) mimicking the Middle and the Late Ordovician conditions. We find that the temper…

New sedimentological and stratigraphical data on the Permian and Triassic in northeastern Utah, USA

International audience; We present the Permian to Triassic sedimentological evolution in the Vernal area, northeastern Utah, todetermine: (1) the magnitude of the Permian-Triassic (P-T) unconformity, (2) the depositional environmentsabove the unconformity, as well as (3) their evolution in space and time. Within this area, Permian depositsconsists of the Weber Sandstone, which represents aeolian deposits, overlain by the Park City Formation,composed of silty and sandy marine limestones, dolomites and phosphatic shales. In some places, anunconformity is observed at the top of the Weber Sandstone, which is directly overlain by the MoenkopiGroup. This formation is mostly composed of siltstone,…

Brachiopod coquinas of the Upper Arenig, Montagne Noire, France.

3 pages

Lithospheric strenght control over depositional environments and foreland accommodation in the Western USA Basin during the Early Triassic

International audience

The role of topography and erosion in the development and architecture of shallow-water coral bioherms (Tortonian-Messinian, Cabo de Gata, SE Spain).

23 pages; International audience; During the Miocene, Mediterranean shallow-water carbonates were rich in scleractinian corals, which thrive in various depositional settings. A Tortonian–Messinian bioherm belt developing in a heterozoan-dominated ramp was investigated along a 1.2 km continuous transect located in the Cabo de Gata region. The interval studied displays four depositional environments from mid-to-inner ramp, dominated by swell waves and storm energy, deposited as a single, large-scale depositional sequence during a 3rd to 4th order transgressive–regressive cycle. The bioherms grew in three phases, and were essentially composed of inplace primary frameworks. Three coral genera w…

Transient metazoan reefs in the aftermath of the end-Permian mass extinction

5 pages; International audience; Recovery from the devastating Permian-Triassic mass extinction about 252 million years ago is usually assumed to have spanned the entire 5 million years of the Early Triassic epoch1,2. The post-crisis interval was characterized by large-scale fluctuations of the global carbon cycle and harsh marine conditions, including a combination of ocean acidification, euxinia, and fluctuating productivity3. During this interval, metazoan-dominated reefs are thought to have been replaced by microbial deposits that are considered the hallmark of the Early Triassic4-7. Here we use field and microscopic investigations to document Early Triassic bioaccumulations and reefs f…

Morphometry of micrite particles in cretaceous microporous limestones of the Middle East: influence on reservoir properties.

24 pages; International audience; Microporosity may account for a significant part of the total porosity of Cretaceous limestone reservoirs of the Middle East. In these microporous facies porosity is moderate to excellent (up to 35%) while permeability is poor to moderate (up to 190 mD). Micritic limestones also may form dense layers with very low porosity and permeability values. Micritic samples were collected from three fields of the Habshan and Mishrif Formations, to examine the spatial relationship with their porosity, permeability and pore throat radius distributions. Two key parameters of the micritic particles are studied using scanning electron microscopy: their morphology (shape a…

The role and contribution of eustasy as a triggering force of the onset of Oceanic Anoxic Events: A case study of the early Aptian OAE1a in the Tethyan margin of Tunisia

<p>Oceanic Anoxic Events (OAEs) are short-lived global carbon cycle perturbations characterized by significant changes in the chemistry, temperature and circulation of the oceans of the world. The forcing mechanisms behind these events remain a subject of discussion, especially for the Jurassic and Cretaceous periods. Typically, these events are thought to be triggered by a contemporaneous emplacement of a large igneous province (LIP) associated with a significant release of CO<sub>2</sub> into the atmosphere and leading to rapid global warming. In turn, induced sharp climatic change promotes an acceleration of the hydrological cycle which intensifi…

Étude multi-isotopique de microbialites actuels au sein d'analogues Précambriens (lacs de cratères volcaniques alcalins)

Paleoecological constraints on reef-coral morphologies in the Tortonian–early Messinian of the Lorca Basin, SE Spain

Abstract Coral reefs represent one of the main carbonate factories that contributed to the control of the stratigraphic architecture of carbonate platforms, which had a widespread development during the late Miocene in the paleo-Mediterranean area. The late Miocene reef complexes of the Lorca Basin in southeastern Spain are composed of five mixed siliciclastic/carbonate units, middle Tortonian to early Messinian in age. The development of coral reefs probably ceased when the first evaporitic event occurred in the basin centre in the early Messinian. This study mainly focuses on the response of reef communities and the modifications of reef organisation to global and regional parameters. At …

Changements environnementaux survenant à la limite Oligocène/Miocène du bassin des Limagnes (Massif central, France).

16 pages; International audience; Continental environments are very sensitive to climatic variations. A unique opportunity to study the climate changes around the Oligocene/Miocene boundary is offered by the Limagne graben Basin (France) where this stage boundary is well constrained by fossils. Indeed, some localities of the Limagne Graben Basin are so rich in mammal remains that they have become a European reference for mammal biostratigraphy. The dominant sedimentary facies of the lacustrine deposits in the northern part of the Limagne Graben Basin are composed of poorly cemented marls and calcarenites containing various plants and animals remains (e.g. algae, fish bones and teeth, gastro…

TRACKING DINOSAURS IN COARSE-GRAINED SEDIMENTS FROM THE UPPER TRIASSIC OF ARDÈCHE (SOUTHEASTERN FRANCE)

ABSTRACT Coarse-grained sediments deposited in high-energy environments are usually considered unfavorable to the preservation of fossil tracks. Here we report dinosaur footprints showing good physical preservation, despite being found in coarse-grained sandstones of alluvial origin from the Upper Triassic of Ardèche, southeastern France. The ichnoassemblage, dominated by Grallator isp., raises questions about the processes leading to the formation and preservation of tracks in coarse-grained sediments. The track-bearing surface is a medium- to coarse-grained quartz arenite that is microconglomeratic locally. The tracking surface grain size ranges from 0.2 to 2 mm and numerous pebbles are p…

Oligo-Miocene lacustrine microbial and metazoan buildups from the Limagne Basin (French Massif Central)

The Limagne Basin (French Massif Central) is an extensive continental lacustrine system accommodating microbial and metazoan buildups from Chattian to Aquitanian age. A description of these buildups and their associated biotic components in Grand Gandaillat and Crechy quarries provides insights into their spatio-temporal distribution patterns. Flats, cauliflowers, domes, cones and coalescent columnar morphologies have been identified with a main laminated mesofabric and laminated, columnar, filamentous and caddisfly-coated microfabrics. Two low-gradient margin models emerged based on the changes in the distribution, morphology and size of the microbial and metazoan-rich deposits through tim…

Ordovician.

Sequence stratigraphy and carbon isotope stratigraphy of an Aptian mixed carbonate-siliciclastic platform to basin transition (Galve sub-basin, NE Spain)

Discussion on Palaeozoic discontinuities in the Kuh-e Surmeh area (Zagros, Iran).

20 pages; International audience; Evidence of several major unconformities in the Lower Palaeozoic succession in Iran lead to question the role of tectonic/eustatism/climate in terms of their formation. The studied Palaeozoic succession in the Kuh-e Surmeh Anticline is characterized by the preservation of two thin Ordovician and Lower Permian Formations separated by a large hiatus encompassing the Upper Ordovician up to the lowermost Permian. The Ordovician sequences were deposited in shallow shoreface to lower offshore environments and the Lower Permian corresponds to a wave-dominated estuarine system evolving to a delta system. These mainly clastic successions represent good reservoirs in…

Incised valleys and tidal seaways: the example of the Miocene Uzès-Castillon basin, SE France.

Abstract The sedimentology and stratigraphy of the Miocene deposits of the Uzès-Castillon basin are revisited. This basin, located in SE France at the junction between the perialpine foreland basin and the W Mediterranean margin, sits in a syncline that formed during the latest Cretaceous Pyrenean tectonic phase. It records the succession of shallow-water mixed siliciclastic to dominantly bioclastic carbonates that alternate with shelf marls. The clastic carbonates were accumulated as a stack of subtidal dunes and bars that were formed by tidal currents channelized in a seaway following the syncline axis. The marls indicate deposition in more protected and locally deeper waters, as interflu…

Reconstitutions environnementales et climatiques multiproxis des paléo-systèmes lacustres des bassins fini-paléozoïques du NE du Massif central

National audience; Les bassins intracontinentaux fini-carbonifères à permiens du nord-est du Massif central (notamment Autun, Decize-La Machine et Aumance) s'inscrivent dans le cadre de l'extension tardi-orogénique de la chaîne varisque, et de l'acmé de la glaciation fini-paléozoïque. La récente réévaluation de leurs successions sédimentaires à dominance silicoclastique en termes de processus et architectures sédimentaires, stratigraphie séquentielle, géochimie élémentaire et isotopique, permet de préciser l'évolution spatio-temporelle des environnements de dépôt: les sédiments détritiques, incluant une large composante volcanoclastique, se sont déposés majoritairement dans des systèmes lac…

Fabric transitions from shell accumulations to reefs: an introduction with Palaeozoic examples.

16 pages

Influence of a major exposure surface on the development of microporous micritic limestones - Example of the Upper Mishrif Formation (Cenomanian) of the Middle East.

18 pages; International audience; Microporous platform top limestones of the Cenomanian Mishrif Formation (offshore Qatar) were studied in order to investigate the diagenetic processes associated with the top-Mishrif subaerial unconformity and its influence on the development of microporosity in underlying carbonates. Petrographical and stable isotope results indicate that complex diagenetic changes occurred during subaerial exposure of the Mishrif Formation, including pervasive dissolution and meteoric cementation, as well as neomorphism of the micritic matrix. Micrites at the top of the Mishrif Formation are coarse (i.e. > 2 μm), sub-rounded and very dull luminescent under cathodoluminesc…

Evolution of depositional settings in the Torrey area during the Smithian (Early Triassic, Utah, USA) and their significance for the biotic recovery

This work focuses on well-exposed Lower Triassic sedimentary rocks in the area of Torrey (south-central Utah, USA). The studied Smithian deposits record a large-scale third-order sea-level cycle, which permits a detailed reconstruction of the evolution of depositional settings. During the middle Smithian, peritidal microbial limestones associated with a rather low-diversity benthic fauna were deposited seaward of the tidal flat siliciclastic red beds. Associated with siliceous sponges, microbial limestones formed small m-scale patch reefs. During the late middle to late Smithian interval, the sedimentary system is characterized by tidal flat dolostones of an interior platform, ooid-bioclast…

Ages and stratigraphical architecture of late Miocene deposits in the Lorca Basin (Betics, SE Spain): New insights for the salinity crisis in marginal basins

International audience; Unlike most Neogene basins of the Betic Cordillera where the Salinity Crisis is dated to the Messinian, a contradictory Tortonian dating was proposed for evaporites of the Lorca Basin. As a consequence, complex structural models have been proposed in the literature to explain this discrepancy in the timing of evaporites. In order to integrate the Lorca Basin into the geological context of the western Mediterranean domain during the Late Miocene, new sedimentological and stratigraphical studies coupled with new dating were performed, which allow us to propose a Messinian age for both diatomite-bearing deposits and evaporites of the Lorca Basin. These new ages challeng…

Facies and depositional settings during the Smithin in the Torrey area (Early Triassic, Utah, USA)

International audience; The Permian-Triassic transition records the most devastating biotic crisis of the Phanerozoic with 90% of the marine genera being eradicated. The aftermath of this extinction is usually portrayed by large environmental perturbations such as ocean acidification, anoxia, euxinia and fluctuating productivity. However, these fluctuating conditions and their impact on the nature and tempo of the biotic recovery are still under debate. Thus, it is important to decipher the nature of the depositional settings and their putative spatio-temporal variations in order to improve our knowledge of post-crisis environments. The present work focuses on well-exposed Lower Triassic se…

Community replacement of neritic carbonate organisms during the late Valanginian platform demise: a new record from the Provence Platform.

24 pages; International audience; The Valanginian is marked by amajor platform demise inducing a hiatus in the northern Tethyan neritic carbonate record from the top of the lower Valanginian to the lower Hauterivian. New biostratigraphic and chemostratigraphic data from the Ollioules section (Provence Platform, southern France) are presented here, demonstrating that a large part of the upper Valanginian is preserved in an inner platform environment. The thick, upper Valanginian, aggrading carbonate succession is observed in an aborted rift domain, implying relatively low subsidence. In this context, a relatively long-term sea-level rise was required to sustain a keep-up style of carbonate p…