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Late Carboniferous to early Permian organic-rich sedimentary successions of late-orogenic continental basins from the northeastern Massif Central (France) coincide with both the Variscan mountain dismantling and the acme of the long-lasting Late Paleozoic Ice Age. Here, we investigate the carbon and nitrogen cycles in the newly dated sedimentary successions of the Decize–La Machine and Autun basins during these geodynamic and climate upheavals. The sedimentary organic matter has been analyzed through Rock-Eval pyrolysis, palynofacies and elemental and isotope geochemistry along cored-wells and outcropping sections, previously accurately defined in terms of paleo-depositional environments. Rock-Eval and palynofacies data have evidenced two origins of organic matter: a phytoplanktonic/bacterial lacustrine origin (Type I organic matter, organic δ13C values around −23.5‰), and a terrestrial origin (vascular land plants, Type III organic matter, organic δ13C values around −20‰), mixed in the deltaic-lacustrine sediments during background sedimentation (mean organic δ13C values around −22‰). Episodes of high organic matter storage, reflected by black shales and coal-bearing deposits (total organic carbon up to 20 and 70%, respectively) are also recognized in the successions, and are characterized by large negative organic carbon isotope excursions down to −29‰. We suggest that these negative isotope excursions reflect secondary processes, such as organic matter remineralization and/or secondary productivity varying under strict local controls, or possibly larger scale climate controls. At times, these negative δ13C excursions are paired with positive δ15N excursions up to +10‰, reflecting water column denitrification and anammox during lake-water stratification episodes. Together, these isotopic signals (i.e., low sedimentary organic δ13C associated with high bulk δ15N values) indicate periods of high primary productivity of surface waters, where nitrogen and carbon cycles are spatially decoupled. These local processes on the sedimentary isotope archives may partially blur our ability to directly reconstruct paleoclimate variations in such continental settings using only C and N isotopes. At last, we explore an organic δ13C-based mixing model to propose ways to disentangle autochthonous versus allochthonous origin of organic matter in lacustrine continental settings.

The organic-rich lacustrine beds of the Autun Basin (France) were deposited from the late Gzhelian (late Carboniferous) to the Sakmarian (early Permian), encompassing the Carboniferous-Permian boundary (∼299 Ma). Those deposits reach up to 1500 m thick, and correspond to a tropical, intra-mountainous late-orogenic basin infilling associated with the Variscan orogeny (Marteau, 1983; Schneider et al., 2006). Organic-rich and laminated facies are attributed to distal lacustrine environments which sometimes alternate with silty to sandy rich deltaic depositional environments (Mercuzot et al., 2019). The four successive formations (respectively the Igornay, Muse, Surmoulin and Millery fms) yield series of oil-shale beds (successively the Moloy, Igornay, Lally Muse, Surmoulin and Les Télots beds) (Marteau, 1983; Garel et al., 2017). The oil-shale beds are at least several m thick in the basin, except for the “Margenne” boghead bed which is only 0.3 m thick (Marteau, 1983; Garel et al., 2017). Recently, accurate U-Pb ages obtained on zircons from volcanic layers of the Autun Basin have placed the Carboniferous-Permian boundary within the Lally oil-shale beds (Pellenard et al., 2017).In this work, we present a detailed study of the 364-m thick Chevrey 1 core, based on a Rock-Eval pyrolysis survey. The Chevrey 1 core encompasses the successive Igornay and Muse fms., including the Lally oil shale bed and the C/P boundary. TOC varies from 0.2 to 21 wt%, whereas HI values range from 22 to 421 mgHC/gTOC. The Lally oil-shale bed seems to correspond to a 2.5-m thick interval of maximum organic preservation between -145.02 m and -142.55 m, with TOC peaks reaching 12-21 wt%. However, the broad organic-rich interval seems much larger, with TOC around 6.1 wt% on average and HI values of 282 mgHC/gTOC on average between -157.3 m and -126.1 m. Moreover, a long-term progressive increase of TOC accumulation, highlighted by several organic pulses is obvious, starting at -282.4 m and pre-dating the Lally oil shale bed occurrence. We thus evidence for the first time that the Lally oil shale bed corresponds to the short-lived apex of a long-term lacustrine organic rich sequence of increasing paleo-productivity and/or paleo-anoxia that is ∼ 200m in thickness and therefore, is not only limited to a thin, (pluri)-meter-thick organic rich interval associated with short-lived anoxia and/or primary productivity pulse, as previously admitted. These findings rise the question of the paleoenvironmental mechanism(s) behind the occurrence of oil-shale intervals within the Autun Basin. Although further works are needed to fully understand those mechanisms, a preliminary cyclostratigraphy study using the Chevrey 1 TOC record suggests that the organic accumulation was likely controlled by climatic cycles in the Milankovitch frequency bands, and that the ∼ 200 m long-term organic trend may be linked to ~2 Myrs eccentricity.

23 pages; International audience; The Late Jurassic was a period of major global carbon cycle perturbations with episodes of anoxia leading to regional accumulation of organic matter in sediments worldwide. The Tubiegatan section (SW Gissar Mountains, Uzbekistan) located in the Northern Tethys, shows atypical organic-rich limestone and marl deposits (up to 6% of total organic carbon) marked by pronounced negative excursions of δ13Ccarb (amplitude of ca. 12‰) and δ13Corg (amplitude of ca. 4‰) recorded during the Middle Oxfordian (Transversarium Zone). A transdisciplinary approach including sedimentology, palynofacies characterization, mineralogy, organic and inorganic geochemistry was carried out to elucidate the origin of these organic-rich deposits. Highest TOC are measured in nodular limestones, and lowest δ13Ccarb values in thinly laminated facies consisting in alternances of infra-millimeter-thick organic and carbonate laminae. In the latter, the presence of organic-carbonate peloids and of possible remnants of exopolymeric substances associated with clay indicate that these structures are probably mineralized laminated benthic microbial mats (i.e., stromatolites). Rock-Eval pyrolysis coupled to palynofacies analyses point to a dominant altered marine organic matter of probable algal/microbial origin, with subordinate continental phytoclasts inputs in the upper part of the organic-rich interval. Trace elements (U/Th, V/Cr and Mo/Al ratios) indicate two anoxic episodes coinciding with the highest TOC, punctuated by dysoxic periods. Such O2-depleted conditions have allowed the preservation and probably the development of anaerobic microbial communities in the microbial mats. In these latter, sulfate reduction probably had a significant contribution to the production of carbonates, which would explain the precipitation of pyrite and the relatively low δ13Ccarb values. The progressive decrease then disappearance of kaolinite from the base of the organic-rich interval, is interpreted as a progressive aridification of the Amu Darya Basin during the Transversarium Zone, culminating with the progradation of a large-scale gypsum sabkha overlying the organic deposits. Overall, the organic-rich deposits could record the onset of the disconnection of the Amu Darya Basin from the open sea to the south, induced by compression and subsequent uplifts in the Afghan and Central Iranian blocks. The elevated evaporation, coupled with the presence of hydrological barriers (such as coral reefs) could have led to the formation of local to regional anoxic conditions in the Amu Darya Basin. Similar microbial organic accumulations are recently known throughout the Tethys (e.g., Arabian Plate, Western Europe) and from other oceans (e.g., Central Atlantic, Pacific) during the Late Jurassic, suggesting common controlling factors. The increase of organic matter storage worldwide coupled with potential methane release could have in turn induced major perturbations of the carbon cycle during the Oxfordian-Kimmeridgian interval. The relatively shallow anoxia model proposed in this study contrasts with the well-known organic carbon-rich pelagic models proposed for the Jurassic anoxia (e.g., Toarcian, Kimmeridgian) and Cretaceous OAEs.

Here in the first part of this publication we discuss the possibilities for the selection of a GSSP for the Berriasian Stage of the Cretaceous System, based on the established methods for correlation in the Tithonian/Berriasian interval. This will be followed, in the second part, by an account of the stratigraphic evidence that justifies the locality of Tre Maroua (Hautes-Alpes, SE France) as the proposed GSSP. Here we discuss the possibilities for correlation in the historical J/K boundary interval, and the evolution of thinking on the positioning of the boundary over recent generations, and in relation to research in the last ten years. The Tithonian/Berriasian boundary level is accepted as occurring within magnetosubzone M19n.2n. The detailed distribution of calpionellids has been recorded at numerous sites, tied to magnetostratigraphy, and the base of the calpionellid Alpina Zone is taken to define the base of the Berriasian Stage. This is at a level just below the distinctive reversed magnetic subzone M19n.1r (the so-called Brodno reversal). We discuss a wide range of magneto­stratigraphic and biostratigraphic data from key localities globally, in the type Berriasian areas of France and wider regions (Le Chouet, Saint Bertrand, Puerto Escano, Rio Argos, Bosso, Brodno, Kurovice, Theodosia etc.). The characteristic datums that typify the J/K boun­dary interval in Tethys and its extensions are detailed, and the correlative viability of various fossil groups is discussed. The boundary level is correlated to well-known J/K sections globally, and a series of secondary markers and proxies are indicated which assist wider correlation. Particularly significant are the primary basal Berriasian marker, the base of the Alpina Subzone (marked by dominance of small Calpionella alpina, Crassicollaria parvula and Tintinopsella carpathica) and secondary markers bracketing the base of the Calpio­nella Zone, notably the FOs of the calcareous nannofossil species Nannoconus wintereri (just below the boundary) and the FO of Nannoconus steinmannii minor (just above). Notable proxies for the boundary are: 1) the base of the Arctoteuthis tehamaensis Zone in boreal and subboreal regions, 2) the dated base of the Alpina Subzone at 140.22 ±0.14 Ma, which also gives a precise age estimate for the system boundary; and 3) the base of radiolarian “unitary zone” 14, which is situated just above the base of the Alpina Subzone.

International audience; In part 1 of this work we discussed the possibilities for the selection of a GSSP for the Berriasian Stage of the Cretaceous System, based on prevailing practical methods for correlation in that J/K interval, traditional usage and the consensus over the best boundary markers that had developed in the last forty years. This consensus has developed further, based on the results of multidisciplinary studies on numerous sites over the last decade. Here in Part 2 we give an account of the application of those results by the Berriasian Working Group (ISCS), and present the stratigraphic evidence that justifies the selection of the locality of Tré Maroua (Hautes-Alpes, SE France) as the proposed GSSP. We describe a 45 m-thick section in the Calcaires Blancs vocontiens – that part of the formation covering the calpio­nellid Chitinoidella, Remanei. Intermedia, Colomi, Alpina, Ferasini, Elliptica and Simplex biozones. The stratigraphic data collected here has been compiled as part of a wider comparative study of complementary Vocontian Basin sites (with localities at Charens, St Bertrand, Belvedere and Le Chouet). Evidence from Tré Maroua thus sits in this substantial regional biostratigraphic and magnetostratigraphic context. For the purposes of the GSSP definition, here we particularly concentrate on the unbroken sequence and biotic markers in the interval immediately below the boundary, the Colomi Subzone (covering circa 675,000 years), and immediately above, the Alpina Subzone (covering circa 725,000 years). Particularly significant fossil datums identified in the Tré Maroua profile are the primary basal Berriasian marker, the base of the Alpina Subzone (a widespread event marked by dominance of small Calpionella alpina, with rare Crassicollaria parvula and Tintinopsella carpathica): the base of the Berriasian Stage is placed at the base of bed 14, which coincides with the base of the Alpina Subzone. Secondary markers bracketing the base of the Calpionella Zone are the FOs of the calcareous nannofossil species Nannoconus wintereri, close below the boundary, and the FO of Nannoconus steinmannii minor, close above. The Tithonian/Berriasian boundary level occurs within M19n.2n, in common with many documented sites, and is just below the distinctive reversed magnetic subzone M19n.1r (the so-called Brodno reversal). We present data which is congruent with magnetostratigraphic and biostratigraphic data from other key localities in France and in wider regions (Le Chouet, Saint Bertrand, Puerto Escaño, Rio Argos, Bosso, Brodno, Kurovice, Theodosia…), and thus the characteristics and datums identified at Tré Maroua are key for correlation and, in general, they typify the J/K boundary interval in Tethys and connected seas.

During the Paleocene–Eocene, the Earth experienced the warmest conditions of the Cenozoic and reduced equator-to-pole temperature gradients. Compared to low- and mid-latitude sites, Paleogene environmental changes are less documented in Arctic regions, although such high latitude areas constitute a critical domain to constrain global climate changes. Floral and faunal assemblages indicative of exceptionally warm and humid conditions during the late Paleocene–early Eocene have been reported in several localities around the Arctic Ocean. Additional studies are required to ascertain the effects of Paleocene–Eocene global environmental changes on western Arctic regions. Here we present multiproxy data from early Eocene deltaic plain sediments of the Mackenzie Delta (Canada). This environment is characterized by littoral forest, including swamp, showing that the mangrove Avicennia grew in Arctic Canada near 75°N under air temperatures averaging 21–22 °C annually and 10–14 °C in winter and with precipitation of 1200–1400 mm/yr. Kaolinite contents are high (up to 75% of clay assemblages), as under a modern subtropical climate. The Avicennia pollens recently found in the New Siberian Islands and in Arctic Canada imply that warm and wet conditions were widespread along the Arctic coast during the early Eocene. It also suggests a marine connection between the Arctic Basin and the mid-latitude oceans. We propose that an oceanic current must have connected the Arctic Basin to the Atlantic and/or Pacific and that an internal current developed in the Arctic Basin since the early Eocene.

International audience; European early Eocene (Ypresian) mammalian biochronology, covering a timespan of about 8 myr, includes three distinct MP (Mammal Paleogene) reference levels MP7, MP8+9 and MP10. These are represented in the unique succession of the Minervois (Southern France) by the localities of Fournes (close to MP7), Sainte-Eulalie (close to MP8+9) and Azillanet (close to MP10). Considering homogenous terrestrial organic matter contribution (type III) as suggested by palynofacies and Rock-Eval pyrolysis, we here demonstrate that the organic carbon isotope curve of the predominantly continental Ypresian of the Minervois closely matches the marine standard carbonate carbon isotope curve. The here studied mammalian faunas and their supposed corresponding MP levels can thus be accurately dated and correlated on a global scale. The endemic Fournes mammal fauna, located just above the Eocene Thermal Maximum 2-ETM2, is assigned to mid-Biochron NP11 Calcareous Nannoplankton Zone. Accordingly, the Fournes mammal site is about 2.5 myr younger than the MP7 reference level of Dormaal (Belgium, latest Biochron NP9), about 1 myr younger than the MP7 mammalian locality of Le Clot in the Corbieres (Southern France, late Biochron NP10 or early Biochron NP11) and very close to the Wasatchian Wa-5 mammalian biozone of Wyoming. A mid-Biochron NP12 age is inferred for the endemic Sainte-Eulalie fauna because of its position at the very top of (or just above) the isotopically negative ``ETM3 interval'', whereas the Azillanet fauna, recorded at the top of a delta C-13(org) positive trend above the ``ETM3 interval'', ranges from late Biochron NP12 to early Biochron NP13. Our results indicate that the short-term hyperthermals ETM2 and ETM3 did not affect the endemic character of the mammalian faunas in Southern and Northern Europe during the MP7 to MP8+9 interval. The end of this mammalian endemism likely occurred during the early phases of the EECO (Early Eocene Climatic Optimum) in early late Biochron NP12.

29 pages; International audience; Sedimentological investigations have been carried out in the southwestern part of the Gissar Range (Uzbekistan) in order to document the stratigraphic evolution of a vast Middle–Upper Jurassic carbonate platform developed on the northern margin of the Amu Darya Basin. Two major sequences are distinguished, based on their contrasting facies pattern, platform configuration and carbon isotope signature: (1) a Callovian Sequence and (2) an Upper Jurassic Sequence, potentially Oxfordian to Kimmeridgian in age. A carbonate ramp with a double proximal-distal polarity developed during the Callovian Sequence. Oo-bioclastic grainstones were produced in two permanently agitated shallow water areas developing to the north and to the south. Patch and pinnacle reefs mainly built up close to the storm-wave base, passing distally to pellet- and foraminiferal-oncoid-rich mid-to outer-ramp deposits. The top of the Callovian Sequence is a regional discontinuity that could have formed by subaerial exposure of the platform. This probable hiatus could record a major climatic change associated to the Middle‒Late Jurassic transition. The Upper Jurassic Sequence consists of metre-thick alternations of pellet/algal-pack- to grainstones, microbial oncoid floatstones, ooid grainstones, and mudstones, which have likely accumulated in a vast lagoon protected by a large-scale barrier reef observed south of the study area. Gypsum and anhydrite content gradually increased towards the top of the Upper Jurassic Sequence, ending up with a thick chicken-wire gypsum accumulation recording the progradation of a large-scale sabkha over the lagoon. This phenomenon is related to a progressive aridification and restriction of the Amu Darya Basin that could have begun during the Middle/Late Oxfordian and reached its climax during the Tithonian with massive halite deposition. Comparable events occurred in Jurassic platforms located along the Tethyan margins, pointing to regional and global controls on sedimentation.

The presently active region of the Congo deep-sea fan (around 330,000 km(2)), called the terminal lobes or lobe complex, covers an area of 2500 km(2) at 4700-5100 m water depth and 750-800 km offshore. It is a unique sedimentary area in the world ocean fed by a submarine canyon and a channel-levee system which presently deliver large amounts of organic carbon originating from the Congo River by turbidity currents. This particularity is due to the deep incision of the shelf by the Congo canyon, up to 30 km into the estuary, which funnels the Congo River sediments into the deep-sea. The connection between the river and the canyon is unique for major world rivers. In 2011, two cruises (WACS leg 2 and Congolobe) were conducted to simultaneously investigate the geology, organic and inorganic geochemistry, and micro- and macro-biology of the terminal lobes of the Congo deep-sea fan. Using this multidisciplinary approach, the morpho-sedimentary features of the lobes were characterized along with the origin and reactivity of organic matter, the recycling and burial of biogenic compounds, the diversity and function of bacterial and archaeal communities within the sediment, and the biodiversity and functioning of the faunal assemblages on the seafloor. Six different sites were selected for this study: Four distributed along the active channel from the lobe complex entrance to the outer rim of the sediment deposition zone, and two positioned cross-axis and at increasing distance from the active channel, thus providing a gradient in turbidite particle delivery and sediment age. This paper aims to provide the general context of this multidisciplinary study. It describes the general features of the site and the overall sampling strategy and provides the initial habitat observations to guide the other in-depth investigations presented in this special issue. Detailed bathymetry of each sampling site using 0.1-1 m resolution multibeam obtained with a remotely operated vehicle (ROV) shows progressive widening and smoothing of the channel-levees with increasing depth and reveals a complex morphology with channel bifurcations, erosional features and massive deposits. Dense ecosystems surveyed in the study area gather high density clusters of two large-sized species of symbiotic Vesicomyidae bivalves and microbial mats. These assemblages, which are rarely observed in sedimentary zones, resemble those based on chemosynthesis at cold-seep sites, such as the active pockmarks encountered along the Congo margin, and share with these sites the dominant vesicomyid species Christineconcha regab. Sedimentation rates estimated in the lobe complex range between 0.5 and 10 cm yr(-1), which is 2-3 orders of magnitude higher than values generally encountered at abyssal depths. The bathymetry, faunal assemblages and sedimentation rates make the Congo lobe complex a highly peculiar deep-sea habitat driven by high inputs of terrigenous material delivered by the Congo channel-levee system. (c) 2016 Elsevier Ltd. All rights reserved. ZAIANGO ANR Congolobe (ANR Blanc SIMI5-6) [11 BS56 030] IFREMER CEA through LSCE U.S. National Science Foundation [OCE-0831156] info:eu-repo/semantics/acceptedVersion

The Congo deep-sea fan is directly connected to the Congo River by a unique submarine canyon. The Congo River delivers up to 2×1012gPOC/yr, a part of which is funnelled by the submarine canyon and feeds the deep-sea environments. The more distal part of the Congo deep-sea fan, the terminal lobe area, has a surface of 2500 km2 and is situated up to 800 km offshore at depths of 4750–5000 m. It is a remarkable place to study the fate and distribution of the organic matter transferred from the continent to the deep ocean via turbidity currents. Forty-two samples were analyzed from the terminal lobes, including sites from the active channel, one of its levees and an abandoned distal channel. Samples were collected using multitube cores and push-cores using a Victor 6000 ROV, which surveyed the dense chemosynthetic habitats that locally characterize the terminal lobes. Palynofacies reveal a remarkably well-preserved, dominantly terrestrial particulate organic matter assemblage, that has been transferred from the continent into the deep-sea by turbidity currents. Delicate plant structures, cuticle fragments and plant cellular material is often preserved, highlighting the efficiency of turbidity currents to transfer terrestrial organic matter to the sea-floor, where it is preserved. Moreover, the palynofacies data reveal a general sorting by density or buoyancy of the organic particles, as the turbulent currents escaped the active channel, feeding the levees and the more distal, abandoned channel area. Finally, in addition to aforementioned hydrodynamic factors controlling the organic matter accumulation, a secondary influence of chemosynthetic habitats on organic matter preservation is also apparent. Palynofacies is therefore a useful tool to record the distribution of organic matter in recent and ancient deep-sea fan environments, an important topic for both academic and petroleum studies.

The early Eocene (ca. 56–47.8 Ma) was an interval of exceptional warmth with reduced pole-to-equator temperature gradients. Climate proxies indicate mean annual air temperatures (MATs) and sea-surface temperatures (SSTs) exceeding 8–18 °C and frost-free, mild winters in polar areas, features that have proven difficult to reproduce with the most elaborate climate models. A full appraisal of the early Eocene polar climate has been, however, limited by possible seasonal biases associated with geochemical proxies and the lack of data from the vast Eurasian Arctic. Here we present multiproxy data from lower-middle Eocene coastal plain sediments of the New Siberian Islands (Russia) showing that taxodioid Cupressaceae, palms, and the mangrove Avicennia grew in Arctic Siberia above 72°N under air temperatures averaging 16–21 °C annually and 5.5–14 °C in winter. Kaolinite contents are exceptionally high (up to 60% of clay assemblages) and comparable to those found in present-day subtropical soils formed under high mean annual precipitation (MAP >1000 mm) and warm (MAT >15 °C) conditions. The Avicennia pollen records the northernmost mangrove growth ever documented and indicates early Eocene SSTs exceeding 13 °C in winter and 18 °C in summer. Considering the high MAP estimated for Arctic Siberia and other pan-Arctic landmasses, we propose that the heat from warm river waters draining into the Arctic might have amplified early Eocene polar warmth. Our results provide the first climate constraints for the early Eocene of Arctic Siberia and support the view that most climate models underestimate polar warming in greenhouse conditions.

International audience; The Congo River, the second largest river in the world, is a major source of organic matter for the deep Atlantic Ocean because of the connection of its estuary to the deep offshore area by a submarine canyon which feeds a vast deep-sea fan. The lobe zone of this deep-sea fan is the final receptacle of the sedimentary inputs presently channelled by the canyon and covers an area of ~2500 km². The quantity and the source of organic matter preserved in recent turbiditic sediments from the distal lobe of the Congo deep-sea fan were assessed using Rock-Eval pyrolysis analyses. Six sites, located at approximately 5000 m water-depth, were investigated. The mud-rich sediments of the distal lobe contain high amounts of organic matter (~3.5 to 4% Corg), the origin of which is a mixture of terrestrial higher-plant debris, soil organic matter and deeply oxidized phytoplanktonic material. Although the respective contribution of terrestrial and marine sources of organic matter cannot be precisely quantified using Rock-Eval analyses, the terrestrial fraction is dominant according to similar hydrogen and oxygen indices of both suspended and bedload sediments from the Congo River and that deposited in the lobe complex. The Rock-Eval signature supports the 70% to 80% of the terrestrial fraction previously estimated using C/N and δ13Corg data. In the background sediment, the organic matter distribution is homogeneous at different scales, from a single turbiditic event to the entire lobe, and changes in accumulation rates only have a limited effect on the quantity and quality of the preserved organic matter. Peculiar areas with chemosynthetic bivalves and/or bacterial mats, explored using ROV Victor 6000, show a Rock-Eval signature more or less similar to background sediment. This high organic carbon content associated to high sedimentation rates (> 2 to 20 mm.yr−1) in the Congo distal lobe complex implies a high burial rate for organic carbon. Consequently, the Congo deep-sea fan represents an enormous sink of terrestrial organic matter when compared to other turbiditic systems over the world.

International audience; The Eocene–Oligocene transition (EOT, ~34 Ma) is the largest global cooling of the Cenozoic Era and led the Earth's climatic system to change from a greenhouse to an icehouse mode. Although it is well documented in marine settings, the few studies focusing on continental environments have demonstrated regional heterogeneities. The study core CDB1, located in the Rennes Basin (Western France), is a unique terrestrial (lacustrine–palustrine) record comprising well-preserved and terrestrial-derived organic-rich sediments encompassing the EOT. Clay minerals and the first organic nitrogen isotope record (d 15 N org) of terrestrial origin for this period are used to reconstruct palaeoclimate changes across this key interval. As suggested in worldwide marine and a few continental records, a stepwise transition from warm/humid conditions in the Late Eocene to cooler/drier conditions in the Early Oligocene is confirmed in the area. In addition, an episode of drier conditions in the Late Eocene and humid/dry cycles in the Early Oligocene are suggested. Terra Nova, 00: 1–9, 2016

Pedogenic nodules, calcitic shells, dispersed organic carbon and bulk rocks affected by low diagenesis are judged to be reliable tools for carbon-isotope chemostratigraphy. Up to now no systematic study has been carried out to check the reliability of fossil wood material for carbon-isotope chemostratigraphy in terrestrial settings. The 235-m thick Wealden facies sediments of the Danube-Bouchon quarry at Hautrage (Hautrage Clays Formation, Mons Basin, Belgium) encompass dark to grey clays and sands, rich in organic matter and coalified-charcoalified fragments of fossil wood, deposited in an alluvial plain during middle Barremian to earliest Aptian. We measured and compared the carbon-isotope ratios of 110 levels of the stratigraphic succession for dispersed organic carbon (δ13CDOC), and fossil wood (δ13CWOOD) collected in the same geological level. In the whole succession, the averages of δ13CDOC and δ13CWOOD have a significant difference of about 0.9‰. The δ13CWOOD is usually heavier than the δ13CDOC, which is consistent with measurements on different constituents of modern trees (branches versus leaves and tissues). In one single stratigraphic level, the variability of δ13CWOOD is much higher (up to 7.3‰) than that of δ13CDOC (0.4‰). Four main causes may explain these results. Firstly, the δ13CDOC averages the isotopic signal of different compounds and tissues (such as leaves, seeds, cuticles) as they become mixed and dispersed. The δ13CWOOD reflects the carbon-isotope ratio of a small part only of one single tree, which is a complex system with δ13C variations over a range of 4‰. Secondly, there is strong δ13C variability between different species of plants. In Hautrage, several gymnosperm genera were collected (including Podocarpoxylon, Taxodioxylon, Brachyoxylon, and Thujoxylon) and numerous fern taxa. Thirdly, coalification and charcoalification can affect the δ13C of the DOC and the various kinds of woods in a different way. Fourthly, the wood fragments may be reworked several times from more ancient geological levels, especially in the alluvial plain environment of Hautrage where thick levels of fluviatile coarse sand deposits are observed. However, in the whole succession, both δ13CWOOD and δ13CDOC curves show similar trends. This suggests that carbon-isotope curves on fossil wood can be matched to carbon-isotope curves on DOC. For the whole trend fossil wood is a relatively good chemostratigraphic tool when sufficient samples are measured in the succession. Whenever possible both control of the wood taxa, and estimation of degree of (char)coalification are however recommended. In one single level, charcoal has more stable δ13CWOOD values than δ13CWOOD of coalified fragments. The δ13C positive trend can be due to several causes, including global pCO2 variations and/or regional changes and/or local environmental conditions in the alluvial plain. If global, the dating of the Hautrage succession may be refined to the late Early Barremian-early Late Barremian by matching palynological and carbon-isotope chemostratigraphical data. © 2010 Elsevier B.V. All rights reserved.

The Taskomirsay section (South Kazakhstan) is a unique Pliensbachian-Toarcian sequence of lignites, clayey layers and silty-sandstones deposited in a fluvial/lacustrine environment with nearby swampy areas. This period, characterized by a drastic climate change, has been particularly studied in Western Tethyan marine environments, whereas very few studies focused on continental settings. Paleoflora analyses, associated with a multi-isotope approach, based on well-preserved Type-III bulk organic nitrogen isotopes (δ15Norg) and hydrogen isotopic composition (δ2H) of n-alkanes, were developed to document paleoclimatic changes in the area. Sporomorph associations and fossil woods revealed a globally warm- to cool-temperate climate – characterized by Xenoxylon, a conifer morphogenus biogeographically related to cool/humid settings – apart from slightly less humid and warmer conditions in the early Toarcian. Warmer conditions are supported by reconstructed Mean Annual Air Temperatures (MAATs), based on the first branched glycerol dialkyl glycerol tetraethers (brGDGTs) ever recorded in the Early Jurassic. Nevertheless, no drastic changes were recorded in the δ15Norg values; its signal being attributed to tenuous equilibrium between water- and nutrient-availability via intense N-recycling. Based on n-alkane distributions, sources of organic matter were separated in two pools: (i) a purely terrestrial (n-C27) and (ii) an “aquatic” pool (n-C23) constituted of vegetation that thrived under almost permanent water supply. The n-alkane δ2H values (− 248 to − 151‰) as well as their amounts and average chain lengths (ACL) are in agreement with cool-temperate conditions in the Pliensbachian and less humid/warmer conditions in the early Toarcian. The isotopic difference between δ2H values of n-C27 and n-C23 (Δ2Hter-aq) suggests enhanced seasonality during the Pliensbachian-Toarcian transition and low seasonality in the early Toarcian, in agreement with temperate climate-regime. Finally, contrasted response to paleoclimate changes between markers suggests different spatial integration of those proxies. The role of sea-level variations for δ2H values might also resolve this contrasted response.

International audience; The terminal lobe complex of the Congo River submarine fan sits on the abyssal Atlantic plain, at 5000 m water depth, 760 km offshore from the river mouth estuarine area. While most rivers deliver particulate material to the continental shelf, particulate matter from the Congo River largely bypasses the shelf and is transported by turbidity currents through the Congo submarine canyon system. We determined the quantity and quality of the organic matter reaching the terminal lobe complex at five sites with marked morphological differences that may influence the distribution of organic matter. A suite of bulk geochemical (% OC, δ13Corg, δ15N, C: N), 137Cs and palynofacies analyses were done on cores collected from the terminal lobe area. These results were also compared to the composition of sediments collected upstream at the Malebo Pool (Congo River).Distal lobe complex sediments contain high amounts of terrestrial organic carbon (3–5 wt.%) that is homogeneously distributed in surficial (22 cm) and deeper sediments (580 cm) silty–clay facies. Strongly altered soil-derived organic matter with well-preserved land plant detritus from the Congo River predominates. A terrestrial soil origin for the particulate load was confirmed by the elevated 137Cs activity in lobe sediments. The vertical distribution of the 137Cs signal suggests that there has been a massive arrival of terrestrial sediments since 1963, consistent with a turbiditic origin. From the locations surveyed, we estimate a maximum accumulation of terrestrial organic carbon of ca. 1 kg OC m− 2 y− 1 for the distal lobe. However, transport modifies the organic matter both in terms of quantity and quality. Observed differences were attributed to preferential degradation of nitrogenous matter during diagenesis and to the addition of highly remineralized marine organic matter.Results from our temporal reference site (E) suggest that organic matter may be preserved in turbidite facies for thousands of years. The good preservation state of the accumulated organic matter shows that turbiditic lobe complexes should be considered as a sink for terrestrial organic carbon in the deep ocean.

International audience; The Cap d'Ailly area (Upper Normandy, France) shows several terrestrial–lagoonal sections recording the negative carbon isotope excursion (CIE) associated with the Paleocene–Eocene Thermal Maximum (PETM; 55.8 Ma). A study of the biomarkers and spore/pollen content of the Vasterival section gave com-plementary information on paleofloral changes that occurred around the Paleocene–Eocene (P–E) bound-ary. Aliphatic hydrocarbon fractions revealed a high abundance of vascular plant biomarkers, including tricyclic diterpanes derived from conifers, fernenes derived from ferns and des-A-triterpenes derived from angiosperms. Whereas the vegetation of the depositional environment surroundings seemed alter-nately dominated by ferns and angiosperms (revealed from biomarkers), the regional flora seemed dom-inated strictly by angiosperms such as Juglandaceae (revealed by pollen). Spore/pollen assemblages revealed no major turnover in the paleovegetation, but slight variation in vegetation composition. How-ever, both biomarkers and spores/pollen exhibited two intervals of rapid floral change: the first occurred around the P–E boundary and the second at the top of the strictly terrestrial unit that coincides with a marine transgression. Comparison of the data with published paleoclimatic results, obtained from the same samples, indicated that the first interval of floral change correlates with strong paleohydrological perturbations, whereas the second is linked to an increasing marine influence.

Environmental contextCarbon and nitrogen isotopes in terrestrial organic matter are widely used for reconstructing past environments, but organic matter is exposed to degradation as soon as it is deposited during what is called early diagenesis. This study explores the effects of this process on organic carbon and nitrogen isotopes, and concludes that it homogenises an environmental signal by integrating all their components. Thus, early diagenesis may not preclude paleoenvironmental reconstructions. AbstractThe effect of early diagenesis on carbon and, especially, nitrogen isotopes (δ13C and δ15N) of organic matter is not well understood and is of interest for accurate paleoenvironmental reconstructions. Wood samples were incubated in distilled water and river water to assess the effects of early diagenesis on carbon and nitrogen dynamics. Elemental content and isotopic composition of carbon and nitrogen as well as mass loss of wood pieces were determined. Mass loss in river water was three times greater than in distilled water. This difference was attributed to the development of two different types of fungi characterised by various degradation rates. Carbon dynamics of wood samples showed similar patterns in both type of water: (i) a sharp increase in carbon content, possibly related to carbohydrate degradation, before it slowly returned towards initial values, and (ii) no significant changes in δ13C values. In contrast, nitrogen dynamics of samples showed complex patterns: (i) N release associated with 15N depletion in distilled water, attributed to uptake of 15N-enriched pool (i.e. proteins) by fungi, and (ii) N accumulation associated with 15N enrichment in river water. The latter pattern was attributed predominantly to microbially mediated importation of 15N-enriched nitrate from river water. Although challenging, the present results suggest that early diagenesis may average an environmental signal by integrating individual signals (woods, fungi, water) and microbial processes. Considering the non-linear behaviour of early diagenesis, this integration is probably almost instantaneous on the geological time scale, which may not preclude paleoenvironmental reconstructions.

International audience; The Paleocene-Eocene boundary (55.8 Ma) is associated with the Paleocene-Eocene Thermal Maximum (PETM), which is characterized by a negative Carbon Isotope Excursion (CIE), reflecting a major perturbation of the carbon cycle, and by an extreme and rapid global warming. The Cap d'Ailly area (Upper Normandy, France), in which previous studies have revealed the Paleocene-Eocene transition, is a reference locality for organic-rich terrestrial and lagoonal deposits of the "Sparnacian" stage, widespread in Northwestern Europe. In this study, we focus on the organic matter content of the Vasterival section. Organic data (Rock-Eval, palynofacies, biomarker analyses and compound specific isotope analyses) were acquired in order to constrain the paleoenvironmental and paleohydrological changes that occurred at the Paleocene-Eocene boundary. Stable carbon isotope compositions of higher plant leaf wax n-alkanes reveal a CIE of − 4.5 ‰, extending throughout the second half of the studied section. Palynofacies observations reveal: (i) an abrupt shift from a closed, quiescent marsh pond to an open eutrophic swamp subjected to algal blooms, concomitant with the onset of the CIE; and (ii) the evolution from a swamp to a tidal flat due to the marine transgression that occurred during the PETM. Higher plant biomarkers and their hydrogen isotopic composition compared to nitrogen analyses suggest: (i) dry episodes just before the PETM that may help to understand the triggering of this hyperthermal event; (ii) a moister climate associated with a stronger seasonality during the early PETM.

International audience; Two sections corresponding respectively to the Shal (Callovian – Lower Berriasian) and Kolur Formations (Berriasian – Valanginian in the sampled interval) have been studied in the Talesh Mountains (North-West Iran), an area whose sedimentary successions formed on the northern margin of the Eastern Tethys during the Mesozoic. This study allowed the identification of the different calpionellid zones and sub-zones defined in basin successions of the Western Tethys. In the upper part of Shal Formation the Chitinoidella boneti (base of the Upper Tithonian) and B1 sub-zones (base of the Calpionella alpina zone, lowermost Berriasian) have been recognized. The rich and diverse calpionellid faunas allowed us to recognize in the Kolur Formation B3 (top of the C. alpina zone), C1, C2 (Calpionella elliptica zone), D1, D2, D3 (Calpionellopsis zone) subzones and E (Calpionellites zone) and F (Tintinnopsella zone). The E zone has been subdivided in two sub-zones: E1 and E2, which is characterized by the disappearance of the genus Calpionellopsis. Thirty calpionellid species have been described. Fifteen of them are new: Calpionellites medius nov. sp., Calpionellites minor nov. sp., Remaniella longocadischiana nov. sp., Remaniella minicadischiana nov. sp., Tintinnopsella curva nov. sp., Tintinnopsella duranddelgai nov. sp., Tintinnopsella elmii nov. sp., Tintinnopsella largovalata nov. sp., Tintinnopsella lehegarati nov. sp., Tintinnopsella longovalata nov. sp., Tintinnopsella maxilonga nov. sp., Tintinnopsella minicarpathica nov. sp., Tintinnopsella pseudoblonga nov. sp., Tintinnopsella pseudocarpathica nov. sp. and Tintinnopsella pseudosimplex nov. sp. Amongst the other pelagic microfossil groups, Globochaete and calcispheres (“microproblematics”), often abundant in Western Tethyan Upper Jurassic – Lower Cretaceous pelagic successions, are absent in the Shal Formation and extremely rare in the Kolur Formation despite its lithofacies usually suited for preservation of such microfossils. It is worth noting that in Kolur section the peak of Cadosina fusca in the D1 sub-zone and the occurrence of Stomiosphaera wanneri in the C zone have been observed similarly to successions of Moroccan external Rif. As in most basins of the Western Tethys, Saccocoma remains are frequent in the upper part of the Shal Formation and disappear after the appearance of Chitinoidella in the uppermost Tithonian. Radiolarians with spherical tests are represented by two morphologies:one of common size, called morphology A, occurs at different levels of both Shal and Kolur Formations, while the larger one, called morphology B, occurs in the Upper Tithonian of the Shal Formation and becomes frequent in the Berriasian – Lower Valanginian beds of the Kolur Formation. The first morphology is relatively frequent in coeval successions of Western Tethyan basins, while the second is rarely reported in the literature. Holothurian sclerites are often abundant in the Lower Berriasian – Lower Valanginian interval, whereas they are rare (or scarcely reported in the literature) in coeval successions of the southern margin of the Western Tethys. Chitinoidella, calpionellids, Saccocoma, protoglobigerinid forams, radiolarian of the morphology A are fossil groups that commonly occur in Tethyan basins. On the contrary, Globochaete and calcispheres were seemingly adapted to local ecological conditions, which were probably different from those of the study area. However, preservation bias for these particular microfossils cannot be excluded in the Kolur section, which is locally affected by faulting.; L’étude de deux coupes correspondant respectivement aux Formations Shal (Callovien – Berriasien inférieur) et Kolur (Berriasien – Valanginien) dans la région du Talesh (Nord-Ouest de l’Iran, marge nord de la Téthys orientale) a permis de caractériser les différentes zones et sous-zones des calpionelles, définies dans des séries des bassins de la Téthys occidentale. Ainsi, les sous-zones à Chitinoidella boneti (base du Tithonien supérieur) et B1 (base de la zone à Calpionella alpina, base du Berriasien inférieur) ont été caractérisées dans la partie supérieure de la Formation Shal. Les sous-zones B3 (sommet de la zone à C. alpina), C1, C2 (zone à Calpionella elliptica), D1, D2, D3 (zone à Calpionellopsis), les zones E (ou à Calpionellites) et F (ou à Tintinnopsella) ont été caractérisées dans la Formation Kolur sur la base d’une riche faune de calpionelles. La zone E a été subdivisée en deux sous-zones : E1 et E2. La première sous-zone est marquée par la persistance du genre Calpionellopsis. Trente espèces de calpionelles ont été décrites. Quinze espèces sont nouvelles, dont 11 du genre Tintinnopsella, deux du genre Remaniella et deux du genre Calpionellites. Parmi les autres microfaunes pélagiques de la limite Jurassique – Crétacé, les Globochaete et les calcisphères (ou microproblématiques), qui sont souvent abondants dans les séries d’âge Jurassique terminal – Crétacé basal des bassins de la Téthys occidentale, sont par contre absents dans la Formation Shal et très rares dans la Formation Kolur. Cette dernière présente pourtant des faciès pélagiques, favorables à la conservation des spécimens de ces deux groupes fossiles. On peut néanmoins signaler, comme dans les séries du Rif externe au Maroc, un pic à Cadosina fusca dans la sous-zone D1 et la présence de Stomiosphaera wanneri dans les niveaux de la zone C. Les Saccocoma, souvent fréquents dans la moitié supérieure de la Formation Shal, disparaissent, comme dans la plupart des séries des bassins de la Téthys occidentale, dans des niveaux assez hauts du Tithonien supérieur, bien après l’apparition de Chitinoidella. Les radiolaires, à coque sphérique, sont représentés par deux morphologies : une de taille normale qualifiée de morphologie A, présente dans les différents niveaux des deux formations étudiées ; une autre de taille plus grande, qualifiée de morphologie B, présente dans les niveaux supérieurs de la Formation Shal (Tithonien supérieur) et devenant fréquente dans les niveaux du Berriasien à Valanginien inférieur de la Formation Kolur. La première morphologie est assez abondante dans les séries de même âge des bassins de la Téthys occidentale ; la seconde y est par contre rarement signalée par les auteurs. Notons que les niveaux du Berriasien inférieur à Valanginien inférieur de la coupe de Kolur contiennent, souvent et en abondance, des sclérites d’holothuries. Les restes de ces organismes sont rares, ou peu signalés dans la littérature, dans les séries de même âge des bassins de la marge sud de la Téthys occidentale. Certains groupes fossiles de part et d’autre de la limite Jurassique – Crétacé sont communs dans les différents bassins du domaine téthysien (Chitinoidella, calpionelles, Saccocoma, protoglobigérines, radiolaires A). Les Globochaete et les calcisphères paraissent par contre mieux adaptés à des conditions écologiques locales qui n’étaient peut-être pas celles de ce secteur de l’Iran, sans exclure les biais de la préservation des microfossiles, notamment dans la coupe de Kolur, localement affectée par des failles.

11 pages; International audience; In Dorset (southern U.K.), the Durlston Bay and Lulworth Cove sections expose lowermost Cretaceous coastal marine and non-marine partly evaporitic sediments (the so-called Purbeckian facies). An interval with organic matter (OM)-rich layers is recognized in both sections. This OM-rich interval is 20 m thick in the middle of the Durlston Bay section. Within these beds, a large OM accumulation is recorded, with total organic carbon (TOC) of up to 8.5 wt%. High hydrogen index (HI) values (up to 956 mgHC/gTOC) point to a Type I OM, generally considered as derived from algal-bacterial biomass. This contrasts with the OM present in the underlying and overlying intervals, displaying in general lower TOC and HI values, and consisting of degraded algal-bacterial material with higher proportions of terrestrial OM. This organic-rich accumulation can be interpreted as a period of enhanced primary productivity within coastal lagoonal/lacustrine settings at times of low sea level. It could also correspond to increasingly reducing waters. The OM distribution found in Dorset correlates well with existing long-term palaeoclimatic patterns, i.e. a latest Jurassic (late Tithonian)-Early Cretaceous (early Berriasian) semi-arid climate replaced during the middle-late Berriasian by a more humid climate. This pattern is recorded elsewhere on both margins of the Tethys, indicating a widespread climate change. In Dorset, deposition of OM-rich beds occurs exactly at the transition between these two climate regimes, probably during the first increase in humidity, which led to enhanced freshwater supply into coastal lakes and lagoons. This suggests a direct or indirect climate control on local development of primary productivity and/or anoxia/ dysoxia within restricted shallow coastal water masses. The proposed environmental model links OM production and preservation with a changing, climate-driven, hydrological regime.

20 pages; International audience; The Purbeck-type section (Durlston Bay, Dorset, UK) exhibits littoral lagoonal to lacustrine facies. It shows a gradual climatic/environmental change from semi-arid conditions associated with evaporites at the Jurassic–Cretaceous transition, to a more humid climate at the end of the Berriasian. Though generally organic-poor (total organic carbon, TOC