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Mudstones from the Argiles de Châtillon Formation exposed in the Boulonnais region of Northern France represent a proximal lateral equivalent of the organic-rich Kimmeridge Clay Formation. The Argiles de Châtillon Formation is composed of two subunits that straddle the Kimmeridgian–Tithonian boundary. Each subunit contains an organic-rich interval. The two conspicuous organic-rich intervals have been linked to either periods of high sea level or greenhouse warming. Here, we use palynology to further understand climate and environmental mechanisms that drove organic matter enrichment. We use bulk organic carbon isotope records (δ13Corg) to correlate the Boulonnais sections with those of the Kimmeridge Clay Formation. The palynological results suggest that the stratigraphically lower organic-rich interval (Kimmeridgian) was deposited under suboxic to anoxic stratified conditions. A large-scale climate shift from cooler/humid to warmer/arid conditions marked the Kimmeridgian–Tithonian boundary, influencing organic matter enrichment in the stratigraphically higher organic-rich interval (Tithonian). In contrast with the lower organic-rich interval, there are no indications of stratified conditions for the higher organic-rich interval. Within this thicker organic-rich interval, cyclic variations in amorphous organic matter distribution, total organic carbon and δ13Corg trends on a 2 m scale are observed. They co-occur with fluctuations of the palynological assemblages, indicative of more humid versus arid climate conditions, likely alternating on a ∼100 kyr eccentricity timescale. Our results show that under the most humid phases of these overall arid climate conditions, sulfurization of carbohydrates was the dominant control on organic matter preservation. This climate-controlled process that drives organic matter enrichment in the Tithonian can be recognized on a basin-wide scale. [ABSTRACT FROM AUTHOR]

Rapid and profound changes in earth surface environments and biota across the Permian-Triassic boundary are well known and relate to the end-Permian mass extinction event. This major crisis is demonstrated by abrupt facies change and the development of microbialite carbonates on the shallow marine shelves around Palaeo-Tethys and western Panthalassa. Microbialites have been described from a range of sites in end-Permian and basal Triassic marine sedimentary rocks, immediately following the end-Permian mass extinction. Here, we present geochemical data primarily focused on microbialites. Our geochemical analysis shows that U, V, Mo and REE (Ce anomaly) may be used as robust redox proxies so that the microbialites record the chemistry of the ancient ambient sea water. Among the three trace metals reputed to be reliable redox proxies, one (V) is correlated here with terrigenous supply, the other two elements (U and Mo) do not show any significant authigenic enrichment, thereby indicating that oxic conditions prevailed during the growth of microbialites. REE profiles show a prominent negative Ce anomaly, also showing that the shallow marine waters were oxic. Our geochemical data are consistent with the presence of some benthic organisms (ostracods, scattered microgastropods, microbrachiopods and foraminifers) in shallow marine waters that survived the mass extinction event. [ABSTRACT FROM AUTHOR]

Abstract: During the last deglaciation, the decaying Laurentide Ice Sheet (LIS) delivered huge volumes of meltwater toward the Gulf of Mexico. The present investigation of clay mineralogy and grain-size characteristics of terrigenous sediments deposited in the Orca Basin (Gulf of Mexico) offers a unique opportunity to link the marine record of these meltwater floods with the reconstructed continental glacial history and the modeled drainage patterns. Five peculiar sedimentary levels, characterized by high smectite content and low CaCO3 content, were identified and occurred simultaneously with major meltwater floods. According to recently published clay mineral distribution maps for North America, these results help to pinpoint the southwestern margin of the LIS as a main contributor to most of the meltwater discharges. In addition, the peculiar mineralogical composition (illite and chlorite-rich) of the sediments characterizing the meltwater episode associated with Heinrich event 1 suggests a provenance from the Great Lakes area, supporting the interpretation of destabilization of the LIS southeastern margin during this event. Decreased terrigenous contribution associated with changing provenance of sediments after 12.9cal ka BP suggests strong modifications of the continental hydrography in relation to Lake Agassiz history and changes in the morphology of Mississippi delta due to rising sea level. [Copyright &y& Elsevier]

Magnetic susceptibility (MS) was measured with high resolution (5 mm) on a 9 m long, 14C dated core from Lake Le Bourget (Savoie, France), spanning the last 7200 years. The strong correlation (R = 0.85) of the MS with the silicate-borne suite of elements (Si, Al, Fe, Mg, K) and anti-correlation with the carbonate content (R = -0.87) allows it to be used as a proxy for the fluctuations of the abundance of riverborne clastic fraction versus authigenic carbonates in sediment. As the Rhône is the only river bringing a significant amount of silicate minerals to the coring site, the MS downstream is interpreted as a proxy of the Rhône suspended load discharge in Lake Le Bourget. This is confirmed over the last 3000 years by the good match with the evolution of hydrological activity of the Rhône as it is known through geomorphological studies of well-dated archaeological sites. Over the last 7200 years, the record is consistent with the regional record of lake water-level fluctuations. While the intensity of the MS signal might be widely affected by the human impact on soil stability, the timing of the period of enhanced hydrological activity appears to be mostly climate-related, and should thus constitute a first step toward a high-resolution (<8 yr) continuous history of hydrological conditions in the NW Alps. [ABSTRACT FROM AUTHOR]

The Late Devonian was a period of drastic environmental changes, as exemplified by a major biotic crisis at the Frasnian–Famennian boundary (FFB) and the onset in Famennian times of glaciations across southern Gondwana. Worldwide evidence for the coeval development of the major Acadian–Eovariscan belt led us to propose a model relating the Late Frasnian–Famennian environmental perturbations to extensive continental uplift through two atmospheric CO2-depleting mechanisms: (1) the intensification of silicate weathering on the continental areas as attested by a major rise in the87Sr/86Sr composition of sea water at the FFB; and (2) the massive burial of organic carbon (Kellwasser events) in partially confined basins due to the collisional-induced reduction of equatorial oceanic communications between the Palaeotethysian and Panthalassic oceans. This process is also suggested to have been controlled by an important primary productivity connected to an increased nutrient availability triggered by the enhanced continental run-off.Terra Nova, 17, 25–34, 2005 [ABSTRACT FROM AUTHOR]

The Frasnian–Famennian (F-F) transition is well exposed in the basinal setting of La Serre (Montagne Noire, France), where oxygen-deficient conditions prevailed in bottom environments. In this paper, we study the F-F transition using inorganic geochemistry (notably, major elements, redox-sensitive and/or sulphide-forming trace metals, and productivity proxies). The results are compared with published data concerning the La Serre section, other F-F sections and other geological formations also deposited in basinal settings. The very high enrichment in redox and productivity tracers indicates that anoxic conditions prevailed across the F-F boundary, and that surface productivity was intense. Such deep-water restricted conditions coupled with high productivity occurred in various places in Late Devonian oceans. Recycling alone cannot account for the intense nutrient supply and therefore the most probable source was via land runoff. We discuss the Eovariscan episode of uplift that stimulated rock weathering, and hence long-term nutrient supply to the seas.Terra Nova, 00, 1–8, 2004 [ABSTRACT FROM AUTHOR]

Dating recent lake sediment records yielding disturbed 210 Pb profiles has been a problem of wide interest in palaeoclimatic and palaeoseismic studies over the last few centuries. When applied to an alpine lake sedimentary record, a high-resolution sedimentological study reveals that the 210 Pb profile is disturbed by the occurrence of single-event deposits triggered by two different mechanisms: flood events deposits and gravity reworking. Removing disturbed layers from the 210 Pb profile yields a logarithmic depth–activity relationship. Using a simple 210 Pb decay model (CFCS) provides an assessment of mean accumulation rate of `continuous sedimentation', as opposed to `event-linked sedimentation'. The correlation of the thickest four gravity-reworked deposits with historically known earthquakes permits both validation and refinement of the age–depth relationship. This refinement highlights variations in accumulation rate consistent with post-Little Ice Age climatic variations. [ABSTRACT FROM AUTHOR]

Examines the mineral magnetic study of Late Quaternary South Caspian Sea sediments. Domination of greigite concentrations on the sediments; Interpretation of the variation of magnetic parameters in terms of greigite grain-size variation; Relation of the variation on the water salinity.