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[1] The Early Toarcian was characterized by two large perturbations to the carbon cycle: a positive trend associated with increased organic matter burial and ocean anoxia, and a pronounced negative carbon isotope excursion (CIE). We contrast the geochemical evolution in the carbonate phases of two successions: one from the Paris Basin (Sancerre core, comprising black shales), the other from the Lusitanian Basin (Peniche section with very minor lithological expression of bottom water anoxia). Our aim was to identify whether these carbon cycle perturbations were related, and differentiate between the common (global) versus regional expressions of the biogeochemical response and ocean chemistry. Our results highlight contrasts in timing of different phases of anoxia in both locations through the widely documented negative CIE. Widespread anoxic conditions were not a necessary prerequisite for generating a pronounced CIE, as required by the recycling (so-called ''Küspert'') model. The production of carbonate simultaneously dropped during the d 13 C negative shift in both locations, likely in response to lowered seawater saturation rate induced by substantial absorption of CO 2 from the atmosphere. The recovery interval was accompanied by a rapid reestablishment of seawater alkalinity, and primary and carbonate productivity in epicontinental seas, as evidenced by high d 13 C and Sr/Ca, in contrast with the more open ocean regime in the Lusitanian Basin. Our results confirm that parallels can be draw between the ocean productivity response and feedback during the Toarcian CIE and the PETM. Both events are characterized by ocean acidification and reduced pelagic calcification followed by a peak in nearshore coccolith productivity, which could have helped the recovery from the perturbation.

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The first centuries AD in the Mediterranean region have generally been associated with a warm, stable climate. High-resolution sedimentary archives sensitive to local environmental change are needed to switch from this general frame to the regional scale. Similarly to cave speleothems, laminated carbonate deposits can grow in the channels of aqueducts which transported water from karstic springs during the Roman period. The deposits of the aqueduct of Nîmes (SE France) are exceptional since they may represent several centuries of paleoenvironmental record with a seasonal resolution. δ18O, δ13C and trace elements were measured in three samples from this aqueduct. The comparison of the geochemical signals with the fine texture of the deposits evidenced the seasonal nature of the lamination observed. This allowed us to document the evolution of environment as recorded through the deposit for the period 50–275 AD. The concretions of the aqueduct of Nîmes document rather stable climatic conditions for the first three centuries AD, as well as a local vegetation change possibly linked to an increased in land use.

International audienceIn order to understand the significance of the worldwide deposition of black shale facies in the Early Toar-cian (∼ 183 Ma), considerable attention has been drawn to this Early Jurassic sub-stage over the last 3 decades. The discovery of a pronounced negative carbon isotope excursion (CIE) within the black shales disrupting the generally positive trend in carbon isotopes has stimulated many studies , particularly with a view to establish the local versus global nature of this major geochemical phenomenon. Here we document the sedimentological and chemostratigraphic evolution of a proximal environment in the Luxembourgian sedimentary area. At Bascharage, Lower Toarcian sediments record the isotopic signature of the Early Toarcian oceanic anoxic event (OAE) by a pronounced positive trend that testifies for widespread anoxia. The expression of the carbon isotope perturbation in this section, however, is unusual compared to adjacent NW European sections. A first −7 ‰ negative CIE, whose onset is recorded at the top of the tenuicosta-tum zone, can be assigned to the well-documented and potentially global Toarcian carbon isotope excursion (T-CIE) with confidence using the well-constrained ammonite bios-tratigraphic framework for this section. In this interval, facies contain only a limited amount of carbonate as a result of intense detrital supply in such a proximal and shallow environment. Stratigraphically higher in the section, the serpentinum zone records a subsequent CIE (−6 ‰) expressed as four negative steps, each being accompanied by positive shifts in the oxygen isotopic composition of carbonate. The preservation state of coccoliths and calcareous dinoflagellates in the second CIE is excellent and comparable to that observed in under-and overlying strata, so this cannot be an artefact of diagenesis. Considering the nature of this record, and the lack of such a pronounced event in the serpentinum zone in coeval sections in Europe, we hypothesise that this second CIE was caused by local factors. The geochemical record of carbonate with a relatively light carbon and relatively heavy oxygen isotopic composition is compatible with the so-called Küspert model, by which a CIE can be explained by an influx of 12 C-rich and cold waters due to upwelling bottom water masses

Well exposed and stratigraphically well constrained by numerous studies, the Zumaia section is one of the best places to conduct studies on the Palaeocene in basin facies. Thus, this section has been chosen [Schmitz et al., 2011] as a stratotype of Selandian basal and terminal limits (GSSP: Global boundary Stratotype Section and Point). The sediments consist of carbonate hemipelagites interbedded with fine carbonate (Maastrichtian to Selandian) and siliciclastic (Thanetian to Eocene) turbidites. The purpose of this work is to geochemically characterize the Selandian by trace element contents (strontium and manganese) and to try to assess the chemical composition of seawater during the Paleocene. Analysis of various separated granulometric fine fractions show that hemipelagic sediments from the Zumaia section present a high preservation quality of the original records of trace-element contents. Late burial diagenesis plays only a minor role and geochemical breaks are not reducible to a change in the nature of carbonate producers. The strontium contents of Paleocene sediments require that the Sr/Ca ratio of seawater was lower than that in the present ocean. The Selandian is characterized by a positive excursion of the strontium curve. This accident is also recognized in several worldwide sections and is related to the platform/basin carbonate sedimentation budget and the intensity of oceanic hydrothermalism. The Mn content of hemipelagites is very high and can reach 2500–3000 ppm in the Paleocene. A comparison of analyses by atomic absorption spectrometry (AAS) and electron paramagnetic resonance (EPR) shows that both Mn2+ (in the calcite lattice) and Mn4+ (as oxide micro nodules) coexist. The Mn content fluctuations are related to the opening phases of the North Atlantic during the Paleocene by submarine volcanism and hydrothermalism in the North Atlantic Igneous Province (NAIP).

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