Dorothée Husson
email: dhusson@earth.northwestern.edu

Bruno Galbrun

Silvia Gardin

Nicolas Thibault

Tempo and duration of short-term environmental perturbations across the Cretaceous-Paleogene boundary

The complex interplay between extraterrestrial events and earth-bound processes that triggered one of the greatest biological crises of the Phanerozoic requires a high resolution timescale. Detailed magnetic susceptibility measurements at the Contessa Highway and Bottaccione sections (Italy) span the Cretaceous-Paleogene boundary and reveal clear orbital signatures in the sedimentary record. Identification of precession and 405 kyr eccentricity cycles allows an estimate of 324+/-40 kyr for the duration of the Maastrichtian part of Chron C29r.

We present in the same high resolution time frame sites in Spain and the North and South Atlantic and bio-horizons, biotic changes, stable isotopic excursions and the decrease in Osmium isotopes recorded in these sections. The onset of 187 Os/ 188 Os decrease coincides with the ! 13 C negative excursion K-PgE1, thus suggesting a first pulse in Deccan volcanism at 66.64 Ma. The K-PgE3 ! 13 C negative excursion is possibly the expression of a second pulse at 66.26 Ma. Late Maastrichtian ! 13 C negative excursions are of low intensity and span durations of one to two eccentricity cycles, whereas early Danian excursions are brief (about 30 kyr) and acute. In Biotic response to late Maastrichtian perturbations occurred with a delay of ca. 200 kyr after the beginning of K-PgE1 shortly before K-PgE3. The biotic perturbation could be thus either a delayed response to K-PgE1, or a direct response to K-PgE3, and possibly, a threshold response to the stepwise buildup of CO2 atmospheric injections. No delay is evident in response to early Danian hyperthermal events. These differences suggest that short-lived, volcanically-derived environmental perturbations were buffered within the stable late Maastrichtian oceanic realm whereas they were amplified by the more sensitive and highly disturbed early Danian oceanic ecosystem.

INTRODUCTION

Resolving the events that triggered and followed the major biological crisis marking the end of the Cretaceous requires a high resolution and well constrained geological timescale. Complex climatic and biotic changes took place during the late Maastrichtian-early Danian transition. The respective roles of Deccan volcanism and the Chicxulub extraterrestrial impact are still debated [START_REF] Keller | Main Deccan volcanism phase ends near the K-T boundary: evidence from the Krishna-Godavari Basin, SE India[END_REF][START_REF] Schulte | The Chicxulub asteroid impact and mass extinction at the Cretaceous-Paleogene boundary[END_REF][START_REF] Archibald | Cretaceous extinctions: multiple causes[END_REF][START_REF] Courtillot | Cretaceous extinctions: the volcanic hypothesis[END_REF][START_REF] Keller | Cretaceous extinctions: evidence overlooked[END_REF][START_REF] Alegret | End-Cretaceous marine mass extinction not caused by productivity collapse[END_REF][START_REF] Renne | Time scales of critical events around the Cretaceous-Paleogene boundary[END_REF].

During the last decades, the progress in cyclostratigraphic methods and astronomical solutions has allowed the development of a Cenozoic astronomical time scale leading to an unprecedented improvement of precision and accuracy [START_REF] Dinares-Turell | Untangling the Palaeocene climatic rhythm: an astronomically calibrated early Palaeocene magnetostratigraphy and biostratigraphy at Zumaia (Basque basin, northern Spain)[END_REF][START_REF] Lourens | The Neogene Period[END_REF][START_REF] Laskar | A long term numerical solution for the insolation quantities of the earth[END_REF][START_REF] Westerhold | Astronomical calibration of the Paleocene time[END_REF][START_REF] Kuiper | SynChronizing Rock Clocks of Earth History[END_REF]Laskar et al. 2010;[START_REF] Hilgen | The Neogene period[END_REF]. The astronomical calibration of the Geologic Time Scale has been recently extended with success down into the late Cretaceous and correlated to carbon-isotope stratigraphy [START_REF] Husson | Astronomical calibration of the Maastrichtian (Late Cretaceous)[END_REF][START_REF] Batenburg | Cyclostratigraphy and astronomical tuning of the Late Maastrichtian at Zumaia (Basque country, Northern Spain)[END_REF]Thibault et al. 2012b). Astronomical calibrations of the early Paleogene and late Cretaceous have mostly been performed independently, not often focusing on the calibration of biotic and environmental changes that occurred across the Cretaceous-Paleogene boundary (K-PgB). The pelagic successions of the Umbria-Marche (Italy) have played a major role in the development of the Cretaceous and Paleogene time scale. These deep water limestones are mostly composed of calcareous plankton, with a very good continuity, allowing the development of a thorough biostratigraphic framework for the Cretaceous [START_REF] Renz | Stratigraphische un Mikropaleontologische Untersuchung der Scaglia (Obere Kreide-Tertiar) in zentralen Apennin[END_REF][START_REF] Renz | Ricerche stratigrafiche et micropaleontologiche sulla Scaglia (Cretaceo superiore-Terziario) dell'Appennino centrale[END_REF][START_REF] Luterbacher | Biostratigrafia del limite Cretaceo-Terziario nell' Appennino centrale[END_REF][START_REF] Gardin | Biomagnetochronology for the upper Campanian -Maastrichtian from the Gubbio area, Italy: new results from the Contessa Highway and Bottaccione sections[END_REF]. Multiple bio-and magnetostratigraphic studies of these sections allowed the micropalaeontological calibration and dating of the C-sequence marine magnetic anomalies, the sections also carrying a very good record of Earth magnetic field reversals [START_REF] Alvarez | Upper Cretaceous-Paleocene magnetic stratigraphy at Gubbio, Italy: V. Type section for the Late Cretaceous-Paleocene geomagnetic reversal time scale[END_REF][START_REF] Lowrie | Upper Cretaceous-Paleocene magnetic stratigraphy at Gubbio, Italy: III. Upper Cretaceous magnetic stratigraphy[END_REF][START_REF] Silva | Cretaceous through Paleocene biostratigraphy of the pelagic sequence at Gubbio, Italy[END_REF][START_REF] Monechi | Late Cretaceous-Eocene nannofossil and magnetostratigraphic correlations near Gubbio, Italy[END_REF]. The Bottaccione section provided, in particular, the first constraint on the location of the Cretaceous-Paleogene boundary within the Chron C29r [START_REF] Alvarez | Upper Cretaceous-Paleocene magnetic stratigraphy at Gubbio, Italy: V. Type section for the Late Cretaceous-Paleocene geomagnetic reversal time scale[END_REF]. The K-PgB transition interval, which was thought in the 1970s to be marked by a global hiatus [START_REF] Alvarez | Upper Cretaceous-Paleocene magnetic stratigraphy at Gubbio, Italy: V. Type section for the Late Cretaceous-Paleocene geomagnetic reversal time scale[END_REF], has later proved to be continuous in this section, and the succession of biotic and abiotic events characterizing this interval is complete. A recent Maastrichtian timescale has been developed by [START_REF] Voigt | Global correlation of Upper Campanian Maastrichtian successions using carbon-isotope stratigraphy: development of a new Maastrichtian timescale[END_REF], based on ! 13 C measurements from several sections, including the Bottaccione and Contessa Highway section. A new biostratigraphic timescale based on Gubbio section has also been presented recently [START_REF] Gardin | Biomagnetochronology for the upper Campanian -Maastrichtian from the Gubbio area, Italy: new results from the Contessa Highway and Bottaccione sections[END_REF]. Cyclostratigraphic analysis of Magnetic Susceptibility variations (MS) proved to be successful in the lower Maastrichtian of the Contessa Highway section, allowing construction of a relative timescale [START_REF] Husson | Astronomical duration of polarity Chron C31r (Lower Maastrichtian): cyclostratigraphy of ODP Site 762 (Indian Ocean) and the Contessa Highway section (Gubbio, Italy)[END_REF]. A decline in the late Maastrichtian marine 187 Os/ 188 Os record of the Bottaccione has been related to the second and main phase of Deccan volcanism [START_REF] Robinson | A highresolution marine 187 Os/ 188 Os record for the late Maastrichtian: Distinguishing the chemical fingerprints of Deccan volcanism and the KP impact event[END_REF]. The Gubbio sections are thus very suitable to investigate the tempo and duration of biotic and environmental changes across the K-PgB event.

We present a new high-resolution cyclostratigraphic time scale for all the bio-horizons, paleoclimatic events and biotic changes spanning the last 450 kyr before the K-PgB and investigate the rates of change and relationships between carbon-isotopic excursions, biotic changes and Deccan volcanism before and after the K-PgB mass extinction.

GEOLOGY AND METHOD

Geological setting

The Upper Cretaceous Scaglia Rossa Formation is located in the central Apennines (Italy), with major outcrops in the Contessa Highway valley and Bottaccione Gorge, near Gubbio. It is composed of hard pelagic limestones, with approximately 10% of foraminifera and 5% of clay in a matrix of calcareous nannofossils [START_REF] Lowrie | Paleogene magnetic stratigraphy in Umbrian pelagic carbonate rocks: The Contessa section, Gubbio[END_REF]. The formation owes its name to its red color, lighter in the Cretaceous than in the Paleogene. An interval approximately 0.50 m thick composed by white limestone occurs in the Cretaceous just before the K-PgB . Magnetite and hematite components, formed during early diagenesis, are responsible for an exceptional record of Earth magnetic field reversals by the Scaglia Rossa Formation limestones [START_REF] Lowrie | Upper Cretaceous-Paleocene magnetic stratigraphy at Gubbio, Italy: III. Upper Cretaceous magnetic stratigraphy[END_REF].

The differences in continuity and accessibility between the Contessa Highway and Bottaccione sections necessitate using a composite section. This composite section corresponds to the uppermost Cretaceous of the Bottaccione section and the lowermost Paleogene from the Contessa Highway section.

Maastrichtian magnetostratigraphy of the Bottaccione section derived from [START_REF] Roggenthen | Upper Cretaceous-Paleocene magnetic stratigraphy at Gubbio, Italy IV. Upper Maastrichtian-Paleocene Magnetic Stratigraphy[END_REF] places the Chrons C29r/C30n boundary at 369 m (344 m on their scale). A higher resolution study by [START_REF] Rocchia | The Cretaceous-Tertiary boundary at Gubbio revisited: vertical extent of the Ir anomaly[END_REF] on the Bottaccione section confirmed the interpretation of [START_REF] Roggenthen | Upper Cretaceous-Paleocene magnetic stratigraphy at Gubbio, Italy IV. Upper Maastrichtian-Paleocene Magnetic Stratigraphy[END_REF], locating the Chrons C29r/C30n boundary between 368.72 and 368.94 m. The magnetostratigraphic interpretation of [START_REF] Lowrie | Paleogene magnetic stratigraphy in Umbrian pelagic carbonate rocks: The Contessa section, Gubbio[END_REF] is used for the Paleogene of the Contessa Highway section.

Biostratigraphy of the Contessa section has been established for this study following the methodology presented by [START_REF] Gardin | Biomagnetochronology for the upper Campanian -Maastrichtian from the Gubbio area, Italy: new results from the Contessa Highway and Bottaccione sections[END_REF].

Cyclostratigraphic data and method

Magnetic Susceptibility (MS) measures the capacity of a substance to acquire magnetization when submitted to an external magnetic field. High frequency variations of MS in sedimentary series are correlated to the terrestrial input in the ocean [START_REF] Ellwood | Magnetosusceptibility event and cyclostratigraphy method applied to marine rocks: Detrital input versus carbonate productivity[END_REF]. This property is easily and quickly measurable with a nondestructive tool on samples or directly on sedimentary cores. MS is thus a good paleoclimatic proxy, used frequently in cyclostratigraphic studies [START_REF] Weedon | Astronomical calibration of the Jurassic timescale from cyclostratigraphy in british mudrock formations[END_REF][START_REF] Norris | Carbon cycling and chronology of climate warming during the Palaeocene/ Eocene transition[END_REF][START_REF] Weedon | Cyclostratigraphy, orbital tuning and inferred productivity for the type Kimmeridge Clay (Late Jurassic), Southern England[END_REF][START_REF] Boulila | High!resolution cyclostratigraphic analysis from magnetic susceptibility in a Lower Kimmeridgian (Upper Jurassic) marl!limestone succession (LaMéouge, Vocontian Basin, France)[END_REF][START_REF] Boulila | Milankovitch and sub!Milankovitch forcing of the Oxfordian (LateJurassic) Terres Noires Formation (SE France) and global implications[END_REF][START_REF] Guo | Cyclostratigraphy of the Induan (Early Triassic) in West Pingdingshan Section, Chaohu, Anhui Province[END_REF][START_REF] Husson | Astronomical calibration of the Maastrichtian (Late Cretaceous)[END_REF][START_REF] Martinez | An orbital floating time scale of the Hauterivian/Barremian GSSP from a magnetic susceptibility signal (Río Argos, Spain)[END_REF][START_REF] Husson | Lower Maastrichtian cyclostratigraphy of the Bidart section (Basque Country, SW France): A remarkable record of precessional forcing[END_REF]. MS was measured on samples from the Contessa Highway and the Bottaccione section every 5 cm using a Kappabridge KLY-2 (data available on Pangea at http://issues.pangaea.de/browse/PDI-7152). Illite, Montmorillonite, Hematite and Magnetite, minerals found in the Scaglia Rossa bear magnetic susceptibility, and could be affected by reworking [START_REF] Lowrie | Upper Cretaceous-Paleocene magnetic stratigraphy at Gubbio, Italy: III. Upper Cretaceous magnetic stratigraphy[END_REF]. Nevertheless the important similarities between Hole 1267B and Gubbio section magnetic susceptibility record indicate a good conservation of the sedimentary record. The amount of diagenetic Glaucony, which possess a relatively high magnetic susceptibility, is not significant in the sediments except in the KPgB clay layer (Elwood et al., 2003). The high magnetic susceptibility values observed at the boundary result however mainly from the presence of magnetic microspherules and hematite [START_REF] Verma | Thermal decomposition pattern and particle size estimation of iron minerals associated with the Cretaceous-Tertiary boundary at Gubbio[END_REF]. MS measurements covering 6 m across the K-PgB, obtained on the Bottaccione section, have been previously compared to several records in Oman, Caribbean, North Atlantic and South Pacific by Elwood et al. (2003), highlighting very similar features between these sites. According to Elwood et al. (2003), these features could be used to locate the K-Pg boundary interval. This is confirmed by [START_REF] Font | A new sedimentary benchmark for the Deccan Traps volcanism[END_REF], who studied MS variations across the K-PgB in Gubbio and Bidart (France) sections. The K-PgB is characterised by an abrupt positive shift of the MS concomitant with the boundary clays. An anomalous interval with very low MS precedes the boundary, due to an unusual Cl-bearing iron oxide [START_REF] Font | A new sedimentary benchmark for the Deccan Traps volcanism[END_REF]. This interval is related by [START_REF] Font | A new sedimentary benchmark for the Deccan Traps volcanism[END_REF] to possible reactions of solid/aqueous aerosols and volcanic gas emitted by the Deccan Traps within atmospheric plume, considering a dry environment. It could be a marker of the Deccan Trap main eruptive phase. A comparison between the MS signal obtained from Gubbio sections and MS variations measured on cores from ODP Hole 1267B highlights very similar features (Fig 2 .A). Previous cyclostratigraphic studies of Site 1267 cores [START_REF] Westerhold | Astronomical calibration of the Paleocene time[END_REF][START_REF] Husson | Astronomical calibration of the Maastrichtian (Late Cretaceous)[END_REF]) highlighted orbital control of the sedimentation by 100 kyr and 405 kyr eccentricity cycles, on both sides of the K-PgB. Similar low and high frequency cycles can be observed in the Maastrichtian of the Gubbio sections and Hole 1267B, with a progressive decrease of the MS mean value until the K-PgB (Fig 2 .B).

At the Bottaccione section, MS values are lower in the white beds covering the last 50 cm of the Cretaceous before the K-PgB. Values in the Paleogene are significantly higher than in the Cretaceous at both sites (Fig 2 .B). The K-PgB is characterised by a very high value, of more than 21.10-8 kg/m -3 in the Bottaccione section. High MS values at the K-PgB are found in several sections, and can be attributed to the presence of multidomain magnetite microspherules [START_REF] Worm | Rock magnetic signature of the Cretaceous-Tertiary boundary[END_REF]. The K-PgB is immediately followed by a broad cycle of about 1.5 m width divided into higher frequency peaks (Fig 2.B). This particular feature is also observed in Hole 1267B. This feature was linked to a high perturbation of the sedimentation following the K-PgB, supposedly hampering cyclostratigraphic analyses of the lowermost Paleogene [START_REF] Herbert | Precessional climate cyclicity in late cretaceous-early tertiary marine sediments: a high resolution Chronometer of cretaceous-tertiary boundary events[END_REF][START_REF] Dinares-Turell | Untangling the Palaeocene climatic rhythm: an astronomically calibrated early Palaeocene magnetostratigraphy and biostratigraphy at Zumaia (Basque basin, northern Spain)[END_REF][START_REF] Westerhold | Astronomical calibration of the Paleocene time[END_REF][START_REF] Kuiper | SynChronizing Rock Clocks of Earth History[END_REF]. A short wavelength cycle with very high amplitude can also be observed in the Contessa Highway record between 342.25 and 342.55 m (Fig 2 .B).

Cyclostratigraphic analysis has been performed using spectral analysis by multitaper method (MTM) [START_REF] Thomson | Spectrum estimation and harmonic analysis[END_REF]. Prior to the analyses, a linear and a polynomial detrending was applied to suppress long-term trends. Links between the cycles detected in the analyzed time series and known orbital parameter variations are assessed using the frequency ratios method [START_REF] Mayer | Milankovitch cyclicity and rock-magnetic signatures of palaeoclimatic change in the early Cretaceous Biancone formation of the southern Alps, Italy[END_REF], based on the orbital frequencies estimated for the Cretaceous [START_REF] Berger | Astronomical forcing through geological time[END_REF][START_REF] Laskar | A long term numerical solution for the insolation quantities of the earth[END_REF]). The red-noise hypothesis is tested using scripts written under Matlab™ (available at http://www.mathworks.com/matlabcentral/ fileexchange/45539-rednoiseconfidencelevels) based on the work of [START_REF] Mudelsee | TAUEST: a computer program for estimating persistence in unevenly spaced weather/ climate time series[END_REF] and [START_REF] Schulz | REDFIT: estimating red-noise spectra directly from unevenly spaced paleoclimatic time series[END_REF].

CYCLOSTRATIGRAPHIC ANALYSIS

The Cretaceous and the Paleogene part of the record are studied separately, considering the very different range of MS values and signal features on either side of the K-PgB. The composite signal is plotted using a log scale to take these discrepancies into account (Fig.

2.B).

Spectral analysis performed on the MS variations of the Cretaceous Bottaccione section (Fig 2 .C) highlights cycles with wavelengths ranging from 0.17 to 0.91 m. High frequency cycles with wavelength of 0.17 and 0.22 m possess a high power. Considering a sedimentation rate of 10-15 m/Myr as estimated by Lowrie et al. (1990), the detected cycles are in the orbital band. Two powerful cycles with wavelengths of 0.17 and 0.22 m would correspond to the two modes of the precession, cycles with a wavelength of about 0.42 m are attributed to an obliquity forcing, and cycles with a wavelengths of 0.91 m to a short eccentricity forcing (Fig 2 .C). This is confirmed by matching of the observed frequency ratios to the predicted orbital parameter frequency ratios.

A spectral analysis performed on the lowermost Paleogene highlights two main cycles with wavelengths of 0.17 and 1.75 m (Fig 2 .C). The low frequency peak seems to correspond to the broad, high amplitude cycle covering an interval from 372.6 to 374.1 m (Fig 2 .D). The strength of the match for the two cycles frequency to the predicted frequency ratios of 405 kyr eccentricity to obliquity is taken as strong support for the proposed average sedimentation rate. Moreover, considering a sedimentation rate of 2.5-3 m/Myr as estimated by Lowrie et al. (1990) for the lowermost Paleogene, cycles with a wavelength of 1.75 m would characterize a record of the 405 kyr eccentricity, whereas 0.17 m cycles correspond to an obliquity forcing. Two high frequency cycles, located at 373.2 and 373.4 m, could correspond to two hyperthermal events, as observed by Coccionni et al. (2012). The expression of the orbital control within the sedimentary record could have been enhanced by these climatic events, or these two high frequency cycles could be an overprint of these events. Further studies based on different paleoclimatic proxies are thus needed to ascertain the nature of these two high frequency MS cycles. A higher sampling rate allowing the recovery of precession cycles, would help to better assess the orbital control, and better understand the strong perturbations of the sedimentation in the interval following the K-PgB event.

A second spectral analysis is performed on the interval from 374 to 377 m, before a cycle with high MS value that disturbs the spectral analysis (Fig 2 .E). Cycles with wavelengths ranging from 0.15 to 0.60 m are detected. Frequency ratios of the high frequency cycles (0.15 m to 0.22 m) and low frequency cycle (0.60 m) are close to the 100 kyr eccentricity to 405 kyr eccentricity frequency ratio. This would suggests an important drop of the sedimentation rate at the beginning of chron C29n, preventing the detection of precession and obliquity cycles. No other evidence of such an important drop of the sedimentation rate can be observed on this section, and the cycles detected have a low confidence level (below 85%). Uncertainties are thus high on this interval, and a study of a longer Paleogene interval is needed to better constrain cycle attributions.

The spectral analyses illustrate a drop of the sedimentation rate across the K-PgB, characterized on the periodograms by a shift of the recorded cycles toward higher frequencies (Fig 2). This is in accordance with Lowrie et al. (1990), who indicated a drop of the sedimentation rate between the Maastrichtian and the lowermost Danian, interpreted as a strong decrease in carbonate productivity.

The detection of an orbital control of the sedimentation in the Bottaccione allows the construction of a cyclostratigraphic time-scale covering the Maastrichtian. The low resolution of the study in the Paleogene of the Contessa section prevents the development of a cyclostratigraphic timescale. The timescale presented here is based only on the GTS 2012 [START_REF] Ogg | Geomagnetic Polarity Time Scale[END_REF] estimate of the Paleogene part of Chron C29r duration, considering a constant sedimentation rate during the lowermost Paleogene. It can be noted that the sedimentation rated inferred through this method is similar to the one obtained using the cyclostratigraphic results.

Due to the chaotic behavior of the solar system [START_REF] Laskar | A long term numerical solution for the insolation quantities of the earth[END_REF]), the 405 kyr component of the eccentricity is the only orbital parameter for which variations remain predictable down to the K-PgB. It is not realistic to perform a direct calibration to the most recent astronomical solutions [START_REF] Laskar | La2010: a new orbital solution for the longterm motion of the Earth[END_REF]) using the identified 405 kyr eccentricity cycles considering the short length of our signal (ca. 800 kyr). The cycle identification and amplitude variations obtained on Gubbio sections need to be ascertained by the study of other sites before any attempt of a calibration with a precession-scale accuracy. The cyclostratigraphic time-frame has thus been created based on the identification of precession cycles in the Maastrichtian. The K-PgB is defined as zero in this time scale, and a value in time has been attributed to each cycle boundary based on its period and cycle counts on both sides of the K-PgB (Fig. 3). The relative age of each point between the boundaries has then been interpolated. Time is negative in the Cretaceous, and positive in the Paleogene. The duration of the precession is based on an average of the two modes of the precession for the Late Cretaceous [START_REF] Laskar | A long term numerical solution for the insolation quantities of the earth[END_REF]). The 100 kyr eccentricity and precession are filtered using a Taner filter [START_REF] Taner | Attributes revisited[END_REF] to highlight their evolution in the Cretaceous (Fig 3). Building this relative timescale allows correcting the sedimentation rate variations and comparing the events on both sides of the Cretaceous-Paleogene boundary.

DISCUSSION

Duration of Chron C29r Maastrichtian

As previously observed on other sedimentary records [START_REF] Herbert | Massive dissociation of gas hydrate during a Jurassic oceanic anoxic event[END_REF][START_REF] Westerhold | Astronomical calibration of the Paleocene time[END_REF][START_REF] Kuiper | SynChronizing Rock Clocks of Earth History[END_REF][START_REF] Husson | Astronomical calibration of the Maastrichtian (Late Cretaceous)[END_REF][START_REF] Batenburg | Cyclostratigraphy and astronomical tuning of the Late Maastrichtian at Zumaia (Basque country, Northern Spain)[END_REF], the K-PgB of the Gubbio area is situated in a minimum of the 405 kyr eccentricity variations in the MS signal. [START_REF] Herbert | Precessional climate cyclicity in late cretaceous-early tertiary marine sediments: a high resolution Chronometer of cretaceous-tertiary boundary events[END_REF] first estimated the duration of Chron C29r based on DSDP Sites from the South Atlantic. This work was later pursued by [START_REF] Herbert | Massive dissociation of gas hydrate during a Jurassic oceanic anoxic event[END_REF], who identified 18.5 precession cycles in the Maastrichtian part of C29r (M-C29r), equivalent to 377 +/-0.2 kyr (Table1) Based on an astronomical calibration of ODP sedimentary records, [START_REF] Westerhold | Astronomical calibration of the Paleocene time[END_REF] estimated the duration of M-C29r between 345+/-11 kyr (calibration option 1) and 327+/-11 kyr (calibration option 2). Astronomical calibration of ODP Hole 1267B by [START_REF] Husson | Astronomical calibration of the Maastrichtian (Late Cretaceous)[END_REF] provided an M-C29r estimate of 300+/-20 kyr, corresponding to 15 precession cycles, slightly less than the previous estimates. A recent cyclostratigraphic study based on limestone-marl alternations in the Zumaia (Spain) section resulted in an estimation of 17.5 precession cycles, equivalent to a duration of 350 +/-11 (option 1) or 340 +/-11 (option 2), respectively considering a K-PgB dated to 65.56+/-0.02 Ma or 65.97 Ma [START_REF] Batenburg | Cyclostratigraphy and astronomical tuning of the Late Maastrichtian at Zumaia (Basque country, Northern Spain)[END_REF]) (Table 1). However, the magnetostratigraphy of the Zumaia section bears large uncertainties due to remagnetization. Therefore, the Chrons C30n/C29r boundary location was not defined directly on the section but by correlating the Zumaia record to ODP Sites 1262 and 1267 [START_REF] Batenburg | Cyclostratigraphy and astronomical tuning of the Late Maastrichtian at Zumaia (Basque country, Northern Spain)[END_REF].

Duration of the M-C29r is estimate here based on the time scale inferred through precession cycles counting, considering a constant sedimentation rate between each cycles boundary. The duration uncertainty takes into account the error margin on the location of the C29r-C30n boundary. Our results for the location for the Chrons C29r/C30n boundary at 369 m from the Bottaccione section (Figs. 2) are in good agreement with previous estimations [START_REF] Roggenthen | Upper Cretaceous-Paleocene magnetic stratigraphy at Gubbio, Italy IV. Upper Maastrichtian-Paleocene Magnetic Stratigraphy[END_REF][START_REF] Rocchia | The Cretaceous-Tertiary boundary at Gubbio revisited: vertical extent of the Ir anomaly[END_REF]). The Cretaceous part of the C29r covers 18 precession cycles, equivalent to a duration of 357 +/-40 kyr (Table 1). A smaller estimation of 300 +/-20 kyr obtained from ODP Hole 1267B study by [START_REF] Husson | Astronomical calibration of the Maastrichtian (Late Cretaceous)[END_REF] may be explained by the recovery gap at 290.3-290.65 mbsf (Fig. 2).

Age estimations of bio-horizons and isotopic event

Many important bio-horizons, as well as biotic and environmental changes in the K-PgB of the Gubbio reference sections have been discussed in the litterature over the years [START_REF] Coccioni | The Dan-C2 hyperthermal event at Gubbio (Italy): Global implications, environmental effects, and cause(s)[END_REF]Coccioni et al. 2012a;Coccioni et al. 2012b;[START_REF] Gardin | Biomagnetochronology for the upper Campanian -Maastrichtian from the Gubbio area, Italy: new results from the Contessa Highway and Bottaccione sections[END_REF] and references therein). The newly constructed cyclostratigraphic time-frame, covering Chron C29r and anchored to the K-PgB at 66.04 Ma [START_REF] Renne | Time scales of critical events around the Cretaceous-Paleogene boundary[END_REF], can thus be used to provide ages and/or durations of these signals (Fig. 4). In addition, some of these results can be compared to Hole 525A, which has recently been calibrated to the astronomical solution [START_REF] Husson | Astronomical calibration of the Maastrichtian (Late Cretaceous)[END_REF].

The first occurrence (FO) of nannofossil Micula prinsii, which approximates the base of Chron C29r [START_REF] Gardin | Biomagnetochronology for the upper Campanian -Maastrichtian from the Gubbio area, Italy: new results from the Contessa Highway and Bottaccione sections[END_REF], is situated at 66.3 Ma in the Bottaccione section and at Site 525 (Table 2, Fig. 4). The acme of nannofossil Micula murus, considered as a good marker of Deccan-induced intense warming in sea-surface waters of the late Maastrichtian [START_REF] Thibault | The Late Maastrichtian nannofossil record of climate change in the South Atlantic DSDP Hole 525a[END_REF]2010), starts in the Bottaccione section at 66.36 Ma and ends 33 kyr prior to the K-PgB. This is entirely consistent with estimations obtained at Site 525A, where the acme of M. murus occurs in coincidence with the negative excursion in benthic foraminiferal ! 18 O (Fig. 4). The FO of Cruciplacolithus intermedius, marker of the base of nannofossil zones NP2 and CP1b, and considered as a proxy for the Chrons C29r/C29n boundary, is situated at 65.67 Ma (Fig. 4). [START_REF] Voigt | Global correlation of Upper Campanian Maastrichtian successions using carbon-isotope stratigraphy: development of a new Maastrichtian timescale[END_REF] identified and named a number of carbon isotopic excursions in the latest Maastrichtian with similar amplitudes across a wide range of shelf and oceanic sections from the Boreal realm, the Tethys, and the Atlantic and Pacific oceans. The slight negative ! 13 C excursions K-PgE1 and K-PgE3 bracket the longer stable interval K-PgE2 at the Bottaccione section [START_REF] Voigt | Global correlation of Upper Campanian Maastrichtian successions using carbon-isotope stratigraphy: development of a new Maastrichtian timescale[END_REF]. K-PgE1 and K-PgE3 span 140 kyr (from ca. 66.65 to ca. 66.51 Ma) and 200 kyr (from ca. 66.32 to ca. 66.12 Ma) respectively (Fig. 4, Table 3).

The DAN-C2 early Paleogene hyperthermal event identified by [START_REF] Coccioni | The Dan-C2 hyperthermal event at Gubbio (Italy): Global implications, environmental effects, and cause(s)[END_REF] in the Contessa Highway section would start at about 65.8 Ma. This event is characterized by two sharp concomitant negative ! 13 C and ! 18 O excursions with short durations, perhaps <50 kyr, named here Dan-C2a and Dan-C2b (Fig. 4, Table 3). The lower C29n hyperthermal event would last only a few kyr and occurs at about 65.73 Ma. This last event, though only defined by one data point, is mirrored in the lithology of the Contessa section by a thin layer of clay, and corresponds to a peak of opportunistic taxa in the benthic foraminifer assemblage, similarly to the layers marking the DAN-C2 events [START_REF] Coccioni | The Dan-C2 hyperthermal event at Gubbio (Italy): Global implications, environmental effects, and cause(s)[END_REF].

Evolution of 187 Os/ 188 Os ratios through the Maastrichtian is characterized by to decrease phases. Our age model shows that the onset of the first 187 Os/ 188 Os decline started at about 66.6 Ma, within the top of Chron C30n, with a shift from 0.6 to 0.42 (Fig. 4,Table3). This decline spaned 240 kyr, in agreement with [START_REF] Robinson | A highresolution marine 187 Os/ 188 Os record for the late Maastrichtian: Distinguishing the chemical fingerprints of Deccan volcanism and the KP impact event[END_REF] rough duration approximation. A stable interval without variations followed from 66.28 to 66.13 Ma. A second sharp 187 Os/ 188 Os decrease marked the end of Chron C29r Cretaceous part, covering 90 kyr in the Bottaccione section, with a decline from 0.42 to 0.25 (Fig. 4 and Table 3).

Paleoenvironmental changes across the Cretaceous-Paleogene boundary

Although it has been argued that Deccan volcanism was initiated slightly before the K-PgB [START_REF] Courtillot | On the ages of flood basalt events[END_REF][START_REF] Keller | Main Deccan volcanism phase ends near the K-T boundary: evidence from the Krishna-Godavari Basin, SE India[END_REF][START_REF] Robinson | A highresolution marine 187 Os/ 188 Os record for the late Maastrichtian: Distinguishing the chemical fingerprints of Deccan volcanism and the KP impact event[END_REF], there is still doubt on the precise timing of the main volcanic phases and their relationship with the K-PgB mass extinction (Chenet et al. 2007;[START_REF] Keller | Main Deccan volcanism phase ends near the K-T boundary: evidence from the Krishna-Godavari Basin, SE India[END_REF][START_REF] Schulte | The Chicxulub asteroid impact and mass extinction at the Cretaceous-Paleogene boundary[END_REF].

It has been shown that 187 Os/ 188 Os variations prior to the KPg-B may be related to weathering of the fresh basalts of the Deccan traps [START_REF] Ravizza | Chemostratigraphic evidence of Deccan volcanism from the marine osmium isotope record[END_REF][START_REF] Robinson | A highresolution marine 187 Os/ 188 Os record for the late Maastrichtian: Distinguishing the chemical fingerprints of Deccan volcanism and the KP impact event[END_REF]). The mantle rocks 187 Os/ 188 OS ratio is about 0.13, an order of magnitude lower than the 1.3 ratio obtained from continental erosion input [START_REF] Ravizza | Chemostratigraphic evidence of Deccan volcanism from the marine osmium isotope record[END_REF]. The residence time of Osmium in the ocean is short, about 10 kyrs [START_REF] Peucker-Ehrenbrink | The marine osmium isotope record[END_REF]. An important decrease in 187 Os/ 188 OS ratio is thus likely to reflect the weathering of the late Maastrichtian large igneous provinces. The second 187 Os/ 188 Os decreased observed in Gubbio sections has been related to a possible second phase of Deccan volcanism or alternatively, it has been attributed to the addition of extraterrestrial Os from the K-Pg impactor by bioturbation mixing in the sediments beneath the K-PgB [START_REF] Robinson | A highresolution marine 187 Os/ 188 Os record for the late Maastrichtian: Distinguishing the chemical fingerprints of Deccan volcanism and the KP impact event[END_REF][START_REF] Ravizza | A geochemical clock in earliest Paleogene pelagic carbonates based on the impact-induced Os isotope excursion at the Cretaceous-Paleogene boundary[END_REF]. This second decrease began 47 kyr before an interval of lower MS values (Table 3) preceding the K-PgB and linked by [START_REF] Font | A new sedimentary benchmark for the Deccan Traps volcanism[END_REF] to possible reactions between aqueous-solid aerosols and volcanic gases in a dry climatic context. K-PgE1 and K-PgE3 negative isotopic excursions are only ca. 0.25 per mil in the Gubbio area and the South Atlantic (Fig. 4). Although of a small amplitude, these events are reliably recorded in other oceanic basins (Sites 305 and 1210B, central Pacific, Stevns-1 and Hemmoor, Chalk Sea Basin) where their magnitude can reach up to 0.5 per mil (Thibault et al. 2012a[START_REF] Voigt | Global correlation of Upper Campanian Maastrichtian successions using carbon-isotope stratigraphy: development of a new Maastrichtian timescale[END_REF]. Major shifts towards lower !13C values in marine organic matter and carbonate have been linked to an increase of atmospheric pCO2 fed by volcanism [START_REF] Kump | Interpreting carbon-isotope excursions: carbonates and organic matter[END_REF]. K-PgE1 occurred simultaneously with the onset of the first decrease in 187 Os/ 188 Os (~66.6 Ma), which suggests a direct relationship between the two geochemical events and the onset of a pulse in Deccan volcanism. Moreover, we note here that the onset of the second decrease in 187 Os/ 188 Os occurred during the K-PgE3 negative ! 13 C excursion (Fig. 4). Apart from the boundary clay sharp ! 13 C excursion which can be explained by a drop of primary productivity [START_REF] Hsu | A 'Strangelove' ocean in the earliest Tertiary[END_REF]Schulte et al. 2010, cum biblio) or as a reduced export production (D 'Hondt et al. 1998), we propose that most of the short-lived negative ! 13 C excursions occurring in the late Maastrichtian and early Danian were actually the expression of Deccan CO2 out-gassing. [START_REF] Chenet | Determination of rapid Deccan eruptions across the KTB using paleomagnetic secular variation: (II) Constraints from analysis of 8 new sections and synthesis for a 3500m-thick composite section[END_REF] have dated Deccan volcanic events based on radiogenic dating and biostratigraphy. Two major volcanic pulses would take place around 65 +/-1 Ma, the first one just before the KPgB and the second one approximately covering the C29r/C29n boundary. The ! 13 C excursion timing proposed here based on cyclostratigraphy is thus in agreement with the Deccan volcanic episode occurring within the C29r Cretaceous part.

The amplitudes of !13C excursions observed here are smaller than the amplitude of other excursions related to volcanism, such as the Permo-Triassic boundary events [START_REF] Kamo | Rapid eruption of Siberian flood-volcanic rocks and evidence for coincidence with the Permian-Triassic boundary and mass extinction at 251Ma[END_REF], the Triassic-Jurassic boundary event [START_REF] Hesselbo | Terrestrial and marine extinction at the Triassic-Jurassic boundary synchronized with major carbon-cycle perturbation: A link to initiation of massive volcanism[END_REF], the Toarcian ocean anoxic event [START_REF] Suan | Duration of the early Toarcian carbon isotope excursion deduced from spectral analysis: Consequence for its possible causes[END_REF][START_REF] Boulila | Astronomical calibration of the Toarcian Stage: Implications for sequence stratigraphy and duration of the early Toarcian OAE[END_REF], where a reinforcement of the excursion by methane degasing has been proposed (Hesselbo et al, 2000), and the Paleocene-Eocene thermal maximum [START_REF] Zachos | A Transient Rise in Tropical Sea Surface Temperature During the Paleocene-Eocene Thermal Maximum[END_REF]. However, the rapidity of these events as demonstrated here does not preclude the possibility that some of these excursions may actually be due to clathrate destabilization. Several studies have shown that massive flood volcanism does not only possibly participate to a raise in atmospheric CO2 by direct injections but also increases the chances to destabilize methane fields by contact metamorphism of sills and dyke intrusions [START_REF] Svensen | Release of methane from a volcanic basin as a mechanism for initial Eocene global warming[END_REF]Retallack and Jahren, 2007;[START_REF] Aarnes | How contact metamorphism can trigger global climate changes: Modeling gas generation around igneous sills in sedimentary basins[END_REF][START_REF] Aarnes | The impact of host-rock composition on devolatilization of sedimentary rocks during contact metamorphism around mafic sheet intrusions[END_REF].

A major environmental perturbation started at ca. 66.35 Ma, as expressed in bottom waters by the decrease in benthic foraminiferal ! 18 O and in surface waters by the dwarfing of planktic foraminifers, the acme of the tropical nannofossil species Micula murus, and a slight decrease in nannofossil species richness [START_REF] Abramovich | Planktonic foraminiferal response to the latest Maastrichtian abrupt warm event: a case study from South Atlantic DSDP Site 525A[END_REF]Keller 2003, Thibault and[START_REF] Thibault | The calcareous nannofossil response to the end-Cretaceous warm event in the Tropical Pacific[END_REF]. Also, this perturbation possibly correlated with a prominent extinction level of benthic faunas at southern high latitudes within the Cretaceous part of Chron C29r [START_REF] Tobin | Extinction patterns, ! 18 O trends, and magnetostratigraphy from a southern high-latitude Cretaceous-Paleogene section: Links with Deccan volcanism[END_REF]. The absence of Lilliput effect in Cheilostome Bryozoans colony following the K-Pg boundary highlights the biotic system complexity, and the importance of the information provided by each organism responses to environmental changes [START_REF] Sogot | The Lilliput Effect in Colonial Organisms: Cheilostome Bryozoans at the Cretaceous-Paleogene Mass Extinction[END_REF]. No causes of environmental perturbation independent from volcanism influence have been detected so far in the uppermost Maastrichtian. Only the last 100 kyrs of the Cretaceous are characterized by a short cooling episode (Wilf et al, 2003), postdating the beginning of foraminifer dwarfism, which is itself very well correlated to the greenhouse warming. Perturbation of the biota began ca. 200 kyr after the first volcanic pulse expressed by KPgE1 and nearly simultaneously to K-PgE3 event. The biotic response could be thus a delayed response to K-PgE1, or a direct response to K-PgE3. [START_REF] Husson | Astronomical calibration of the Maastrichtian (Late Cretaceous)[END_REF]. Bottaccione section: magnetostratigraphy from [START_REF] Rocchia | The Cretaceous-Tertiary boundary at Gubbio revisited: vertical extent of the Ir anomaly[END_REF], biostratigraphy from [START_REF] Gardin | Biomagnetochronology for the upper Campanian -Maastrichtian from the Gubbio area, Italy: new results from the Contessa Highway and Bottaccione sections[END_REF] and this study, Osmium data from [START_REF] Robinson | A highresolution marine 187 Os/ 188 Os record for the late Maastrichtian: Distinguishing the chemical fingerprints of Deccan volcanism and the KP impact event[END_REF], and !13C from bentic foraminifers data from [START_REF] Voigt | Global correlation of Upper Campanian Maastrichtian successions using carbon-isotope stratigraphy: development of a new Maastrichtian timescale[END_REF]. Contessa section: magnetostratigraphy from [START_REF] Lowrie | Paleogene magnetic stratigraphy in Umbrian pelagic carbonate rocks: The Contessa section, Gubbio[END_REF], biostratigraphy from Coccioni et al. (2012b) and this study, magnetic susceptibility from Coccioni et al. (2012b) and this study, and !13C from bulk data from Coccioni et al. (2012b). Zumaia section: !13C from bulk data from [START_REF] Batenburg | Cyclostratigraphy and astronomical tuning of the Late Maastrichtian at Zumaia (Basque country, Northern Spain)[END_REF]. Hole 1049C: !18O from bulk data from Coccioni et al. (2012b). Hole 525A: magnetostratigraphy from [START_REF] Chave | 40 K-40 Ar dating of the Main Deccan large igneous province: Further evidence of KTB age and short duration[END_REF], biostratigraphic data from [START_REF] Thibault | The Late Maastrichtian nannofossil record of climate change in the South Atlantic DSDP Hole 525a[END_REF], Osmium data from [START_REF] Robinson | A highresolution marine 187 Os/ 188 Os record for the late Maastrichtian: Distinguishing the chemical fingerprints of Deccan volcanism and the KP impact event[END_REF], !18O data from Li and Keller (1998a;1998b), combined abundance of planktonic foraminifers dwarfed species from Abramovitch and [START_REF] Abramovich | Planktonic foraminiferal response to the latest Maastrichtian abrupt warm event: a case study from South Atlantic DSDP Site 525A[END_REF], and grey level variations from [START_REF] Husson | Astronomical duration of polarity Chron C31r (Lower Maastrichtian): cyclostratigraphy of ODP Site 762 (Indian Ocean) and the Contessa Highway section (Gubbio, Italy)[END_REF]. Numbers in italic indicate the isotopic events identified and named by [START_REF] Voigt | Global correlation of Upper Campanian Maastrichtian successions using carbon-isotope stratigraphy: development of a new Maastrichtian timescale[END_REF]. These events are separated by discontinuous lines. Black arrows indicate short-lived negative ! 13 C excursions that possibly mark volcanic pulses, as defined by [START_REF] Coccioni | The Dan-C2 hyperthermal event at Gubbio (Italy): Global implications, environmental effects, and cause(s)[END_REF]. Red arrows indicate early Danian hyperthermal events associated to ! 13 C excursions.

CN= Calcareous Nannofossils, PF= Planktonic Foraminifers.

The absence of a direct biotic and climatic response to the first excursion in ! 13 C and coincident decrease in Os isotopes suggest buffering of environmental perturbations in the late Maastrichtian oceanic realm. In addition to these extreme volcanic pulses, continuous minor eruptions probably contributed to increase atmospheric CO2 levels and other greenhouse gases, resulting in intense warming of surface and bottom waters. Although no warming is expressed in planktic foraminifer ! 18 O at Site 525A, nannofossil cool-water taxa show a marked decrease at this Site within the top of Chron C30n, prior to the acme of Micula murus [START_REF] Thibault | The Late Maastrichtian nannofossil record of climate change in the South Atlantic DSDP Hole 525a[END_REF]). In the tropical Pacific, the relative abundance of Micula murus actually started to increase slightly in the top of Chron C30n [START_REF] Thibault | The calcareous nannofossil response to the end-Cretaceous warm event in the Tropical Pacific[END_REF]). In addition, atmospheric temperatures estimated through leaf-margin analysis of terrestrial plants in North Dakota suggest an onset of warming ca. 150 kyr before the C30n/C29r reversal (Wilf et al. 2003). These results suggest that warming in the atmosphere and oceanic surface waters occurred before the intense warming of bottom waters, possibly in coincidence with K-PgE1 and the onset of the 187 Os/ 188 Os decline. The delayed biotic changes in the calcareous plankton regarding the beginning of the volcanic pulses thus evoke a threshold response to a maximum temperature increase in sea-surface waters within Chron C29r. Comparing the Maastrichtian ! 13 C excursions to those of the Danian, we observe that shortlived environmental perturbations and their associated time response are different before and after the impact event. In contrast with late Maastrichtian perturbations, early Danian isotopic excursions at the Contessa section are larger (>0.5 per mil) and seems to span shorter durations (<50 kyr for the two sharp negative peaks of the DAN-C2 event and a few kyr only for the lower C29n event). A longer record is needed on Zumaia section to highlight these events. In addition, the biotic response, as expressed by the increase of opportunistic forms of benthic foraminifers and calcareous nannofossils coincided exactly with the timing of these events [START_REF] Coccioni | The Dan-C2 hyperthermal event at Gubbio (Italy): Global implications, environmental effects, and cause(s)[END_REF]. Biotic recovery in the early Paleogene varied between the South Atlantic and Indian Ocean, and the Pacific and neritic Atlantic, and ranged from 350 kyr to 2 Myr after the K-PgB mass extinction (Hull and Norris 2011). Moreover, it has been hypothesized that the transition from the early recovery communities to later communities has been enabled by local short-term environmental perturbations (Hull et al. 2011). For example, such perturbations were coincident with assemblage turnover in the North Pacific (Hull et al. 2011). During the recovery, heterogeneous Danian paleoecosytems were very sensitive and reacted rapidly to short environmental pertubations (D 'Hondt et al 1998;[START_REF] Hondt | Consequences of the Cretaceous/Paleogene Mass Extinction for Marine Ecosystems[END_REF].

Table 3: Age estimations of Maastrichtian events considering an age of 66.04 for the Cretaceous-Paleogene boundary according to the most recent radiogenic dating [START_REF] Renne | Time scales of critical events around the Cretaceous-Paleogene boundary[END_REF].

If all the short-lived negative ! 13 C excursions occurring in the late Maastrichtian and early Danian are were the expression of volcanic pulses, then the contrast in their amplitude and durations on both sides of the boundary must be discussed. This contrast may suggest a difference in the intensity of volcanic pulses across the K-Pg that is not indicated in the study of the pile of Deccan lavas across the K-PgB (Chenet et al. 2007;[START_REF] Chenet | Determination of rapid Deccan eruptions across the KTB using paleomagnetic secular variation: (II) Constraints from analysis of 8 new sections and synthesis for a 3500m-thick composite section[END_REF]. More likely, this contrast actually reflects the expression of a different response of oceanic ecosystems to similar perturbations across the K-PgB. The stable oceanic ecosystem of the late Maastrichtian could buffer environmental perturbations through a series of complex feedbacks whereas the fragile and highly disturbed early Danian oceanic ecosystem likely amplified any additional environmental perturbations that occurred after the extraterrestrial impact.

CONCLUSIONS

Cyclostratigraphic study performed on MS variations from the Contessa Highway and Bottaccione sections (Gubbio, Italy) has allowed the construction of a precise relative timescale of Chron C29r Maastrichtian part. Our results provide an estimation of Chron C29r Maastrichtian duration (365 +/-40 kyr), which agrees with previous estimations. Ascertaining more precisely the duration of the Paleogene part of the C29r would benefit from a study with an even higher sampling rate, considering the remaining uncertainties on two high frequency cycles.

The temporal framework based on this timescale brings forward precise dating of biohorizons, biotic changes, stable isotopic excursions and changes in Osmium isotope composition recorded in the Gubbio sections and in the astronomically calibrated Site 525A (South Atlantic). This comparison highlights the synchronicity of Maastrichtian K-PgE1 and K-PgE3 ! 13 C negative excursions with the two-step decrease in Osmium isotopes, previously interpreted as a marker for the main Cretaceous phase of Deccan volcanism.

This study highlight that the durations and magnitude of these ! 13 C short-lived excursions are different across the KPg-B. Danian isotopic excursions are larger in magnitude and span shorter durations (ca. 30 kyr for each peak of the DAN-C2 event, a few kyr for the lower C29n event vs. 130 and 140 kyr for K-PgE1 and K-PgE3).

The biotic response to Danian perturbations is nearly instantaneous whereas a 200 kyr delayed response of the late Maastrichtian biota to environmental perturbations related to the first volcanic pulse, suggests a threshold reaction to the atmospheric CO2 buildup.

These differences reflect different sensitivities in the late Maastrichtian and early Danian carbon cycle and ecosystems. The stable late Maastrichtian oceanic ecosystem could buffer environmental perturbations by complex feedbacks. In contrast, the Danian ecosystem, greatly weakened after the extraterrestrial impact, have amplified additional Deccan-induced environmental perturbations.

Figure 1 :

 1 Figure 1: A) Map of the Contessa and Bottaccione sections location (From Monechi et al., 1985) B) Photograph of the Cretaceous-Paleogene boundary at the Bottaccione section highlighting the white limestone layers preceding the boundary.

Figure 2 :

 2 Figure 2: Cyclostratigraphic analysis of Magnetic Susceptibility variations from the Contessa Highway and the Bottacione sections (Italy) on both sides of the Cretaceous-Paleogene boundary (B). Lithology of the Contessa Highway section for the C29r interval is from Coccioni et al. (2010). The MS signal from ODP Hole 1267B is also presented for comparison (A). The analysis method used was the multitaper method, completed by a Chi2 test to assess the reliability of the cycles detected. Comparison to MS variations from ODP Hole 1267B (South Atlantic) highlight a high similarity between the two signals. Precession and 100 kyr eccentricity variations are well defined in the Cretaceous, as highlighted by the spectral analysis of this interval (C), whereas the perturbations of the sedimentation rate following the K-PgB affect the record of the orbital parameters variations in the Paleogene. Results from the lowermost Paleogene spectral analysis (D) are very different from from analysis results of the C29n-C28n interval (E).

Figure 3 :

 3 Figure 3: Cyclostratigraphic framework covering the Maastrichtian part of Chron C29r on Gubbio sections, ODP Site 1267B and DSDP Site 525A. The temporal frame for Gubbio sections is based on the identification of the precession cycles for the Cretaceous part of the MS variations. The temporal frame for the Contessa is based on the GTS 2012 (Ogg 2012) estimate for the duration of the Paleogene C29r part. The very good Cretaceous record of the Bottaccione allowed a filtering highlighting the evolution of 100 kyr cycles and precession. Numbers in gray squares indicate the biohorizons from Gardin et al. (2012) and this study, and Coccioni et al. (2012b): 1= FO M. prinsii, 2=FO P. hantkeninoides, 3= FO P. eugubina, 4= FO C. intermedius. Magnetostratigraphy 1) from Lowrie et al. (1982) for the Paleogene and Rocchia et al. (1990) for the Maastrichtian 2) from Westerhold et al. (2008) for the Paleogene and Zachos et al. (2004) 3) from[START_REF] Chave | 40 K-40 Ar dating of the Main Deccan large igneous province: Further evidence of KTB age and short duration[END_REF].

Figure 4 :

 4 Figure 4: Correlation between the Gubbio sections, DSDP Hole 525A, Zumaia section and ODP Hole 1049C. The relative time scale for the Bottaccione section has been tied to a K-PgB dated to 66.04 Ma, in agreement with Renne et al. (2013) most recent radiogenic dating. The Paleogene timescale is based on the GTS 2012 (Ogg 2012) estimation for the duration of the Paleogene part of Chron C29r, considering a constant sedimentation rate during this interval. Age model of Hole 525A comes from the astronomical calibration of this site by Husson et al. (2011). Bottaccione section: magnetostratigraphy from Rocchia et al. (1990), biostratigraphy from Gardin et al. (2012) and this study, Osmium data from Robinson et al. (2009), and !13C from bentic foraminifers data from Voigt et al. (2012). Contessa section: magnetostratigraphy from Lowrie et al. (1982), biostratigraphy from Coccioni et al. (2012b) and this study, magnetic susceptibility from Coccioni et al. (2012b) and this study, and !13C from bulk data from Coccioni et al. (2012b). Zumaia section: !13C from bulk data from Batenburg et al. (2012).Hole 1049C: !18O from bulk data fromCoccioni et al. (2012b). Hole 525A: magnetostratigraphy from[START_REF] Chave | 40 K-40 Ar dating of the Main Deccan large igneous province: Further evidence of KTB age and short duration[END_REF], biostratigraphic data from[START_REF] Thibault | The Late Maastrichtian nannofossil record of climate change in the South Atlantic DSDP Hole 525a[END_REF], Osmium data from[START_REF] Robinson | A highresolution marine 187 Os/ 188 Os record for the late Maastrichtian: Distinguishing the chemical fingerprints of Deccan volcanism and the KP impact event[END_REF], !18O data fromLi and Keller (1998a; 1998b), combined abundance of planktonic foraminifers dwarfed species from Abramovitch and[START_REF] Abramovich | Planktonic foraminiferal response to the latest Maastrichtian abrupt warm event: a case study from South Atlantic DSDP Site 525A[END_REF], and grey level variations from[START_REF] Husson | Astronomical duration of polarity Chron C31r (Lower Maastrichtian): cyclostratigraphy of ODP Site 762 (Indian Ocean) and the Contessa Highway section (Gubbio, Italy)[END_REF]. Numbers in italic indicate the isotopic events identified and named by[START_REF] Voigt | Global correlation of Upper Campanian Maastrichtian successions using carbon-isotope stratigraphy: development of a new Maastrichtian timescale[END_REF]. These events are separated by discontinuous lines. Black arrows indicate short-lived negative ! 13 C excursions that possibly mark volcanic pulses, as defined by[START_REF] Coccioni | The Dan-C2 hyperthermal event at Gubbio (Italy): Global implications, environmental effects, and cause(s)[END_REF]. Red arrows indicate early Danian hyperthermal events associated to ! 13 C excursions.CN= Calcareous Nannofossils, PF= Planktonic Foraminifers.

Table 1 :

 1 Available cyclostratigraphic estimations of the duration of the Chron C29r Maastrichtian in kyr. Pc = precession cycles identified. For this study, uncertainties are based on the uncertainties on the positions of the Chron boundaries and on the cycle identifications (+/-1 precession cycle).

Table 2 :

 2 Age estimations of Chron C29r boundaries, Maastrichtian and Paleogene bio-horizons considering an age of 66.04 for the Cretaceous-Paleogene boundary according to the most recent radiogenic dating[START_REF] Renne | Time scales of critical events around the Cretaceous-Paleogene boundary[END_REF]. Biostratigraphic data are from[START_REF] Gardin | Biomagnetochronology for the upper Campanian -Maastrichtian from the Gubbio area, Italy: new results from the Contessa Highway and Bottaccione sections[END_REF].

ACKNOWLEDGEMENTS

This study was supported by the Agence Nationale de la Recherche (grant ASTS-CM.) N.T. warmly thanks Dave Kemp for fruitful discussions. D.H. is grateful to Brad Sageman for useful comments. The authors thank Rodolfo Coccioni for his help during the fieldtrip and useful advices. Many thanks to two anonymous reviewers for their productive comments.


Mathilde Marchand

Lynda Aissani
email: lynda.aissani@irstea.fr

Pascal Mallard

Fabrice Béline

Jean-Pierre Réveret

Odour and Life Cycle Assessment (LCA) in waste management: a local assessment proposal

Keywords: Odour, Waste Management, Life Cycle Assessment (LCA), USEtox, Spatial differentiation

Environmental assessment of Municipal Solid Waste (MSW) management is essential. Life Cycle Assessment (LCA) is a powerful and widely used method, which implements causal chains (impact pathways) between the studied processes and their environmental impacts. However, in waste management, the method presents some weaknesses. For example, there is no impact category related to odour, whose assessment is nevertheless essential, especially when the organic fraction of waste is concerned. Odour interferes with human welfare and comfort. Sometimes, it can become a nuisance and be described as a "socio-environmental" impact.

To integrate the impact of odour in waste management plans, it is necessary to build an odourimpact pathway. The aim of this paper is to present a first attempt to build such an impact pathway up to the so-called midpoint step (i.e. the level of discomfort to human beings).

The methodology we developed is based on the cause/effect chain according to the descriptors of the Site Dependent approach. Unlike classical LCA, the classification step is more important and characterization is aimed at computing the characterization factor. The change in this classification step allows for working on the occurrence of odour impacts. To determine impact occurrence, it is necessary to integrate local conditions into odour assessment. This was done using (i) the USEtox model in which local conditions to assess odour impacts are integrated and (ii) the framework of a new methodology that takes into account background concentrations).

The methodology was implemented in a case study, i.e. by computing atmospheric emission of ethyl benzene during composting (2.93.10 -2 kg.d -1 ). The characterization factor for ethyl benzene was equal to 3.02.10 -3 kg eq. Benzene per /kg emitted ethyl benzene. The daily emission of ethyl benzene generated an odour impact equal to 6.6.10 -5 kg eq. benzene.

With that first odour mid-point impact, we paved the way for the construction of a whole odour pathway (going up to end-point impacts or damages). However, several limits were identified such as data availability, the model under use and the use of average daily data which is less relevant than emission peaks. We should also recall that our methodology is not intended for predicting nuisance likely to disturb populations living nearby the facility. Its first objective is to provide an indicator that fits with LCA methodology in order to help local decision-makers to differentiate waste management scenarios based on exhaustive LCA.

Introduction

In Europe, the amount of waste produced in some countries is related to the degree of urbanization, types and patterns of consumption, as well as to households' income level and lifestyle. In 2009, Western Europe inhabitants (EU 27) produced an average 513 kg of Municipal Solid Waste (MSW) [START_REF]du 19 Novembre 2008 relative aux déchets et abrogeant certaines directives[END_REF], while French inhabitants produced 535 kg. The French production of MSW appears to have stabilized to around 42 million tons per year for several years.

In 2009, 7.8 million tons were recycled, 5.5 million tons were treated in organic plants, [START_REF] Aissani | Integration of spatial and temporal parameters and the risk of accident to the Life Cycle Assessment: Application to hydrogen and gasoline patterns[END_REF] million tons were turned into energy and 10 million tons were eliminated in landfills (Figure 1). The importance of local issues is steadily increasing for regulatory but also for ideological reasons. To get approval from the population, local decision-makers have to integrate local issues into decision-making.

To improve waste management and in particular to reduce its impacts, consulting offices that help local decision-makers use different environmental assessment tools for decision support such as the Ecological Footprint, the Carbon Footprint or Life Cycle Assessment (LCA). LCA appears to be more often used with regard to its multi-criteria character. However, despite its advantages, it presents some methodological and application limitations. Many of these limitations are intrinsic to the methodology and some are related to its application to the field of waste management.

LCA makes it possible to assess the potential environmental impacts of a system or product by identifying and quantifying the associated inputs and outputs. LCA is defined by ISO 14040 [START_REF]Environmental management -Life cycle assessment -Principles and framework[END_REF] as "a compilation of inputs, outputs and potential environmental impacts of a product system throughout its life cycle". The input and output flows of a system, identified in the inventory step (the second step of the LCA methodology) are linked to their potential environmental impacts, through causal chains called pathways. Their application field is quite large, because several impact categories can be assessed in the same study.

According to the standard ISO 14040 [START_REF]Environmental management -Life cycle assessment -Principles and framework[END_REF] and the SETAC, LCA methodology is divided into four steps:

-Goal and scope definition. The reasons for carrying out the LCA study are explained [START_REF]Environmental management -Life cycle assessment -Principles and framework[END_REF][START_REF]Environmental management -Life Cycle Assessment -Requirements and guidelines[END_REF] and the purpose, the scope, the nature and the function of the system, the functional unit and the boundaries are determined; -Inventory analysis: mass and energy flows throughout the system are quantified from mass and energy balances and turned into consumption and emission flows, called inventory data; inventory data must be related to the functional unit which is at the basis of inventory quantification.

-Impact assessment. The relationship between inventory data and potential environmental impact are established in two steps: classification, which assigns emission/consumption values to the different impact categories, and characterization, which quantifies potential environmental impacts [START_REF]Environmental management -Life cycle assessment -Principles and framework[END_REF]. The term "potential" is used because calculated impacts in LCA are not "real" impacts but possible ones, due to missing knowledge about the environmental fate of compounds, the mechanisms of impact occurrence but also synergy or antagonism phenomena between compounds [START_REF] Potting | The linear nature of environmental impact from emissions in lifecycle assessment[END_REF][START_REF] Potting | Spatial differentiation in life-cycle assessment via the site-dependent characterization of environmental impact from emissions[END_REF].

-Interpretation of results, based on the results from the previous steps. It is possible to conclude and issue recommendations (consistent with the objectives) to identify actions aimed at reducing the impact of human activities on the environmental system.

The use of LCA in MSW management, called "waste LCA" here, is a voluntary initiative aimed at informing decision-makers from a global environmental perspective. Waste LCA can be performed for different reasons. At a regional scale, waste LCA allows us to compare different waste management scenarios. At a national scale, waste LCA allows us to assess waste policies. In this paper, we deal with waste LCA at a regional scale.

The methodological specificity of waste LCA is its scope definition. In this study, the term "life cycle" refers to when the product becomes a waste that the owner wishes to dispose of (Figure 2). This means that waste LCA does not include emission and consumption associated to previous life cycle steps, i.e. before a product becomes a waste. Different steps of waste management are integrated: collection, sorting, transfer, recycling, recovery (with pre-treatment and treatment), i.e. energy and material collection, recovery and disposal. Waste production prevention is usually not taken into account because it especially concerns consumption patterns, although some authors consider that it is part of waste management and should therefore be included in waste LCA [START_REF] Cleary | The incorporation of waste prevention activities into life cycle assessments of municipal solid waste management systems: Methodological issues[END_REF].

The collection and treatment steps are called "foreground activities" (Figure 2), as impacts related to these steps are directly related to waste management, and the geographical scale of these activities is local. Decision-makers can monitor and control these activities, as opposed to "background activities" which are often located at another geographic scale and are indirectly First, we emphasize the need for this impact category, then we present the methodology for designing the impact pathway and finally we apply it. The fact that spatial differentiation is limited or absent (spatial and temporal parameters of emission and target populations are not integrated) poses a problem in the local impact assessment context of odours. Integration of local impact assessment into LCA will have to be improved by taking into account spatial and temporal conditions.

The odour issue in waste management

In the field of waste management, odour causes dissatisfaction and many complaints from local populations. In France, odour represents the second cause for complaints after noise [START_REF]Inspection des Installations Classées[END_REF].

The word "odour" is specifically defined as a molecule that can be perceived by a human being or an animal and which generates various impressions (pleasant, unpleasant, or indifferent).

In waste management, odours are caused by the biodegradation of organic matter during either aerobic (composting) or anaerobic (anaerobic digestion) processes. Odorous emissions vary according to the type of organic waste and the technical parameters of the process.

In waste management decision-making, odour nuisance is often related to composting facilities projects. Composting plants are considered as a source of unpleasant odour emissions which can cause olfactory nuisance to the people living nearby. The growing demand from local populations in terms of quality of life and well-being increases the number of olfactory assessment studies in the field of waste management. To quantify that nuisance, engineering consulting firms use the normative framework which defines the baseline of olfactometry (odour analysis): nose juries are formed, and laboratory materials and procedures are defined. However olfactometry is an a posteriori approach and does not meet the needs of prospective approaches that need an a priori assessment (for example during waste management planning). In decision-making, odours must therefore be assessed in the same way as other conventional environmental impacts (like global warming for example) in a priori assessment procedures. Moreover, odours can have an impact on health: repetitive unpleasant odours are not only a discomfort but can also have an adverse effect on population health by causing stress, fatigue and even depression [START_REF] Aatamila | Odour annoyance and physical symptoms among residents living near waste treatment centres[END_REF]. To take this parameter into account in environmental assessments, and especially in LCA, it is necessary to build a new impact category as well as a new impact pathway. The latter corresponds to the causal chain from gaseous emission to its final effect on environment (Figure 3). This study aims at building up that pathway, with the following limits: we only consider chronic emissions and emission peaks in normal functioning (degraded functioning is not taken into account) and we stop at the discomfort and inconvenience step that we call "effect". We do not consider the route from effect to odour-caused damage, i.e. stress, fatigue and anxiety.

The need for a local approach in odour pathway development

The pathway from emission to effect highly depends on local conditions which influence the fate of compounds within the environment, exposure parameters and effects on targets. It is easy to understand that if these local conditions are not taken into account in assessments, the robustness of the study can be questioned.

To take into account spatial and temporal conditions, it is necessary to focus on the second and third steps of LCA, i.e. inventory and impact assessment steps. In classical LCA, it is assumed that a standard environment is impacted. This is called the Site Generic approach. According to this approach, the characteristics of impacted environments (where emission takes place after physical, chemical and biological phenomena) do not influence the occurrence or the intensity of impacts because they do not taken into account in assessment. This approach is relevant for global impacts (global warming, depletion of the ozone layer or depletion of fossil resources), but not when local impacts are dealt with (e.g. eutrophication, ecotoxicity, toxicity…). For toxicity, it is necessary to take into account emission characteristics, environmental distribution, background concentrations (i.e. taking into account the compound which is already present in the medium) and target sensitivity [START_REF] Potting | The linear nature of environmental impact from emissions in lifecycle assessment[END_REF]. For these reasons, spatial differentiation is absolutely needed. It can be carried out using the Site Dependent approach.

Potting and Hauschild established a preliminary basis for the Site Dependent approach [START_REF] Potting | Spatial differentiation in life-cycle assessment via the site-dependent characterization of environmental impact from emissions[END_REF]. This approach is built according to the theoretical cause/effect chain leading to an environmental impact. The chain describes the mechanism whereby an impact results from the emission of a compound in the environment (Figure 4). The link between the amount of emitted compounds and the intensity of their environmental impacts is made of the successive steps of the cause and effect chain.

Unlike what is classically done in LCA, we do not use this cause/effect chain for impact quantification but to determine impact occurrence. 2008) highlighted the pervasiveness and the importance of spatial and temporal parameters throughout the cause/effect chain of a local impact [START_REF] Aissani | Integration of spatial and temporal parameters and the risk of accident to the Life Cycle Assessment: Application to hydrogen and gasoline patterns[END_REF]. They determine the appearance and intensity of the environmental impacts.

According to that chain, the Site Dependent approach is made up of five items with the following descriptors:

-Characterization of emission and emission source: quantity, time/frequency, emission compartment (air, water, soil), location and source type; -Fate analysis: compound distribution between environmental compartments, dilution, immobilization, removal and degradation; -Exposure analysis: characteristics of the impacted environment (sensitivity), increase of environmental and background concentrations; -Effect analysis: no-effect concentration and critical concentration; -Damage analysis: type and magnitude of the impact.

In this study, the chain is built up to the effect analysis. Local parameters are integrated using the USEtox model.

The new methodology framework

This new methodology aims to develop the first steps (i.e. up to the effect analysis) of a pathway for odour as a new impact category (Figure 3). The main challenge of this new methodology is to determine the potential effect of an odorous emission on a human population.

According to Figure 3, the odour impact pathway is built from the following items:

-Emission: we consider chronic emissions and emission peaks; -Fate analysis: we take into account degradation, dispersion and transfer phenomena; -Exposure analysis : the only exposure route considered is inhalation; -Effect analysis: we determine the effects of odorous compound emission on human beings; The methodology should follow LCA methodology for any impact assessment, i.e. a classification step based on the cause/effect chain to determine impact occurrence, and a characterization step based on the calculation of a characterization factor if impact occurrence is confirmed. The purpose is to calculate a potential disturbance impact defined for different types of odours. The link between potential odour and potential damage (nuisance), including impacts on human health, is not developed here.

Classification

This new methodology framework follows the cause/effect chain according to the descriptors of the Site Dependent approach. In LCA, a similar cause/effect chain has already been modelled using a mechanistic model called "USEtox".

The USEtox model

USEtox results from a scientific consensus based on comparison of existing models for toxicity assessment [START_REF] Rosenbaum | USEtox human exposure and toxicity factors for comparative assessment of toxic emissions in life cycle analysis: sensitivity to key chemical properties[END_REF]. It is becoming a reference to assess toxicity in LCA. It is built according to the Site Dependent approach to calculate characterization factors for human toxicity and aquatic ecotoxicity in different environmental compartments (air, water and soil) [START_REF] Hauschild | Building a model based on scientific consensus for life cycle impact assessment of chemicals: The search for harmony and parsimony[END_REF]. Throughout the cause and effect chain, the model determines fate, exposure and effect analyses in order to obtain a set of characterization factors (Figure 5). The continental box is a virtual continent, i.e. an average value of all continents on earth from average continental data. This is similar for the urban scale where average urban data are used.

Each box is set with data according to its scale (Figure 6a). In our study, the scale of boxes is different from USEtox default version and they need to be modified.

Emission characteristics

As in classical LCA, the inventory step deals with identifying emission, here the odorous compounds emitted by composting facilities. The aim of this part is:

-To determine whether the compound can generate an odour impact; -To get spatial information relevant for future fate analyses.

This methodology is only carried out for compounds previously identified and routinely produced by the composting process of municipal waste.

After the classification step, the main characteristics of the emitted compound, its emission and emission compartment have to be defined:

-Emission type (smokestack or diffuse emission); -Emission frequency (occasional or chronic emission); -Period of emission (long or short); -Emission compartment (air, water or soil); -Emitted quantity; -Physical, chemical and biological characteristics of the compound; -Physical, chemical and biological characteristics of the emission compartment.

Fate analysis

Fate analysis is necessary to take into account transfer, degradation and diffusion of compounds after their emission. It allows us to determine the compound concentrations people are exposed to. It is performed using the USEtox framework. However, for odour impact assessment, the use of the USEtox model for fate analysis is restricted to determining the environmental concentration of the compound after emission. It is necessary to adapt USEtox. Indeed, in odour assessment the urban and continental scales are macroscopic.

To adapt USEtox to an odour context, the size of the three boxes and their environmental compartment characteristics (such as temperature, wind speed, rain rate…) have been changed (Tab 1). This scale change has led to the modification of transfer between local fresh water and global fresh water. A sensitivity analysis was performed to identify the relevant and sensitive parameters of the environmental compartments in the USEtox model. Among all the environmental parameters reported in USEtox (Tab 1), only three seemed relevant for odour assessment and were therefore submitted to a sensitivity analysis: temperature, wind speed and rain rate. For the other parameters (for example: depth of fresh water, river flow, and run-off fraction) default values present in USEtox are used. After changing box sizes and the choice of sensitive parameters, the fate analysis was performed and the environmental concentration of the compound was calculated consistently with the Site Dependent approach.

Exposure analysis

The exposure analysis aims to incorporate a spatial dimension to determine whether the geographic location of the emission and the presence of human beings sensitive to the emitted compound coincide. The exposure concentration is the sum of the concentration due to current emission (previously calculated with USEtox model) and of the background concentration of the compound, i.e. the amount of the compound currently present in the environment, independently of the considered emission [START_REF] Potting | The linear nature of environmental impact from emissions in lifecycle assessment[END_REF]. Adding the background concentration allows us to take into account local conditions of impacted environments and to obtain the real exposure concentration.

Effect analysis

The effect analysis allows for determining the effect of a compound on human beings. To define that effect, we calculated an Effect Ratio (ER) from the exposure concentration and olfactory threshold of the studied compound (Eq2).

ER sub expo i

Olfactory threshold sub (Eq 2)

The olfactory threshold is available in chemical databases. The effect ratio can be distributed into three intervals (Figure 8): [0; α], [α; β] and [β; + ∞[. The α parameter is a "safety factor". This safety factor is set to 1.10 -3 for our preliminary research work. The β parameter is 1. When the effect ratio is in the first interval, we consider there is no olfactory impact risk. When the effect ratio is in second or third intervals, we consider there is an olfactory impact risk. However, in the second interval, we admit the existence of a "fuzzy zone" related to the cocktail effect which is not taken into account. When the effect ratio is in the third interval, the characterization factor and the impact are calculated, as shown in the next section.

Computation of the characterization factor and quantification of the odour impact

The characterization factor is not calculated the same way as in USEtox. Besides the determination of fate, exposure and effect factors is also different.

The characterization factor involves not only the studied compound but also a reference compound. The latter is defined from the compost wheel [START_REF] Rosenfeld | The use of an odour wheel classification for the evaluation of human health risk criteria for compost facilities[END_REF]. For each odour type, we identify one reference compound (Figure 7). For example, in the odour type "solvent/hydrocarbon", we choose the benzene compound as a reference compound. In the "sweet" type we choose the butanone compound as reference. We propose that the characterization factor be the ratio of the olfactory threshold of a studied compound and the one of its reference compound. The odour impact is then calculated by multiplying this characterization factor by the mass of the emitted compound (data obtained in the inventory step).

A new framework scene

The different items previously developed lead to a new methodology which consists in two steps: a complex classification procedure to check that an impact does exist, and impact characterization (Figure 8). This methodological proposal deeply modifies the roles of the classification and characterization steps. Indeed, in traditional LCA, classification is a simple qualitative step to associate compound emission with different impact categories. In this work, the classification step is more important and characterization is aimed at computing the characterization factor. The change in this classification step allows for working on the occurrence of odour impacts. This methodological point is developed in the discussion section.

To illustrate our methodological proposal, here is an example with emission of ethyl benzene during composting of municipal solid waste.

Case study with ethyl benzene emission during composting

This case study aims to provide an example of odorous compound that can be analyzed using the new methodology. We chose ethyl benzene, which belongs to the family of halogenated volatile organic compounds (VOC). To develop the methodology, we used data from a French project named "CleanWasT" (ANR-08-ECOT-004 -"Assessment of clean and sustainable waste management technologies"). During the project, we measured several VOCs related to the functioning of a composting plant.

We chose ethyl benzene for two reasons:

-It is one of the analyzed compounds that displayed high concentrations; -Its odour type is specific: "solvent and hydrocarbon"; The methodological steps are presented following Figure 4. We chose to localize ethyl benzene emission in the Brittany area (French west region).

Emission characteristics

Ethyl benzene emission occurs in silo ventilator outlets. The type of emission is smokestack. Ethyl benzene concentration is 10.68 kg.y -1 , or 2.93.10 -2 kg.d -1 . Ethyl benzene concentration in the facility air compartment and in the local air compartment is therefore estimated to be 1.21.10 -14 kg.m -3 . Because we considered an average daily emission and calculated a steady-state concentration, emission peaks do not appear.

Exposure analysis

According to the European Monitoring and Evaluation Program (EMEP) database on air quality measurement, we admit an ethyl benzene background concentration in urban air of 1.40.10 -10 kg.m -3 [START_REF]European monitoring and Evaluation Program: EMEP VOC data[END_REF]. In this case, the exposure concentration is equal to the environmental concentration, i.e. 1.40.10 -10 kg.m -3 .

Effect analysis

According to Cometto-Muniz and Abraham [START_REF] Cometto-Muniz | Olfactory detectability of homologous nalkylbenzenes as reflected by concentration-detection functions in humans[END_REF], the olfactory threshold of ethyl benzene is 2.6.10 -8 kg.m -3 . The effect ratio for ethyl benzene emission is calculated from the exposure concentration (1.40.10 -10 km/m 3 ) and the olfactory threshold. In this case, the effect ratio is 2.6.10 -8 kg.m -3 . The effect ratio as related to ethyl benzene emission is 5.38.10 -3 .

To determine interval limits, we used a safety factor of 10 -1 for the first limit, and the second limit was 1. We then defined our three classification intervals:

-[0; 1.10 -3 ]: no impact is expected in that zone; -]1.10 -3 ; 1]: in that interval, we admit the existence of a "fuzzy zone" where the olfactory impact risk is not clearly identified; -]1; + ∞[ : there is a clearly identified olfactory impact risk.

For the ethyl benzene example, the effect ratio falls into the second interval. We therefore admit there is an olfactory impact risk potential related to ethyl benzene emission during the composting of municipal solid waste.

Quantification of the characterization factor and of odour impact

To calculate the characterization factor of ethyl benzene emission, it is necessary to select a reference compound corresponding to its odour type. In the compost odour wheel (Figure 7), we classified ethyl benzene in the solvent/hydrocarbon odour type. For that odour type, the reference compound is benzene. According to Nagata (2003), benzene olfactory threshold is 8.6.10 -6 kg.m -3 [17]. Based on ethyl benzene and benzene olfactory thresholds, we calculated a characterization factor: 3.02.10 -3 kg eq. benzene.kg emitted ethyl benzene -1 .

Finally, based on the characterization factor and ethyl benzene mass (from inventory step: 2.93.10 - 2 kg.d -1 ), we quantified the impact: 6.6.10 -5 kg eq benzene.d -1 .

This numerical value should not be considered independently. The proposed methodology allows for quantifying the impact of odour as related to municipal solid waste treatment in order to compare it to other odour impact quantifications in alternative waste treatment scenarios. Furthermore, our methodology cannot be compared to other characterization methods because current methods do not take into account the impact of odours.

Discussion

The main objective of this paper was to determine the impact pathway of a new impact category: odour. The next part is dedicated to the interest and limits of this new methodology.

Impact of odour in waste management

The aim of the methodology was to develop an impact pathway of a new impact category: odour.

In order to use it in waste management system comparisons, the users have to be able to provide reliable and exhaustive characterization of the impact of odour in all compared systems. However, literature about emissions during the composting process is very poor and available information is very heterogeneous as it depends on the composition of input waste and on the composting process. In the coming years, data availability and their range should be improved and this methodology should be more applicable.

Odours result from a cocktail of compounds

The odours people can smell do not usually result from just one compound but are due to cocktails of compounds. Some synergistic and antagonistic phenomena still remain undetermined. Therefore such phenomena were not taken into account in our new methodology because of the lack of basic knowledge in that field.

Currently, in our newly-developed methodology, a ratio < 1 means no impact. However, we observed odour impacts when the ratio was lower than one. This observation is linked to the cocktail effect which is not taken into account.

Limitations of a steady-state system

Most models are built according to a steady-state calculation in order to assess transfer and degradation phenomena and a resulting compound concentration in different environmental compartments (air, water and soil). Therefore, these models need daily emission and users have to calculate an average daily emission for the functional unit. This average daily emission is used on an infinite time-scale by the models. Then two important limitations can be observed:

-Calculating average daily emissions erases emission peaks of odorous compounds. And yet odour phenomena are frequently due to emission peaks, not to chronic emission; -The resulting concentration represents the concentration at the steady-state and not the peak just after emission that causes olfactory discomfort. These limitations are linked to the difference in persistence between compound emission and their consideration for odour impact assessment.

Contribution of the new methodology

In conventional LCA, a qualitative link between a compound and its potential impacts is made. This link depends on the potential polluting character of the compound. Impact occurrence is a function of intensity and occurrence probability, and occurrence probability determines impact appearance. This parameter strongly depends on local conditions and is not assessed in conventional LCA. To assess it, it is necessary to include local conditions.

Conclusions

In the French context of municipal solid waste management, local decision-makers use an environmental assessment tool called LCA to assess the environmental impacts of the different waste management scenarios. The global character of LCA leads to irrelevant assessment of local impacts because local impacts depend on local characteristics of the emission source and on impacted environments. However, in waste management and decision-making, the place of local impacts is very important and their assessment should be as robust as possible. Olfactory discomfort is one of these relevant local issues for the environmental assessment of waste management.

To assess the impact of odour with LCA, it is necessary to develop a new impact pathway because this impact category does not exist yet. The objective of this paper is to explain the construction of this impact pathway and take ethyl benzene as an example. The methodological proposal is built according to the partial cause and effect chain with the following items: emission characteristics, fate analysis, exposure analysis and effect analysis. The methodology is applicable in a general way. We chose to apply it to municipal solid waste management because of its local issues.

The application of our methodology to ethyl benzene emission allowed us to obtain an impact result of 6.6.10 -5 kg eq benzene.d -1 . This numerical value should not be considered independently. Our methodology allows for quantifying the impact of odours related to municipal solid waste treatment plants and comparing it to other odour impact quantification for alternative waste treatment scenarios. This work is the first step in odour impact assessment and aiming to have odours taken into account in waste management decision-making. To integrate our methodological proposal into future assessment tools it will be necessary to supply databases with odour measurements, i.e. data measured in composting plants, background concentrations, olfactory thresholds… Our new methodology also needs to be improved by understanding and integrating the cocktail effect between compounds. It determines odour impact (midpoint), not olfactory annoyance (endpoint). In order to characterize olfactory annoyance, it appears necessary to integrate social sciences into our approach. 17. Nagata, Y.: Measurement of odour threshold by triangle odour bag method. In., pp. 118-127.

Ministry of the Environment, Government of Japan, Odor measurement review, Office of Odor, Noise and Vibration Environmental Management Bureau, (2003)

Figure 1 :

 1 Figure 1: French household waste in 2009 (million tons) Along with time and production changes, waste management in Europe and France had become a major priority [2-3]. However, MSW are managed at a local scale such as counties in France. Pressure on local decision-makers requires them to integrate local issues in their decisions. Local management is based on local environmental issues which are determined by local conditions.

Figure 2 :

 2 Figure 2: Scope of LCA applied to MSW management

Figure 3 :

 3 Figure 3: Complete odour impact pathway

Figure 5 :

 5 Figure 5: The USEtox framework The characterization factor is calculated from the fate (FF), exposure (XF) and effect (EF) factors (Eq1). CF=FF×XF×EF (Eq1)

Figure

  Figure 6a and b: USEtox box translation (from a) to b)) for local impact assessment and transfers between environmental boxes and compartments

Figure 7 :

 7 Figure 7: Compost odour wheel

Figure 8 :

 8 Figure 8: The new methodology framework

Figure 1 :Figure 2 :Figure 3 :Figure 4 :Figure 5 :Figure 7 :Figure 8 :

 1234578 Figure 1: French household waste in 2009 (million tons) Figure 2: Scope of LCA applied to MSW managementFigure 3: Complete odour impact pathway Figure 4: Cause/effect chain of environmental impact Figure 5: The USEtox framework Figure 6a and b: USEtox box translation (from a) to b)) for local impact assessment and transfers between environmental boxes and compartments Figure 7: Compost odour wheel Figure 8: The new methodology framework

  is a nested model that works across three environmental compartments, i.e. global, continental and urban boxes. The first two boxes are composed of several environmental compartments, i.e. air, fresh water, sea water, agricultural soils and natural soils, whereas the urban box is made up of the air compartment only. The global box represents the earth with global data.

	The USEtox model
	Classification
	Characterization
	Damage

  Legend[sub]: concentration of emitted substance; i: environmental compartment; [ ] expo i : exposure concentration in compartment i;[sub] bac : background concentration; α and β: classification factors; I: impact and m: mass We hypothesised that it was emitted it in a French county in the Brittany region (west of France). The local data for that territory are collected in landscape spreadsheets of the USEtox model (Tab 1). To analyze odour impact, we modelled the "facility" box with the following dimensions: a 2,500 m 2 square (corresponding to the average dimensions of composting plants) and a local box represented by a 36 km 2 square corresponding to the average dispersion area of odorous compounds (3 km). The environmental characteristics of the facility box are identical to the local box because USEtox is a nested model and box dimensions are very similar.

	5.2 Fate analysis	Emission	Determined by USEtox
					Flow	[sub] i
	Classification	Exposure [sub] i [sub] expo i = [sub] i + [sub] bac	Fate analysis Exposure analysis Effect analysis	Fate [sub] expo i Effect Effect ratio (ER)
	No impact Tab 1: Environmental parameters applied to our methodology in the ethyl benzene case [0; α] ]α; β] ]β; + ∞[ [sub] expo i
	Environmental box	Environmental data	Modified value	Olfactory threshold sub Default value
		Local box Characterization	Characterization factor (CF) Impact factor 22.12 km² 13.88 km² Fresh water fraction area Olfactory threshold sub Olfactory threshold ref Land area Sea area 0.0045 Natural soil fraction area 0.0865 Agricultural soil fraction area 0.8485	I = m x CF 9.01.10 6 km² 9.87.10 5 km² 0.03 0.485 0.485
			Other soils fraction area	0.0605	1.00.10 -20
			Temperature		11.3 °C	12 °C
			Wind speed		3.5 m.s -1	3 m.s -1
			Rain rate		669 mm.y -1	700 mm.y -1
			Fresh water depth	2.5 m	2.5 m
			River flow from continental to
			global or from global to	0.32	0
			continental
			Run-off fraction		0.25	0.25
			Infiltrated Fraction	0.25	0.25
			Soil erosion		0.03 mm.y -1	0.03 mm.y -1
		Facility box	Land area		0.0025 km²	240 km²
			Natural soil fraction area	0.05	0.67
			Area fraction other soils fraction area	0.95	0.33

ACKNOWLEDGMENTS

The authors would like to thank Pr. Bellon-Maurel V. (ELSA-Irstea) for his helpful comments on the manuscript. They also would like to thank the members of the CleanWasT and Proddeval (convention number 0906C0081) projects.