domain: sdu sde

text:
Bueno G Taitson
email: thierry.allard@upmc.fr

Dating kaolinite from the Neogene Içá Formation and overlying laterites, central Amazonia, Brazil: constraints for a stratigraphic correlation

Keywords: geochronology, electron paramagnetic resonance, dosimetry, artificial irradiation, radiation-induced defects, sediments

The Neogene Içá Formation is a major sedimentary deposit in central Amazonia (Brazil) that is critical to the understanding and modeling of the evolution of the Amazon Basin. However, its chronostratigraphy is poorly defined, mostly because it is not fossiliferous and it does not contain volcanic ash levels. This study is the first attempt at the absolute dating of the sediments and overlying soils of the Içá Formation by electron paramagnetic resonance (EPR) of radiation-induced defects in kaolinite (RIDs). Four profiles of unconsolidated sediments overlaid by lateritic soils from the Barcelos region (Amazonia, Brazil) were studied. The concentration of RIDs was assessed from EPR spectra through a simplified procedure on a selected set of samples, excluding those showing too strong of interference from the signal of trace vanadyl complexes. It is shown that in such sedimentary material, both the microscopic distribution of thorium (together with uranium) and the origin of kaolinite, either detrital or authigenic, are critical for kaolinite dating. Considering an argued authigenic origin and two scenarios of Th distribution, it appears that most of the present chronologic data support the stratigraphic correlation with the Madre de Dios sedimentary Formation in Peru previously proposed in the literature for the Içá Formation (9.5 -2.5 Ma). This study also shows a rejuvenation process of kaolinite both in the uppermost soil and at depth of the profiles. This rejuvenation occurred during paleoclimatic periods already revealed in other weathering covers from the Amazon Basin and possibly resulted from downward weathering in the topsoil and water table or lateral weathering at depth

Introduction

Explicative and predictive models of the evolution of continental surfaces require the dating of sediments and soils in relation to the influence of geologic events such as orogeneses and thus tectonic plate drifts, local paleoclimates and paleogeography. Among the greatest basins in the world is the Amazon Basin, which represents 40% of the South American subcontinent. It is deeply seated on Paleozoic craton and sediment deposits (Hoorn and Wesselingh, 2010). In the Brazilian section of the basin, the weathering covers consist mainly of laterites that developed on various parent rocks and represent 80% of the basin area, according to th Projeto Radam documents (Projeto Radam, 1972[START_REF] Lourenço | PROJETO RADAMBRASIL[END_REF]Fritsch et al. 2011 and references therein). The long-term history of the Amazon Basin is described by increasingly detailed geologic and palaeogeographic studies (see Hoorn and Wesselingh, 2010). The present concerns include, e.g., explaining the great biological diversity of Amazonia (Hoorn et al., 2010) and determining the ages and conditions of genesis of natural resources such as kaolins of sedimentary or pedologic origin [START_REF] Da Costa | The contribution of lateritization processes to the formation of the kaolin deposits from eastern Amazon[END_REF][START_REF] Sousa | Mineralogical, micromorphological and geochemical evolution of the kaolin facies deposit from the Capim region (northern Brazil)[END_REF][START_REF] Montes | Systèmes sols ferrallitiques-podzols et genèse des kaolins[END_REF][START_REF] Lucas | Biogeochemistry of an Amazonian podzol-ferralsol soil system with white kaolin[END_REF]. The Neogene represents a particularly noticeable period in the history of the Amazon Basin because it coincides with the development of the modern eastward Amazon River system [START_REF] Horbe | Provenance of Pliocene and recent sedimentary deposits in western Amazônia, Brazil: Consequences for the paleodrainage of the Solimões-Amazonas River[END_REF][START_REF] Rossetti | Mid-Late Pleistocene OSL chronology in western Amazonia and implications for the transcontinental Amazon pathway[END_REF].

In this work, we focus on the dating of unconsolidated sediments occurring at the regional scale and assigned, from our detailed observations in the field and from remote sensing maps, to the Neogene Içá Formation in Brazil, which crops out widely in the central Amazon Basin (Figure 1). Its still disputed area may reach 1.000.000 km 2 [START_REF] Fritsch | Deciphering the weathering processes using environmental mineralogy and geochemistry: Towards an integrated model of laterite and podzol genesis in the Upper Amazon Basin[END_REF]CPRM, 2010). It occurs at approximately 100-140 m a.s.l. and lies unconformably on the Solimões Formation. The chronostratigraphy of the Içá Formation in Brazil is poorly known owing to the lack of fossils or datable material such as volcanic ash within it.

However, it is assumed to correlate with another formation in Perù, the Madre de Dios Formation, which developed after the Pan-Amazonian Ucayali Peneplain at the beginning of the Quechua II orogenic event [START_REF] Campbell | The Pan-Amazonian Ucayali Peneplain, late Neogene sedimentation in Amazonia, and the birth of the modern Amazon River system[END_REF]. The Madre de Dios Formation was deposited between 9.5 Ma and 2.5 Ma, as assessed from the dating of local ash levels in circumscribing levels [START_REF] Campbell | The Pan-Amazonian Ucayali Peneplain, late Neogene sedimentation in Amazonia, and the birth of the modern Amazon River system[END_REF].

Thus far, it has not been possible to perform absolute dating of the Içá Formation itself with K-Ar in volcanic ash or in K-bearing manganese oxides, but one of its main components, i.e., kaolinite, may be considered a potential geochronometer. Kaolinite contains radiationinduced defects (RIDs) that accumulate with time as a result of ambient radioactivity [START_REF] Clozel | Nature and stability of radiation induced defects in natural kaolinites: New results and a reappraisal of published works[END_REF]. Consequently, RIDs can be used in various geological applications [START_REF] Muller | Tracing Kaolinites through Their Defect Centers : Kaolinite Paragenesis in a Laterite (Cameroon)[END_REF][START_REF] Muller | Radiation-induced defects in kaolinites: indirect assessment of radionuclide migration in the geosphere[END_REF][START_REF] Allard | Radiationinduced defects in clay minerals: A review[END_REF], especially as geochronometers in tropical weathering covers such as laterites [START_REF] Balan | Formation and evolution of lateritic profiles in the middle Amazon Basin: Insights from radiation-induced defects in kaolinite[END_REF][START_REF] Allard | Combined dating of goethites and kaolinites from ferruginous duricrusts. Deciphering the Late Neogene erosion history of Central Amazonia[END_REF][START_REF] Mathian | Unraveling weathering episodes in Tertiary regoliths by kaolinite dating (Western Ghats, India)[END_REF]. The time range covered by this approach is consistent with geological periods and is appropriate for dating kaolinite-containing tropical sediments and soils. In a previous study, one sample of iron duricrust developed on Içá sediments was dated by electron paramagnetic resonance spectroscopy of trapped kaolinite particles, yielding an age of 1.7-4.0 Ma [START_REF] Allard | Combined dating of goethites and kaolinites from ferruginous duricrusts. Deciphering the Late Neogene erosion history of Central Amazonia[END_REF]. An important difficulty in dating detrital sediment deposition arises when these sediments are preserved from diagenetic transformations. In this situation, the kaolinite may not have formed in the sediment during or just after deposition but previously in the soils (possibly laterites) that predated erosion, transport and deposition in the basin. Consequently, the methodology for detrital kaolinites potentially overestimates deposition ages, except when the residence time in uphill soils (i.e., as the source of eroded and deposited material) is negligible with respect to the age of the sediment deposition. Thus, authigenic or detrital origins of clay minerals must be documented to enforce the challenging task of dating recent sediments using kaolinite.

The main objectives of this study are to estimate the ages of some deposits from the Içá Formation and overlying soils collected in the central Amazon Basin. Subsequently, the data are compared to the time range determined for the analogous Madre de Dios Formation by [START_REF] Campbell | The Pan-Amazonian Ucayali Peneplain, late Neogene sedimentation in Amazonia, and the birth of the modern Amazon River system[END_REF] to question the stratigraphic correlation between these formations and to discuss the proposal that the Içá Formation was deposited between the major events corresponding to the Ucayali peneplanation and the eastward setting of the Amazon drainage.

Geological background

As stated by [START_REF] Hoorn | Neogene Amazonia : Introduction to the special issue[END_REF], the Neogene history of Amazonia remains obscure, mainly because of the difficulty of finding relevant outcrops and because of scarce chronostratigraphic determinations. For example, the determinant period of the eastward onset of the Amazon system that occurred in the late Miocene or Pliocene has been debated many times (see, e.g., [START_REF] Figueiredo | Late Miocene onset of the Amazon river and the Amazon deep-sea fan: evidence from the Foz do Amazonas Basin[END_REF][START_REF] Campbell | Late Miocene onset of the Amazon River and the Amazon deep-sea fan: Evidence from the Foz do Amazonas Basin: comment[END_REF]. Among major geologic units, the Içá Formation covers a large part of central Amazonia, although its actual extent remains controversial, extending over 300,000 [START_REF] Rossetti | New geological framework for Western Amazonia (Brazil) and implications for biogeography and evolution[END_REF], 500,000 [START_REF] De Souza | Sintese da hidrogeologia nas bacias sedimentares do Amazonas e do Solimões: Sistemas aquiferso Içá-Solimões e Alter do Chão[END_REF] and up to 1,000,000 km 2 (CPRM, 2010) (Figure 1). The Içá Formation was first described by [START_REF] Maia | Projeto carvão no Alto Amazonas[END_REF] as a continental sedimentary series deposited in a fluvial context and located in the Amazonas state, Brazil [START_REF] Reis | Geologia e recursos minerais do estado do Amazonas. Manaus[END_REF]. It covers the Solimoes Formation corresponding partly to the large wetland Pebas paleoenvironment (10-11 Ma Miocene sediments, [START_REF] Latrubesse | Late Miocene continental sedimentation in southwestern Amazonia and its regional significance: biotic and geological evidence[END_REF] and is deposited above the widespread erosive Ucayali unconformity that marks the Quechua II tectonic phase of the Andes [START_REF] Campbell | The Pan-Amazonian Ucayali Peneplain, late Neogene sedimentation in Amazonia, and the birth of the modern Amazon River system[END_REF].

Sediments from the Içá Formation consist of unconsolidated sands with silty and clayey lenses exhibiting various sedimentary patterns including cross-bedding and ripple marks [START_REF] Horbe | Provenance of Pliocene and recent sedimentary deposits in western Amazônia, Brazil: Consequences for the paleodrainage of the Solimões-Amazonas River[END_REF]. According to [START_REF] De Almeida | Large barchanoid dunes in the Amazon river and the rock record : implications for interpreting large river systems[END_REF], the Içá Formation also contains large sedimentary structures that correspond to barchanoid dunes settled as deep channel deposits. Primary detrital minerals indicate that the main sediment source areas include Mesoproterozoic regions from the Amazonian craton and adjacent NW to SW provinces together with some Andean contribution [START_REF] Horbe | Provenance of Pliocene and recent sedimentary deposits in western Amazônia, Brazil: Consequences for the paleodrainage of the Solimões-Amazonas River[END_REF].

Dating studies on the Içá Formation are scarce and provide inhomogeneous data.

Sediments from the Içá Formation were first thought to be Plio-Pleistocene based on stratigraphic correlations [START_REF] Maia | Projeto carvão no Alto Amazonas[END_REF] or pollen studies [START_REF] Latrubesse | A Formação Solimões: uma formação do Mio-Plioceno da Amazônia sul-ocidental[END_REF][START_REF] Rossetti | New geological framework for Western Amazonia (Brazil) and implications for biogeography and evolution[END_REF]. In addition, absolute dating by optically stimulated luminescence of sediments from central, southwestern and northern Amazonia yielded recent ages corresponding to tens to hundreds of thousands of years before the present, i.e., within the Pleistocene period [START_REF] Rossetti | Mid-Late Pleistocene OSL chronology in western Amazonia and implications for the transcontinental Amazon pathway[END_REF][START_REF] Passos | Pleistocene-Holocene sedimentary deposits of the Solimões-Amazonas fluvial system, Western Amazonia[END_REF], in line with the Pleistocene-Holocene ages proposed by [START_REF] Rossetti | New geological framework for Western Amazonia (Brazil) and implications for biogeography and evolution[END_REF]. The Içá Formation was also stratigraphically correlated to the Madre de Dios Formation in Peru [START_REF] Campbell | The Pan-Amazonian Ucayali Peneplain, late Neogene sedimentation in Amazonia, and the birth of the modern Amazon River system[END_REF], which consists of unconsolidated fluvial sands and sediments accumulated in a mega-lake complex (deltaic and fluvial-lacustrine) in its uppermost horizons. The Madre de Dios Formation was dated using 40 Ar/ 39 Ar on volcanic ash occurring at the top and bottom of the sedimentary sequence [START_REF] Campbell | Cenozoic chronostratigraphy of the southwestern Amazon Basin[END_REF]. The sediments started to be deposited before 9 Ma and ended after 3.1 Ma, providing time constraints for important paleofaunas from the Amazon Basin.

Subsequently, it was proposed that the analogous, stratigraphically correlated Içá Formation from Brazil was deposited in this period in the time range of approximately 9.5 -2.5 Ma [START_REF] Campbell | The Pan-Amazonian Ucayali Peneplain, late Neogene sedimentation in Amazonia, and the birth of the modern Amazon River system[END_REF]. The model by [START_REF] Campbell | The Pan-Amazonian Ucayali Peneplain, late Neogene sedimentation in Amazonia, and the birth of the modern Amazon River system[END_REF] also stated that the Amazonian Basin behaved as a single sedimentary basin during this period and that the modern Amazon system began forming at the end of the Pliocene, approximately 2.5 Ma ago.

Materials and methods

Selected profiles

The selected sediments belong to a regional formation that we assign to the Içá Formation. In fact, because of the presence of unconsolidated sediments in the entire region and their location in the landscape with respect to the plateau, their facies could not be confused with terraces, floodplains or modern alluvial deposits of limited extent. These observations are supported by the geological map of the region produced by the CPRM(Figure 1). Four selected sedimentary profiles occur in a sequence from upstream to downstream of the Demini River, north of Barcelos to the Rio Negro bank. All of them are composed of interspersed levels of unconsolidated clayey and sandy sediments more or less impregnated with iron oxides and overlaid by oxisols (Figure 2). The four P1, P2, P3, and P4 profiles were named according to the closest human inhabited localities. The first profile is P3 (Acampamento), located on the right bank of the Demini River (0°15'52.1"N, 62°46'20.0"W; elevation: 45 m). The P2 profile is named Tabocal and outcrops 50 km downstream and south of Profile 3 (0°02'52.8"S, 62°45'41.5"W, elevation: 46 m). The P1 profile (Sumaúma) is approximately 45 km downstream of Profile 2 (0°22'00.9"S, 62°46'28.7"W. Elevation: 35 m).

The P4 profile (Tucandeira) is on the right side of the Rio Negro River (1°02'41.8"S, 62°49'09.5"W. Elevation: 20 m) downstream of Barcelos city and the Demini River mouth (Figure 1, Figure 2).

The base levels of profiles suggest some similarities with the A subunit proposed by [START_REF] Campbell | The Pan-Amazonian Ucayali Peneplain, late Neogene sedimentation in Amazonia, and the birth of the modern Amazon River system[END_REF], owing to, e.g., the occurrence of fossil plants or coarse sand layers.

However, the three horizons tentatively proposed by this author are not clearly distinguished in the 4 studied profiles, which are much shallower (10-17 m) than the reference profiles from the Madre de Dios Formation and may be eroded, weathered, only partly outcropping or exhibiting lateral differentiation of facies.

Collection and preparation of samples

All the samples were deferrated with citrate-dithionite-bicarbonate reagent, following the procedure described in [START_REF] Mehra | Iron oxide removal from soils and clays by dithionitecitrate buffered with sodium bicarbonate[END_REF], to minimize the interference of iron oxides during the EPR analysis. The fraction < 5 µm was separated by size sorting in sedimentation columns to concentrate the kaolinite.

The kaolinite GB1 from St Austell, Great Britain [START_REF] Allard | Radiation-induced paramagnetic defects in natural kaolinites : alpha dosimetry with ion beam irradiation[END_REF] was used as a reference for the signal of RIDs. A reference VO 2+ -rich dickite, Dimex, originating from Mexico, was also used to assign the resonances of the vanadyl complex in the spectra of Içá samples.

Chemical analyses

The concentrations of U, Th and K were measured in raw samples ground below 80 µm by ICP-AES and ICP-MS techniques at the Service d'Analyse des Roches et des Minéraux (SARM at the Centre de Recherches Pétrographiques et Géochimiques,CRPG, Nancy, France). Analytical details and errors regarding the measurements are described at http://www.crpg.cnrs-nancy.fr/SARM/index.html.

Irradiation

-

He + irradiation: The samples were deposited on stainless steel plates and irradiated with 1.5 MeV He + ions in the Aramis linear accelerator (Centre de Sciences Nucléaires et de Sciences de la Matière (CSNSM), Orsay, France). The range of 1.5 MeV He + ions in kaolinite is 4 µm, as calculated with the SRIM code [START_REF] Ziegler | SRIM -The stopping and range of ions in matter[END_REF]. Thus, samples of kaolinite were deposited by sedimentation on stainless steel plates with a thickness of 4 µm so that all the ion beam energy was absorbed in the clay mineral structure. The irradiated samples were subsequently heated for 2 hours at 250 °C to anneal the unstable defects, according to the procedure of [START_REF] Allard | Kaolinite as an in situ dosimeter for past radionuclide migration at the earth's surface[END_REF]. Dosimetry curves were derived from irradiations in the 3.10 11 -10 13 ions/cm 2 fluence range corresponding to doses within the range of 70 -2342 kGy, which appeared to be appropriate for most conditions in lateritic covers [START_REF] Balan | Formation and evolution of lateritic profiles in the middle Amazon Basin: Insights from radiation-induced defects in kaolinite[END_REF][START_REF] Allard | Combined dating of goethites and kaolinites from ferruginous duricrusts. Deciphering the Late Neogene erosion history of Central Amazonia[END_REF][START_REF] Mathian | Unraveling weathering episodes in Tertiary regoliths by kaolinite dating (Western Ghats, India)[END_REF].

-Neutron irradiation: Thin sections of selected samples were irradiated by thermal neutrons to produce induced fission tracks and subsequent U mapping at the microscopic scale (see, e.g., [START_REF] Price | A simple method for measuring low uranium concentrations in natural crystals[END_REF] for the related methodology). This was performed on the FRMII reactor, Munich, Germany, according to the procedure by Sélo (1983), by putting a Kapton film on the thin section before irradiation. A cumulative flux of 6.9 x 10 15 neutrons/cm 2 was used during irradiation. The fission tracks formed in the Kapton foils were revealed through reaction with a hypochlorite solution (14% NaClO and 12% NaCl) at 100 °C for 9 min. Then, the tracks were counted using an optical microscope with a x 1000 magnification. The homogeneity of the neutron flux was verified using a standard of 50 ppm uranium in glass provided by the National Institute of Standards and Technology.

Electron Paramagnetic Resonance

Electron paramagnetic resonance spectroscopy (EPR) is a very sensitive method that allows the detection of paramagnetic species, i.e., species with unpaired electrons. This concerns, e.g., several ions of transition elements (Fe 3+ , V 4+ , Cr 3+ , Mn 2+ …) together with free radicals [START_REF] Ikeya | New applications of electron spin resonance. Dating, dosimetry and microscopy[END_REF]. EPR spectra were recorded on kaolinite powder samples in the X-band (≈ 9.4 GHz) at ambient temperature with a Bruker EMXplus TM spectrometer. The acquisition parameters were set as 3 or 5 Gauss (1 Gauss = 10 -4 Tesla) for the modulation amplitude of the radiation-induced defects (RID) or structural Fe 3+ species, respectively, and 40 mW for microwave power. The data were normalized for sample mass, receiver gain and a constant resonant cavity filling factor. The EPR spectra were defined by their effective spectroscopic factor g values derived from the resonance condition:

hν = gβH 0 ( 1
)
where h is the Planck constant; ν is the resonance frequency; g is the Landé factor, which is a tensor with eigenvalues g xx , g yy , and g zz ; β is the Bohr magneton; and H o is the external magnetic field. The principal values of g were checked by comparison with a GB1 kaolinite used as a standard for RIDs [START_REF] Allard | Radiation-induced paramagnetic defects in natural kaolinites : alpha dosimetry with ion beam irradiation[END_REF].

The concentrations of radiation-induced defects in kaolinite were estimated from a measurement of the maximum amplitude of the EPR spectra in the 3300-3700 Gauss range and expressed in arbitrary units. The error in the radiation-induced defect concentration was ± 10%, taking into account the mass, positioning in the cavity, and apparatus deviation.

Gamma spectrometry

Seven raw soil and sediment samples from the four profiles (see Table 1) were selected for measurement of activities of isotopes from the uranium and thorium decay chains to estimate the possible Rn loss or gain and the resulting correction of the dose rate [START_REF] Yokoyama | Direct non-destructive dating of marine sediments, manganese nodules and corals by high-resolution gamma-ray spectrometry[END_REF]. The analysis was performed by high-resolution low background gamma-ray spectrometry using a germanium detector at low temperature. The ( 222 Rn) was determined using the peaks of 14 Bi at 609 keV and 214 Pb at 352 keV [START_REF] Yokoyama | Direct non-destructive dating of marine sediments, manganese nodules and corals by high-resolution gamma-ray spectrometry[END_REF].

Paleodose determination

The artificially irradiated samples were heated at 250 °C for 2 hours to anneal the less stable defects according to the procedure of [START_REF] Allard | Radiation-induced paramagnetic defects in natural kaolinites : alpha dosimetry with ion beam irradiation[END_REF] and [START_REF] Balan | Formation and evolution of lateritic profiles in the middle Amazon Basin: Insights from radiation-induced defects in kaolinite[END_REF]. Then, depending on the sample, the experimental dosimetry data (i.e., concentration of defects versus dose) were fitted using either a single exponential function (e.g., [START_REF] Allard | Radiation-induced paramagnetic defects in natural kaolinites : alpha dosimetry with ion beam irradiation[END_REF] or the combination of an exponential and linear function [START_REF] Duval | Dose response curve of the ESR signal of the Aluminum center in quartz grains extracted from sediment[END_REF]:

[C] = [Cs](1-exp(-λ (D+P))) (1) [C] = [Cs](1-exp(-λ(D+P))) + LF (D+P) (2)
where [C] is the present concentration of RIDs, [Cs] is their saturation value, λ is an efficiency exponential factor, P is the paleodose, D is the artificial dose and LF is a linear factor.

Dating

In the absence of significant thermal resetting, the paleodose is then linearly related to the dose rate, and the kaolinite age is obtained as:

Age = Paleodose/Dose-rate (3)
The dose rate can be calculated using the U, Th and K contents measured by ICP-AES and ICP-MS techniques and tabulated elementary values provided by [START_REF] Aitken | Thermoluminescence dating[END_REF].

Results and discussion

U/Th geochemistry

The radiation-induced defects are produced by the radiation arising mainly from U and Th decay chains and, to a lesser extent, from the 40 K isotope. Consequently, geochemical data on these elements are required to constrain the calculation of the dose rate experienced by the clay minerals. The weight concentrations are as follows. For uranium, the concentration varies from approximately 0.5 to 4.7 ppm. The concentration of thorium ranges from 2 to 15.9 ppm. That of potassium is between 0.01 and 1.37% of K. These concentrations correspond to standard values for laterites or sediments derived from laterites (see, e.g., [START_REF] Chabaux | Tracing and dating recent chemical transfers in weathering profiles by traceelement geochemistry and 238 U-234 U-230 Th disequilibria: the example of the Kaya lateritic toposequence (Burkina-Faso)[END_REF][START_REF] Sousa | Mineralogical, micromorphological and geochemical evolution of the kaolin facies deposit from the Capim region (northern Brazil)[END_REF][START_REF] Da Costa | On the geology, mineralogy and geochemistry of the bauxite-bearing regolith in the lower Amazon Basin: Evidence of genetic relationships[END_REF][START_REF] Balan | Formation and evolution of lateritic profiles in the middle Amazon Basin: Insights from radiation-induced defects in kaolinite[END_REF]. The concentrations of U and Th show a linear dependence (Figure 3). This suggests that, except for a few data indicated in Figure 3 that are distant from the linear trend, uranium and thorium are associated with the same clay fraction and are possibly hosted by the same phases. As thorium is classically considered a geochemically invariant element, it is inferred that no preferential migration of U (i.e., loss or accumulation) occurred in the profile. The observed correlation thus implies that the most labile fraction of uranium was leached away soon after sediment deposition or in the material that predated the deposition. It is clearly seen for sediments and soils that kaolinite is by far the dominant secondary mineral. Illite is negligible except in the P4 profile and the P1-620 sample, where it is minor.

The potential consequences of such a composition with minor illite are discussed in the EPR results section. In addition, the samples from the P4 profile as well as the P2-240 soil sample contain significant amounts of quartz. Moreover, the long-range crystalline order of the kaolinites can be assessed on the XRD patterns through, e.g., the Hinckley ordering index (Hinckey, 1963). Thus, the (1-10) and ( 11 Thin sections are typical of unconsolidated sands with dominant quartz minerals in a clayey matrix (Figure 4 A,B). In addition, localized iron oxides are observed with surrounding diffuse haloes of irregular shape (Figure 4 A,B). This latter facies indicates postdeposition weathering of iron oxides. The clay matrix does not exhibit well-ordered kaolinite crystals at the scale of optical microscopy. This is in contrast to what is observed, e.g., in transformed sediments from the older Alter do Chao Formation [START_REF] Balan | Formation and evolution of lateritic profiles in the middle Amazon Basin: Insights from radiation-induced defects in kaolinite[END_REF][START_REF] Lucas | Genèse et fonctionnement des sols en milieu equatorial[END_REF] or deposits at the base of weathering profiles from the eastern Amazon [START_REF] Sousa | Mineralogical, micromorphological and geochemical evolution of the kaolin facies deposit from the Capim region (northern Brazil)[END_REF][START_REF] Da Costa | The contribution of lateritization processes to the formation of the kaolin deposits from eastern Amazon[END_REF]. The or dispersed, as reported in Table 1 for the matrix component. This proportion is used for the correction of the dose rate (see 4.4.2 section).

EPR spectra of soil and sediment samples

The full-range EPR spectra of the sediment and soil samples (Figure SI 2) exhibit the classical signals observed in natural kaolinite samples (see, e.g., [START_REF] Muller | Genetic Significance of Paramagnetic Centers in Kaolinites[END_REF]. The so-called Fe(I) and Fe(II) signals at low magnetic fields (g≈4.3) are typical of structural Fe 3+ .

They arise from two different structural site geometries related to variations in kaolinite stacking order. Accordingly, the relative amplitude of the Fe(I) signal to that of the Fe(II)

signal (Figure 5) can be used as an index of structural disorder (see, e.g., [START_REF] Balan | Structural Fe 3+ in natural kaolinites: new insights from electron paramagnetic resonance spectra fitting at X and Q-band frequencies[END_REF][START_REF] Balan | Inheritance versus neoformation of kaolinite during lateritic soil formation : a case study in the middle Amazon Basin[END_REF]. Most samples show quite similar spectra for structural Fe 3+ within each profile, indicating a medium degree of local crystalline disorder. Sample P3-340 and all those from the P4 profile are more disordered, as attested by a stronger contribution of the Fe(I) resonance (Figure 5). The P4 profile belongs to a watershed located on the right bank of the Rio Negro and, according to its mineralogy (constant presence of illite), is expected to correspond to different material sources deposited in a sub-basin. Moreover, it cannot be excluded that illite, observed in this profile, also partly interferes in the samples from the P4 profiles, as this clay mineral exhibits a dominant resonance located at the position of Fe(I) [START_REF] Morichon | Evidence of native radiationinduced paramagnetic defects in natural illites from unconformity-type uranium deposits[END_REF]. Proceeding in further detail, the fine observation of the shape of the structural Fe 3+ spectrum, i.e., the relative contributions of the Fe(I) and Fe(II) signals, allows the determination of four groups of sedimentary kaolinite populations according to their degree of disorder (Table 1), which is critical information for dosimetry (see [START_REF] Allard | Kaolinite as an in situ dosimeter for past radionuclide migration at the earth's surface[END_REF]. In fact, a relationship was shown between the dosimetry parameters, i.e., the behavior under irradiation, and the degree of local structural disorder. Consequently, it is assumed that kaolinite samples with the same degree of local disorder (as determined using the structural, paramagnetic Fe 3+ as a local probe) have similar dosimetry curves or efficiencies, albeit with different paleodoses, as this last parameter depends on age and radioactivity.

In addition, the strong signal responsible for the baseline is assigned to superparamagnetic iron oxides lato sensu, i.e., irrespective of their actual structure or composition [START_REF] Muller | Genetic Significance of Paramagnetic Centers in Kaolinites[END_REF].

In the g=2 region, at and from either side of the 3530 Gauss magnetic field value, several narrow signals are observed. An enlarged view of this region is shown in Figure 6, which exhibits the typical hyperfine structure of the vanadyl complex associated with kaolinite, with outermost parallel components and central perpendicular components [START_REF] Muller | Genetic Significance of Paramagnetic Centers in Kaolinites[END_REF], which can be identified with the reference VO 2+ -rich dickite (Dimex). The corresponding signal is present in most samples. Only two samples, P1-350 and P4-1000, have a negligible or no VO 2+ signal (Figure 6). In these cases, the observed doublet with principal components at g par = 2.049 and g perp = 2.002 is characteristic of RIDs in kaolinite, as seen by comparison to the GB1 reference kaolinite. For vanadyl-containing kaolinite, the central VO 2+ signal overlaps the spectrum of RIDs. The amplitude of the g perp = 2.002 signal of RIDs was thus estimated by subtraction of the overlapping vanadyl signal. For this purpose, the contribution of vanadyl was evaluated using the Dimex reference and the isolated g ≈ 1.881 resonance, which is assigned to VO 2+ only (Figure 6, Figure SI 3). As seen in Table 1, the proportion of RID signals in the g = 2 resonance for the selected samples was significant (> 25%) and often major. Using this procedure, 6 samples of soils and 10 samples of sediments could be selected for the present study. Their RID content corrected from the vanadyl contribution is reported in Table 1. They include two samples with 100% RID signals (P1-350 and P4-1000). The presence of minor illite may potentially interfere with the kaolinite RID signal in the P4 profile, as this clay mineral can contain RIDs very similar to the kaolinite ones [START_REF] Allard | Radiationinduced defects in clay minerals: A review[END_REF] that cannot be isolated in the X-band. Consequently, in this case, we assumed that the potential RIDs in illite behaved similarly to those in kaolinite in terms of dosimetry, so their contribution remained minor. Based on their location in the profiles, their degree of kaolinite crystalline disorder, their significant RID concentrations and their origin in both soils and sediments, seven samples were chosen for artificial irradiation. interference, corresponds to the first point of the dosimetry curve. It varies within 0.8 -5.9 (arbitrary units), i.e., over one order of magnitude. Two types of growth curves are observed, corresponding to exponential (Equation 1) or exponential plus linear (Equation 2) functions.

Although classical (see, e.g., [START_REF] Mathian | Unraveling weathering episodes in Tertiary regoliths by kaolinite dating (Western Ghats, India)[END_REF], the actual origin of these two different behaviors under irradiation has not yet been elucidated. For the samples that were not artificially irradiated, the reference dosimetry parameters of the same group, identified from structural order parameters, were used to calculate the paleodoses. Within the same structural group, references from soils were used for soil samples, and data for sediments were used for sediments. In the case of sediment group I, two sets of extrapolation parameters were available, corresponding to P1-350 and P1-760. The resulting paleodoses may vary over a factor of 2.6, as seen for P2-660, P2-900, and P3-210 (Table 1). Based on these data, the uncertainty of the paleodose resulting from extrapolation is at least 50% around the average value. The resulting paleodoses vary within 10.92 to 133.92 kGy, i.e., over one order of magnitude (Table 1). Within each profile, the lowest paleodoses are observed for the soil samples. The average error for the paleodose in the cases for which irradiation could be performed is considered to be 20-30% according to the estimates of [START_REF] Allard | Combined dating of goethites and kaolinites from ferruginous duricrusts. Deciphering the Late Neogene erosion history of Central Amazonia[END_REF] and [START_REF] Mathian | Unraveling weathering episodes in Tertiary regoliths by kaolinite dating (Western Ghats, India)[END_REF].

Assessment of dose rates

To determine the age of kaolinite samples, it is necessary to calculate the dose rate that prevails in each sample. The raw dose rate is calculated from the tabulated elementary dose rates for U, Th and K and the concentrations of these elements (see, e.g., [START_REF] Aitken | Thermoluminescence dating[END_REF] prior to several corrections detailed below.

The first correction addresses the opening of the geochemical system that may affect the dose rate. As the samples correspond to unconsolidated sediments with connected porosity, a degree of system opening was expected, which may dominantly arise from Rn loss or gain, as this element is an inert gas with little interaction with solids. Because radon loss disrupts the decay chains of natural U and Th, the dose rate for open systems can be significantly lower than that of closed systems. In contrast, if Rn accumulates, the dose rate may be higher than that expected from the measured U concentration in a closed system at secular equilibrium. The gain or loss of Rn in reference samples was estimated from the gamma spectrometry data, providing the values reported in Table 1. In the sample series, the extreme values are 35% (increasing dose rate) for Rn gain and -9% for Rn loss (decreasing dose rate). Interestingly, these significant Rn gains and losses are observed in the soil and sediment samples, respectively.

The second correction arises from the geometry of the system according to two factors derived from the presence of minerals such as quartz that do not host radioelements. On the one hand, quartz crystals are diluting agents for the effective concentration of radioelements, so the dose rate must be increased and normalized to the clayey matrix (kaolinite) content. In fact, quartz crystals are considered to contain no or negligible U, Th-bearing inclusions, according to observations with optical or scanning electron microscopy. The concentration of radioelements in the clay fraction is higher than that in the bulk quartz-containing sample. On the other hand, a part of the dose is deposited in quartz and does not affect the clay. To account for the factors that modify the dose rate, a simple model (SI 5) was used to assess the correction as a function of the range of radiation, size of quartz grains and concentration of clayey matrix (kaolinite). It concerns only alpha particles, the average range of which (20 µm in silicates) is much smaller than the diameter of quartz grains. The average size of the quartz grains was assessed on thin sections and, when thin sections were not available, by considering the same values for close samples in the profiles (SI 6). Correction concerning alpha particles in U and Th decay chains was solely considered because the dose rate linked to this radiation totals 90% of the total dose rate in an infinite closed system [START_REF] Aitken | Thermoluminescence dating[END_REF]. The concentration of the clay phase was estimated from the Al 2 O 3 concentration of the raw samples (see Table 1 and Figure SI 7 for sediments) by assuming that kaolinite was the dominant Al-bearing phase, which was verified for most samples by XRD (Figure SI 1). In fact, all samples from the P1, P2, P3 profiles contain only traces of illite. Nevertheless, the kaolinite content of some samples may be overestimated: P3-465 actually contains significant gibbsite content in addition to kaolinite, and the P4 samples also contain minor illite.

The third correction to the dose rate arises from the spatial distribution of uranium.

This element may occur either concentrated in host minerals or dispersed in the matrix. Ubearing phases are revealed by induced fission track mapping as concentrations with radial distributions ("urchin"-like) that induce a specific balance of alpha radiation dose (Figure 4C). The alpha particles have a mean energy of 5 MeV in the uranium decay chain, which corresponds to a 20 µm range in silicates as calculated from the SRIM code of radiationmatter interaction [START_REF] Ziegler | SRIM -The stopping and range of ions in matter[END_REF]. In contrast, the ranges of beta and gamma radiation are millimetric and deca-centimetric, respectively. Consequently, the alpha particles only concern a thin rim around the U-bearing minerals and do not interact with the bulk clay sample. Thus, for U-bearing minerals, the contribution of alpha particles is not considered in the dose rate calculation corresponding to the bulk samples analyzed by EPR, leading to a lower effective dose-rate value. The proportion of uranium concentrated in minerals or dispersed in the matrix, as determined from fission track analysis (FT), was used to correct the dose rate experienced by the kaolinite. Seven samples were selected for the FT analysis.

The resulting values of the U proportion in the matrix are 26.1 -57.9% (Table 1). The values for the samples not analyzed by fission tracks were determined in this range of values by considering the closest soil samples between them on one side and the sediments on the other side in the same profile. No model value of the proportion of U in the matrix was taken from another profile or from a soil to a sediment (Table 1). In the case of P1-530 and P1-620, two model values were available (from P1-350 and P1-760); thus, their average value was considered. P1-530, P2-530 and P2-900, which were distant from the U/Th chemical trend, have the highest U% in the matrix. In contrast, some samples with high U% in the matrix are not anomalous in the U/Th trend. The average water content is estimated to be 20% according to the study on laterite water content by [START_REF] Bruno | Soil moisture dynamics in an eastern Amazonian tropical forest[END_REF], which implies a 20% decrease in the dose rate (Hennig and Grun, 1983). In addition to uranium, the spatial distribution of thorium is critical for the calculation of dose rate, as its concentration is significantly higher (Table 1). However, these data cannot be easily obtained with the current equipment, owing to the trace content of thorium (approximately 4-20 ppm in our study). Consequently, two scenarios were considered herein: a homogeneous distribution in the matrix (named Th HOMO )

or a spatial distribution similar to that determined for uranium by induced FT (referred to as Th vsU ). The first scenario is supported by the well-known low solubility of thorium, which explains why this element is often used as a geochemical invariant in the weathering mass budget of laterites (see, e.g., [START_REF] Braun | Mobilization and redistribution of REEs and thorium in a syenitic lateritic profile: a mass balance study[END_REF][START_REF] Balan | Metamictization and chemical durability of detrital zircon[END_REF], whereas the second scenario is supported by the common association of U and Th to similar accessory minerals such as zircon or monazite. The resulting dose rates, i.e., after the different abovementioned corrections, are reported in Table 1. The error in the dose rate is estimated to be 10%, according to the analytical errors in the U, Th, and K concentrations.

Ages of soils and sediments

The calculated ages of the soils and sediments from the Içá Formation are reported in Table 1. They vary from 0.6 to 19.6 Ma, i.e., over one order of magnitude. The average age for the soils is 2.98 Ma (0.9 -5.0 range) for Th vsU and 2.07 Ma (0.6-3.5 range) for Th HOMO .

For the sediments, it is 9.37 Ma (4.2 -19.6 Ma range) for Th vsU and 6.56 Ma (2.3-15.1 Ma range) for Th HOMO . As expected, the ages from the Th vsU scenario are significantly older than those from the Th HOMO scenario. In both scenarios, it is verified that the soils are younger than the sediments, which is expected given that the former overlie the latter. In addition, there is no simple relation as a function of depth except for an increasing trend in the sediment followed by a decreasing trend as the supergene weathering begins to affect the sediment.

In this study, we consider an authigenic origin of kaolinite. The materials from our sequence do not correspond, in terms of crystal chemistry of structural iron, to detrital eroded soils such as those described by [START_REF] Balan | Formation and evolution of lateritic profiles in the middle Amazon Basin: Insights from radiation-induced defects in kaolinite[END_REF]. Other arguments support authigenic origin. In particular, the P1, P2 and P3 profiles exhibit younger material both in the topsoil and at depth. This nonmonotonous evolution as a function of depth suggests rejuvenation processes of kaolinite both at the surface (soil formation) and at the bottom of profiles. The weathering at depth may have occurred as a result of another front, in line with Nahon (2003), who proposed the existence of several fronts in a profile, and possibly arose from the contribution of the water table or laterally flowing solutions. This was accompanied by a preservation of the sedimentologic structures such as cross beds at depth, while the kaolinites experienced dissolution crystallization processes, such as in a saprolite horizon. The influence of the topsoil weathering conditions may have also impacted levels as deep as P1-350, which is described in the field as a sedimentary level and which is also younger than the underlying level (Table 1). Thus, such a level might contain a mixture of inherited and neoformed clays.

The occurrence of coexisting generations of kaolinite (i.e., populations with known ages of formation) in the same level was discussed for transition horizons of laterites from the region of Manaus by [START_REF] Balan | Formation and evolution of lateritic profiles in the middle Amazon Basin: Insights from radiation-induced defects in kaolinite[END_REF].

The EPR spectra of structural iron between the soil and sediment levels are very similar, suggesting similar conditions of formation, as if a common supergene geochemical process triggered the kaolinite evolution. In addition, in the sediment samples, there is a rough increase in age as a function of the clay content as estimated from the Al 2 O 3 concentration (Figure SI 7). This suggests that the system was more stable in clay-rich levels and more open and susceptible to dissolution-recrystallization in the sediments richer in sand (although dissolution of quartz in the most weathered levels may also have occurred). This would indicate that the environmental conditions, i.e., water drainage (infiltration or influence of a water table), were conducive to the recrystallization of kaolinite. This is an argument in favor of an authigenic origin of kaolinite, in line with the previous observations on the weathered Alter do Chao sediments in the Manaus region by [START_REF] Balan | Formation and evolution of lateritic profiles in the middle Amazon Basin: Insights from radiation-induced defects in kaolinite[END_REF], although very wellordered kaolinite occurred in this material. In addition, some early diagenesis of kaolin sediment may have occurred soon after deposition.

To proceed further in the discussion, data are presented as a paleodose/dose-rate diagram where the points are distributed according to isochrons (Figure 8). The two Th vsU and Th HOMO scenarios are considered and compared to the age range proposed by [START_REF] Campbell | The Pan-Amazonian Ucayali Peneplain, late Neogene sedimentation in Amazonia, and the birth of the modern Amazon River system[END_REF] for the deposition of the Içá Formation, according to a stratigraphic correlation with the Madre de Dios Formation from Perù. The Campbell age range occurs between 2.5 and 9.5

Ma; thus, this domain lies (in yellow) between these two corresponding isochrons at 2.5 and 9.5 Ma. The soil data are located at the bottom of the diagram, consistent with their lower ages. In the Th HOMO scenario, it is seen that all the data from sediments, whether from artificial irradiations (red) or extrapolation (green), are within the 9.5 -2.5 Ma range proposed by

Campbell for the deposition of the Içá Formation, even if the error bars indicate slightly older values for some ages (Figure 8 A). The Th HOMO scenario strongly supports the stratigraphic correlation by [START_REF] Campbell | The Pan-Amazonian Ucayali Peneplain, late Neogene sedimentation in Amazonia, and the birth of the modern Amazon River system[END_REF]. In addition, the ages of the Içá Formation are significantly younger than those of kaolinite samples from the Alter do Chao sediment at 22.2 -65.3 Ma [START_REF] Balan | Formation and evolution of lateritic profiles in the middle Amazon Basin: Insights from radiation-induced defects in kaolinite[END_REF], as seen in Table 2. They are close to the ages of the oxisols and intermediate horizons from the Manaus region (5.7-19.2 Ma, including the transition horizons; [START_REF] Balan | Formation and evolution of lateritic profiles in the middle Amazon Basin: Insights from radiation-induced defects in kaolinite[END_REF] and some samples from Sao Gabriel laterites (0.21-1.68 Ma for the Ferralsol and 1.03-5.98 Ma for the Acrisol; [START_REF] Mathian | Kaolinite dating from Acrisol and Ferralsol: a new key to understanding the landscape evolution in NW Amazonia (Brazil) Geoderma[END_REF]. This suggests that common paleoclimatic episodes are revealed in the secondary mineral record at the scale of the Amazon Basin. The range of ages for the Iça samples is also consistent with the kaolinite from duricrusts collected in the Barcelos or Sao Gabriel regions (Table 2 and [START_REF] Allard | Combined dating of goethites and kaolinites from ferruginous duricrusts. Deciphering the Late Neogene erosion history of Central Amazonia[END_REF]. In addition to the sediments, data from the Quaternary (Pleistocene) period corresponding to some soils are due to weathering processes that rejuvenated the kaolinites and deleted the record of deposition. These data are in line with previous estimates on Içà sediments by other authors, although these estimates were not supported by absolute dating [START_REF] Santos | Projeto Norte da Amazônia, Domínio Baixo Rio Negro; Geologia da Folha NA[END_REF][START_REF] Maia | Projeto carvão no Alto Amazonas[END_REF][START_REF] Lourenço | PROJETO RADAMBRASIL[END_REF][START_REF] Latrubesse | A Formação Solimões: uma formação do Mio-Plioceno da Amazônia sul-ocidental[END_REF][START_REF] Rossetti | New geological framework for Western Amazonia (Brazil) and implications for biogeography and evolution[END_REF].

In the second Th vsU scenario, the distribution of the data is mostly preserved, except for 4 samples of sediments that correspond to ages old enough to lie slightly above the upper limit of the range proposed by [START_REF] Campbell | The Pan-Amazonian Ucayali Peneplain, late Neogene sedimentation in Amazonia, and the birth of the modern Amazon River system[END_REF]. This does not necessarily contradict the stratigraphic correlation considering the large error associated with our age determination; thus, decisive arguments are still lacking for these 4 samples. In fact, the data presented in this study do not exclude that such samples may contain, at least partly, kaolinites with a detrital origin predating the deposition of the sediments.

Conclusions

The EPR dating of kaolinite from regional sediments assigned to the Içá Formation specifies the chronostratigraphy of the corresponding region of Amazonia. The data indicate ages in the upper Miocene-Pleistocene period, which encompasses the estimates provided so far in the literature by several authors. In addition, this supports the correlation with the sedimentary Madre de Dios Formation in Perù. To comprehend the scope of the presented chronological data, the key issues are the distribution of thorium at the microscopic scale and the determination of whether the origin of the kaolinite is authigenic (formation in situ), detrital (inheritance from older laterites), or a mixture of the two. From the crystal chemistry data, related scenarios are proposed that allow us to calculate the ages of formation for kaolinite. These data suggest that some sediments are relictual in the middle of the profiles, whereas the rejuvenation of kaolinite is evidenced both in the uppermost soils and at depth.

The proposed approach appears to be appropriate for ancient kaolinitic sediments where diagenesis undoubtedly took place or where the possible lifetime in preexisting soils prior to erosion and deposition in the sedimentary basin was significantly short compared to the lifetime of the clay in the sediments. Irrespective of the considered model, most data are consistent with the stratigraphic correlation of [START_REF] Campbell | The Pan-Amazonian Ucayali Peneplain, late Neogene sedimentation in Amazonia, and the birth of the modern Amazon River system[END_REF], except a few with higher ages in the second scenario that could possibly correspond at least partly to detrital kaolinite generations.

  238 U content was measured by a gamma ray of 234 Pa (its daughter) at 63.3 keV. The 232 Th was measured by the peaks of 228 Ra ( 228 Ac at 911.1 keV) and 228 Th ( 208 Tl at 583.2 keV representing 35% of disintegration of 212 Bi). To estimate the possible Rn loss or gain and the resulting correction of the dose rate, 226 Ra was measured by radiation at 186.1 keV, and radon

  4.2. Mineralogic and petrographic observations using optical and scanning electron microscopyThe mineralogy of the <5 µm samples is revealed by XRD powder patterns (FigureSI 1).

  presence of well-structured kaolinite booklets several tens of microns in size would be a clear indication of authigenic origin because such particles would certainly not have resisted erosion and transport processes before deposition.SEM observations show ubiquitous small (<1 µm) kaolinite phases (often present with traces of potassium), as shown for P1-760 and P4-1000 in Figure4 (D-F). Kaolinite is a phyllosilicate with a microscopic structure arranged as platelets, particularly visible in the case of well-ordered kaolinites that often display a booklet-like arrangement. Scarce booklets of several microns are also observed that are not tightly joined (Figure4, E) or have small thicknesses (Figure4, F). This suggests some degree of structural damage tentatively assigned to limited transport of particles. However, nothing conclusive can be inferred about the detrital or authigenic origin of the associated, dominant, fine particles of kaolinite.Mapping of uranium derived from induced fission track experiments is shown for one representative sample P4-1000 in Figure4C. There is a clear contribution from uraniumbearing or uranium-trapping minerals that could be, for instance, zircon grains ("urchin"-like track clusters with radial orientation (central part of Figure4 C) or iron oxides (composite group of tracks with multiple orientations (not shown)). The rest of the uranium is associated with the clayey matrix (isolated tracks, Figure4 C). Track counting in the selected areas allows the measurement of the proportion of these two fractions of uranium, either clustered

  RIDs as well as the dosimetry parameters derived from data fitting are reported in Tables SI 4 a,b. The concentrations of defects are plotted as a function of irradiation dose in Figure 7. The natural concentration of RIDs, after correction of the VO 2+

Figure 1 :

 1 Figure 1: Maps of the studied region. (A) Location of the study area (white rectangle)

Figure 2 :

 2 Figure 2: Studied profiles and location of the selected samples.

Figure 3 :

 3 Figure 3: Plot of the uranium and thorium concentrations in all raw samples (before

Figure 4 :

 4 Figure 4: Optical microscopy in natural light: thin sections of P2-530 (A) and P4-1000

Figure 5 :

 5 Figure 5: Total EPR spectra of kaolinite groups of local crystalline disorder determined from the signal of structural Fe 3+ (according to the relative amplitudes of the so-

Figure 6 :

 6 Figure 6: Normalized EPR spectra in the g = 2 region. Notice the hyperfine structure of vanadyl compared to VO 2+ -rich reference dickite from Mexico (Dimex) and the RID signal

Figure 7 :

 7 Figure 7: Dosimetry with He + ions. Experimental data are fitted, when appropriate, by

Figure 8 :

 8 Figure 8: Diagrams of paleodose versus dose rate for sediments (full squares) and soils

  Figure'2'

  Table SI 4a: concentrations of RIDs (arbitrary units) in artificial He + -irradiation experiments. Data in italics correspond to aberrant points. Table SI 4b: dosimetry parameters : [Cs] saturation (arbitrary units), λ exponential factor (kGy -1 ), LF linear factor, if required (kGy -1 )

	929	Table SI 6: Estimated radius of quartz grains with assumed spherical shape
	930
	931
		Sample	Material Thin		Estimated
					section		Quartz
							Radius
							(µm)
		Fluence (ions/cm 2 ) P1-150* FT 0 P1-300 3e+11 P1-350* FT 6e+11 P1-530 1e+12 P1-620* P1-760* FT		Dose Soil (kGy) 0 soil 70 sdt 140 sdt 234 sdt sdt	P1-150 X 1.31 3.79 X 5.22 6.98 X	P1-350 10 3.87 10 5.26 37 6.98 50 9.39 37 20	P1-620 2.12 7.52 9.02 11.6	P1-760 1.37 4.4 4.81 6.61	P2-240 0.99 3.95 5.90 7.11	P2-530 2.29 4.63 6.29 8.29	P4-50 1.52 3.80 4.61 5.05	P4-1000 5.90 8.30 8.70 11.94
		3e+12 6e+12 P2-20 1e+13 P2-150 P2-240*		702 1405 soil 2342 soil soil	14.32 25.82 40.72	16.58 25.68 10 10 10	25.71 34.9 41.16	17.63 23.02 35.94	17.61 30.58 44.18	17.41 22.44 38.89	8.04 10.00 12.92	17.60 25.80 39.70
		P2-530* FT		sdt	X			100
		P2-660		sdt				50
		P2-900		sdt				50
		P3-210		sdt				25
		P3-465 FT		sdt	X			25
		Sample P4-50* FT P4-1000* FT	soil sdt	X X	[Cs]	10 50	λ		LF
	932	P1-150			2.81		0.01835	0.0160407
	933	P1-350			7.93		0.0087	0.0136
		P1-620		41.04		0.0014
		P1-760		31.56		0.000952
		P2-240			2.91		0.0208818	0.0187
		P2-530		26.16		0.0013
		P4-50			4.471		0.0141608	0.0038
		P4-1000			6.96		0.0070	0.0128

Acknowledgments: This study was supported by the CAPES COFECUB and PICS/CNRS programs. Ibtissem Boukais (IMPMC) is acknowledged regarding the fission track counting. Madeleine Selo is thanked for discussion on the induced fission track methodology.

We now consider the radiation dose, D U , corr , deposited in a heterogeneous medium composed of spherical quartz grains of radius r embedded in a homogeneous kaolinite matrix. The wt. concentration of kaolinite and quartz are [kao] and [Qtz], respectively. For a medium where uranium only occurs in the clayey fraction and is absent in quartz grains, two effects have to be considered: an increase of the U concentration in the clay matrix, due to the excluding effect of quartz, and a decrease of the deposited dose in the matrix due to the absorption of radiation by the quartz grains. A balance of the energy deposited in the sample gives: M tot D U = D U,corr (M qtz, irr + M kao ) (Eq. 1) where M tot, M kao and M qtz,irr are the sample mass, the kaolinite mass and the irradiated quartz mass, respectively. Assuming that the size of the quartz grains is large with respect to the penetration depth d of alpha particles, the volume occupied by the irradiated quartz V qtz,irr is that of a spherical shell of thickness d: V qtz,irr = 4/3 π r 3 -4/3 π (r-d) 3 The fraction of irradiated quartz is thus: f =V qtz,irr / V qtz = 1 -(1-a) 3 with a=d/r, leading to f = a(a 2 -3a+3) Accordingly, Eq. 1 leads to: D U, corr = D U / (f [Qtz] + [kao]) Taking for instance C qtz =0.9, C kao =0.1, r=50 µm, d=20 µm one obtains: a= 0.4, f=0.784 and D U, corr = 1.24 x D U


Innovative approaches to turn agricultural waste into ecological and economic assets

• NoAW (2016-2020): a EU-financed project involving 32 international partners, coordinated by INRAE (France)

• NoAW develops a circular economy approach applicable to agricultural wastes on a territorial and seasonal basis

• NoAW investigates the potential of agro-waste and byproducts to be converted into a portfolio of ecoefficient products: bio-energy, bio-fertilizers, bio-packaging and bio-molecules  WP5: New business concepts for a cross-sector valorization of agro-waste and by-products

Valorizing agricultural waste and by-products

 Agricultural waste and by-products = plant or animal residues that are not (or not further) processed into food or feed (OECD 1997)  Estimated amount of agro-waste annually: 998 million tons (Obi et al. 2016)  Different valorisation opportunities in alternative sectors leading to new products and applications, with a lower or higher value, depending on volume (Rood et al. 2017)  Challenging because of heterogeneity of resources, changes in volumes and quality over time  Business model innovation (BMI) needed due to market liberalisation, increased competition and changing socio-economic conditions (Taran et al., 2015), thus as response to internal and external triggers and incentives (Foss & Saebi, 2017;Geissdoerfer et al., 2018).

 BMI consists of changing a business model by creating, diversifying, acquiring or transforming it (Pieroni et al., 2019).

 BMI can concern different business model elements or the BM itselfgoing beyond process, product, or organizational innovation, as entire reconfiguration of the business model, and as a source of disruption and changing the logic of entire industries (Massa & Tucci, 2014).

 BMI in the context of circular economy is a recent field of research (Bocken et al., 2019;Pieroni et al., 2019;Lopez et al., 2019) > new term 'Circular Business Models'

Research question and methodology

How do business models innovate in order to contribute to the transition to a circular bio-economy via agro-waste and by-product valorisation?

 8 cases from France, Germany, Italy and the Netherlands studied in the NOAW project

Results

 Two main ways how business models in the agricultural sector innovate in order to valorise waste and by-products.

1. Innovate the business model itself:

(i)
completely new start-ups (associations or limited liability companies), with a direct focus on agro-waste and by-product valorisation (ii) business reconfigurations and from rather classical farm or food processing activities to specialised companies (linear chains) or integrated business parks (circular)

2. Adapt single business model elements:

(i)

Figure :

 : Figure: Value pyramid for biomass valorisation

-

  Cases from project-partner countries -Represent different types of business models -Companies valorizing agro-waste and by-products Semi-structured interviews, literature (scientific, websites…) and on-site visits for each case.Data analysed according to the type of initiative, resources and transformation processes, value propositions, key partners, customers, strategic approaches and types of business model innovation. create cross-sector synergies among local actors for cereal by-product valorisation (intermediator)• Husks valorised for eco-insulation and decoration (former use: heating or animal litter)• Organisational, technological BMI• Originally distillery cooperative, evolvement to a specialized firm for valorisation of wine coproducts• Product diversification to a large portfolio going from low to high added value via new technologies• Technological innovation type

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  Business models in the agricultural domain are obliged to innovate themselves towards new configurations in order to close material loops, reach jointly a competitive advantage and switch to a circular economy Technological innovation types are dominant and often precede organisational and social innovations, but a combined approach is also often observed  Interesting cases of BMI exist, but real disruptive technological or organisational innovations are still rare and then, they do not always reach a marketable scale and/or are not economically viable  What would be needed in order to facilitate BMI towards a circular bio-economy?(policies, subsidies, changing consumer behaviour, different market conditions…?)

		Conclusion
		Striving for new or higher value-added products, applications or ingredients
	(ii)	Combine new value propositions (product, service and/or technology platforms)
	(iii) Create new partnerships and cooperation
	(iv) Reach new customers or distribution channels

Donner & De Vries, INRAE, 30/11/2020

http://noaw2020.eu/ The project has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement No 688338.

Thank you very much for your attention!

mechthild.donner@inrae.fr