Romain Sibille
email: romain.sibille@psi.ch

Nicolas Gauthier

Elsa Lhotel

Victor Porée

Vladimir Pomjakushin

Russell A Ewings

Toby G Perring

Jacques Ollivier

Andrew Wildes

Clemens Ritter

Thomas C Hansen

David A Keen

Gøran J Nilsen

Lukas Keller

Sylvain Petit
email: sylvain.petit@cea.fr

Tom Fennell

A quantum liquid of magnetic octupoles on the pyrochlore lattice

Spin liquids are highly correlated yet disordered states formed by the entanglement of magnetic dipoles 1 .

Theories typically define such states using gauge fields and deconfined quasiparticle excitations that emerge from a simple rule governing the local ground state of a frustrated magnet. For example, the '2-in-2-out' ice rule for dipole moments on a tetrahedron can lead to a quantum spin ice in rare-earth pyrochlores -a state described by a lattice gauge theory of quantum electrodynamics 2-4 . However, f-electron ions often carry multipole degrees of freedom of higher rank than dipoles, leading to intriguing behaviours and 'hidden' orders 5-6 . Here we show that the correlated ground state of a Ce 3+based pyrochlore, Ce2Sn2O7, is a quantum liquid of magnetic octupoles. Our neutron scattering results are consistent with the formation of a fluid-like state of matter, but the intensity distribution is weighted to larger scattering vectors, which indicates that the correlated degrees of freedom have a more complex magnetization density than that typical of magnetic dipoles in a spin liquid. The temperature evolution of the bulk properties in the correlated regime below 1 Kelvin is well reproduced using a model of dipoleoctupole doublets on a pyrochlore lattice 7-8 . The nature and strength of the octupole-octupole couplings, together with the existence of a continuum of excitations attributed to spinons, provides further evidence for a quantum ice of octupoles governed by a '2-plus-2-minus' rule. Our work identifies Ce2Sn2O7 as a unique example of a material where frustrated multipoles form a 'hidden' topological order, thus generalizing observations on quantum spin liquids to multipolar phases that can support novel types of emergent fields and excitations. The composite 'dipole-octupole' nature of the degrees of freedom and their evolution as a function of temperature or magnetic field provide new ways of controlling emergent phenomena in quantum materials.

In materials with strong electronic correlations, numerous phenomena and associated phase transitions are explained in terms of ordered structures where individual degrees of freedom can be described using the first term of a multipolar expansion (dipole moments). However, further terms are required to explain an increasing number of novel phenomena in condensed matter physics. Such multipole moments, where order is 'hidden' from usual probes, characterize the anisotropic distributions of electric and magnetic charges around given points of the crystal structure. Multipoles can arise at the atomic scale from spin-orbit coupling, leading to well-characterized examples of 'hidden' orders such as in Ce1-xLaxB6 or NpO2 (refs. 5,6). In the heavy-fermion material URu2Si2, multipoles are proposed to explain a mysterious electronic state appearing below a phase transition involving a large entropy change [START_REF] Kuramoto | Multipole Orders and Fluctuations in Strongly Correlated Electron Systems[END_REF][START_REF] Santini | Multipolar interactions in f-electron systems: The paradigm of actinide dioxides[END_REF][START_REF] Ikeda | Emergent rank-5 nematic order in URu2Si2[END_REF] . Multipoles can also emerge from atomic clusters, such as in the spin-liquid regime of Gd3Ga5O12 with effective magnetic multipoles formed from 10-spin loops [START_REF] Paddison | Hidden order in spin liquid Gd3Ga5O12[END_REF] . A number of studies have also pointed to the role of unconventional odd-parity multipoles to explain phase transitions that break both space inversion and time reversal. This was discussed for example in the context of the pseudogap region of high-transitiontemperature superconductors [START_REF] Lovesey | Ferro-type order of magneto-electric quadrupoles as an order-parameter for the pseudo-gap phase of a cuprate superconductor[END_REF][START_REF] Fechner | Quasistatic magnetoelectric multipoles as order parameter for pseudogap phase in cuprate superconductors[END_REF] and in related iridates [START_REF] Zhao | Evidence of an odd-parity hidden order in a spin-orbit coupled correlated iridate[END_REF] , as well as in metals with unconventional properties [START_REF] Watanabe | Magnetic hexadecapole order and magnetopiezoelectric metal state in Ba1-xKxMn2As2[END_REF][START_REF] Hayami | Electric Toroidal Quadrupoles in the Spin-Orbit-Coupled Metal Cd2Re2O7[END_REF] and in magnetoelectric insulators [START_REF] Spaldin | The toroidal moment in condensed-matter physics and its relation to the magnetoelectric effect[END_REF][START_REF] Di Matteo | Orbital currents, anapoles, and magnetic quadrupoles in CuO[END_REF] .

Although sometimes hosting exotic behaviours, materials with multipolar orders can still be explained in the framework of symmetry-breaking phase transitions. Understanding physics beyond this paradigm is a major challenge, to which a significant part is contributed by spin liquids forming topological orders [START_REF] Wen | Quantum orders and symmetric spin liquids[END_REF] . Such phases are defined by patterns of long-range quantum entanglements and fractionalized excitations -quasiparticles that cannot be constructed as combinations of the elementary constituents of the system. In 2-and 3-dimensional magnets, theoretical models of quantum spin liquids are now well-established and their applicability extends to a variety of frustrated spin systems [START_REF] Savary | Quantum spin liquids: a review[END_REF] . However, connecting these predictions with experimental results remains difficult [START_REF] Knolle | A Field Guide to Spin Liquids[END_REF] . Measurements of fractionalized excitations were reported in model materials of Heisenberg spins with S = 1/2 or 1, such as the kagome lattice of Cu 2+ ions in the 2-dimensional herbertsmithite mineral [START_REF] Han | Fractionalized excitations in the spin-liquid state of a kagome-lattice antiferromagnet[END_REF] or the 3dimensional pyrochlore lattice of Ni 2+ ions in NaCaNi2F7 (ref. 21). Alternatively, indications for quantum spin liquid physics exist in materials where the low-temperature degrees of freedom are Seff = 1/2 pseudo-spins of a spinorbital-entangled ground state doublet, such as in the 5d-electron H3LiIr2O6 (ref. 22) and 4f-electron YbMgGaO4 (ref. 23) materials. However, these materials can still be described on the basis of magnetic dipoles where the effect of spin-orbit coupling is limited to the creation of spin-space anisotropies.

In magnetic rare-earth pyrochlores, distinct types of spin-orbital-entangled doublets of Seff = 1/2 are allowed by the local trigonal D3d symmetry (ref. 24). Ions with odd numbers of 4f electrons have their ground-state degeneracy imposed by Kramers' theorem, in which case the pseudo-spins have components that transform either like magnetic dipoles only or like magnetic dipoles and magnetic octupoles (rank-3 multipoles) [START_REF] Rau | Frustrated Quantum Rare-Earth Pyrochlores[END_REF] . Alternatively, pseudospins based on 'non-Kramers' doublets owe their degeneracy to the site symmetry and support magnetic dipole and electric quadrupole components [START_REF] Rau | Frustrated Quantum Rare-Earth Pyrochlores[END_REF] . Interactions between pseudo-spins sometimes involve only one component, in which case all terms in the Hamiltonian commute and the resulting phases are classical 1 . A famed example is the spin-ice state [START_REF] Castelnovo | Spin Ice, Fractionalization, and Topological Order[END_REF] found in Ho2Ti2O7 and Dy2Ti2O7, where magnetic dipoles of moment value m ~ 10 µB correspond to the 𝑧 component 𝜏 # $ of each pseudo-spin -the direction along the local trigonal axis connecting the centre of the elementary tetrahedron with its vertex. Interactions in this case are dominated by classical dipole-dipole forces acting as ferromagnetic first-neighbour couplings (Edipolar ~ +2 K), as required to make the '2-in-2-out' ice constraint effective. The result is a manifold of degenerate ice-rule states understood as the vacuum of an emergent Coulomb gauge field. However, in the absence of significant interactions 𝒥 ± between pseudo-spin components 𝜏 # ± transverse to 𝜏 # $ (ref. 26), spin ices freeze and fall out of equilibrium at low temperature. Introducing zero-point fluctuations in order to stabilize a quantum spin ice requires a perturbative term [START_REF] Gingras | Quantum spin ice: a search for gapless quantum spin liquids in pyrochlore magnets[END_REF] , which, for instance, was proposed in non-Kramers Pr 3+ -based pyrochlores where 𝒥 ± corresponds to interactions between electric quadrupoles [START_REF] Onoda | Quantum Melting of Spin Ice: Emergent Cooperative Quadrupole and Chirality[END_REF] . Here we reveal experimental signatures of a state where the dominant term in the Hamiltonian couples magnetic octupoles (𝜏 # ' ) while weaker interactions between magnetic dipoles (𝜏 # $ ) play the role of the transverse exchange, resulting in an octupolar quantum spin liquid predicted by theory [START_REF] Huang | Quantum Spin Ices and Topological Phases from Dipolar-Octupolar Doublets on the Pyrochlore Lattice[END_REF][START_REF] Li | Symmetry enriched U(1) topological orders for dipole-octupole doublets on a pyrochlore lattice[END_REF] . This is realized in Ce2Sn2O7, where muon-spin relaxation measurements have ruled out the presence of magnetic order at least down to a temperature T of 0.02 K, while signatures of a correlated state were shown to appear in the bulk properties below T ~ 1 K -that is 50 times higher, therefore pointing to a mysterious quantum phase [START_REF] Sibille | Candidate Quantum Spin Liquid in the Ce 3+ Pyrochlore Stannate Ce2Sn2O7[END_REF] .

We first report inelastic neutron scattering measurements at a low temperature T of 6 K (Fig. 1a-c), probing the crystal-field states of Ce 3+ ions in our phase-pure sample of formula Ce2Sn2O7.00±0.01 (see Extended data).

Measurements with an incident energy Ei of 150 meV reveal two magnetic excitations that are easily identified at energy transfers E ~ 51 and 110 meV. These excitations are transitions from the ground to the excited Kramers doublets within the J = 5/2 multiplet of Ce 3+ , which itself results from the spin-orbital entanglement of the electron spin S = 1/2 and orbital angular momentum L = 3. Higher-multiplet transitions are also visible from the data (Fig. 1b-c). We have fitted the neutron data to a crystal-field Hamiltonian using the complete set of 14 intermediatecoupling basis states of the J = 5/2 and J = 7/2 multiplets (Fig. 1d), as required by the comparable strengths of the crystal-field and spin-orbit interactions in light rare-earths (see Extended data for full description of the fitting). The resulting crystal-field parameters allow to reproduce the high-temperature behaviour of the magnetic susceptibility χ to a high accuracy, as shown in Fig. 1e, where the effective magnetic dipole moment μeff µ (χ×T) 1/2 -a sharplydiscriminating quantity -is plotted as a function of temperature. At temperatures much below the first excited crystal-field level but above the correlated regime, that is between 1 and 10 K, the magnetic dipole moment is m ~ 1.2 µB. This value translates into classical dipole-dipole couplings of about 0.025 K (Edipolar µ m 2 ), which is small compared to the scale of the dominant interactions and confirms that the low-temperature correlated state originates from quantum-mechanical exchange interactions [START_REF] Sibille | Candidate Quantum Spin Liquid in the Ce 3+ Pyrochlore Stannate Ce2Sn2O7[END_REF] . The wavefunction of the ground-state Kramers doublet |±⟩ obtained from the neutron data is essentially any linear combination of the *𝑚 , -= ±3/22 states, which corresponds to the case where pseudo-spins form a composite object, carrying both a magnetic dipole and a magnetic octupole (ref. 8).

We now focus on the nature of the correlated ground state using energy-integrated neutron scattering data recorded at temperatures inside and outside this regime, which by difference gives access to the Fourier transform of the total magnetization density -a product of the correlation function and Fourier transform of the magnetization density of the degrees of freedom. Using cold neutrons, which restricts the access to low scattering vectors only, we fail to provide evidence for a diffuse signal in energy-integrated experiments that would indicate correlations of magnetic dipoles (see Extended data). Instead, a signal of diffuse neutron scattering appears at higher scattering vectors accessible using thermal neutrons (Fig. 2a-c). The intensity distribution is zero at low scattering vectors Q < 4 Å -1 but grows at higher scattering vectors, where a maximum is reached around Q ~ 8 Å -1 . This behaviour is precisely that expected from the Fourier transform of magnetic octupoles calculated from the type of groundstate wavefunction in Ce2Sn2O7 (Extended data). The octupolar scattering increases in amplitude upon cooling below 1 K, concomitantly with the drop in the effective magnetic moment from ~ 1.2 µB in the range between T = 1 and 10 K down to ~ 0.7 µB at ~ 0.1 K (Fig. 3a). The temperature dependence of both these quantities can be understood as the evolution of the mixing of the wavefunctions of the two states of the single-ion doublet under the effect of correlations. The interactions mix the otherwise degenerate *𝑚 , -= ±3/22 states, forming new split eigenstates that minimize the energy of the system due to different magnetic dipole and octupole moment sizes.

For dominant octupole-octupole couplings, the octupole moment strengthens at the expense of the dipole moment, as shown in Fig. 1e, where the magnetic charge density of the ground-state doublet wavefunction is represented for different values of the dipole moment 𝐽 $ .

In the following, we rationalize our observations of octupolar scattering on the basis of the Hamiltonian for rareearth pyrochlores with 'dipole-octupole' doublets ℋ 56 = ∑ 8𝒥 99 𝜏 # 9 𝜏 : 9 + 𝒥 '' 𝜏 # ' 𝜏 : ' + 𝒥 $$ 𝜏 # $ 𝜏 : $ + 𝒥 and 𝜏 # $ transform like magnetic dipoles while 𝜏 # ' behaves as an octupole moment [START_REF] Huang | Quantum Spin Ices and Topological Phases from Dipolar-Octupolar Doublets on the Pyrochlore Lattice[END_REF][START_REF] Li | Symmetry enriched U(1) topological orders for dipole-octupole doublets on a pyrochlore lattice[END_REF][START_REF] Rau | Frustrated Quantum Rare-Earth Pyrochlores[END_REF] . We use a simplified version of the generic Hamiltonian considering 𝒥 99 = 𝒥 9$ = 0, which still captures the essential physics of octupolar phases. Within this approximation and using mean-field calculations, two sets of 𝒥 '' and 𝒥 $$ parameters were found to reproduce the bulk magnetic properties at low temperature (see Fig. 3a-b, and the details of the calculations described in the Extended data). The drop of the effective magnetic moment below 1 K is well reproduced using a dominant octupole-octupole interaction of either 𝒥 '' = + 0.48 ± 0.06 K or 𝒥 '' = -0.16 ± 0.02 K, and a small but finite dipole-dipole coupling 𝒥 $$ = +0.03 ± 0.01 K. Positive and negative 𝒥 '' values correspond to phases where the magnetic charge density of the octupoles on a tetrahedron is constrained by '2-plus-2-minus' (see Fig. 2d) and 'all-plus-all-minus' rules, respectively, where 'plus' and 'minus' designate the two possible local mean-values of the octupolar operator associated with 𝜏 # ' . A dominant and negative 𝒥 '' implies that the octupoles are not frustrated and form a 'hidden' ordered ground state, which can be excluded based on the absence of signatures of a phase transition to a long-range ordered state in both our heatcapacity and thermal-neutron scattering measurements. Meanwhile, the case governed by 𝒥 '' > 0 is frustrated and leads to an extensively degenerate manifold of octupole ice configurations (Fig. 2d), for which our Monte Carlo simulations predict diffuse neutron scattering at high scattering vectors shown in Fig. 2e and clearly distinguishable from that expected for a manifold of dipole ice configurations in Ce2Sn2O7 (Fig. 2f,g). The calculated octupolar diffuse scattering has the high degree of structure in reciprocal space typical of ice phases, and its powder averaging reproduces the experimental data as shown in Fig. 2c. The octupole ice scattering is about several hundred times weaker than the value expected for spin-ice scattering, even with the small dipole-moment of Ce2Sn2O7, which itself is much weaker than that of classical spin ices like Ho2Ti2O7.

The finite value of 𝒥 $$ obtained from the fit of the bulk magnetic properties (Fig. 3a-b) implies 𝒥 ± /𝒥 '' = -𝒥 $$ /4𝒥 '' ≈ -0.015, where 𝒥 '' = 0.48 K and 𝒥 ± follows the convention of the nearest-neighbour pseudo-spin 1/2 quantum spin ice model [START_REF] Curnoe | Structural distortion and the spin liquid state in Tb2Ti2O7[END_REF][START_REF] Lee | Generic quantum spin ice[END_REF] after appropriate permutation of the pseudo-spin components [START_REF] Huang | Quantum Spin Ices and Topological Phases from Dipolar-Octupolar Doublets on the Pyrochlore Lattice[END_REF][START_REF] Li | Symmetry enriched U(1) topological orders for dipole-octupole doublets on a pyrochlore lattice[END_REF] . The octupolar quantum spin ice is predicted to be stable in the range 0 < 𝒥 ± /𝒥 '' < 0. 19 (ref. 8), and it is also established that the U(1) quantum spin liquid is robust against perturbations and particularly stable in the regime where transverse exchange is frustrated ( 𝒥 ± < 0 ) (ref. 30-34). Therefore, it is natural to conjecture that 𝒥 ± /𝒥 '' ≈ -0.015 also falls in the octupolar quantum spin ice regime where, under applied magnetic field, theory predicts an Anderson-Higgs transition towards an ordered phase of dipole moments [START_REF] Li | Symmetry enriched U(1) topological orders for dipole-octupole doublets on a pyrochlore lattice[END_REF] . The critical field of this transition is of the order of 1.5 to 3 ℎ/𝒥 '' , depending on the direction of the applied magnetic field ℎ, which translates into values of 0.5 to 1 Tesla for 𝒥 '' = +0.48 K. This is in good agreement with the appearance of magnetic Bragg peaks at similar field values in the elastic scattering of cold neutrons at 0.05 K (see Extended data). The same set of 𝒥 $$ and 𝒥 '' parameters also reproduces the evolution of the heat capacity at low temperature under applied magnetic field (Fig. 3c).

We expect the emergent excitations in Ce2Sn2O7 to be measurable using neutron spectroscopy, because 𝒥 $$ allows neutron-active transitions between the two states of the doublet split by 𝒥 '' . Low-energy neutron spectroscopy data indeed reveal the presence of low-energy excitations that are dipolar in nature (Fig. 4). In addition, the spectra measured in the correlated regime of Ce2Sn2O7 do not display a resolution-limited excitation centred on a unique energy transfer -as would be expected for the 'hidden' ordered phase set by 𝒥 '' < 0, but instead have the continuous character of fractionalized excitations in a quantum spin liquid (Fig. 4c,f). We attribute the continuum in Ce2Sn2O7 to the gapped spinons of the U(1) quantum spin liquid, which are foreseen in inelastic neutron scattering of octupolar quantum spin ices [START_REF] Li | Symmetry enriched U(1) topological orders for dipole-octupole doublets on a pyrochlore lattice[END_REF] , including when 𝒥 ± is frustrated 34 . The continuum extends up to at least 0.3 meV (Fig. 4e); that is approximately one order of magnitude larger than the dominant exchange interaction 𝒥 '' ≈ 0.05 meV around which the spectrum is peaked, and both of these characteristics are consistent with theoretical predictions [START_REF] Gingras | Quantum spin ice: a search for gapless quantum spin liquids in pyrochlore magnets[END_REF][35][36][37] . Moreover, the low-energy edge of the spectra shown in Fig. 4b,e is reminiscent of the threshold proposed for the effect of the emergent photon -the gapless excitation in the lattice gauge theory of quantum spin ice [START_REF] Hermele | Pyrochlore photons: The U(1) spin liquid in a S = ½ threedimensional frustrated magnet[END_REF][START_REF] Benton | Seeing the light: Experimental signatures of emergent electromagnetism in a quantum spin ice[END_REF][START_REF] Gingras | Quantum spin ice: a search for gapless quantum spin liquids in pyrochlore magnets[END_REF] -on the production of spinons, which leads to an abrupt onset in the density of states 37 . We note that the gapless photon itself is not expected to contribute to the inelastic neutron scattering of an octupolar quantum spin ice 8 , at least not in the form of dipolar magnetic neutron scattering, and that the estimated photon bandwidth is of the order of the ring exchange 𝑔 ≡ 12𝒥 ± R /𝒥 '' S ≈ 10 TU meV, which is much smaller than the energy scale of the inelastic scattering in Fig. 4.

The octupolar quantum spin ice scenario might also explain recent observations of quantum spin liquid dynamics in Ce2Zr2O7 (ref. 38-39). In particular, the continuum of dipolar neutron scattering observed in ref. 39 indeed shows similar finite-energy centres and widths as in Fig. 4, and therefore can be used together with other measured properties that are similar in both materials to conclude that octupolar quantum spin ice is common among Ce 3+ pyrochlores. In their work 39 , Gao et al. argue that Ce2Zr2O7 should be in the π-flux phase of quantum spin ice 34 , which is consistent with our estimates of exchange parameters (𝒥 ± < 0), while our work further shows that the spin ice manifold is constructed from octupoles. In contrast, the interpretation of Gaudet et al. 38 that the inelastic neutron scattering in Ce2Zr2O7 should be compared with the equal-time structure factor of a quantum spin ice, where the calculation 3 includes photon scattering but no spinons, appears inconsistent with our data and interpretation. However, the comparison of the two materials should be contrasted by the fact that the oxygen stoichiometry in Ce2Sn2O7 is well controlled and precisely measured (see Extended data), so that the amount of non-magnetic Ce 4+ is known to be less than 1%, while the lattice constant of the studied samples of Ce2Zr2O7 suggests about 10% of Ce 4+ (ref. 38). Such a level of site dilution is likely to have a significant effect on the correlations, even though the local moment of the ~ 90% of Ce 3+ is protected against disorder due to their Kramers' nature.

The discovery of the octupole ice in Ce2Sn2O7 is remarkable for several reasons: it is an example of frustrated multipoles, showing convincing consistency with the expectations of a well-established 3-dimensional model -the U(1) quantum spin liquid; it is one of very few materials to enter phases primarily driven by higher multipolar interactions [START_REF] Kuramoto | Multipole Orders and Fluctuations in Strongly Correlated Electron Systems[END_REF][START_REF] Santini | Multipolar interactions in f-electron systems: The paradigm of actinide dioxides[END_REF] , and certainly a unique example of a quantum liquid in this context. Finally, degrees of freedom in the octupole ice are quantum objects whose dual 'dipole-octupole' nature can be controlled using magnetic fields [START_REF] Li | Symmetry enriched U(1) topological orders for dipole-octupole doublets on a pyrochlore lattice[END_REF] or -as our results demonstrate -as a function of temperature, which gives interesting perspectives in the field of quantum many-body systems and future related technologies.

Figure 1 |∓ 3 / 22 .Figure 2 |

 13222 Figure 1 | Dipole-octupole degrees of freedom. Energy spectra measured at 6 K (a-c) and recorded using incident neutrons of different energies as specified on the top right-hand corner of each panel. The solid lines are fits of the experimental data (black squares) using Gaussian peaks (peaks within each spectrum are constrained to the same width), and the resulting energy positions are shown in panel d. The energies and intensities of the magnetic excitations were used to adjust the six parameters of a crystal field Hamiltonian, which gives the ground-state doublet wavefunction |±⟩ = 0.87* 𝐹 X/S S

Figure 4 |

 4 Figure 4 | Magnetic excitations. Left panels show low-energy inelastic neutron scattering data measured at 0.6 K (red) and 5 K (blue) using incident energies Ei of 0.82 meV (a, l = 10 Å) and 1.28 meV (d, l = 8 Å), which give energy resolutions of 0.011 meV and 0.020 meV at the elastic line, respectively. These spectra as a function of energy transfer E are integrated over the entire range of accessible scattering vectors Q shown on the (E,Q) maps (see right panels c and f for l = 10 Å and l = 8 Å, respectively). Assuming that the difference scattering 𝑆(𝐸) between 0.6 K and 5 K is entirely magnetic, we show in the middle panels (b and e for l = 10 Å and l = 8 Å, respectively) the imaginary part of the dynamic spin susceptibility (blue points with error bars corresponding to ±1 standard error) calculated as𝜒 __ (𝐸) = 𝑆(𝐸) × [1 -exp(-𝐸/𝑘 f 𝑇)],where 𝐸 is the neutron energy transfer and 𝑘 f is the Boltzmann's constant. We model the magnetic scattering using 𝜒 __ (𝐸) = G𝐸/[(𝐸 -D) S + G S ] (red line) -a Lorentzian peak shape where G and D characterise the damping and energy centre, respectively, which we use as phenomenological parameters to compare with results on Ce2Zr2O7 (ref.39). The width and energy center determined for l = 10 Å are G = 0.025±0.003 meV and D = 0.039±0.003 meV, respectively (G = 0.024±0.001 meV and D = 0.045±0.002 meV for l = 8 Å). Panels c and f show difference (E,Q) maps (0.6 -5 K) summarizing the wavevector dependence of the spin excitations as a function of energy. These plots give strong support to the existence of a gapped continuum of fractionalized spin excitations, which we attribute to the spinon excitations of the octupolar quantum spin ice[START_REF] Li | Symmetry enriched U(1) topological orders for dipole-octupole doublets on a pyrochlore lattice[END_REF]34 (see main text). The phenomenological form employed to fit the spectra in panels b and e happens to capture the features expected from theory for the spinon excitations in a quantum spin ice (onset, peak, and extent)4,35-37 .

Acknowledgements

This work is based on experiments performed at the Swiss spallation neutron source SINQ, Paul Scherrer Institute, Villigen, Switzerland. Experiments at the ISIS Neutron and Muon Source were supported by a beamtime allocation RB1510524 from the Science and Technology Facilities Council. Additional neutron scattering experiments were also carried out at the Institut Laue Langevin, ILL, Grenoble, France. We thank M. Kenzelmann, O. Zaharko, Y.-P. Huang, M. Müller and C. Mudry for useful discussions. We thank C. Paulsen for the use of his magnetometers; P. Lachkar for help with the PPMS; B. Fåk for assisting on IN4c, E. Pomjakushina and D. Gawryluk for providing help and access to the solid-state chemistry laboratory; and M. Zolliker and M. Bartkowiak for dedicated work on running the dilution refrigerators at SINQ. R.S. thanks N. Shannon for fruitful exchanges and great hospitality at OIST; as well as H. Yan for enlightening conversations. We acknowledge funding from the Swiss National Science Foundation (Grant No. 200021_179150 and Fellowship No. P2EZP2 178542).

as a function of temperature T and the magnetization M as a function of magnetic field H, respectively (ref. 28). The lines are the best fits using the Hamiltonian for rare-earth pyrochlores with 'dipole-octupole' doublets ℋ 56 = ∑ 8𝒥 99 𝜏 # 9 𝜏 : 9 + 𝒥 '' 𝜏 # ' 𝜏 : ' + 𝒥 $$ 𝜏 # $ 𝜏 : $ + 𝒥 9$ (𝜏 # 9 𝜏 : $ + 𝜏 # $ 𝜏 : [START_REF] Ikeda | Emergent rank-5 nematic order in URu2Si2[END_REF] )> ?#:@

, where the components 𝜏 # [START_REF] Ikeda | Emergent rank-5 nematic order in URu2Si2[END_REF] and 𝜏 # $ of the pseudo-spin operator 𝜏 ⃗ # = (𝜏 # 9 , 𝜏 # ' , 𝜏 # $ ) transform like magnetic dipoles, while 𝜏 # ' behaves as an octupole moment (refs. 7-8). We consider 𝒥 99 = 𝒥 9$ = 0 and we show here the fits for the hypothesis 𝒥 '' > 0, which gives the octupole-octupole interaction 𝒥 '' = +0.48 ± 0.06 K and the dipole-dipole interaction 𝒥 $$ = +0.03 ± 0.01 K. The discrepancy between the experimental effective moment and the fitted curve is due to the mean-field nature of the model, which is sufficient to evaluate the main ingredients of the Hamiltonian but cannot account exactly for all details in the quantum regime, and the logarithmic temperature scale of panel a makes this particularly apparent. The same set of parameters also reproduces the field dependence of the magnetic contribution to the heat capacity, shown in panel c for field intervals of 1 T (points with error bars corresponding to ±1 standard error), as obtained from measurements of the heat capacity of Ce2Sn2O7 and of the non-magnetic analogue La2Sn2O7. The temperature dependence of the integrated octupolar scattering is presented in panel a (black points with error bars corresponding to ±1 standard error), showing the increase of octupolar scattering upon cooling in the correlated regime and at the expense of the dipole moment represented by the effective magnetic moment (the grey curve is a guideline). The dominant octupole-octupole interaction 𝒥 '' and the small finite value of the dipole-dipole coupling 𝒥 $$ indicate that Ce2Sn2O7 is in the octupolar quantum spin ice phase ( 𝒥 ± /𝒥 '' = -𝒥 $$ /4𝒥 '' ≈ -0.015 ). In this regime, we anticipate the excitation spectrum to have the continuous character expected for the fractionalized excitations of a quantum spin liquid, which we show is the case in Figure 4.

Competing financial interests

The authors declare no competing financial interests.

Methods

Sample preparation

A 28-grams polycrystalline sample of Ce2Sn2O7 was prepared by the solid-state reaction described in Ref. 31.

CeO2 was added to appropriate amounts of SnO2 and Sn (the Sn 4+ /Sn 0 ratio is imposed in order to reduce all the Ce 4+ cations to Ce 3+ ). The resulting mixture was carefully mixed in a rotary blender for several hours under air, in order to prevent agglomeration of metallic tin. The mixture was then placed into an alumina crucible for several heat treatments of 24-hours each until complete reaction. The first heat treatment was at 900 Celsius and the following ones at 1000 Celsius, all under flowing argon after long purging of the tube furnace, and using slow heating and cooling ramps (1 Celsius per minute).

As a non-magnetic reference material, La2Sn2O7 was synthesised from La2O3 calcinated at 800 Celsius for several hours and mixed with SnO2 in a rotary blender. The phase-pure lanthanum stannate was obtained by heating under air at 1200 Celsius for 72 hours, with intermediate regrinding each 24 hours.

Our sample of Ce2Sn2O7 was characterized by high-resolution neutron powder diffraction, pair distribution function, and thermogravimetric measurements, all indicating the presence of a single phase of formula Ce2Sn2O7.00±0.01 in our sample (see Extended data), thus forming a perfect pyrochlore lattice of Ce 3+ ions.

Bulk properties measurements

Magnetization data were measured in the temperature range from 1.8 to 300 K in an applied magnetic field of 0.01 Tesla using a Quantum Design MPMS-XL SQUID magnetometer. Additional magnetization, and ac-susceptibility (see Extended data), measurements were made as a function of temperature and field, from T = 0.07 to 4.2 K and from µ0H = 0 to 8 T, using SQUID magnetometers equipped with a miniature dilution refrigerator developed at the Institut Néel, CNRS in Grenoble. The heat capacity of pelletized samples of both Ce2Sn2O7 and La2Sn2O7 was measured down to 0.3 K using a Quantum Design PPMS.

Neutron scattering experiments

The inelastic high-energy neutron scattering experiment was performed on the MAPS spectrometer 32 at the ISIS Neutron Facility in Didcot, UK. Data were evaluated using HORACE software suite 33 . Each of the Ce2Sn2O7 and La2Sn2O7 samples were mounted inside aluminium foil pouches, which were then mounted in annular geometry inside aluminium cans. The crystal field splitting of Ce 3+ was evaluated by comparing Ce2Sn2O7 and La2Sn2O7 data, which allows to distinguish among contributions from crystal field and phonon excitations. The spectra of magnetic neutron scattering intensity as a function of energy transfer presented in Fig. 1a-c were obtained from low-angle data from Ce2Sn2O7 with high-angle data from Ce2Sn2O7 subtracted, using a scale factor determined from La2Sn2O7 data (Ref. 34). Unlabelled signals in the spectra of Fig. 1a-c are attributed to residual phonon scattering from Ce2Sn2O7 or hydrogen-containing contaminants formed through exposure to air. Note that the range of scattering vectors Q is not constant as a function of energy transfer in the spectra of Fig. 1a-c, thus peak intensities have to be extrapolated to Q = 0 by correction for the magnetic form factor. The SPECTRE program 35 was used to fit the neutron data to the crystal-field Hamiltonian.

The energy-integrated thermal-neutron scattering experiment was performed on the HRPT diffractometer at SINQ, PSI in Villigen, Switzerland 36 . Measurements were performed with the sample enclosed in a copper can and cooled down using a dilution refrigerator. Each pattern was measured during 6 to 12 hours, and the differences were made by subtracting data recorded at 5 K with the exact same statistics, resulting in the experimental data shown in Fig. 2a-c. A similar experiment was repeated on the D20 diffractometer at the Institut Laue Langevin in Grenoble,

France 37 , resulting in the second set of data points shown in Fig. 2c.

The inelastic low-energy neutron scattering experiment was performed on the IN5 spectrometer at Institut Laue Langevin in Grenoble, France 38 . Measurements were performed with the sample enclosed in a copper can and cooled down using a dilution refrigerator.

Calculations

For the visualisation of the magnetic degrees of freedom (Fig. 1e and Fig. 2d,f), we represent the magnetization by its corresponding magnetic charge distribution defined as 𝜌 jklmno#p (𝒓) = -∇ • 𝑚(𝒓). This charge distribution is calculated using the spherical Racah tensor operators on the wavefunction of the ground state 39 , projected on the ground multiplet 2 F5/2.

Fits of the bulk magnetic properties are based on calculations carried out on the basis of a mean-field treatment of a Hamiltonian, considering the dipolar exchange as well as an octupolar coupling between the crystal-electric field ground doublet states of the Ce 3+ ion. This Hamiltonian is written in terms of a pseudospin 1/2 spanning these states.

The elastic neutron cross sections of the octupole ice (Fig. 2e) and dipole ice (Fig. 2g) for Ce2Sn2O7 were calculated numerically using Monte Carlo simulations performed assuming 100 random realisations of the corresponding ice lattices (see Extended data). Each random lattice contained 5488 sites.

Data availability

The data that support the plots within this paper and other findings of this study are available from the corresponding authors upon reasonable request (R.S. for all of the experimental data, and S.P. for the mean-field fits of the bulk properties and Monte Carlo simulations). The datasets for the inelastic neutron scattering experiment on MAPS and MERLIN are available from the ISIS Neutron and Muon Source Data Catalogue [START_REF] Sibille Romain | Crystal electric field excitations of pyrochlore quantum antiferromagnet Ce2Sn2O7[END_REF][START_REF] Sibille Romain | Hidden correlations in Ce2Sn2O7, STFC ISIS Neutron and Muon Source[END_REF] .

The datasets for the polarized neutron scattering experiment on D7 (see extended data), the thermal-neutron inelastic measurements on IN4 (see extended data) and the diffraction experiment on D20 are available from the Institute Laue-Langevin data portal [START_REF] Sibille Romain | Investigation of the exotic low temperature groundstate of the Seff = 1/2 pyrochlore antiferromagnet Ce2Sn2O7[END_REF][START_REF] Sibille Romain | Investigation of the exotic low temperature groundstate of the Seff = 1/2 pyrochlore antiferromagnet Ce2Sn2O7 -continuation[END_REF][START_REF] Sibille Romain | Crystal electronic field excitations of pyrochlore antiferromagnet Ce2Sn2O7[END_REF][START_REF] Sibille Romain | Hidden Correlations in a Quantum Liquid of Magnetic Octupoles[END_REF] .


Jean-François F Berger
email: jean-francois.berger@univ-lyon2.fr

Raphaelle Guilbert-Berger

Marrast Anaïs

Olivia Munoz

Guy Hervé

A Barra

J A Lopez Saez

S Pérez-Díaz

Marjan Mashkour

K Debue

First contribution of the excavation and chronostratigraphic study of the Ruways 1 Neolithic shell midden

à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

| INTRODUCTION

The French Agence nationale de la recherche (ANR) NeoArabia research project is an international multidisciplinary and multiscalar project that questions whether cli matic and environmental changes could be an explanation for Neolithic cultural developments (c. 6500-2800 yr BC), and whether the populations of eastern Arabia developed specific modes of adaptation to increase their resilience to mid-Holocene climatic variability. In this perspective, a contextual and interdisciplinary work is being conducted in the search to construct a viable Neolithic coastal fisher-gatherer-pastoral model. This work is based on the excavation of fine sedimentary units and a broad interdisciplinary practice combining archaeosciences (geoarchaeology, archaeozoolmaterial culture. Nevertheless, little is known of the characteristics of the coastal sites, the spatial pattern of mobility of the populations, and the activities they practised. Indeed, in the world of Arabian archaeology, few excavations have been planned from the perspective of environmental archaeology and site formation processes, with the main effort most often focusing on the study of material culture and its diffusion, especially economic and ritual aspects (tombs).

The Ruways-1 (RWY-1) shell middens excavation stimulated several themes of complementary analyses on a vast we will present the spectrum of these ongoing studies in this paper. The RWY-1 site, located between the Oman Sea and a vast paleo-lagoon supplied by several wadis from the Jabal Safran, was occupied over nearly three millennia (from the end of the seventh to the fourth millennium yr BC). It provides an opportunity to better understand the development of the Arabian Neolithic through its long sequence of occupation, its sedimentary strength (2-3-m depth), and the presence of a very old Neolithic level at the base of the site (6300-6100 yr BC), whose status and cultural characterisation are still under discussion in the absence of lithic fossil-directors. The combination of stratigraphic excavation and a large geoarchaeological study of the entire site allows us to understand the site formation process and the spatial distribution of the occupations according to cultural periods (helped by the presence of many artificial stratigraphic sec tions created by the exploitation of a quarry).

We here summarise the different tasks in progress on the current RWY-1 excavation and attempt to draw up their main contributions to the practice of multidisciplinary and integrated environmental archaeology. We discuss the impact of the site formation processes for the analysis of archaeological archives, and their contribution to the elaboration of a socioenvironmental discourse on the coastal Neolithic resiliency of Eastern Arabia.

| NEOLITHIC ARABIAN

COASTAL ARCHAEOLOGY CONTEXT AND STATE OF THE ART

Along the Oman coast, the concept of a "Neolithic package" is questionable, pottery is absent and evidence for sedentism is poor (Crassard & Dreschler, 2013); only the presence of domesticated animals in archaeozoological assemblages, the lithic and beads technics and network developments and a certain vision of the socio-environmental space permits the labelling of these groups in Arabia as Neolithic. Coastal environments and marine resources were an important factor in Neolithic development, notably because they presented an apparent resilience to climatic variations. The explanation of cultural changes under climato-environmental constraints has been the subject of numerous academic debates, particularly since the advent of the processual approach [START_REF] Binford | New perspectives in archeology[END_REF][START_REF] Cleuziou | Ra's al-Jinz and the prehistoric coastal cultures of the Ja'alan[END_REF][START_REF] Renfrew | Archaeology: The key concepts[END_REF] and the recent theorisation of a deterministic explanation of cultural changes [START_REF] Clare | Warfare in Late Neolithic/Early Chalcolithic Pisidia, southwestern Turkey: Climate induced social unrest in the late 7th millennium cal BC[END_REF][START_REF] Cullen | Climate change and the collapse of the Akkadian empire: Evidence from the deep sea[END_REF][START_REF] Weiss | The genesis and collapse of third millennium north Mesopotamian civilization[END_REF], which have recently been modulated by hypotheses favouring more societal adaptation and bifurcation processes [START_REF] Berger | The 8200 cal BP abrupt environmental change and the Neolithic transition: A Mediterranean perspective[END_REF]. Several archaeology-related studies have since been dedicated to the production of specific data on societal vulnerability and adaptation during the early-mid-Holocene [START_REF] Berger | Interactions between climate change and human activities during the early to mid-Holocene in the eastern Mediterranean basins[END_REF][START_REF] Borrell | Synchronous environmental and cultural change in the emergence of agricultural economies 10,000 years ago in the Levant[END_REF][START_REF] Flohr | Evidence of resilience to past climate change in Southwest Asia: Early farming communities and the 9.2 and 8.2 ka events[END_REF]. However, few of them have been concerned with the Arabian confirm the richness of these archaeological archives for documenting the socio-environmental dynamics, but also the richness of its complex sedimentary structure and the importance of conducting fine and multidisciplinary excavations to answer questions about the rhythms and functions of occupations and the causalities of socioenvironmental changes.

K E Y W O R D S

Coastal Neolithic, geoarcheology, shell midden, site catchment, site formation processes, Sultanate of Oman Peninsula and the context of coastal areas [START_REF] Parker | Geomorphological and palaeoenvironmental investigations in the southeastern Arabian Gulf region and the implication for the archaeology of the region[END_REF][START_REF] Preston | From nomadic herder-hunters to sedentary farmers: The relationship between climate change and ancient subsistence strategies in south-eastern Arabia[END_REF]. As environmental variability has to be considered an integral part of the historical process [START_REF] Butzer | Collapse, environment, and society[END_REF][START_REF] Roy Ladurie | The mind and method of the historian[END_REF], the confrontation between human and climato-environmental trajectories is be coming imperative, although the chronology of both is often approximate, which then complicates a robust discussion of causalities. Some environmental systems are more resilient than others to anthropogenic or climatic changes and their cascading feedbacks [START_REF] Butzer | Collapse, environment, and society[END_REF]. The determination of a precise lagoon, estuary and mangrove ecosystems history is ongoing along the eastern Arabian coast, and the progressive disappearance or reduction in these habitats will soon be documented, allowing the detection of new keys to discuss societal-environmental interactions. There is little doubt that the presence of mangrove swamps played a fundamental role in the selection of areas where settlements were established. Many of the Neolithic sites lie at the mouth of wadi deltas or estuaries that supplied fresh water, and were therefore subject to rapid coastal sedimentation [START_REF] Berger | The dynamics of mangrove ecosystems, changes in sea level and the strategies of Neolithic settlements along the coast of Oman (6000-3000 cal. BC)[END_REF][START_REF] Biagi | The shell-midden sites of RH-5 and RH-6 (Muscat, Sultanate of Oman) in their environmental setting[END_REF][START_REF] Woodroffe | Development of mangrove forests from a geological perspective[END_REF]. As a consequence, their subsistence economy was often based, almost exclusively, on the exploitation of marine and mangrove swamp resources [START_REF] Biagi | The prehistoric fisher-gatherers of the western coast of the Arabian Sea: A case of seasonal sedentarization?[END_REF][START_REF] Munoz | Transition to agriculture in South-East Arabia: Insights from oral conditions[END_REF][START_REF] Zazzo | Diet and mobility in a late Neolithic population of coastal Oman inferred from radiocarbon dating and stable isotope analysis[END_REF][START_REF] Zazzo | A revised radiocarbon chronology of the aceramic shell-midden of Ra's al-Hamra 6 (Muscat, Sultanate of Oman): Implication for occupational sequence, marine reservoir age and human mobility[END_REF]. The Arabian Sea mangroves can be considered to have been highly productive on many levels for the prehistoric subsistence economies [START_REF] Berger | The dynamics of mangrove ecosystems, changes in sea level and the strategies of Neolithic settlements along the coast of Oman (6000-3000 cal. BC)[END_REF][START_REF] Biagi | The prehistoric fisher-gatherers of the western coast of the Arabian Sea: A case of seasonal sedentarization?[END_REF][START_REF] Tengberg | Les forêts de la mer. Exploitation et évolution des mangroves en Arabie orientale du Néolithique à l'époque islamique[END_REF].

The interaction between humans and their environment operates over a number of different spatial and temporal scales, and evidence for these is apparent in eastern Arabia, where the sub-arid to arid zone was subject to rapidly changing environmental conditions after the onset of the humid period around 7000 yr BC [START_REF] Parker | Geomorphological and palaeoenvironmental investigations in the southeastern Arabian Gulf region and the implication for the archaeology of the region[END_REF]. Firstly, the region is located in the frontier zone between dry and wet tropical systems where the monsoon has reduced its activity and gradually shifted southward (Yemen) since the middle Holocene [START_REF] Fleitmann | Holocene ITCZ and Indian monsoon dynamics recorded in stalagmites from Oman and Yemen (Socotra)[END_REF][START_REF] Lézine | Timing of the southward retreat of the ITCZ at the end of the Holocene Humid Period in Southern Arabia: Data-model comparison[END_REF], and it has constantly been impacted by the dynamics of the vast marine upwelling off Oman (regional scale of the system). The NeoArabia ANR project is based on the consideration that the shell midden archives of the eastern Arabian coast allow us to explore through time the modes of societal adaptability in stress conditions in an intra-site-specific context (local scale). Nevertheless, the understanding of their spatial organisation and their mode of accumulation must be well understood beforehand.

Regional chronocultural patterns defined by cumulative probability density function (CPDF) techniques often appear insufficient for characterising socio-environmental relationships with climate and environmental changes [START_REF] Berger | Interactions between climate change and human activities during the early to mid-Holocene in the eastern Mediterranean basins[END_REF][START_REF] Flohr | Evidence of resilience to past climate change in Southwest Asia: Early farming communities and the 9.2 and 8.2 ka events[END_REF]. With extensive application of stratigraphy, as well as spatial analysis at the site scale, the in-site approach aims to reveal continuity/discontinuity in occupation and cultural changes with sensitive timing. Systematic intra-site stratigraphic, taphonomic, and geochronologic evaluations should reveal more robust data to verify whether site abandonment or abrupt decreases in occupation density are real, and not artificially created by insufficient control of the site formation processes or poor control of absolute chronology [START_REF] Berger | Vers une révision de la transition méso-néolithique sur le site de Sidari (Corfou, Grèce): nouvelles données géoarchéologiques et radiocarbones, évaluation des processus post-dépositionnels[END_REF]Lespez et al., 2016;[START_REF] Marciniak | Fragmenting times: Interpreting a Bayesian chronology for the late Neolithic occupation of Çatalhöyük East, Turkey[END_REF]. It was with this in mind that a stratigraphically controlled excavation at RWY-1 was decided on, facilitated by the presence of numerous artificially created sedimentary stratigraphies created during quarrying works. This combined approach of archaeological surveys and systematic chronostratigraphic studies should provide extensive knowledge on the site's occupation, facilitating comparisons with off-site studies of the coastal archives.

| GEOMORPHOLOGICAL,

ARCHAEOLO GICAL AND STRATIGRAPHICAL CONTEXTS OF THE RWY-1 SITE

The Neolithic RWY-1 shell midden (governorate of al-Sharqquiyah, Sultanate of Oman) is located in the centre of a wide open and flat north-east-south-west coastline combining many wadi estuaries with vast sabkhas, many kilometres in size, which are largely invaded by a system of barchanoid dunes (Fig. 1a). Previous works showed that large mid-Holocene lagoons and sedimentary mangrove archives were preserved under the surface of these recent sabkhas, with these having being fed by more perennial and powerful wadis under monsoon control [START_REF] Berger | The dynamics of mangrove ecosystems, changes in sea level and the strategies of Neolithic settlements along the coast of Oman (6000-3000 cal. BC)[END_REF]. The surface of its height in relation to the sabkha that borders it to the west 1b). This site has been prospected on the surface for 20 years by the "Ja'alan-Dhofar" French Archaeological Mission in the Sultanate of Oman, to characterise the age and potential duration of occupation (sixth-fourth millennia yr BC). It has now been excavated over the past 3 years in the context of the NeoArabia ANR project, in collaboration with the Ministry of Heritage and Culture of Oman. The site was heavily damaged at the beginning of 2010 by bulldozers obtaining ballast for public works. This destruction of nearly half of the site surface has presented the opportunity to observe long continuous stratigraphic sections. The front of the ballast quarry has created an observable semi-circular stratigraphic section the shell midden (Fig. 1b). Around 90% of the western part of the site has been destroyed, but we were able to observe, record and sample its stratigraphy in 2013-2014, before its near total destruction. Zooming in on the appropriate google images allows the current situation of the site to be observed, showing the heavy impact from the recent extension of a gravel quarry, which destroyed more than half of the initial surface of the site (see the pink areas; Fig. 1d). The area in blue contains archaeological remains from the seventh to fifth millennium yr BC, the green area remains from the seventh to fourth millennium yr BC, and the orange area a concentration of remnants from the fourth millennium, mainly identified on the surface. This type of systematic stratigraphic approach, associated with a geochronological study, is very rarely addressed by

F I G U R E 1
(a) Location of the RWY-1 site in the eastern Arabian region with the main archaeological sites studied in the NeoArabia Project (black circles). (b) 3D view of Ja'alan from the north-east with the main geological units, the geological faults, the current coastal sabkhas and the site of RWY-1. (c) Zoom-in of a Google Earth satellite image with the trace of the RWY-1 site and the position of a t opographical dGPS transect between the Oman Sea and the bottom of the sabkha. The yellow topographic profile at the top reveals the presence of two successive shell middens (SM1 and SM2), culminating at 10 and 12 m respectively. (d) A focus on the spatial organisation of the RWY-1 shell midden, located on a cemented Pleistocene gravelly alluvial formation, shown on a Google Earth framework with the locations of the main stratigraphic studies (see a and b in Fig. 2) and archaeological formations dated by millennium [Colour figure can be viewed at wileyonlinelibrary.com] Arabian Neolithic archaeology, because of the often small size of the excavations, which are often constrained by very thick and complex archaeologically stratified sequences. Indeed, few excavation areas larger than 10 m 2 exist [START_REF] Borgi | The early set tlement of HD-5 at Ra s al-Ḥadd, Sultanate of Oman (fourththird millennium BCE)[END_REF][START_REF] Cavulli | The Holocene settlement of KHB-1 (Ra's Al Khabbah, Sultanate of Oman): An overview[END_REF] outside the preventive archaeology context [START_REF] Marcucci | New investigations at the prehistoric shell midden of Ra's al-Hamra 6 (Sultanate of Oman): Results of the 2012 and 2013 excavation seasons[END_REF]RAA, Usai, 2006), and most of the studies conducted in Ja'alan over the past 40 years are one-off 2 and are too punctual [START_REF] Charpentier | Un village de pêcheurs néolithiques de la péninsule d'Oman: Suwayh 2 (SWY-2), première campagne de fouille[END_REF][START_REF] Charpentier | Conquering new territories: When the first black boats sailed to Masirah Island[END_REF]. Unfortunately, such contexts do not make it possible to ensure that the ex cavations carried out were properly representative. This has been the case on very rare occasions, and for more recent periods and contexts with significantly reduced sedimentary thicknesses more favourable to extensive archaeological stripping [START_REF] Azzarà | Architecture and building techniques at the Early Bronze Age site of HD-6, Rā s al-Ḥadd, Sultanate of Oman[END_REF][START_REF] Cattani | New excavations at the Umm an-Nar site Ras al-Hadd HD-1, Sultanate of Oman (seasons 2016-2018): Insights on cultural interaction and long-distance trade[END_REF][START_REF] Cavulli | The Holocene settlement of KHB-1 (Ra's Al Khabbah, Sultanate of Oman): An overview[END_REF].

The overall plan is to conduct an excavation strictly modelled on the previously detailed stratigraphic sequence for analysis of the continuous rhythmicity of occupation from the to determining, as soon as possible, the socio-environmental strategies developed by the Neolithic populations, revealing the technical and economic variations of their occupation through the analysis of material culture, wildlife and ecofact remains that are present at a very high chronological resolution (from 25 to 5 years). The aim is to enable a comparison with off-site palaeoenvironmental data documenting the evolution of the environment and climate in nearby palaeo-lagoon ar chives, to reveal the causes of socio-environmental phenomena. The precision of the excavation depends mainly on the sedimentation rate, and the equilibrium between the speed of aeolian sedimentation and that of anthropogenic deposition. In RWY-1, time controls were made from the scale of the site to that of the complex micro-laminated structures of some fire strictly in accordance with the sedimentary structure, were fa voured, to permit analysis of the rhythmicity and temporality of the deposits (annual and seasonal).

| SITE FORMATION PROCESSES

Understanding the process of formation and post-depositional evolution of these complex sites is accessible thanks to the presence of numerous stratigraphical sections artificially dug in the quarry, and a chronostratigraphic framework based on many 14 C and optically stimulated luminescence (OSL)

F I G U R E 2
sedimentary units, the geologically analysed sequences (log), and a part of the radiocarbon dating series in cal yr BC age (mainly on charcoal, except those noted as being from shell). The vertical green arrows indicate a vertical aggradation, the horizontal arrows a lateral aggradation, and clear bi-partition between 14 C dates of the seventh-sixth millennia yr BC and those of the fourth millennium yr BC. No radiocarbon dates from the fifth millennium were recorded in this sequence (this could be due to either absence or destruction of the archaeological sequence) [Colour figure can be viewed at wileyonlinelibrary.com] dates. The effects of natural agents are particularly pronounced in the arid context, where the protecting vegetation is very sparse and strong winds are very frequent and intensive. We know by analysis of pollen from the mid-Holocene that ecological conditions were different, being less arid and closer to an arboreal steppe with the presence of mangrove ecosystems in the intertidal areas of deltas and estuaries [START_REF] Lézine | Mangroves of Oman during the late Holocene: Climatic implications and impact on human settlements[END_REF]. Atmospheric agents such as rain then had a more significant and regular impact, particularly through flooding of estuarine areas. In the shell middens, we therefore have to consider the combined effects of anthropogenic agencies and aeolian processes of deposition, with the shell midden being the product of these two main sedimentary factors. The thickness and frequency of fire-floor surfaces (in clay fire soles or in pebbles) or pure anthropogenic accumulation from the detritus of consumed products (shells, fish, ashes and charcoal) reflects the density of Neolithic occupation. These accumulations clearly show the structuring of the intra-site space under the effect of human activities, which can only be partially understood during punctual ex cavations such as ours, but which can be tracked on continuous stratigraphic transects such as quarry fronts. Sequential and chronostratigraphic analysis of these transects reveals the rhythmicity and time frame of the occupations. Lateral sedimentary progradation can be observed during the densest occupation phases, indicating an extension of the occupied surface. Time is then no longer recorded only vertically, but also laterally (Fig. 2a). Natural post-depositional alterations are also observed, with reprecipitated salts (gypsum) or calcium carbonates from evaporation of rain being punctual in these semi-arid regions. These are mainly observed on the most ashy facies, which sometimes appear compacted, and are associated with the formation of small millimetric CaCO 3 nodules during moister episodes.

Ten main sedimentary units were observed and dated from the bottom of a shell midden represented by cemented gravels of a Pleistocene fluvial-deltaic sequence (>400 ka BP by OSL dating; Fig. 2a). The Neolithic occupation represented by the eastern main shell midden developed between 6300 and 4600-4400 yr BC. The first horizons of occupation are located in Pleistocene relictual palaeochannels filled by yellow aeolian sands (6300-5800 yr BC). The sedimentation of the shell midden shows vertical and lateral aggradation phases, especially in sections relating to the second part of the sixth millennium yr BC, where the anthropogenic deposits are dense. The fifth millennium yr BC is illustrated as being subject to more energetic and destructive aeolian processes, which result in truncation phases to some of the older anthropogenic formations (Fig. 2a). Erosion by the wind continued until recent times (eighteenth-nineteenth century AD) based on OSL dating (see Section 9). The western shell midden, now totally destroyed by quarrying activity, illustrates a long hiatus between the seventh-sixth millennium yr BC and the fourth millennium yr BC, whose mainly sandy sedimentary formations were deposited following a truncation covering more than a millennium (Fig. 2b).

The impact of wind on sedimentation is almost permanent (a mixture of consumption of debris or charcoal with deposition of wind-driven sand), and appears to show fluctuations in intensity (the size and density of particles and of remobilised artifacts). In phases of greater stability, the effects of the wind appear only in the form of small discontinuous sorted sand beds (perhaps the result of storms?) within otherwise purely anthropogenic formations. During phases of almost continuous wind activity, regular beds of well-sorted horizontal or oblique small shell debris or fish bones are observed between sandy accumulations. Truncation by wind action is sometimes observed, from the micro-local scale (decimetricsized deflation bowls) to the local scale (deflation corridors over several meters that permanently weaken the shell middens; Fig. 2a). In the second case, these probably correspond to hyper-arid periods (cf. unit VI around 5000-4800 yr BC), and the destruction of a large part of the previous formations over several meters is observed. These phenomena complicate the stratigraphic interpretation of the site.

| PALAEOECONOMIC AND SITE

CATCHMENT ANALYSES

The multi-proxy analysis (charcoal, charred seeds, pollen, marine molluscs, crustaceans, fish, turtles, birds, land and marine mammal bones) provides a preliminary reconstruction of the subsistence strategies. The faunal remains collected during the 2017 and 2018 excavations are currently being studied at the laboratory of archaeozoology and archaeobotany at the National Museum of Natural History in Paris, using the modern comparative osteological collections for the taxonomic identification of the remains. The results of the archaeomalacological study show that the marine shells are mainly culinary waste (Fig. 3), with the main species being the clam Marcia recens (syn. Marcia marmorata). Several other species were also collected for food on a smaller scale, such as oysters (Ostreidae), the clam Callista umbonella (syn. Amiantis umbonella ), brown mussel Perna perna (syn. Perna picta), crowned turban shell Lunella coronate, and cowry Cypraea sp. The main environment exploited was the muddy sand from the lagoon, used for the gathering of Marcia recens. Marine shells were also used as raw materials for manufacturing objects like decorative elements, tools, and fishing hooks.

The ichthyological study revealed thousands of small vertebrae belonging to small fish species or juvenile specimens, which can take refuge in the pneumatophores of the mangrove to hide from predators. This illustrates a subsistence activity mainly oriented towards exploitation of the lagoon and mangrove swamps (Fig. 3), with the presence of many mullet (Mugilidae), bigeye scad (Selar crumenophthalmus ), and sardines (Clupeidae), as well as many juvenile sea bream (Sparidae) and sea catfish (Ariidae). Neolithic people from RWY-1 probably used fishing nets with small meshes.

These preliminary results of the study of marine resources show that the Neolithic populations of RWY-1 had a subsistence activity mainly focused on exploitation of the lagoons, which were probably very extensive in the western part of the site (see Section 11). RWY-1 appears to be a fishing station where Neolithic communities were able to exploit the entire intertidal zone to collect bivalves, and also to have access to lagoon waters where they could lay their fishing nets, as is the case on other sites on the Ja'alan coast such as SWY-1 [START_REF] Marrast | Sharks in the lagoon? Fishing exploitation at the Neolithic site of Suwayh 1 (Ash Sharqiyah region, Arabian Sea, Sultanate of Oman)[END_REF][START_REF] Martin | Stratégies et statut de la collecte des mollusques marins sur les sites côtiers d'Oman du Néolithique à l'âge du Bronze: apport des sites de Suwayh 1, Ra's al-Khabbah 1 et Ra's al-Jinz 2[END_REF].

In general, the preservation of vertebrate remains is poor because of the loss of organic material and high fragmentation. Besides fish, the vertebrate assemblage of Ruways 1 is composed of a few mammalian and reptilian remains (Fig. 4). The mammalian remains belonged to ovicaprids, and in some cases it was possible to identify the bones to the level of the species. This is the case for a talus allocated to a goat (Fig. 4: 1). In other cases, it was not possible to distinguish between sheep and goat (Fig. 4: 2). Ruways 1, like other Neolithic sites in Oman, is remarkable for the presence of canid bones among the faunal assemblages. A complete calcaneus of a dog (Fig. 4: 3) and a distal part of a humerus (Fig. 4: 4) were recovered from the site, and highlight once more the importance of these taxa for consumption in this part of the world. Other mammals exploited in Ruways are dolphins, a single vertebra of which was recovered practically complete (Fig. 4: 5). Finally, marine turtle bones are also present in the remains, as demonstrated by a relatively large shell that was consolidated before removal (Fig. 4: 7). This shell belonged to a green sea turtle, common in most of the coastal sites of Oman. Study of the turtle remains is still ongoing.

Analyses of the floral macro-remains have also been performed, specifically the different types of fuelwood obtained from local vegetation communities, with these fuelwood remains being very frequent in the numerous fireplaces or ashy layers of the site. Despite the still partial data, the charcoal remains reveal that the mangrove environment, which has nowadays disappeared, was present at least until the end of the fifth millennium yr BC. After two seasons of study (2017)(2018) and the analysis of two-thirds of the RWY-1 sequence, with more than 1000 charcoal fragments having been analysed, a similar pattern emerges in the relative presence of taxa, though with some differences ( Avicennia occurring in 87% of the samples, Rhizophora in 53%) in relation to Chenopods. The very limited range of species at the anthracological level

F I G U R E 3
Illustration of the main shellfish and fish taxa identified in the first RWY-1 studies. Seashell photographs: archaeological specimens from RWY-1. Fish photographs: fresh fish from the MNHN osteological collection of fish for the Indo-Pacific area [Colour figure can be viewed at wileyonlinelibrary.com] is surprising, given that the other Neolithic sites for which charcoal analyses have been performed generally present a more varied situation (cf. Ras al Hamra 5-6; [START_REF] Biagi | The shell-midden sites of RH-5 and RH-6 (Muscat, Sultanate of Oman) in their environmental setting[END_REF]. This would suggest that mangroves were the only source of timber and firewood for the local groups over a period of several centuries.

The remarkable presence of Rhizophora cf mucronata is of note; it is a species no longer growing along the coasts of the Arabian Sea (refuges are found in more humid tropical areas). Avicennia sp., known to be the most tolerant in terms of environmental conditions, were observed in the region until at least the Early Bronze Age [START_REF] Cartwright | Reconstructing the use of coastal resources at Ra s al-Ḥadd, Oman, in the third millennium BC[END_REF], and are now present in the Khor al Jaramah (north Ja'alan), where they were recently reintroduced. Their presence confirms results from the pollen assemblages (see Section 10), the frequent presence of mangrove-adapted species like the gastropod Terebralia palustris , and the exploitation by Neolithic peoples of the two arboreal species of mangrove. Further research should provide details on the origin, evolution and death of the local mangroves, which probably locally disappeared at different times and for different reasons (climatic changes and human pressure).

STUDIES

The 16 current levels studied (from 5 to 20) from the 3 m 2 S1 excavation of the Ruways shell midden have already delivered 2728 lithic objects (excepted sketches). These include knapped flint pieces, shaped or crushed sandstone or limestone pebbles, and net sinkers; the whole being associated with numerous beads, faunal remains (including several pol ished bone objects), and a large mass of marine shells, including some used as scrapers.

Throughout the sequence, the Ruways 1 site is characterised by intense craftworking activity, as we were able to identify the presence of a workshop for the manufacture of drills and net sinkers, and most probably a workshop for the processing of beads (which are quite common along the coast of the

F I G U R E 5
Illustrations of the RWY-1 lithic material (from the upper part of the archaeological sequence between 5200 and 4600 yr BC). 1. Net sinkers in sandstone and calcareous rock from the levels 5-6. 2. Arrow heads: a, b, c: bifacial points from levels 6-10; d, e: trihedral points from levels 8 and 9 (pressure retouches, around 5100-5200 yr BC). 3. A large scraper. 4. Production of bladelets from a great variety of flint material, with a soft striking debitage (some of them are probably imported in the form of finished products). 5. Presentation of drill points on various flint materials from levels 5-6 [Colour figure can be viewed at wileyonlinelibrary.com] Arabian Sea) [START_REF] Brunet | Les perles en pierre de la péninsule omanaise du Néolithique et de l'âge du Bronze: approche synthétique[END_REF]. The site also presents records of many domestic activities related to fishing, hunting and most likely gathering (the presence of a circular cup anvil). Several fireplaces have been identified during the excavations, and these attest to culinary activities. At the same time, the density of shaped flint suggests that it was knapped on site, and the fragmentation rate from production, particularly of blades, leads us to consider a high utilisation rate (Fig. 5).

In addition, analysis of the raw materials and economic strategies of the Ruways trimmers' workings revealed the presence of the production of different blanks, particularly in early phases around 5200 yr BC. Moreover, although the great majority of the production remained rudimentary (chips, bladelet chips, small irregular blades), some isolated blades attest to a high degree of expertise and are in sharp contrast with the rest of the shaping industry (Fig. 5). These latter items could testify to importations from specialist workshops at the micro-regional scale.

| SCLEROCHRO NOLO GICAL

STUDY OF BIVALVE SHELL S AND SEASO NALIT Y OF OCCUPATION F I G U R E 6

Different steps of the marking experiment (a-h) and observation of the growth increment and chemical marking from the thin section of a shell of Marcia recens (#M.68 from the non-broken cage) marked on 15 January 2018, and taken out of seawater on 14 April 2018 (i-k). as well as in quantity, forming the so-called "shell middens". Among the bivalve taxa, the Veneridae dominate, with Marcia recens, Callista umbonella and Circenita callipyga . These three species could have been gathered from the intertidal zone at the edge of the mangrove environment. Similar to dendrochronology, sclerochronology is the study of the testaceous part of biological organisms, such as the shells of molluscs. Growth line patterns and the chemical composition of these shells can provide information on the biology of the species, as well as on the environment in which they grew [START_REF] Buddemeier | Sclerochronology: A data source for reef systems models[END_REF][START_REF] Gosselin | Sclerochronogical studies in the Humboldt Current System, a highly variable ecosystem[END_REF][START_REF] Jones | Sclerochronology-Rading the record of the molluscan shell[END_REF][START_REF] Schöne | The curse of physiology-Challenges and opportunities in the interpretation of geochemical data from mollusc shells[END_REF][START_REF] Wanamaker | Gulf of Maine reveal changes in seawater temperature seasonality during the Medieval Climate Anomaly and the Little Ice Age[END_REF]. In an archaeological context, periods of human residence in coastal settlements can be deduced via de termination of the season of the mollusc catch and paleo-climatic parameters, such as inferred sea surface temperatures [START_REF] Andrus | Shell midden sclerochronology[END_REF]. For this purpose, a preliminary calibration study on living specimens was implemented during the winter of 2017-2018 to characterise the growth patterns (e.g. rhythm and variation of growth) of the three bivalve species (Fig. 6: a-h).

The first results of the marking experiments in Oman and UAE provide insights into the respective time frameworks of the three species. M. recens, C. umbonella and C. callipyga show a common tidal growth rhythm. After a period of about one month, M. recens and C. callipyga were disturbed in their growth by an environmental event that may have been related to a punctual winter flood (Fig. 6: i-k). Further research on bivalve shells will provide knowledge on the seasonality of occupation sites and paleo-environments, which will be cross-referenced with the other information gathered during this interdisciplinary study.

A regular pattern of Neolithic transhumance between the inland regions and the west coast of what is now the United Arab Emirates has not been proved by analyses of 87 Sr/ 86 Sr ratios of Neolithic skeletons [START_REF] Kutterer | Neolithic nomadism in southeast Arabia-Strontium and oxygen isotope ratios in human tooth enamel from al-Buhais 18 and Umm al-Quwain 2 in the Emirates of Sharjah and Umm al-Quwain (UAE)[END_REF]. The pattern of animal exploitation at UAQ2 [START_REF] Mashkour | Middle to late Neolithic animal exploitation at UAQ2 (5500-4000 cal. BC): An Ubaid-related coastal site at Umm al-Quwain Emirate, United Arab Emirates[END_REF] also documents a year-round residency on the coast. Mobility to the interior seems to be more associated with herder or hunter pathways than with the general population. For the fourth millennium Ja'alan communities, a micro-regional seasonal nomadism model is proposed, comparing the different scales of movement with both the territory and re sources [START_REF] Cavulli | Thoughts on nomadism in Middle Holocene Oman[END_REF]. The cross-discipline approach used for the RWY-1 data (fauna, sclerochronology, pollen, geoarchaeology) should provide answers to these es sential questions, allowing an understanding of the status of sites and Neolithic strategies within the East Arabic region.

| MIDDLE NEOLITHIC HUMAN

REMAINS AND BURIAL S AT RWY-1

During the last survey and excavation season at RWY-1, several human remains were brought to light, most of which were related to burials partially or totally damaged by the quarry extraction works carried out in the shell midden during recent years. In total, three graves, including three adult individuals and one child aged 4 ± 1 years, were recognisable from human bones cut by the north-western and south-eastern sections in the quarry. A few other scattered human remains were also found in the quarry debris, but these could not be linked to graves in the section. These finds are of considerable interest, because their stratigraphic position shows that they belong to the middle Neolithic period, during the second half of the sixth millennium yr BC, for which no other human remains or burial evidence has yet been recovered in Oman. Findings of the most ancient human remains have so far come from the UAE at Faya 10 (Kutterer, 2012), Marawah 11 [START_REF] Beech | Excavation at the Neolithic settlement of MR11 on Marawah Island, Abu Dhabi, UAE[END_REF] and in the large Neolithic cemetery at Jebel Buhais [START_REF] De Beauclair | Funerary rites in a Neolithic nomad community in Southeastern Arabia: The case of al-Buhais 18[END_REF][START_REF] Uerpmann | Funeral monuments and human remains from Jebel al-Buhais, vol. 1. The archaeology of Jebel al-Buhais[END_REF], with contexts dating from the seventh to fifth millennium yr BC. Although the graves documented at RWY-1 share common characteristics with those known from later sites (pit graves, accompanied by ornaments and faunal remains; see [START_REF] Bortolini | Life and death in prehistoric Oman: Insights from Late Neolithic and Early Bronze Age funerary practices (4th-3rd mill. BC). In The archaeological heritage of Oman[END_REF][START_REF] Marcucci | New investigations at the prehistoric shell midden of Ra's al-Hamra 6 (Sultanate of Oman): Results of the 2012 and 2013 excavation seasons[END_REF][START_REF] Salvatori | The prehistoric necropolis at Ra's al-Hamra 5 (Muscat -Oman)[END_REF], some are unique in the position of the individuals. Indeed, in two graves the subjects were placed in a lying position on their backs, which is totally unparalleled in the region. The ongoing anthropological study should provide valuable information on dietary practices and the health status of individuals.

| ABSOLUTE CHRO NOLO GY AND RESE RVOIR EFFECT STUDY

Sequential analysis has concentrated on the central part of the shell midden, which is highly anthropogenic and about 30 m long (Fig. 2a). Ruways 1 is already an exceptional site according to the absolute chronological data, as the first Neolithic occupation is very old (late centuries of the seventh millennium yr BC), being confirmed in three parts of the site by two distinct radiocarbon dates on the same level in the log2 sequence (6378-6069 on shellfish with a small average delta R value still temporary in RWY-1 (28,625 ± 58 years) and 6424-6250 on charcoal), and by three OSL dates immediately posterior to this oldest occupation (6323 ± 485 yr BC to 5725 ± 583 yr BC, Richard et al., submitted). The site is more than 6-7 centuries older than the other oldest dates obtained regionally (SWY-1, SWY-11 and SWY-20) [START_REF] Charpentier | Hunter-gatherers of the "empty quarter of the early Holocene" to the last Neolithic societies: Chronology of the late prehistory of south-eastern Arabia (8000-3100 BC)[END_REF], and five centuries older than the known chronology of Ras dah SM-10 (Masirah Island) [START_REF] Charpentier | Prehistory and palaeo-geography of the coastal fringes of the Wahiba Sands and Bar al-Hikman, Sultanate of Oman[END_REF].

The second goal in RWY-1 is to develop a specific study on the reservoir effect of the stratified shell accumulations dated by the radiocarbon method (with the radiocarbon lab oratory of the University of Lyon and the Artemis National Planning), combining on the same levels the dating of samples of lagoon and marine shells and terrestrial charcoals. The complementarity of the OSL method was tested in the sandiest parts of the archaeological sequence, where no charcoal was preserved because of an unfavourable environment (Richard et al., submitted). In order to complete the chronology of the site, sediments (n = 12) were sampled in phases I, II, VII, VIII and IX. Ten of these samples were dated using the quartz signal reached or was close to saturation, thereluminescence signal. The age obtained at the base of the se quence (phase I) indicates a deposition time during the Middle Pleistocene, before 437 ka. For the later phases, luminescence BC (phase II) to 3225 ± 275 yr BC (phase VIII) (Richard et al., submitted). OSL ages obtained for phase IX range from 1389 ± 186 yr BC to the modern period (1764 ± 15 to 1917 ± 9 AD), suggesting that the sediment from the top of sequence was recently reworked by wind activity in this area.

For a given region, the difference between the local marine 14 C age and the global model marine 14 C age is given by ∆ R, whose estimation is necessary to calibrate the 14 C ages of marine samples. This offset in the local marine 14 C ages from the global modelled mean can be determined from the 14 C dating of terrestrial material (charcoal, seeds) and marine shell pairs collected from the same stratigraphic horizon. For the moment, our study is based on 12 dates using combined values from the ubiquitous shells of Marcia recens and charcoal, and 12 dates using the more marine shell Lunella coronata, which are being analysed at the radiocarbon laboratory of Lyon. Preliminary results with low values of ∆R (50-150 years) strongly oscillate between the seventh and sixth millennia yr BC; these are very different from previous estimations proposed for the mid-Holocene period (240-720 years) [START_REF] Staubwasser | South Asian monsoon climate change and radiocarbon in the Arabian Sea during early and middle Holocene[END_REF][START_REF] Uerpmann | Radiocarbon dating of shell middens in the Sultanate of Oman[END_REF], but closer to the robust calculations made in an archaeological context for the mid-sixth and the mid-fifth millennium cal yr BC at Ra's al-Hamra 6 where ΔR values range from 99 ± 27 to 207 ± 43 14 C yr [START_REF] Zazzo | A revised radiocarbon chronology of the aceramic shell-midden of Ra's al-Hamra 6 (Muscat, Sultanate of Oman): Implication for occupational sequence, marine reservoir age and human mobility[END_REF], for the forth millennium at Ra's al-Hamra 5 (ΔR= 255 ± 55 14 C yr; [START_REF] Zazzo | Variability in the marine radiocarbon reservoir effect in Muscat (Sultanate of Oman) during the 4th millennium BC: reflexion of taphonomy or environment?[END_REF]2014) or for the third millennium yr BC (Early Bronze Age) : 210 ± 15 years [START_REF] Saliège | Estimation de l'effet réservoir 14 C marin en mer d' Arabie[END_REF]. The forthcoming results should make it possible to decide on dates for almost the entire Neolithic period.

1 0 | IN-SITE CLIMATE AND

ENVIRONMENT SIGNAL S

The Ja'alan coast is today associated with an arid tropical desert with sudanian to sub-sudanian vegetation. However, pollen [START_REF] Lézine | Mangroves of Oman during the late Holocene: Climatic implications and impact on human settlements[END_REF][START_REF] Lézine | Timing of the southward retreat of the ITCZ at the end of the Holocene Humid Period in Southern Arabia: Data-model comparison[END_REF] and geoarchaeological studies suggest that the mid-Holocene conditions were different [START_REF] Berger | The dynamics of mangrove ecosystems, changes in sea level and the strategies of Neolithic settlements along the coast of Oman (6000-3000 cal. BC)[END_REF]. Conditions along the eastern Arabian coast have changed, with past latitudinal monsoon circulation changes through time [START_REF] Fleitmann | Holocene ITCZ and Indian monsoon dynamics recorded in stalagmites from Oman and Yemen (Socotra)[END_REF][START_REF] Parker | Geomorphological and palaeoenvironmental investigations in the southeastern Arabian Gulf region and the implication for the archaeology of the region[END_REF]. Local variation in climatic change is still too rarely attested to archaeological sites or continental river archives close to sites occupied by the first Neolithic communities of the eastern Mediterranean [START_REF] Berger | The 8200 cal BP abrupt environmental change and the Neolithic transition: A Mediterranean perspective[END_REF][START_REF] Berger | Interactions between climate change and human activities during the early to mid-Holocene in the eastern Mediterranean basins[END_REF][START_REF] Lespez | Middle Holocene rapid environmental changes and human adaptation in Greece[END_REF]Zielhoffer et al., 2012). The inferences for climatic impacts are most often indirect, being derived from glacial, marine or continental archives like speleothems [START_REF] Cremaschi | Early-Middle Holocene environmental changes and pre-Neolithic human occupations as re corded in the cavities of Jebel Qara (Dhofar, southern Sultanate of Oman)[END_REF][START_REF] Cullen | Climate change and the collapse of the Akkadian empire: Evidence from the deep sea[END_REF][START_REF] Fleitmann | Holocene ITCZ and Indian monsoon dynamics recorded in stalagmites from Oman and Yemen (Socotra)[END_REF][START_REF] Staubwasser | Climate change at the 4.2 ka BP termination of the Indus valley civilization and Holocene south Asian monsoon variability[END_REF]. One of the purposes of the RWY-1 excavation was to identify climatic signals recorded in different forms in the sedimentary sequence (by sedimentological, geochemical, palynological, and anthracological techniques).

The fine analysis of anthropogenic and environmental records in the stratigraphies of the shell middens are associated with coherent sedimentological and geochemical sig nals recovered by studies of sequential sedimentations. Eight sequences have been selected from the east to west part of the site along the artificial stratigraphies, to document all the sedimentary processes with the most precision. We have chosen to discuss two of them (log 1ab and log 2), to demonstrate their promising potential (Fig. 2a and Fig. 7). Coincidental high bromine/titanium ratios (an indicator of organic matter), high magnetic susceptibility values (an indicator of fire and fireplaces with production of maghemite oxide), total organic matter (loss-on-ignition), and sulphur, characterise the anthropogenic deposits. These show strong correlations with potassium/titanium ratios, which probably represent local in creases in soil weathering (more atmospheric humidity favourable to anthropogenic deposits in periods of low wind input). Aeolian accumulations by wind activity (in yellow hatching) appear in inverse correlation with anthropogenic indicators (Fig. 7). They are associated with a high rubidium/titanium ratio, and high D50 (median) and D99 (superior unipercentile) grain size indicator values, which infer an increase in sediment size and wind energy, and together with high values of calcium carbonates indicate carbonates as the main source of the aeolian dust. Two main arid phases are recorded, the first between 6200 and 5300-5200 yr BC, and the second between 5000-4900 and 4200 yr BC. The main anthropogenic production is centred on the period 5300-5200 to 5000 yr BC. This diagram also shows the sedimentary contraction of the fifth millennium yr BC in this part of the site, which is better documented in other parts of the site.

Intra-site palynological analysis is used on the same sequences to determine the evolution of the vegetal landscape, the climatic conditions, and in-site anthropogenic activities. In this case, this study is particularly interesting because of the great scarcity of palynological analysis in the region in relation to global changes, coastal ecosystems (lagoons, mangroves), fluctuations in marine upwelling and population concentrations [START_REF] Lézine | Mangroves of Oman during the late Holocene: Climatic implications and impact on human settlements[END_REF]. The first results from Ruways 1 (log 1ab and 2) show different taxa from 5500 yr BC, which can be grouped into five ecological groups. One includes the two mangrove taxa (Avicennia and Rhizophora), another the wetland taxa including Cyperaceae, Typha and Tamarix, that is, plants related to a high water table and little salinity in the water. There are a whole series of local and semidesert taxa (Acacia, Aizoaceae, Artemisia, Asteraceae, Calligonum, Chenopodiaceae, Combretaceae, Ephedra, Poaceae, Prosopis, Tribulus and Ziziphus), although Chenopodiaceae may also be related to high concentrations of salt on the surface. There is also a group of regional taxa from the Omani mountains located in the north-east of Ja'alan ( Dodonaea, Olea europaea type, Podocarpus, Juniperus type, Myrica and Ericaceae ), and finally there are the non-pollen palynomorphs of a coprophile nature (Cercophora, Chaetomium , Sordaria and Sporoemiella), which confirm the presence of faunal pastoral remains. Regarding evolution, the base of the sequence (log 2) represents a time when the mangroves were much more abundant than today, reaching their maximum (both Avicennia and Rhizophora). In log 1a and log 1b, the mangroves are reduced, but they are still important, almost always with high values. In the top of log 1b (fifth millennium yr BC), the mangroves show an abrupt reduction, at the same time as an increase in wetland taxa, Chenopodiaceae, Poaceae and Artemisia, and especially the coprophilous fungi.

1 1 | LOCAL PA LAEOGEOGRAPHY

AND ENVIRONMENT RECONSTRUCTION

Palaeogeographic parameters are affected by physical forces such as sea-level changes, climate and tidal amplitude and duration, as well as the quantity of fresh water inflow associated with monsoon systems, which have determined and im pacted the location of settlement networks and the economic strategies of the first Arabian Neolithic populations along the eastern Arabian coast [START_REF] Berger | The dynamics of mangrove ecosystems, changes in sea level and the strategies of Neolithic settlements along the coast of Oman (6000-3000 cal. BC)[END_REF]. Mangrove ecosystems represent a natural resource base for silviculture and a large range of economic products, and also provide habitats for rare fauna (fish, shellfish, birds and crustacean species). Geomorphological and environmental studies have shown that during the middle of the fifth millennium yr BC, a maximal marine transgression caused a major phase of lagoon expansion and the optimum conditions for mangrove forests, which are occupied today mainly by sabkhas [START_REF] Berger | The dynamics of mangrove ecosystems, changes in sea level and the strategies of Neolithic settlements along the coast of Oman (6000-3000 cal. BC)[END_REF][START_REF] Glover | Mangroves, molluscs and man: Archaeological evidence for biogeographical changes in mangrove around the Arabian Peninsula[END_REF][START_REF] Sanlaville | L'évolution des espaces littoraux du Golfe Persique et du Golfe d'Oman depuis la Phase finale de la transgression post-glaciaire[END_REF]. To correlate the evolution of the occupation strategies of the RWY-1 site with the local palaeogeographic, eustatic and climato-environmental records resulting from the sedimentary lagoon, the mangrove and sabkha archives, and the regional data resulting from the archives of the Indian Ocean (marine cores), a systematic off-site geoarchaeological and geophysical survey was made in 2017 and 2018 across the large current sabkha located in the western part of the site (Fig. 8a). This sabkha of more than 10 km 2 shows two closed and infilled khors, located on either side of the current village of Ruways, towards which converge the non-perennial and meandriform beds of the two main wadis (Fig. 8a). They were most probably widely open to the Arabian Sea during the middle Holocene, and connected with large lagoons and wadis. We performed electrical resistivity tomography (ERT) across the sabkhas to determine the sedimentary structures and locate the best area for coring operations (Fig. 8b), obtained topographical transects by dGPS to position the ERT profile, the cores, and the current structure of the local landscape, and finally obtained four thermic mechanical corings from depths of 3-5 m (with a Cobra corer) to obtain a series of the geological archives from the current sabkhas (Fig. 8a). The ERT of the current sabkha has successfully reproduced the geometry of its river-lagoon formations (Fig. 8b). It has distinguished the four main sedimentary units in the upper 10 m filling. A deep, probably late Quaternary, alluvial formation (from -8 to -3 m) is shown in blue, the coarse sandy to gravelly alluvial pre-mid-Holocene formations organised in a in yellow, fluvial-lagoon silty-sand formations asso ciated the maximum marine (around -3 part the current sabkha, consisting of red silts and gypsum interbedded with aeolian sands and sometimes dune formcores in the deeper part of the fine fluvial-lagoon formation have confirmed the superficial sedimentary structure of the hinterland sabkha and its absolute chronology by radiocarbon dating of shells. One lithological sequence of the C3 core is presented in Fig. 8c. This confirms the contemporaneous development of an open lagoon associated with a mangrove forest between the second half of the sixth and the end of the fifth millennium yr BC (the subject of ongoing sediment and pollen studies).

2 | CO NCLUSIONS

The current appearance of the shell midden is the result of a long interaction between natural and anthropogenic processes of aggradation and phases of truncation by wind. Only quarrying activities and the provision of long continuous sequences have allowed us to understand and render this long history.

RWY-1 is a site with a long sequence of occupation (6380-3400 yr BC), with probable occupation at the beginning of the middle Neolithic, which is still unprecedented in Ja'alan in a stratified context (6380-6000 yr BC), but which must be possible to relate to the Neolithic horizons of the wadi Wuttaya dated 6170-5980 yr BC [START_REF] Uerpmann | Structuring the late stone age of southeastern Arabia[END_REF], which has close technological similarities with the Pre-Pottery Neolithic B (PPNB) B. They can also be associated with the last Fasad-point industries at sites near Ra's al Jins-37 and Al-Haddah-BJD1 in Ja'alan, which do not have 14 C dates [START_REF] Charpentier | Hunter-gatherers of the "empty quarter of the early Holocene" to the last Neolithic societies: Chronology of the late prehistory of south-eastern Arabia (8000-3100 BC)[END_REF]. RWY-1 is also associated with very old Neolithic burials (5300-5200 yr BC) that represent particular funeral rituals under analysis, and presents a great potential to reconstruct the economic strategies of Neolithic coastal populations, which were strongly oriented with the exploitation of lagoons and mangrove ecosystems (A. Marrast, PhD thesis, and a collective study of the MNHN-Paris team). The lithic industry is based on predominant expedients in the 15 upper units, which contrast with the little elaborate expertise (arrowheads). The combined radiocarbon dates of the shellfish and charcoal, currently being finalised, will make it possible to propose a reference for the micro-regional marine reservoir effect between the end of the seventh and fourth millennia yr BC. Finally, a systematic chrono-and lithostratigraphic study allows us to better determine the evolution of the shell middens, from their building to their partial erosion (site formation processes). The multidisciplinary analysis of this site and the neighbouring geological cores will, in the coming months, allow the first socio-environmental model for the Ja'alan Neolithic to be proposed, with this model covering three millennia.

ACK NOWLEDGEMENTS

The NeoArabia project is funded by the French National Research Agency (ANR-16-CE03-00007/Neoarabia). We thank the Laboratoire de Mesure du Carbone 14, UMS

F

  Capra , talus. 2: B2 US18. Caprini mandible fragment of the articulation. 3: A2 US18. Canis sp. Calcaneus. 4: S1 A2 US6B distal humerus Canis sp. 5: B3 US13b dolphin vertebra. 6: B2 US12a long bone (humerus) shaft of a medium-sized ungulate. 7: B2 US11b marine turtle shell [Colour figure can be viewed at wileyonlinelibrary. com] 6 | T Y PO-TECHNOLO GICA L

  (a and b) Size, colour and form diversity among Marcia recens and Circenita callypiga species. (c and d) Each of the caught bivalves were tagged, sized and weighed. (e) Bivalves were kept alive in seawater with a compressor system for aeration. (f) Marking was performed in nally rinsed o their original place of growth and split into two cages where they grew for 89 days. (i Thin section of a shell demonstrating its birth left side) to its (pallial margin, side). (j) Left #M.68. The black line shows the cutting line as well as the piece of shell used to make the thin section. (k Detail of the end of the growth of specimen #M.68 (pallial margin) under fluorescent light (upper right panel) and reflected light (lower right panel). The black dotted line shows the beginning of the disturbed growth period [Colour figure can be viewed at wileyonlinelibrary.com]

F

  Sedimentological and geochemical diagram of log 1a/b and 2 (western RWY-1 stratigraphic section). Dates are in cal. yr BC [Colour figure can be viewed at wileyonlinelibrary.com]

F

  Map of the Ruways micro-region with the proposed Neolithic extension of a wide open lagoon with mangrove ecosystems (in purple) and the two khors situated on each side of the current village of Ruways, with the position of the four geological cores (yellow stars) and the RWY-1 site (orange area). (b) Electrical resistivity tomography section of the current sabkha located in the western part of the RWY-1 site, with the main superficial sedimentary formations and the location of core 4. (c) Lithological sequence of core 4 with the radiocarbon dating series on shells in BP and in cal. yr BC age [Colour figure can be viewed at wileyonlinelibrary.com]

2572, ARTEMIS in Saclay for 14 C measurements by SMA in the frame of the National Service to CEA, CNRS, IRD, IRSN and Ministère de la Culture et de la Communication. We also deeply thank the Oman Ministry of Heritage and Culture (Muscat, Oman) for kind permission to conduct field work in the regions of Ja'alan and for their help during field missions, and the French archaeological mission of the MAE (partner of this ANR). We would also like to thank Mr Karl Embleton for his review of the English version and finally the OMEAA platform of the UMR 5600 EVS in Lyon 2 University for its laboratory and field material support.

Funding information Grant/Award Number: ANR-16-CE03-00007; French National Research Agency; Ministère de project tries to understand how environmental, social, economic in the Indo-Arabian monsoon, marine