Low-frequency Cycles Research Articles

Record of the Climatic Variability and the Sedimentary Dynamics during the Last Two Millennia at Sebkha Dkhila, Eastern Tunisia

This paper aimed to study the record of the climatic variability during the last two millennia within the sebkha of Dkhila. Six climatic stages were recognized along the 104 cm core: the Warming Present (WP), the Late Little Ice Age (Late LIA), the Early Little Ice Age (ELIA), the Medieval Climatic Anomaly (MCA), the Dark Age (DA), and the Roman Warm Period (RWP). The WP stretches along the uppermost 1 cm with a high grey scale as sign of a dry climate. The Late LIA is located between 1 cm and 6 cm. The ELIA is located between 6 cm and 40 cm. The MCA spanning from 40 cm to 72 cm is marked by a sharp increase of the GS revealing a wet period. The DA appears along the part between 72 cm and 84 cm; a shift from light to dark sediments is recorded. The RWP appears between 84 cm and 104 cm. Based on the grain size distribution, two low frequency cycles were identified indicating radical global changes of climatic conditions, the differential tectonics, and the groundwater fluctuations. On the other hand, high frequency cycles indicate local modifications of the climatic conditions.

Effect of chemical micro-heterogeneity on the susceptibility to local failure of the metal of the heat-affected zone of welded joints

The mechanism of the effect of chemical and structural micro-heterogeneity on the susceptibility to local failure of the metal of the heat-affected zone of welded joints in 12Cr18Ni12Ti steel in the conditions of high-temperature low-frequency low cycle loading is substantiated theoretically and by experiments. The method is proposed for the evaluation of the probability of fluctuation formation of the regions of chemical micro-heterogeneity, taking into account the growth of austenite grains in welding and the effect of heat input.

Phase resolved optical emission spectroscopy of dual frequency capacitively coupled plasma

In this article we use phase resolved optical emission spectroscopy to study emission pattern in plasma sheath of dual frequency capacitively coupled plasma in Ar and Ar-O2 discharge. Two emission patterns are found in sheath region of radio frequency coupled powered electrode. The first pattern is related to electron impact excitation because of the sheath expansion. The second pattern is caused by electron impact excitation of secondary electrons. Two emission patterns are also highly modulated with the low frequency cycle. Under the condition of argon discharge, the emission intensities of the two excitation processes are very similar. The emission structure by secondary electrons becomes weak with the increase of O2 content in the gas mixture. In addition, we also use phase resolved optical emission spectroscopy to study low frequency cycle averaged axial emission profile of excited atomic argon at 751 nm in Ar-O2 mixture gas. Distance from the powered electrode (about 3.8 mm) is defined as the boundary sheath of dual frequency capacitively coupled plasma.

Variability to sedimentary dynamics and climatic conditions during the last two millennia at sebkha Souassi in eastern Tunisia

AbstractThis paper covers work intended to study the interplay of sedimentary dynamics and climatic variability over the last two millennia within Tunisia’s sebkha Souassi. Based on the Visual Core Description, and magnetic susceptibility, we date the core from sebkha Souassi to the last two millennia. Genetic grain-size distribution then provided a basis for the identification of six climatic stages, i.e. the Warming Present (WP), the Late Little Ice Age (Late LIA), the Early Little Ice Age (ELIA), the Medieval Climatic Anomaly (MCA), the Dark Ages (DA), and the Roman Warm Period (RWP). The WP stretches across the uppermost 3 cm, with a high grey scale indicating a dry climate. The Late LIA is located between 3 and 7 cm, and the ELIA between 7 and 28 cm. Intermediate values for GS indicate that this stage may be classified as moderate. The MCA spanning from 28 to 40 cm is marked by a sharp decrease in GS indicative of a wet period. The DA appear along the part between 40 and 79 cm, a shift from light to dark sediments being recorded. The RWP in turn appears between 79 and 114 cm. Based on the grain-size distribution, two low-frequency cycles were identified, indicating radical global changes in climatic conditions, differential tectonics and groundwater fluctuations. High-frequency cycles in turn attest to local modifications of climatic conditions.

Central drive and proprioceptive control of antennal movements in the walking stick insect

In terrestrial locomotion, active touch sensing is an important source of near-range information. Walking stick insects show active tactile exploration behaviour by continuously sampling the ambient space with their antennae. Here, we identify central and proprioceptive contributions to the control of this behaviour. First, we investigate the potential role of synaptic drive to central neural networks using pilocarpine, an agonist of muscarinic acetylcholine receptors. In an in situ preparation, pilocarpine induced rhythmic antennal movements with a persisting pattern of inter-joint coordination, matching that seen in intact walking animals, albeit with lower cycle frequency. After de-cerebration, stick insects were still able to walk but no longer moved their antennae during walking. Here, pilocarpine still induced antennal movement, suggesting that synaptic drive to central neural networks involved in antennal movement generation occurred in the brain and not in the suboesophageal ganglion. During intact walking, these networks are likely to receive activation by ascending input. Second, we show persistent coupling of both antennal joints during intact walking, with the distal scape–pedicel joint (SP) always leading the proximal head–scape joint (HS). Ablation of joint proprioceptors had no effect on this overall pattern of inter-joint coordination but could affect the magnitude of the phase-lag. Third, we revise the description of antennal hair fields and show that complete ablation of all seven hair fields strongly affects antennal movements. Ablating dorsal hair fields mainly affected the working-ranges of antennal joints: Ablation of the dorso-medial pedicellar hair plate caused a ventral shift of the SP working-range. Ablation of the dorsal scapal hair plate considerably expanded the dorsal HS working-range, and, in combination with ablation of pedicellar hair fields, increased the SP working-range, too. We conclude that the working-ranges of both joints are under proprioceptive control of dorsal antennal hair fields. Thus, both synaptic drive to central neural networks and proprioceptive feedback are involved in the control of active tactile exploration behaviour in stick insects.

High power impulse magnetron sputtering discharge

The high power impulse magnetron sputtering (HiPIMS) discharge is a recent addition to plasma based sputtering technology. In HiPIMS, high power is applied to the magnetron target in unipolar pulses at low duty cycle and low repetition frequency while keeping the average power about 2 orders of magnitude lower than the peak power. This results in a high plasma density, and high ionization fraction of the sputtered vapor, which allows better control of the film growth by controlling the energy and direction of the deposition species. This is a significant advantage over conventional dc magnetron sputtering where the sputtered vapor consists mainly of neutral species. The HiPIMS discharge is now an established ionized physical vapor deposition technique, which is easily scalable and has been successfully introduced into various industrial applications. The authors give an overview of the development of the HiPIMS discharge, and the underlying mechanisms that dictate the discharge properties. First, an introduction to the magnetron sputtering discharge and its various configurations and modifications is given. Then the development and properties of the high power pulsed power supply are discussed, followed by an overview of the measured plasma parameters in the HiPIMS discharge, the electron energy and density, the ion energy, ion flux and plasma composition, and a discussion on the deposition rate. Finally, some of the models that have been developed to gain understanding of the discharge processes are reviewed, including the phenomenological material pathway model, and the ionization region model.

Comparative sequence stratigraphy and organic geochemistry of gas shales: Commonality or coincidence?

Comparison of some Paleozoic and Mesozoic gas shales has revealed a generally common sequence stratigraphy, consisting of, from the base upward: combined sequence boundary/transgressive surface of erosion (SB/TSE) upon which sits a transgressive systems tract (TST) enriched in organic matter, then a somewhat ‘cleaner gamma-ray’ highstand or regressive systems tract (HST/RST). When resolvable, this stratigraphy occurs at 2nd, 3rd, and 4th order relative sea level cyclicity, forming couplets of relatively organic-rich (TST and condensed section-CS) and organic-poor (HST/RST) strata at these time scales. A higher order sequence stratigraphy can be developed for Mesozoic shales than for Paleozoic shales owing to greater biostratigraphic age resolution of the former. The higher frequency cycles are superimposed upon lower frequency cycles, giving rise to a complex stratigraphy of several couplets of differing thickness and distribution. These documented common characteristics provide the basis for a unifying, general sequence stratigraphic model for shales which can be utilized to identify, predict and map the most productive facies within a shale stratigraphic interval.There also are several commonalities in geochemistry of gas shales. Prolific gas shales are usually >200 ft (65 m) thick, contain >3% TOC, have Hydrogen Index values >350 mg HC/g, contain Type II kerogen and have organic maturity values >1.1% Ro. Organic-rich shales typically contain minerals such as pyrite and phosphates (apatite) and show biomarker ratios (pristane/phytane, steranes distribution, C13–C20 regular isoprenoids and C18 aryl isoprenoids) indicative of anoxic conditions during source rock deposition. In high maturity areas, there is a reversal in ethane isotope abundance owing to secondary cracking of hydrocarbons; such a reversal is normally associated with best gas production. Relative hydrocarbon potential (S1 + S2/TOC) is a geochemical parameter which reflects oxygenation conditions in the depositional environment. It can be related to relative sea level fluctuations within a sequence stratigraphic context.Understanding the sequence stratigraphy of shale provides a powerful tool not only for regional-to-local stratigraphic correlations from well logs and seismic reflection records, but also for high-grading stratigraphic intervals most favorable for preservation of organic matter and gas generation and storage.

Numerical simulations of cyclic behaviour in the Parallel Ice Sheet Model (PISM)

AbstractNumerical experiments are conducted on a synthetic topography with a three-dimensional thermomechanically coupled ice-sheet model, the Parallel Ice Sheet Model (PISM). Within the model, combined stress balances are connected to evolving thermodynamics and hydrology. The sensitivity of cyclic behaviour to changes in sliding-law parameters and the climate input is studied. Multiple types of oscillations were found, with strong variations in both amplitude and frequency. A physical description is given, in which these variations and transitions from one oscillation type to another are linked to the interplay of stresses, heat transport and hydrological processes. High-frequency oscillations (period 114-169 years), which are shown to have a major impact on ice velocities and a small effect on the ice volume, are related to variations in the water distribution at the base. Low-frequency cycles (period 1000+ years), which have a major impact on both velocities and ice volume, are linked to changes in the thermal regime. Oscillation characteristics are shown to be strongly sensitive to changes in sliding-law parameters and the prescribed surface temperature and mass balance. Incorporating a surface-height dependence of the mass balance is shown to provide an additional feedback, which may induce long- period oscillations.

Comment

Comment

Tides and long-term modulations in the Caribbean Sea

The tidal signal and its long-term variation in the Caribbean Sea is analyzed on the basis of hourly records from thirteen tide gauges five of which span more than 20 years. The seven larger tidal constituents are studied, namely the fortnightly term Mf, diurnal K1, O1, and P1, and semidiurnal M2, S2 and N2. The 18.61 year nodal modulation is clearly identifiable in almost all the examined constituents of lunar origin. However, its signal in M2 is less clear while it is almost imperceptible in N2, where the 8.85 year cycle caused by the eccentricity of the Moon's orbit and the orientation of its major axis variation dominates the long-term variability. The effect of the nodal variation in the amplitude and phase lag of the various tidal constituents is in agreement (within the 95% error limits) with the theoretical gravitational estimate, with the exception of the 8.85 year cycle in N2, where larger values are found. Overall, in the Caribbean the net effect of the low frequency cycles can change the maximum tidal range from 16.5% to 23.5% in a nodal cycle. Although the Caribbean is a micro-tidal environment this still results in changes of the range of up to 8.4 cm. Significant, spatially coherent trends are found for the amplitude of S2 (2.3 to 8.8 mm/cy.

LOW-FREQUENCY OSCILLATIONS IN GLOBAL SIMULATIONS OF BLACK HOLE ACCRETION

We have identified the presence of large-scale, low-frequency dynamo cycles in a long-duration, global, magnetohydrodynamic (MHD) simulation of black hole accretion. Such cycles had been seen previously in local shearing box simulations, but we discuss their evolution over 1,500 inner disk orbits of a global pi/4 disk wedge spanning two orders of magnitude in radius and seven scale heights in elevation above/below the disk midplane. The observed cycles manifest themselves as oscillations in azimuthal magnetic field occupying a region that extends into a low-density corona several scale heights above the disk. The cycle frequencies are ten to twenty times lower than the local orbital frequency, making them potentially interesting sources of low-frequency variability when scaled to real astrophysical systems. Furthermore, power spectra derived from the full time series reveal that the cycles manifest themselves at discrete, narrow-band frequencies that often share power across broad radial ranges. We explore possible connections between these simulated cycles and observed low-frequency quasi-periodic oscillations (LFQPOs) in galactic black hole binary systems, finding that dynamo cycles have the appropriate frequencies and are located in a spatial region associated with X-ray emission in real systems. Derived observational proxies, however, fail to feature peaks with RMS amplitudes comparable to LFQPO observations, suggesting that further theoretical work and more sophisticated simulations will be required to form a complete theory of dynamo-driven LFQPOs. Nonetheless, this work clearly illustrates that global MHD dynamos exhibit quasi-periodic behavior on timescales much longer than those derived from test particle considerations.

Differential Buck DC–DC Chopper Mode Inverters With High-Frequency Link

A circuit configuration and a circuit topological family of differential buck dc-dc chopper mode inverter with high-frequency link are proposed in this paper. The circuit configuration, the topology family, the instantaneous output voltage and the capacitance current feedback control strategy, the steady principle characteristic, and the design criteria for the key circuit parameters are fully investigated in this paper. The circuit configuration is differentially composed of two identical isolated bidirectional buck dc-dc choppers with the same input and output LC filters. These two choppers generate unipolarity sinusoidal pulse width modulation voltage waveforms with positive and negative half low-frequency cycle separately. Each dc-dc chopper consists of high frequency inverter, high frequency transformer, and high frequency rectifier. The circuit topological family includes six circuit topologies, namely, one-transistor forward mode, push-pull mode, push-pull forward mode, two-transistor forward mode, half-bridge mode, and full-bridge mode. Taking one-transistor mode circuit topology as example, the prototype is designed and implemented. The results from the theoretical analysis and principle test indicate that the inverters have advantages of high frequency galvanic isolation, simple topology, bidirectional power flow, single-stage power conversion, high conversion efficiency, high-quality output voltage waveform, and strong adaptability to various loads.

In vitro measurements of respiratory mechanics during HFPV using a mechanical lung model

High-frequency percussive ventilation (HFPV) may be defined as flow-regulated time-cycled ventilation that creates controlled pressure and delivers a series of high-frequency subtidal volumes in combination with low-frequency breathing cycles. In recent years, the usefulness of HFPV has been clinically assessed as an alternative to conventional mechanical ventilation. In the clinical practice, HFPV is not an intuitive ventilatory modality and the absence of real-time delivered volume monitoring produces disaffection among the physicians. For this purpose, it would be useful to develop a monitor able to realize a complete online characterization of high-frequency percussive ventilators and to identify the best combination of their parameters according to the specific pathological situation. This paper describes an innovative acquisition and elaboration system based on the use of new generation pressure transducers presenting high sensitivity and fast response. Such a system is compact and inexpensive, and it allows the user to carry out a more correct online characterization of high-frequency percussive ventilators. This output allowed best real-time ventilatory setting, minimizing the potential baro-volutrauma hazard.

Cyclic patterns of malaria incidence in Burundi

Abstract Best available descriptions of malaria incidence and mortality dynamics are important to improve and evaluate the implementation of programs to monitor (e.g., remote sensing) and control disease, especially in endemic zones. High-frequency (e.g., semi-annual and seasonal) cycles in malaria incidence have been observed in various countries and they coincide with cycles in the natural environment (e.g., temperature, heliogeophysical activity, etc.). However, neither trend nor cyclical oscillations beyond a 6-month (0.5-year) period for this vector-borne disease were reported in a recent analysis on monthly notifications in Burundi for the years 1997–2003. Since the examination of graphical plots indicated an eventual existence of trans-year (multiannual) variations, we further analyzed the same data in more detail. Here we explore whether low-frequency cycles (beyond seasonality) might exist (e.g., trans-year cycles with periods of 13–24 months or longer). Monthly incidence rate per 100 inhabitants from the Province of Karuzi, Burundi, over the years 1997–2003 was analysed. The exploration of underlying chronomes (time structures) was done by linear and non-linear parametric regression models, autocorrelation, spectral analysis (e.g., fast Fourier transforms), periodogram regression analysis (PRA) and wavelet transform (WT). By using a periodogram regression analysis, we describe a multicomponent cyclic chronome with periods T>12 months (19 and 86 months, all at P<0.05). Notably, the strongest cyclic pattern in the periodogram of the detrended malaria rates (whereas the peak was suppressed and beyond the semi-annual cycle of 6 months) was ≈1.5–1.6 years (T=19.0 months, R=0.32). A dynamic pattern of “shortening” of the length (period) of the cycles was observed during the pre-epidemic interval (from 8–9 to 5–6 months and from 20–22 to 16–18 months in years 1997–2000) that can be used to anticipate a forthcoming incidence increase and epidemic levels of malaria at a regional level. Indeed, these cycles in malaria incidence correspond to cyclic components of heliogeophysical activity (HGA) such as the sunspot cycle impulses of 0.5–2.0 years as well as the quasi-biennial solar magnetic cycle of 1.5–2.5 years and further, detailed analyses are warranted to investigate such relationships. A multicomponent dynamic cyclical pattern of malaria incidence variations in Burundi (1997–2003) exists thus allowing further, more specific analyses and modelling as well as correlations with similar environmental cycles to be explored. These results might also contribute to better estimates for forecasting, prevention and understanding of malaria dynamics and aetiology.

Interpretation of crank torque during an all-out cycling exercise at high pedal rate

The use of cycle ergometers with strain gauges bonded on to the cranks enables the evaluation of strength, velocity and power. However, the torque measured at the end of downstroke is higher at high velocity than at medium velocity in contradiction with the force–velocity relationship. Kinematic data were collected with a camera during sprints on a Lode ergometer with strain gauges. Leg mechanical energy (E Leg) and its derivative (dE Leg/dt) were calculated from the sum of the kinetic and potential energies. The opposition of P ext (output at crank level) and dE Leg/dt before bottom dead centre suggested a transformation of E Leg into external work, explaining the higher torque at the end of downstroke at peak velocity. Another explanation is that the leg muscles worked on different parts of their torque–angle relationships as the phase between knee and ankle angles was different at low and high cycling frequencies. Musculo-skeletal net power output (algebraic sum of P ext and dE Leg/dt) indicated that musculo-skeletal structures participated in the upward movement, whereas P ext was negative.

Scaling Characteristics of Precipitation Data over Texas

The question addressed in this study was: do the number and magnitude of dry and wet spells occur in a scale invariant manner in the state of Texas or not? To answer this question, a large set of monthly precipitation data from 75 grid points spread across Texas was employed to investigate the spatial variability in the scaling properties of number and magnitude of dry and wet spells. No coherent regional differences were found. Using a power-law analysis, time-scale properties of dry and wet spells were examined, and power-law coefficients were related to the various truncation levels. A linear relationship was found between fractal dimensions of the numbers of dry and wet spells, whereas power-law coefficients of the magnitude remained constant for all truncation levels. Also, significant low-frequency patterns of precipitation were found when the wavelet transform was used. Generally, interannual cycles were found to be significant for the state of Texas. Low-frequency cycles had no distinguishable impacts on the grid point precipitation values where significant deviations from the power law occurred.

Cyclic Turbulent Instabilities in a Thin Slab Mold. Part I: Physical Model

A water-physical model of a funnel-type thin slab mold fed by a two-port submerged entry nozzle (SEN) was employed to characterize the flow of liquid steel using dye tracer, particle image velocimetry, and video recording experiments. The overflow fluid flow pattern was the typical double-roll flow. A cyclic, low-frequency (≈0.01 s−1), and energetic flow distortion of a short-lived (8 to 12 seconds) inducing high meniscus oscillation was identified. Its intensity grew with high casting speeds (5 and 7 m/min) and with a shallow SEN immersion position (200 mm from the meniscus level to the SEN tip). This distortion originated from the apparent existence of vortex flows located below the two discharging jets, which are formed by shear stresses in their ends that act on the surrounding fluid. These vortexes exert momentum transfer upward through a cascade mechanism from the lowest part of the discharging jets until reaching the region close to the SEN tip. This cascade momentum transfer widens the separation of both jets, enhancing the fluid velocities of the upper rolls, which promotes a high-amplitude standing wave. It is inferred, based on the experimental results, that this flow distortion originated from an instantaneous unbalance of the turbulent kinetic energy in the discharging jets. The negative production of kinetic energy is ascribed as the source of this unbalance, which is compensated by a higher contribution of the turbulent kinetic energy through mean convection and turbulent transport mechanisms manifested through higher velocities. After the restoration of the energy balance, the system yields a stable meniscus to repeat the low-frequency cycle.

Pulse electrodeposition of Ni–P matrix composite coatings reinforced by SiC particles

Ni–P/SiC composite coatings were produced under both direct and extended pulse current conditions from an additive-free modified Watts type bath at various hydrodynamic conditions. Structural analysis revealed an amorphous phase of Ni–P matrix for the majority of coatings, except for those prepared under low duty cycle and high frequency pulses that exhibited mainly the crystalline Ni 12P 5 compound. The practice of pulse plating regime led to composite coatings with higher incorporation rate of SiC particles (up to 22 wt.%) and microhardness values (up to 7.2 GPa) than those produced under direct current conditions. It has been revealed that increased micron-SiC codeposition percentage resulted in decrease of P content in the amorphous matrix and increase of the deposits’ hardness values. After annealing at 400 °C the amorphous matrix was crystallized to phases of Ni, Ni 2P, and Ni 3P, the formation of which depends on the P content. As-plated deposits exhibiting Ni 12P 5 phase preserved this crystalline structure after thermal treatment. Annealed coatings exhibited almost double values of microhardness relative to those of the as-deposited coatings.

The high power impulse magnetron sputtering discharge as an ionized physical vapor deposition tool

Various magnetron sputtering tools have been developed that provide a high degree of ionization of the sputtered vapor referred to as ionized physical vapor deposition (IPVD). The ions can be controlled with respect to energy and direction as they arrive to the growth surface which allows for increased control of film properties during growth. Here, the design parameters for IPVD systems are briefly reviewed. The first sputter based IPVD systems utilized a secondary plasma source between the target and the substrate in order to generate a highly ionized sputtered vapor. High power impulse magnetron sputtering (HiPIMS) is a recent sputtering technique that utilizes IPVD where a high density plasma is created by applying high power pulses at low frequency and low duty cycle to a magnetron sputtering device. A summary of the key experimental findings for the HiPIMS discharge is given. Measurements of the temporal and spatial behavior of the plasma parameters indicate electron density peak, that expands from the target with a fixed velocity. The discharge develops from an inert sputtering gas dominated to a sputtered vapor dominated during the pulse. The high electron density results in a high degree of ionization of the deposition material.

Tectonic and eustatic control on a mixed siliciclastic–carbonate platform during the Late Oxfordian–Kimmeridgian (La Rochelle platform, western France)

Boreal and Tethyan realms of Western Europe present significant sedimentological, paleontological, and stratigraphic differences. The purpose of this study is to constrain regional versus global controls on the dynamics of a sedimentary system located at the interface of these two realms in order to better understand the origin of their differences. Detailed sedimentological, palynofacies and calcareous nannofossil analyses were performed on two sections from the La Rochelle platform (western France). The Pas section includes part of the Late Oxfordian and Early Kimmeridgian, and the Rocher d'Yves section is assigned to the Late Kimmeridgian. They correspond to monotonous marl–argillaceous limestone alternations. Limestones are essentially mudstones with echinoderms, bivalves and foraminifera that suggest low-energy, open-marine conditions. Highly bioclastic and/or peloidal deposits occur commonly, and show wackestones to wacke-pack-grainstones textures. These deposits indicate frequent high-energy events, and are interpreted as storm deposits. Marls dominate in the most proximal depositional environments, while calcareous deposits are more important in more distal environments. The Rocher d'Yves section is globally more marly than the Pas section, suggesting a more proximal setting. Palynofacies are dominated by woody particles, suggesting shallow-water, proximal depositional environments. Calcareous nannofossils are ascidian spicules, coccoliths, and schizospheres. Watznaueria britannica dominate calcareous nannofossil assemblages in the Pas section. The Rocher d'Yves assemblages are quasi-exclusively composed of Cyclagelosphaera margerelii, and indicate more proximal paleoenvironments than those of the Pas section. Different orders of depositional sequences are defined, with sequence boundaries corresponding to the most rapid relative sea-level falls. They are hierarchically stacked, and correlate, on the basis of ammonite zones, with the sequences of contemporaneous sections from Tethyan and boreal realms. The stacking pattern of these sequences suggests an orbital control on sedimentation. Small-, medium- and large-scale sequences correspond to precession (20 ky) cycles and to 100 ky and 400 ky eccentricity cycles, respectively. The elementary sequences have durations shorter than 20 ky. The Kimmeridgian was a period of global sea-level rise that ended in the Late Kimmeridgian. More proximal depositional environments in the Rocher d'Yves section (Late Kimmeridgian) than in the Pas section (Early Kimmeridgian) imply a progradation of the La Rochelle platform during the Kimmeridgian. This progradation resulted from a slowdown of the subsidence in the Aquitaine Basin during the Kimmeridgian, corresponding to the first steps of Atlantic Ocean opening. High-frequency cycles on the La Rochelle platform formed in sync with Milankovitch orbital cycles, while tectonics controlled the formation of the low-frequency cycles.