Orbital calibration of the Early Kimmeridgian (southeastern France): implications for geochronology and sequence stratigraphy

Classic stratigraphic methods rarely provide high‐resolution correlations between intrabasinal sedimentary sequences, which are important to understand the origin of sedimentation process and its environmental change. In this study, we investigate high‐resolution cyclostratigraphic correlation from magnetic susceptibility in two Early Kimmeridgian pelagic marl‐limestone successions, at La Méouge and Châteauneuf‐d'Oze, southeastern France. Spectral analysis reveals the complete suite of orbital frequencies (precession, obliquity, and eccentricity) with the marl‐limestone couplets being primarily precession‐driven. Frequencies detected by the spectral analysis are similar between the sections, but their relative amplitudes are somewhat different, linked to the palaeoenvironmental position and the completeness of the sections. High‐resolution correlation reveals two significant hiatuses at Châteauneuf‐d’Oze. Early Kimmeridgian Platynota, Hypselocyclum, and Divisum ammonite zones were orbitally calibrated for an ultra‐high resolution assessment of geological time. Finally, strong 405‐kyr eccentricity cycles are recorded as third‐order depositional sequences.     

A data mining based approach to predict spatiotemporal changes in satellite images

The interpretation of remotely sensed images in a spatiotemporal context is becoming a valuable research topic. However, the constant growth of data volume in remote sensing imaging makes reaching conclusions based on collected data a challenging task. Recently, data mining appears to be a promising research field leading to several interesting discoveries in various areas such as marketing, surveillance, fraud detection and scientific discovery. By integrating data mining and image interpretation techniques, accurate and relevant information (i.e. functional relation between observed parcels and a set of informational contents) can be automatically elicited.     

Quantification of water exchange between a hill reservoir and groundwater using hydrological and isotopic modelling (El Gouazine, Tunisia)

Stable isotope compositions (¹⁸O and ²H), determined for underground and surface waters from the watershed of a hill reservoir and downstream from the reservoir, suggest that (i) the reservoir water, which is more or less evaporated, represents a mixture between surface waters (rainfall, runoff) and the upstream alluvial groundwater meteoric in origin; (ii) the downstream alluvial groundwater have a stable isotope composition of a previously infiltrated reservoir water. The ¹⁸O isotope enrichment modelling of the mixed reservoir water shows that an input flux of 50 m³ day⁻¹ is balanced by an output flux of 300 m³ day⁻¹ when the reservoir water level is above 4.5 m, and by an output flux of 170 m³ day⁻¹ when water levels are lower. The contribution of hill reservoirs to local groundwater movements must be considered in any regional scale hydrological investigations of areas that contain hill reservoirs. To cite this article: O. Grünberger et al., C. R. Geoscience 336 (2004).

Résumé

La composition isotopique (¹⁸O et ²H) d'eaux souterraines et superficielles, déterminée pour le bassin versant d'une retenue collinaire et sa partie aval, suggère (i) que l'eau de la retenue, qui est plus ou moins évaporée, représente un mélange entre les eaux de surface (pluie, ruissellement) et la nappe alluviale amont d'origine météorique et (ii) que la nappe alluviale aval a la composition isotopique d'une eau de la retenue anciennement infiltrée. La modélisation de l'enrichissement en isotope ¹⁸O pour l'eau mélangée de la retenue montre qu'un flux entrant de 50 m³ j⁻¹ est compensé par un flux sortant de 300 m³ j⁻¹, lorsque le niveau d'eau de la retenue est supérieur à 4,5 m, et par un flux sortant de 170 m³ j⁻¹ en dessous. La contribution des lacs collinaires aux écoulements souterrains doit être prise en compte pour de futures études hydrologiques à l'échelle régionale. Pour citer cet article : O. Grünberger et al., C. R. Geoscience 336 (2004).     

High-resolution cyclostratigraphic analysis from magnetic susceptibility in a Lower Kimmeridgian (Upper Jurassic) marl–limestone succession (La Méouge,Vocontian Basin,France)

High-resolution magnetic susceptibility (MS) analysis was carried out on a Lower Kimmeridgian alternating marl–limestone succession of pelagic origin that crops out at La Méouge (Vocontian Basin, southeastern France). The aim of the study was to characterize the strong, dm-scale sedimentary cyclicity of the succession at a very high resolution, and to analyze the cycles for evidence of astronomical forcing. From marl to limestone, MS varies progressively and closely tracks the highest frequency cyclicity corresponding to the basic marl–limestone couplets. Long-term wavelength cycling modulates the high-frequency cyclicity (couplets), and appears to be controlled by clay content. Spectral analysis of the MS record reveals the presence of the complete suite of orbital frequencies in the precession, obliquity, and eccentricity (95–128 ka and 405 ka) bands with very high amplitude of the precession index cycles originating from dm-scale couplets. 405 ka-eccentricity cycles are very pronounced in the MS maxima of the marl members of the couplets, suggesting eccentricity-driven detrital input to the basin. 405 ka-orbital tuning of the MS maxima further sharpens all of the orbital frequencies present in the succession. These results are similar to those of previous studies at La Méouge that used carbonate content observed in field. Our results are also in accordance with cyclostratigraphic studies in Spain and Canada that report dominant precession index forcing. By contrast, in the Kimmeridge Clay (Dorset, UK), obliquity forcing dominates cyclic sedimentation, with weaker influence from the precession index. Ammonite zone duration estimates are made by counting the interpreted precession cycles, and provide an ultra-high resolution assessment of geologic time. In sum, this study demonstrates the power of the MS as a proxy in characterizing the high-resolution cyclostratigraphy of Mesozoic sections, particularly in alternating marl–limestone successions, and for high-resolution correlation and astronomical calibration of the geologic time scale.     

Milankovitch and sub‐Milankovitch forcing of the Oxfordian (Late Jurassic) Terres Noires Formation (SE France) and global implications

High‐resolution analysis (2277 samples) of magnetic susceptibility (MS) was performed on ～700‐m‐thick Early–Middle Oxfordian marine marls of the Terres Noires Formation, SE France. MS variations within these sediments record sub‐Milankovitch to Milankovitch frequencies with long‐term eccentricity (405 kyr and ～2 Myr) being the most prominent. The 405 kyr cycle was used as a high‐resolution geochronometer for astronomical calibration of this poorly constrained interval of Late Jurassic time. The estimated duration of this Early–Middle Oxfordian interval concurs with the current International Geologic Time Scale GTS2004 (～4 Myr), but the estimated durations of the corresponding ammonite zones are notably different. The calibration improves the resolution and accuracy of the M‐sequence magnetic anomaly block model that was previously used to establish the Oxfordian time scale. Additionally, the 405 kyr cyclicity is linked to third‐order sea‐level depositional sequences observed for Early–Middle Oxfordian time. Strong ～2 Myr cycles are consistent with long‐term eccentricity modulation predicted for the Late Jurassic. These cycles do not match second‐order sequences that have been documented for European basins; this raises questions about the definition and hierarchy of depositional sequences in the Mesozoic eustatic chart. Our results require substantial revisions to the chart, which is frequently used as a reference for the correlation of widely separated palaeogeographic domains. Finally, a long‐term trend in the MS data reflects a progressive carbonate enrichment of the marls expressing an Early Oxfordian global cooling followed gradually by a warming in the Middle Oxfordian. This trend also records a major transgressive interval likely peaking at the Transversarium ammonite zone of the Middle Oxfordian.