Recent organic-rich deep sedimentation off Southwest Africa: keys for understanding the deep offshore petroleum source-rock distribution.
The Atlantic South-eastern margin is influenced by the presence of broad upwelling cells associated with the Benguela Current System. Sedimentary records of cores taken from 35°S to 10°S between 1000 to 4000m depth show extraordinarily high organic carbon (OM) contents for this deep and oxygenated environment. Thus this margin is different from classically known models of preservation in deep setting by the bottom water anoxia or redepositional processes Temporal variability of organic carbon observed along this margin from the north of Walvis ridge to South Africa, shows an enrichment in total organic carbon (TOC) during the Last Glacial Maximum (20kyrs) with respect to Holocene Climatic Optimum(8kyrs). It is the same for biogenic silica, mainly related to diatoms input, which follows the same climatic logic. Carbonate contents are negatively correlated with TOC and biogenic silica. The Lüderitz upwelling cell is presently the most productive area of the Benguela Current System, during at least 280 kyrs, and abundant OM accumulates on the adjacent slope sediments even at great water depth. Results indicate that OM is more oxidized at 3606 m water depth than on the upper slope sediments (1029 m) although petroleum quality of OM throughout the deep-water core remains surprisingly high for hemipelagic deep-sea sediments (HI = 200 to 400 mg HC/g TOC). The petroleum quality of OM accumulated on the upper slope is consistently high: HI average 450 mg HC/g TOC. Organic sedimentation in front of Lüderitz is modellised with the software DIONISOS (IFP), in the aim of developping a 3D stratigraphic model and predicting petroleum quality and quantity of organic matter along the margin. The first step in modelling the deep organic matter sedimentation is to decipher between the main controlling factors the key parameters to be introduce in the model DIONISOS. This imply to define simple laws for productivity, degradation, advection of sediment, etc. Rock Eval parameters shows that organic sedimentation along the margin can be considered as an important source-rock sedimentation. Source-Rock Potential Index (SPI) calculations are in agreement with a maximum of a potential hydrocarbon formation in front of Lüderitz, from shallow depth (500m), to deeper depth (2000m). We believe that the probability that such organic-rich facies occurred in the past in equivalent oceanographic settings at the edge of large oceanic basins should be carefully considered in deep offshore exploration.
(21/02/2026)
MNHN, UPMC, CNRS, ISTO, INSU - CNRS, UO, CNRS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, IFPEN, LMMNHN, MNHN, CNRS
MD 140 / PRIVILEGE cruise, RV Marion Dufresne
The French acronym MD 140/PRIVILEGE stands for integrated program valorised by IFREMER, LSCE, EPOC in geology. The survey covers 3 programs: the PRISMA, CADICOR, and PRIMAROSA sud 1. The objectives are: High resolution study of sediments and carbonate mounds (deep coral) off Morocco (CADICOR project), slides of submarine slopes related to seisms on the Algerian margin (PRISMA project), edification of deep sedimentary bodies linked to the circulation of Mediterranean water in the gulf of Cadiz and late Quaternary paleoclimatic variability, Ocean-Continent relationship (PRIMAROSA project). The related programs are Ifremer's margin program, IMAGES, GDR Marge, PNEDC, ECLIPSE Eurostrataform, Geomound, etc.
(21/02/2026)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, IFREMER, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA, PALEOCEAN, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA
Relations entre qualité du substrat, flux de matières et activités humaines. Connaissance pour la gestion des ressources en eau de la Région Aquitaine
Les résultats de ce travail de recherche, confirment une fois de plus l'absence de déterminisme apparent entre qualité du substrat et occupation des sols. Ils montrent qu'il n'y a pas de variables prépondérantes ou explicatives de facteurs sociaux ou physiques qui soient responsables des variations affectant les milieux étudiés. Cependant, les analyses régressives des rapports entre homme et milieu montrent les liens étroits entre habitat et types de sol. L'action humaine a des effets sur la couverture végétale, sur les sols et sur l'hydraulique qui avec le climat et la topographie constituent les principaux facteurs d'érosion.
(21/02/2026)
ITEM, UPPA, UPPA, IPRA, UPPA, CNRS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Recent sedimentation of organic matter along the SE Atlantic Margin : A key for understanding deep offshore petroleum source rocks.
Classical views for the deposition of organic-rich sediments in deep-sea environments invoke two principal types of oceanographic and sedimentologic settings. The first is confined basins in which stratified oxygen depleted waters lead to anoxic preservation of organic matter in the water column and in underlying sediments (Demaison and Moore, 1980). The second is an open ocean setting where the episodic mass transfers due to slope sediment instability lead to the rapid burial of outer-shelf and upper slope-derived organic matter and its consequent preservation due to limited oxic or anoxic degradation (Stow, 1987). Other studies have shown, however, that organic matter in modern deep-sea sediments may occur in high amounts where oxygen is not significantly depleted (Pedersen and Calvert, 1990). Recent studies have demonstrated that highly biological productive areas, such as the upwelling zones associated to the Benguela Current in S-E Atlantic, may deliver sufficient quantity of organic material to (1) outbalance the degradative capacity of the water column and (2) sustain the formation of organic-rich sediments even in deep and oxygenated conditions (Bertrand et al., 2003). It appears that the S-E Atlantic margins provide a good example for revisiting the sedimentology of organic matter in deep water environments in the frame of the GDR Marges Continentales. This may have important implications for a better understanding of the distribution of ancient source rocks in deep offshore petroleum systems (Huc et al., 2001; Bertrand et al., 2003).
(pp. 6p., 21/02/2026)
MNHN, UPMC, CNRS, ISTO, INSU - CNRS, UO, CNRS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, IFPEN, LMMNHN, MNHN, CNRS, G2R, UHP, INPL, CREGU, CNRS
Roller modelling in the context of undertow prediction
In this paper we investigate the energy-based roller equations previously published by Stive and De Vriend (1994) and Dally and Brown (1995). Although these models differ by a factor of 2 in one of their terms, the same parameter values are commonly used to solve them. Our aim is to elucidate these discrepancies and to explore the physical adequacy of the roller models by using an inverse modelling technique based on undertow measurements. Comparison with Cox (1995) experimental data on regular waves propagating on a planar beach shows that a realistic contribution of potential energy in the roller equation should be included.
(pp. 318-330, 21/02/2026)
LEGI, UJF, Grenoble INP, CNRS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Tracing the source of Upper Palaeolithic shell beads by strontium isotope dating
While the identification of the source of shells used as personal ornaments is crucial for determining home range and exchange networks of prehistoric hunter-gatherers, it is often difficult to identify the coastal versus fossil origin of the shells as most genera used as beads were available both at beaches and fossil outcrops. Here we present the first application of 87Sr/86Sr isotope dating to identify the origin of Upper Palaeolithic shell beads. We analysed four out of a collection of one thousand Dentalium shells associated to the La Madeleine child burial dated to 10; 190G100 BP and one Dentalium from the occupation layers of this site. 87Sr/86Sr ratios indicate that shells were collected by Late Upper Palaeolithic beadworkers on far away beaches rather than at nearer Miocene outcrops. This may be due to the narrowness of Miocene Dentalium shells, incompatible with the size of bone needles used to sew these shell beads on clothes.
(Journal of Archaeological Science. vol. 31, n° 0305-4403, pp. 1481-1488, 21/02/2026)
ArScAn, UP1, UP8, UPN, MCC, CNRS, PACEA, UB, CNRS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
A stationary Mediterranean forest in southweastern Iberia during OIS 3 ? A reply to Carrion.
(Quaternary Science Reviews. vol. 23, n° 0277-3791, pp. 1217-1224., 21/02/2026)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, PACEA, UB, CNRS
Environmental impact of early Basque mining and smelting recorded in a high ash minerogenic peat deposit
More than four metres of core, covering almost 5000 years of deposition, were collected in a high ash minerogenic peat deposit located in the High Aldudes valley (Basque country), an area well known for its mineral abundance, exploited from Roman Times at least.Although minerogenic peatlands are not generally considered as the best archives to reconstruct past atmospheric metal deposition history, lead isotopic geochemistry demonstrates the integrity of the Pb record at least within the three upper meters; that is to say over the last four millennia.Zn, Cd and Cumay have been widely redistributed either by biological cycling, advective groundwater movements, or diffusional processes.Anthr opogenic lead input phases are clearly pinpointed by positive shifts in PbySc ratios with concomitant sharp drops in 206Pby207Pb ratios.They are often accompanied by significant declines in tree taxa, interpreted as increasing demand for wood to supply energy for local mining andyor metallurgical operations.Periods of mining andyor smelting activity are identified during Antiquity and Modern Times, and are also confirmed by textual and field evidence.Inputs from the Rio Tinto (Southern Spain), often invoked as a major lead contributor to the European atmosphere during Roman Times, were not detected here.This remote source was probably masked by local inputs. Other mining andyor smelting phases, only suspected by archaeologists, are here identified as early as the Bronze Age.Although the durations of these phases are possibly overestimated because of detrital inputs consequent to the release of lead from polluted soils over a long period of time after major pollutant inputs, the periods at which pollution peaks occur are in good agreement with archaeological knowledge and palaeo-botanical data.Thecombination of geochemical and palaeo-botanical techniques with field archaeology, therefore provides a powerful tool in studying the interaction of early human societies with their environment, as regards early mining and smelting.
(Science of the Total Environment, n° 0048-9697, pp. pp. 197-214, 21/02/2026)
GéoSol, INRA, UB, LCE, CNRS, UFC, UBFC, Inrap, LA, EHESS, UT2J, Comue de Toulouse, UT3, Comue de Toulouse, CNRS, UB, CNRS, UNIGE, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Holocene climate in the Atlantic sector of the Southern Ocean: Controlled by insolation or oceanic circulation?
Figure 1. Locality of TN057-17 site and other sites with data presented here. 1-TN057-13PC4 (Hodell et al., 2001). 2-Block Lake, South Georgia (Rosqvist and Schubert, 2003). 3-GeoB3313-1 (Lamy et al., 2002). 4-Ocean Drilling Program Leg 178, Site 1098C (Do-mack et al., 2001). Sites 5-15 are ice cores from Masson et al. (2000), and sites 5-7 are Ross Sea sector cores: 5-Byrd Dome; 6-Taylor Dome; 7-Dominion Range; 8-Plateau Remote; 9-D47; 10-KM105. Sites 11-15 are East Antarctic sector cores: 11-Dome B; 12-Komsomolskaya; 13-Vostok; 14-Dome C; 15-Law Dome. Stars mark records with positive correlation to late Holocene TN057-17 sea-surface temperature. Circles are sites with negative correlation to same. Winter sea-ice extent and Antarctic Polar Front from Orsi et al. (1995) and L.H. Burckle (2001, personal commun.). ABSTRACT The Holocene climate of the Southern Ocean is not well understood , mainly because of the lack of high-resolution reconstructions of ocean surface properties. Here we present a 12,500-yr-long, decadal-scale record of Holocene sea-surface temperatures and sea-ice presence from the Polar Front of the East Atlantic Southern Ocean. The record shows gradual climate change, with no abrupt Neoglacial cooling, and an unprecedented late Holocene warming. The dominant forcing factor appears to be precessional insolation; Northern Hemisphere summer insolation correlates to at least the early to middle Holocene climate trend. Spectral analysis reveals centennial-scale cyclic climate changes with periods of 1220, 1070, 400, and 150 yr. The record shows good correlation to East Antarctic ice cores and to climate records from South Georgia and Bunger Oasis. However, the record shows out-of-phase behavior with regard to climate records from the western Antarctic Peninsula and the Peru-Chile Current; such behavior hints at a climatic divide through Patagonia, the Drake Passage, and between West and East Antarctica.
(Geology. vol. 32, n° 0091-7613, pp. 317, 21/02/2026)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Evolution and relationship between 3 dissolved gases (oxygen, methane, and carbon dioxide) over a 10-year period (1994-2003) in a river downstream of a new intertropical dam
(21/02/2026)
EDF R&D, EDF [E.D.F.], EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, LAERO, IRD, UT3, Comue de Toulouse, INSU - CNRS, CNRS, CNRM, INSU - CNRS, CNRS, Comue de Toulouse