Jean-Claude Aloïsi

Modern pollen deposition in the Rhone delta area (Lagoonal and marine sediments), France

The investigation identifies the two main types of pollen sedimentation in the Rhone delta, and presents synthetic pollen spectra in terms of ecological groups in order to predict the pollen source areas. Two different domains are studied: the lagoonal zone occupied by the Vaccares where atmospheric pollen imput predominates and the Rhone mouth area (river delta and prodelta) where fluvial pollen influx prevails. The reflection of local and regional vegetation in the surface sediment pollen spectra is carefully discussed with reference to atmospheric pollen records and to water sample analyses. This work is designed to help the interpretation of past pollen spectra and paleovegetation and through them also paleoclimate reconstructions.

Present-day rhythmic deposition in the grand Rhone prodelta (NW Mediterranean) according to high-resolution pollen analyses

Abstract A high-resolution pollen study (136 samples) has been performed on the KTR05 core (738 cm long) located in the modern Grand Rhône prodelta. The objectives were (1) to evaluate the palynological and sedimentological record quality of a prodelta in comparison with fluvial inputs (2) and to quantify lost sediment (resuspensions) in this area. The core covers more than the last thirty years. By comparison with the modern pollen rain both in the Rhône delta and in the mid-drainage basin (Lyon), a seasonal forcing in pollen deposition has been demonstrated. Monthly pollen successions can be evidenced in a well preserved sequence, providing an estimate of the true sedimentation rate (60 cm.yr−1). Importance of disturbed or incomplete sequences suggests that most of the sediment first deposited in the prodelta (around ⅔) has been resuspended. Sedimentological and palynological data record not only seasonal but fluvial impact. The progressive shift of the prodelta has been evidenced firstly with sedimentology and secondly with palynology. Despite high fluvial impact, pollen grains in the KTR05 core are representatives of the vegetation of the Rhône drainage basin. The apparent homogeneity of the pollen spectra evidences the high reliability of palynology applied on prodeltaic area, at least in a microtidal environment.

The Ebro and the Rhone deep-sea fans: First comparative study☆

Abstract Bathymetric and continuous-seismic profiles enable us to define the main morphological and structural outlines of the Ebro and Rhone deep-sea fans. Despite great differences of morphology and volume, these two fans are characterized by a similar structure with a 500 milliseconds thick series of superposed lenticular acoustic units lying above more homogeneous sediments. These units are tentatively attributed to channel-infilling, associated with overbank deposits shifting through time. Nevertheless, some of them may represent large sedimentary slides, especially off the Ebro river.

Evidence for an early land use in the Rhône delta (Mediterranean France) as recorded by late Holocene fluvial paleoenvironments (1640-100 BC)

Abstract The overall objective of this paper is to describe the late Holocene (1640–100 BC) sedimentary and biological evolution of the Rhône–delta–plain, to interpret the sedimentary facies and palynofacies as the result of the effects of fluvial dynamic fluctuations and relative sea level change and to evaluate the paleohydrological constraints in the development of the land use and settlements of the Camargue. Focus is made on the upper part of VIII core drilled on NE of the Vaccares lagoon. By combining sedimentology, palynology, magnetic susceptibility and archeological data, this study allowed to identify the superposition of three types of paleo-environments (marsh, fluvial floodplain, levee/crevasse splay). This sequence indicates a gradual extension of fluvial environments between the end of the second millennium BC and the 1st century BC. The variability of fluvial dynamic is evident during this period with important flood events which contrast with periods of low flow. Pollen record can be a good marker of the fluvial dynamic variability. The expression of the riparian tree pollen grains in the coarser floodplain deposits could correspond to increased fluvial influence and probably to erosion of riverbank during flood events. The local plants are associated to the low energy sedimentary environments. Focuses are made on the relations between the evolution of the environment and land use. The development of the cereal culture in the floodplain of the Rhone delta has been demonstrated between 1640–1410 and 100 BC. The last alluviation of the Rhone perturbs the research of the archaeological sites in the central part of the delta but the existence of the rural villages from the first part of the first millennium BC is highly possible.

Sedimentary Processes in Mediterranean Deltas and Shelves

Recent studies enable us to compare the geographic and physiographic settings, general structural configuration, emerged delta evolution, hydrodynamic regime, suspended transport processes, and geometry of recent shelf deposits seaward of the four major Mediterranean deltas: the Rhone, Ebro, Po, and Nile. This synthesis indicates that some features of the deltas and adjacent continental shelves appear to have remained constant during the last high sea-level stand (Holocene) around the Mediterranean. These include prismatic geometry of Holocene deposits; nearshore smectite-rich prodelta muds; multilayer system of suspended sediments on the continental shelf, with a bottom nepheloid layer; and longitudinal bottom and surface currents. Sedimentation depends on the balance between climatic-eustatic changes, river discharge, and current dispersal.

Quaternary sedimentary deposits on the Cameroon shelf: Characterization of facies and late quaternary shorelines

Abstract Several high-resolution (SPARKER) seismic-reflection surveys, associated with 450 dredgings and 75 Kullenberg core samplings, allowed the definition of the main Quaternary sedimentary bodies of the Cameroon shelf. The distribution of the Holocene mantle is very uneven: its thickness reaches 40 m at the northern end of the shelf where there are sandy stratified deposits in the lower part and a High System Tract in the upper part. These deposits cross obliquely offshore and towards the south where the Holocene is either absent or localized as backfill in low-level ravines. This distribution is controlled by the Sanaga flow deflected northwards by the predominantly SW swell and by the Niger River flow driven southwards by the Guinean current. The sensu lato Pleistocene mantle is substantial in the north where fluvio-deltaic sands issued from the Nigerian complex. Southward coarse sands from the Sanaga-Nyong complex accumulate in progradient structures. In the southern part of the plateau, the Cenozoic-Mesozoic and Pre-Cambrian substratum at the outcrop is indented by extensive unevenness defining asedimentary shoals and Pleistocene-silted depressions. These depressions present paralic littoral successions towards the coast and circa-littoral to littoral successions seawards. As a result of the last eustatic movements, the roof of these successions has been planed off and has been more and less intensely modified. In some cases it is possible to date the last oscillations of the shoreline, using 14 C.

Detailed morphology, structure and main growth pattern of the Rhône deep-sea fan

Abstract A sea-beam survey of the Rhone deep-sea fan and its vector canyon shows unexpected morphological features such as striking similarities with continental landforms encountered especially in alluvial plain areas or desertic countries. The structure of this fan, as shown by continuous seismic profiles, results from the stacking up of numerous lenticular acoustic units displaying specific seismic characters. It is suggested that the building of the fan began as early as the lower Pliocene with a growth pattern tightly associated with climatic fluctuations.

Evidence for an early land use in the Rhône delta (Mediterranean France) as recorded by late Holocene fluvial paleoenvironments (1640–100 BC)Preuves d’une mise en culture précoce de la plaine deltaïque du Rhône (France méditerranéenne) enregistrées par les séquences fluviales de l’Holocène récent (1640–100 av. J.-C.).

Abstract The overall objective of this paper is to describe the late Holocene (1640–100 BC) sedimentary and biological evolution of the Rhone–delta–plain, to interpret the sedimentary facies and palynofacies as the result of the effects of fluvial dynamic fluctuations and relative sea level change and to evaluate the paleohydrological constraints in the development of the land use and settlements of the Camargue. Focus is made on the upper part of VIII core drilled on NE of the Vaccares lagoon. By combining sedimentology, palynology, magnetic susceptibility and archeological data, this study allowed to identify the superposition of three types of paleo-environments (marsh, fluvial floodplain, levee/crevasse splay). This sequence indicates a gradual extension of fluvial environments between the end of the second millennium BC and the 1st century BC. The variability of fluvial dynamic is evident during this period with important flood events which contrast with periods of low flow. Pollen record can be a good marker of the fluvial dynamic variability. The expression of the riparian tree pollen grains in the coarser floodplain deposits could correspond to increased fluvial influence and probably to erosion of riverbank during flood events. The local plants are associated to the low energy sedimentary environments. Focuses are made on the relations between the evolution of the environment and land use. The development of the cereal culture in the floodplain of the Rhone delta has been demonstrated between 1640–1410 and 100 BC. The last alluviation of the Rhone perturbs the research of the archaeological sites in the central part of the delta but the existence of the rural villages from the first part of the first millennium BC is highly possible.