Pierre Cugny

Influence of intermittent hydropeaking on the longitudinal zonation patterns of benthic invertebrates in a mountain stream

The longitudinal zonation patterns of invertebrate species were studied in the River Oriege (Pyrenees, France) from 920 to 819 m a.s.l. At 912 m a.s.l., the river receives hypolimnetic water diverted from a nearby reservoir lake, and the natural flow may be enhanced several times a day from 1 to 11 m 3 s -1 in summer and winter, and from 5 to 15 m 3 s -1 during spring spates. During hydropeaking, the water was cooled in summer and slightly warmed in winter, but this was attenuated 3500 m downstream from the plant. Invertebrate densities were recorded in July (end of spates) and October (low flow period) at ten sampling sites : a reference site upstream of the hydrostations discharge point (site 1), and nine sites each 400m below the outlet (sites 2-10). The longitudinal distribution of invertebrate taxa was studied using Factorial Analyses, taxa and sites were clustered using Analysis of Dynamic Cluster. The hydroelectric facility did not clearly modify the qualitative composition of the benthic fauna, but clearly affected the longitudinal zonation of several populations. The low abundance of several species below the outlet reflected the impact of both hydropeaking and zonation. These species were high mountain species, the density of which decreases towards downstream sites in the Pyrenees, and low mountain species, the density of which naturally decreases towards upstream sites. Some taxa disappeared in the regulated section, so their distribution in the River Oriege was primarily influenced by hydropeaking. Finally, some taxa preferentially lived in the lower section of the river where the impact of peaking flows was strongly attenuated, so their longitudinal distribution was first governed by their natural longitudinal zonation. Under this kind of river regulation (natural discharge and temperature except during periods of power generation, intermittent hydropeaking from a separate reservoir) modifications of the thermal regime had a minor effect on the population dynamics, unlike hydraulic disturbances which strongly influenced the structural attributes of benthic communities.

Comparative study of the Lower and Mid-Cretaceous sequences on different Maghrebian shelves and basins-their place in the evolution of the North African Atlantic and Neotethysian margins

Abstract The Lower and Mid-Cretaceous sequences known from Morocco (coastal Essaouira-Agadir-Safi Basin and Eastern Rif Foreland), in Western Algeria (Daǐa Mountains) and finally in Southern Tunisia (Chott Range and Saharian Shelf) are presented from a biostratigraphic and sedimentologic viewpoint. This work shows, for the period considered, common features in the geodynamic evolution of the different regions, such as: 1. - generalization of the carbonate facies in the Early Cretaceous (Berrisian) and at the end of the Mid-Cretaceous (Cenomanian-Turonian) times; 2. - delineation of important discontinuities in the Valanginian and Bedoulian times. This evolution gives evidence of an undeniable influence of eustatism in this Northern part of Africa. Nevertheless, detailed differences allow us to distinguish: 3. - an “Atlantic-type” evolution characterized by discontinuities with gaps (Safi) or sudden variations of thickness (Essaouira-Agadir) at the Berriasian/Valanginian boundary, related to the Neocimmerian rifting and block-faulting phase. Later on, this evolution is underlined by a progressive acceleration of subsidence at the Aptian/Albian boundary, due to the removal of the mid-oceanic doming; 4. - a “Neotethysian-type” evolution (Eastern Rif Foreland, Western Algeria and Southern Tunisia) where local tectonic movements have probably generated the rapid growth of the external marly Bedoulian basins and the spreading of the Wealdian-type (Valanginian to Barremian) and Utrillas (Albian) terrigenous depositional systems. The latest event is linked to the Austrian tectonic phase responsible of variable gaps towards the Aptian to Albian transition.

Reconstitution, en Corse, au Jurassique moyen–supérieur, de la marge européenne de l'océan Liguro-Piémontais, grâce à des niveaux repères à Praekurnubia crusei (foraminifère)

Abstract By means of the Upper Bathonian–Callovian isochron time-line marked by some calcareous key-beds bearing Praekurnubia crusei Redmond (benthonic Foraminifer), identified both in the ophiolitic ‘Balagne Nappe’ and in the continental ‘Prepiedmontese Zone’, an attempt of palinspastic reconstruction of the European margin of the Ligurian-Piedmont Ocean, in Corsica, during Middle–Upper Jurassic times, is herein proposed. The bayonet transect reaches to the west the autochthonous cover of the Hercynian Corsica. It shows, during the syn-rift phase (Dogger), the subdivision of the margin into tilted blocks inducing strong differential subsidences (particularly between the Caporalino half-horst and the adjacent half-grabens) and, during the post-rift phase (Malm), the sealing of the previous palaeostructures by the Kimmeridgian shelf-type limestones preceeding the general flooding of the Lowermost Cretaceous times.

Le probleme de la limite Cretace-Tertiaire en Corse-du-Sud

In the autochthonous unit of Punta-di-Calcina (southern Corsica, France), Upper Cretaceous deposits are reworked (clasts of orbitoid-bearing limestones, Globotruncanidae) within marine lowstand breccias of Danian age, that are overlying Jurassic limestones or granitic basement. These Danian breccias can be dated by means of subautochthonous planktonic foraminifera (Globigerinidae and Hedbergellidae), belonging to the Plb and Plc subzones. The K/T boundary coincides with an ante-Danian submarine erosional surface (major unconformity) underlining the gap of the whole Cretaceous. It is probably impossible to find the iridium-level of the K/T boundary along this surface. This stratigraphic framework suggests the occurrence of main (compressional ?) tectonic movements just before the beginning of the Palaeocene, inducing deep erosions on a Corsican-Sardinian block partially covered at this time by Maastrichtian marine carbonate platforms, now disappeared.

Diachronism in the sedimentary cover around the Troodos ophiolitic massif (Cyprus)

The detailed micropaleontologic study of the sedimentary series overlying the youngest ophiolitic basalts of the Troodos massif (Cyprus), confirms the late Campanian age of the top of the oldest terrigenous cover (Kannaviou Formation) topping these ophiolites themselves assigned to Cenomanian-Turonian. It also demonstrates for the first time the strong diachronism of the Lefkara Formation chalky limestones, unconformably overlying either the Kannaviou Fm. sandstones and clays, or the oceanic basalts. This diachronism over short distances and the on-lap of the Lefkara Fm. are revealed by varying stratigraphic gaps within the Paleocene-Miocene interval and are indicated by new age datings of the transgressive basal part of the Lefkara Fm. along six principal sections: late Thanetian (Zone P5) at the Pano Lefkara typelocality; early Ypresian (Sub-zone P6a) at Agia Anna; earliest Bartonian (Zone P13) at Kannaviou and Analiontas; early-middle Lutetian (Zones P10 to P11) at Kofinou; Langhian (Zone N8) at Choulou. Maastrichtian deposits are missing and Maastrichtian Globotruncanidae/Heterohelicidae only observed as individual reworked specimens within well-dated Tertiary levels. Finally, we discuss the influence of the Tertiary extensional brittle tectonics on this diachronism, the on-lap processes and the differential subsidences occurring after the late Cretaceous/? early-middle Paleocene folding (Laramian compression).