Éditeur(s) : HAL CCSD Blackwell Publishing
Résumé : International audience
Pliocene and Pleistocene deposits from Grande-Terre (Guadeloupe archipelago, French Lesser Antilles) provide a remarkable example of an isolated carbonate system built in an active margin setting, with sedimentation both controlled by rapid sea-level changes and tectonic movements. Based on new field, sedimentological and palaeontological analyses, these deposits have been organized into four sedimentary sequences (S1 to S4) separated by three subaerial erosion surfaces (SB0, SB1 and SB2). Sequences S1 and S2 ('Calcaires inférieurs à rhodolithes') deposited during the late Zanclean to early Gelasian (planktonic foraminiferal Zones PL2 to PL5) in low subsidence conditions, on a distally steepened ramp dipping eastward. Red algal-rich deposits, which dominate the western part of Grande-Terre, change to planktonic foraminifer-rich deposits eastward. Vertical movements of tens of metres were responsible for the formation of SB0 and SB1. Sequence S3 ('Formation volcano-sédimentaire', 'Calcaires supérieurs à rhodolithes' and 'Calcaires à Agaricia') was deposited during the late Piacenzian to early Calabrian (Zones PL5 to PT1a) on a distally steepened, red algal-dominated ramp that changes upward into a homoclinal, coral-dominated ramp. Deposition of Sequence S3 occurred during a eustatic cycle in quiet tectonic conditions. Its uppermost boundary, the major erosion surface SB2, is related to the Cala1 eustatic sea-level fall. Finally, Sequence S4 ('Calcaires à Acropora') probably formed during the Calabrian, developing as a coral-dominated platform during a eustatic cycle in quiet tectonic conditions. The final emergence of the island could then have occurred in late Calabrian times.
ISSN: 1469-3496

hal-00760906
https://hal.archives-ouvertes.fr/hal-00760906
DOI : 10.1111/j.1365-3091.2011.01311.x

Éditeur(s) : HAL CCSD Royal Society, The
Résumé : International audience
Since its original description as a chordate, the Late Devonian Scaumenella mesacanthi has been interpreted alternately as a prochordate, a larval ostracoderm and an immature acanthodian. For the past 30 years, these minute specimens were generally considered as decayed acanthodians, most of them belonging to Triazeugacanthus affinis. Among the abundant material of `Scaumenella', we identified a size series of 188 specimens of Triazeugacanthus based on otolith characteristics. Despite taphonomic alteration, we describe proportional growth and progressive appearance of skeletal elements through size increase. Three ontogenetic stages are identified based on squamation extent, ossification completion and allometric growth. We demonstrate that what has been interpreted previously as various degrees of decomposition corresponds to ontogenetic changes.
ISSN: 1744-9561

hal-01545474
https://hal.archives-ouvertes.fr/hal-01545474
DOI : 10.1098/rsbl.2014.0950

Éditeur(s) : ISTPM
Résumé : A micropaleontological study of sediment sampling on the French Guiana coast showed the occurrence of an important fauna of actual planktonic and benthic Foraminifera.
Revue des Travaux de l'Institut des Pêches Maritimes (0035-2276) (ISTPM), 1977-12 , Vol. 41 , N. 4 , P. 403-416

Droits : Ifremer
http://archimer.ifremer.fr/doc/1977/publication-1992.pdf
http://archimer.ifremer.fr/doc/00000/1992/

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
New investigations in the Neogene Boudinar basin (Morocco) provide new information about the Messinian Salinity Crisis (MSC) and Zanclean reflooding in the southern part of the Alboran realm (westernmost Mediterranean). Based on a new field, sedimentological and palaeontological analyses, the age and the geometry of both the Messinian erosional surface (MES) and the overlying deposits have been determined. The MES is of late Messinian age and was emplaced in subaerial settings. In the Boudinar basin, a maximum of 200 m of Miocene sediments was eroded, including late Messinian gypsum blocks. The original geometry of the MES is preserved only when it is overlain by late Messinian continental deposits, conglomeratic alluvial fans or lacustrine marly sediments. These sediments are interpreted as indicators of the sea-level fall during the MSC. Elsewhere in the basin, the contact between late Messinian and early Pliocene deposits is a low-angle dipping, smooth surface that corresponds to the early Pliocene transgression surface that subsequently re-shaped the regressive MES. The early Pliocene deposits are characterized by: (i) their onlap onto either the basement of the Rif chain or the late Miocene deposits; (ii) lagoonal deposits at the base to offshore marls and sands at the top (earliest Pliocene; 5.33–5.04 Ma interval; foraminifer zone PL1); (iii) marine recovery occurring in the 5.32–5.26 Ma interval; and (iv) the change from lagoonal to offshore environments occurring within deposits tens of metres thick. This information indicates that at least the end of the reflooding period was progressive, not catastrophic as previously thought.
ISSN: 0037-0738

hal-01306672
https://hal.archives-ouvertes.fr/hal-01306672
DOI : 10.1016/j.sedgeo.2015.12.014

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
The lower Pleistocene Kritika Member of the Rhodes Formation is composed of predominantly siliciclastic deposits that are sometimes intercalated with hardbottoms formed by drowning of former beachrock beds. A wide variety of sclerobionts occur in this environment, very different from the poorest soft‐bottom populations occurring in other levels of the Kritika Member. The most characteristic, abundant and frequently diverse are the encrusting forms: coralline algae, bivalves, serpulid worms, and bryozoans. Numerous other groups of sessile and vagile organisms are associated with these crust‐forming communities. A number of skeletal organisms (sometimes including zooxanthellate coral colonies) formed small carbonate buildups on top of several beachrock beds. Boring organisms also occur. Evidence for a two‐step deepening succession over the previously formed beachrock is provided by palaeontological and sedimentological data. The rapidly cemented sandy‐conglomeratic beds were first colonised by a relatively shallow‐water (around 20 m) biocoenosis of mostly encrusting organisms. Another association, with encrusting and erect organisms, was later established in a deeper environment (20-40 m). A comparison with Holocene beachrock occurring on the coast of Rhodes was also undertaken. Their submerged part provided habitat for poorer but similar biotas to those occurring in the Kritika Member. The lower Pleistocene beachrock and associated organogenic fossil assemblages indicate repeated drowning episodes during deposition of the Kritika Member and provide help in sequence stratigraphic interpretations of these siliciclastic deposits. Notably, they can be used as indicators of relative sea‐level changes.
ISSN: 0031-0182

hal-00795591
https://hal.archives-ouvertes.fr/hal-00795591
DOI : 10.1016/j.palaeo.2012.09.007