Pierre Moissette

Changes in vegetation and marine environments in the eastern Mediterranean (Rhodes, Greece) during the Early and Middle Pleistocene

Pollen records, marine faunal associations and stable isotope compositions of sediments from Rhodes, Greece, have been determined to track environmental changes in the eastern Mediterranean during the Early and Middle Pleistocene. A detailed chronostratigraphic curve, based on magnetostratigraphic data, was obtained by correlating pollen spectra with the Mediterranean oxygen isotopic curve of Ocean Drilling Program Site 975. Five sedimentary sequences that correspond to marine oxygen isotope stage (MIS) 31–27 and to MIS 20–17 have been investigated in the confined Tsampika microbasin. High-amplitude Pinus variations confirm glacio-eustatic changes deduced from changes in marine faunal associations and sedimentary depositional environments. Reflecting climatic cycles identified in the marine carbonate oxygen isotope record, eight vegetation successions (characterized by the dominance first of mesothermic elements, then of mid- and high-altitude elements with Pinus, and ending with maxima in herb and steppe elements) have been documented. Most of them were probably driven by changes in insolation occurring in high northern latitudes (obliquity impact) during the late Early Pleistocene and early Middle Pleistocene.

SPECTACULAR PRESERVATION OF SEAGRASSES AND SEAGRASS-ASSOCIATED COMMUNITIES FROM THE PLIOCENE OF RHODES, GREECE

Abstract An exceptionally well-preserved fossil seagrass community occurs in the late Pliocene of the Greek Island of Rhodes. The siliciclastic deposits of the Kritika section (Kritika Member, Rhodes Formation) contain several beds of clay and fine-grained sand with abundant remains of the leaves of Posidonia oceanica. A coarser sand bed with in situ rhizomes of the same endemic Mediterranean phanerogam also was found. Samples yield a diverse skeletal assemblage of 121 species of crustose coralline algae, foraminifers, annelids, gastropods, bivalves, encrusting bryozoans, and ostracodes, some of which also live exclusively on the leaves of present-day P. oceanica. The community of organisms associated with the rhizomes is slightly poorer (57 species), with bivalves appearing as distinctively abundant components of this assemblage (21 species). An analysis of the relationships between skeletal organisms and fossil leaves and rhizomes shows that the majority of them lived together in the same seagrass-vegetated environment, were transported a short distance from their natural habitat, and buried very rapidly in fine-grained sediments, thus preserving this remarkable assemblage almost intact. The rhizomes were preserved in growth position within a coarse-grained sand trapped by their horizontal and vertical network. The fossil assemblage compares well in terms of major skeletal components with modern shallow-water P. oceanica meadows. This study also provides evidence for the presence during the Pliocene of an already well-established and widespread seagrass community with biotopes comparable to those of the present-day Mediterranean.

Changes in bryozoan assemblages and bathymetric variations. Examples from the Messinian of northwest Algeria

Abstract Studies of Recent bryozoan faunas have shown that there is a correlation between colonial growth forms and various physical factors of the environment, especially bathymetry. Each given assemblage of zoarial forms can thus be related to a certain depth interval. In marine Neogene deposits numerous extant bryozoan species occur and some of them have more or less restricted depth ranges: they are used here to complement the indications given by the analysis of growth forms. In the Messinian (uppermost Miocene) of northwestern Algeria a general feature is the occurrence of well-developed diatomaceous deposits interbedded with marl beds where benthic invertebrate remains are often abundant. In the five sections under study bryozoans are represented by 87 species belonging to nine different colonial growth forms. Four different assemblages of these zoarial forms, characterised by presence/absence and number of fragments, are distinguished, corresponding to four depth intervals. The first and deepest assemblage (upper bathyal to lower circalittoral) occurs in the bottom part of the sections where colonies of a conescharelliniform species strongly predominate. The second assemblage (lower circalittoral) is represented by several species belonging to various zoarial forms: conescharelliniform, cellariiform, vinculariiform, adeoniform, and reteporiform. The third assemblage (upper circalittoral) is characterised by the absence of conescharelliniforms, but membraniporiforms and celleporiforms are abundantly represented, together with numerous erect colony fragments. In the fourth assemblage (infralittoral) membraniporiforms and celleporiforms predominate, although a number of erect zoarial forms are sometimes associated in various proportions. The presence of several extant bryozoan species associated with each of these four assemblages is used as a confirmation for the suggested depth intervals. A gradual shallowing is thus indicated by the study of the bryozoan assemblages through the five Messinian sections. The discussion shows that modern data on zoarial forms and species bathymetric distributions are clearly applicable to Cenozoic faunas but that caution must be exercised when using results obtained from different oceanographic regions.

Palaeoenvironmental reconstruction of the Sarmatian (Middle Miocene) Central Paratethys based on palaeontological and geochemical analyses of foraminifera, ostracods, gastropods and rodents

Paleoenvironmental changes in the upper Middle Miocene Central Parathetys were reconstructed by using qualitative and quantitative palaeontological analyses of foraminifera and ostracods, coupled with trace elemental (Mg/Ca) and stable isotope (delta(18)O and delta(13)C) analyses of their carbonate skeletons and of gastropod sheets. Mean annual air temperatures were estimated using the oxygen isotope composition of contemporaneous rodent teeth. The studied aquatic fossils come from two boreholes in the Zsambek basin (northern central Hungary), while the terrestrial ones are from localities in NE Hungary and E Romania. In the studied Sarmatian successions, three zones could be distinguished, based on palaeontological and geochemical results. At the Badenian/Sarmatian boundary, faunal diversity decreased markedly. In the lower zone a transgressive event culminated in a seawater incursion into the semi-open basin system of the Central Paratheys. Stable bottom-water temperature (similar to 15 degrees C) and variable salinites (20-22%) are estimated for the Early Sarmatian Sea. The faunal changes (notably a strong reduction in biodiversity) occuring at the boundary between the lower and the middle zone can be explained by a sea-leval highstand with dysoxic conditions. A relative sea-level fall is documented at the end of this middle zone. After a short regressive event, a marine connection between the Paratethys and Mediterranean was established at the beginning of the upper zone. This is indicated by an increased microfaunal diversity and the re-appearance of marine Bademan ostracods and foraminifera, which are completely absent from the older Samatian series. During the upper zone, the temperatures and salmities are estimated to have fluctuated from 15 degrees C to 21 degrees C and from 15 parts per thousand to 43 parts per thousand, respectively.

Coral microbialite environment in a Middle Miocene reef of Hungary

Abstract The presence of microbial crusts (microbialites) is reported here for the first time from a Middle Miocene (Badenian) coral reef in Hungary. The succession of initiation and development of the microbial crusts is described in relation to the reef architecture. The main features of the palaeoenvironment are discussed, with focus on the associated invertebrate faunas, mostly corals, molluscs, bryozoans, and crabs. We conclude that the microbial crusts developed under normal marine conditions and were a significant contributor to reef framework development, including its strengthening through calcification of the microbial organisms. Microbialites are anticipated in other Early and Middle Miocene coral reef occurrences of the Mediterranean–Paratethys realm, and to date may have simply escaped positive recognition.

Signification écologique des associations d'ostracodes de la coupe de Kritika (Pliocène supérieur, Rhodes, Grèce)

Resume Les populations dostracodes ont ete etudiees dans 19 prelevements effectues dans la serie lithologique a caractere marin du Pliocene superieur de la coupe de Kritika (Ile de Rhodes, Grece). 124 especes dostracodes appartenant a 44 genres ont ete reconnues. Les associations de ces especes revelent deux milieux de vie : le premier (50–100 m) a la base fait partie de letage circalittoral, le deuxieme (5–25 m) appartient a letage infralittoral. Les pourcentages de chacune des especes sont compares dans les differents prelevements, ainsi que les indices biocoenotiques (richesse specifique, abondance, taux de renouvellement et equitabilite). A la base de la coupe, Costa edwardsii et Bosquetina rhodiensis dominent nettement. Les indices biocoenotiques indiquent un biotope dont les conditions denvironnement sont stables. Le facteur principal de lanalyse des correspondances binaires oppose ces echantillons a ceux dans lesquels ces deux especes sont absentes. En effet, a partir dun niveau a terriers, C. edwarsii et B. rhodiensis disparaissent et le renouvellement faunistique est de 100 % ; ceci traduit de nouvelles conditions denvironnement destabilisees ulterieurement, puis interrompues par un episode dhypoxie.

Bryozoaires récoltés dans les unités messiniennes de sondages offshore dans le Golfe de Gabès (Tunisie)

Resume Deux sondages offshore realises dans le golfe de Gabes (Tunisie) ont livre 37 especes de bryozoaires. La plupart de ces especes proviennent des calcaires coralliens de la formation Melqart (Messinien inferieur). Les proportions des 7 formes zoariales representees, ainsi que lecologie des especes actuelles, indiquent des profondeurs de depot de quelques metres a une dizaine de metres, dans des eaux chaudes de type tropical. Une comparaison avec les faunes de bryozoaires des recifs messiniens du Maroc et dAlgerie montre que les diversites et les compositions specifiques sont relativement proches, mais que les affinites avec le Maroc sont plus marquees. Les donnees sur les bryozoaires des recifs coralliens actuels semblent indiquer un milieu ouvert, a linterieur dune plate-forme carbonatee developpee.

Pleistocene rolling stones or large bryozoan nodules in a mixed siliciclastic-carbonate environment (Rhodes, Greece)

Abstract Spectacular accumulations of abundant bryozoan nodules (bryoliths) occur in the early Pleistocene coarse-grained, mixed carbonate-siliciclastic deposits of the Cape Arkhangelos Calcarenite of Rhodes, Greece. These bryoliths are always associated with numerous bivalves (mostly ostreids and pectinids) and serpulid worms, together with other rarer skeletal organisms. The spheroidal bryoliths vary in diameter from 1 cm to 16 cm, and those with a more ellipsoidal shape range from 0.8 cm to 22 cm in length and from 0.7 cm to 16 cm in width; an elongated bryolith of exceptional size (40 cm) was even found. The bryoliths are composed almost exclusively of the anascan cheilostome Calpensia nobilis and are nucleated on gravels, pebbles, or bivalve shells. After settlement of bryozoan crusts, the bryoliths increased in size by repeated overturning of these mobile hard substrates by longshore currents. The bryoliths developed at depths of 20–40 m on a flat shoal between emerged areas where bottom currents episodically accelerated during storms. The currents also transported the bryoliths, together with other skeletal elements, into deeper settings (40–80 m) where they could continue their growth, upward or downward, or be colonized by other organisms.

Crustacés décapodes des faciès marno-diatomitiques du Messinien d'Oranie (Algérie Occidentale)

Resume Des restes de Decapodes (carapaces mais surtout appendices) ont ete trouves dans les interacalations marneuses des diatomites du Messinien (Miocene superieur) de la region dOran (Algerie occidentale). Ils appartiennent a 16 taxons correspondant a 8 familles differentes: Callianassidae, Galatheidae, Parthenopidae, Majidae, Cancridae, Portunidae, Xanthidae et 1 famille incertae sedis. Leur description est suivie dun bref examen de leurs affinites avec les autres faunes de Decapodes du Messinien, du Neogene mediterraneen et de lActuel.

Facies associations in warm-temperate siliciclastic deposits: insights from early Pleistocene eastern Mediterranean (Rhodes, Greece)

Diverse, abundant and usually well-preserved communities of skeletal organisms occur inn the lower Pleistocene (Gelasian) siliciclastic deposits of the Greek island of Rhodes.n Benthic foraminifers, molluscs and bryozoans have been studied in four measured andn sampled sections located in the northern part of the island. Among these bottom-dwellingn organisms, numerous extant taxa are good environmental indicators and, combined with fieldn observations and sedimentological data, they provide information on the probablen conditions in which they developed. The siliciclastic deposits of the Kritika Formationn have been divided into 14 different bio- and lithofacies, which have been further groupedn into four facies associations corresponding to four different environmental settings: (1)n continental to fluviatile; (2) brackish-water (lagoonal/deltaic); (3) infralittoral (0–20n m); and (4) upper circalittoral (depths of 20–40 m, but also down to c. 50–60 m). Among the marine facies associations, several characteristic biocoenoses haven been recognized: soft-bottoms (fine to coarse sands and gravels); seagrass meadows;n biogenic calcareous crusts on drowned beachrock slabs; red algal rhodoliths; and bivalven shell beds. In the studied sections, 13 superimposed genetic sequences have beenn documented. The repetition of similar facies associations within each sequence suggests:n (1) a possibly eustasy-controlled, cyclic sedimentation; (2) a general subsidence ofn Rhodes during the deposition of the studied facies associations; and (3) a mostly constantn range of environmental conditions (i.e. sedimentation rates and temperature) throughoutn the Gelasian.