Efterpi Koskeridou

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.

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.

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 in the lower Pleistocene (Gelasian) siliciclastic deposits of the Greek island of Rhodes. Benthic foraminifers, molluscs and bryozoans have been studied in four measured and sampled sections located in the northern part of the island. Among these bottom-dwelling organisms, numerous extant taxa are good environmental indicators and, combined with field observations and sedimentological data, they provide information on the probable conditions in which they developed. The siliciclastic deposits of the Kritika Formation have been divided into 14 different bio- and lithofacies, which have been further grouped into four facies associations corresponding to four different environmental settings: (1) continental to fluviatile; (2) brackish-water (lagoonal/deltaic); (3) infralittoral (0–20 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 have been recognized: soft-bottoms (fine to coarse sands and gravels); seagrass meadows; biogenic calcareous crusts on drowned beachrock slabs; red algal rhodoliths; and bivalve shell beds. In the studied sections, 13 superimposed genetic sequences have been documented. The repetition of similar facies associations within each sequence suggests: (1) a possibly eustasy-controlled, cyclic sedimentation; (2) a general subsidence of Rhodes during the deposition of the studied facies associations; and (3) a mostly constant range of environmental conditions (i.e. sedimentation rates and temperature) throughout the Gelasian.

Tectonic motions in oblique subduction forearcs: insights from the revisited middle and upper Pleistocene deposits of Rhodes (Greece)

Abstract: The sedimentary model of coastal deposits in eastern Rhodes over the last 2 Ma is refined and improved in accuracy. New field investigations and U/Th dating of Spondylus bivalve shells, combined with micropalaeontological and sedimentological data, allow the recognition of four synthems separated by major erosional surfaces. We present here evidence for two of these erosional surfaces. This new model allows the identification and quantification of the vertical movements recorded by the studied exposures. The history of these vertical motions is characterized by two periods of uplift and two periods of subsidence. Such an evolution is unique at the regional scale in the eastern Hellenic forearc. We interpret these results as reflecting the individualization of Rhodes as a single tectonic block during increasing trench bending. This trench bending is accommodated by an increase in the curvature of the forearc during the last 2 Ma. Supplementary material: U/Th dating on spondylid shells, index calcareous nannofossils and Khallithea and Faliraki Road sections are available at https://doi.org/10.6084/m9.figshare.c.4211357