Hara Drinia

Foraminiferal stratigraphy and palaeoecological implications in turbidite-like deposits from the Early Tortonian (Late Miocene) of Greece

The Lower Tortonian Ag. Giannis section, in Gavdos Island, Greece, consists of an outer neritic to upper bathyal, marly hemipelagic sequence which is interrupted by thick turbidite-like sandy deposits. During deposition of the marly intervals, reworking was considerably reduced. This paper contributes to knowledge concerning benthic foraminiferal response to dynamic sedimentary environments. Important palaeoecological information for benthic foraminiferal assemblages was gathered and analyzed in order to create a regionally consistent picture of the palaeoenvironment. Samples were analyzed statistically in order to identify the different palaeoenvironmental settings during turbiditic sedimentation. Undisturbed basal marls of the section are characterized by the predominance of a diversified Uvigerina striatissima assemblage typified by a broad variety of morphotypes with different inferred habitat preferences and feeding strategies, indicating rather well-oxygenated bottom waters. This environmental stability was subsequently disrupted by recurrent deposition of turbidite-like sands. A low-diversity Valvulineria complanata-Globobulimina sp. assemblage is dominant in this part of the succession, as these specialized endobenthic species could keep pace with high-energy sedimentary settings. Just above the turbidites, a “recolonization” fauna (Bolivina alata assemblage), composed entirely of infaunal elements is observed, indicating a nutrient-rich substrate. This oligotypic fauna is later replaced by a more diversified microfauna capable of occupying a wider range of ecological niches.

Neogene non-tropical carbonate sedimentation in a warm temperate biogeographic province (Rethymnon Formation, Eastern Crete, Greece)

The Apostoli Basin, in the central-west part of Crete, was formed as a fore-arc type basin related to the convergent plate boundary between the African and the Eurasian plates. Most of the Neogene sediments filling the basin were deposited in a terrestrial to shallow marine environment. The succession is a transgressive cycle, which culminates in the alternation of Rethymnon bioclastic limestones with marls, documenting the important Tortonian marine transgression. The Rethymnon limestones are classified as a typical non-tropical carbonate lithofacies. Two particular lithofacies have been recognized: (a) a rhodalgal-type lithofacies, characterized by predominance of encrusting coralline algae and bryozoans, and (b) an echinofor-type lithofacies, characterized by predominance of echinoderms and/or benthic foraminifera. The coralline algae occur mostly as in situ spheroidal or branched rhodoliths, whereas benthic foraminifera are mainly represented by larger foraminifera. In both lithofacies, typical tropical carbonate elements are lacking. Skeletal elements consisted of low- and high-Mg calcite. Although the observed lithofacies possess many similarities with facies of non-tropical carbonates, the presence of large benthic foraminifera suggests development in a warm temperate biogeographic province. The depositional environment corresponds to a shallow ramp, the sediments being deposited in a nearshore environment and under conditions analogous to those prevailing in the present-day circalittoral bottoms of the Mediterranean Sea. The main carbonate accumulation area is located at the factory area itself (rhodalgal-type sediments), and downslope from the factory area (echinofor-type sediments). In the classic zonation of Mediterranean benthic assemblages of Peres and Picard [Rec. Trav. Stn. Mar. (1964)], the rhodalgal-type sediments of the Rethymnon Fm correspond to the ‘‘Facies a Pralines’’, developed in areas strongly controlled by currents (e.g., tops of plateaus), and the echinofor-type sediments to the ‘‘Detritique Cotier’’ bioclastic deposits, derived mostly by bioerosion and fragmentation of local and adjacent calcareous benthic communities. D 2002 Published by Elsevier Science B.V.

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.

Mortality in a predator-free insular environment:the dwarf deer of Crete

ABSTRACT Age-graded fossils of Pleistocene endemic Cretan deer (Candiacervus spp.) reveal unexpectedly high juvenile mortality similar to that reported for extant mainland ruminants, despite the fact that these deer lived in a predator-free environment and became extinct before any plausible date for human arrival. Age profiles show that deer surviving past the fawn stage were relatively long-lived for ruminants, indicating that high juvenile mortality was not an expression of their living a “fast” life. Although the effects on survivorship of such variables as fatal accidents, starvation, and disease are difficult to gauge in extinct taxa, the presence of extreme morphological variability within nominal species/ecomorphs of Candiacervus is consistent with the view that high juvenile mortality can function as a key innovation permitting rapid adaptation in insular contexts.

Palaeoenvironmental reconstruction of the Oligocene Afales Basin, Ithaki island, western Greece

Assemblages of benthic foraminifera from one clastic succession in the Afales Basin (Ithaki Island, western Greece) were investigated to reconstruct palaeoenvironmental conditions during the Oligocene. The section consists of alternating hemipelagic marls and detrital deposits, designated as flysch-like beds, attributed to biostratigraphic Zones P20 and P21. Planktic percentages are mostly high (66–80%). Benthic foraminiferal assemblages comprise calcareous and agglutinated taxa (up to 15%). The prevalence of epifaunal foraminifera indicates good ventilation of the bottom water resulting from basin morphology, which enabled the undisturbed flow of water throughout the basin. Palaeodepth estimates imply bathyal deposition, from about 800 to 1200 m deep. The benthic foraminiferal fauna is of high diversity along the section, as is expected in deep marine environments. The abundances of the most common foraminiferal taxa (Cibicidoides spp., Oridorsalis umbonatus, Gyroidinoides spp., Stilostomella spp., Nodosariidae, Nuttallides umbonifera) are quite variable and imply generally oligotrophic to mesotrophic environmental conditions with variable organic flux.

Palaeoceanography of the Miocene (Tortonian) deposits of the Pre-Apulian zone, western Greece, as recorded by foraminifer and stable isotope records

An integrated faunal and geochemical dataset has been generated by the study of a late Miocene (early Tortonian) sedimentary section outcropping at Manassi, Levkas Island (eastern Mediterranean). Quantitative analysis of benthic foraminifers from the 25-m-thick section indicates changes of bottom palaeoecological conditions in this part of the eastern Mediterranean, during the analyzed time interval. Benthic foraminifer assemblages are typical of a bathyal environment and testify to relatively oxygenated conditions with low to moderate food supply alternating with periods with an increase in organic matter content. The long-term palaeoceanographic analyses indicate an anti-estuarine circulation model based on the benthic foraminifer and stable isotope results, which evolved in a strong estuarine circulation. The positive relationship existing between the plankton δ18O and δ13C, in most of the record, agrees well with the hypothesis of a variable contribution of runoff. In three stratigraphic levels, samples record heavy bottom water δ18O and δ13C values and light surface δ18O values, representing a wet, warm, estuarine climate with a stratified water column. In two stratigraphic levels, samples have depleted δ13C and δ18O values for both surface and bottom waters. These two samples represent wet, warm climates with some ocean mixing and stratification. The stable isotope signal of foraminifer tests from the Manassi section was influenced by the global temperature changes, but the local factors also played an important role. The palaeoenvironments derived from stable isotope analysis in this study are interpreted as responses to the local tectonic instability together with monsoon intensities that enhanced continental runoff, characteristic for the time interval studied in the study area. Due to the limited data available from this study, no correlations with the precessional, obliquity, or eccentricity cycles can be made.

Morphology of articular surfaces can solve aphylogenetic issue: one instead of two ancestors for Candiacervus (Mammalia: Cervoidea)

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The response of benthic foraminifera to palaeoenvironmental disturbance: A quantitative approach in turbidite-like successions

Benthic foraminifera were collected from a number of samples of a turbidite-like succession, and quantitatively investigated with the aim to describe and interpret their distributional pattern prior, during and after the turbidite events. The foraminiferal assemblages contain indigenous benthic taxa that represent combined bottom-water and bottom-sediment controlled benthic environments and allochthonous benthic shelf taxa that are transported downslope into deeper-water biotopes. Considerable differences in diversity, community organization, feeding and habitat preferences are detected among benthic foraminiferal assemblages below, across and above the turbiditic episodes. Prior to the deposition of the turbiditic sands, the benthic foraminiferal assemblage is indicative of a strong preference of environments with highly elevated food supply, but sheltered from direct disturbance. This stability was disrupted by the recurrent deposition of turbiditic sands. In the lower part of the turbiditic sequence, some specialized endobenthic forms, such as Valvulineria complanata and Nonion spp. could keep pace with high sedimentation reflecting enhanced supply of organic matter by transport. In the upper part of the turbiditic sequence, an opportunistic fauna (Bolivina spathulata assemblage), entirely composed of infaunal elements, is observed, indicating a nutrient-rich substrate. The reduction in the dominance of Bolivina spp. and the reappearance of both infaunal and epifaunal taxa reflects the recovery of the benthic ecosystem.