Papers by Konstantina Agiadi
The Lago Mare phase at the end of the Messinian Salinity Crisis (MSC) in the Mediterranean has lo... more The Lago Mare phase at the end of the Messinian Salinity Crisis (MSC) in the Mediterranean has long been known for the Paratethyan affinities of its biota. The taxonomic level of these affinities and their origin, however, is subject to divergent interpretations. Here, we have studied otoliths of the Gobioidei from late Miocene and early Pliocene deposits from Italy and Greece and revised earlier studies including time-equivalent data from Romania and NW Turkey. Nowadays, gobies constitute the most speciose marine fish family in Europe and the most diverse endemic family in the Ponto-Caspian region. Furthermore, they are highly adapted to nearshore shallow marine, brackish, and freshwater environments, which makes them excellent candidates to explore short-term connections of waterways of different nature.
Fossil records of nearshore, shallow marine fish communities are rare. Here, we present the rich ... more Fossil records of nearshore, shallow marine fish communities are rare. Here, we present the rich and diverse fish fauna of a coastal setting in the eastern part of the Mediterranean during the early Pliocene, which comprises 54 taxa, 77% of which are extant and currently occupy the same shores. We analyse these assemblages to estimate the palaeodepth, the substratum and the climatic and oceanographic conditions prevailing in the region at the time. Furthermore, we review the stratigraphic and geographic distribution of the identified taxa from the Tortonian until today, to establish patterns and trends in the evolution of the Mediterranean coastal fish fauna. Contrary to expectations, the Pliocene coastal fauna is very similar to the Miocene and to the Pleistocene in terms of functional traits as well as taxonomically. Replacements of species seem to have been gradual, through multiple extirpations and reintroductions that led to the final extinction of mostly tropical species from the basin, while subtropicaltemperate taxa invaded to take their place.
The eastern Mediterranean marine ecosystem is undergoing massive modification due to biological i... more The eastern Mediterranean marine ecosystem is undergoing massive modification due to biological invasions, overfishing, habitat deterioration, and climate warming. Our ability to quantify these changes is severely hindered by the lack of an appropriate baseline; most ecological datasets date back a few decades only and show already strong signatures of impact. Surficial death assemblages (DAs) offer an alternative data source that provides baseline information on community structure and composition. In this study, we reconstruct the marine fish fauna of the southern shallow Israeli shelf before the opening of the Suez Canal based on fish otoliths. We quantify the age of the otolith DAs by radiocarbon dating, and describe its taxonomic composition, geographic affinity, and trophic structure. Additionally, we test by radiocarbon dating the hypothesis that Bregmaceros, a presumed Lessepsian invader with continuous presence in the Mediterranean throughout the late Cenozoic, is a relict species. The otolith DA dates back to the mid-Holocene because 75% of the dated otoliths of the native species are older than the opening of the Suez Canal in 1869, suggesting that the DA is a proper baseline for quantifying modern impacts. Consistently, 97% of the otoliths and 88% of the species we collected belong to native Mediterranean species. The native anchovy Engraulis encrasicolus dominates the DAs, although gobiids are the most diverse group (14 species, 28%). The DAs show similar trophic structure to present-day pristine Mediterranean coastal fish assemblages. Two non-indigenous species are recorded here for the first time in the Mediterranean Sea, Amblygobius albimaculatus and Callogobius sp., highlighting the importance of DAs for detecting non-indigenous species. Finally, Bregmaceros otoliths are modern, not supporting the previous hypothesis that the taxon is a Pleistocene relict.
Basin Research , 2017
This integrated study (field observations, micropalaeontology, magnetostratigraphy, geochemistry,... more This integrated study (field observations, micropalaeontology, magnetostratigraphy, geochemistry, borehole data and seismic profiles) of the Messinian-Zanclean deposits on Zakynthos Island (Ionian Sea) focuses on the sedimentary succession recording the pre-evaporitic phase of the Messinian salinity crisis (MSC) through the re-establishment of the marine conditions in a transitional area between the eastern and the western Mediterranean. Two intervals are distinguished through the palaeoenvironmental reconstruction of the pre-evaporitic Messinian in Kalamaki: (a) 6.45-6.122 Ma and (b) 6.122-5.97 Ma. Both the planktonic foraminifer and the fish assemblages indicate a cooling phase punctuated by hypersalinity episodes at around 6.05 Ma. Two evaporite units are recognized and associated with the tectonic evolution of the Kalamaki-Argassi area. The Primary Lower Gyp-sum (PLG) unit was deposited during the first MSC stage (5.971-5.60 Ma) in late-Messinian marginal basins within the pre-Apulian foreland basin and in the wedge-top (<300 m) developed over the Ionian zone. During the second MSC stage (5.60-5.55 Ma), the PLG evaporites were deeply eroded in the forebulge-backbulge and the wedge-top areas, and supplied the foreland basin's depocentre with gypsum turbidites assigned to the Resedimented Lower Gypsum (RLG) unit. In this study, we propose a simple model for the Neogene-Pliocene continental foreland-directed migration of the Hellenide thrusting, which explains the palaeogeography of the Zakynthos basin. The diapiric movements of the Ionian Triassic evaporites regulated the configuration and the overall subsidence of the foreland basin and, therefore, the MSC expression in this area.
Paleoceanography and Paleoclimatology, 2019
The Messinian Salinity Crisis (MSC; 5.97-5.33 Ma) is an enigmatic episode of paleoceanographic ch... more The Messinian Salinity Crisis (MSC; 5.97-5.33 Ma) is an enigmatic episode of paleoceanographic change, when kilometer-thick evaporite units were deposited in the Mediterranean basin. Here we use geochemical (biomarker and isotope) data to reconstruct sea surface temperature, salinity, and productivity-preservation changes in the Mediterranean basin just before the MSC. The proxy data indicate that the Mediterranean Sea was significantly saltier and colder between 6.415 and 6.151 Ma, than between 6.151 and 5.971 Ma. Salinity decrease at 6.151 Ma seems to be a relatively fast event just preceding the inception of a warming phase that lasted almost uninterrupted until the MSC onset. The water exchange with the Paratethys could have caused, along with the African rivers, an increased freshwater supply, resulting in normal marine Mediterranean waters between 6.151 and 5.971 Ma, despite the severe restriction of marine connections with the Atlantic at that time. Sea surface temperature changes determined a sharp drop in productivity and/or preservation of organic matter, marked by deposition of calcareous marls. Productivity and preservation were relatively high and constant until 6.01 Ma. Afterward, increased influx of terrestrial organic matter and probably enhanced water column stratification prevailed. Around 5.971 Ma, modifications in aquatic versus terrestrially derived biomarkers indicate changes in organic matter influx at the MSC onset. Plain Language Summary More than five million years ago, the Mediterranean Sea underwent astonishing changes in its hydrological budget leading to the formation of hypersaline water bodies and the deposition of a more than 1,000-m salt giant. The way toward the hypersaline conditions of the Messinian Salinity Crisis (5.97-5.33 Ma) was marked by gradual closure of Mediterranean oceanic seaways. Data reveal that the Mediterranean Sea was 8‰ saltier and, in average, 1.2 °C colder between 6.415 and 6.151 Ma, than between 6.151 and 5.971 Ma. At 6.151 Ma, a salinity decrease from 47‰ toward normal marine of 39‰ was a fast event just preceding the inception of a warming lasting almost uninterrupted until the Messinian Salinity Crisis onset.
Quaternary Science Reviews, 2019
Early Pleistocene (Calabrian) clays of the Lindos Bay Formation have been uplifted and are expose... more Early Pleistocene (Calabrian) clays of the Lindos Bay Formation have been uplifted and are exposed today on the eastern coast of Rhodes (Hellenic forearc, Greece). The hemipelagic origin of these sediments and the excellent preservation of the microfossils they contain, make the Lindos Bay Formation a unique element in the eastern Mediterranean, which has the potential to constitute a paleoclimate referential framework of the region for the Early-Middle Pleistocene Transition (EMPT). In this context, 98 samples were collected in the type locality section of the Lindos Bay Formation. Stable isotope (d 18 O, d 13 C) analyses were carried out on benthic (Uvigerina peregrina) and planktonic (Globigerina bulloides) forami-nifera for the interval between ~1100 ka and ~858 ka. We identify and continuously reconstruct the climate cycles that occurred between Marine Isotope Stages (MIS) 32 and 21. Counts of planktonic foraminifera were further carried out and allow connecting the conditions occurring locally in the surface waters with the glacial-interglacial cycles during the onset of the EMPT. While (sub)tropical taxa dominate the assemblages, glacials were associated with short-term (<~10 kyr) influxes of temperate to subpolar species suggesting cooling and/or increasing productivity in the surface waters correlating with the deposition of sapropels in the eastern Mediterranean deep sea. Finally, planktonic/benthic forami-niferal ratios show that the section deposited at upper bathyal depths between ~450 m and ~150 m. During the late Early Pleistocene, the eastern coast of Rhodes has locally undergone repeated, transient and possibly very rapid vertical motions which are overprinted on a regional tectonically-forced regressive trend.
Palaeogeography, Palaeoclimatology, Palaeoecology, 2018
In the eastern Mediterranean, the island of Crete offers excellent exposures of upper Miocene mar... more In the eastern Mediterranean, the island of Crete offers excellent exposures of upper Miocene marine deposits. Three detailed sections of the Tortonian/Messinian sedimentary succession were measured and sampled in three different basins (from west to east: Chania, Heraklion, and Sitia). The biostratigraphic analysis based on planktonic foraminifera yielded ages ranging from about 7.58 to 6.72 Ma. Nine bioevents were also recognised and provided good correlations between the studied sections. Rich benthic faunas (commonly occurring together with fish otoliths) have furthermore been recovered and analysed: foraminifera, mollusc (mostly bivalves), bryozoans, and ostracods. The autochthonous assemblages suggest deposition at middle-upper bathyal depths at the base and outer-inner shelf in the upper parts of the sections. The shallowing upward trend observed in all three sections is accompanied by the occurrence in a few Messinian levels of allochthonous fossils transported downslope and deposited in deep-water environments. Dysoxic episodes were moreover recorded in some beds, mostly in the Messinian. A comparison with other coeval basins and faunas indicates that similar palaeoenvir-onmental conditions predominated throughout the Mediterranean Sea during the late Miocene. This is consistent with the postulate of open connections (through marine corridors) between the Mediterranean and the Atlantic, presumably until late in the Messinian.
Geobios, 2019
Coastal fish assemblages are especially vulnerable to environmental changes, but little is known ... more Coastal fish assemblages are especially vulnerable to environmental changes, but little is known about their evolution through time, mainly due to the scarcity of fossil material from such settings. The aim of this study is to characterize the early Pleistocene coastal fish assemblages of the eastern Mediterranean and to reconstruct the related paleobathymetric and paleoecologic conditions. Based on otolith findings, we identified thirty-seven teleost fish species from three sedimentary outcrops on the northeastern part of Rhodes Island (southeastern Aegean, Greece, Eastern Mediterranean), which have been placed within the Gelasian (early Pleistocene). The stratigraphic distribution of fifteen taxa is expanded for this interval, while five species are reported for the first time as fossils. The otolith assemblages provided paleodepth estimates indicative of shallow coastal environments. The ecosystem consisted mostly of substrates of sand and mud, with significant rocky micro-habitats and underwater vegetation; the climate was subtropical. These data complement existing knowledge on the study area, while providing new information on the composition of the ichthyofauna of the eastern Mediterranean during the Gelasian.
Quaternary Science Reviews, 2018
Marine bioinvasions affect ecosystems in irreversible ways, creating socioeconomic problems world... more Marine bioinvasions affect ecosystems in irreversible ways, creating socioeconomic problems worldwide. In particular, eastern Mediterranean marine fish faunas today are significantly disturbed due to overfishing, habitat deterioration, the Lessepsian invasion, and climate change. Isolating the impact of each parameter is difficult, because pre-anthropogenic activity data are lacking. In this study, we use the paleontological record to infer the causes and mechanisms behind marine fish invasions, focusing on the Mediterranean basin, which is a restricted basin and a biological hotspot, where the effects of climatic and oceanographic changes are amplified. Therefore, the Mediterranean Sea is an ideal area to study marine biological invasions in relation to abrupt climate changes. Furthermore, we focus on the Pleis-tocene, which was a period of intense glacialeinterglacial changes. Thus, we investigate the effect of climate changes on the fish fauna of an eastern Mediterranean shelf, by identifying the fish otoliths in the EarlyeMiddle Pleistocene marine sediments of Rhodes (Greece). We offer a synthesis of the Mediter-ranean marine fish from the Tortonian until today and hypothesize on the conditions that drove marine fish distribution range shifts during the Pleistocene. We reconstruct the paleobathymetric evolution of the study areas based on fish otoliths, and we consider taphonomy in our interpretations. The Pleistocene climatic variability induced periodic and gradual replacements of fish taxa. Episodic invasions of cold-water North Atlantic mesopelagic species are correlated with intervals of climatic deterioration, specifically during marine isotope stages 50, 44, 36, 20, and 18.
Journal of the Geological Society of London, 2019
The sedimentary model of coastal deposits in eastern Rhodes over the last 2 Ma is refined and imp... more 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.
In the present study, we investigate the Mediterranean–Paratethys connection during the late Mioc... more In the present study, we investigate the Mediterranean–Paratethys connection during the late Miocene in Strymon Basin (North Aegean, northeastern Mediterranean) and compare this onshore sequence with the adjacent offshore Prinos-Nestos sequence, before, during, and after the Messinian Salinity Crisis (MSC). Strymon Basin was a peripheral shallow-water basin during the first MSC stage. The Akropotamos sections expose a clastic sequence with gypsum intercalations, which is dated in the Messinian based on the ostracod and calcareous nannofossil assemblages. This sequence records the Primary Lower Gypsum deposition in a shallow marine environment and its passage via the Messinian erosional surface to a brackish environment with changing salinity conditions similar to the Paratethyan depositional environments. The sequence is capped by a travertine marker horizon observed across the entire Strymon Basin indicating freshwater environment. The Miocene–Pliocene transition is characterized by salinity changes caused by the interaction between Atlantic-Mediterranean and Paratethyan waters, predating the marine reflooding at the end of the MSC, which is attested by the overlying Pliocene open marine deposits. The offshore Prinos-Nestos basin incorporates the Nestos intermediate basin and the Prinos intermediate-deep basin. Borehole and seismic profile data from the offshore Prinos-Nestos oil field reflect a thick clastic sequence, topped by turbidites, and followed by an evaporitic unit deposited during the Messinian. In the Nestos slope area, the evaporite unit consists of anhydrite-shale alternations. Toward the basin's depocenter (Prinos Basin), anhydrite is replaced by halite. The sequence is overlain by Pliocene–Holocene deltaic prograding deposits. Sedimentologic and biostratigraphic data show that the thick halite-shale couplets in the deepest part of the offshore Prinos-Nestos Basin were deposited under permanent marine conditions, suggesting no desiccation before, during, and after the MSC. Conclusively, the present results indicate that a connection between the Mediterranean and the Paratethys was occasionally established before the Pliocene reflooding and favor the non-desiccation MSC model for the deep marine evaporite deposition.
biostratigraphic and geographic distribution of 32 taxa is significantly expanded into the Torton... more biostratigraphic and geographic distribution of 32 taxa is significantly expanded into the Tortonian, whereas 13 species are recorded for the first time from the Messinian. Four stages are distinguished in the area's paleoenvironmental evolution. (1) The Potamida area was an open marine environment with depths exceeding 150 m between ~7.5-7.45 Ma. (2) Between 7.45-7.36 Ma, the results suggest depths between 300-400 m. (3) The depositional depth increases between 7.36-7.28 Ma to 400-550 m. (4) Later on, approximately between 6.8-6.6 Ma, the depth is again estimated around 100-150 m.
Agiadi K, Triantaphyllou M, Girone A, Karakitsios V, Dermitzakis M (2010) Paleobathymetric interp... more Agiadi K, Triantaphyllou M, Girone A, Karakitsios V, Dermitzakis M (2010) Paleobathymetric interpretation of the fish otoliths from the lower -middle quaternary deposits of Kephallonia and Zakynthos islands (Ionian Sea, Western Greece). Riv Ital Paleontol S 116 (1): 63-78 Bañon R, Arronte JC, Serrano A, Sánchez, F (2011) First records of purplemouthed conger Pseudophichthys splendens (Anguilliformes: Congridae) from the Galicia Bank (NW Spain). A northward range extension of their distribution in the eastern Atlantic. Cybium 35(3):
Agiadi K, Triantaphyllou M, Girone A, Karakitsios V, Dermitzakis M (2010) Paleobathymetric interp... more Agiadi K, Triantaphyllou M, Girone A, Karakitsios V, Dermitzakis M (2010) Paleobathymetric interpretation of the fish otoliths from the lower -middle quaternary deposits of Kephallonia and Zakynthos islands (Ionian Sea, Western Greece). Riv Ital Paleontol S 116 (1): 63-78 Bañon R, Arronte JC, Serrano A, Sánchez, F (2011) First records of purplemouthed conger Pseudophichthys splendens (Anguilliformes: Congridae) from the Galicia Bank (NW Spain). A northward range extension of their distribution in the eastern Atlantic. Cybium 35(3):
This integrated study (field observations, micropalaeontology, magnetostratigraphy, geochemistry,... more This integrated study (field observations, micropalaeontology, magnetostratigraphy, geochemistry, borehole data and seismic profiles) of the Messinian–Zanclean deposits on Zakynthos Island (Ionian Sea) focuses on the sedimentary succession recording the pre-evaporitic phase of the Messinian salinity crisis (MSC) through the re-establishment of the marine conditions in a transitional area between the eastern and the western Mediterranean. Two intervals are distinguished through the palaeoenvironmental reconstruction of the pre-evaporitic Messinian in Kalamaki: (a) 6.45–6.122 Ma and (b) 6.122–5.97 Ma. Both the planktonic foraminifer and the fish assemblages indicate a cooling phase punctuated by hypersalinity episodes at around 6.05 Ma. Two evaporite units are recognized and associated with the tectonic evolution of the Kalamaki–Argassi area. The Primary Lower Gypsum (PLG) unit was deposited during the first MSC stage (5.971–5.60 Ma) in late-Messinian marginal basins within the pre-Apulian foreland basin and in the wedge-top (<300 m) developed over the Ionian zone. During the second MSC stage (5.60–5.55 Ma), the PLG evaporites were deeply eroded in the forebulge–backbulge and the wedge-top areas, and supplied the foreland basin's depocentre with gypsum turbidites assigned to the Resedimented Lower Gypsum (RLG) unit. In this study, we propose a simple model for the Neogene–Pliocene continental foreland-directed migration of the Hellenide thrusting, which explains the palaeogeography of the Zakynthos basin. The diapiric movements of the Ionian Triassic evaporites regulated the configuration and the overall subsidence of the foreland basin and, therefore, the MSC expression in this area.
One of the most enigmatic features of long-term Cenozoic climatic evolution, with some analog pot... more One of the most enigmatic features of long-term Cenozoic climatic evolution, with some analog potential for present/future global climate change, is the last sustained warm and high-atmospheric CO 2 interval in Earth's history, which started after the end of the Messinian Salinity Crisis (5.971–5.332 Ma) in the Mediterranean Sea. We present high-resolution, astronomically-tuned climate (Mg/Ca, δ 18 O) and productivity (Ba/Ca, δ 13 C) proxy records from the planktonic foraminifera Globigerinoides obliquus in the Kalamaki section (Zakynthos Island, Greece), which sheds new light on the early Pliocene Mediterranean hydrographic dynamics, and the associated climatic transition from 5.33 to 5.11 Ma. We recognized four distinct climatic phases with variable amplitude changes: (1) very warm climate interval prior to 5.28 Ma characterized by minimum ice volume, large salinity fluctuations, enhanced productivity, and intense river runoff, (2) stable paleoceanographic conditions from 5.28 to 5.23 Ma, which reflect a relatively warm and mesotrophic to eutrophic open-marine environment with improved ventilation, (3) a brief interval (20 ky) characterized by the most pronounced ice growth and intense cooling (∼5 °C) coupled with the abrupt decrease of ventilation and primary productivity, and (4) reinstate-ment of relatively stable conditions (warm and well-ventilated mesotrophic upper water column) in conjunction with relatively stable sea-level after 5.21 Ma. Overall, the succession of these phases provides an explanation for the more variable Mediterranean climate and stronger hydrographic variability with respect to other regions during the early Pliocene.
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Papers by Konstantina Agiadi