N. Kontopoulos

Sedimentation and basin evolution of the Oligocene-Miocene Mesohellenic basin, Greece

The Oligocene-Miocene Mesohellenic basin of northern Greece and southern Albania is filled with up to 4 km of marine turbidites and basin margin strata. Surface outcrops include fan deltas, prodeltaic facies, and sandy and shaly submarine fan facies. All these facies in outcrop can be directly correlated with seismic facies in the subsurface, which in turn are compared with seismic facies in modern sandy submarine fans. Twelve seismic markers provide a stratigraphic framework that has been dated by new nannofossil biostratigraphy. Lowstand facies include erosional channels on the basin slope that aggrade basinward with sandy overbank levees to give composite sand bodies with an overall lobelike character. Distally, these pass into sandy channel-termination depositional lobes. Highstand facies are characterized by shaly basin slopes and shaly turbidites in the basin, with irregular reflections interpreted to represent shallow channels and slumps. The stratigraphic occurrence of lowstand facies compares closely with published eustatic sea level curves. The basin has the potential for significant gas, principally in stratigraphic traps. The Mesohellenic basin developed as a strike-slip half graben, synchronous with the Ionian foreland basin to the west of a mountain belt formed by the Pindos nappes.

Thrust dissection control of deep-water clastic dispersal patterns in the Klematia–Paramythia foreland basin, western Greece

The Klematia–Paramythia basin is an internal part of the middle Ionian zone of the Hellenide orogen in western Greece. It consists of Middle Eocene to Late Miocene turbidites, up to 3300 m thick, which were deposited in a series of submarine fans. Field studies suggest that the configuration and the depositional environments of the basin were affected by two tectonic phases. During the first tectonic phase, in Middle Eocene to Late Oligocene times, a foreland basin was formed west of the Pindos Thrust front. During the second tectonic phase, in the Early Miocene, the Ionian zone (a part of the foreland basin) was subdivided by internal thrusting into three sub-basins (internal, middle and external) and changed to a complex type foreland basin. Comparison of the type and facies associations of the turbidite deposits that accumulated within the basin suggests that these two tectonic phases had a significant effect on sedimentary dispersal patterns. During the first tectonic phase in the Klematia–Paramythia basin (when it was part of the foreland basin), fine-grained turbidites, up to 1050 m thick, accumulated on the distal part of a submarine fan. The lower part (900 m thick) of these deposits consists of thin to thick interbedded sandstone/mudstone beds which are interpreted as lobes and lobe-fringe (outer-fan) deposits. The upper parts (150 m thick) of these deposits are composed of very thin to thin siltstone/mudstone beds, representing a basin plain environment. During the second tectonic phase, sediments up to 2260 m thick were deposited in the Klematia–Paramythia basin. These deposits are interpreted as lobes and lobe-fringe (outer-fan) fine-grained turbidites in the central part of the basin, channel and interchannel deposits (inner-fan) in some areas of the periphery of the basin, and shelf deposits in the northern and southern terminations of the basin.

Messinian evaporites in Zakynthos, Greece

Abstract Messinian gypsum deposits of central Zakynthos consist of 10–15 m of gypsum turbidites intercalated in a terrigenous turbidite succession. Most of the turbidites are fine grained and thin bedded, perhaps transported by dense briny underflows, but one widespread 2–3 m thick bed of coarse gypsum crystals may have resulted from erosion in shallow water during a sea-level fall. The thickness of overlying terrigenous turbidite and Pliocene shelf sediments shows that the gypsum turbidites accumulated in water depths of less than a few hundred metres. Pollen suggest cooling immediately prior to gypsum deposition and cool dry conditions on land during evaporite formation. Warmer, wetter conditions returned immediately following gypsum deposition. Dinoflagellates provide no evidence for hypersaline marine conditions at the depositional site. In contrast, in eastern Zakynthos, the gypsum unit appears to have accumulated in shallow water and is unconformably overlain by shallow-water Pliocene sediments.

Depositional environments, sediment characteristics, palaeoecological analysis and environmental assessment of an internationally protected shallow Mediterranean lagoon, Gialova Lagoon – Navarino Bay, Greece

This study presents sedimentological, palaeoecological and geochemical data from a shallow Mediterranean coastal lagoon which has been severely influenced by human intervention over the last 70 years. The Gialova Lagoon is protected by international conventions and is listed in the Natura 2000 European Community Network as Special Protection Area (SPA) and Site of Community Importance (SCI). The spatial variability of sediment characteristics such as grain size, total organic carbon (TOC) and moment measures, mean, sorting, kurtosis and skewness were calculated. Moreover, micro- and macrofossil and sediment geochemical analyses were carried out on six gravity core samples. Study of the above parameters indicates that the anthropogenic impact and intervention are reflected in the micro- (ostracods, foraminifera, charophytes) and macrofossil (molluscs) taxa corresponding to different depositional environmental facies, representing a brackish lagoon with the influence of (a) fresh water inflow, (b) shallow marine environment and (c) hypoxic and dystrophic conditions. The geochemical characteristics and the calculation of the degree of sediment contamination using enrichment factors (EF), contamination factors (C i f ) and the index of geo-accumulation (I geo ) indicate a recent relative improvement of the lagoon towards the upper layers of the gravity cores, rendering the lagoon as unpolluted to moderately polluted. This combinatorial study of sediment geochemical characteristics, as well as the downcore micro- and macrofossil assemblages, can be considered as a baseline for future monitoring in accordance with European Union directives, and for any future engineering interventions for the lagoon environmental maintenance and conservation; as this is the first time that geochemical and downcore palaeoecological data have been presented from this lagoon.

Pliocene–Pleistocene fluvial/wave-dominated deltaic sedimentation: the Pamisos delta, southwest Peloponnesus, Greece

A fluvial /wave-dominated delta was formed during late Pliocene times in southwestPeloponnesus, influenced by NNW—SSE and ENE—WSW trending faults. The depositional patternremained unchanged through early Pleistocene times, when the pre-existing active faults with WNW—ESE extension were combined with an eastward asymmetrical subsidence of the graben. Inthe deltaic environment, marshes, lakes and lagoons were created in the western parts, whereas largequantities of sediments were deposited in the central and eastern parts adjacent to basin marginsof steeper relief. This study combines grain size parameters, total organic matter, carbonate and clay mineralogyand structural analysis to: (a) determine the pattern of sedimentation in sub-environments and (b)create a fluvial/wave-type deltaic depositional model, and distinguish between delta-plain, delta-front and pro-delta environments. The Pliocene-Pleistocene, fluvial/wave-dominated delta model inthis study can be used to predict deltaic sedimentation in analogous basins.