A. Zelilidis

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.

Drainage evolution in a rifted basin, Corinth graben, Greece

Abstract Intrabasinal basement highs and transfer faults, distance from source, and the underlying geology influence the drainage pattern and the evolution of the 41 river basins in the northern Peloponnesus. These rivers were classified as antecedent (10), multistory (17), re-established (5) and juvenile (9) drainage types. Antecedent drainage is when a river has maintained its original direction of flow across later tectonic topography. Multistory drainage consists of a re-established drainage and of a reverse drainage. Reverse drainage, when flow direction along part of a river is reversed, consists of two opposing drainage components: a misfit and a reverse element; the area between these two elements, termed “wind gap”, is a dry valley. Re-established drainage is when a reverse element returns to its original flow direction. Juvenile drainage consists of small incising and headward-eroding streams. The sediments that the rivers flow across (soft uncohesive marls or coarse-grained deposits and Pre-Neogene basement with limestones), river power (strong close to the source or weak far from the source), presence or absence of transfer faults and tilted blocks due to the activity of synthetic and antithetic faults, all influence whether an antecedent drainage will remain unchanged or will be changed to a reverse drainage. When transfer faults cross-cut the area of a wind gap and the underlying sediments were soft uncohesive marls, reverse drainage changed to a re-established drainage. In other cases, where transfer faults were absent and underlying deposits were coarse-grained sediments or limestones, in the area of the wind gap, then reverse drainage remained unchanged.

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.

Geometry and sequence stratigraphy of the Late Eocene-Early Oligocene shelf and basin floor to slope turbidite systems, Lemnos Island, NE Greece

The Late Eocene-Early Oligocene sedimentary fill of the Lemnos Island, NE Greece, is represented by a submarine fan and shelf deposits. Turbidites in the system occur as a laterally isolated body, with one sediment influx center present. The influx center is a proximal distributary channel that occupies a position approximately in the fan’s center and displays the coarsest sediment in the study area. It also suggests in association with the main palaeocurrent direction toward NE a curved shape for the fan. The stratigraphic succession of the submarine fans indicates that their sedimentation started during the base level fall and completed shortly after the base level rise. As a consequence, the study area was filled by turbidites that correspond to forced regressive, lowstand normal regressive, and transgressive genetic units. The progradational bedsets, within the basal part of the turbidite deposits, recorded the history of the base level fall. The mixed progradational/aggradational style of the upper part of the submarine fan system suggests that the regression of the shoreline is driven by sediment supply during a period of base-level rise at the shoreline, or at a time of baselevel stillstand. The overlying shelf facies consist of thick to medium bedded sandstones and mudstones, which display a general thinning upward trend. The base of the mudstone facies that overlie the thick-bedded, amalgamated sandstones corresponds to a transgressive surface. This surface separates the low-stand deposits (thick-bedded sandstones) from the high stand deposits (mudstone facies), suggesting that deposition of shelf facies occurred during a transgressive system tract.

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.