the genesis of the nissi peatland (northwestern greece) as an example of peat and lignite deposit...

International Journal of

International Journal of Coal Geology 26 (1994) 63-77 ELSEVIER

The genesis of the Nissi peatland (northwestern Greece) as an example of peat and lignite deposit

formation in Greece

K i m o n Chris tanis

Department of Geology, University of Patras, GR-26110 Rio-Patras, Greece

(Received July 22, 1993; revised version accepted January 26, 1994 )

Abstract

The Nissi Fen is located in a 12 km 2 intramontane basin in northwestern Greece. Since the last glacial, limnotelmatic and pure telmatic conditions, controlled mainly by karstic springs and partly by surface waters, favoured peat formation in the basin, resulting in the accumulation of a peat deposit up to 15 m thick. The present fen occupies a large area of almost 9 km 2. Flora cover comprises mainly Cyperaceae (Cladium mariscus and Carex species), while Phragmites australis extend along the banks of a river flowing through the basin, as well as around a lake in the southern part of the fen. These species also contributed to the peat formation. The Nissi peatland shows many genetic similarities to the Phi- lippi peat deposit, Eastern Macedonia, and may be considered as a recent analogue to the lignite deposits in the basins of Ptolemais, Western Macedonia and Megalopolis, the Peloponnese.

1. Introduction

Peat is an organic sediment consisting of plant remains that accumulate in mires. These mires can be split into two groups: topogenous and ombrogenous, depend- ing on the main factors controlling their formation. The formation of the topogenous mires depends on the topography; they form in low-lying areas, which are flooded by surface and spring water (rheotrophic mire or fen ). The ombrogenous mires form under humid climates and the water supply is due to precipitation (ombrotrophic mire or raised bog).

In Greece only minor occurrences of ombrogenous mires have been reported (Mavrommatis, 1972; Athanasiadis, 1977 ); they are located in the high, moun- tainous areas bordering Bulgaria and the former Yugoslavia. However, a few to-

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pogenous mires with herbaceous vegetation and shrubs are known, all of which are formed by terrestrialization (that is, by filling up of lakes), and/or by paludification (by flooding of flat areas due to the relative rise of the groundwater table) (Broussoulis et al., 1978; Melidonis, 1981: Christanis, 1983a,b: 1992; Bo- tis et al., 1993 ). Up to now, no fens have been found in deltaic areas and forest swamps do not exist in Greece.

The Nissi Fen is located in a 12 km 2 intramontane basin, about 20 km west of the city of Edessa, northwestern Greece (Fig. 1 ). The altitude of the basin lies between 475 and 480 m above sea level, while the surrounding mountains rise up to 1000 m. The small Edessaios (or Agras) River, which springs from the Mav- ropigi (Black Spring) and a small lake at the western basin margin, collects the water from other karstic springs and flows through the basin from west to east (Fig. 2 ), running towards the plains of Macedonia.

In the 1950s, the Greek Public Power Corporation (P.P.C.) constructed a 6.5 km long tunnel through the mountains, in order to transport water from the Ve-

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Fig. 1. Location of Greek peat and lignite deposits referred to in the text. D = Drama; P h = Philippi; N = Nissi; P = Small Prespa; F= Florina; P t = Ptolemais, K = Kalodiki; ,4 = Aliveri: M = Megalopolis.

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66 K. Christanis / International Journal ~l(i'oal Geology 26 (1994) 63- 77

A'

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Fig. 3. Diagrammatic cross-section of the Nissi peatland. 1= peat, including mud; 2 = calcareous mud, chalk, calc tufa; 3 = alluvial deposits; 4 = limestone; d = ditch; E = Edessaios river bed; p = pool.

goritis Lake (located in the west) into the basin. A ditch (Figs. 2 and 3 ) was also dug in the basin in a W-E direction, in order to facilitate the water supply east- wards. The aim of these works was to ensure the water supply to the hydroelectric power plant of Agras (50 MW), which is located downstream from the study area. Moreover, a dam a few hundred metres long was constructed along the left bank of the Edessaios river, in order to protect the lower area, lying between the alluvial fan of Nissi and the river, from flooding.

In the years 1975-1977 the fen was drilled and sampled by the P.P.C. It was found that the peat bed is more than 15 m thick and the reserves exceed 50× 10 6

m 3 of natural peat (Public Power Corporation, 1979). At first, construction of a 120 MW thermoelectric power plant using peat fuel was planned. Later, interest was shown in using the peat for agricultural and horticultural purposes. Due to protests by the inhabitants against the peat mining, both projects have been can- celled. The fen is now used as meadow and pasture, while in the drained area between Nissi Village and the Edessaios River poplars are cultivated.

2. Regional setting

The basin, as well as its northern, southern and eastern margins, belongs to the geotectonic zone of Almopia, which, in the study area (Fig. 2), consists mainly of Upper Cretaceous limestones, calcareous conglomerates and small occurrences of serpentinites and tuffaceous schists. The Almopian zone is overthrust westwards onto the Pelagonian zone, which comprises the western basinal margins and consists of Upper Cretaceous limestones and Palaeocene flysch (Mer- cier and Vergely, 1988 ). Two groups of normal faults can be distinguished in the study area, striking ENE and NNW. The latter set resulted in the basin formation (see discussion ).

Alluvial deposits of fluviatile origin and Middle Pleistocene age (Mercier and

K. Christanis / International Journal of Coal Geology 26 (I 994) 63- 77 67

Vergely, 1988 ) were probably formed by a distributary of the Palaeo-Aliakmon river, which today runs from west to east towards the Aegean sea, a few kilo- metres to the south of the study area. The alluvial deposits mainly cross the eastern narrow part of the fen in an almost NE-SW direction and occur at the floor of the peat in this area (Public Power Corporation, 1979 ). This indicates that at least the eastern narrow part of the basin was formed after the Middle Pleisto- cene. The many alluvial fans emanating from side valleys show a centripetal pat- tern and tend to flush the basin with inorganic material of fluvioterrestrial origin. The most extended fans are those of Nissi in the north and Vryta in the south (Fig. 2).

According to the lithological data of about 97 boreholes drilled by the P.P.C. ( 1979 ), the sedimentary filling of the basin is mainly of limnic and telmatic origin. At depths between 35 and 43 m under the present surface, thin peaty lignite (?) seams are included in the limnic sediments. A peat deposit reaching up to the present basin surface has also been formed. The peat formation outcrops over an area of almost 9 km 2. The average peat thickness is 5.5 m and in several places exceeds 12 m. The thickest peat bed occurs at the northern basinal area, close to the foot of the northern hill. The peat floor consists of sand, silt, clay, calcareous mud and chalk. Calc tufa (logged as travertine in P.P.C.'s protocols) has also been drilled in several places. The intercalation of clastic debris from the margins remained only locally restricted, except in the area of the expansion of the Vryta and Nissi alluvial fans. The total thickness of the basinal sediments remains un- known. P.P.C.'s deepest boreholes reached a maximum depth of 87 m without entering into crystalline bedrock. The lack of biostratigraphical data does not per- mit any suggestion about the time of the basin formation, but the absence of Pli- ocene sediments in the marginal area of the basin led to the conclusion that the basin formation took place during the Early to Middle Pleistocene, by post-A1- pidic faulting tectonics. The subsidence necessary to provide the sedimentary area, in which the plants have grown and the peat has accumulated, has been caused by the erosion of the basinal karstic bedrock (Lob, 1992 ).

The groundwater table lies near the basin surface (at 478.5 m above sea level). The seasonal fluctuation is limited to + 0.3 m. The aquifer is fed mainly by karstic waters, which are derived from springs lying mainly at the western edge of the basin, but also from a mire spring east of the village of Vryta. The run-off from the surrounding drainage area is generally restricted and seasonally irregular (Soulios, 1978 ).

There is a shallow pond (less than 1 m deep) in the central part of the basin. To the south, a lake with a maximum depth of 3.5 m occupies an area of almost 0.4 km 2. The pond and the lake are in the tectonically most subsided parts of the basin. Their shape (Fig. 2) reveals the prevailing direction of neotectonic faulting in the area, which strikes NNW-SSE.

The area has a humid, Mediterranean climate. The average temperature in Jan- uary is 3.5°C, and 23°C in August. The average annual precipitation is as much as 725 mm (Soulios, 1978).

68 K. ( 'hrLvtams / Intcrpzatmpza/ Join'ha/ q / ( 'ou/ (;eo/ogr 26 ( / 994i r 3- 7:

3. Field and laboratory procedures

The field work was carried out in 1991-92 during three visits to the area. The main helophytic communities on the present mire surface were identified and classified by dominant species. The extent of the main communities was mapped (Christanis and Papadaki, 1992). The stratigraphy of the uppermost deposits was determined by coring. Sixteen boreholes (Fig. 2) were made with an Edel- mann hand-driven corer, up to a depth of 10 m. The cored sediments were examined macroscopically and logged on site. The degree of peat decomposition was estimated according to the von Post method, which is based on the preser- vation of plant remains and the quantity and colour of the pressed-out water ( Schneekloth, 1981 ).

Moisture and ash content of samples, taken from boreholes N-2 and N-15, each representing depth intervals of 20 cm, were determined firstly by oven drying at 105°C for 48 h and then by burning in a muffle furnace at 550°C for 4 h. In addition, pH (in H20) and electrical conductivity measurements were carried

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• peat ~ clay gyttja

detritic / i ~' '~'~, gyttja clay

calcareous root remains of gyttja 7" Iris pseudacorus

Fig. 4. Lithological, palaeobotanical and 14C age data in the N-2 and N-15 borehole profiles. H = humification degree (after yon Post ); CI, Ph, S= tissues of Cladiurn, Phragrnites and Sphagnum respectively; cl, G= pollen of CladiuJn and Gramineae, respectively; CI, Ca, M, P, C, L = fruits and seeds of Cladium, Carex, Mentha, Polygonurn, Ceratophyllurn and Lythrum, respectively; O= Oogonia of Characeae.

K. Christanis / International Journal of Coal Geology 26 (1994) 63- 77 69

out. The procedures used followed the guidelines given by the Peat Institute of the Low Saxonian Geological Survey, Germany (Goetzke, 1974).

Five peat samples each of the N-2 and N-15 cores, obtained from different depths (0.5, 1.5, 2.4, 4.0, 8.4 m and 2.0, 2.5, 3.2, 4.1, 5.6 m, respectively; Fig. 4), each representing a 40 cm thick peat layer, were examined palaeobotanically for plant macroremains by Dr. J. Schwaar of the Soil Technological Institute, Bre- men, Germany. Additionally, three peat samples obtained at depths of 4.2 and 8.6 m from the N-2 core and at 6.4 m from the N-15 core were dated with 14C by Dr. Y. Maniatis and G. Fakorellis, National Center of Scientific Research (N.C.S.R.-Demokritos), Athens, Greece.

4. Results

The helophytic vegetation on the fen surface consists of Cladium mariscus, many Carex species, Phragmites australis, Scirpus lacustris, Typha angustifolia, Iris pseudacorus, Cyperus, etc. Three main zones of vegetation are distinguished: the Cladium, Carex and Phragmites zones (Fig. 2 ).

The Cladium zone consists almost exclusively of Cladium mariscus. It grows in places with restricted drainage, in the neighbourhood of fresh water flows, which are rich in calcium ions; in this case close to (but not on) the banks of the Edes- saios river. In the southern part of the fen, east of the Vryta village, Cladium occur in a wet area supplied by karstic spring waters. In the Carex zone, Carex spp. predominate, but Typha, Juncus and Scirpus also form clusters and isolated Cyperus, Alisma plantago-aquatica and Equisetum palustris also occur. Apart from Phragmites australis, the Phragmites zone also includes clusters of Carex and some Scirpus and Iris pseudacorus. Moreover, aquatic shrubs, mainly Salix cinerea, Sambucus nigra and Solanum dulcamara (Lavrentiadis, 1956; Pavlides, 1989) form islets in the eastern part of the fen and Populus are cultivated in the fen areas which have already been drained.

The Cladium and the Carex zones seem to be genetically connected to a pure telmatic regime, while Phragmites mainly occupy the areas around the pond and the lake, as well as the narrow zones along the banks of the Edessaios river, that is, they prefer a limno- or fluvio-telmatic environment.

The peat shows a relative homogenous matrix, consisting mainly of fine roots (felt texture); epidermis pieces of Phragmites australis, fruits and seeds from Cladium mariscus and various Carex spp., pieces of reddish, woody roots from Iris pseudacorus etc., were also observed. The peat has a brown to brown-reddish colour. Wood or charcoal horizons have not been found. The degree of humification estimated after the field method of von Post ranges between 4 and 6. No sharp change in the degree of humification or in the peat-forming plant communities with depth was recorded.

The peat is developed up to the surface. Only in the northern and southern parts of the basin, is the peat covered by clastic material derived from the alluvial fans of Nissi and Vryta, respectively (Fig. 2 ).

70 K. Christanis /International Journal oJ Uoa/ Geology 26 (1994) ~3- 77

The sediments intercalated with the peat up to the depth drilled ( 10 m) do not exceed a thickness of 30 cm at most. They are of limnic and limnotelmatic origin (i.e., clays, calcareous muds and organogenic mudswgyttjae). The small thick- nesses of these layers and the similarity of their plant macroremains to those in the peat show that interruptions of the telmatic environment in favour ofa limnic one were locally restricted and only of short duration (Fig. 3 ).

According to the data obtained from the palaeobotanical determinations, Cladium mariscus and subordinate Carex riparia predominate in the samples of the N-2 borehole up to a depth of 9 m, while in the N-I 5 samples remains of Cladium mariscus and Phragmites australis have been recognized. Moreover, in some of the N-15 samples Carex spp., aquatic (Ceratophyllum demersum) and subaquatic plants (Chara spp. ), as well as various terrestrial and semiterrestrial plants, such as Polygonum spp., contribute to the peat formation. These indicate that at the N- 15 coring site the prevailing conditions were not purely telmatic, as were those at the N-2 site, but they have been strongly influenced by the fluvioterrestrial (alluvial fan) and the limnic regimes. This contention is also sup- ported by the limnic lithofacies in this part of the fen (Fig. 4 ).

The preliminary determinations of the physical and chemical properties of the peat and the other organogenic sediments can be summarized as follows: The moisture content of the N-2 samples ranges between 87% and 90%, that of the N- 15 between 84% and 88%. The ash contents of the N-2 and N-15 (moisture free) samples lie between 5% and 20% and 7-24%, respectively, without showing any trend with increasing depth. The pH of the peat from both cores ranges between 5.1 and 6.5, while the electrical conductivity values lie between 50 and 260/tS/ cm. The generally higher ash content of the N-15 cores compared with that of the N-2 samples can be explained by a greater supply of inorganic material, which is transported fenwards by surface waters. In the northern and central fen the influence from the clastic material was limited. Further determinations, such as those of the chemical composition of ash from the peat samples, will be carried out in the future and may provide more accurate chemostratigraphic data on the peat- forming conditions (Christanis, 1983a ).

Chassapis et al. (1989) carried out chemical analyses on representative samples from some Greek lignite and peat deposits. According to their results, the Nissi peat has an average moisture content of 85.9% and an ash content (on a dry basis ) of 18.5%. The gross calorific value is ~ 800 kcal/kg (on an ash-free basis). The dry and ash-free peat contains 35% fixed carbon and 65% volatile matter, while the elemental composition is 57% C, 36% O, 5.6% H, 0.8% N and 0.6% S. Analyses of six samples from three boreholes made by the P.P.C. (1979) do not differ significantly.

Bottema (1974) carried out palynological examinations in samples obtained from one shallow borehole in the northeastern part of the fen, ~ 4 km southeast of the village of Nissi. There, the peat closely intercalates with gyttjae. The fen conditions are marked by the predominance of pollen of Gramineae, Cyperaceae, Cladium, Sparganium, Salix, etc., while the open water conditions are marked by Nymphea, Potamogeton and Myriophyllum. From the coordinates of the drill


site it can be seen that Bottema cored in the northeastern marginal area of the peatland, and he therefore found the bedrock at a depth of 7.25 m. According to Bottema's radiocarbon dates, carded out on samples from various depths, the Pleistocene/Holoeene boundary lies just above the bedrock and the calculated sedimentation rates vary between 0.3 and 1.2 mm/yr, with a mean value for the whole limnotelmatic sequence of 0.65 mm/yr.

The N-2 core at depths of 4.2 and 8.6 m under the present fen surface gave ~4C dates of 4,756 + 83 and 16,151 + 272 yr B.P., respectively, which correspond after correction to real ages to 5,460 ___ 133 and 19,050 +_ 305 yr B.P. These dates reflect a mean sedimentation rate of 0.76 mm/yr for the uppermost 4.2 m thick peat layer and 0.32 mm/yr for the deeper horizons. The sample from the southern fen (borehole N-15 from a depth of 6.4 m) is 14C dated to 8,034 +__ 122 yr B.P., which, after correction, corresponds to a real age of 8,924 _+ 374 yr B.P. Therefore, in the N-15 area the sedimentation rate was about 0.71 mm/yr. These rates are similar to those found in the Nissi Fen by Bottema (1974), as well as in other Greek fens, such as Philippi (Christanis, 1983a) and Kalodiki (Botis et al., 1993 ). Con- sidering a mean accumulation rate for the Holocene peat of 0.7 mm/yr , the Hol- ocene/Pleistocene boundary at the N-2 site lies at a depth of 7.4 m under the present surface, while the mean sedimentation rate of the Pleistocene peat is ~ 0.13 ram/yr.

5. Discussion

The development of the Nissi peat formation is reconstructed based on the results from this study and the coring data of the P.P.C. The Edessaios basin was formed during the late phase of the alpidic tectogenesis. No ehronostratigraphic data are available on the time of the basin formation, but an Early to Middle Pleistocene age may be suggested.

During the Pleistocene, the lacustrine regime was dominant in the basin. A great lake covering the whole basin was formed, into which karstic spring and surface waters flowed. They resulted in the deposition of calcareous (calcareous mud, partially chalk and ealc tufa) and elastic sediments (sand, silt and clay), respectively. The calcareous sediments were deposited mainly in the western part of the basin; namely, in the west of the axis between the two major alluvial fans (Nissi, Vryta), which provided the elastic material. The latter was deposited in the basinal area to the east of the aforementioned axis (Fig. 5a). The rest of the alluvial fans, situated at the northern edge of the basin, contributed little or not at all to the elastic influx.

The western narrow basinal margin, namely the area between the borehole sites Nos 5 and 13 (Fig. 2), was affected many times by terrestrialization (Fig. 5b). This area corresponded to the shore of the Pleistocene lake, this is proved by the close intercalation of clay, peat and calcareous mud found down to a depth of 55 m (the lowest depth explored). A few short interruptions of the lacustrine in favour of the telmatic environment were also noticed in larger parts of the basin.

72 K. ( hr~.stani.s .; l n [o~ml lona l . l oumla / qt ( oa i Geo/o~,:! 2ti (1994) ~,.~- : 7

N

(a)

(b)

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~ Z - r = -=- ~--~- :_~ _--~Z~ --- (d)

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Fig. 5. Schematic maps of five stages in the development of the Nissi peatland. (a) and (b) Middle (7) Pleistocene. (c) Last glacial. (d) Early Holocene. (e) Late Holocene. /=fen; 2=lake; C=CaCO3- rich water; 3= present alluvial fan.


They are marked by the formation of thin peaty lignite (?) seams in the northern and in the central basin. In the southern part, where today the lake exists, limnic conditions predominated continuously at this time.

In the last glacial (Wiirm) the water level in the basin dropped due to hydrological-hydrogeological and/or tectonic factors. The drop in the water level is attributed either to the general aridity of the last glacial (Bottema, 1978; Frenzel, 1980) or the enlargement of the basinal opening to the east. The infilling process was restricted to the northern part of the lake. There, the peat spread upwards and outwards and accumulated with a mean rate of ~ 0.13 mm/yr , while the southern part of the basin was occupied by open water, fed mainly by the alluvial fan of Vryta (Fig. 5c).

With the onset of the Holocene the process of lake filling gradually migrated southwards and the entire basin was transformed to a fen. After the initial stage of lake congestion, due to the growth of peat-forming plants (terrestrialization), the paludification process continued. Pure telmatic conditions predominated throughout the entire peat sequence in the northern part of the fen, favouring the growth of Cyperaceae, such as the calciphilous Cladium mariscus, Carex and subordinate Scirpus and Cyperus. On the other hand, in the central and southern part of the basin peat accumulation was very often interrupted by a lacustrine regime, marked mainly by the sedimentation of organogenic and calcareous mud and clay. Springs emanating into the fen supplied the southwestern part (N-15 site) with karstic waters and favoured the growth of Cladium, together with Phragmites, Typha and aquatic-subaquatic plants, which contributed to the formation of peat and organogenic sediments (Fig. 5d).

The lateral and temporal intercalation of peat with limnic and limnotelmatic facies (Liittig, 1991 ), as well as the lack of marker horizons in the Nissi peatland (i.e., isochronic lithofacies), such as the volcanic tephra layers in the peatlands of Philippi (Christanis, 198 3a,b) and Kalodiki (Botis et al., 1993 ), do not per- mit any assessment of the formation of isochronous peat layers and the neotectonic faulting activity in the area. Obviously, the pond and the lake in the basin formed due to faults active in the Holocene. Considering the results of radiocarbon dating at the N-2 and N- 15 sites together with the dates of Bottema (1974), it can be concluded that the Holocene peat accumulated in almost every part of the basin with a mean rate of ~ 0.7 mm/yr , since it is approximately equal at the three sites. This presumes a uniform subsidence of the crystalline basement, followed by uniform compaction of the deposited peat everywhere in the basin, at least during Holocene.

T~vo major alluvial fans have temporarily interrupted peat formation, provid- ing the fen with clastic material: the Nissi fan to the south and the Vryta fan to the north and east. Their activity during the Holocene was not significantly an- tagonistic to the peat formation, as it was in the earlier period. In the late Holo- cene the southern part of the basin tectonically subsided, the fen was 'drowned', peat accumulation was interrupted and the present lake formed. The Edessaios River did not change its bed during the Holocene. No evidence of migration was

74 K, ("hristanis / International Journal of(hal Geology 26 (1994) 63- 77

found, but a discontinuous 'operation' of the river bed may be suggested (Fig. 5e).

Lob (1992) considers karst hydrology as the controlling factor in the formation of the Nissi peatland. Subsidence by erosion of the basinal karstic bedrock interrupted the continuous closing of the lake, which would have taken place if there were progressive plant and peat deposition. This would have been a cyclic process. Therefore, he suggests a limnotelmatic environment for peat accumulation, however, according to the results of this study, a pure telmatic regime is proposed for the northern part of the fen, where the thickest peat formation occurs, and for the southwestern fen.

6. The Nissi Fen compared to other Greek peatlands and lignite deposits

Apart from their own significance as unique hydrobiotopes, mires offer important information about contemporary depositional environments, peat-forming plant communities, peat facies, geological settings, hydrology, physical and chemical parameters, all of which define the character of a mire. Although these data cannot be directly correlated between different geological periods, mainly due to the evolution of the flora, they contribute to the understanding of the genetic rules which govern peat accumulation, and consequently coal formation.

The investigations of Recent and sub-Recent fens in Greece are all of fens formed in intramontane basins: no fens in paralic environments are known. The main peat-forming plants are reeds and sedges: indications of swamp forests have never been found. In some fens, limnotelmatic environments have favoured the formation of the appropriate biotopes for peat growth (Small Prespa, Kalodiki and partially in Nissi; Fig. 1 ), consisting mainly ofaquatic and subaquatic plants, as well as Phragmites and Typha. In other fens pure telmatic regimes have led to peat accumulation (Philippi and Nissi). In these, the Carex genera, comprising a large number of species, have grown both in drier and in wetter areas. Karstic springs have provided water rich in calcareous compounds, favouring the growth of Cladium. In general, karst hydrology is an important factor controlling the type and growth of the peat-forming plant communities, as well as the influx of clastic material into the fen, and, hence, the type of peatland in Greece (Liittig, 1971; Christanis, 1983a,b).

Peat accumulation rates during the Holocene lie between 0.5 and 1 mm/yr in the Philippi basin, 0.6 mm/yr in Kalodiki and 0.7 mm/yr in the Nissi Fen and are similar to those in many recent mires of the temperate zone (Teichmiiller and Teichmiiller, 1982; Styan and Bustin, 1983; Moore, 1987). In contrast, the Last Glacial values were generally limited to < 0.4, < 0.1 and ~ 0.1 mm/yr , respectively (Christanis, 1983a; Boris et al., 1993). These values (0.1 mm/yr ) correspond to peat accumulation rates estimated in recent mires of the Arctic region (McCabe, 1987 ). The cool and add climate during the last glacial did not totally arrest biomass production and accumulation in the Greek fens, as it did in north-

K. Christanis /International Journal of Coal Geology 26 (1994) 63-77 75

era latitudes, but it drastically retarded it. The climatic amelioration in the Hol- ocene, which was followed by an increase in humidity, probably resulted in the acceleration of peat deposition.

Intramontane basins represent potential settings for developing coal deposits in Greece, while paralic basins do not comprise significant deposits of mineable Greek coal. The largest deposits are located in the intramontane basins of Flor- ina-Ptolemais-Kozani (Western Macedonia), Drama (Eastern Macedonia), Aliveri (Euboea, Central Greece), Megalopolis (Peloponnese; Fig. 1 ). Concern- ing the geological setting, the biofacies and lithofacies (Fig. 4), the Nissi Fen can be proposed as an analogue of the thick peat beds in the Philippi basin, and of the Ptolemais, Drama, and Megalopolis lignite deposits. All of them originated from a reed-sedge vegetation, formed under pure telmatic to limnotelmatic conditions and by the influence of karst hydrology; that is, in environments similar to that which dominated in the Nissi Fen (Weyland et al., 1960; Vinken, 1965; Teich- miiller, 1968; Hiltermann and Liittig, 1969; Kaouras et al., 1991 ). These contrast with older lignite deposits in the basins of Aliveri (Lower Miocene), and of Flor- ina, for example, Vevi (Middle Miocene) and Vegora (Upper Miocene/Lower Pliocene), in that the lignites are xylite-rich, evidence of an arborescent origin, and represent successions of forest swamp environments with mainly Taxodi- aceae (Velitzelos, 1979; Lawatscheck, 1985; Jacobs, 1988; Riegel et al., 1989 ).

7. Conclusions

In the Nissi Fen the peat has accumulated since the last glacial under limnotelmatic conditions. After the infilling of the former lake, which coincided with the Pleistocene/Holocene boundary, the peat continued to accumulate in a purely telmatic environment, which was interrupted only by laterally and temporarily restricted limnic facies.

Peat accumulation rates in Greek fens during the Holocene are similar to those of recent mires in the temperate zone, while during the last glacial the rates were similar to the present rates in Arctic mires.

The geological setting, depositional environment and peat-forming plant communities of the Nissi Fen are similar to the Philippi peat deposit and can be considered as the precursor of a lignite deposit analogous to those in the basins of Ptolemais, Drama and Megalopolis.

Acknowledgments

The author would like to thank Dr. J. Schwaar, Soil Technological Institute, Bremen/Germany, for the palaeobotanical examination of the peat samples, and Dr. Y. Maniatis and G. Fakorellis, N.C.S.R.-Demokritos, Athens, for carrying out the radiocarbon dating. Many thanks go to A. Athanasiou, P.P.C., for provid- ing P.P.C.'s protocols, as well as, to J. Broussoulis and A. Papadaki, I.G.M.E.,

76 K. ( "hristanis / lmernattonal Journal o/Coa/ Geology 26 (I 994) :~3- 77

At hens , a n d Dr. A. L i v a n i o u - T i n i a k o u , B o t a n i c a l In s t i t u t e , U n i v e r s i t y o f Pa t ras , Greece , for he lp fu l d i s c u s s i o n s d u r i n g th i s p ro jec t . I a lso t h a n k m y s t u d e n t s D. M e n t o u , E. Sokos , A. B o u z i n o s a n d M. K o n s t a n t i n o u for t h e i r a s s i s t ance d u r i n g the f ie ld work , e spec i a l l y d u r i n g the dr i l l ing . F i n a n c i a l s u p p o r t was, in par t , re- c e i v e d f r o m the R e s e a r c h Off ice o f the U n i v e r s i t y o f Pa t ra s .

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the genesis of the nissi peatland (northwestern greece) as an example of peat and lignite deposit...

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