This paper presents the geological structure of the entire region of northwestern Greece (Epirus). Four geotectonic zones (Subpelagonian, Pindos, Gavrovo, and Ionian) develop in this area, overthrusting one another, their compression axes trending NE-SW. Normal, reverse, and strike-slip faults with main directions NNW-SSE, NE-SW, and E-W have influenced the geological formations. In the context of this paper, the results of all previous, relevant studies were considered, summarized and reviewed, in order to provide a brief historical recursion and present some of the most important discoveries made in the area, from 1840 until present. All these results were evaluated and combined, the geological formations were grouped according to their characteristics and field work enabled the confirmation or addition of new data, which led to the compilation of a new geological map, using GIS techniques, for the improved visualization of the geological and tectonic structure of northwestern Greece. This map illustrates a lot of new data, based on detailed geological-tectonic mapping, depicting the precise boundaries of the geological formations, detecting of Neogene and Quaternary sediments and evaluating fault activity. The knowledge and illustration of an area’s geological structure constitute a dynamic tool for further scientific research and economic development.
The knowledge of geology of an area contributes to the exploration and exploitation of rocks and minerals with economic benefits, prognosis of natural disasters, evaluation, and overcome of environmental problems, definition of paleo-environ- mental conditions, successful construction of engineering works, etc. Therefore, the good understanding and knowledge of the geological structure of an area contribute variously to the improvement of human life quality and solution of its significant problems.
The geological structure of northwestern Greece (Epirus;
definition of the strike and dip of beds, comparison and correlation of different geological formations. Based on the existing literature data and the field work results, the geological formations have been grouped. Neotectonic mapping has been carried out based on field observations, fault mapping and tectonic analysis computing the orientations of the stress axes. All above-mentioned works have resulted in the compilation of two maps at 1:100,000 scale, by GIS techniques:
(a) A map showing the distribution of geotectonic zones (
(b) A new geological map of northwestern Greece (Epirus;
The region of Epirus covers an area of 9203 km2 and it constitutes 6.97% of Greek territory. Epirus is characterized by a sharp relief and a plenty of surface waters. Pindos, being the major mountain chain of Greece, dominates and its highest point has an altitude of 2637 m. The plains (25.8%) are limited to the areas of Arta and Preveza and along the rivers of Acheron and Kalamas. The mountains occupy a percentage of 74.2% of the total area while high dips and deep valleys (e.g. Vikos, Arachthos and Acherontas) are identified. Some of the most important mountains of Epirus are as follows: Smolikas (2637 m), Grammos (2520 m), Tymfi (or Gamila, 2497 m), Athamanian Mountains (or Tzoumerka, 2393 m), Lakmos (or Peristeri, 2295 m), Douskos (Nemertsika or Meropi, 2198 m), Tomaros (1974 m), Valtos Mountains (1852 m), Mitsikeli (1810 m), Mourgana (1806 m), Souli Mounts (1615 m) etc. Significant rivers may be referred to the following ones: Aoos, Arachthos, Kalamas (or Thyamis), Louros, and Acherontas. A significant element of the hydrogeological situation of Epirus constitutes the Pamvotis Lake (or Ioannina Lake). The watershed of the water district of Epirus is defined by the Amvrakikos Gulf in the south and it continues northwards along the Mountains of Valtos, Athamanian, Northern Pindos, and Grammos. Finally, the northern boundaries of this water district are defined by the Greek-Albanian borders.
Epirus is made up of the geological formations belonging to the Subpelagonian, Pindos, Gavrovo, and Ionian Geotectonic Zones as well as of post-alpine formations [
During 19th century, Boué [
During the first half of 20th century, Renz [
Aubouin [
Zone in the western continental Greece, divided it into Internal, Central, and External (from east to west) and analyzed its stratigraphy and tectonics. He studied the tangential structures and showed that Epirus is made up of syncline and anticline structures which overthrust towards the west while the eastern anticlines incline eastwards. He also indicated the existence of strike-slip faults considering that these faults are older than folds and overthrusts. Finally, he determined the age of this overthrust tectonic activity in the Middle-Upper Miocene period.
Researchers from Institute of Geology and Subsurface Research-IGRS and Institut Francais du Petrole-IFP examined the presence of normal faults of Jurassic age in the Ionian Zone for first time [
Bernoulli and Renz [
Pomoni-Papaioannou [
King [
Pomoni-Papaioannou [
Horner [
According to Doutsos [
Karakitsios [
Sorel [
Karakitsios [
Rondoyanni [
Nikolaou [
In addition, a plenty of scientific publications have contributed to the better understanding of the geological structure of northwestern Greece. Among them, the publications of Nikolaou [
As it has been above-mentioned, Epirus is made up of geological formations belonging to the Subpelagonian, Pindos, Gavrovo, and Ionian Zones (from east to west), and sediments of Upper Eocene-Quaternary age deposited over them. A detailed description of the geological formations and lithostratigraphic structure of each zone based on previous studies (since 1840) and personal field observations follows. These formations have been grouped and the lithostratigraphical columns, which correspond to this grouping, are presented for each zone. The distribution of these formations is illustrated in the geological map of
Particularly in terms of the correct approach of thegeological structure of northwestern Greece, apart from gathering all the relevant literature, the study focused on detailed geological-tectonic mapping, identifying the following:
(a) The lithological types of all the formations constituting the area’s lithology,
(b) The common features of such formations, apart from their age, for the purpose of grouping them correctly,
(c) The locations of geological boundaries, as in several cases field observations showed that the boundaries differed from the relevant locations illustrated in existing maps, and
(d) The tectonic structures which were grouped in faults, folds and overthrusts and classified-evaluated as to their activity degree, inactive, potentially active, and non active.
Notably, the background of the map is the area’s terrain in 3D form, as produ- ced by the ArcGIS software (source: www.esri.com), for the reader’s improved understanding and the optimum illustration of the real picture.
Specifically, combining and synthesizing all the literature and the field work data emerged the following geological formations.
The post-alpine sediments of Epirus include:
(a) Molassic formations of Upper Eocene-Miocene age deposited in the Mesohellenic Trough [
(b) Neogene and Quaternary sediments overlying unconformably the alpine formations and the molassic formations in grabens and erosional basins.
The Neogene and Quaternary sediments occupy the basin of Ioannina and large part of southern Epirus (e.g. areas of Arta, Preveza, Parga etc.). In general, rapid changes of lithological phases, horizontally and vertically, with parallel changes of terrestrial, marine and lacustrine facies in the formations of the same age as a result of neotectonic activity in combination with morphogenetic processes. The Neogene and Quaternary sediments have a variable thickness and contribute significantly to the development of aquifers [
The Quaternary sediments consist of Holocene and Pleistocene deposits:
(a) The Holocene sediments occur in wide extent and include dunes and coastal sands, creeping and landsliding materials, shoals (rich in organic material), scree (
(b) The Pleistocene sediments are represented by glacial deposits-qg of Wurm and Riss age [
Riss, a glacier phase took place creating glacial deposits as moraines (at altitudes up to 1400 m) and glacier valleys (altitudes higher than 1900 m) forming old scree. In addition, deposits of internal basins (terra rossa-tr;
(a) Clays, sands, marls, conglomerates and rubbles-pebbles, of Upper Plioce- ne-Lower Pleistocene age, and
(b) Clays and clay-marls (Ne) of Upper Miocene-Lower Pliocene (Seravallian) age with intercalations of crystalline gypsum occurring in the area Riza-Kastro- ssykia, northwestern of Preveza.
In the Preveza-Loutsa area, the Neogene formations have been deformed intensely resulting in creation of folds in which the axes have a NW-SE direction. Minor occurrences of Neogene sediments are observed in the areas of Konitsa, Delvinaki, Parapotamos and Parga.
In the Subpelagonian Zone, towards the Pindos Zone, a large trough was for- med during the final orogenetic activity of Upper Eocene age, in which very thick molassic sediments were deposited during Oligocene-Middle Miocene. This is the Mesohellenic Trough-mt extended in a NW-SE direction from the Greek-Albanian borders to the areas of Kastoria, Grevena, Kalampaka and south-
wards [
(a) Eptachorio Formation of Oligocene age. It consists of upper beds (marls with thin sandstone intercalations, intermediate sandstones, lower marls), transition beds (blue or green-yellow silty marls alternating with fine-grained to micro-conglomeratic sandstones) and base layers (alternations of polygenetic conglomerates with fine-grained to micro-conglomeratic sandstones and marls). In this formation, consecutive layers of marls-siltstones and mainly grey-blue coloured siltstones dominate, while sandstones have a smaller participation and conglomerates even smaller.
(b) Pentalofos Formation of Oligocene-Lower Miocene (Aquitanian) age. It consists of sandstone series with polygenetic conglomerates, upper series of conglomerates and sandstones (cohesive marls and fine-grained marly sandstones), intermediate marls, polygenetic conglomerates and sandstones.
The Subpelagonian Zone [
The ophiolites mainly consist of peridotites and serpentinites and are accompanied by red cherts. The ophiolites of the Kastanea overthrust sheets accompanied by cherts are dated as of Jurassic age.
The Pindos Zone [
The schist-chert formation-P.JC-k,sh of Jurassic age is composed of multicoloured cherts (radiolaritic, blue, green, brown, red and black coloured), clays, sandstones, siliceous limestones, and red cherts. The lower members consist of
alternations of red platy limestones and cherts with gradual transition towards marly limestones (grey to white coloured) and decreased presence of cherts (Upper Triassic-Lias). The multicoloured cherts with thin layers of clayey-siliceous material, pellites, and limestones constitute the characteristic stratigraphic horizon of the Pindos Zone of Dogger-Tithonian age. Limestones with Calpionella of Upper Tithonian-Valanginian age consist of (a) red and yellow-green limestones including red-green cherts, in the lower members, and (b) red limestones with thin layers of clayey-marly material and cherts as well as brecciated limestones and calc-limestones including cherts, in the upper members [
On the schist-chert formation, the called first flysch of Pindos Zone-P.C-fl,k has been developed. This flysch consists of (a) alternations of marls, radioralites, cherts, and marly schales, (b) sandstones, (c) pelagic sandstone, brecciated limestones, and pellites of Lower Cretaceous age. The pelagic platy limestones-P.C-k with siliceous material layers (cherts) of Upper Cretaceous age constitute the result of carbonate sedimentation, which took place during this period without any interruption and unconformity [
A series of transition beds-P.bk of Late Cretaceous (Maestrichtian-Danian) age is composed of alternations of platy limestones, sandstones, and shales (
The flysch-P.fl formed during Danian/Lower Pliocene-Upper Eocene is called as second flysch (or flysch) of the Pindos Zone in contrast with the Lower Cre- taceous first flysch of the same zone. It constitutes the main flysch and consists of rhythmic alternation of sandstones and marls with local conglomerates (lenticular layers of small thickness) and limestones. It is considered as the most
typical and representative flysch of the Greek territory. In the clayey-sandstone sediments, olistholiths are often observed with dimensions ranging from a few cm to many meters. These olistholiths are originated from the sandstone rocks of this flysch and have slid into its argillaceous parts. In addition, they are intensely fractured. The total process of the sedimentation and tectonics in the area resulted in the occurrence of the above-mentioned formation as a chaotic mixture and created a formation called internationally as wildflysch. In many locations, the flysch of the Pindos Zone has been intensely folded (
Ophiolitic masses have been placed tectonically on the flysch of the Pindos Zone. These masses constitute a complicated petrological and geological unit which is extended widely in the mountainous area among Metsovo, Panagia, Vovoussa, Abdela, Samarina and Smolikas Mountain. The tectonic nappe in the areas of Grammos Mountain and Amarantos Konitsa occupies a smaller extent. These ophiolites have not originated from the Pindos Zone since they don’t occur within the overthrust sheets of the Pindos Zone. So, it is suggested that they have come from the Subpelagonian Zone and their tectonic contact with the Tertiary flysch has been observed. This complicated tectonic nappe consists of (from top to ba- se):
(a) Transgressive series of the Subpelagonian Zone composed of clastic, brecciated, medium to thick-bedded limestones with Rudists,
(b) Ophiolitic complex consisting of ultabasic and basic rocks as peridotites, pyroxenites, gabbros, harzburgites, dunites, dolerites, diabases, spilites, diorites, basalts, serpentinites, pillow lavas, and amphibolites, and
(c) The mixture formation-mélange composed of fragments from Middle Triassic and Upper Jurassic lavas, cherts, serpentinites, clastic volcanics, limestones and gabbro which are enclosed as olistholiths or tectonic inclusions in the cement of siltstone composition [
The mélange and carbonate formations of this trangressive series accompany the ophiolites [
The Gavrovo Zone is located between the Pindos Zone and the Ionian one (
The Gavrozo Zone characterized by continuous neritic carbonate sedimentation, without clayey or siliceous layers, during Triassic-Upper Eocene (
Plate and their total thickness is about 1800 m. The Gavrovo Zone is made up of the following lithological formations [
(a) Limestones of Cretaceous (Senonian-Maestrichtian) age (G.JC-kd). They
constitute clastic, light-coloured to grey, compact, bioclastic, locally dolomitized limestones with numerous fragments of Rudists in the upper part.
(b) Limestones of Paleocene-Eocene age (G.E-k). These carbonate formations are described as black, micritic, platy and locally bioclastic and brecciated limestones.
(c) Flysch of Upper Eocene (Priabonian)-Late Oligocene age (G.fl). The lower members consist of coarse to fine-grained and platy sandstones-G.fl-s with a few layers/alternations of clayey marls and small lenticular intercalations of conglomerates. The thickness of the sandstone beds reaches 3 m and it reduces gradually upwards. In the upper part, silty and clayey marls domimate. Sandstone layers and conglomerates of sandstone and calcareous cobbles occur in these marly beds. This flysch is differentiated lithologically from the flysch formations of the Pindos and Ionian Zones. Its main feature is the significant presence of conglomerates which often form banks having thickness more than 2 m. In addition, semi-rounded or well-rounded calcareous or cherty cobbles and gravels are observed in the siltstone mass [
The Ionian Zone occupies the largest part (78%) of Epirus (western part) extended in NW-SE direction between the Zones of Gavrovo and Pindos (
The oldest carbonate rocks, deposited on the Triassic evaporites, are the neritic Upper Triassiclimestones(Foustapidima)-I.T-k consisting of (a) black sublithographic limestones containing fossils, (b) light-coloured, intensely tectonized do- lomites without fossils, (c) calcareous breccias, and (d) marly limestones [
Triassic evaporites and breccias associated with them constitute the base of the Ionian Zone (
the wetting of the remaining anhydrite and its change to gypsum [
Next formation is the neritic Pantokratoras limestones, of Lower Jurassic age (Lower-Middle Lias). They consist of massive and compact limestones (
Next formations of the Ionian Zone are the Ammonitico Rosso-I.J-kd (limestones) and the lateral equivalent Posidonia Bed-IJ-sh (shales with Posidonia) of Middle Jurassic age (Upper Lias-Dogger-Lower Malm or Toarcian-Aalenian) [
deep subbasins.
The next lithostratigraphic formation is limestones with filaments-I.J-kd, of Middle Jurassic (Bajosian-Callovian) or locally Middle Bathonian age [
The upper/siliceous shales with Posidonia-I.J-sh, known as Radiolarites [
The distribution of the syn-rift formations of Ammonitico Rosso, Posidonia beds (Shales with Posidonia), limestones with filaments and upper Shales with Posidonia in combination with other tectonic or stratigraphic data show that their deposition took place in different subbasins (semi-trenches) resulted from the internal differentiation of the Ionian Zone. The extensional tectonic activity in combination with the salt movement (halokinesis of evaporites) caused this differentiation [
Following the upper siliceous shales with Posidonia, the next formation is the pelagic Vigla limestones-I.C-kd of Lower-Upper Cretaceous (Berriasian-Lower Senonian) age [
often [
The next post-rift formation is the Upper Sennonian limestones-I.C-k dated by the presence of Foraminifera Globotruncanids [
The pelagic Paleocene-Eocene limestones-I.E-kfollow and their age has been determined by the presence of abundant Foraminifera [
The youngest formation of the Ionian Zone is flysch-I.fl of Upper Eocene-Lower Miocene (Aquitanian-Burdigalian) age when the folding of this Zone took place (
pending on the percentage of the predominant materials; i.e. marls (I.fl-m), sandstones (I.fl-s) and conglomerates (I.fl-c), as shown in the map of
During Burdigalian (Lower Miocene), the deposition of marine molasse sediments consisting of blue marls (Ne) with banks of psammitic organic limestone took place. The deposition of younger molasse sediments was continued in Middle Miocene and then, during the emergence-orogenesis of the Ionian Zone (from east to west). The molasse sediments were deposited on the western margins of the elevated parts [
The stratigraghy of the Ionian Zone is related closely to its evolution from carbonate platform to pelagic sedimentation basin, which began in Middle Lias (Lower Jurassic). The formations, which deposited before the differentiation of Zone as basin between the Gavrovo and Paxoi Zones, constitute the pre-rift formations [
The resulting picture of the geological and tectonic structure of northwestern Greece (Epirus) is summarized in the new Geological Map of
The geopolitical location of Epirus, along with the elements of economic interest encountered in the area, such as the oil deposits which are detected at various locations by the scientific teams of IGRS-IFP [
Taking into account the views mentioned by various researchers and the field work data, a short presentation of geological structure and tectonic conditions for each zone follows.
The Subpelagonian Zone, located east of the Pindos Zone and west of Pelagonian Zone, constitutes a small part in the northeastern part of Epirus and consists of ophiolites with deep marine sediments (schist-chert formation) deposited either on carbonate rocks or not. In the area of the Subpelagonian Zone, the Me- sohellenic Trough was developed during Oligocene-Middle Miocene filled with post-alpine molassic sediments.
The Pindos Zone, of Upper Triassic-Upper Eocene age, is extended in a general N-S direction as a tectonic nappe. It consists of Paleocene-Eocene flysch, alternations of platy limestones with sandstones and argillites of Late Cretaceous age (transition zone), Upper Cretaceous pelagic platy limestones with siliceous intercalations, Lower Cretaceous flysch-first flysch, Jurassic schist-chert formation, Upper Triassic platy to thin-platy limestones and clastic formation of Triassic age. The Pindos Zone constitutes a tectonic nappe overthrusted on the Ionian Zone. The tectonic individual overthrust sheets are overthrusted onto each other from east to west and their axes are oriented in directions ranging from N-S to NNW-SSE. Characteristic tectonic structures constitute the Athamanian Mounts (Tzoumerka) and Mt. Lakmos.
The Gavrovo Zone, of Triassic-Oligocene age, is located west of the Pindos Zone. It occurs in the southeastern part of Epirus, in the area of Valtos Mountains. It consists of the following geological formations: Upper Eocene-Oligocene flysch, Jurassic-Upper Eocene neritic limestones rich in fossils (Eocene carbonate series, Cretaceous limestones) and Upper Triassic dolomites. Totally, the Gavrovo Zone constitutes an anticlinical structure having an axis of NNW-SSE direction and it is characterized by heavy type tectonics.
The Ionian Zone, of Triassic-Lower Miocene age, oriented in N-S direction occupies the largest part of Epirus. It extends west of the Gavrovo Zone and consists of the following geological formations: Late Eocene-Lower Miocene flysch, Paleocene-Eocene semi-pelagic platy limestones, Upper Senonian limestones, Upper Jurassic-Upper Cretaceous platy limestones rich in radiolaria alternating with siliceous and chert series (Vigla limestones), limestones rich in Filaments, shales with Posidonia and Ammonitico Rosso of Middle-Upper Jurassic age, Lower Jurassic Siniae and Louros limestones, calcareous breccias and Upper Triassiclimestones of Upper Triassic age and Triassic evaporites (gypsum and salt). Mio-Pliocene sediments and alluvial deposits have been deposited over the Late Eocene-Lower Miocene flysch. The tectonic setting of the Ionian Zone is characterized by a series of parallel mega-synclines or mega-anticlines, thrusted or overthrusted onto each other westward. Their axes are generally oriented in a NW-SE direction, while southwards their directions are changed ranging from NNW-SSE and NNE-SSW intersected by E-W strike-slip faults.
Based on the lithology and types of rocks for each geotectonic zone, the geological structure of northwestern Greece consists of the following main-inde- pen-dently of zones-geological formations:
- Ophiolites of Jurassic age,
- Limestones, dolomites, and schist-cherts of Mesozoic age,
- Flysch of Upper Cretaceous age,
- Limestones of Paleocene-Burdigalian age,
- Flysch of Maestrichtian-Aquitanian age,
- Brackish Neogene sediments of Miocene-Paleocene age, and
- Quaternary deposits (scree, coastal conglomerates, fluvial deposits etc).
Summarizing the study-assessment of the Map of
(a) The area of the Subpelagonian and Pindos Zones, where the ophiolite and flysch formations are encountered, whose locations are largely inconsistent with the respective locations derived from the mapping of the Metsovo and Pentalofo sheets of the Geological Map of Greece, of the Institute of Geology and Mineral Exploration-IGME by Brunn [
(b) All the areas of the map, are covered by Neogene and Quaternary deposits. Such deposits are of particular interest, because based on their stratigraphic succession, one can evaluate the neotectonic activity of area.
It is worth mentioning that the field works particularly focused on the detection and identification of tectonic elements, contribute to the completeness and accuracy of a geological map. These elements are the product of systematic study and observation, evaluation of fault activity, and detailed geologicaltectonic mapping. According to the international classification of faults, they were classified as active, potentially active and non active. All this data are completely new, presented here for the first time and it provides useful information on the area’s degree of activity and the potential occurrence of earthquakes, thus, leading to the better perception of a region’s neotectonic evolution.
The knowledge of the geological structure constitutes the cornerstone for further research, as it results in understanding of the relief and drainage network evolution. Plenty of scientific works combine their data with the geological structure. The existing geological data may be changed due to field observations in the frame of a detailed geological study. Field works can modify the bibliographic references to a dynamic tool resulting in updated or new conclusions about the geological setting and the geotectonic structure of a study area combining new with old data. Despite a large number of scientists have studied an area, there are undiscovered and unknown elements well hidden by the geological time.
Ntokos, D. (2017) Synthesis of Literature and Field Work Data Leading to the Compilation of a New Geological Map―A Review of Geology of Northwestern Greece. International Journal of Geosciences, 8, 205-236. https://doi.org/10.4236/ijg.2017.82009