Microfacies and Depositional Conditions of Jurassic to Eocene Carbonates: Implication on Ionian Basin Evolution

Abstract

In order to decipher the paleo-depositional environments, during the Late Jurassic to Early Eocene syn-rift stage, at the margins of the Ionian basin, two different areas with exposed long sequences have been selected, Kastos Island (external margin) and Araxos peninsula (internal margin), and were examined by means of microfacies analysis and biostratigraphy. On Kastos Island, based on lithological and sedimentological features, the following depositional environments have been recognized: an open marine/restricted environment prevailed during the Early Jurassic (“Pantokrator” limestones), changing upwards into deep-sea and slope environments during the Late Jurassic and Early Cretaceous (Vigla limestones). The Upper Cretaceous (Senonian limestones) is characterized by a slope environment, whereas during the Paleogene, deep-sea and toe of slope conditions prevailed. In Araxos peninsula, Lower Cretaceous deposits (“Vigla” limestones) were accumulated in a deep-sea environment; Upper Cretaceous ones (Senonian limestones) were deposited in slope or toe of slope conditions. Paleocene limestones correspond to a deep-sea environment. In Araxos peninsula, changes occurred during the Cretaceous, whereas on Kastos Island, they occurred during the Paleocene/Eocene, related to different stages of tectonic activity in the Ionian basin from east to west.

1. Introduction

Microfacies analysis of carbonate rocks requires knowledge of modern carbonates and a good understanding of biological and geological changes during Earth history. Many criteria that are important in facies interpretation cannot be recognized sufficiently in small-scale microfacies.

Paleoenvironmental interpretations deriving from microfacies analyses should be controlled by lithological criteria and sedimentary structures evaluated by the high information potential provided by fossils and biogenic structures as well. Microfacies sampling requires an understanding of the meaning of bedding and the respective depositional characters as they are reflected by sedimentary structures [1,2,3,4].

Several classification protocols have been proposed for the classification of limestones, taking in mind morphological and/or genetic factors, which emphasize on specific properties, such as color, size of crystals, composition, fabric, and texture. In general, the classification is based on the grain size and fabric properties of the rocks [5]. The most common classifications are: (A) the classification of Folk [6] is based on the classification and fabric maturation of limestones. It is purely morphometric and has limited genetic extensions, regarding the possible level of energy, transport, and deposition of grains. Folk [6] found that most carbonate rocks are composed of: 1. non-skeletal grains, 2. skeletal grains, 3. microcrystalline calcite or micrite, 4. crystalline calcite or sparite as a cement chemically formed filling the voids between the grains of carbonate rocks. (Β) The classification of Dunham [7] is a fabric-based classification, distinguishing between those carbonate rocks whose grains are in contact with or simply coexist within a carbonate filler.

In both classifications, the purpose is not only to classify the rock, but also to provide information on the energy levels of the depositional environment. According to Folk [6], a micrite or biomicrite indicates a low-energy depositional environment while a biosparite indicates high-energy conditions. According to Dunham [7], mudstone and wackestone correspond to a low energy environment, in contrast with packstone and grainstone that refer to high-energy conditions.

Lithology, texture, grain types, fossils and their percentages, sediment structures, color, and fabric character are taken into account for the determination and interpretation of carbonate facies. A detailed description of carbonate facies requires field, as well as microscopic observations to determine it [5]. Therefore, herein the model of Wilson [8] for the determination of the carbonate facies is followed with twenty-four (24) standard microfacies (SMF), corresponding to nine (9) standard facies zones (FZ), from open deep-sea basin environments, the slope, the edge of the platform, and the inner platform [5,9].

The aim of this paper is to define in detail the depositional environments of the carbonate Mesozoic sequence of the Ionian Basin, in the external sub-basin (Kastos Island) and the internal sub-basin (Araxos peninsula), respectively. The target is the vertical and lateral depositional condition changes both internal to the same age and different age formations, and so on the reconstruction of geodynamic conditions during sedimentation and their support to rebuild of the geological map. The achievement of the above was made using microfacies analysis. The taphonomy and paleoecology of macrofauna have also been used in order to reconstruct the depositional environments and the dynamic conditions in different positions across the basin, and to support the previous lithofacies results. Microfossils have been used to provide paleoecological and biostratigraphic data, and the chronostratigraphy of the studied lithological formations particularly from Kastos Island has been reconsidered. The results were used, both for the revision of existing geological maps as well as for the correlation of the different depositional conditions between the studied parts of the basin.

2. Geological Setting

2.1. Ionian Basin

The Mesozoic-Paleogene Ionian basin is part of the external Hellenides orogen, bounded westwards by the Ionian Thrust and eastwards by the Gavrovo Thrust (Figure 1). The Pre-Apulian (or Paxoi zone) to the west is regarded as the eastern margin of the Apulian platform, in Albania, Croatia, and Italy, where similar rocks occur [10,11,12].

The sedimentary fill of the basin is sub-divided into pre-rift, syn-rift, and post-rift tectono-sedimentary sequences [12,13,14] the syn-rift and post-rift sequences are merged into one (syn-rift: [15,16,17]) (Figure 2):

(i) The pre-rift sequence begins with evaporites (Lower to Middle Triassic) at the base (over 2000 m thick). These deposits evolve upwards into the Middle-Upper Triassic (Ladinian to Rhaetian) “Foustapidima” limestones (50–150 m thick), and the Lower Jurassic (Hettangian to Sinemurian) “Pantokrator” limestones (over 1000 m thick).

(ii) The syn-rift sequence was deposited during the extension and deepening of the Ionian basin, accompanied by its internal structural differentiation into small sub-basins with half-graben geometry, displaying abrupt thickness changes within each other [13,14]. The syn-rift sequence is composed of Upper Jurassic to Lower Eocene deposits. At the base, it consists of the Lower Jurassic (Pliensbachian) pelagic “Siniais” limestones and their lateral equivalent the hemipelagic “Louros” limestones (20–150 m thick). These deposits underlay the Lower to Upper Jurassic (Toarcian to Tithonian) “Ammonitico Rosso,” “Limestones with filaments,” and “Posidonia beds” (20–200 m thick). Variations in thickness and formation changes across the basin are observed very often due to the half-graben geometry, thus different basin depths are commonly observed.

The Lower Cretaceous (Berriasian to Turonian) is characterized by “Vigla limestones” and the laterally equivalent “Vigla shales,” 200–600 m in total thickness. The “Vigla” formation locally overlies the pre-rift sequence and thickness variations indicate persistent differential subsidence. “Vigla limestones” consist of thin-bedded grey mudstone to wackestone in rhythmic alternations with chert intervals and rare shale intercalations “Vigla shales” consist of limestones with chert intervals and dark grey to green or red shale intercalations. According to [18], the “Vigla formation” was studied in the three parts of the Ionian basin independently for the two different units. In detail, “Vigla” limestones in the external parts of the basin consist of white, light grey to yellowish micrites, and radiolarian biomicrites (wackestones to packstones and rarely mudstones). In the middle part of the basin, it consists of yellow to red marly limestones or shaly limestones and chert alternations, as well as clay layers that are usually green and red. The calcareous beds consist mainly of micrites (mudstones, wackestones), biomicrites with foraminifera and radiolaria (foraminiferal or radiolarian wackestones to packstones), and siliceous biomicrites (Si-wackestones, packstones). In the internal parts of the basin, it consists of compact, thick-bedded, bituminous, dolomitic limestones, locally weathered, with lenses of slightly dolomitized microbreccia and thin cherty layers, chert intercalations, and nodules. The non-dolomitized beds are micritic limestones with and without radiolaria and microbreccia with thick chert intercalations. “Vigla” shales in the external parts of the basin have a micritic matrix, consist of floatstones, rudstones, and rare grainstones and packstones with micritic or biomicritic intercalations which are locally numerous. Occasionally, chert nodules and yellowish layers are also observed. In the middle part of the basin the limestones are microclastic, bioclastic, or microbreccia with a micritic matrix (wackestones, packstones, floatstones, rudstones), intercalated with micrites and biomicrites. Chert layers are rarely observed. The internal parts of the basin are characterized by massive, thick-bedded microbreccia to breccia containing rudists and coral fragments. Rarely, layers of the platy to thick-bedded micritic to biomicritic limestones (wackestones, packstones) are intercalated. Nodules and thin layers of chert are observed locally. Over the latter, the Upper Cretaceous “Senonian limestones” (Coniacian to Maastrichtian) were deposited. They range from 200 to 400 m in thickness and contain both nodular and bedded chert. The Upper Cretaceous deposits, mentioned as “clastic limestones” (“Senonian limestones”) and expanding from the western to the eastern part of the basin [18], and practically from the external to the internal Ionian zone, vary throughout the basin: A. in the external (western) parts of the basin they have a micritic matrix, consisting of floatstones, rudstones, and rarely grainstones and packstones with micritic or biomicritic intercalations. Occasionally, chert nodules and yellowish cherty layers are also observed. B. in the middle part of the basin, the limestones are microclastic, bioclastic, or contain microbreccia with a micritic matrix (wackestones, packstones, floatstones, and rudstones), intercalated with micrites and biomicrites. Chert layers are rarely observed. C. in the internal (eastern) part, limestones are massive, and thick-bedded with microbreccia to breccia containing rudist and coral fragments. Rarely, layers of platy to thick-bedded micritic to biomicritic limestones are intercalated, whereas nodules and thin layers of chert are observed locally.

The Paleocene rocks have similar lithofacies as the Upper Cretaceous “Senonian limestones,” with prominent microbreccia that derived from the erosion of the Cretaceous carbonates from both the Gavrovo platform (to the east) and the Apulian platform (to the west), known as “limestones with microbreccia”. At some horizons, bedded or nodular chert is also found.

The Lower Eocene rocks comprise “platy limestones” and platy wackestones/mudstones with Globigerinidae and nodular cherts, especially in the central area of the Ionian basin. These deposits look similar to the “Vigla limestones” but they lack bedded cherts.

Within the Ionian Zone, the Upper Cretaceous-Eocene resedimented carbonates are considered as one of the main reservoir sequences and exploration targets in western Greece [12,14]. They correspond to the producing reservoir rocks in the Katalokon oil field and host proved prolific reservoirs in the Ionian zone of Albania [19] and in the central and southern Adriatic offshore Italy [11,20]. However, the distribution of these resedimented carbonates (calcareous turbidites and coarser breccia) in western Greece is still poorly constrained.

Sedimentation within the Ionian basin in Albania was controlled by the tectonic instabilities of both shelf margins (Sazani and Kruja platforms). During the Cretaceous period, the deposition in the Ionian basin was characterized by hemipelagites, at the base, and by the overlying breccia and calciturbidites, produced from the eroded margins, due to their strong tectonic instability [12,21,22].

Other examples can be taken from the other side of the Adriatic Sea, the Apulian platform with its margins and slope located at the Gargano peninsula and Maiella Mountain in Italy [11,23,24,25]. During Cretaceous to Lower Eocene, steep submarine escarpments characterized the Apulian carbonate platform margins presenting significant erosion. Breccia accumulated at the toe of the escarpment interbedded with clinostratified deposits and bioclastic turbidites (around the Gargano promontory and Maiella Mountain, (Morrone di Pacento, Cima delle Murelle, the Grotte and Orfento formations in Maiella Platform)). Along the platform margins, significant rudist colonies existed. These colonies were subsequently eroded and were redeposited as skeletal material at the toe of the slope [25,26].

2.2. Studied Areas

After our previous studies [15,16,17] which showed different depositional conditions either due to their different tectonic activity or due to the different influence of the neighboring existing platforms (Apulian to the west and Gavrovo to the east), the same two areas were selected for the detailed study of this work. The above differences referred to different mineralogy of siliceous concretions, different kinds of soft-sediment deformations, and different influences of tectonic activity (normal or transfer faults) in Ionian basin depositional conditions.

Kastos Island is located in the Ionian Sea and it belongs to the Ionian zone, specifically to the external Ionian zone (Figure 3). The external Ionian zone and the Pre-Apulian zone to the west form the outer continental margin of the Apulian Platform in the Ionian and Adriatic Seas [25].

On Kastos Island and according to the geological map of IGME sheet Kalamos [27] Jurassic to Eocene deposits crop out, nevertheless, the Mesozoic sedimentary sequence is incomplete. The oldest deposits, the Lower Jurassic “Pantokrator” limestones, crop out at the southeastern side of Kastos Island, whereas the younger Eocene carbonates are visible on the western side. There is only one site at the southern part of the island where Jurassic shales with a “Posidonia” outcrop. In all other sites, there is no evidence for the presence of Jurassic shales in the transition from Lower Jurassic “Pantokrator” limestones to Lower Cretaceous “Vigla” limestones. In general, dip direction is to the west with a dip up to 45°, and only in the southwestern part dip direction is to the south and dip up to 60°.

Araxos peninsula is located in NW Peloponnesus (Figure 4) and it belongs to the internal Ionian zone. In more detail, Araxos peninsula is situated at the western end of Patraikos Gulf, and during Late Pliocene to present, it was affected by the tectonic regime that formed the WNW trending extensional Patras-Corinth Basin. Thus, its formation was controlled by back-arc extension behind the Hellenic trench and is characterized by WNW–ESE normal faults and NNE–SSW transfer faults [28,29,30,31]. Western Greece has been affected by rotation up to 50° clockwise (-cw) [32,33,34,35,36], which took place in two stages/episodes of about 25° each: the first one occurred before the Late Miocene and the second one during the Plio-Pleistocene.

3. Materials and Methods

The studied material consists of ninety-two (92) samples collected from Lower Jurassic to Eocene carbonates of Kastos Island and forty (40) samples collected from the Cretaceous carbonate rocks of Araxos peninsula (Figure S1). The selection of samples was based on lithology and facies alternations. All samples were cut and thin sections were prepared. The latter were studied for microfacies analysis in order to establish the temporal and spatial changes and the evolution of the respective depositional paleoenvironment in the two studied areas. The textural characters of microfacies types were defined according to Dunham’s [7] classification modified by Embry and Klovan [38] and Flügel [5] and their description includes biogenic and inorganic dominant components [39]. In addition, foraminiferal assemblages provide considerable support to the interpretation of depth and depositional environments [40,41] as well as providing biostratigraphic and consequently chronostratigraphic data, in order to define the chronological context of the studied sequences. Hence, benthic and mainly planktonic foraminifera, and where applicable calpionellids, were determined, and their stratigraphic ranges were considered to determine the age of the studied sedimentary sequences [42].

As Kastos Island was undoubtedly subjected to a compressional regime, it seems strange to present generally no deformation. Similarly, Araxos peninsula was influenced by a thrust fault situated west of the studied area [15,16,17], during a compressional regime. Based on these facts, the first sampling was focused on the age determination and facies analysis in specific areas as previously published works have highlighted. After the first results, additional sampling focused on the transitional zones between different age formations in order to highlight the depositional conditions’ changes.

4. Results

4.1. Kastos Island

4.1.1. Facies Analysis and Zones

Based on geographic and stratigraphic criteria, the studied area is organized into six specific regions: “North Kastos Island” where Lower Cretaceous to Paleocene formations are outcropping, “West and Central Kastos Island” with Lower to Upper Cretaceous outcrops, “Kastos Village” with Jurassic to Upper Cretaceous outcrops, “Sarakiniko Bay” with Lower Cretaceous to Upper Eocene outcrops, and “South Kastos Island” with Lower Jurassic to Lower Cretaceous outcrops.

The main textural and compositional characteristics of the studied total thin sections, as well as the sedimentary features of the distinguished microfacies are presented in

Table 1. Description of microfacies analysis of samples from Kastos Island and their age determination. Note the difference between the pre-existing age determinations and the new data of the present study.

Samples	Description of Facies Analysis	Facies Zones	Age Based on Geological Map	Fossils	Age Based on Fossils
KI92	Mudstone/wackestone (mud to grain supported), sparse micrites, skeletan grains (SMF3)	Deep sea (FZ1)	Paleocene	Radiolaria, Bivalve filaments, Globigerinotheka sp., Turborotalia sp., Turborotalia cerroazulensis, Catapsydrax cf. dissimilis, Pseudohastigerina micra, Globigerina sp.	Eocene (Bartonian-Priabonian)
KI91	Grained supported, wackestone/packstone, biomicrites, skeletan grains (SMF3)	Deep sea (FZ1)	Paleocene	Radiolaria, Globigerinotheka sp., Catapsydrax sp., Acarinina sp.	middle Eocene
KI90	Mudstone/wackestone, biοmicrites, skeletan grains (SMF3)	Deep sea (FZ1)	Paleocene	Radiolaria, Globigerinotheka sp., Acarinina soldadoensis, Subbotina inaequispira	Eocene (Lutetian)
KI89	Grained supported, packstone, biosparite, peloids, calcite vein, peloids, plaktonic foraminifera, microcrystalline calcite (SMF3)	Toe of Slope (FZ3)	Paleocene	Globigerinotheka sp., Turborotalia centralis, Acarinina coalingensis, Globigerina sp., Discocyclina sp.	Eocene (Lutetian)
KI88	Grained supported, packstone/grainstone, biosparite, calcite vein, plaktonic foraminifera, microcrystalline (SMF3)	Toe of Slope (FZ3)	Paleocene	Globigerinotheka sp., Turborotalia centralis, Acarinina primitiva, Discocyclina sp., Assilina sp., Lepidocyclina sp., Lockhartia sp., Rotaliidae	Eocene (lower Lutetian)
KI87	Wackestone/packstone, biomicrite, skeletal grains, calcite vein (SMF3)	Toe of Slope (FZ3)	Paleocene	Morozovella aequa, Acarinina coalingensis, Acarinina bulbrooki, Acarinina cf. esnaensis	Eocene (Ypresian)
KI86	On the top: packstone with biomicrites and the other section with lamination of mudstone-wackestone (SMF3)	Deep sea (FZ1)	Paleocene	Morozovella formosa, Igorina sp., Globalomalina planoconica, Acarinina bulbrooki	Eocene (Ypresian)
KI85	Mudstone with calcite veins (SMF1)	Deep sea (FZ1)	Paleocene	Radiolaria, Morozovella sp., Acarinina sp.	Paleocene
KI84	Wackestone with sparse biomicrite skeletan grains, foraminifera, calcite veins (SMF3)	Deep sea (FZ1)	Paleocene	Morozovella angulata, Morozovella aequa, Morozovella conicotruncana, Planorotalites chapmani, Subbotina inaequispira	Paleocene (Selandian-Thanetian)
KI83	Thinly laminated alternation of mudstone to wackestone (SMF3)	Deep sea (FZ1)	Senonian	Morozovella angulata, Subbotina velascoensis, Parasubbotina varianta	Paleocene (Selandian-Thanetian)
KI82	Mudstone/wackestone, peloids or oxides, calcite veins (SMF3)	Deep sea (FZ1)	Paleocene	Morozovella angulata, Planorotalites pseudomenardi	Paleocene (Selandian-Thanetian)
KI81	Mudstone (SMF3)	Deep sea (FZ1)	Paleocene	Radiolaria, Morozovella angulata, Planorotalites sp.	Paleocene (Selandian-Thanetian)
KI80	Packstone microbrecciated, few skeletan grains, microsparite (SMF4)	Slope (FZ4)	Senonian	Miliolidae, Bivalve fragments, Parasubbotina pseudobulloides	Paleocene (Danian-Selandian)
KI79	Packstone, microbrecciated (SMF4)	Toe of slope (FZ3)	Eocene	Miliolidae, Globotruncana ventricosa, Globotruncana cf orientalis	Late Cretaceous (Campanian- Maastrichtian)
KI78	Grainstone, microbreccia (SMF5)	Slope (FZ4)	Senonian	Helvetotruncana helvetica	Late Cretaceous, Senonian (Turonian)
KI77	Grainstone, microbrecciated, microcrystalline? (SMF2)	Deep shelf (FZ2)	Senonian		Late Cretaceous (Senonian)
KI76	Mudstone (SMF3)	Deep sea (FZ1)	Paleocne-Eocene?	Radiolaria, Rotalipora cushmani, Clavihedbergella simplex, Hedbergella planispira	Late Cretaceous (Cenomanian)
KI75	Mudstone (SMF3)	Deep sea (FZ1)	Jurassic	Radiolaria	Late Cretaceous
KI74	Mudstone (SMF3)	Deep sea (FZ1)	Jurassic	Radiolaria	Late Cretaceous
KI73	chert (SMF3)	Deep sea (FZ1)	Jurassic	Radiolaria, Clypeina jurassica	Late Cretaceous (Kimmeridian- Tithonian)
KI72	Wackestone/packstone, microbrecciated, skeletan grains (SMF4)	Toe of Slope (FZ3)	Paleocene	Radiolaria, Rugoglobigerina sp., Globotruncana cf. arca, Globotruncana neotricarinata, Globotruncana orientalis, Globotruncanita cf conica	Late Cretaceous (Maastrichtian)
KI71	Grainstone, microbrecciated	Toe of Slope (FZ3)	Paleocene		Late Cretaceous
KI70	Wackestone, skeletal graines, micrites (SMF3)	Deep sea (FZ1)	Senonian	Radiolaria, Clavihedbrgella simplex, Hedbergella planispira, Rotalipora cushmani, Praeglobotruncana delrioensis, Thalmanninella appenninica, Thalmanninella greenhornensis, Thalmanninella globotruncanoides, Whiteinella archaeocretacea	Late Cretaceous (Cenomanian)
KI69	Mudstone (SMF3)	Deep sea (FZ1)	Jurassic	Radiolaria	Late Cretaceous
KI68	Packstone, microbioclastic, microcrystalline (SMF2)	Deep sea/deep shelf (FZ1-2)	Senonian	Blefuscuiana gorbachikae, Blefuscuiana occulta, Blefuscuiana praetrocoidea, Globigerinelloides cf. ferreolensis, Globigerinelloides gottisi, Globigerinelloides barri, Globigerinelloides blowi	Early Cretaceous (Aptian)
KI67	Wackestone, microbioclastic (SMF2)	Deep sea (FZ1)	Senonian	Radiolaria, Planomalina cheniurensis, Globigerinelloides sp., Blowiella blowi, Blowiella gottisi, Hedbergella sp.	Early Cretaceous (Aptian)
KI66	Packstone, microbioclastic, microcrystalline (SMF2)	Deep sea-deep shelf (FZ1-2)	Senonian	Radiolaria, Blefuscuiana gorbachikae, Globigerinelloides barri, Globigerinelloides algerianus, Claviblowiella saundersi, Planomalina sp., Schackoina cepedai	Early Cretaceous (Aptian)
KI65	Mudstone with micriticous fossiliferous and calcite veins, stylolites (SMF3)	Deep sea (FZ1)	Vigla	Radiolaria, Blowiella gottisi, Blowiella blowi, Hedbergella delrionensis, Globigerinelloides aptiensis, ?Lenticulina sp.	Early Cretaceous (Aptian)
KI64	Mudstone with micriticous fossiliferous (SMF3)	Deep sea (FZ1)	Vigla	Radiolaria, Blowiella gottisi, Blowiella blowi, Hedbergella delrionensis, Globigerinelloides sp., Hedbergella trocoidea, Hedbergella sp., Gorbachikella cf kugleri	Early Cretaceous (Aptian)
KI63	Wackestone/Packstone, microbioclastic, microcrystalline, lamination (SMF3)	Deep sea (FZ1)	Senonian	Radiolaria, Ticinella cf. praeticinencis, Hedbergella cf. planispira	Early Cretaceous (Albian)
KI62	Mudstone/wackestone, microbioclastic (SMF1)	Toe of Slope (FZ3)	Senonian	Radiolaria, Hedbergella rischi, Hedbergella planispira, Hedbergella trocoidea, Hedbergella delrioensis, Hedbergella cf. kuznetsovae, Clavihedbergella simplex, Ticinella roberti, Alanlordella bentonensis	Early Cretaceous (Albian)
KI61	Mudstone with micriticous fossiliferous and calcite veins, stylolites (SMF3)	Deep sea (FZ1)	Vigla	Radiolaria, Blowiella gottisi, Hedbergella delrionensis	Early Cretaceous (Albian)
KI60	A. Mudstone with micrite skeletan grains (SMF3), B. Packstone, microbioclastic, microcrystalline, lamination (SMF2)	A. Deep sea (FZ1), B. Deep sea (FZ1)	Paleocene	Radiolaria, Hedbergella rischi	Early Cretaceous (Albian)
KI59	Mudstone-Wackestone, skeletal grains, fossiliferous biomicrite (SMF3)	Deep sea (FZ1)	Senonian	Radiolaria (Spumellaria, Nasselaria)	Early Cretaceous
KI58	Packstone microbrecciated, few skeletan grains, microsparite (SMF4)	Slope (FZ4)	Senonian
KI57	Packstone microbrecciated, few skeletan grains, microsparite (SMF4)	Slope (FZ4)	Senonian	Miliolidae, Triloculina sp.
KI56	Packstone/grainstone, microbrecciated, few skeletan grains, microsparite (SMF4)	Slope (FZ4)	Senonian	Benthic foraminifera
KI55	Packstone/grainstone, microbrecciated, few skeletan grains, microsparite (SMF4)	Slope (FZ4)	Senonian	Miliolidae, Lenticulina sp.
KI54	Mudstone to packstone, microcrystalline, fossiliferous biomicrite (SMF2)	Deep sea (FZ1)	Eocene	Calpionellidae, Lorenziella cf. hungarica, Tintinnopsella cf. carpathica, Clavihedbergella eocretacea, Praehedbergella sigali	Early Cretaceous (Valanginian)
KI53	A. Mudstone/wackestone, skeletan grains, fossiliferous biomicrite, siliceous veins (SMF3), B. a zone which is Wackestone-Packstone, microlithoclastic, spiculite (SMF1-2)	A. Deep sea (FZ1) B. Deep sea (FZ1)	Eocene	Radiolaria, Calpionellidae, Lorenziella cf. hungarica Clavihedbergella eocretacea Praehedbergella sigali Conoglobigerina sp. Lenticulina sp.	Early Cretaceous (Valanginian)
KI52	Mudstone/wackestone, skeletal grains, fossiliferous biomicrite (SMF3)	Deep sea (FZ1)	Eocene	Radiolaria, Calpionellidae, Lorenziella cf. hungarica, Tintinnopsella cf. carpathica, Calpionellites cf. darderi, Clavihedbergella eocretacea Praehedbergella sigali	Early Cretaceous (Valanginian)
KI51	A. Mudstone to wackestone, microbreccia (SMF2), B. Packstone to grainstone, stylolites (SMF2)	A. Deep sea (FZ1), B. Deep sea (FZ1)	Paleocene	Radiolaria, Planomalina cherouniensis, Blowiella blowi, Blowiella gottisi	Early Cretaceus (Aptian)
KI50	Wackestone/packstone, microbreccia (SMF2)	Deep sea (FZ1)	Paleocene	Radiolaria, Blefuscuianna aptianna, Praehedbergella cf. sigali, Globigerinelloides sp, Blowiella blowi, Blowiella gottisi	Early Cretaceus (Aptian)
KI49	Wackestone and locally packstone, microbreccia (SMF2)	Deep sea (FZ1)	Paleocene	Blowiella sp.	Early Cretaceus (Aptian)
KI48	Wackestone, microbreccia, lamination, grainstone flows, stylolites (SMF2)	Deep sea (FZ1)	Paleocene	Radiolaria, Hedbergella planispira, Hedbergella delrioensis, Praehedbergella sp., Globigerinelloides algerianus, Blowiella duboisi, Blowiella sp.	Early Cretaceus (Aptian)
KI47	Wackestone/packstone and locally grainstone, microbreccia, lamination (SMF2)	Deep sea (FZ1)	Paleocene	Blowiella sp., Globigerinelloides sp.	Early Cretaceus (Aptian)
KI46	Wackestone, (crystallization), skeletan grains (SMF3)	Deep sea (FZ1)	Vigla	Radiolaria	Early Cretaceous
KI45	Wackestone/packstone, micrite skeletan grains (SMF3)	Deep sea (FZ1)	Vigla	Radiolaria	Early Cretaceous
KI44	Mudstone, quite cracked (SMF3)	Deep sea (FZ1)	Vigla	Radiolaria	Early Cretaceous
KI43	Wackestone, micrite skeletan grains, calcite vein (SMF3)	Deep sea (FZ1)	Vigla	Radiolaria	Early Cretaceous
KI42	Mudstone/wackestone, skeletan grains, calcite vein, biomicrite (SMF3)	Deep sea (FZ1)	Vigla	Radiolaria	Early Cretaceous
KI41	Mudstone, biomicrite (SMF3)	Deep sea (FZ1)	Senonian	Radiolaria, Blowiella maridalensis, Hedbergella delrionensis, Globigerinelloides algerianus, Globigerinelloides ferreolensis, Blefuscuianna aptiana	Early Cretaceus (Aptian)
KI40	Mudstone, lamination? (SMF3)	Deep sea (FZ1)	Senonian	Radiolaria, Hedbergella rischi, Hedbergella delrioensis, Hedbergella planispira, Shackoina sp.	Early Cretaceous (Albian)
KI39	Mudstone/wackestone, skeletan grains, biomicrite, Stylolites (SMF3)	Deep sea (FZ1)	Vigla	Radiolaria, A few bivalve filaments, Calpionellidae, Tintinnopsella cf longovalata, Tintinnopsella cf carpathica	Early Cretaceous (Valanginian)
KI38	Mudstone, skeletan grains, biomicrite (SMF3)	Deep sea (FZ1)	Vigla	Radiolaria, A few bivalve filaments, Favusella sp., Blefuscuianna cf aptianna, Blowiella sp., Schackoina cepedai	Early Cretaceous (Aptian)
KI37	Mudstone, skeletal grains, fossiliferous biomicrite (SMF3)	Deep sea (FZ1)	Vigla	Radiolaria, Hedbergella planispira, Alanlordella bentonensis	Early Cretaceous (Albian)
KI36	Mudstone, skeletan grains (SMF3)	Deep sea (FZ1)	Vigla	Radiolaria, Hedbergella rischi, Hedbergella cf trocoidea, Planomalina sp., Clavihedbrgella simplex	Early Cretaceous (Albian)
KI35	Mudstone (SMF3)	Deep sea (FZ1)	Vigla	Radiolaria, Favusella hoterivica, Blowiella sp.	Early Cretaceous (Berriasian-Aptian)
KI34	Mudstone/Wackestone, skeletal grains, fossiliferous biomicrite, stylolites (SMF3)	Deep sea (FZ1)	Vigla	Radiolaria Calpionellidae, Tintinnopsella sp., Tintinnopsella cf. carpathica, Calpionellites cf. coronatus	Early Cretaceous (Valanginian)
KI33	Mudstone/Wackestone, skeletal grains, fossiliferous biomicrite (SMF3)	Deep sea (FZ1)	Vigla	Radiolaria Calpionellidae, Tintinnopsella cf. Longovalata, Tintinnopsella cf. carpathica	Early Cretaceous (Berriasian- Valanginian)
KI32	Mudstone/Wackestone, skeletal grains, fossiliferous biomicrite (SMF3)	Deep sea (FZ1)	Vigla	Radiolaria Calpionellidae, Tintinnopsella sp.	Early Cretaceous (Tithonian- Valanginian)
KI31	Mudstone/Wackestone, skeletal grains, fossiliferous biomicrite (SMF3)	Deep sea (FZ1)	Vigla	Radiolaria, cf Favusella hoterivica	Early Cretaceous (Berriasian- Barremian)
KI30	Mudstone/Wackestone, skeletan graines, micrites, calcite vein (SMF3)	Deep sea (FZ1)	Vigla	?Conoglobigerina sp.	Early Cretaceous (Berriasian- Valanginian)
KI29	Mudstone and microspar, microcrystalline (SMF3)	Deep sea (FZ1)	Paleocene-Eocene?		Early Cretaceous
KI28	Mudstone (SMF3)	Deep sea (FZ1)	Paleocne-Eocene?	Radiolaria, Shackoina cepedai, Blefuscuiana aptiana, Hedbergella delrionensis	Early Cretaceous (Aptian)
KI27	Mudstone (SMF3)	Deep sea (FZ1)	Paleocne-Eocene?	Radiolaria, Blowiella blowi, Praehedbergella cf sigali, Hedbergella similis	Early Cretaceous (Aptian)
KI26	Wackestone/mudstone, locally lamination (SMF3)	Deep sea (FZ1)	Paleocne-Eocene?	Radiolaria, Blowiella gottisi, Biglobigerinella barri, Shackoina cepedai, Blefuscuiana aptiana, Blefuscuiana kuznetsovae, Planomalina cheniourensis, Globigerinelloides sp.	Early Cretaceous (Aptian)
KI25	Mudstone (SMF3)	Deep sea (FZ1)	Vigla	Radiolaria, Blefuscuiana sp.	Early Cretaceous (Barremian-Albian)
KI24	Mudstone (SMF3)	Deep sea (FZ1)	Jurassic	Radiolaria	Early Cretaceous
KI23	Mudstone (SMF3)	Deep sea (FZ1)	Jurassic	Radiolaria, Calpionellidae, Tintinnopsella sp.	Early Cretaceous (Tithonian- Valanginian)
KI22	Mudstone (SMF3)	Deep sea (FZ1)	Jurassic	Radiolaria, Blowiella sp., Blefuscuianna kuznetsovae	Early Cretaceous (Aptian)
KI21	Mudstone (SMF3)	Deep sea (FZ1)	Vigla	Radiolaria	Early Cretaceous
KI20	Mudstone (SMF3)	Deep sea (FZ1)	Jurassic	Radiolaria	Early Cretaceous
KI19	Mudstone, stylolites (SMF3)	Deep sea (FZ1)	Jurassic	Radiolaria, Favusella hoterivica	Early Cretaceous (Berriasian- Barremian)
KI18	Mudstone/wackestone (SMF3)	Deep sea (FZ1)	Vigla	Radiolaria, Blowiella sp., Hedbergella derlionensis, Hedbergella trocoidea	Early Cretaceous
KI17	Mudstone (SMF3)	Deep sea (FZ1)	Vigla	Radiolaria
KI16	Mudstone, stylolites (SMF3)	Deep sea (FZ1)	Jurassic	Radiolaria, a few Bivalve filaments Calpionellidae, Calpionellites sp., Tintinnopsella sp.	Early Cretaceous (Valanginian)
KI15	Wackestone/grainstone and sometimes boundstone (SMF18)	Open marine/restricted (FZ7-8)	Jurassic	Siphovalvulina sp.	Early Jurassic
KI14	Wackeston/grainstone and sometimes boundstone (SMF18)	Open marine/restricted (FZ7-8)	Jurassic	Siphovalvulina sp., Duotaxis sp.	Early Jurassic
KI13	Wackeston/grainstone and sometimes boundstone (SMF18)	Open marine/restricted (FZ7-8)	Jurassic		Early Jurassic
KI12	Grainstone (SMF18)	Open marine/restricted (FZ7-8)	Jurassic	?Coronipora sp.	Early Jurassic
KI11	Grainstone (SMF18)	Open marine/restricted (FZ7-8)	Jurassic	Siphovalvulina sp., Duotaxis sp., Triloculina sp.	Early Jurassic
KI10	Wackestone/grainstone and sometimes boundstone (SMF18)	Open marine-restricted (FZ7-8)	Jurassic	Thaumatoporella sp., Siphovalvulina sp.	Early Jurassic
KI9	Grainstone and sometimes boundstone (SMF18)	Open marine/restricted (FZ7-8)	Jurassic	Thaumatoporella sp., Siphovalvulina sp.	Early Jurassic
KI8	Grainstone and sometimes boundstone, locally pelsparite (SMF18-19)	Open marine/restricted (FZ7-8)	Jurassic	Thaumatoporella sp.	Early Jurassic
KI7	Grainstone and sometimes boundstone (SMF18)	Open marine/restricted (FZ7-8)	Jurassic	Thaumatoporella sp., Siphovalvulina sp., Triloculina sp., Miliolidae	Early Jurassic
KI6	Wackestone/grainstone and sometimes boundstone (SMF18)	Open marine/restricted (FZ7-8)	Jurassic	Thaumatoporella sp., Siphovalvulina sp.	Early Jurassic
KI5	Wackestone/grainstone and locally boundstone (SMF18-19)	Open marine/restricted (FZ7-8)	Jurassic	Thaumatoporella sp., Siphovalvulina sp., Miliolidae	Early Jurassic
KI4	Wackestone/grainstone (SMF18-19)	Open marine/restricted (FZ7-8)	Jurassic	Thaumatoporella sp., Siphovalvulina sp.	Early Jurassic
KI3	A. Grainstone with peloids (pelsparite) (SMF18), B. Mudstone with lamination (SMF2), stylolites, Facies A probably an exoclast from pantokrator formation limestone	A. Open marine/restricted (FZ7-8) B.Deep sea (FZ1)	Jurassic	Radiolaria, Miliolidae	Early Jurassic
KI2	Grainstone/boundstone (SMF18)	Open marine (FZ7)	Jurassic	Thaumatoporella sp., Siphovalvulina sp., Algae	Jurassic
KI1	Wackestone/packstone (SMF3)	Toe of Slope (FZ3)	Jurassic	Bivalve filaments	Jurassic

, corresponding to different depositional environments or standard facies zones [5].

More specifically, the Lower Jurassic (“Pantokrator” limestones) deposits consisting of wackestone-grainstone and locally boundstone limestones (SMF18-19) are biomicrites to biosparites accumulated in an open marine-restricted environment (FZ7-8).

The Lower Cretaceous deposits (Vigla limestones) were classified as mudstone/wackestone limestones consisting of micrites to biomicrites with planktonic foraminifera and radiolaria (standard microfacies SMF1-3), indicating a deep-sea to slope environment (FZ1-4). In the Lower Cretaceous (Valanginian), the observed mudstone-wackestone limestones consist of biomicrites with skeletal grains and spiculites (SMF3, SMF1) and are associated with a deep-sea environment (FZ1).

Calciturbidites of Late Cretaceous were classified as packstones biomicrites with microbreccia and planktonic foraminifera (SMF4) in a slope environment (FZ4).

The Paleocene deposits consist of mudstone to wackestone biomicrites with skeletal grains (SMF3) and sometimes packstone biomicrites (SMF4).

In addition, the Lower Eocene deposits consist of wackestone-packstone biomicrites (SMF3) and are related to a deep-sea or toe of slope environment (FZ1 to FZ3).

4.1.2. Biostratigraphy of Kastos Island

The biostratigraphic analysis, on the selected thin sections, revealed the following assemblages (Table 1):

The age determinations (Table 1) do not fully support the pre-existing age results as they are reported in the geological map (Kalamos geological sheet) concerning the Ionian zone rock exposures on Kastos Island. Representative photographs showing textures and characteristic fossils are presented in Figure 5.

4.2. Araxos Peninsula

4.2.1. Facies Analysis and Zones

The studied area is organized into three specific areas: “Gianiskari beach” where Lower Cretaceous to Upper Cretaceous formations crop out, “on the road” with Upper Cretaceous calciturbidites and breccia-microbreccia outcrops, and “Quarry” (old and new) Upper Cretaceous to Paleocene outcrops.

In detail, the following microfacies were determined and their supported facies zones that were recognized (

Table 2. Detailed description of studied thin sections where depositional facies, fossils, and the age of the studied deposits are presented in Araxos peninsula.

Samples	Area	Description of Facies Analysis	Facies Zones	Age Based on Geological Map	Fossils	Age Based on Fossils
AP40	Quarry	Pelagic wackestone. Most of the planktonic foraminifera tests oriented parallel to the bedding. Calcite veins. (SMF3)	Deep sea/Deep shelf (FZ1/FZ2)	Senonian	Radiolaria, Morozovella aequa	Paleocene (Selandian-Thanetian)
AP39	Quarry	Pelagic wackestone (SMF3)	Deep shelf (FZ2)	Paleocene	Radiolaria, Parasubbotina pseudobulloides, Acarinina sp., Subbotina sp., Igorina pussila, Chiloguemberlita sp.	Paleocene (Selandian)
AP38	Quarry	Wackestone with a “flow” of packstone with planktonic foraminifera (SMF3)	Toe of Slope (FZ3)	Senonian	Ostracods, planktonic foraminifera	Late Cretaceous (Senonian)
AP37	Quarry	Calciturbidite (calcilutite), Packstone (SMF4)	Slope (FZ4)	Senonian	Radiolaria, small planktonic foraminifera	Late Cretaceous (Senonian)
AP36	Quarry	Micro brecciated limestone with nodules just over decollement surface (SMF4)	Slope (FZ4)	Senonian	Radiolaria, small planktonic foraminifera	Late Cretaceous (Senonian)
AP35	Gianiskari	Mudstone/wackestone (SMF3)	Deep sea (FZ1)	Senonian	Radiolaria	Late Cretaceous (Senonian)
AP34	Quarry	Calciturbidite (calcarenite), Packstone with small-sized bioclasts of shoal fauna (rudists, benthic forams and echinoderms). Mudstone/wackestone (SMF4)	Slope (FZ4)	Senonian	Radiolaria, Heterohelicidae, small planktonic foraminifera	Late Cretaceous (Senonian)
AP33	Quarry	Pelagic mudstone with Globotruncana (SMF3)	Deep shelf (FZ2)	Senonian	Hedbergella sp., cf. Abathomphalus mayaroensis	Late Cretaceous (Maastrichtian)
AP32	Quarry	Wackestone and calcite veins filled with coarse calcite grains. Calciturbidite (calcilutite), wackestone/packstone with small-sized bioclasts (rudists, echinoderms) (SMF4)	Slope (FZ4)	Senonian	Radiolaria, Globotruncana arca, Globotruncanella havanensis, Rugoglobigerina sp., Heterohelix sp., ?Abathomphalus mayaroensis	Late Cretaceous (Maastrichtian)
AP31	Quarry	Calciturbidite (Calcirudite), floatstone with bioclasts and intraclasts (SMF5)	Slope (FZ4)	Senonian	Algae, Echinoderm fragments, Rudist fragments, Rudist, Miliolidae, Textularia sp., Cuneolina sp., Quinqueloculina sp., Nezzazata sp., Alanlordella messinae, Orbitoides media, Globotruncana arca Globotruncana linneiana, Globotruncana cf. ventricosa Globotruncanella havanensis, Globotruncanita stuarti, Globotruncanita pettersi, Contusotruncana sp., Gannserina gannseri, Rugoglobigerina sp., Rugoglobigerina rugosa, Heterohelix sp., Abathomphalus mayaroensis	Late Cretaceous (Maastrichtian)
AP30	Quarry	Calciturbidite (calcirudite), floatstone/packstone with coarse bioclasts (SMF5)	Slope (FZ4)	Senonian	Algae, Echinoderm fragments, Rudist fragments, Miliolidae, Cuneolina sp., Orbitoides sp., Lepidorbitoides sp., Globotruncanita stuarti, Rotalia sp., Rugoglobigerina rugosa, Ostrascods, Abathomphalus mayaroensis	Late Cretaceous (Maastrichtian)
AP29	Quarry	Calciturbidite (calcirudite), floatstone with bioclasts of rudists, benthic forams from a nearby shoal (SMF5)	Slope (FZ4)	Senonian	Algae, Dacycladacae, Mollusc fragments, Rudist fragments, Miliolidae, Cuneolina sp., Orbitoides media, Lepidorbitoides sp., Sulcoperculina sp., Siderolites calcitrapoides, Alanlordella messinae, Globotruncana esnehensis, Globotruncana ventricosa Globotruncanita stuarti, cf. Contusotruncana contusa, Gannserina gannseri, Rugoglobigerina sp., Abathomphalus mayaroensis	Late Cretaceous (Maastrichtian)
AP28	On the road	Biomicrite, floatstone/ packstone (SMF4)	Toe of Slope (FZ3)	Senonian	Globotruncanaarca, Globotruncanita stuarti, Rugoglobigerinarugosa, Abathomphalus mayaroensis, Rudist fragments, Orbitoides sp.	Late Cretaceous (Maastrichtian)
AP27	On the road	Microbreccia biolithoclastic packstone. Bioclasts (SMF2)	Deep shelf/Deep sea (FZ1/FZ2)	Senonian	Globotruncanitastuarti, Abathomphalus mayaroensis, Rugoglobigerinarugosa, Radiolaria	Late Cretaceous (Maastrichtian)
AP26	On the road	Allochthonous bioclastic rudstone/ floatstone breccia, geopetal fractures (SMF5)	Slope (FZ4)	Senonian	Rudist fragments, Radiolaria, Miliolidae, Algae, Orbitoides sp., Globotruncana cf. bulloides	Late Cretaceous (Campanian–Maastrichtian)
AP25	Quarry	Allochthonous bio-lithoclastic packstone/rudstone, oosparite endoclast, micritic endoclast (SMF5)	Slope (FZ4)	Senonian	Lepidorbitoidessp., Rudist fragments, Mollusc fragments, Sulcoperulina sp.	Late Cretaceous (Campanian–Maastrichtian)
AP24	Quarry	Allochthonous bio-lithoclastic packstone with microsparite and micritic clasts (SMF4)	Toe of Slope (FZ3)	Senonian	Rotaliidae, Hedbergella sp., Rugoglobicerina sp.,Miliolidae, Gansserina gansseri, Globotruncana arca	Late Cretaceous (Campanian–Maastrichtian)
AP23	Quarry	Allochthonous bio-lithoclastic packstone. Coarse crystalline mosaic of calcite with micritic clasts and fenestral caves. Also the typical dog- teeth cement has developed around some breccia and suggests meteoric diagenesis (SMF5)	Slope (FZ4)	Senonian	Radiolaria, Rotaliidae, Hedbergella sp., Miliolidae, Gansserina gansseri	Late Cretaceous (Campanian–Maastrichtian)
AP22	Quarry	In places, grainstone/rudstone (higher energy). Floatstone/rudstone with bioclasts of rudists and mollusk fragments, intraclasts with benthic foraminifera. Environment with high energy (SMF5)	Slope (FZ4)	Senonian	G astropod fragments, Rudist fragments, Bivalve filaments, Miliolidae, Quinqueloculina sp., ?Nezzazata sp., Orbitoides media, Rugoglobigerina rugosa, Heterohelix sp., Hedbergella sp., Abathomphalus mayaroensis	Late Cretaceous (Campanian–Maastrichtian)
AP21	Quarry	In places, grainstone/rudstone (higher energy). Wackestone (SMF5)	Slope (FZ4)	Senonian	Radiolaria, Rugoglobigerina sp., Rugoglobigerina rugosa, Rugoglobigerina pennyi, Planomalina sp., Hedbergella sp.	Late Cretaceous (Campanian–Maastrichtian)
AP20	Quarry	Allochthonous bio-lithoclastic packstone/rudstone, oosparite endoclast, micritic endoclast (SMF5)	Slope (FZ4)	Senonian	Mollusc fragments, Benthic foraminifera fragments	Late Cretaceous (Campanian–Maastrichtian)
AP19	Quarry	Allochthonous bio-lithoclastic packstone/rudstone, oosparite endoclast, micritic endoclast (SMF5)	Slope (FZ4)	Senonian	Orbitoides sp., Orbitoides cf. media, Lepidorbitoides sp., Siderolites calcitrapoides, Textularia sp., Mollusc fragments, Algae fragment	Late Cretaceous (Campanian–Maastrichtian)
AP18	On the road	Biopelmicrite with scattered benthic foraminifera and echinoderm fragments. Fenestral caves maybe to meteoric diagenesis (SMF19)	Restricted platform (FZ8)	Senonian	Quinqueloculinasp., Spiroloculina sp., Pseudolituonella sp., Cuneolina sp., Textulariidae, Miliolidae	Late Cretaceous (Campanian–Maastrichtian)
AP17	Quarry	Packstone/grainstone, with endoclast (SMF4)	Toe of Slope (FZ3)	Senonian	Globotruncanita cf. stuartiformis, Globotruncana linneiana, Globotruncana ventricosa, Cuneolina sp., Rudist fragments, Mollusc fragments	Late Cretaceous (Campanian)
AP16	Quarry	Microbracciated limestone with abundant bioclastic fragments and micritic clasts, ooids fragments, geopetal fabrics (SMF5)	Slope (FZ4)	Senonian	Miliolidae, Mollusc fragments, Cuneolina sp., ?Globotruncanita stuartiformis, Rugoglobicerina sp.	Late Cretaceous (lower Campanian)
AP15	Quarry	Wackestone /Packstone with material derived from reef organisms (SMF4)	Slope (FZ4)	Senonian	Radiolaria, algae, Echinoderm fragments, Rudist fragments, Miliolidae, Rotaliidae, Textularia sp., Nodosaria sp., Orbitoides media	Late Cretaceous (Santonian–Maastrichtian)
AP14	Quarry	Bioclastic Packstone (SMF4)	Slope (FZ4)	Senonian	Alanlordella messinae, Rugoglobigerina sp., Radiolaria	Late Cretaceous (Santonian–Maastrichtian)
AP13	On the road	Calciturbidite (calcarenite), Packstone with small-sized bioclasts of shoal fauna (rudists, benthic forams and echinoderms). Packstone/wackestone (SMF4)	Slope (FZ4)	Senonian	Radiolaria, Rugoglobigerina sp., Marginotruncana pseudolinneiana Planomalina sp. Hedbergella sp., Globigerinelloides sp.	Late Cretaceous (Turonian–Santonian)
AP12		Microbrecciated, two different facies separated by unconformity a. mudstone (SMF1) b. microcrystalline with calcite vein	Deep sea (FZ1)			Middle Cretaceous
AP11		a.Mudstone microcrystalline b. a zone which is Wackestone- Packstone, microlithoclastic (SMF3)	Deep sea/deep shelf (FZ1/2)			Middle Cretaceous
AP10	Gianiskari beach	Τhe same as above, wackestone with bioclast fragments (SMF3)	Deep sea (FZ1)	Vigla	Radiolaria, Algae	Early Cretaceous (Albian)
AP9	Gianiskari beach	Biomicrite. Wackestone with bioclasts and ooids(transported) (SMF3)	Deep sea/deep shelf (FZ1/2)	Vigla	Radiolaria	Early Cretaceous (Albian)
AP8	Gianiskari beach	Mudstone crossed by crosscutting veins (SMF3)	Deep sea (FZ1)	Vigla	Radiolaria	Early Cretaceous (Albian)
AP7	Gianiskari beach	Wackestone with pelagic fauna (calcified radiolaria?) (SMF3)	Deep sea (FZ1)	Vigla	Radiolaria, Ticinella sp	Early Cretaceous (Valanginian)
AP6	Gianiskari beach	Wackestone. Calcite veins have been obderved (SMF3)	Deep sea (FZ1)	Vigla	Radiolaria, Ticinella sp	Early Cretaceous (Valanginian)
AP5	Gianiskari beach	Mudstone (SMF1)	Deep sea (FZ1)			Early Cretaceous
AP4	Gianiskari beach	Mudstone, skeletan grains, biomicrite (SMF3)	Deep sea (FZ1)			Early Cretaceous
AP3	Gianiskari beach	Calciturbidite (calcarenite), Wackestone with sparse pelagic fauna (calcified radiolarian?) (SMF2)	Deep shelf (FZ2)	Vigla	Radiolaria, Algae, Calpionelidae	Early Cretaceous (Tithonian–Valanginian)
AP2	Gianiskari beach	Two facies: a. mudstone-wackestone, skeletan grains, microcrystalline (SMF3), b. wackestone-packstone (SMF2)	a. deep sea (FZ1), b. deep sea/deep shelf (FZ1-2)	Vigla	Calpionellidae	Early Cretaceous (Tithonian–Valanginian)
AP1	Gianiskari beach	Packstone-Wackestone, skeletal grains, fossiliferous biomicrite, calcite vein (SMF3)	Deep sea (FZ1)	Vigla	Calpionellidae	Early Cretaceous (Tithonian–Valanginian)

), are:

More specifically, the Lower Cretaceous deposits (Vigla limestones) were classified as mudstone/wackestone limestones consisting of micrites to biomicrites with planktonic foraminifera and radiolaria (standard microfacies SMF1-3), indicating a deep-sea to slope environment (FZ1-4). In the Lower Cretaceous (Valanginian), the observed mudstone-wackestone limestones, consist of biomicrites with skeletal grains and spiculites (SMF3, SMF1) and are associated with a deep-sea environment (FZ1).

The Upper Cretaceous calciturbidites were classified as packstone biomicrites with microbreccia and planktonic foraminifera (SMF4) in a slope environment (FZ4).

The Paleocene deposits consist of grain-supported wackestone-grainestone biomicrites with skeletal grains.

4.2.2. Biostratigraphy of Araxos Peninsula

The age determination (Table 2) supports the pre-existing results reported in the geological map concerning the Ionian zone rock exposures sheet Nea Manolas [38]. In particular, they confirm the Lower Cretaceous age for the “Vigla” limestones, the Upper Cretaceous age for the calciturbidites and brecciated limestones, and the Paleocene age for the uppermost part of the studied carbonate sequence.

Representative photographs showing sedimentological textures and characteristic fossils are presented in Figure 6.

5. Discussion

Integrated data obtained from the microfacies analysis of the studied sections (Jurassic to Eocene deposits in Kastos Island and Early Cretaceous to Eocene in Araxos peninsula) represent an efficient interpretation tool for reconstructing temporal trends in the spatial distribution of distinct microfacies types.

By means of microfacies analysis, on Kastos Island different depositional environments were identified. In general, results show a general transition from open marine and/or restricted conditions during the Early Jurassic (“Pantokrator formation”) to deep-sea conditions during the Late Jurassic (Jurassic radiolarites and shales with “Posidonia”) and Early Cretaceous (“Vigla formation”). Gradually, during the Late Cretaceous (“Senonian formation”), the deep-sea conditions changed to slope conditions introducing a gradual shallowing. Paleocene and Eocene present many internal changes between deep-sea to toe of slope conditions. It seems that at the Paleocene/Eocene boundary, the shallowest conditions are represented by the toe of the slope, whereas during the Eocene, a general gradual deepening upwards to deep-sea conditions occurred.

Moreover, the deformation that was recognized within the Jurassic shales with “Posidonia” in the southern part of the island, the fact that the underlying Jurassic “Pantokrator” limestones and the overlying Lower Cretaceous “Vigla” limestones remained undeformed, and that in the same area the Jurassic “Pantokrator formation” limestones are found in contact with “Vigla” limestones without the presence of Jurassic shales support the idea that the Jurassic shales likely slumped from the top of “Pantokrator formation” just after sedimentation and moved basinwards.

From the above, it is suggested that the syn-rift stage started just after the sedimentation of the Jurassic shales. Consequently, the absence of Jurassic shales in the transitional zone from “Pantokrator” to “Vigla” formations could be plausible due to erosion.

In Araxos peninsula, and due to the fact that only the upper part of the Lower Cretaceous deposits is outcropping whereas the Jurassic deposits are absent, only a few changes in the depositional conditions were observed. The Lower Cretaceous “Vigla” limestones show changes from deep-sea to middle and outer slope, whereas the Upper Cretaceous “Senonian” deposits showed many internal changes in the paleoenvironment from deep sea to toe of slope, and slope inner platform-middle and outer platform.

Comparing the two different studied areas, where both Lower and Upper Cretaceous deposits were accumulated in quite different depositional conditions, it seems that Cretaceous sediments on Kastos Island were deposited in more stable and deeper conditions than those of Araxos peninsula, where several internal changes indicate shallower depositional conditions (Figure 7).

According to geological and tectonic reconstructions [15], the western margins of the external Ionian sub-basin include both Ithaca Island (close to the western margins) and Kastos Island (central part of the sub-basin, according to this work). Therefore, based on their microfacies features, a comparison between Araxos peninsula (internal Ionian sub-basin) and Ithaca Island could be plausible as both areas represent the margins of a sub-basin very close to a platform from where breccia, microbreccia, or calciturbidites were produced. Additionally, as the above two areas are characterized by the presence of rudist and coral fragments, the above idea is supported.

Moreover, and regardless of microfacies analysis, the age determination of the studied samples showed great differences between previous geological mapping and the existing different rock formations.

In Kastos Island, several discrepancies were identified related to the studied outcrops. The outcrops of “Vigla shales” were found in restricted areas, thus they are not so thick and laterally extended as the published geological map shows (Figure 8).

The age determination from different outcrops east of Sarakiniko bay showed that Paleocene to Eocene deposits, as far as the northern part of Kastos Island is concerned, are absent. The fact that the western coastline of Kastos Island is characterized by “Vigla formation” introduces a new geological approach for the Kastos evolution (Figure 9).

In order to evaluate the new perception for Kastos Island evolution, four selected cross-sections were created presenting the new idea of Kastos evolution. It is critical to mention that the number of analyzed samples cannot support in total the proposed model and many new samples must be analyzed in order to find the exact boundaries between the different formations, to recognize the depositional changes either internal to each formation or between different formations.

In the new proposed geological map, two recent faults, as recognized and measured in the field, were added in order to help and establish the idea of a geological setting. With the above two new faults, an attempt was made in order to show the contact between different age formations. Additionally, Jurassic shales with “Posidonia” were found at least in one restricted area and this outcrop was also added to the new geological map.

Nevertheless, a question that has been raised from the new geological map and the existing additional faults is if all or some of the faults that appeared in the geological map are characterized by inversion tectonics. Most likely, they started their activity as normal faults, during Jurassic to Eocene, later acted as compressional faults, during Eocene to Miocene, and now transformed again to normal faults [15,43].

In Araxos peninsula, there are some minor internal changes to the Lower Cretaceous “Vigla formation,” where “Vigla shales” were added to the geological map. The east-dipping bedding without any obvious unconformities from Lower Cretaceous to Eocene formations in relation with the fact that the oldest deposits are outcropping to the west indicate the existence of a thrust fault west of the studied area (Figure 10), which acted after sedimentation and during the compressional regime, whereas the existing normal faults with west-dipping surfaces seem to be synsedimentary faults, and which acted during the syn-rift stage.

6. Conclusions

The goal of this study was the recognition of the different depositional conditions from one area to the other, both in the same age rocks and in different age rocks. Microfacies analysis results showed that on Kastos Island, the following depositional environments have been recognized: deep sea and deep shelf, toe of slope to slope, and open marine to restricted platform. In detail, the Lower Jurassic (“Pantokrator” limestones) deposits consist of SMF18-19 microfacies that were accumulated in an open marine-restricted environment (FZ7-8). The Lower Cretaceous deposits (“Vigla” limestones) are composed of standard microfacies SMF1-3, indicating deep sea to slope environments (FZ1-4), and in particular, the Valanginian ones by SMF3 and SMF1 microfacies are associated with deep sea environments (FZ1).

In Araxos peninsula, the Lower Cretaceous “Vigla” limestones consist of standard microfacies SMF3 and SMF2, indicating a deep-sea environment (FZ1-FZ2). The Upper Cretaceous microbreccia or breccia deposits consist of SMF5 microfacies which indicate a source of the exoclasts from a restricted or shallow shelf environment (FZ8) with the influence of meteoric water, whereas calciturbidites characterized bySMF4 microfacies and being interbedded by layers with radiolaria or planktonic foraminifera (SMF3), suggest slope or toe of slope depositional conditions (FZ3-4). Deep-sea conditions apply for the Paleocene calciturbidites containing planktonic foraminifera and radiolaria (SMF3), corresponding to a deep-sea environment (FZ1-2).

The above-described microfacies analysis and the recognition of facies zones introduce depositional changes in Araxos peninsula during the Cretaceous and several depositional changes on Kastos Island during the Paleocene/Eocene. Changes in depositional conditions could be related to different stages of tectonic activity in the Ionian basin from east to west. It seems that sedimentary conditions during the Cretaceous were clearly different between Kastos Island and Araxos peninsula, supporting the pre-existing results of our previously published works with different scientific approaches, such as the mineralogy of siliceous concretions or the tectonic influence (normal and transfer faults) on soft-sediment deformation during the sedimentation or on calciturbidites studies and their relation to the source areas [16,17].

Therefore, microfacies analysis introduced that the Cretaceous deposits were accumulated in quite different depositional conditions in the two studied areas. Kastos Island was characterized by more stable and deeper conditions and probably represents the deeper parts of the external Ionian sub-basin. On the other hand, Araxos peninsula was situated in the western margins of the external Ionian sub-basin, where shallower depositional conditions have been determined.

Finally, due to the results of this study, with fieldwork, microfacies analysis, and age determination the geological map of Kastos Island was reconstructed.