An isolated platform refers to a gentle platform dominated by carbonate sedimentary build-ups and surrounded by deep seas. The platform periphery transits to abyssal sea or deep lacustrine by steep slopes or cliffs. A typical representative of isolated platform in the modern sedimentation is the Bahamas Platform in the Caribbean Sea^[1,2]. Close to source rock, isolated platforms are likely to form large monolithic reef oil and gas reservoirs, so they have attracted much attention in oil and gas explo- ration. Since 2015, in the exploration of deep-water isolated reefs around the Eratosthenes Seamount (ESM) in the Eastern Mediterranean, four gas fields, Zohr, Calypso, Glaucus and Onesiphoros have been discovered. The largest gas field among them has geological reserves of 8500×10⁸ m³. The technological success rate of exploratory wells in this area is 100%^[3,4,5], foretelling a good exploration prospect of isolated carbonate platforms in the area. Compared with hot spots on both sides of the South Atlantic and in the Gulf of Mexico, the deep-water area of the Eastern Mediterranean has a lower exploration degree. Limited by offshore seismic technologies and low understanding level, previous studies on this area mainly focused on regional geology^{[6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21]} and the only few discoveries such as Tamar, Leviathan, and Zohr^[3,4,5]. The formation conditions, distribution laws, sedimentary build-ups, and relationships of ESM and its surrounding isolated reefs in the deep-water area in the Eastern Mediterranean with hydrocarbon accumulation have not been studied in depth, making the next exploration direction unclear. Based on the fine interpretation of two-dimensional seismic data in the Cyprus Seas, basin formation and evolution, basin structure and sedimentary filling difference of this area have been analyzed. Combined with the anatomy of oil and gas reservoirs discovered, different hydrocarbon accumulation models have been established, favorable hydrocarbon accumulation combinations (play) and next exploration direction in the area have also been discussed, in the hope to provide references for selecting strategic prospective areas and evaluating new projects.

The Eastern Mediterranean is located at the intersection of the Eurasian Plate and the African-Arab Plate. It is a residual ocean basin formed by the closure of the Neo-Tethys Ocean^{[7-8, 16-20]}, and part of the Tethys tectonic domain^{[7-8, 16-20]} (Fig. 1). The north of the Eastern Mediterranean Cyprus-Greek Arc is the “trench-arc-basin” accretion system involved in the Alpine orogenic belt. The central part is the oval ESM in NE-SW strike in the deep-water area of the southern Cyprus Island. This paper refers to the seamount and its periphery as the Eratosthenes Seamount Basin (ESMB). It collides with the Cyprus Island in the north, and next to the Nile Delta Basin in the south, adjacent to the Levant Basin and Herodotus Basin respectively in the east and west (Fig. 1). Previous researches suggested that the isolated platforms such as ESM were micro-continents splitting from the African-Arab Plate in the early stage, and were closely related to the formation and contraction of the Neo-Tethys Ocean. Their tectonic evolution has experienced four stages, intracontinental rift, intercontinental rift, passive drift, and late stage reconstruction which encompasses three stages, subduction reduction, initial collision, and collision reconstruction (Fig. 2).

During the Middle Triassic-Early Jurassic intracontinental rift stage, a series of horst-type fault blocks such as ESM were formed. The north margin of the Africa-Arab continent entered a major splitting period during Middle Triassic-Early Jurassic (Fig. 2a). There are a large amount of Triassic intraplate basalt developing in the southern margin of Turkey, northwestern Syria, and the Cyprus Island^[20]. The northeast-southwest extensional faults and magmatic activities are extensive at the margins of Egypt and Levant. Drilling data show that the Lower Jurassic on the current coast of the Levant Margin has a thickness of more than 3 km^[16,17], indicating that the Tauride- Anatolide Plate and Eratosthenes and other micro-continents began to split from the current northern margin of the Africa-Arab Plate^{[16,17,18,19,20,21,22,23]}. At that time, the Nile Delta, Levant, and other basins on the northern margin of the Africa-Arab Continent belonged to a large rift basin in the intracontinental rift stage^[16,17], where the structural pattern of alternate horsts and grabens was formed, and ESM was the largest horst block among the horsts (Fig. 2a).

In the Middle Jurassic intercontinental rift stage, ESM and other horst-type fault blocks began to form isolated platforms. During the Middle Triassic-Early Jurassic, extensional rifting lasted, resulting in a narrow oceanic crust between the Tauride-Anatolide Plate and the Africa-Arab Plate during Middle Jurassic; the southern part of the Neo-Tethys Ocean opened, resulting in intercontinental rift basins, and coming up of oceanic crust in the north of the ESM which was roughly parallel to the current Cyprus Arc^{[23,24,25,26,27]}. The ESM Basin and the Nile Delta Basin in the south and the lower part of the Levant Basin in the east still had alternate horsts and grabens^{[28,29,30,31]}, which is consistent with the severely thinned continental crust revealed by gravity, magnetic and seismic refraction data^{[23,24,25,26,27]}, indicating that the Neo-Tethys splitting did not lead to the formation of oceanic spreading ridge (Fig. 2b). At this time, the ESM and other horst-type paleo-uplifts were in isolated distribution in the ocean and were not affected by terrigenous clasts. Coupled with warm and humid climate, carbonate build-ups started to deposit^{[10,11,12,13,14,15]} (Fig. 2b).

During the drift stage from the Late-Middle Jurassic to Late Cretaceous Turonian, a broad passive continental margin basin was formed, and the isolated platforms such as ESM developed successively. The Middle Jurassic Bathonian-Late Cretaceous Turonian was the main period of disintegration of the Pangaea Supercontinent^[16,17]. The separation of Eurasia from Gondwana further strengthened the expansion of the Southern Neo-Tethys Ocean, which was manifested in the rapid northward drift of the Tauride-Anatolide Plate with the expansion of the Southern Neo-Tethys Ocean, and the Tauride-Anatolide Plate drifted to about N15° in the Turonian of the Late Cretaceous^[21], which was also the peak expansion period of the Southern Neo-Tethys (Fig. 2c). Throughout the whole drift stage, the isolated platforms such as ESM only suffered exposure and erosion during the Tithonian period of the Late Jurassic as the sea level dropped and had been developing successively. In the Middle Jurassic Bathonian to Late Cretaceous Turonian, shallow-water carbonate platform sedimentary build-ups developed on the rift strata in the Eratosthenes micro-continental plate, which has been confirmed by Ocean Drilling Program (ODP) Site 967^{[10,11,12,13,14,15]} (Fig. 2c).

Since the Late Cretaceous Cenomanian, as the Southern Neo-Tethys Ocean gradually subducted and closed, the isolated platforms such as ESM have undergone reversal transformation to various degrees. The Southern Neo-Tethys Ocean began to subduct northward in the Late Cretaceous Senonian Period^{[15, 18-20, 32-34]}, forming a trench-arc-basin system^{[10, 16-17, 19-20, 32-34]} (Fig. 2d). At the end of the Cretaceous, under the influence of subduction, the northern margin of the African-Arab Continent was squeezed in NW-SE direction, leading to the compression and reversal of Neo-Tethys extensional faults, and forming the famous Syrian arc fold belt^{[6-7, 35]}. Along with the subduction during the Late Cretaceous Senonian, the relative sea level in the area rose sharply, consequently, the shallow-water platforms such as ESM were submerged, and deep-water marlite deposit started to develop^{[10,11,12,13,14,15]} (Fig. 2d).

During the Paleogene, as the Southern Neo-Tethys Ocean continued to subduct northward^[36,37], micro-continents such as Eratosthenes still had submerged platform deposits developed^{[10,11,12,13,14,15]} (Fig. 2d).

The collision between the Arab Plate and the Eurasian Plate intensified during the Early Miocene^[28,29,30], and the southward migration of the subduction zone resulted in the regional uplift of the Eratosthenes micro-continent^{[10,11,12,13,14,15,16,17,18,19,20]}. Coincident with relative sea level drop, shallow-water platform sediments developed again in the micro-continents such as Eratosthenes, which has been confirmed by ODP Leg160 and Zohr1 ^{[3, 10-15]}.

The closure of the Strait of Gibraltar during the Messinian period at the end of the Miocene cut off the connection between the Mediterranean and the Atlantic Ocean. Due to the dry and hot climate, the Eastern Mediterranean was dried up and deposited thousands of meters of salt rocks, while the Levant and Egypt margins and the Eratosthenes micro-continent were exposed and eroded^[38,39,40] (Fig. 2e). During this period, the subduction plates detached^[41], and the converging mode of the plates changed from subduction to horizontal compression and collision, and the Eratosthenes micro-continent block and the Cyprus Arc also began to collide (Fig. 2e). The opening of the Strait of Gibraltar during the Early Pliocene restored the abyssal sedimentary environment in the Eastern Mediterranean. The Eratosthenes micro-continent block was submerged by deep water and began to develop deep-water fine-grained sediments. Meanwhile, the deposition of carbonate rocks on the Levant and Egyptian margins also ended^{[28-30, 38-40]} (Fig. 2f).

Based on the understanding of the formation and evolution process of isolated platforms such as ESM, 6770 km of 2D seismic data in the deep waters of the Eastern Mediterranean, namely southern Cyprus, was interpreted finely. Based on the top structure of the Upper Cretaceous Turonian, the Cyprus Sea is divided into five first-order tectonic units, Eratosthenes Uplift in the center, alternate sag-uplift structural zone in the west, depression belt in the east, alternate sag-uplift structural zone in the south, and thrust nappe structural zone in the north (Fig. 3). The Eratosthenes uplift belt and the uplifts of western and southern structural belts identified by seismic facies are all isolated carbonate platforms. Comparative analysis of seismic facies reveals that three types of isolated platform deposits, single patch reef, single atoll and multiple reef-beach complexes, were formed in different paleomorphological environments.

2.1.1. ESM large-scale isolated platform

The ESM large-scale isolated platform mainly has build-ups of reef-beach complexes. During the Middle Jurassic Bajocian, the splitting of Neo-Tethys in the Eastern Mediterranean entered into the intercontinental rift stage. The ESM horst-type fault block covered an area of about 8750 km², and was surrounded by deep waters and located near the equator. Large sedimentary build-ups of isolated carbonate platform began to deposit on the basement of large paleo-uplift. Two stages of shallow-water carbonate sedimentary build-ups have been identified from seismic data, which are dominated by the sedimentary model of multiple reef-beach complex build-ups.

The reflection wave group (H2-H3) of the first stage of Mesozoic shallow-water carbonate platform is characterized by low frequency, strong amplitude, and medium continuity, and has alternate hummocky and sub-parallel reflection structures horizontally (Fig. 4). The reflection wave group represents the Middle Jurassic Bajocian- Upper Cretaceous Turonian, in which multiple hummocky reflections indicate individual reef build-ups, and the sub-parallel reflections indicate the filling of inter-reef grain shoal (Fig. 4). The reason for forming this type of multiple patch-like reefs on the wide platform and grain shoals filling between reefs is as follows: the ESM was a large paleo-uplift at the end of the rifting stage, and small horst and graben structures developed on it resulting in uneven terrain. The reef build-ups were likely to form in the structural highs, and the paleo-uplift structure background with wide and gentle slopes leading to undevelopment of margin reefs in the ESM isolated platform. Thus waves could enter the platform to erode and reform the organic reefs, thereby forming high-energy grain shoal deposits in the low-lying areas between the reefs (Fig. 4). This set of shallow-water carbonate rock is generally thicker at the axis and thinner on both flanks, with the maximum thickness of 1500 m at the axis. This is consistent with the characteristics of isolated platform sedimentary build-ups with rapid vertical aggradation in the structural highs of axis as the water depth increases. It is worth noting that a regionally distributed strong reflection interface divides the Mesozoic shallow-water platform into two sets of reflection wave groups: the lower reflection wave group represents the shallow-water platform with a relatively uniform thickness, and the upper reflection wave group shows the shallow-water platform which thins from the axis to the wings (Fig. 4). Above the strong reflection interface, the baselap reflection characteristics can be identified (Fig. 4). Combined with the thickness characteristics of the upper reflection wave group, it is concluded that the strong reflection interface represents a transgressive interface: at the end of the deposition of shallow-water platform represented by the lower reflection wave group, a transgression event happened, consequently, the sedimentary range of the platform evidently shrank from the two wings to the axis. Subsequently, with the rapid deposition and construction of reefs and the erosion and reformation of waves in the axis structural highs in the intra-platform reef, bioclasts from the axis began to prograde toward both wings (Fig. 4). In addition, there is a set of thick high-frequency and blank reflections above the shallow-water platform stratum, which represents the Upper Cretaceous Senonian-Paleogene. Well ODP967 drilled on the northern flank of the ESM encountered the Upper Cretaceous and Eocene of about 300 m thick (Fig. 5), revealing the Upper Cretaceous and Eocene are a set of organic-rich laminar marl deposits with a large number of biological pores and planktonic foraminifera (Fig. 6a, 6b), as well as siliceous flint strips, which are the characteristics of submerged platform facies in deep-water and low-energy environment^{[10,11,12,13,14,15]} (Fig. 5). According to reflection time and structural position, it may correspond to the blank reflection stratum above the H3 interface (Fig. 4), and is deep-water fine-grained sediment filling.

The second stage of Miocene shallow-water carbonate platform (H5-H6) is different from the first stage in two aspects: (1) it is thinner and uniform in thickness. The entire Miocene drilled by Well ODP966 is only 186 m thick^{[10,11,12,13,14,15]} (Fig. 5); (2) it is much better in continuity. Wells ODP966 and ODP965 reveal that the Miocene in the area is interbedded grainstone, packstone, and wackestone (Fig. 5), dominated by bioclastic shoal (Fig. 6c, 6d), with coral bioclastic ^{[10,11,12,13,14,15]} (Fig. 6c). The stratum corresponds to a set of continuously parallel reflection with low frequency and strong amplitude (Fig. 4). The reason is that the exposure and denudation of the Eratosthenes shallow-water isolated platform during the Messinian at the end of the Miocene made the formation become thinner and uniform in thickness. Moreover, the wave reformation on the large, wide and gentle slopes formed bioclastic shoal, making the seismic reflection better in continuity.

The exposure and denudation of the Miocene Messinian stopped the deposition of shallow-water platform in Eratosthenes and gave rise to the regional structural unconformity interface at the top of the Miocene in this area, which corresponds to a strong reflection interface H6 on seismic section (Fig. 4). Since the Pliocene, deep-sea fine-grained deposits have developed in this area (Fig. 5), which corresponds to a set of parallel and continuous reflections with weak amplitude and high frequency (Fig. 4).

2.1.2. Isolated platforms in the alternate sag-uplift structural zone on the south of Eratosthenes

During the Middle Jurassic Bajocian period, the Neo- Tethys intracontinental rift stage ended, and shallow- water carbonate platform sedimentary build-ups began to develop on the horst-type fault blocks smaller than ESM in the alternate sag-uplift structural zone on the south of Eratosthenes (Fig. 7). The earliest stage of shallow-water platform sedimentary build-up there is roughly the same in geological period as the first stage in ESM, but different in the style of sedimentary build-ups somewhat. Mainly controlled by medium-small paleo- structural highs, these sedimentary build-ups mainly come in two types, single patch reef and single atoll. The single patch reefs are generally located on relatively narrow small horst-type fault blocks, and are indicated by typical hummocky reflections. They are caused by inherited aggradation along the paleomorphological highs (Fig. 7). The single atolls are generally located on platforms with relatively large area and relatively flat terrain, which are characterized by thick sediments at the platform margin and thin sediments in internal platform. On seismic sections, the hummocky chaotic reflections corresponding to the platform-margin high-energy reef-beach facies belt and sub-parallel continuous reflections corresponding to low-energy static lagoon in the platform can be seen (Fig. 7). The margin surrounding the platform develops high-energy reef facies belt (Fig. 7), which has been confirmed by the Cretaceous high-quality reef reservoirs encountered in Wells Zhor and Calypso1^[4].

During the Late Cretaceous, the isolated platforms in the alternate sag-uplift structural zone on the south of Eratosthenes were submerged by deep water and this situation lasted to the Oligocene (Fig. 7). On seismic sections, the hummocky reflection characteristic of the platform margin isn’t evident, with mudstone and marl of submerged platform facies. On seismic sections, the top boundary of the submerged platform facies is a flat reflection interface (H5) (Fig. 7).

During the Miocene, shallow-water platform build-ups developed again in these isolated platforms. They still come in single patch reef and single atoll (Fig. 7), and have been confirmed by Wells Zohr1, Calypso1 and Glaucus-1^[3,4,5]. This stage is roughly equivalent to the shallow-water platform sedimentary build-ups of the second stage of ESM, but is over 800 m thick at maximum and is covered by evaporite rock depositing in Messinian at the end of Miocene.

During the Miocene Messinian, the development of evaporite caused by the drying up of the Eastern Mediterranean ended the sedimentary build-up history of the isolated platforms in the alternate sag-uplift structural zone on the south of Eratosthenes and also led to the burial of these isolated platforms (Fig. 7). Since the Pliocene, abyssal fine-grained rock deposit has been developed in the area, which is indicated by a set of parallel and continuous reflections with weak-medium amplitude and high-frequency on seismic sections (Fig. 7).

2.1.3. Isolated platforms in the alternate sag-uplift structural zone on the west of Eratosthenes

As the alternate sag-uplift structural zone on the west of Eratosthenes has undergone the same tectonic evolution process as that on the south of Eratosthenes, the uplift structures of the two have the same structural conditions to form isolated platforms and the same process of platform sedimentary build-ups. Similar to the isolated platforms to the south of Eratosthenes, two sets of single atoll and patch reef isolated shallow-water sedimentary strata developed in the Mesozoic (Middle Jurassic Bajocian- Upper Cretaceous Turonian) and the Miocene on the horst-type fault blocks formed during the intracontinental rift stage, with a set of submerged platform deep-water sedimentary stratum sandwiched between them (Fig. 8). On seismic sections, these isolated shallow-water platforms have similar seismic facies reflection characteristics with those to the west of Eratosthenes, namely, the hummocky chaotic reflection corresponding to single patch reef (Fig. 8), or the platform margin hummocky chaotic reflection indicating single atoll and intraplatform parallel and continuous reflection. On the Miocene isolated shallow water platforms to the west of Eratosthenes, there is also a set of blank and chaotic reflection representing the Messinian evaporite, indicating that the isolated platforms were buried by thick evaporite in Messinian, thus ending the history of carbonate platform sedimentary build-ups (Fig. 8). Since the Pliocene, abyssal fine-grained rock deposits have also been developed in this structural zone (Fig. 8).

During the Middle Triassic-Early Jurassic, a series of NE-SW trending horst-type fault blocks were formed in the deep waters of the Eastern Mediterranean along with the NW-SW trending splitting of Neo-Tethys, among which the ESM was the largest. After the splitting, under the background of abyssal sedimentary environment lacking terrigenous clastic input, these horst-type fault blocks began to develop isolated carbonate platform deposits due to their high paleomorphological locations. It can be seen that the forming of horst-type fault blocks during the splitting of the Neo-Tethys is a prerequisite for the development of isolated carbonate platforms in the subsequent drift stage, which also controls the distribution of isolated carbonate platforms in the deep waters of the Eastern Mediterranean.

Seismic facies analysis reveals (Figs. 9 and 10) that isolated platforms are common on the central Eratosthenes uplift zone and the highs in those two alternate sag-uplift structural zones on the south of Eratosthenes and on the west of Eratosthenes, respectively. Laterally, under the control of different paleo-tectonic environments, three types of shallow-water isolated carbonate platform build-ups are formed: the single patch reefs on small and narrow low bulges in the alternate sag-uplift structural zones on the south and east of Eratosthenes, the single atolls on the medium and open gentle low bugles in the alternate sag-uplift structural zones on the south and east of Eratosthenes, and the aggregate of multiple reef-beach complexes on the large, gentle and open bulges in the central Eratosthenes. Longitudinally, the two stages of shallow-water platform sedimentary build-ups in the Middle Jurassic Bajocian-Upper Cretaceous Turonian and Miocene respectively turn up in the reef-beach complex isolated platform in central Eratosthenes and single patch reef-type platform and single atoll-type platform the alternate sag-uplift structural zones on the south and east of Eratosthenes. It is worth noting that several reef-beach complex-type platforms in central Eratosthenes are on large, gentle and open paleo-uplifts and are compressed and uplifted at the end of Miocene. Therefore, the bioclastic beaches controlled by wave reformation are better developed.

Based on the temporal and spatial distribution characteristics of the three types of isolated carbonate platforms in the Eastern Mediterranean of Cyprus, together with regional source rock, reservoir and caprock conditions, three major favorable hydrocarbon accumulation zones in central Eratosthenes, the alternate sag-uplift structural zones on the south and east of Eratosthenes have been sorted out to clarify favorable exploration direction and target (Fig. 11).

The ESM large-scale isolated platform has multiple reef-beach complex accumulation zones, and the Middle Jurassic Bajocian-Upper Cretaceous Turonian accumulation combination (play) in the lower part has great exploration potential. The ESM large-scale isolated platform has two sets of reservoirs, namely, the Miocene and Middle Jurassic Bajocian-Upper Cretaceous Turonian reef-beach complex top-down. Of them, ocean drilling project encountered shallow Miocene, but no oil and gas have been discovered due to the shallow burial depth and lack of effective caprock. The potential target is the lower Middle Jurassic Bajocian-Upper Cretaceous Turonian reef-beach complex. This set of reef-beach complex is speculated to have good reservoir properties, large scale and good continuity on plane and longitudinal superposition based on seismic facies analogy (Fig. 11). Although there is no salt caprock formed at the end of Miocene, the reservoir is covered by thick deep-water fine-grained muddy limestone and limy mudstone (Fig. 11). There are two types of effective source rocks: one is the shallow biogenic gas confirmed by the large discovery in southern Zhor, which mainly comes from immature source rock at a buried depth of less than 3000 m above and around the ESM uplift; another is the thermogenic gas, which mainly comes from mature source rocks deeply buried in the periphery of the ESM, mainly including Triassic-Jurassic marine shale^[42] (Fig. 11). In addition, the ESM is an inherited paleo-uplift, forming large-scale structural-stratigraphic traps with organic reefs, with structural amplitudes of more than 1500 m. Hence, the paleo-uplift has been always hydrocarbon migration and accumulation area, and can form the Middle Jurassic Bajocian-Upper Cretaceous Turonian play (Fig. 11). Moreover, the play has moderate burial depth, large thickness and wide distribution of reservoirs. In addition, the beach bodies are relatively developed under the background of paleo-uplift and the reservoir connectivity is good. This play has good geological conditions to form a giant and monolithic gas field (Fig. 11).

The medium-small single reefs in the alternate sag-uplift structural zones on the south of Eratosthenes are independent accumulation zones, and single patch reefs and single atolls all can form large gas fields. The alternate sag-uplift structural zone on the south of Eratosthenes has only single small patch reefs and single medium atolls, with two sets of plays, i.e., the Middle Jurassic Bajocian-Upper Cretaceous Turonian and Miocene in the accumulation zone (Fig. 11). The Middle Jurassic Bajocian-Upper Cretaceous Turonian organic reef play below is directly covered by the Upper Cretaceous Cenomanian-Oligocene marl caprock, and is linked with the underlying Triassic-Lower Jurassic rift neritic source rocks through faults, forming a superior source rock-reservoir-caprock combination with source rock at the bottom, reservoir in the middle, and caprock in the top (Fig. 11). The development of the marl caprock represents the formation time of the Mesozoic reef trap, that is, the Oligocene. Since its formation, the reef trap has been always at the structural high and long on the direction of oil and gas migration (Fig. 11). The peak of hydrocarbon generation and expulsion of the Lower Mesozoic major source rocks in this area was later than the formation time of the trap, which ensures the effectiveness of the trap. Oil and gas generated by the Triassic-Lower Jurassic rift shallow marine source rocks and Middle Jurassic-Upper Cretaceous deep marine source rocks continuously charged into the Mesozoic platform margin reef traps in the area through fault zones and slope zones respectively, forming a large hydrocarbon accumulation zone (Fig. 11). The Upper Miocene reef reservoir is directly covered by thick Messinian evaporite rock, forming an excellent reservoir-caprock combination (Fig. 11). The Oligocene-Miocene source rocks located in the depression areas on both sides of the platform margin are the major source of oil and gas for the Miocene platform margin organic reef trap. These source rocks, with mainly terrestrial organic matter, are currently immature-low mature and in the window of massive biogenic gas generation^[42]. The biogenic gas has been migrating along the slope belt to the Miocene platform margin organic reef trap at the structural high continuously, meanwhile, the thermogenic gas generated by the pre-Oligocene source rocks can also charge into the trap, making this area a large-scale enrichment zone of natural gas (Fig. 11). The thick and tight salt caprock has a strong sealing effect on natural gas reservoirs and can prevent large-scale escape of natural gas, thereby playing a vital role in the formation of the natural gas enrichment zone (Fig. 11). The superior accumulation conditions of this accumulation zone have been confirmed by exploration. Out of the four independent reefs encountered so far, the two independent atolls (Zohr and Calypso) have natural gas reserves of 8500×10⁸ m³ and 1150×10⁸ m³ discovered respectively; the two independent patch reefs (Glaucus and Onesiphoros) have natural gas reserves of 1400×10⁸ m³ and 140×10⁸ m³ discovered respectively. All the types of isolated reef bodies have the geological conditions to form large gas reservoir.

Like those isolated platforms to the south of Eratosthenes, the medium-small single reefs to the west of Eratosthenes also have good exploration prospects. The alternate sag-uplift structural zone on the west of Eratosthenes was formed at the same time with that on the south of Eratosthenes, and experienced the same sedimentary build-up process. On seismic sections, a series of independent patch reefs and atolls have been identified in this zone (Fig. 8). From analogue, they have the same hydrocarbon accumulation conditions. Although not yet been drilled, they are speculated to have good exploration prospects too.

The formation and evolution of a series of isolated carbonate platforms (such as ESM) in the Eastern Mediterranean are closely related to the opening and closing of the Neo-Tethys Ocean. For their tectonic background, some horst-type fault blocks split from the Africa-Arab Plate during the Middle Triassic-Early Jurassic intracontinental rift stage. Then they experienced the Middle Jurassic intercontinental rift stage, Late Middle Jurassic-Late Cretaceous Turonian passive drift stage, and successive carbonate build-up in the Late Cretaceous Senonian-Miocene subduction stage. Under the effect of moderate-slight reversal occurring during the Late Miocene Messinian due to the closing of the Neo-Tethys Ocean, currently, they are still in the passive continental marginal basin stage.

Three types of isolated platforms are formed under different paleo-tectonic settings: single patch reef platform controlled by small and narrow horst-type fault block, single atoll platform controlled by medium size and wide and gentle horst-type fault block, and multiple reef-beach complex type platform controlled by large and broad paleo-high, in ESM and the surrounding area. The first two types are universal at the highs in the alternate sag-uplift structural zones on the south and west of Eratosthenes, and the third type only occurs in the ESM. Vertically, as a result of fluctuation of sea level, two sets of reef build-ups, i.e. the Middle Jurassic Bajocian-Upper Cretaceous Turonian and the Miocene, develop in the ESM paleo-highs, as well as the highs in the alternate sag-uplift structural zones on the south and west of Eratosthenes.

Wells drilled have been confirmed the first two types of isolated platforms controlled by the uplifts to the south of Eratosthenes have good natural gas accumulation conditions. At present, some similar isolated platforms to the south and west of Eratosthenes have not been drilled yet. No oil and gas wells have been drilled in multiple reef-beach complex-type isolated platforms in the central Eratosthenes uplift zone. In addition to the reservoir conditions for forming giant monolithic gas pools, there are also two sets of effective source rocks that can generate shallow biogenic gas and middle-deep thermogenic gas respectively. The ancient structures were formed early and had successive sedimentary build-ups, thus they have been always favorable zones for hydrocarbon migration and accumulation. All these platforms have good exploration prospects.