Individual beds of the Eocene carbonate suite are characterised by low angle cross-laminations of bioclastic, siliciclastic, pelletal, lithoclastic packstones and mudstones (see Fig. 2, Samples 6–2 from base to top). The constituents of the grain supported laminations include in a descending order of importance: angular fragments of bioclasts, coral and bryozoan fragments, larger benthic foraminifera, sub-angular to sub-rounded quartz grains >60 μm in diameter, sub-rounded Lutetian and uppermost Cretaceous lithoclasts, red algal fragments, echinoderm debris, lamellibranches debris and planktonic foraminifera. The constituents of the mud-supported laminations include in a descending order of importance: mud sized debris, planktonic foraminifera and rare sub-rounded uppermost Cretaceous lithoclasts. Overall, the environment of deposition of the thin cross-laminated heterogeneous grain supported facies and homogeneous mud supported facies points to shallow water conditions in the back reef–lagoon area close to wave base that is periodically subjected to flooding episodes (see Fig. 3). The high-energy fabrics of their thin beds <15 cm thick suggest a minimal accommodation space rather than slow sedimentation rates. The source of the Cretaceous lithoclasts is likely from nearby exposures and the raised western Beirut block but the provenance of the quartz sands remains problematic. The grainstone facies of Layer 5 of the Eocene suite is of shallow water deposit close to the wave base but it includes an exceptional deposit of small fossil fish of the Bregmacerotidae family (Plate 1).

The foraminiferal assemblages observed in the studied thin sections include small benthic foraminifera such as Textularia spp. (Plate 2, a), Bolivina sp. (Plate 3, a), and rare benthic foraminifera that consist of long biostratigraphically long-ranging Cenozoic forms, such as Elphidium sp. (Plate 2, b), Victoriella sp., and fragments of Operculina sp. (Plate 2, c). The >10% abundance of planktonic foraminifera from many studied samples narrows their age of deposition. For example, the presence of Porticulasphaera tropicalis Blow and Banner, Globigerinatheka barri Brönnimann (Plate 3, b), Dentoglobigerina venezuelana (Hedberg), Globigerina praebulloides Blow (Plate 3, c) and Turborotalia centralis (Cushman and Bermudez) (Plate 3, d) nominally indicate a late Bartonian–early Priabonian (Planktonic Zone [PZ] P14–P15, 39.2–35.1 Ma, see [7, 10]). However, the association of the larger benthic foraminifera Borelis sp. (Plate 2, c, d) with the planktonic assemblage narrows the age dating of the Eocene carbonate suite to the early Priabonian age (see [7, 11]).

Other than these in situ assemblages, reworked and allochthonous assemblages include reworked Paleocene and Early Eocene planktonic forms such as Acarinina nitida (Martin), (Plate 3, e) and Morozovella sp. (Plate 3, f). The allochthonous forms in the Cretaceous lithoclasts contain Late Cretaceous planktonic foraminifera assemblages which include Globigerinelloides spp., Gansserina gansseri (Bolli) (Plate 4, a), Pseudotextularia elegans (Rzehak) (Plate 4, b), Hedbergella spp., Heterohelix globulosa (Ehrenberg), Globotruncana spp., and the frequently present Globotruncana aegyptiaca Nakkady (Plate 4, c). These assemblages indicate an age of late Campanian to Maastrichtian (PZ Campanian 3–Maastrichtian 3, see [7, 11]).

The fish deposits of the high-energy bed (layer RML5) belong to the Bregmacerotidae family and are represented by the single genus Bregmaceros. They are small-sized, pelagic, 1–2 cm cod-like fish (Gadiformes), and their age range is from the Eocene to the Holocene [12]. The species is herein identified as B. filamentosus (Priem, 1908), and ranges from the Middle Eocene to Early Oligocene (PZ P10a–P21a, see [7], and has been reported from the Mediterranean region and its surrounding areas including Georgia (Middle to Late Eocene) and Iran (Middle Eocene to Early Oligocene) [12–14].

The bed thicknesses and sedimentology of the Eocene sections of Site 1 and Site 2 indicate a decrease in the accommodation space for carbonates from north to south, and from the late Lutetian to the early Priabonian. However, they are not the only occurrence of the North Beirut Eocene inner platform carbonates. Indeed, BouDagher-Fadel and Noujaim Clark [1] had recorded a marine terrace of Lutetian/Bartonian age in the southwest corner of the studied area (Site 3). This site represents the terrace of the archaeological excavation adjacent to St. George’s Cathedral (Fig. 1). The terrace occurs against the thin hard beds of the basin Maastrichtian basin carbonates, and includes reworked cyclically sorted, coarse cobble to pebble sized Campanian, Maastrichtian and Lutetian lithoclasts bound by Lutetian–Bartonian marine cements. This suggest the concurrent presence of a nearby source of uppermost Cretaceous and Lutetian exposures [1]. The initial reporting of the dates of these outcrops by Dubertret [2] was Eocene and Cretaceous (Senonian) that has since been refined in BouDagher-Fadel and Noujaim Clark [1].

The 1951 “Notice Explicative of Beirut Geological map 1/50,000”, by Dubertret, records another location of Eocene carbonates from an excavation performed south of the central harbour area (Site 4, Fig. 1). This exposure contains thin beds of marls and carbonates rich in reworked terminal Cretaceous planktonic foraminifera, and in situ Early Eocene foraminifera. Although the precise dating of these exposures cannot be inferred, these rocks are probably Early Eocene in age, representing the coastal onlap as far south of downtown Beirut.

The archaeological excavation of the Middle Miocene outcrop of Site 2 lies conformably on the youngest Eocene (early Priabonian) strata. The basal Miocene beds, 50 cm thick, are the only described carbonate beds under a suite of strata concealed by urbanisation (Fig. 5). These beds are characterised by cross-laminated structures, with laminations of coarse packstones and finer wackestones that include reworked uppermost Cretaceous and Middle Eocene lithoclasts suggesting nearby sediment provenance (Figs 1, 4–5). The packstone and wackestone fabrics enclose, in descending order of importance, lamellibranches bioclasts, coral and bryozoan debris, echinoderm fragments, red algal debris, and planktonic and larger benthic foraminifera. The in situ foraminiferal assemblage includes Globigerinoides trilobus (Reuss), Orbulina universa d’Orbigny (Plate 3, g–h), and Borelis melo (Fichtel and Moll), which characterise an age range of Middle Langhian to Serravallian [7, 10]. Borelis melo ranges in the Mediterranean from the Middle to Late Miocene (Langhian–Messinian) including the PZ N8b–N17 [16], however, the presence of O. universa indicates an assemblage not older than N9. This assemblage, therefore, indicates that these deposits can be correlated with the PZ N9–N17 (15–5.8 Ma). The dominance of Miliolidae and Textularidae in the larger benthic foraminifera assemblage indicates that a shallow neritic environment prevailed during the deposition of these beds. The heterogeneous, fine to >80 μm bioclastic content, the allochthonous rare sub-rounded to sub-angular quartz grains, and lithoclasts of older sediments suggest that sedimentation took place close to the wave base in an inner shelf lagoon.

The preserved platform deposits of the Mio/Pliocene age occur in the east central harbour area at Sites 6 and 8, where recent excavations have uncovered dark grey argillaceous carbonates of inner platform, lagoonal sediments (Figs 1, 4). These deposits (Site 6) include reworked Cretaceous planktonic foraminifera, and an in situ planktonic foraminifera assemblage not older than Late Miocene, PZ N17 (8.6 Ma). However, the presence of S. subdehiscens (Blow), Truncorotalia crassaformis (Galloway and Wissler), Globorotalia inflata (d’Orbigny) and Orbulina universa (d’Orbigny) indicate a Late Miocene to early Pliocene age range (PZ N17 – N19, 8.6 – 3.8 Ma, see [7, 11]). The argillaceous carbonates’ occurrences suggest a marine incursion filling the topographic low between the two east and west uplifts of North Beirut (Achrafieh and West Beirut) (see location map Figs 1, 4). To the east of these inner platform sediments, a shoreline carbonate section (Site 2) forms an apron of sediments against the rising northern foothill of Achrafieh. The uncovered bedrock of the Site 2 excavation exposes a shoreline sequence of shore to backshore layers at the base and a beach-rock sedimentary structure on top (Figs 2, 6).

The pit floor of the excavation consists of coarse siliciclastics and carbonate bioclastic debris overlain by a grain supported limestone layer (30 cm thick) composed of low-angle, cross-laminated fabrics of well-rounded sand sized lithoclastic grainstone. The lithoclast grains are bound with meniscus cements that are indicative of meteoric fresh waters, percolating through the vadose zone, in the backshore environment of deposition (see Layer 10 in Figs 6, 7a, b).

The uppermost layer of the bedrock (Layer 9) is 1 m+ thick. It is characterised by saucer shaped sedimentary structures and low angle cross-stratified bedding, that is interpreted as a lithified beach-rock structure during a sea level rise (Fig. 6). Its heterogeneous fabric is made of coarse cobble to sand sized clasts in a matrix of bioclastic lithoclastic grainstone (see lithoclast 8 in Fig. 6). The binding cement of its bioclastic and lithoclastic components is of micrite and microspar, indicative of the mixing marine phreatic and freshwater zones (see Fig. 8). Two populations of autochthonous and allochthonous bioclasts include, in a descending order of importance: planktonic foraminifera such as Globigerina spp. (Plate 4, a–c), larger benthic foraminifera, peloids, bioclasts (lamellibranches and bryozoan debris), lithoclasts, algal debris and iron rich reworked lithoclasts. The youngest planktonic foraminifera of the assemblage are S. dehiscens (Parker and Jones) (Plate 3, i), S. subdehiscens (Blow), (Plate 3, j), and O. universa (d’Orbigny), (Plate 3, h, k). The presence of S. subdehiscens and S. dehiscens indicate an age of Early Pliocene, PZ N19, 5.3–3.8 Ma. The allochthonous population of bioclasts include Cretaceous (late Campanian 3b – Maastrichtian, 74.5–66 Ma). The upper Eocene (Priabonian) and middle Miocene (Langhian) cobble to pebble sized lithoclasts in the matrix of the beach rock suggesting a nearby source of supply.

The components of the shoreline carbonate section indicate a lower Pliocene shoreline forming in the earlier wave cut erosional stage during a relative sea level drop, or at the onset of the staged uplifts of Achrafieh’s hillside. This was followed by a relative sea level rise cementing the contents in a beach-rock structure (Figs 4, 9d).

Holocene marine conglomerates and siliciclastics of a raised beach at the site of the Beirut Old Train Station (Site 7, Fig. 1) had been described by Zumoffen [17] and Sanlaville [3] where it occurs approximately 100 m downdip of the early Pliocene shoreline carbonate section of Site 2. The relationship of these two shorelines illustrates the multi-phased uplifts of the Achrafieh hillside (see Figs 1 and 9d).

Carbonate rocks exposed in the area of the Beirut Harbour are dated as Paleogene and Neogene based on the microfossil assemblage. This new biostratigraphic data gives a clearer picture of the structural evolution of Beirut. Lithoclasts of the latest Cretaceous, middle Eocene and oldest middle Miocene age detected within these carbonates point to uplift and erosion phases of beds of this age from nearby areas. Four diagrams summarise the structural and geological evolution of the harbour area (Fig. 9).

In situ foraminifera assemblages provided a relative age of Eocene and Miocene for the. parasequences. However, the youngest allochthonous lithoclasts in these same beds, provide information on the carbonates present in the area prior to erosion, and also serve to date the earliest uplift that would have occurred in the source area.

A debate has been developed on the timing of the uplift of Mount Lebanon in relation to the structural deformation along the Dead Sea fault zone. For example, Gomez et al. [18] indicated that Mount Lebanon started rising during the Middle Miocene and continued during the Late Miocene. Previous works by BouDagher-Fadel and Noujaim Clark [1] support this timing when recording Langhian lithoclasts in younger Serravallian and Tortonian–Messinian carbonates of coastal Tyre of south Lebanon and at the Jabal Terbol mid-Langhian–Tortonian section of north maritime Lebanon.

In the case of the Eocene carbonates at Site 3, the inclusion of lithoclasts are dated as Campanian, Maastrichtian and Lutetian in the shoreline/marine terrace sequence. This confirms that the down thrown side of the NNE SSW (F1) fault would have included the latest Cretaceous and middle Eocene beds before their marine erosion during the Lutetian/Bartonian time. The displacement along the F1 fault (Site 3) is inferred to have occurred nearer the end of the Middle Eocene (Bartonian), as indicated by foraminifera. The areal extent of the Lutetian carbonates are inferred to have covered the F1 fault, before the displacement along its side and the uplift of West Beirut and F1 compartments. In addition, younger (Late Eocene) Priabonian beds at Site 2 lateral to Site 3 include Lutetian and Cretaceous lithoclasts confirming the presence of nearby exposures of Lutetian and terminal Cretaceous beds to Site 2 (see Fig. 9b,c).

The Langhian and Serravallian (Mid-Miocene) carbonates of the harbour area include only in situ inner platform microfauna. The exception is at Site 2, by the eastern side of the harbour area, where the conformable Langhian–Serravallian bed contains Lutetian and Cretaceous lithoclasts. The nearby source of that foreign supply to the recipient Langhian–Serravallian sediments is likely to have been from the few preserved Lutetian and Bartonian exposures of the harbour area.

The lower Pliocene shoreline by the uplifted Eocene–Miocene conformable section of Site 2 includes middle Miocene lithoclasts. These were sourced either from the rising block of the middle Miocene beds (Achrafieh) and/or from the exposures in the south west of the harbour area. The occurrence of Mio/Pliocene argillaceous carbonates (Site 6 and Site 8) due south of the harbour area implies marine sedimentation filling a platform low between the uplifted reliefs of West Beirut and Achrafieh Eastern hillside (Fig. 9d).

Differential Cenozoic structural highs occur along the maritime Lebanon because of the rise of the Mount Lebanon during the Paleocene until the Late Miocene [1]. The latest rise was concurrent to the platform narrowing and establishment of shorelines close to the present-day coastline. The structural uplift of West Beirut in the late Middle Eocene was initiated while the African and Arabian plates were still united. The uplift of this area was possibly related to local tectonics. However, its reactivation during the mid-Miocene and early Pliocene took place several millions of years later after the African and Arabian plates had separated.

The Dead Sea Transform fault in Lebanon, called the Yammouneh Transform fault, separates the two plates. Transpressive and transtensional stresses along the fault zone caused the rise of the Mount Lebanon on the one hand, and the extensional landward basins such as today’s Yammouneh inland rhombic basin in the Bekaa Valley, on the other hand. The structural geology describing these occurrences had listed two phases of uplift of Mount Lebanon during the Middle Miocene and the Late Miocene, but the present study and that of BouDagher-Fadel and Noujaim Clark [1] further calibrates the uplift phases of Mount Lebanon. For example, the dating of individual Middle and Late Miocene beds or parasequences have shown a steady supply of older uppermost Cretaceous, Paleocene, Middle Eocene and lower Middle Miocene lithoclasts into recipient Langhian–Serravallian strata and Tortonian strata in north Lebanon (Jabal Terbol); in Langhian–Serravallian strata and lower Pliocene strata in Beirut (Site 2); in lower Langhian strata from sections of coastal Tyre of south Lebanon. These dating markers from the studied coastal outcrops provide the timing of the differential uplifts that had occurred during the earliest Middle Miocene in the south of Lebanon, the Middle Miocene in Beirut and Jabal Terbol north of Lebanon, the Late Miocene in the Jabal Terbol and latest early Pliocene in Beirut (see Fig. 10).