Formation and destruction of the Eratosthenes Seamount, Eastern Mediterranean Sea, and implications for collisional processes.

The first of two tectonic-oriented objectives during Leg 160 in the Eastern Mediterranean Sea (April-May, 1995) was concerned with study of processes of genesis and incipient collision of the Eratosthenes Seamount, a substantial crustal feature, with the active margin of the Eurasian plate to the north, represented by southern Cyprus. The upper part of the Eratosthenes Seamount (upper several hundred meters) was found to include both shallow- and deep-water carbonates dating back to pre- Aptian time (Early Cretaceous). Shallow-water platform carbonate deposition, similar to that of the onshore Levant continental margin to the east (part of the North African plate), was followed by submergence to bathyal depths in the Late Cretaceous to middle Eocene, punctuated by depositional and tectonic hiatuses. Tectonic uplift (~1 km) was followed by shallow-water carbonate deposition in the Miocene. The platform was subaerially exposed during the Messinian desiccation crisis. During the early Pliocene, the platform subsided to bathyal depths associated with localized accumulation of limestone debris flows. Subsidence accelerated in the late Pliocene-early Pleistocene. Interpretation of site-survey seismic data suggests that the base of the northern slope of the Eratosthenes Seamount is in the processes of detachment to form an allochthonous thrust slice, with implications for the formation of on-land melange terrains. Comparisons can be made with the collapse, high-angle faulting, and partial subduction of the mainly igneous Daisha Seamount in the Japan trench, and counterparts in the Mariana and Izu-Bonin fore-arcs, and elsewhere. The break-up of the Eratosthenes Seamount was achieved by loading-related flexural subsidence, accompanied by high-angle normal faulting, which may have exploited pre-existing structural weaknesses. Subsidence of the Eratosthenes Seamount was synchronous with rapid surface uplift of the over-riding plate, represented by the late Pliocene-mid-Pleistocene uplift of the Troodos ophiolite and its sedimentary cover. The flexural and isostatic effects of sediment loading and flooding of the Mediterranean Sea after the Messinian also influenced subsidence of the Eratosthenes Seamount, to some extent. The ultimate fate of the Eratosthenes Seamount is likely to be preservation as allochthonous slices, mainly limestone, within a subduction-accretion complex, forming part of a collisional suture zone. Accretionary units similar to the Eratosthenes Seamount are indeed found within the Tethyan orogenic belt to the north, in areas including Turkey and Greece

Lithofacies evidence for the Cretaceous-Paleogene sedimentary history of Eratosthenes Seamount, Eastern Mediterranean, in its regional tectonic context (Sites 966 and 967)

Drilling during Leg 160 penetrated an Early-Late Cretaceous and early Oligocene succession of carbonates in Hole 967E, beneath the lower northern slope of Eratosthenes Seamount. Middle Eocene pelagic carbonates were also recovered in Hole 966F, beneath the plateau area of the seamount. The base of the succession at Site 967 comprises shallow-water limestones, including coral and calcareous red algae, and occasional large foraminifers, that are interpreted as accumulations in a lagoonal setting within a carbonate platform. Neritic sedimentation ended in the upper Aptian (Lower Cretaceous) and was followed by an Upper Cretaceous pelagic carbonate succession that spans the interval from upper Cenomanian to Maastrichtian. Upper Cretaceous pelagic carbonates are locally organic rich and contain common replacement chert. In Hole 967E, Maastrichtian pelagic carbonates are unconformably overlain by lithologically similar chalks of early Oligocene age, with evidence of extensive reworking of older taxa. Minor tectonic instability is indicated by the presence of syndepositional neptunian dikes and fissures. In Hole 966F, middle Eocene pelagic chalks include reworked biota, chert, and organic-rich layers. The Eratosthenes Upper Cretaceous and Paleogene bathyal carbonates accumulated on a relatively level, submerged platform, isolated from terrigenous or gravity input. The transition from a shallow, carbonate platform to a bathyal setting (Turonian or earlier), took place before submergence of carbonate platforms in the Levant (in the Coniacian). Upper Cretaceous deposition on Eratosthenes is interpreted to have taken place seawards of a zone of high biogenic productivity that affected the Levant continental margin. Eratosthenes was also located well south of the zone of ophiolite genesis and tectonic displacement in the Upper Cretaceous. Overall, the Cretaceous and Paleogene carbonates of Eratosthenes are consistent with accumulation on an initially shallow, then submerged, carbonate platform isolated within a southern branch of the Neotethyan ocean, adjacent to the North African continental margin

Mesozoic-Tertiary tectonic evolution of the easternmost Mediterranean area: integration of marine and land evidence.

This paper presents a synthesis of Holocene to Late Paleozoic marine and land evidence from the easternmost Mediterranean area, in the light of recent ODP Leg 160 drilling results from the Eratosthenes Seamount. The synthesis is founded on three key conclusions derived from marine- and land-based study over the last decade. First, the North African and Levant coastal and offshore areas represent a Mesozoic rifted continental margin of Triassic age, with the Levantine Basin being underlain by oceanic crust. Second, Mesozoic ophiolites and related continental margin units in southern Turkey and Cyprus represent tectonically emplaced remnants of a southerly Neotethyan oceanic basin and are not far-travelled units derived from a single Neotethys far to the north. Third, the present boundary of the African and Eurasian plates runs approximately east-west across the easternmost Mediterranean and is located between Cyprus and the Eratosthenes Seamount. The marine and land geology of the easternmost Mediterranean is discussed utilizing four north-south segments, followed by presentation of a plate tectonic reconstruction for the Late Permian to Holocene time

Significance of lower Pliocene mass-flow deposits for the timing and process of collision of the Eratosthenes Seamount with the Cyprus active margin.

On the crestal area of the Eratosthenes Seamount at Site 966 an important “chaotic” interval composed of clast-rich, matrixsupported sediments (here named the Mass-Flow Unit) was recovered in five boreholes, situated up to 70 m apart. These sediments overlie shallow-water limestones of Miocene age and are, in turn, overlain by deep-water nannofossil ooze and sapropels of early Pliocene-Pleistocene age. Nannofossils and planktonic foraminifers indicate an early Pliocene age for the matrix, and a late Miocene to early Pliocene age for clasts within the Mass-Flow Unit. Clasts of shallow-water limestone and nannofossil chalk are both present. The matrix is mainly nannofossil ooze admixed with silt-sized reworked carbonate grains, minor quartz, and terrigenous clay. Whole-rock X-ray diffraction reveals variable quantities of calcite, dolomite, and aragonite, together with minor quartz and pyrite. Fibrous carbonate is seen in several thin sections. Limestone clasts have undergone extensive dissolution, followed by variable meteoric water cementation, presumably during Messinian emergence. Comparable Miocene-Pliocene settings onshore in Cyprus are the following: (1) formation of lower Pliocene carbonate debris flows, similar to those at Site 966, related to extensional faulting; (2) Messinian erosion, karstification, and talus formation on the flanks of a graben undergoing active crustal extension during the late Miocene; (3) formation of deep channel and related debris flows of late Pliocene age. Of these, the first and second show similarities with the Eratosthenes Mass-Flow Unit. The Florence Rise also shows some similarities. A depositional-tectonic model is proposed for the Site 966 Mass-Flow Unit, in which the Miocene limestone of Eratosthenes Seamount was subaerially exposed and diagenetically altered during the Messinian salinity crisis. This was followed by marine transgression and accumulation of lower Pliocene nannofossil ooze. Extensional faulting was active during the early Pliocene (and possibly earlier), resulting in subaqueous mass wasting of Miocene limestones and large-scale gravity reworking of nannofossil oozes as multiple debris flows. Tilting continued during emplacement of debris flows, resulting in interstratal shearing, slumping, and minor high-angle faulting. Formation of the Mass-Flow Unit is interpreted to relate to the initial stages of collision of the Eratosthenes Seamount with the Cyprus active margin to the north. In this interpretation, the Eratosthenes Seamount was flexurally loaded by the advancing plate and underwent initial block faulting, followed by collapse and subsidence

Late Miocene paleoenvironments and tectonic setting of the southern margin of Cyprus and the Eratosthenes Seamount

During drilling of Leg 160 in the Eastern Mediterranean (April-May, 1995), Messinian (i.e., uppermost Miocene) facies were identified at a site at the base of the Cyprus slope (Site 968) and at two sites on the Eratosthenes Seamount (Sites 965 and 967). The new results can be compared with the recovery of Messinian evaporites from the Florence Rise west of Cyprus (Deep Sea Drilling Project Sites 375 and 376), with onshore southern Cyprus, and with other Mediterranean basins. The Messinian at Site 968 is dominated by dark, anoxic muds and minor turbiditic silts and sands that contain grains of pelagic limestone, chert, and ophiolitic rocks, all derived from onshore southern Cyprus. Minor intercalations of fine- to rarely coarse-grained gypsum show evidence of gravity reworking. At Site 967, on the lower southern slopes of the Eratosthenes Seamount, the existence of a thin (<5 m) interval of gypsum was inferred from both geophysical logging and pore-water geochemical studies. Postcruise studies have led to the recognition of an important Messinian/Pliocene boundary interval in Hole 967A, with accumulation of brackish water, Lago Mare-type sediments containing ostracods. A thin unit (approximately 6 m) of Messinian paleosols and caliche was recovered at Site 955 on the upper slopes of the seamount. On the crestal area of the seamount at Site 966, Messinian is absent, and lower Pliocene sediment rests unconformably on diagenetically altered Miocene shallow-water limestone. A terrigenous-dominated succession at Site 968 at the base of the Cyprus slope resembles the upper Messinian interval cored on the Florence Rise west of Cyprus (Sites 375 and 376). Both areas lie on the trend of the Cyprus active margin that accommodates convergence of the Eurasian and African Plates. The Eratosthenes Seamount was already a raised feature in the Miocene, above the level of Messinian evaporite precipitation. The northern upper slope area (Site 965) and the seamount plateau area then formed part of a laterally extensive carbonate platform, followed by breakup and subsidence in Pliocene-Pleistocene time. However, the northern lower slope area (Site 967) lay beyond the area of shallow-water carbonate deposition in the Miocene and continued to accumulate pelagic carbonates, as recorded by Eocene, Oligocene, and Miocene planktonic biota that were reworked within chalky debris flows before the Messinian. Thin Messinian gypsum (<5 m) then accumulated, possibly under fault control, followed by marine transgression, with accumulation of laminated ooze containing ferruginous oxide. Overall, the late Miocene-early Pliocene paleoenvironments document the subduction and initial states of breakup of the Eratosthenes Seamount as it began to collide with Cyprus active margin to the north

Miocene shallow-water carbonates on the Eratosthenes Seamount, easternmost Mediterranean Sea

Miocene shallow-water limestones of the Eratosthenes Seamount add considerably to the picture of widespread and heterogeneous Mediterranean Miocene reef development. Shallow-water limestones were cored at two sites on the Eratosthenes Seamount during Ocean Drilling Program Leg 160, one on the plateau area and one on the upper northern slopes. The limestones at Site 966 are dated as Miocene by use of benthic foraminifers, whereas those at Site 965, although lacking diagnostic fossils, are inferred to be of late Miocene age from the evidence of preliminary strontium isotopic dating. At Site 966, shallow-water limestones are underlain by upper Eocene bathyal pelagic carbonates and overlain by a mass-flow unit of early Pliocene age; by contrast, at Site 965, paleosols, of assumed Messinian age, overlie the Miocene limestones. The limestones at both sites are mainly composed of calcareous red algae (often as rhodoliths), coral (e.g., Porites), large benthic foraminifers, bivalves, echinoderm plates, and minor sponge spicules. The frame-building material is mainly reworked by gravity (where locally coarse) and by ocean currents (where finer grained). Sediment at Site 965 is relatively coarse, which suggests a proximal reef setting. Planktonic foraminifers are common, indicating proximity to an open-marine setting. By contrast, bioclastic material at Site 966 is mainly relatively fine grained and accumulated in a lagoonal setting, characterized by lime-mud, with some in situ microbialmat development. Carbonates at both sites underwent a similar diagenetic history. Early void-filling cement included fibrous, acicular cement, of marine origin. Minor aragonite is preserved locally, but primary carbonate is recrystallized to low-magnesian calcite. The development of extensive dissolution porosity and calcite cement are attributed to flushing by meteoric waters during the Messinian, a period of emergence of the Eratosthenes Seamount. Common dolomite possibly formed in a mixing zone-related setting associated with marine transgression in the early Pliocene. Minor opal and microcrystalline chert may owe its origin to dissolution of sponge spicules that are still locally preserved. Comparisons with other Miocene Mediterranean reef limestones indicate many similarities with lower Miocene reefs in southeastern Cyprus; the latter developed as scattered patch reefs on a flat, relatively tectonically stable area. There are also marked similarities with the upper Miocene reefs of the Pelagian Block in the Central Mediterranean that were isolated from terrigenous input by surrounding deep-water basins. Alternatively, the lower Miocene Eratosthenes reefs possibly formed an atoll-like structure, with coral-calcareous algal growths around the periphery, and lime mud accumulation within an internal lagoon, similar to many modern atolls. Shallow-water carbonate deposition was initiated after the Paleogene, following about 1 km of tectonic uplift, and was terminated by the late Miocene salinity crisis

Testing alternative tectonic models for the Permian-Pleistocene tectonic development of the Kyrenia Range, N Cyprus: Implications for E Mediterranean Tethyan palaeogeography

Three published alternative tectonic models of the Permian-Pleistocene development of the Kyrenia Range, N Cyprus are tested, supported by new field, geochemical and micropalaeontological evidence: 1. The Kyrenia Range represents the northern continental margin of the S Neotethys, close to its present relative position. The range initiated as a Permian-Cretaceous rift/passive margin, switching to a N-facing active margin during Late Cretaceous-Neogene; 2. The Range was located along the N African continental margin until the Neogene when northward subduction transferred it to the southern margin of the Eurasian plate; 3. The Range is a far-travelled allochthon that was emplaced to near its present position, probably during the Eocene.In the light of regional comparisons, especially with southern Turkey, the combined evidence mainly supports tectonic model 1. Sedimentary and palaeontological data show that the restored stratigraphy of the Kyrenia Range indicates Late Permian initial rifting and Early-Middle Triassic advanced rifting, followed by Jurassic-Early Cretaceous passive margin subsidence. Small exposures of ophiolite-related melange located between the Mesozoic carbonate platform and the overlying latest Cretaceous-Palaeogene deep-water volcanic-sedimentary succession include evidence of HP/LT metamorphism, pointing to Late Cretaceous subduction. MORB/boninites, diabase-gabbro and extensive harzburgitic serpentinite originated as a SSZ ophiolite, together with a possible high-grade metamorphic sole (garnet amphibolite) and an accretionary prism (E-MORB/OIB; metachert). Microfossil evidence indicates exhumation of the melange and the underlying platform prior to Late Maastrichtian. A mass-transport complex formed within a compression-related foredeep during the Middle Eocene. Associated southward thrusting and folding culminated in emergence and subaerial erosion, generating a major unconformity, that was followed by subaerial and then marine deltaic deposits (Late Eocene-Oligocene). Following major Late Miocene southward thrusting, uplift of the Kyrenia Range took place during the Pleistocene, related to collision of the leading edge of the North African plate (Eratosthenes Seamount) with the Eurasian (Anatolian) plate

Late Palaeozoic extensional volcanism along the northern margin of Gondwana in southern Turkey: implications for Palaeotethyan development

The Late Palaeozoic-Early Mesozoic Tethyan development of the Eastern Mediterranean region remains debatable, especially in Turkey, where alternative northward and southward subduction hypotheses are proposed. Relevant to this debate, new whole-rock geochemical data are provided here for early Carboniferous (Late Tournaisian-Late Visean; c. 340-350 Ma) tuffaceous sedimentary rocks within the cataloturan thrust sheet (Aladag nappe), eastern Taurides. The tuffs accumulated from evolved alkaline volcanism, variably mixed with terrigenous and radiolarian-rich sediments. In addition, Late Palaeozoic meta-volcanic rocks, c. 150 km farther NE, within the Binboga (= Malatya) metamorphics (a low-grade high-pressure unit), are indicative of a within-plate setting. An impersistent geochemical subduction signature in these volcanics may represent an inherited, rather than contemporaneous, subduction influence, mainly because of the absence of a continental margin arc or of arc-derived tuff. Both the Binboga metamorphics and the cataloturan thrust sheet (Aladag nappe) restore generally to the north of the relatively autochthonous Tauride carbonate platform (Geyik Dag), within the carbonate platform bordering north-Gondwana. The cataloturan thrust sheet is interpreted, specifically, as a c. E-W, deep-water, volcanically active rift that progressively infilled. Regional geological evidence suggests that melange units (Konya Complex, Afyon zone), Teke Dere unit, Lycian nappes), and Chios-Karaburun melange, E Aegean) accreted to the north-Gondwana continental margin during the late Carboniferous; this was coupled with localised calc-alkaline granitic magmatism (Afyon zone of Anatolide crustal block). We propose an interpretation in which Late Devonian-Carboniferous alkaline intra-plate volcanism relates to extension/rifting along the north-Gondwana margin. In contrast, the melange accretion and granitic magmatism could relate to short-lived late Carboniferous southward subduction that accompanied the diachronous closure of Palaeotethys

The Beysehir-Hoyran-Hadim Nappes: genesis and emplacement of Mesozoic marginal and oceanic units of the northern Neotethys in southern Turkey

The Beysehir-Hoyran-Hadim Nappes crop out over 700 km from NW to SE. Above a regionally autochthonous Tauride carbonate platform the Beysehir-Hoyran Nappes begin with a thrust sheet (c. 400 m) of mainly redeposited carbonates, quartzose sandstones and mudstones of Mid-Late Triassic age, interpreted as a proximal slope-base-of-slope succession. Above is a thrust sheet (c. 1 km) of Middle-Upper Triassic intermediate-acidic extrusive rocks, volcaniclastic rocks and minor pelagic carbonates, interpreted as a continental rift. Thin (,100 m) Upper Triassic-Upper Cretaceous pelagic carbonate and radiolarian chert lie depositionally above. The uppermost thrust sheet comprises broken formation and melange, including Jurassic shallow-water carbonate, radiolarian chert and Upper Cretaceous pelagic limestone. Zones of tectonic- sedimentary melange separate higher units. The Beysehir-Hoyran Nappes document Triassic rifting and Jurassic-Cretaceous passive margin subsidence bordering the Northern Neotethys. A harzburgitic ophiolite probably formed above a north-dipping subduction zone within the ocean basin. The ophiolite was emplaced southwards onto the northern margin of the Tauride platform in latest Cretaceous time. The nappe pile and underlying platform (Hadim Nappe) were thrust further south in Late Eocene time. Assuming in-sequence thrusting, the Beysehir-Hoyran Nappes restore to a location north of a Neotethyan spreading axis. More probably, they originated near the south margin of the Northern Neotethys, but reached their position by outof- sequence thrusting. Formation within a southerly strand of the Northern Neotethys (Inner Tauride ocean) is more probable than within the main Northern Neotethys further north