Late Miocene paleoenvironments and tectonic setting of the southern margin of Cyprus and the Eratosthenes Seamount
Robertson, Alastair H F
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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.