Eratosthenes Seamount: an oceanographic yardstick recording the Late Mesozoic-Tertiary geological history of the Eastern Mediterranean.
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Date
1998Author
Robertson, Alastair H F
Mart, Yossi
Metadata
Abstract
Three boreholes were drilled on the northern slope of the Eratosthenes Seamount during Leg 160. Lithological data were
obtained back to the Early Cretaceous. Lithological correlation of shallow-marine sedimentary rocks reveals similarities in the
Lower Cretaceous lithological successions of the Eratosthenes Seamount with the southern Levant passive margin. Bathyal
chalks of Coniacian-Maastrichtian to middle Eocene age recovered from the Eratosthenes Seamount at Site 967 are also comparable
with similar sedimentary units in the Levant. Both the southern margin of the Levant basin and the Eratosthenes Seamount
subsided to bathyal depths during Late Cretaceous-Paleogene time. These correlated successions differ from
contemporaneous units in southern Cyprus that are dominated by the Upper Cretaceous Troodos ophiolite and its deep-sea sedimentary
cover. The presence of shallow-marine limestones of Miocene age on the Eratosthenes Seamount indicates uplift
before, or during, the Miocene, whereas the overlying Pliocene-Pleistocene successions comprise unlithified hemipelagic sediments
that accumulated in deeper water following tectonic subsidence. Previously obtained geophysical data suggest that the
Eratosthenes Seamount has variable crustal characteristics. Seismic refraction data reveal an intermediate crustal layer of seismic
velocity of 6.1-6.3 km/s beneath the seamount, which also extends under Cyprus, but then wedges out southward under the
Levant basin. A large magnetic anomaly that underlies the seamount and its perimeter was previously correlated with the Troodos
ophiolite. However, seismic reflection profiles reveal the existence of an important northward-dipping thrust fault separating
Cyprus from the Eratosthenes Seamount. Taken together, the geophysical and geological evidence indicate that the tectonic
evolution of the Eratosthenes Seamount is linked to that of the North African continental margin from early Mesozoic time
onward. The seamount was in a shallow-marine depositional setting in the Early Cretaceous, then subsided to bathyal depths in
the Late Cretaceous. It was later uplifted, as indicated by the Miocene shallow-marine limestones recovered from Sites 965 and
966. Then, during Pliocene-Pleistocene time, the Eratosthenes Seamount was thrust beneath Cyprus because of collision of the
African and the Eurasian plates.