Deep-water basins within the Mesozoic carbonate platform of Argolis, Greece

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In the past the classic Argolis area of the central southern Hellenides was interpreted as comprised of essentially in situ carbonate platforms and basins, or, alternatively of far-travelled thrust sheets derived from a Mesozoic ocean basin sited well to the east (Vardar ocean). Our fieldwork, however, demonstrates that at two key localities an important unit of Middle Triassic-Early Jurassic deep-water redeposited carbonates (Asklipion Unit) passes laterally into shallow-water platform carbonates (Pantakrator Unit). The deep-water limestones represent basins within the platform, rather than far-travelled thrust sheets, while other slices of deep-water limestone record a platform margin, further east. The basins originated during Middle Triassic (Ladinian) rifting of the Neotethys and are floored by extrusive rocks of intermediate composition. Highly condensed Ammonitico Rosso pelagic limestones accumulated on an inferred volcanic seamount during the Mid-Late Triassic (Anisian-Carnian). The platforms slowly subsided in Early Jurassic time, while the basins partly filled with redeposited carbonates (Adhami Limestone). Shallow-water carbonates locally transgressed the margins of the deeper-water basins. The platforms were submerged in the Mid-Jurassic (Toarcian- Bathonian), with the deposition of pink pelagic Ammonitico Rosso, followed by marked subsidence and ribbon radiolarite deposition below the carbonate compensation depth (e.g. Koliaki Chert). In early Late Jurassic time (Kimmeridgian), the area was regionally compressed ('Eohellenic' phase), and the intraplatform basins, founded on thinned continental crust were inverted, and thrust up to several kilometres over the adjacent platform units. The deformed continental margin then flexurally subsided, ahead of emplacing Jurassic ophiolites, largely olistostromes (Migdhalitsa Unit). After taking account of up to 90 degrees clockwise palaeorotation of assumed Neotectonic age, kinematic indicators and facies trends suggest the ophiolite was derived from a Pindos ocean basin originally sited to the west. Early Cretaceous transgression resulted in the deposition of shallow-water limestone and was followed by Late Cretaceous deep-water limestone, then terrigenous flysch accumulation in a foreland basin related to final suturing of the Neotethyan ocean. Later, the area was dissected by a series of mainly E-W trending, high-angle Neotectonic normal faults, related to the Aegean back-arc extensional system.

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Journal of the Geological Society

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