Alakir çay group, antalya complex, SW Turkey: A deformed mesozoic carbonate margin

Abstract

The Alakir çay Group comprises complexly deformed Mesozoic sedimentary rocks originally deposited along a passive carbonate margin. The sediments now form a tectonically imbricated stack of thrust sheets (Kumluca Zone) emplaced westwards over a relatively autochthonous carbonate platform (Bey Dağlari Zone). The Kumluca Zone is bounded tectonically to the east by mafic and ultramafic rocks with related sediments (Gödene Zone), representing oceanic crust produced during early stages of continental separation and originally forming the more distal part of the margin. Detailed mapping and structural analysis allow the thrust sheets to be pulled back to reconstruct a stretch of the carbonate margin about 10 km wide by 25 km long. Within the thrust sheets, fragmentary basal sequences of quartzose sandstones (Hatip Formation), derived from the north, were laid down during late Triassic continental rifting. Subsequent late Triassic Halobia- and radiolarian-bearing calcilutites (Bozyer Foramtion) are comparable with ‘peri-platform’ deep-water oozes found, for example, in the Bahamas. An end-Triassic hiatus involved substantial down-margin sediment redeposition. Jurassic to early Cretaceous sediments include both non-calcareous and calcareous silts laid down together with radiolarites in deep water below the carbonate compensation depth (Karabük Formation). An upward transition to Cretaceous planktonic foraminiferal chalks is seen in some more proximal sequences. Tectonic disruption of the margin began in latest Cretaceous time and ended with westward thrusting over the carbonate platform in the Miocene. Small-scale facies variation of the margin is illustrated by unstretching the thrust sheets and correlation of 33 measured logs. Particularly, the sediments become more distal across the margin away from the carbonate platform. Along-margin variation is especially evident in the thickness and composition of redeposited carbonates in the late Triassic hemipelagic rocks. Comparison with other carbonate margin sequences in the Antalya Complex and elsewher implies that the Alakir çay sediments represent deep-water outer-margin facies which lapped over adjacent oceanic crust: more proximal redeposited carbonates are not seen, perhaps due to overthrusting.