Miocene basin evolution of the Isparta Angle, southern Turkey

Abstract

The study of basins developed on top of older suture zones is demonstrably important in the Tethyan region where rifting and convergence have occurred repeatedly from the Mesozoic to the present-day. In southern Turkey, three Miocene basins developed in the Isparta Angle suture zone. Two of these, the Aksu and Köprü basins, are orientated north-south, parallel to pre-Miocene lineaments in the basement (e. g. Antalya Complex). These basins are underlain by a mosaic of deformed Mesozoic carbonate platforms, deep-sea sediments and ophiolitic units. The Manavgat basin, to the east, overlies Permian meta-carbonates (Alanya Massif) deformed by NW-SE trending basement structures. The northern margin of the Manavgat basin, in the south-east of the area, is also orientated NW-SE, but it was open to the Mediterranean Sea to the south.

Prior to Burdigalian-Langhian transgression, a thick (-1.5km) succession of predominantly continental conglomerates and sandstones accumulated in the south of the Aksu and Köprü basins (Kizildag Formation). Coeval thrusting of the Lycian Nappes on the western limb of the Isparta angle is inferred to have induced block faulting of the foreland, exploiting pre-existing basement weaknesses and generating accommodation space.

In the Manavgat basin palaeocurrents and south-to-north diachroneity of transgression demonstrate that the Alanya Massif formed a palaeogeographic high to the north of the basin. This was colonised by coral and algal fringing reefs, which shed abundant shallow-water debris, deposited as calcarenites in Langhian times (Oymapinar Limestone). Elsewhere, to the south and west, Late Burdigalian-Langhian patch reefs developed within coastal fan-delta conglomeratic sequences. Detailed study of the interaction between coral growth and clastic influx reveals that relative sea level rise outstripped sediment influx at this time.

Extensional faulting during the Langhian in the Manavgat basin generated numerous micro-faults which trend parallel to NW-SE basement lineaments. This faulting led to the deposition of localised talus (Cakallar Formation) and formation of an asymmetrical horst-graben structure. Reef deposition was abruptly terminated and 3-500m of Serravallian planktic foraminiferal marls (Geceleme Formation) then accumulated as post-rift fill. In the Aksu and Köprü basins, a correlative transition from shallow-water carbonates to deeper-water turbidite deposition (Karpuzcay Formation) is observed. Palaeocurrents from the Koprii basin suggest that N-S striking lineaments in the basement funnelled sediment southwards in the north of the basin, but had little topographic expression in the south.

In the Early Tortonian, the Geceleme Formation in the Manavgat basin passed rapidly up into slumped siltstones, sandstones and coarse conglomerates, containing large (~10m) detached blocks of Alanya Massif metacarbonate. Debris-flow processes dominated the deposition of this succession (Karpuzçay Formation) and together with foraminiferal studies, document uplift and infill of the basin during Tortonian-Messinian times. In the north of the Aksu and Koprii basins, uplift caused a transition from Karpuzçay turbidites to shallow-marine fan-delta conglomerates with rare patch reefs.

At the end of the Miocene, a compressional event caused the reactivation of the NS striking lineaments in the Isparta Angle and small-scale inversion of the horst-graben structure in the Manavgat basin. East- and west-vergent faults and large -scale recumbent folds deformed Miocene and basement rocks. Compressional forces, oblique or orthogonal to the N-S fabric of the Isparta Angle, could have been generated both by movement of the Lycian Nappes to the north-west and westward escape of the Anatolian block. On a more regional scale, the Isparta Angle basins appear to be part of a transtensional system which linked the Aegean arc to the west with the Cyprus arc to the east.