Original paper

Late Triassic carbonate breccias and boulders from the Sub-Pelagonian Platform in Attica, Greece: constraints on the platform evolution

Kati, Marianna; Magganas, Andreas; Zambetakis-Lekkas, Alexandra; Logotheti, Vasilia

Abstract

The study of carbonate breccias and loose boulders from two horizons in the Late Triassic succession of the Sub-Pelagonian platform, in southwestern Attica (Mount Aigaleo), reveals two “source” areas for the clasts. The massive breccias are entirely composed of resedimented carbonates derived from the inner parts (peritidal) and reefal margin of the platform, represented by the coeval, Dachstein-type shallow-water facies of the “Pantokrator Limestones”. Their textural characteristics accompanied by the presence of polyphase fractures and sedimentary dykes imply little transportation of the clasts and deposition mostly through submarine rockfalls, related to syndepositional tectonic activity. In contrast, the accumulated boulders comprise mainly olistholiths originating from a carbonate-producing system dominated by mud mound-type deposits. Most of the boulder clasts are represented by microbial boundstones (automicrite facies) and abundant early marine cements, lacking a rigid framework built by skeletal metazoans. The remaining lithotypes represent detrital carbonates, intensively fractured open-platform carbonates and polymictic breccias comprising submarine polygenic mass-flow carbonate slope deposits. All boulder lithotypes apparently record different parts of a platform-to-slope transition within an intrashelf depression activated along the western margin of the Pelagonian Platform during the Late Triassic. The development of the two contemporaneous carbonate factories was mainly tectonically-controlled and was most probably initiated during the Permo-Triassic rifting stage of the Hellenides.

Keywords

intraplatform depressionautomicrite faciescarbonate slope depositshellenidessynsedimentary tectonics