Sedimentation in Pull-Apart Basins: Active Examples in Eastern Turkey

Abstract

The Erzincan, Susehri, Niksar, and Lake Hazar basins are actively evolving pull-apart basins in eastern Turkey. Their structural, drainage, and depositional systems generally support a pull-apart basin sedimentation model based on ancient pull-apart basin deposits. This model involves marginal coarse-grained sedimentation adjacent to master faults, axial fine-grained sedimentation away from master faults, and high sedimentation rates. However, studies of the Turkish pull-apart basins suggest the following refinements in the model. (1) Detailed sedimentary facies patterns and the dominant facies of a pull-apart basin vary according to basin shape, climate, drainage character, and volcanic activity. Depositional environments near fault-bounded margins include alluvial fan, fan delta, and alluvial apron. Depositional environments in central areas away from fault-bounded margins include active braid plain, inactive braid plain, meander plain, salt playa, marsh, lacustrine, mouth-bar delta, and volcanic. (2) If internally drained, a pull-apart basin is likely to contain axial and transverse drainages. If externally drained, the drainage pattern varies and may exit the basin axially or transversely. (3) Pull-apart basin shapes are not necessarily rhomboidal. Comparison of data from the Turkish pull-aparts with other modern and ancient pull-apart basins suggests that sediment thickness (y) is related to length of a pull-apart basin parallel to master fault overlap (x) by the equation y = .08x + .26. This relationship predicts sediment thickness in the Erzincan, Susehri, Niksar, and Lake Hazar pull-apart basins is 2.9, 2.1, 1.5, and 0.68 km, respectively.