Highstand vs. lowstand turbidite system growth in the Makran active margin: Imprints of high-frequency external controls on sediment delivery mechanisms to deep water systems

Late Quaternary turbidite system growth along the Makran convergent margin is investigated through a set of deep-sea cores from upper slope and piggy-back basins to deep basin plain settings. High-resolution stratigraphy in these various depositional environments permits reconstruction of the evolution of sand-to-mud ratio, sedimentation rates, frequencies, and thickness of turbidite deposits during the last 25 ka BP. This study demonstrates how tectonics, climate and eustasy can interplay at high resolution (<20 ka) and control the input of terrigeneous sediment along the tectonically active Makran convergent margin, in a source-to-sink perspective. The Makran turbidite system growth has been continuous throughout sea-level lowstand, transgressive, and highstand conditions. However, the frequency, rates, and nature of sediment supply varied in response to climate, sea-level, and tectonically induced changes in source-to-sink sediment dispersal modes. These changes include conditions of sediment production and availability in the drainage basin, capacity of transport from fluvial systems, and rates of sediment storage on the shelf and upperslope areas. Climate in the hinterland appears as a first-order control on the properties of turbidity currents that feed the turbidite system, controlling the average sand-to-mud ratio in the deep water deposits. The onset of sea-level highstand after similar to 8 ka BP resulted in a notable change in turbidite system growth, characterized by the occurrence of large volume, thick turbidity currents (>300 m thick along the continental slope) originated from successive, multiple slide or slump-induced surges. Their related deposits have low recurrence intervals, close to those calculated from the large magnitude earthquake and tsunami record in the Makran area. Comparison with the Nile and Indus turbidite systems growth during the Late Quaternary provides an evaluation of the relative importance of shared forcing parameters (i.e. monsoon-induced phases of arid/humid conditions and post-glacial sea-level rise), in significantly different basin settings. The Indus fan appears mainly controlled by eustasy during the last 25 ka. Inversely, similarities are found between the Nile and Makran turbidite systems, where sea-level changes are modulated by the climate impact on fluvial dynamics in the hinterland. However, the Makran turbidite system growth is continuous through times, because both the uplift in the coastal area and the fluvial dynamics of short, mountainous river systems allow high sediment transfer rates to the marine basin, even though arid conditions and associated low water fluxes. Earthquake-induced highstand turbidite deposits form a thick sedimentary succession in the Oman abyssal plain, and are significant in the geologic record. This study finally illustrates how the complex interplay between external (allogenic) forcings can complicate the interpretation of high-resolution sedimentary successions in turbidite-filled basins. (C) 2010 Elsevier B.V. All rights reserved.