Turbidity currents and their deposits can be investigated using several methods, i.e. direct monitoring, physical and numerical modelling, sediment cores and outcrops. The present study focuses on thin clayey sand turbidites found in Lake Hazar (Turkey) occurring in eleven clusters of closely spaced thin beds. Depositional processes and sources for three of those eleven clusters are studied at three coring sites. Bathymetrical data and seismic reflection profiles are used to understand the specific geomorphology of each site. X-ray, thin sections and CT-scans imagery combined with grain-size, geochemical and mineralogical measurements on the cores allow characterisation of the turbidites. Turbidites included in each cluster were produced by remobilization of surficial slope sediment, a process identified in very few studies worldwide. Three types of turbidites are distinguished and compared with deposits obtained in flume studies published in the literature. Type 1 is made of an ungraded clayey silt layer issued from a cohesive flow. Type 2 is composed of a partially graded clayey sand layer overlain by a mud cap, attributed to a transitional flow. Type 3 corresponds to a graded clayey sand layer overlain by a mud cap issued from a turbulence-dominated flow. While the published experimental studies show that turbulence is damped by cohesion for low clay content, type 3 deposits of this study show evidence for a turbulence dominated mechanism despite their high clay content. This divergence may in part relate to input variables such as water chemistry and clay mineralogy that are not routinely considered in experimental studies. Furthermore, the large sedimentological variety observed in the turbidites from one coring site to another is related to the evolution of a sediment flow within a field scale basin made of a complex physiography that cannot be tackled by flume experiments.
Bibliographical noteKAUST Repository Item: Exported on 2020-10-01
Acknowledgements: This research was funded by the European Commission Marie Curie Excellence Grant Project “Understanding the irregularity of seismic cycles: A case study in Turkey” (MEXT- CT-2005-025617: Seismic Cycles), hosted by the Seismology Section of the Royal Observatory of Belgium. Coring was carried out in collaboration with Istanbul Technical University, Eastern Mediterranean Centre for Oceanography and Limnology (ITU-EMCOL). The authors thank X. Boes, E. Damcı, D. Acar and C. Somuncuoğlu for their efforts during the coring mission. Many thanks to Nathalie Fagel (Dept. of Geology, Université de Liège) for core storage and XRD measurements. The authors are grateful to Philippe Martinez (Université de Bordeaux), Anne-Lise Develle and Christian Beck (EDYTEM, Université Savoie Mont Blanc) regarding XRF core scanning. Many thanks to Joshua Griffiths (University of Liverpool) for fruitful discussions on clay minerals. Associate Editor Jaco Baas and two anonymous reviewers are gratefully acknowledged for their reviews and valuable comments made on earlier versions of this paper. We particularly thank reviewer Michael Clare for his thorough reviews which substantially improved the manuscript.