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1 Southampton Oceanography Centre, University of Southampton, Southampton SO14 3ZH, UK davs{at}soc.soton.ac.uk
2 National Institute of Oceanography, Karachi, Pakistan
3 Faculty of Earth Sciences, Vreije Universiteit, 1081 HV Amsterdam, Netherlands
The Makran slope-apron system is a stepped convergent margin across an active subduction complex. Shallow penetration piston cores have been recovered from the upper-slope region, three mid-slope basins and the abyssal plain. At most sites the upper 5–14 m of cored section is dominated by fine-grained, thin- to medium-bedded turbidites, averaging 5–10 turbidite events per metre of section. Oxygen isotope stratigraphy yields mean sedimentation rates of 50–95 cm ka–1 and a turbidite frequency of one event per 200–300 a. The upper-slope site has fewer turbidites and a greater proportion of hemipelagic mud. Fine-grained turbidite sequences are common, with top-cut-out and base-cut-out sequences most evident. Markov chain analysis of the transition between turbidite divisions confirms the normal T0–T8 order of sequence divisions. In some cases there is an upward gradation into a hemiturbidite facies. The range of turbidite bed thicknesses can be approximated by both power-law and log-normal distributions, typical of seismic triggering on an active margin, or of frequent river-flood sediment input. Small-scale vertical variations of turbidite bed thickness recognized by autocorrelation techniques can be interpreted as the result of bed-relief compensation effects (compensation cycles). The lateral distribution of both turbidites and hemipelagites is influenced by sediment focusing along pathways between slope basins. At a larger scale, climate, sea-level and tectonic effects have all played an important role in shaping margin sedimentation.
