Quaternary sedimentation on the Makran margin: turbidity current–hemipelagic interaction in an active slope-apron system
Published:January 01, 2002
Dorrik A. V. Stow, Ali R. Tabrez, Marteen A. Prins, 2002. "Quaternary sedimentation on the Makran margin: turbidity current–hemipelagic interaction in an active slope-apron system", The Tectonic and Climatic Evolution of the Arabian Sea Region, P. D. Clift, D. Kroon, C. Gaedicke, J. Craig
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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.
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The Tectonic and Climatic Evolution of the Arabian Sea Region
Over long periods of time the tectonic evolution of the solid Earth has been recognized as the major control on the development of the global climate system. Tectonic activity acts in one of two different ways to influence regional and global climate: (i) through the opening and closing of oceanic gateways and its effect on the circulation patterns in the global ocean; (ii) through the growth and erosion of orogenic belts, resulting in changes in oceanic chemistry and disruption of atmospheric circulation. The Arabian Sea region has several features that make it the best area for studies of climate and palaeoceanographic responses to tectonic activity, most notably in the context of the South Asian monsoon and its relationship to the growth of high topography in the adjacent Himalayas and Tibet.
The Tectonic and Climatic Evolution of the Arabian Sea Region brings together a collection of recent studies on the area from a wide group of international contributors. The paper range from high resolution, Holocene palaeoceanographic studies of the Pakistan margin to regional tectonic reconstructions of the ocean basin and surrounding margins throughout the Cenozoic. Marine geophysics, stratigraphy, isotope chemistry and neotectonics come together in a multidisciplinary approach to the study of interactions of land and sea. while much work remains to be done to understand fully the tectonic and climatic evolution of the Arabian Sea, a great deal has been achieved since the last major review, as detailed in the 26 contributions. This volume is essential reading for palaeoceanographers, sedimentologists and geophysicists. It will also be interest to structural geologists and those working in the petroleum industry.