Interaction between accretionary thrust faulting and slope sedimentation at the frontal Makran accretionary prism and its implications for hydrocarbon fluid seepage

Abstract

[1] Using high-resolution seismic profiles and other geophysical data, collected during R/V Meteor Cruise M74/2, we investigate the distribution patterns of shallow sediments, their structure and deformation processes, and their role in the migration, accumulation and seepage of hydrocarbon-rich fluids. Here, we show that rapid syn-kinematic sedimentation at the frontal Makran accretionary prism provides a mechanism by which emerging imbricated thrust packets override the footwall at the seafloor without significant masswasting and destruction of fault-related anticline in the hanging wall. These anticlines may rise high above the seafloor to form plate-boundary-parallel ridges, and distinguish from simple thrust blocks seen at convergent margins elsewhere. With the fast burial of many thrust faults by the syn-kinematic sediments, anticlinal growth structures form in these synkinematic sediments by continuous thrust activity. The anticlinal structures preserved within the cores of the ridges or formed from these syn-kinematic sediments act as structural traps for migrating hydrocarbon-rich fluids, above which fluid escape structures are generated leading to seafloor seeps. Most of the discovered hydrocarbon seeps around Sixth Ridge are sourced from these traps. Despite the compressional environment and the rapid syn-kinematic sedimentation rates, shallow subsurface of the frontal Makran is a normally pressured regime, in which the buoyancy of hydrocarbons may account for the fluid migration. In this important respect, the Makran accretionary prism differs from many other convergent margins and accretionary prisms, where fluid flow is largely driven by tectonically induced overpressure.Citation: Ding, F., V. Spiess, N. Fekete, B. Murton, M. Brüning, and G. Bohrmann (2010), Interaction between accretionary thrust faulting and slope sedimentation at the frontal Makran accretionary prism and its implications for hydrocarbon fluid seepage,

Formation of seep carbonates along the Makran convergent margin, northern Arabian Sea and a molecular and isotopic approach to constrain the carbon isotopic composition of parent methane

“…The uppermost subducted sediments form abundant anticlinal hinges where shallow gas accumulates and migrates along normal faults to seep at the seafloor (Ding et al, 2010;Römer et al, 2012;Smith et al, 2014). Seismic studies revealed a bottom simulating A C C E P T E D M A N U S C R I P T…”

Interaction between hydrocarbon seepage, chemosynthetic communities, and bottom water redox at cold seeps of the Makran accretionary prism: insights from habitat-specific pore water sampling and modeling

“…At the Makran subduction zone, oceanic crust of the Arabian plate and the Omara micro-plate dips northward underneath the Eurasian plate to form the Makran accretionary prism. The deformation front of the Makran prism is located south of the first accretionary ridge at about 3000 m water depth and strikes West to East, parallel to the coastline of Pakistan (Kukowski et al, 2000(Kukowski et al, , 2001Ding et al, 2010). Convergence rates range from 36.5-42 mm yr −1 (Kukowski et al, 2001).…”

“…Kukowski et al (2001) pointed out that sediments above the décollement are being accreted by imbricate thrusting, forming well defined coast-parallel accretionary ridges. This N-S cascade of accretionary ridges was mapped in 1997 ( Kukowski et al, 2000) and a distinct bottom simulating seismic reflector indicative for the phase boundary between free gas below and solid gas hydrates above has been described for the area (Kaul et al, 2000;von Rad et al, 2000;Ding et al, 2010).…”

The effect of meter-scale lateral oxygen gradients at the sediment-water interface on selected organic matter based alteration, productivity and temperature proxies

“…The Makran accretionary prism contains numerous cold seeps, which are areas of fluid and gas emissions from the sea floor (von Rad et al, 1995(von Rad et al, , 1996. R/V Meteor cruise M74/2-3, during which the samples used in this study were retrieved, was an interdisciplinary cruise specifically scheduled to explore the Makran continental margin for further fluid escape structures (Bohrmann et al, 2008) driven by tectonically induced overpressure (Ding et al, 2010). Coupled to the upward gas migration at seep sites are chemosynthetic communities that rely on the supply of reduced compounds such as hydrogen sulfide and methane (Suess et al, 1985).…”