A tectonic pulse in the Makran accretionary prism recorded in Iranian coastal sediments

Abstract

Many recent studies of syndeformational sediments in a wide range of tectonic environments have improved our understanding of the development of individual or regional deformation structures. Here, we report studies of growth strata that imply an unexpected tectonic history within part of the Makran accretionary prism, currently the largest on Earth. We interpret the lithostratigraphy and ichnofacies of Plio-Pleistocene marine deposits logged along part of the Makran coast in terms of their palaeoenvironments. Lateral trends in thickness and depositional facies of rock units (and erosional surfaces among them) are correlated and then related to displacements along syndepositional faults that are distinguishable from changes in global sea level. Past studies of accretionary prisms have emphasized thrusting at the deformation front offshore. However, at the shoreline we find episodes of deposition during subsidence, as a result of oblique-slip normal faulting, alternating with episodes of erosion during uplift, driven by oblique-slip thrusting. The absolute timing of these displacements is not yet known. However, faults above a deep zone of subcretion (or underplating), well behind the surficial deformation front, have clearly undergone episodic reversals in throw that imply alternations in lateral shortening and extension.