Correlation of fluvial terraces and temporal steady-state incision on the onshore Makran accretionary wedge in southeastern Iran: Insight from channel profiles and 10Be exposure dating of strath terraces

Abstract

We describe and summarize the geomorphology of fluvial terraces along the four major rivers draining the central, onshore Makran accretionary wedge in Iran, and describe uplifted marine terraces on the coast of this region. Thirty-five strath terraces at different sites were dated using in situ–produced cosmogenic 10 Be concentrations from surfaces and depth profiles. These new measurements reveal abandonment ages between ca. 15 and 380 ka. The age distribution allows determining the chronology of terrace levels and establishing regional correlations between two major regional levels. The geographically widespread correspondence suggests that these two levels result from a regional, climatically driven force. Systematic dating also provides evidence for time and spatial variations in incision rate, which enables distinguishing between a regionally uniform incision rate of 0.3–0.4 mm/a and higher local incision and/or uplift (~0.8 mm/a) rates. These spatial changes are consistent with where localized tectonic activity is recognized in the field. We also dated, using 14 C in shells, four uplifted marine terraces on the coast of the study area. Comparing incision rates derived from strath terraces (0.3 mm/a) with published uplift estimates from marine terraces (0.2 mm/a) reveals that fluvial rivers responded to a regional, long-term incision and surface uplift pattern. This rate reflects the tectonically steady state of the wedge on a regional scale. Locally high incision rates delineate active faults and folds, indicating that perfect steady state is unlikely on short length scales.