Palaeoenvironmental changes in the Khuran Estuary of SE coastal Iran during the last two millennia, based on the analysis of a sediment core

Abstract

Late Holocene palaeoenvironments of the northern Strait of Hormoz and the palaeohydrology of the SE Zagros were reconstructed using multi-proxy analysis (e.g. magnetic susceptibility (MS), grain size analysis, total organic matter %, CaCO3%, C/N ratio, and foraminiferal assemblage) of a radiocarbon-dated sediment core (KHU) from the Khuran Estuary. High sedimentation rate (1.23 cm yr−1) and elevated grain size, MS, C/N ratio, as well as the abundance of porcelaneous foraminifers (Quinqueloculina sp.), revealed that during the first three centuries CE, sediments settled in a relatively high accommodation space with strong tidal currents and raised terrigenous sediment input from the SE Zagros. About four centuries later, the gradual disappearance of porcelaneous taxa and the dominance of agglutinated and hyaline ones, besides the increasing C/N ratio, indicated that geomorphological conditions became favourable for mangroves. MS reduction and negative correlation between MS and grain size showed that during this period the relative proportion of terrigenous particles in sediment decreased which, in turn, confirms a reduction of river discharge. Afterwards, the abundance of mud aggregates, low C/N ratio and a dramatic reduction of foraminifers showed that a < 1 m thick sediment unit representing a relatively long period (1.4 cal kyr BP onwards; sedimentation rate: 0.06 cm yr−1) was deposited within a high marsh environment being mostly above mean high water. Generally, correlations between proxy records of the core KHU with Zagros lakes and other archives from African lakes and Greenland re-inforce the reconstruction of atmospheric teleconnection between the North Atlantic and the interior of West Asia during the late Holocene.