Wetland deposits in Lower Zayandeh Rud plain – Sedimentary features and chronostratigraphical context

Downstream of the City of Isfahan, the Zayandeh Rud passes extensive alluvial plains bordered by large piedmonts, a large sand dune field, and several, partly salt-crusted playas. Little information is available on the nature and chronostratigraphy of the superficial deposits of these landforms. As described in the literature, black sediment layers occur in Seghzi Playa and in the plain of Varzaneh, possibly representing wetland deposits and/or paleosols. In both cases, these layers would indicate sediment deposition/soil formation under a more humid climate than the modern-day arid one. In addition, the recent archaeological surveys in the area have identified a large number of Bronze Age sites dating to the ۳rd millennium BCE and not located directly near the river, raising questions about how settlers managed access to water and if past occupation took place under more favorable paleoenvironmental conditions. We investigate several exposures and sediment cores with sequences of black layers and sandwiching eolian, alluvial, and fluvial deposits encountered in close vicinity of Bronze Age settlements. Sedimentary properties, including texture, organic carbon content, and major and trace element composition, indicate formation of black layers in a wetland environment. Radiocarbon and luminescence dating provide evidence for three phases of wetland formation, namely the Lateglacial, the Early Middle Holocene, and the transition from Middle to Late Holocene. Although the latter of these phases shows temporal overlap with Bronze Age occupations, more information on the extent and nature of the paleowetlands is needed to characterize paleoenvironmental conditions during times of past human occupation.

کلیدواژه ها:

Wetland deposits ، radiocarbon and luminescence dating ، paleoclimate ، Iranian Highlands