Sedimentary and environmental characteristics of the Gilan–Mazenderan plain, northern Iran: influence of long- and short-term Caspian water level fluctuations on geomorphology

Abstract

The south-southwestern Caspian coastal lowland in Iran, or the Gilan-Mazenderan plain, is a relatively narrow but long, composite depositional area of late Quaternary age. The Sefid Rud delta, the Anzali Lake (connected to the Caspian Sea by a meandering outlet 3.5 km long) and storm-dominated beaches are its prominent sedimentary features. They are controlled by the present water level of the Caspian Sea at -26.36 m in 2000. The Late Pleistocene-Holocene deposits of the lowland, which are covered commonly by a modern loess-origin soil, mainly consist of alternations of marine and non-marine sediments. The marine units form coastal terraces at 19-20 m (I), 2-0 m (II) and -6/-8 m (III) corresponing to the Late Khvalinian and Neocaspian transgressions. The deposits of the youngest terrace (terrace III) that represents a prograding beach-ridge complex are a consequence of several medium-term, cyclic water level oscillations in Late Holocene. Just after the initiation of the beach-ridge complex, Lake Anzali formed by damming of rivers and then by progradation of the complex in time forced to form the outlet of the lake. The nearest medium-term cycle lasted c. 65 years between 1930-1995 and the records showed that it included a lot of shortterm (c. 4-5 yrs) and very short-term (week to months) water level oscillations. During the last erratic rise of sea level (1977)(1978)(1979)(1980)(1981)(1982)(1983)(1984)(1985)(1986)(1987)(1988)(1989)(1990)(1991)(1992)(1993)(1994)(1995)(1996), the area of Lake Anzali doubled; the delta and the coastal sands including modern beaches were eroded on c. 30-100 m. Overall, a step-like morphology, repetition of marine and non-marine facies and also water level records of the last 75 years indicate that the ancient and recent deposition on the coastal lowland has been controlled by long-medium-and short-term fluctuations of the Caspian Sea level.

River inflow and salinity changes in the Caspian Sea during the last 5500 years

“…However because high percentages and concentrations have been obtained in the cores, with even a slightly higher representation in the two northern ones, I. caspienense must be a species of much lower salinities. It has also been observed in the surface sediment of the Anzali lagoon, Iran (Kazancı et al, 2004).…”

“…An increase in morphological diversity (correlated to a wider range of salinities encountered) was also detected (Marret et al, 2004). For the whole of the CS, only surface samples have been published (Marret et al, 2004), including some from the Anzali lagoon (Kazancı et al, 2004). A record of the last 200 years has been published for the nearby KBG and, although the species list of the KBG is similar to that of the CS, the assemblages are dominated by a form of Lingulodinium machaerophorum (form A) and by Spiniferites belerius.…”

“…The modern assemblages are dominated by I. caspienense (e.g. 49.4% in US02) (Marret et al, 2004;Kazancı et al, 2004). By analogy, this suggests that the salinities of the I. caspienense phases were broadly similar to those of the present.…”

“…During periods of higher water levels, the KBG is surrounded by a steppe-like vegetation, whereas during periods of low water levels, it is more like desert with the emerged land areas colonised by Chenopodiaceae. In addition to the surface samples of Tarasov et al (1998), some surface pollen samples are now available for the Anzali lagoon, on the coast of Iran (Kazancı et al, 2004) and for the Aral Sea .…”

Caspian sea-level changes during the last millennium: historical and geological evidence from the south Caspian Sea

“…Holocene Caspian sea-level (CSL) changes have been a key focus of geological research (Mamedov, 1997;Rychagov, 1997;Kroonenberg et al, 2000;Karpychev, 2001;Kazancı et al, 2004;Hoogendoorn et al, 2005;Lahijani et al, 2009;Dolukhanov et al, 2010;Leroy et al, 2011;Kakroodi et al, 2012;Naderi Beni et al, 2013), mostly based on the indirect interpretation of a variety of proxy data.…”