Facies variability and depositional settings of Laguna Salada de Chiprana, an Iberian hypersaline lake

Hypersaline lakes are unique depositional environments that are highly sen- sitive to climatic changes and anthropogenic pressures. Strong physicochem- ical gradients and the interplay of physical, chemical and biological depositional processes coupled to variable preservation potential associated with these environments generate highly complex sedimentary sequences. This study aimed to investigate spatio-temporal variations throughout the last three centuries in the sedimentary sequence of Laguna Salada de Chi- prana, a small, permanent hypersaline lake situated in Northeast Spain. Short sediment cores reveal a complex sedimentary sequence influenced by detrital, chemically-induced and biogenically-influenced depositional pro- cesses. Nine facies associated with six sedimentological units represent six periods of environmental change beginning from approximately pre-1800 AD to the present day. They include: (i) a shallow, permanent saline lake that experienced brief periods of anoxia and drawdown between pre-1800 AD and ca 1850 AD. This was succeeded by: (ii) increased lake levels and detrital input to the lake from ca 1850 to 1900 AD; and (iii) a fall in lake levels and the establishment of microbial mats within bottom waters fluctuating between oxic and anoxic conditions from ca 1900 to 1950 AD. (iv) From ca 1950/1960 AD, a minor increase in lake levels and colonization of the littoral and sub-littoral zones by macrophytic vegetation occurred; followed by (v) falling lake levels and increasing salinity between 1960 and 1970 AD leading to widespread encrustation of macrophytes in the littoral zones by carbon- ate–evaporite precipitates. Finally (vi), from ca 1970 AD to the present day, falling lake levels, elevated salinity and widespread colonization of the lake by microbial mats characterize the sedimentary environment. Climate recon- structions and documentary evidence indicate that depositional evolution was mostly controlled by changes in farming practices and irrigation poli- cies. Understanding Laguna Salada de Chiprana’s depositional evolution contributes to future definitions of high-resolution palaeoenvironmental models, not only within the Iberian Peninsula but also in other locations where saline–hypersaline lakes act as a key source of palaeoenvironmental information.