Minimum duration of a Miocene lake phase in the hyperarid core of the Atacama Desert, Chile

In 2017, sediment cores were drilled in the PAG clay pan in the hyperarid core of the Atacama Desert as part of CRC1211 (Earth - Evolution at the Dry Limit). The aim of the endeavour was to deduce the climate history of this region from the sedimentary record. The core composite established from the individual core runs goes down to a depth of approx. 52 metres. The core is composed of three major lithological facies. Below 29.2 metre composite depth (mcd), the core consists of fine-grained silty-clayey sediments, which are cyclically interspersed with layers of gypsum. These sediments are interpreted as lacustrine strata. They are overlain by coarse sediments with clasts up to several centimetre in size, which are referred to as colluvial sediments. The upper around seven metre are formed by fine-grained clay pan sediments. The geochronological framework of the core was investigated using various dating methods, most of which were unable to provide reliable ages. For the lake sediments no absolute ages could be obtained. However, U-Pb ages of zircons of a tephra layers, at the transition between the lake and coarse-grained facies suggest a Miocene age for the lake deposits. To constrain the age framework of the lake phase, magnetic polarity stratigraphy was combined with an analysis of gypsum cyclicity that is interpreted as an orbital signal. Here, we present and discuss the results of the study, which provides a new age model for this lacustrine part of the core and thus, sheds new light on an extended pluvial phase in the Atacama Desert.