The duration of a Miocene lake phase in the hyperarid core of the Atacama Desert approached by magnetic polarity stratigraphy and cyclostratigraphy

The Collaborative Research Center (SFB) 1211 “Earth – Evolution at the Dry Limit” investigates the diverse relationships and feedback loops between water availability, the evolution of life, and environmental factors. A focus region for these analyses is the hyperarid core of the Atacama Desert. Due to the uplift of the Andes and the associated erosion, geological archives that provide information about long-term evolution are rare on the Chilean continent. Clastic sediment archives located in endorheic basins in the coastal cordillera therefore offer a rare opportunity to study the history of local precipitation and its relationship to the development of landscape, climate, and organisms. The Playa Adamito Grande (PAG) clay pan is located 16 km from the coast and 11 km south of the Rio Loa (21°32'26.4“S 69°54'46.5”W). In 2017, four long drill cores were recovered and assembled into a composite profile with a total depth of 51.7 m composite depth (mcd). The sediment sequence exhibits a layered architecture with approximately 20 m of fine-grained clastic playa lake deposits at its base. Establishing the chronological framework of the entire core was challenging. This study focuses on the chronology of the playa deposits in the lowest section of the sediment sequence. We provide an overview on the project and its challenges and report on the results of the mineral magnetic and paleomagnetic analyses and on the attempt to obtain further age constraints by orbital tuning of the Ca/Ti ratio.