Landscape modification in response to repeated onset of hyperarid paleoclimate states since 14 Ma, Atacama Desert, Chile

Abstract

The landscape of the hyperarid Atacama Desert in northern Chile records extremely slow change on Earth’s surface. Disputed ages for the onset of hyperaridity range from the late Paleogene through the Pleistocene. A long-term paleoclimate record is recorded in a nonmarine basin whose fill is primarily alluvial strata. For this setting, the primary proxies for climate state are the mineralogical and chemical composition of soil, which varies across a precipitation gradient, and the landforms and deposits of alluvial fans. During the most recent ∼15 million years, five climate-related landscape stages are resolved for the Pampa del Tamarugal sedimentary basin, with each successively younger stage inset lower in the local topography than its predecessor. The earliest landscape stage is expressed as a set of alluvial strata inherited from a time of arid or semi-arid climate, ca. 14–12 Ma. The younger four landscape stages generated a composite long-lasting exposure surface. Predominantly hyperarid conditions have persisted since ca. 12 ± 1 Ma, during which four intervals of arid to semi-arid climate occurred. Each wet interval was short lived, a million years or less, whereas some of the hyperarid periods were lengthy, 1–5 m.y. The hyperarid intervals were roughly 11–5.5 Ma, 4.5–4 Ma, 3.6–2.6 Ma, 2.2–1 Ma, and repeated intervals during the last 1 m.y. The onset of hyperaridity ca. 12 Ma likely reflects the growth of the Andes Mountains above a climate threshold. In contrast, sea surface temperature variability likely has controlled Atacama paleoclimate changes since the late Miocene.