The origins and implications of paleochannels in hyperarid, tectonically active regions: The northern Atacama Desert, Chile

Abstract

Preserved remnants of fluvial activity in deserts constitute evidence for changing boundary conditions. The Atacama Desert of northern Chile is the global end-member for aridity, so the history of relict stream networks in this region is a record of how landscapes develop under extreme conditions. On Pampa de Tana in northern Chile (19.4°S), a series of channel forms that are presently inactive but in the past flowed westward are incised into the surface of a fault bounded, topographically elevated portion of the El Diablo Formation, a regionally extensive, relict pediment. We measure cosmic-ray produced 10 Be, 26 Al and 21 Ne in fluvial deposits to date the timing of abandonment of three channels and couple this with topographic profile information from a SPOT-6 derived, 2 m resolution digital elevation model. We find two of the channels were abandoned approximately >5.6 Myr and 2.0 Myr ago. One channel is still capable of flow and has ages suggesting it was fluvially active within the last few hundred thousand years. Using the paleochannel ages measured here and published ages for the end of aggradation of the El Diablo Formation we estimate the rates of fluvial channel incision before channel abandonment, and uplift rates on the faults after channel abandonment. Maximum uplift rates of ~12 m/Myr over the last 2 Myr are found. In general, while rates of uplift are relatively low they are several-fold more rapid than the rates of fluvial incision prior to channel abandonment. This implies that westward channel flow was interrupted by uplift of topography above a blind NW-SE striking reverse fault that affects the Central Depression, an alluvial forearc basin. We consider also that shrinkage of the upstream catchment area by stream capture, promoted via headward erosion and lateral expansion of adjacent canyons (quebradas) could be a factor in the abandonment of the channels on Pampa de Tana. Our results highlight the polygenetic nature of this landscape and show that relatively minor amounts of fault displacement in hyperarid regions can have implications for stream network evolution. Even subtle topographic uplift upstream should be taken into account when fluvial deposits are used as proxies for long-term environmental conditions.

Paleoseismic Evidence of anMw7 Pre‐Hispanic Earthquake in the Peruvian Forearc

“…There is growing evidence that Quaternary faulting within the forearc and Western Cordillera of South Perú has variable kinematics in space and time (Audin et al, 2006;Benavente et al, 2017;Binnie et al, 2020;Hall et al, 2012;Loveless et al, 2009; this study). Our observations from the IFS demonstrate that the boundary between the forearc and Western Cordillera failed in at least one large earthquake accommodating left-lateral transpression around 600-years ago (Figure 11a).…”

Conflictos Por El Uso Del Agua en Una Región Árida: Caso Tacna, Perú

“…La región se encuentra ubicada al sur de Perú y norte de Chile (Figura 1), pertenece a la cabecera del Desierto de Atacama, caracterizado como el más árido del mundo (Houston and Hartley, 2003;Ritter et al, 2019). En esta región, los restos conservados de actividad fluvial constituyen una prueba de las condiciones cambiantes de los límites, el Desierto de Atacama en el norte de Chile es un testigo mundial de aridez, por lo que la historia de las redes de arroyos relictos en esta región es un registro de cómo se desarrollan los paisajes en condiciones extremas (Binnie et al, 2020). La zona andina corresponde al sector centro-oeste del Altiplano, en el que la precipitación acumulada anual es relativamente baja (300-700 mm/año) y la variabilidad temporal es muy marcada, períodos húmedos de diciembre a marzo y muy secos de abril a noviembre (Garreaud et al, 2003;Garreaud et al, 2010;Ritter et al, 2019).…”

Late Miocene - Quaternary forearc uplift in southern Peru: new insights from 10Be dates and rocky coastal sequences

“…Cosmogenic dating has been applied successfully to marine terraces (Trull et al, 1995;Perg et al, 2001;Kim and Sutherland, 2004;Quezada et al, 2007;Alvarez-Marron et al, 2008;Saillard et al, 2009Saillard et al, , 2011Kong et al, 2011;Rodriguez et al, 2013;Binnie et al, 2016;Martinod et al, 2016b;Binnie et al, 2020) and rock shore platforms (Choi et al, 2012;Regard et al, 2012;Hurst et al, 2016;Raimbault et al, 2018;Swirad et al, 2020).…”