Late Quaternary paleohydrology and surficial processes of the Atacama Desert, Chile: Evidence from wetland deposits and stable isotopes of soil salts

Persistent Link:
http://hdl.handle.net/10150/279910
Title:
Late Quaternary paleohydrology and surficial processes of the Atacama Desert, Chile: Evidence from wetland deposits and stable isotopes of soil salts
Author:
Rech, Jason Arnold
Issue Date:
2001
Publisher:
The University of Arizona.
Rights:
Copyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.
Abstract:
The origin of pedogenic salts in the Atacama Desert has long been debated. Possible salt sources include in situ weathering at the soil site, local sources such as aerosols from the adjacent Pacific Ocean or salt-encrusted playas, and extra-local atmospheric dust. To identify the origin of Ca and S in Atacama soil salts, we determined δ ³⁴S and ⁸⁷Sr/⁸⁶Sr values of soil gypsum/anhydrite and ⁸⁷Sr/⁸⁶Sr values of calcium carbonate along three east-west trending transects in the Atacama. Our results demonstrate the strong influence of marine aerosols on soil gypsum/anhydrite development in areas where marine fog penetrates inland. In areas where the Coastal Cordillera is >1200 m, however, coastal fog cannot penetrate inland and the contribution of marine aerosols to soils is greatly reduced. Salts in inland soils appear to originate from eolian redistribution of playa salts that are precipitated from evaporated ground water. This ground water has acquired its dissolved solids from water-rock interactions (both thermal and low-temperature) along flowpaths from recharge areas in the Andes. The spatial distribution of high-grade nitrate deposits appears to correspond with areas that receive the lowest fluxes of local dust, supporting arguments for an atmospheric source of nitrate. Ground water in the Atacama is derived from precipitation in the High Andes (>3500 m) that infiltrates soils and then flows down the Pacific slope of the Andes to feed aquifers within the hyperarid core of the Atacama Desert. At many locations, ground water surfaces and creates springs, marshes, and wetlands. In order to track late Quaternary fluctuations in ground-water recharge, paleowetland deposits at eight separate locations (between 18°-26°S) were mapped and dated. Over 200 AMS ¹⁴C dates on a variety of materials provide firm age control on these deposits. Replication of time-stratigraphic units from an assortment of hydrologic settings and varying distances from recharge areas in the Andes show that ground-water systems are responding to regional changes in climate and that response times are probably short (<1000 years). Results suggest that the wettest period represented by deposits was during the late Glacial/early Holocene (∼16-9.5 ka B.P.) and that a moderately wet period occurred during the mid-Holocene (8--3 ka B.P.). Major drops in Atacama water tables, due to regional drought, occurred between 9.5-8 and ∼3 ka B.P. The late Holocene was characterized by generally lower water tables than during the mid-Holocene and subject to more frequent water table drops. Fluctuations in tropical Pacific Sea Surface Temperatures, the Walker Circulation, and ENSO variability is thought to be the major control on precipitation over this region during the late Quaternary.
Type:
text; Dissertation-Reproduction (electronic)
Keywords:
Geology.
Degree Name:
Ph.D.
Degree Level:
doctoral
Degree Program:
Graduate College; Geosciences
Degree Grantor:
University of Arizona
Advisor:
Quade, Jay

Full metadata record

DC FieldValue Language
dc.language.isoen_USen_US
dc.titleLate Quaternary paleohydrology and surficial processes of the Atacama Desert, Chile: Evidence from wetland deposits and stable isotopes of soil saltsen_US
dc.creatorRech, Jason Arnolden_US
dc.contributor.authorRech, Jason Arnolden_US
dc.date.issued2001en_US
dc.publisherThe University of Arizona.en_US
dc.rightsCopyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.en_US
dc.description.abstractThe origin of pedogenic salts in the Atacama Desert has long been debated. Possible salt sources include in situ weathering at the soil site, local sources such as aerosols from the adjacent Pacific Ocean or salt-encrusted playas, and extra-local atmospheric dust. To identify the origin of Ca and S in Atacama soil salts, we determined δ ³⁴S and ⁸⁷Sr/⁸⁶Sr values of soil gypsum/anhydrite and ⁸⁷Sr/⁸⁶Sr values of calcium carbonate along three east-west trending transects in the Atacama. Our results demonstrate the strong influence of marine aerosols on soil gypsum/anhydrite development in areas where marine fog penetrates inland. In areas where the Coastal Cordillera is >1200 m, however, coastal fog cannot penetrate inland and the contribution of marine aerosols to soils is greatly reduced. Salts in inland soils appear to originate from eolian redistribution of playa salts that are precipitated from evaporated ground water. This ground water has acquired its dissolved solids from water-rock interactions (both thermal and low-temperature) along flowpaths from recharge areas in the Andes. The spatial distribution of high-grade nitrate deposits appears to correspond with areas that receive the lowest fluxes of local dust, supporting arguments for an atmospheric source of nitrate. Ground water in the Atacama is derived from precipitation in the High Andes (>3500 m) that infiltrates soils and then flows down the Pacific slope of the Andes to feed aquifers within the hyperarid core of the Atacama Desert. At many locations, ground water surfaces and creates springs, marshes, and wetlands. In order to track late Quaternary fluctuations in ground-water recharge, paleowetland deposits at eight separate locations (between 18°-26°S) were mapped and dated. Over 200 AMS ¹⁴C dates on a variety of materials provide firm age control on these deposits. Replication of time-stratigraphic units from an assortment of hydrologic settings and varying distances from recharge areas in the Andes show that ground-water systems are responding to regional changes in climate and that response times are probably short (<1000 years). Results suggest that the wettest period represented by deposits was during the late Glacial/early Holocene (∼16-9.5 ka B.P.) and that a moderately wet period occurred during the mid-Holocene (8--3 ka B.P.). Major drops in Atacama water tables, due to regional drought, occurred between 9.5-8 and ∼3 ka B.P. The late Holocene was characterized by generally lower water tables than during the mid-Holocene and subject to more frequent water table drops. Fluctuations in tropical Pacific Sea Surface Temperatures, the Walker Circulation, and ENSO variability is thought to be the major control on precipitation over this region during the late Quaternary.en_US
dc.typetexten_US
dc.typeDissertation-Reproduction (electronic)en_US
dc.subjectGeology.en_US
thesis.degree.namePh.D.en_US
thesis.degree.leveldoctoralen_US
thesis.degree.disciplineGraduate Collegeen_US
thesis.degree.disciplineGeosciencesen_US
thesis.degree.grantorUniversity of Arizonaen_US
dc.contributor.advisorQuade, Jayen_US
dc.identifier.proquest3040122en_US
dc.identifier.bibrecord.b42456599en_US
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