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Drainage and base-level adjustments during evolution of a late Pleistocene piggyback basin, Eastern Cordillera, Central Andes of northwestern Argentina

Gustavo Gonzalez Bonorino and Liliana del Valle Abascal
Drainage and base-level adjustments during evolution of a late Pleistocene piggyback basin, Eastern Cordillera, Central Andes of northwestern Argentina
Geological Society of America Bulletin (October 2012) 124 (11-12): 1858-1870

Abstract

In northwestern Argentina, mid-Pleistocene out-of-sequence thrusting further disrupted the Andean foreland, giving rise to the Lerma piggyback basin within the Eastern Cordillera. Emergent topography along the eastern edge of the basin, as well as in its interior, interfered with preexisting eastward-flowing river courses. In the northern part of the Lerma basin, rivers temporarily incised across the new topography, yielding wind and water gaps, and in places preserving straths with treads tilted upstream, revealing their tectonic origin. Application of Hack's law shows correspondence between the active and the abandoned channel profiles. Bed profiles of wind gaps are distinct from those of nearby consequent streams. Defeated and deflected northern streams coalesced into a trunk stream, which maintained an open channel across the eastern bounding ranges. River defeat may have been related to rain shadowing by the growing topographic barrier and retention of easterly derived moisture outside the Lerma basin. In the southern Lerma basin, river courses were not generally capable of sustaining active water gaps. Instead, they were deflected southward, and their discharges fed ancient Lake Lerma. Lake expansion ensued until water level reached a structural low, through which lake waters outflowed from the basin and subsequently incised across the eastern bounding ranges. The relative success of northern rivers in incising across the rising topographic barrier is mainly attributed to their greater channel gradients at the point of incision, combined with high rainfall levels. Longitudinal channel profiles show that rivers in the northern Lerma basin had approached their base level of erosion before uplift of the eastern bounding ranges. After this disturbance, the system continues to approach a new base level of erosion, modified by sediment aggradation within the basin. Speculatively, mid-Pleistocene out-of-sequence thrusting is attributed to basement uplift in the distal foreland.


ISSN: 0016-7606
EISSN: 1943-2674
Coden: BUGMAF
Serial Title: Geological Society of America Bulletin
Serial Volume: 124
Serial Issue: 11-12
Title: Drainage and base-level adjustments during evolution of a late Pleistocene piggyback basin, Eastern Cordillera, Central Andes of northwestern Argentina
Affiliation: Universidad Tecnologica Nacional, Consejo Nacional de Investigaciones Cientificas-Centro Austral de Investigaciones Cientificas, Ushuaia, Argentina
Pages: 1858-1870
Published: 20121002
Text Language: English
Publisher: Geological Society of America (GSA), Boulder, CO, United States
References: 62
Accession Number: 2012-096834
Categories: Quaternary geology
Document Type: Serial
Bibliographic Level: Analytic
Annotation: Accessed on October 11, 2012
Illustration Description: illus. incl. sects., geol. sketch map
Source Medium: WWW
S26°30'00" - S22°00'00", W67°00'00" - W64°00'00"
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2019, American Geosciences Institute. Reference includes data from GeoScienceWorld, Alexandria, VA, United States. Reference includes data supplied by the Geological Society of America, Boulder, CO, United States
Update Code: 201251
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