Magnetic polarity stratigraphy of the Miocene Rio Azul section, Precordillera thrust belt, San Juan Province, Argentina

Journal Article · Sun Jul 01 00:00:00 EDT 1990 · Journal of Geology; (USA)

DOI:https://doi.org/10.1086/629422· OSTI ID:6224597

Jordan, T E; Beer, J A ^[1]; Rutty, P M ^[2]; McRae, L E; Tabbutt, K ^[3]; Damanti, J F ^[4]

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1. Cornell University, Ithaca, NY (USA)
2. Dartmouth College, Hanover, NH (USA) Stanford Univ., CA (USA)
3. Dartmouth College, Hanover, NH (USA)
4. Union College, Schenechtady, NY (USA)

The chronostratigraphy of synorogenic strata of Rio Azul in the Bermejo foreland basin, Argentine Andes, reveals details of Miocene tectonic activity and deposition. Chronostratigraphic interpretations are based on magnetic polarity stratigraphy and zircon fission-track dates of interbedded volcanic ashes. The Rio Azul section is located within the Precordillera thrust belt, uplifted and rotated by motion on subjacent faults. The 3,200 m thick section coarsens upward, from sandstone and mudstone (Cuculi Formation) to conglomerate (El Corral Formation). The radiometric ages indicate the entire section is of middle to late Miocene age, and the authors correlate the magnetic polarity pattern of each fault block to the magnetic polarity time scale. The lower 500 m of the section apparently ranges from approximately 16 to 12 Ma, although the age of the lowest 100 m is quite uncertain. The fault-bounded block from 500 to 1,000 m probably correlates to approximately 13.5-12.5 Ma. The block from 1,000 to 2,000 m correlates to approximately 12.5-10 Ma. Given the lack of unconformities in the coarse uppermost 1,200 m of section and a zircon fission track age within the conglomerates, the authors speculate that the upper part of the section was deposited very rapidly; the top of the section is probably no younger than about 8 to 9 Ma. These correlations and similarities of facies, paleocurrents, and provenance imply that the Cuculi Formation represents the proximal facies correlative to the Jarillal Formation of Sierra de Huaco, and that the El Corral conglomerates are the up-dip equivalent of the Huachipampa Formation of Huaco. These results are consistent with a paleogeographic model of a major drainage reorganization in the Bermejo foreland basin at about 10 Ma. It is clear, however, that thrusting in the Precordillera began more than 2 m.y. prior to the drainage reorganization.

• OSTI ID: 6224597
• Journal Information: Journal of Geology; (USA), Vol. 98:4; ISSN 0022-1376
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
ARGENTINA
GEOLOGIC FORMATIONS
PALEOMAGNETISM
STRATIGRAPHY
AGE ESTIMATION
ANDES
CONGLOMERATES
DEPOSITION
FISSION TRACKS
GEOLOGIC HISTORY
GROUND UPLIFT
MIOCENE EPOCH
ROTATION
SANDSTONES
SEDIMENTARY BASINS
SEDIMENTATION
SEDIMENTS
SILTSTONES
TECTONICS
VOLCANIC ROCKS
ZIRCON
CENOZOIC ERA
DEVELOPING COUNTRIES
GEOLOGIC AGES
GEOLOGIC STRUCTURES
GEOLOGY
IGNEOUS ROCKS
LATIN AMERICA
MAGNETISM
MINERALS
MOTION
MOUNTAINS
OXYGEN COMPOUNDS
PARTICLE TRACKS
ROCKS
SEDIMENTARY ROCKS
SILICATE MINERALS
SILICATES
SILICON COMPOUNDS
SOUTH AMERICA
TERTIARY PERIOD
TRANSITION ELEMENT COMPOUNDS
ZIRCONIUM COMPOUNDS
ZIRCONIUM SILICATES
580000* - Geosciences