HR: 0800h
AN: T21C-0492    [Abstracts]
TI: Sedimentary Architecture, Provenance, and Drainage Reorganization Associated With the Establishment of the Southern Margin of the Central Andean Puna Plateau, NW Argentina
AU: * Carrapa, B
EM: carrapa@geo.uni-potsdam.de
AF: Universtiy of Potsdam, Karl Liebknecht Str. 24, Golm, Potsdam, 14476 Germany
AU: Mortimer, E
EM: estellem@geo.uni-potsdam.de
AF: Universtiy of Potsdam, Karl Liebknecht Str. 24, Golm, Potsdam, 14476 Germany
AU: Hauer, J
EM: jchauer@rz.uni-potsdam.de
AF: Universtiy of Potsdam, Karl Liebknecht Str. 24, Golm, Potsdam, 14476 Germany
AU: Strecker, M
EM: strecker@rz.uni-potsdam.de
AF: Universtiy of Potsdam, Karl Liebknecht Str. 24, Golm, Potsdam, 14476 Germany
AB: The tectonic, topographic, and geomorphic evolution of the central Andean Puna Plateau to its present-day character is still a matter of debate. The ongoing discussion entails a series of fundamental questions concerning the timing and mechanisms of plateau uplift, exhumation of individual ranges and the formation of intramontane basins within the plateau, and associated processes of foreland deformation and compartmentalization. Tertiary sedimentary basins straddling the southern margin of the Puna Plateau provide an exceptional record of the most recent stages of plateau development, spanning the last 10 My. Sedimentary facies and architecture of these basin-fills are controlled, at a first order, by the development of the plateau. Sedimentologic analysis and apatite fission track thermochronology (AFT) of the basin-fill and adjacent ranges provide us with tools to unravel the late Cenozoic development of the Puna Plateau. Investigations of two such marginal sedimentary basins, the Fiambal{a}' and El Cajon-Campo Arenal, reveal similar facies and depositional architectures; but strikingly, exhibit the same evolution in sediment provenance. In the Fiambal{a}'Basin, sedimentation, which commenced at ca. 8 Ma, is initially dominated by unconstrained tabular alluvial facies, which evolved into more channelized fluvial deposits up-section. Interfingering of these deposits with formerly vegetated floodplains and paleosol-bearing horizons is observed. In the El Cajon-Campo Arenal basin, sedimentation commenced at ca.10 Ma, and is dominated by channelized fluvial facies that interfinger with deposits of former vegetated floodplains. Within this section, 40 m of lake sediments are recorded ca. 6-5 Ma. In both basins, these units are superseded by thick, late Pliocene fanglomerates, which are being incised today. In both basins provenance data record a change in source region, from ranges to the west to more northerly sources. Paleocurrent indicators in both basins record a change in paleoflow from initially eastward to later southward flow. This changeover took place at about 6 to 5 Ma when the change in character between tabular and channelized facies in the Fiambal{a}' Basin is observed, and immediately above the lake sediments in the El Cajon-Campo Arenal Basin. The more northern provenance of sediments reflects lithologies from the Puna, and therefore records the exhumation and erosion of the plateau at this time (ca. 6-5 Ma). The Puna region must have thus existed as a topographic entity by late Pliocene. This interpretation is further supported by AFT data from the Fiambal{a}' Basin revealing that the southern plateau margin had a minimum relief of ca. 1800 m by ~5 Ma. AFT data from the El Cajon-Campo Arenal Basin constrain the exhumation of an intra-basin range, coinciding with the development of the plateau to the north. Interestingly, independent data from both the Altiplano to the north and the Puna point to a regional uplift event occurring in the last ca. 8-5 My. We hypothesize that our AFT data, changes in facies architecture, and provenance reflect the basins' response to a regional pattern of plateau growth and the establishment of the southern Puna margin by late Pliocene time.
DE: 1140 Thermochronology
DE: 1815 Erosion
DE: 8102 Continental contractional orogenic belts and inversion tectonics
DE: 8169 Sedimentary basin processes
SC: Tectonophysics [T]
MN: Fall Meeting 2005