Sedimentological response of an alluvial system to Neogene thrust tectonics, Atacama Desert, northern Chile

Abstract

The Llano de la Paciencia is a thrust sheet top basin in which the sedimentological and topographic evolution can be linked to thrust tip propagation. It is an elongate gravel plain which borders the Salar de Atacama, a major intermontane basin in the Andean forearc of northern Chile. The Llano is bounded to the west by the Cerros de Purilactis a Cretaceous–Paleocene sequence uplifted by the Frontal Domeyko Thrust. The eastern margin of the Llano is formed by the Cordillera de la Sal which was uplifted by a linked back thrust-frontal thrust system. The Salar de Atacama is thus divided into a number of discrete sub-basins: the Llano de la Paciencia, the Pampa Visachita and the western sub-Llano which from east-west are bounded by the Cordillera de la Sal, the northern imbricates and the ignimbrite back thrust. Two phases of sedimentological evolution can be distinguished within the Llano on the basis of Quaternary to Recent sediment dispersal patterns. Initially, Phase 1 alluvial fan lobes prograded eastwards into the main Salar de Atacama basin. Subsequently, uplift of the Cordillera de la Sal deflected drainage systems southwards parallel to the structural strike. These Phase 2 alluvial deposits drain into the Salar de Atacama at the lateral termination of the Cordillera de la Sal frontal thrust. In places where thrust tip ramps are emergent within the Llano, gullies have been incised into the drainage pathways. This has resulted in the reworking of the early Phase 1 gravels and progradation of the Phase 2 fan lobes. The evolution of the Llano de la Paciencia illustrates the close link between topography and syntectonic alluvial drainage patterns in an arid intermontane basin.

Uplift of the western Altiplano plateau: Evidence from the Precordillera between 20° and 21°S (northern Chile)

“…Here, Jolley et al [1990], Mpodozis et al [2000], Kuhn [2002], Jordan et al [2002], and Muñoz et al [2002] report west and east vergent faults and minor contractional structures at the toe of the flanks of both Cordilleras and in the Salar. Formation of these structures has occurred during an earlier Paleogene contraction succeeded by a stage of late Miocene (circa 10-11 Ma) to recent reactivation, as indicated by ongoing upper crustal seismicity.…”

Cenozoic subsurface stratigraphy and structure of the Salar de Atacama Basin, northern Chile

“…4). Despite the evidence that, in certain sections, these environments succeed one another transitionally (Flint, 1985;Jolley et al, 1990;Kape, 1996;Wilkes and Gö rler, 1994), unconformities within sequence K are clear beneath the Salar (Fig. 3).…”

“…These strata are characterized by complex facies and thickness changes that include a sensitive record of drainage basin evolution, relative uplift at the margins of the basin, and subsidence. Hooper and Flint (1987), Flint et al (1993), Jolley et al (1990), Wilkes and Gö rler (1994), Kape (1996), Arriagada (1999), Arriagada et al (2000), Blanco et al (2000), and Mpodozis et al (2000Mpodozis et al ( , 2005 have contributed to our understanding of the evolution of the Salar de Atacama Basin through studies of rock exposures on the west flank of the basin in the Cerros de Purilactis, Cuesta de Barros Arana, and El Bordo Escarpment (all of which form the eastern border of the Cordillera Domeyko) and the Cordillera de la Sal ( Figs. 1 and 2).…”

Caledonide influences on the Old Red Sandstone fluvial systems of the Oslo Region, Norway

“…The development of piggyback basins is known to have a direct effect on fluvial facies associations and palaeocurrent directions (see e.g. Jolley et al 1990;Ramos et al 2002). Topography developed in such a setting could be responsible for the internal differences of the Ringerike Group.…”

“…This model also explains deposition by high-energy and laterally mobile braided streams in the southern Ringerike Group, as the fluvial system would have been diverted along one of the steepened ramp structures (Morley 1986(Morley , 1987 that ran parallel to the foreland side of the thrust anticline. Jolley et al (1990) have illustrated that diversion of fluvial systems in this way (as opposed to tectonically influenced entrenchment) is dependent on high uplift rates (i.e. the Scandian Phase) and extent and low erosional powers of the rivers (i.e.…”