Water Resource Distribution and Tectonics in the Tulum Valley, Western Central Argentina

Tulum Valley extends over a broken foreland basin comprised between the geological province Precordillera Oriental [1] to the west, and the Sierras Pampeanas Occidentales to the east, on the active deformation front of the Central Andes which, in turn, features a dominant compressive system associated to the Nazca-South American plates drift system (Figure 1). The main structural configuration of the basin is explained by the planar geometry of the Nazca plate subducting under the South American plate [2-6]. Tulum Valley is located in central-western Argentina, in a particularly arid region of the Province of San Juan. The population of this valley, where the province’s capital city of San Juan lies, is 629.530 inhabitants [7]. The climate is arid to desertic (Bwk, Koeppen) where daily and seasonal temperatures vary greatly. The annual mean temperature ranges from 14°C to 19°C. The annual rainfall values range within 100-124 mm. The basin is filled by Quaternary sediment and Tertiary sedimentites. Extensive geoforms are developed, such as the alluvial fan of San Juan river that holds an underground water basin extending over 3700 km2 [8,9]. Tectonic action is the predominant source for the formation of geological features of this valley and its fault system of Quaternary activity. This system represents most of the active deformation known up to date in Argentina [10] Tulum Valley shows significant faulting, such as the Tulum Fault System [11] that intersects the valley with a NNE-SSW trending. These are thrust faults, almost vertical, bordering the uplift blocks of the broken foreland basin, which give rise to flexural basins [12]. The present study was made on three sectors in the Tulum Valley. The first zone related to an area of greater richness of groundwater, in the middle sector of the alluvial fan of the San Juan River, in the underground free aquifer. The second zone corresponds to the depocenter of the basin, which receives all the contributions of both groundwater and surface-water. The zone is linked to paleo-swamps and organics soils in the past wetter environment. The third zone is the Tulum fault system. A map of residual gravimetric anomalies using an upward continuation filter and enhancement through first vertical derivate is presented. Tectonic environments and main tectonic structures were delimited in the map. These are associated with the distribution of water resources in this desert region, with the highest population density in the San Juan province. Both groundwater and surface-water are highly demanded resources due to their scarcity. This panorama worsens through time due to a marked population growth and its associated rise in social and economic development (Figure 1).