Background

The Andes is the second highest mountain belt in the world and the highest mountain belt in an ocean-continent subduction zone. From the North to South it is divided into the Northern, Central and Southern Andes. The Central Andes is further divided into five tectonomorphic zones from the West to the East - the Western Cordillera, the Central Andean Plateau (Altiplano and Puna plateau), the Eastern Cordillera, the Interandean Zone and the Sub Andes.

  Cross Section of the Central Andean Plateau (Garzione et al, in preparation)

The uplift history of the Altiplano plateau of the Andes mountain belt is highly debated. Two end member models of uplift are - gradual surface uplift between ~45 Ma and present (Elger et al., 2005; McQuarrie et al, 2005) versus stable elevations punctuated by pulses of rapid surface uplift Garzione et al, 2006, 2008). The rapid surface uplift theory is based on stable isotopic data (δ18O and ∆47) from sedimentary carbonates and plant leaf physiognomy (Gregory-Wodzicki et al,1998,2000) that suggest that one such event occurred between ~10 and 6 Ma in the north-central Altiplano and Eastern Cordillera. Further, studies (Garzione et al, 2006; Garzione et al, 2008; Smith et al, 2009) suggest that the rapid uplift pulse in north-central Altiplano was preceded by a similar pulse in the southern Altiplano, which indicates time progressive uplift of the plateau along its length. However, in absence of data from the northern most part of the plateau, it is not possible to conclude anything at this stage. Proper characterization of the uplift history is important for not only interpretation of geodynamic processes causing surface uplift but also because uplift of such scale has huge impact on the regional climate (Ehlers and Poulsen, 2009; Poulsen et al, 2010; Insel et al, 2012).

 

Study Area

The study area is Descanso-Yauri basin and it is located in the northern most part of the Altiplano Plateau in Southern Peru. It extends from ~14 to 15° S and from 71 to 72 ° W.

  Map of the study area - Descanso Yauri basin (Cerpa and Meza , 2001)    

The deposits of the basin are divided into Member A, Member B and Member C (Cerpa and Meza, 2001). The only age constraints of the basin come from the three dated tuff horizons. The oldest (18.74+ 0.19 Ma) and the youngest (11.66+0.13 Ma) being two tuff horizons from the top of Member A (Boudesseul et al, 2000) and from middle of Member C (Cerpa and Meza, 2001) respectively. The youngest age of the basin is  still unknown. The deposits of the basin are fluvial and lacustrine sedimentary rocks, dominated by conglomerate, sandstone, mudstone and some limestone and tuff. Extensive paleosol carbonates are present in Member B.

 

Importance of this Study

While unaltered carbonate rock and paleosol samples can provide estimation of climate and elevation, they do not provide any age information. With the poor age constraint of the study area any additional age information, especially from the youngest unit Member C is extremely important. This study focuses on characterization of fossils  the Member C . Proper identification of the fossils can not only provide age information if they are index fossils but also about the paleoenvirnoment.

 

.