Geoscience Frontiers 5 (2014) 249e259 Contents lists available at SciVerse ScienceDirect China University of Geosciences (Beijing) Geoscience Frontiers journal homepage: www.elsevier.com/locate/gsf Research paper Palaeogeographic reconstruction of Minchin palaeolake system, South America: The influence of astronomical forcing Andrea Sánchez-Saldías a,*, Richard A. Fariña b a Universidad de la República, Facultad de Ciencias, Departamento de Astronomía, Iguá 4225, 11400 Montevideo, Uruguay b Universidad de la República, Facultad de Ciencias, Laboratorio de Paleobiología, Iguá 4225, 11400 Montevideo, Uruguay article info abstract Article history: Current palaeoclimatic reconstructions for the Río de la Plata region during the latest Pleistocene (30,000 Received 3 December 2012 e10,000 yr BP) propose dry conditions, with rainfall at the Last Glacial Maximum amounting to one-third Received in revised form of today’s precipitation. Despite the consequential low primary productivity inferred, an impressive 17 May 2013 megafauna existed in the area at that time. Here we explore the influence of the flooding from a huge Accepted 2 June 2013 extinct system of water bodies in the Andean Altiplano as a likely source for wet regimes that might have Available online 1 July 2013 increased the primary productivity and, hence, the vast number of megaherbivores. The system was reconstructed using specifically combined software resources, including Insola, Global Mapper v13, Keywords: Planetary science Surfer and Matlab. Changes in water volume and area covered were related to climatic change, assessed Climate science through a model of astronomical forcing that describes the changes in insolation at the top of the at- Quaternary mosphere in the last 50,000 yr BP. The model was validated by comparing its results with several proxies 18 Palaeoecology (CH4,CO2,D, O) from dated cores taken from the ice covering Antarctic lakes Vostok and EPICA Dome C. Megafauna It is concluded that the Altiplano Lake system drained towards the southeast in the rainy seasons and Paraná Basin that it must have been a major source of water for the Paraná-Plata Basin, consequently enhancing primary productivity within it. Ó 2013, China University of Geosciences (Beijing) and Peking University. Production and hosting by Elsevier B.V. All rights reserved. 1. Introduction Serbian astronomer Milutin Milankovitch (1941) and is considered a major factor in environmental reconstructions (Berger, 1977, 1.1. Astronomical forcing 1980; Huybers, 2006). Apart from some caution posed by the conventional climato- During Quaternary periodic cycles in glaciation-deglaciation, logical approach, which claims the Earth atmosphere has its own temperature fluctuations determined high-latitude ice accumula- physical dynamics and is only crudely influenced by these cycles, tion and major variations in sea-level, as well as climatic, envi- astronomical forcing is considered the main cause of Quaternary ronmental and even geographical changes. These cycles are glacial-interglacial episodes. Since the original proposal by explained by periodic variations in insolation patterns due to Milankovitch (1941),refinements have arisen from improvements changes in the Earth’s orbital and rotational elements. This so- in numerical, computer-based algorithms for calculating the inso- called astronomical forcing theory was first proposed by the lation and also from the gathering of proxy data e a measured variable used to infer the value of another variable of interest in climate research. In Section 3.1 we show evidence of a strong fit between insolation and proxies using a simple model without any * Corresponding author. Tel.: þ598 25258624; fax: þ598 25258630. additional assumptions about atmospheric behaviour. E-mail addresses: andrea@fisica.edu.uy, [email protected] (A. Sánchez-Saldías). 1.2. Late Pleistocene palaeoclimate in mid-latitude South America Peer-review under responsibility of China University of Geosciences (Beijing) Among other climatic changes, and as a consequence of the lower availability of water circulating in the atmosphere during the colder parts of these Milankovitch cycles, many regions of the Earth Production and hosting by Elsevier had dryer climates than today. For example, the areas neighbouring 1674-9871/$ e see front matter Ó 2013, China University of Geosciences (Beijing) and Peking University. Production and hosting by Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.gsf.2013.06.004 250 A. Sánchez-Saldías, R.A. Fariña / Geoscience Frontiers 5 (2014) 249e259 the present day Río de la Plata have been reconstructed in a clas- Here we review the geological evidence and reconstruct the sical work by Iriondo and García (1993) as much dryer and slightly palaeolake using digital procedures. We also test the possibility colder during the Last Glacial Maximum, with precipitation at that it had a substantial drainage to the Paraná Basin and, hence, about 350 mm and temperatures lower by 2.5e3 C, with more could have been a major source of water through such tributaries as marked seasonality. Even though more recent studies propose a Palaeopilcomayo and Palaeoparaná, which helped increase the more complex scenario (e.g., Garreaud et al., 2008; Zech et al., primary productivity to the levels required to support the 2009; Heil et al., 2010), the general approximation remains valid megafauna. 18 for our purposes. Analysis of oxygen isotopic ratios (d Oice) and insoluble dust On the other hand, the assemblage of megamammals that were from ice cores extracted from the Sajama Desert (Thompson et al., widespread in the region at that time includes up to 12 species with 1998) provide a time constrain of about 30,000 yr before present adult body masses over one tonne found at the same site (Fariña for the existence of the palaeolake, named Minchin in honour of et al., 2013). Darwin (1839) himself was astonished by such di- the British engineer and geographer John B. Minchin (Minchin, versity of megamammals and subtitled Chapter V of his journal of 1882; Steinmann et al., 1904), whereas carbonate-encrusted the Beagle’s Voyage “Large animals do not require luxuriant vege- shoreline deposits dated by 14C and U/Th techniques yielded tation”, in which commented that the association between giant even older ages between 44e34 and 68e72 kyBP (Rondeau, 1990; animals and forests was not always necessary and that “yet in Fornari et al., 2001; Placzek et al., 2006). Previous palaeolakes former days, numerous large animals were supported on the plains have also been described as forming a complex series called now covered by a thin and scanty vegetation”. Mataro, Cabana and Ballivián (Servant and Fontes, 1978; Lavenu Darwin’s perception was later assessed with modern tools of et al., 1984). Recently, several cycles with different lake configu- energetics and palaeoecology (Fariña, 1996), from which it was rations have been recognised for the last glacial period (Lavenu concluded that the rainfall inferred would have been insufficient to et al., 1984; Mourguiart et al., 1997; Sylvestre et al., 1999; yield a primary productivity high enough to support so many large Placzek et al., 2006, 2013): Ouki/Salinas Lake cycle between mammals. 125 kyBP and 80 kyBP, Inca Huasi Lake cycle about 46 kyBP, Sajsi Here we propose a possible source of water e that coming from Lake cycle between 24 kyBP and 20 kyBP, Tauca Lake cycle be- the drainage of a palaeolake system inferred to have existed in the tween 18 kyBP and 14 kyBP and Coipasa Lake cycle between 11 Altiplano region (Thompson et al., 1998). kyBP and 12.8 kyBP. Placzek et al. (2006) also proposed dropping the original name Minchin on the grounds that it has been used 1.3. Palaeolakes with different and even contradictory meanings. However, we intend here to continue its usage and, hence, maintain the hom- The Andean Altiplano palaeolake system is reconstructed as a age to the original discoverer of the whole system, which includes drainage basin of nearly 200,000 km2 lying between the western the northern Titicaca Basin, the southern Poopó-Coipasa-Uyuni (Occidental) Cordillera and the eastern (Oriental) Cordillera at an Basin and the connecting Desaguadero River Basin (Fig. 1), based average height of 3800 m above sea-level (masl). At present, Lake on the notion that these water bodies worked and still work as a Titicaca is found in the northern Altiplano at 3812 masl. Its area is system. 8372 km2, its depth is 281 m and the whole basin covers about Indeed, due to the associated effects of increase in pre- 56,270 km2. In the southern Altiplano, connected with Titicaca by cipitations, decrease in temperature and deglaciation processes the Desaguadero River, is Poopó Lake (3686 masl, 3191 km2 in area, (Blodgett et al., 1997), Lake Titicaca overflowed and discharged into 3 m deep and 27,700 km2 in basin area). Currently, the southern Poopó during the late Pleistocene, flooding both Coipasa and Uyuni Altiplano is a dry area that contains very scarce water bodies like salares (Baker et al., 2001), a phenomenon that also takes place Poopó Lake, but instead is characterised by two huge salares (salt today (Roche et al., 1991), albeit at a smaller scale. flats): Coipasa (3657 masl, 2218 km2 in area) and Uyuni (3663 masl, These changes in water volume and area were related to climatic 10582 km2 in area). change, that is here assessed through an astronomical forcing In the past, however, several large lakes have been proposed to model that describes the changes in insolation at the top of the have existed (Minchin, 1882; Steinmann et al., 1904; Servant and atmosphere over the last 50,000 yr. The model is validated by Fontes, 1978; Blodgett et al., 1997; Argollo and Mourguiart, 2000; comparing the computed insolation with several proxies (CH4,CO2, Placzek et al., 2006, 2011, 2013). The first attempts to date these D, 18O) from dated cores taken from the ice covering Antarctic lakes palaeolakes are those of Servant and Fontes (1978).