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Ouki was an ancient lake in the Bolivian
Altiplano The Altiplano (Spanish language, Spanish for "high plain"), Collao (Quechuan languages, Quechua and Aymara language, Aymara: Qullaw, meaning "place of the Qulla people, Qulla") or Andean Plateau, in west-central South America, is the most extens ...
. Its existence was postulated in 2006 by a group of scientists who had subdivided the
Lake Minchin Lake Tauca is a former lake in the Altiplano of Bolivia. It is also known as Lake Pocoyu for its constituent lakes: Lake Poopó, Salar de Coipasa and Salar de Uyuni. The lake covered large parts of the southern Altiplano between the Eastern Co ...
lake cycle into several lake phases. The
Lake Minchin Lake Tauca is a former lake in the Altiplano of Bolivia. It is also known as Lake Pocoyu for its constituent lakes: Lake Poopó, Salar de Coipasa and Salar de Uyuni. The lake covered large parts of the southern Altiplano between the Eastern Co ...
cycle had been previously identified in 1904 as a now disappeared lake in the central Altiplano. Sediments attributed to Lake Minchin may rather be part of Ouki. The dating is uncertain, with
radiocarbon Carbon-14, C-14, C or radiocarbon, is a radioactive isotope of carbon with an atomic nucleus containing 6 protons and 8 neutrons. Its presence in organic matter is the basis of the radiocarbon dating method pioneered by Willard Libby and coll ...
and uranium-thorium dating yielding different dates spanning the time between 28,200 and 125,990 ± 9,580 years ago. Whether Ouki existed is a subject of controversy. In 2011, scientists claimed that the lake did not exist outside of the
Lake Poopo A lake is often a naturally occurring, relatively large and fixed body of water on or near the Earth's surface. It is localized in a depression (geology), basin or interconnected basins surrounded by dry land. Lakes lie completely on land an ...
basin. The formation of Ouki is associated with a major glaciation and was probably caused by increased precipitation, which has also been observed elsewhere.


General characteristics

Ouki may have reached a water level of approximately with preserved shorelines at
Lake Poopó Lake Poopó ( ) was a large saline lake in a shallow depression in the Altiplano in Oruro Department, Bolivia, at an altitude of approximately . Due to the lake's length and width (), it made up the eastern half of Oruro, known as a mining r ...
, and it may have covered the
Salar de Uyuni Salar de Uyuni (or "Salar de Tunupa") is the world's largest salt flat, or playa, at in area. It is in the Daniel Campos Province in Potosí in southwest Bolivia, near the crest of the Andes at an elevation of above sea level. The Salar wa ...
, the Salar de Coipasa and the Lake Poopó area, although the
Uyuni Uyuni ( Aymara, ''uyu'' pen (enclosure), yard, cemetery, ''-ni'' a suffix to indicate ownership, "the one that has got a pen", "the one with a pen") is a city in the southwest of Bolivia. Uyuni primarily serves as a gateway for tourists visiting ...
and
Coipasa __NOTOC__ Lago Coipasa is a lake in Sabaya Province, Oruro Department, Bolivia. At an elevation of 3657 m, its surface area is 806 km². It is located on the western part of Altiplano, 20 km north of Salar de Uyuni and south of the main ...
basins may rather have been filled by a separate postulated lake,
Lake Salinas Lake Salinas is a salt lake in the Arequipa Region in Peru. It is situated in the Arequipa Province, San Juan de Tarucani District, Tarucani District.escale.minedu.gob.pe - UGEL map of the ''Arequipa Sur'' (Arequipa Region) See also * List of lak ...
. Estimates of the surface area depend on the assumed lake levels and whether the lake covered only the Lake Poopó basin or also the Uyuni/Coipasa basins. Estimates range from . The Ouki lake is one of the so-called deep lake cycles, along with
Lake Tauca Lake Tauca is a former lake in the Altiplano of Bolivia. It is also known as Lake Pocoyu for its constituent lakes: Lake Poopó, Salar de Coipasa and Salar de Uyuni. The lake covered large parts of the southern Altiplano between the Eastern Co ...
, from which it may have separated during a period when water levels dropped below altitude. At a locality called Vinto, it has left characteristic
tufa Tufa is a variety of limestone formed when carbonate minerals precipitation (chemistry), precipitate out of water in ambient temperature, unheated rivers or lakes. hot spring, Geothermally heated hot springs sometimes produce similar (but less ...
deposits which have shapes of inverted cones. The depth of the lake did not exceed . The subsequent Salinas lake cycle may simply be a shrinking stage of the Ouki lake. Likewise, the existence of Lake Minchin may be in part based on misattributing deposits left by Ouki. The Ouki lake cycle may be subdivided into individual phases in the future. The Ouki lake may have been populated by species such as ''
Pisidium ''Pisidium'' is a genus of very small or minute freshwater clams known as pill clams or pea clams, aquatic bivalve molluscs in the family Sphaeriidae, the pea clams and fingernail clams. In some bivalve classification systems, the family Spha ...
''
bivalves Bivalvia () or bivalves, in previous centuries referred to as the Lamellibranchiata and Pelecypoda, is a class of aquatic molluscs (marine and freshwater) that have laterally compressed soft bodies enclosed by a calcified exoskeleton consis ...
,
ostracode Ostracods, or ostracodes, are a class of the Crustacea (class Ostracoda), sometimes known as seed shrimp. Some 33,000 species (only 13,000 of which are extant) have been identified,Brandão, S.N.; Antonietto, L.S; Nery, D.G.; Santos, S.G.; Karano ...
s and the '' Biomphalaria andecola'' snail. Waters had a high concentration of
strontium Strontium is a chemical element; it has symbol Sr and atomic number 38. An alkaline earth metal, it is a soft silver-white yellowish metallic element that is highly chemically reactive. The metal forms a dark oxide layer when it is exposed to ...
. While one model inferred from strontium isotope data assumes that most of the Ouki water was contributed by the Poopó basin, another called "Ouki B" assumes a 69% contribution by waters from
Lake Titicaca Lake Titicaca (; ; ) is a large freshwater lake in the Andes mountains on the border of Bolivia and Peru. It is often called the highest navigable lake in the world. Titicaca is the largest lake in South America, both in terms of the volume of ...
and no contribution from the Coipasa and Uyuni basins, which is less likely. Waters from the Poopó basin would have spilled into the Uyuni/Coipasa basin. The drying of the lake left deposits containing
amphibole Amphibole ( ) is a group of inosilicate minerals, forming prism or needlelike crystals, composed of double chain tetrahedra, linked at the vertices and generally containing ions of iron and/or magnesium in their structures. Its IMA symbol is ...
,
illite Illite, also called hydromica or hydromuscovite, is a group of closely related non-expanding clay minerals. Illite is a secondary mineral precipitate, and an example of a phyllosilicate, or layered alumino-silicate. Its structure is a 2:1 sandw ...
,
plagioclase Plagioclase ( ) is a series of Silicate minerals#Tectosilicates, tectosilicate (framework silicate) minerals within the feldspar group. Rather than referring to a particular mineral with a specific chemical composition, plagioclase is a continu ...
feldspar Feldspar ( ; sometimes spelled felspar) is a group of rock-forming aluminium tectosilicate minerals, also containing other cations such as sodium, calcium, potassium, or barium. The most common members of the feldspar group are the ''plagiocl ...
,
potassium Potassium is a chemical element; it has Symbol (chemistry), symbol K (from Neo-Latin ) and atomic number19. It is a silvery white metal that is soft enough to easily cut with a knife. Potassium metal reacts rapidly with atmospheric oxygen to ...
feldspar,
kaolinite Kaolinite ( ; also called kaolin) is a clay mineral, with the chemical composition Al2 Si2 O5( OH)4. It is a layered silicate mineral, with one tetrahedral sheet of silica () linked through oxygen atoms to one octahedral sheet of alumina () ...
,
pyroxene The pyroxenes (commonly abbreviated Px) are a group of important rock-forming inosilicate minerals found in many igneous and metamorphic rocks. Pyroxenes have the general formula , where X represents ions of calcium (Ca), sodium (Na), iron ( ...
,
quartz Quartz is a hard, crystalline mineral composed of silica (silicon dioxide). The Atom, atoms are linked in a continuous framework of SiO4 silicon–oxygen Tetrahedral molecular geometry, tetrahedra, with each oxygen being shared between two tet ...
and
smectite A smectite (; ; ) is a mineral mixture of various swelling sheet silicates (phyllosilicates), which have a three-layer 2:1 (TOT) structure and belong to the clay minerals. Smectites mainly consist of montmorillonite, but can often contain secon ...
.


Dating

Various radiometric dates have been obtained for the postulated Ouki paleolake from tufa, wood and fossils of
Bulimulidae Bulimulidae is a taxonomic family of medium-sized to large, air-breathing, tropical and sub-tropical land snails, terrestrial pulmonate gastropod molluscs in the superfamily Orthalicoidea.MolluscaBase eds. (2020). MolluscaBase. Bulimulidae Tryon, ...
and '' Littoridina'', mostly within the basin of Lake Poopo. There is noticeable disagreement between
radiometric Radiometry is a set of techniques for measuring electromagnetic radiation, including visible light. Radiometric techniques in optics characterize the distribution of the radiation's power in space, as opposed to photometric techniques, which ch ...
dates obtained by uranium-thorium dating and dates obtained by
radiocarbon Carbon-14, C-14, C or radiocarbon, is a radioactive isotope of carbon with an atomic nucleus containing 6 protons and 8 neutrons. Its presence in organic matter is the basis of the radiocarbon dating method pioneered by Willard Libby and coll ...
dating, probably because Ouki is so old that radiocarbon dating becomes unreliable. The former yield ages ranging between 120,000 and 98,000 years ago. The latter produce ages between 45,200 and 28,200 years ago. Radiocarbon dates of such old samples can easily suffer from contamination by modern carbon, creating spuriously young ages. The uranium-thorium dates range between 96,740 ±5,560 and 125,990 ± 9,580 years ago. The exact lake level history is poorly known, but between 115,000 and 100,000 years ago, the water was higher than elevation. The Ouki stage took place during
marine isotope stage Marine isotope stages (MIS), marine oxygen-isotope stages, or oxygen isotope stages (OIS), are alternating warm and cool periods in the Earth's paleoclimate, deduced from Oxygen isotope ratio cycle, oxygen isotope data derived from deep sea core ...
5. Episodes of increased lake size lake level changes coincide with cold periods in the
North Atlantic The Atlantic Ocean is the second largest of the world's five oceanic divisions, with an area of about . It covers approximately 17% of Earth's surface and about 24% of its water surface area. During the Age of Discovery, it was known for ...
. Alternatively, if radiocarbon dates of 44,609 ± 927 to 33,422 ± 1937 are attributed to Ouki, sediments in the Uyuni basin attributed to Lake Minchin would instead belong to Ouki.


Context

Lake Ouki's formation may have been caused by an increase in precipitation, and may be further associated with changes in the position of the ITCZ and
La Nina LA most frequently refers to Los Angeles, the second most populous city in the United States of America. La, LA, or L.A. may also refer to: Arts and entertainment Music *La (musical note), or A, the sixth note *"L.A.", a song by Elliott Smit ...
-like conditions. The increase of precipitation may have amounted to 50–100%. The Ouki lake cycle occurred during a major
glaciation A glacial period (alternatively glacial or glaciation) is an interval of time (thousands of years) within an ice age that is marked by colder temperatures and glacier advances. Interglacials, on the other hand, are periods of warmer climate be ...
that may also be recorded from
moraine A moraine is any accumulation of unconsolidated debris (regolith and Rock (geology), rock), sometimes referred to as glacial till, that occurs in both currently and formerly glaciated regions, and that has been previously carried along by a gla ...
deposits in the southern Puna, as well as at a time of low summer insolation in the southern hemisphere but with a southward expansion of the South American
monsoon A monsoon () is traditionally a seasonal reversing wind accompanied by corresponding changes in precipitation but is now used to describe seasonal changes in Atmosphere of Earth, atmospheric circulation and precipitation associated with annu ...
. Lake levels in Lake Huinaymarca, the southern basin of Lake Tauca, were low during the proposed Ouki period. Sediments in the Majes River valley indicate humid conditions during the proposed Ouki period, as do lake level records in the
Atacama The Atacama Desert () is a desert plateau located on the Pacific coast of South America, in the north of Chile. Stretching over a strip of land west of the Andes Mountains, it covers an area of , which increases to if the barren lower slopes ...
. The humid period in
Peru Peru, officially the Republic of Peru, is a country in western South America. It is bordered in the north by Ecuador and Colombia, in the east by Brazil, in the southeast by Bolivia, in the south by Chile, and in the south and west by the Pac ...
during the Ouki phase may be associated with several large
landslide Landslides, also known as landslips, rockslips or rockslides, are several forms of mass wasting that may include a wide range of ground movements, such as rockfalls, mudflows, shallow or deep-seated slope failures and debris flows. Landslides ...
s such as the
Chuquibamba Chuquibamba ( Quechua: ''Chuqipampa'', ''chuqi'' means "ore" and ''pampa'' means "plain") is a town in southern Peru, capital of the province Condesuyos in the region Arequipa Arequipa (; Aymara language, Aymara and ), also known by its nic ...
landslide complex and the Caqilluco landslides, although other researchers did not find an increase in landslide activity there. Accumulation of sediments in the
Pativilca Pativilca is a town in central Peru, capital of the district Pativilca in the province Barranca in the region Lima Lima ( ; ), founded in 1535 as the Ciudad de los Reyes (, Spanish for "City of Biblical Magi, Kings"), is the capital and la ...
valley and fluvial activity at
Lima Lima ( ; ), founded in 1535 as the Ciudad de los Reyes (, Spanish for "City of Biblical Magi, Kings"), is the capital and largest city of Peru. It is located in the valleys of the Chillón River, Chillón, Rímac River, Rímac and Lurín Rive ...
and in the
Lomas de Lachay Lachay National Reserve () is a protected area in the region of Lima Region, Lima, Peru.https://www.gob.pe/institucion/sernanp/informes-publicaciones/1718927-reserva-nacional-de-lachay Lomas de Lachay - SERNANP (in spanish) The reserve is located ...
in Peru also coincide with the Ouki humid period.


Controversy

The existence of this lake was questioned in 2011, based on the lack of evidence for such a lake in drill cores of Salar de Uyuni. It is unknown whether the Poopó basin lake extended to the Uyuni/Coipasa basins as well. The sill separating the Poopó and Uyuni/Coipasa basins may not have been breached until 80,000–60,000 years ago. In 2013, it was suggested that the "L4" lacustrine stage, which has been identified in drill cores taken from Salar de Uyuni, may be the Ouki/ Salinas lake phase.


References


Sources

* * * * * * * {{coord missing, Bolivia Geology of Bolivia Former lakes of South America Pleistocene Lakes of Bolivia Glacial lakes