Pisco Basin

Pisco Basin () is a sedimentary basin extending over in southwestern Peru.Solís Mundaca, 2018, p.1 The basin has a 2-kilometre (1.25-mile) thick sedimentary fill, which is about half the thickness of more northern foreland basins in Peru.

The oldest known sediments are the Eocene sandstones of the Caballas Formation, while the youngest deposits, the fossiliferous Pisco Formation, date to the Early Pleistocene. In relation to present-day, topography the fill of Pisco Basin makes the upper part of the Coastal Cordillera of southern Peru, the coastal plains, the Ica-Nazca Depression and the Andean foothills.León et al. 2007, p. 7.

The basin is renowned for hosting various highly fossiliferous stratigraphic units; the Pisco Formation has provided a wealth of marine mammals (including sloths), birds, fish and other groups, as have the Chilcatay, Otuma and Paracas Formations.

Stratigraphy + Stratigraphy of Pisco Basin Age SALMA UnitsDunbar et al., 1990 Environment LithologyDeVries et al., 2017León et al. 2007, p. 45. Pleistocene Uquian Pisco Lagoonal to near-shore Bioclastic conglomerate, sandstone Middle Miocene Colloncuran Early Miocene Colhuehuapian Chilcatay Marine Siltstone, sandstone Late Oligocene Deseadan Early OligoceneLate Eocene TinguiriricanDivisaderan Otuma Marine embayment Bioclastic sandstone, sandstone, silty sandstone, mudstone, dolomitic sediment Late Eocene Divisaderan Paracas Yumaque Mudrock, phosphatic shale, diatomite, porcellanite, chert Late Eocene Mustersan Los Choros Inner shelf, shoreface, intertidal Bioclastic conglomerate, sandstone, siltstone, mudrock Eocene Casamayoran Caballas Fluvial Sandstone, tuff, coal

Tectonic and sedimentary evolution The basin developed in a setting of extensional tectonics from Eocene to the Late Miocene with short-lived episode of basin inversion in the Middle Miocene.León et al. 2007, p. 146. Late Pliocene and Pleistocene uplift of the basin may be consequence of the subduction of Nazca Ridge.León et al. 2007, p. 145.

Sedimentary strata of the basin shows evidence for a series of marine transgressions during the last 50 million years.DeVries, 1998 These marine transgressions occurred in a sequence 41-34 Ma, 31-28 Ma, 25-16 Ma, 15-11 Ma, 10-5 Ma, and 4-2 Ma. The end of most of the marine transgressions is thought to be associated either with global sea level falls or compressional events in the Andes.

Oligo-Miocene transgression The marine Oligo-Miocene (25–16 Ma) marine transgression is evidenced by a series of sedimentary strata containing fossils of marine diatoms, Peruchilus snails and Pitar and Cucullaea clams.Macharé et al., 1988 Oligo-Miocene marine environments in the Pisco Basin range from littoral to shelf. Moquegua Basin southeast of Pisco Basin appear to have been unaffected by the transgression.

Within the Andean margin contemporary marine transgressions are also known from southern Chile, Patagonia and Colombia. As such the marine transgression is thought to represent a regional phenomenon with the steadily rising central Andes being an exception.

Paleontology Pisco Formation

Chilcatay Formation Group Fossils Notes Mammals Chilcacetus cavirhinus, Huaridelphis raimondii, Incacetus broggii, Inticetus vertizi, Macrosqualodelphis ukupachai, Notocetus vanbenedeni, cf. Kentriodon sp., Cetotheriidae indet., Eurhinodelphinidae indet., Mysticeti indet., Odontoceti indet., Pinnipedia indet., Physeteroidea indet., Squalodelphinidae indet. Birds Palaeospheniscus sp. Reptiles Testudines indet. Fish Carcharhinus cf. brachurus, Carcharodon hastalis, Carcharodon subauriculatus, Hemipristis cf. serra, Isurus desori

Otuma Formation Group Fossils Notes Mammals Cynthiacetus peruvianus, Basilosauridae indet. Birds Icadyptes salasi, Inkayacu paracasensis, Spheniscidae indet. Fish Engraulis sp., Sardinops sp.

Paracas Formation Group Fossils Notes Mammals Ocucajea picklingi, Supayacetus muizoni, Basilosauridae indet., Mystacodon selenensis, Peregocetus pacificus, Perucetus colossus Birds Perudyptes devriesi Fish Pristis sp., Myliobatis sp., Clupeiformes sp.

See also Arauco Basin, Chile Altiplano Basin, Peru, Chile, Bolivia Caldera Basin, Chile Cocinetas Basin, Colombia Urumaco Formation, Venezuela

Notes and references Notes

References

Bibliography

Stratigraphy

Geology publications

Paleontology publications

Further reading Chilcatay Formation

Paracas Group

Pisco Formation