Pisco Basin

Pisco Basin (Spanish: Cuenca de Pisco) is a sedimentary basin extending over 300 kilometres (190 mi) in southwestern Peru.^[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.^[2]

Pisco Basin
Cuenca de Pisco
Coordinates	14°15′S 76°0′W
Etymology	City of Pisco, Peru
Location	Western South America
Country	Peru
State(s)	Ica Region
Cities	Pisco
Characteristics
On/Offshore	Both
Part of	Circum-Pacific forearc basins
Area	300 km (190 mi)
Hydrology
Sea(s)	Eastern Pacific Ocean
River(s)	Pisco River
Geology
Basin type	Forearc basin
Orogeny	Andean
Age	Eocene–Pliocene
Stratigraphy	Stratigraphy

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.^{[2][note 1]} 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.^[3]

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^{[note 2]}

Age[2][5]	SALMA[note 3]	Units[2][5]		Environment[2][5]	Lithology[2][5][6]
Pleistocene	Uquian	Pisco		Lagoonal to near-shore	Bioclastic conglomerate, sandstone
Middle Miocene	Colloncuran
Early Miocene	Colhuehuapian	Chilcatay		Marine	Siltstone, sandstone
Late Oligocene	Deseadan
Early Oligocene Late Eocene	Tinguirirican Divisaderan	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.^[7] Late Pliocene and Pleistocene uplift of the basin may be consequence of the subduction of Nazca Ridge.^[2][8]

Sedimentary strata of the basin shows evidence for a series of marine transgressions during the last 50 million years.^[9] 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.^[9] 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.^[9]

Oligo-Miocene transgression

The marine Oligo-Miocene (25–16 Ma^[9]) marine transgression is evidenced by a series of sedimentary strata containing fossils of marine diatoms, Peruchilus snails and Pitar and Cucullaea clams.^[10] Oligo-Miocene marine environments in the Pisco Basin range from littoral to shelf.^[10] Moquegua Basin southeast of Pisco Basin appear to have been unaffected by the transgression.^[10]

Within the Andean margin contemporary marine transgressions are also known from southern Chile, Patagonia and Colombia.^[10] As such the marine transgression is thought to represent a regional phenomenon with the steadily rising central Andes being an exception.^[10]

Paleontology

Pisco Formation

Main article: Pisco Formation § Fauna

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.	[11][12] [13][14]
Birds	Palaeospheniscus sp.	[14]
Reptiles	Testudines indet.	[11]
Fish	Carcharhinus cf. brachurus, Carcharodon hastalis, Carcharodon subauriculatus, Hemipristis cf. serra, Isurus desori	[13] [15][16]

Otuma Formation

Group	Fossils	Notes
Mammals	Cynthiacetus peruvianus, Basilosauridae indet.	[17][18]
Birds	Icadyptes salasi, Inkayacu paracasensis, Spheniscidae indet.	[19][20] [21]
Fish	Engraulis sp., Sardinops sp.	[21]

Paracas Formation

Group	Fossils	Notes
Mammals	Ocucajea picklingi, Supayacetus muizoni, Basilosauridae indet., Mystacodon selenensis, Peregocetus pacificus, Perucetus colossus	[22][23] [24][25][26][27]
Birds	Perudyptes devriesi	[28]
Fish	Pristis sp., Myliobatis sp., Clupeiformes sp.	[29][25]

See also

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