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Araripe Basin
Araripe Basin
Bacia do Araripe
	Geologic map of the Araripe Basin
	Outline of the Chapada do Araripe in the basin
Coordinates	7°23′12″S 40°9′11″W / 7.38667°S 40.15306°W
Etymology	Chapada do Araripe
Location	South America
Region	Northeast
Country	Brazil
State(s)	Ceará, Pernambuco, Piauí
Cities	Crato, Ceará
Characteristics
On/Offshore	Onshore
Boundaries	Patos & Pernambuco lineaments
Part of	Brazilian onshore basins
Area	~8,000 km2 (3,100 sq mi)
Geology
Basin type	Rift basin
Plate	South American
Orogeny	Break-up of Gondwana
Age	Middle Jurassic-Albian
Stratigraphy	Stratigraphy

The Araripe Basin (Portuguese: Bacia do Araripe) is a rift basin covering about 8,000 square kilometres (3,100 sq mi),^[1] in Ceará, Piauí and Pernambuco states of northeastern Brazil. It is bounded by the Patos and Pernambuco lineaments,^[2] and is situated east of the Parnaíba Basin, southwest of the Rio do Peixe Basin and northwest of the Tucano and Jatobá Basins.^[3]

The basin has provided a variety of unique fossils in the Crato and Santana Formations and includes the Araripe Geopark, a member of the UNESCO Global Geoparks since 2006.^[4] The pterosaurs Araripesaurus and Araripedactylus (now considered a nomen dubium), crocodylian Araripesuchus, the turtle Araripemys, amphibian Arariphrynus, the fish Araripelepidotes and the insect Araripenymphes were named after the basin. The bituminous shales of the Ipubi Formation in the Araripe Basin have potential for shale gas development.^[5]

Basin history

The tectono-sedimentary evolution of the Araripe Basin, located in the Borborema Geologic Province, encompasses four stages, with five tectonostratigraphic phases:^[6]
1) Syneclise phase - Silurian to Devonian - characterized by tectonic quiescence in the Borborema Province. It is represented by the deposits of the Cariri Formation, that include medium to coarse-grained quartz sandstones, locally conglomeratic, deposited in large braided fluvial systems
2) Pre-rift phase - Tithonian - characterized by the mechanical subsidence due to lithosphere thinning that preceded the rift. It is represented by the Brejo Santo Formation, that comprises red shales and claystones, and the Missão Velha Formation, constituted by medium to coarse-grained quartz-feldspathic sandstones, locally conglomeratic, that contains entire trunks and fragments of silicified wood (Dadoxilon benderi) conifer
3) Rift phase - Berriasian to Hauterivian - characterized by increasing mechanical subsidence that created a system of grabens and half grabens. It is represented by the Abaiara Formation, that includes shales, siltstones, sandstones and conglomerates
4) Post-Rift I phase - Aptian to Albian - characterized by thermal subsidence. The lowermost unit Barbalha Formation, represents a fluviolacustrine phase and is composed of red and gray shales, siltstones and claystones.

The Santana Group was formed during this stage and comprises three stratigraphic units:

Crato Formation that is composed of six intervals of laminated limestones (C1 to C6), interbedded with calciferous siltstones and marls, and is very rich in fossils of vertebrate and invertebrate organisms
Ipubi Formation, that is mainly composed of organic-rich, black greenish bituminous shales, claystones and algal limestones that are interbedded with gypsum-anhydrite beds
Romualdo Formation, that represents a calciferous siliciclastic succession composed of fine to medium-grained sandstones, argillaceous siltstones, calciferous shales, and limestones, very rich in fossils. This formation recorded the marine proto-Atlantic incursion that involved the Araripe Basin, and other interior basins and created a large seaway throughout the Borborema Province during the Albian

5) Post-rift II phase - Albian to Cenomanian - characterized by a major sag phase, and is formed by two stratigraphic units:

Araripina Formation, that occurs in the western region of the basin and is composed by rhythmites and heterolithic layers of reddish, purplish and yellowish fine-grained sandstone and mudstone
Exu Formation, that comprises medium-to coarse grained sandstones, fine grained clayey sandstones and local conglomeratic beds

Stratigraphy

Age	Group	Formation	Sequence	Notes
Cenozoic	alluvium
Albian	Araripe	Exu	Post-rift	^[7]^[8]
		Arajara		^[7]^[8]
		Araripina		^[9]
Albian Aptian	Santana	Romualdo		^[8]
		Ipubi		^[8]^[10]
		Crato		^[7]^[8]
	Araripe	Barbalha/Rio da Batateira		^[7]^[8]^[9]
Early Cretaceous	Vale do Carirí	Abaiara	Pre- and syn-rift	^[8]^[9]
Early Cretaceous		Missão Velha		^[7]^[8]^[9]
Late Jurassic		Missão Velha
Late Jurassic		Brejo Santo
Middle Jurassic		Brejo Santo
Early Jurassic	hiatus
Triassic
Permian
Carboniferous
Devonian	Paleozoic sequence	Mauriti Mucuri	Pre-rift
Silurian	Paleozoic sequence	Mauriti Mucuri	Pre-rift
Ordovician	hiatus
Cambrian	hiatus
Precambrian	Basement

References

^ Neto et al., 2013, p.1
^ Bianca Carvalho Vieira; André Salgado; Leonardo Santos (2015-03-05). Landscapes and Landforms of Brazil. Springer. p. 232. ISBN 9789401780230.
^ Assine, 1992, p.290
^ (in Portuguese) Chapada do Araripe vira parque geológico
^ Neto et al., 2013, p.3
^ Fabin et al., 2018, pp.2051-2052
^ ^a ^b ^c ^d Bétard et al., 2017, p.10
^ ^a ^b ^c ^d ^e ^f ^g Assine, 1992, p.291
^ ^a ^b ^c ^d Scherer et al., 2013, p.28
^ Ribeiro et al., 2011, p.62