Description of the stratotype section and proposal of hypostratotype section of the Lower Cretaceous Quiricó formation, São Francisco Basin, Brazil

Abstract

The Quiricó Formation presents an abundant and diversified fossil record, and is the only formation from the Cretaceous of the São Francisco basin with the occurrence of ostracodes. This formation was described from the banks of the Quiricó creek, tributary of the Prata river, which is the type locality. However, a stratotype section was not described. The present work presents the description of the stratotype section of the Quiricó Formation and proposal of hypostratotype section, based on the lithologic description and fossiliferous occurrences. The studied sections are located in the Minas Gerais State, Brazil: 1. stratotype section of the Quiricó Formation, by the banks of Quiricó and São José creeks, Presidente Olegário County; 2. hypostratotype section of the Tereza Farm, near the Olhos D’água community, João Pinheiro County.

Key words
Hypostratotype section; Ostracoda; Quiricó Formation; Stratotype section

INTRODUCTION

The Quiricó Formation was first introduced by Barbosa (1965), to designate a Continental Cretaceous succession of sandstone layers intercalated with claystone layers outcropping by the banks of the Quiricó creek, tributary of the Prata river, Minas Gerais State. Also, a type locality was stablished; however, the stratotype section was never formally described. Therefore, the present work describes the stratotype section of the Quiricó Formation, and formally proposes a hypostratotype section, following the procedures of the International Stratigraphic Guide (Salvador 1994, Murphy & Salvador 1999) and North American Commission on Stratigraphic Nomenclature (2005).

The International Stratigraphic Guide (Salvador 1994, Murphy & Salvador 1999), which was developed to promote international agreement on stratigraphic classification, states that a formal lithostratigraphic unit should have a stratotype (type section) and type locality with a clear and precise definition and characterization, in order to define the stratigraphic unit. Also, the designation of a hypostratotype section – supplementary reference section proposed after the original designation – might extend the knowledge of the lithostratigraphic unit and complement its definition (Murphy & Salvador 1999, North American Commission on Stratigraphic Nomenclature 2005). From the description of the stratotype section, a new step in stratigraphy, especially regarding advanced correlation studies, is open to be conducted in the São Francisco basin, as well as other basins of Gondwana.

Locality

The present work approaches two sections of the Quiricó Formation, from the Minas Gerais State, southeastern Brazil, which are: stratotype section of the Quiricó Formation, from the banks of the Quiricó and São José creeks, Presidente Olegário County; hypostratotype section of the Quiricó Formation from the Tereza Farm, João Pinheiro County (Fig. 1). Both Quiricó and São José creeks are confluents and tributary of the Prata river and they are very close to each other. The São José creek begins near the BR-365 and flows into the Quiricó, which then names the body of water (Fig. 2).

Figure 1
Localization map with the regional geology (modified from GeoSGB – CPRM).

Figure 2
Localization map of the stratotype section of the Quiricó Formation. The base of the section is located in the banks of the Quiricó creek and the top of the section in the banks of the São José creek. Central coordinates of the image: 23K, 386746.81 mE, 7970178.48 mN (adapted from Google Earth).

GEOLOGIC SETTINGS

The São Francisco basin is an intracratonic basin. The basement of the basin is constituted by Proterozoic sedimentary rocks, covered by Phanerozoic sedimentary rocks. The Phanerozoic cover consists of sedimentary remnants of the Permian-Carboniferous, sedimentary rocks of the Lower Cretaceous, volcanic rocks of the Upper Cretaceous, and by a plateau composed of sandstones of the Upper Cretaceous. From base to top, the stratigraphic column of the São Francisco basin was filled by four supersequences: rift, intracratonic, intracratonic-foreland and sanfranciscan (Zalán & Silva 2007)

The rift supersequence, from Paleoproterozoic to Mesoproterozoic, is constituted by the Supergroup Espinhaço. The Neoproterozoic intracratonic supersequence is constituted by the Macaúbas and Paranoá groups. The Neoproterozoic intracratonic-foreland supersequence is constituted by the Bambuí Group (Zalán & Silva 2007).

The Phanerozoic sequence of the São Francisco basin is distributed among the states of Minas Gerais, Bahia, Piauí, Tocantins, and Maranhão (Bueno 2012). From base to top, the groups are: Santa Fé, Permian-Carboniferous; Areado, Lower Cretaceous; and Mata da Corda and Urucuia, Upper Cretaceous (Fig. 3) (Campos & Do Carmo 2005, Zalán & Silva 2007). The Santa Fe Group consists of glacial records with fluvio-glacial, glacial-lacustrine and periglacial eolian facies. The Areado Group consists of sedimentary rocks, and will be approached in detail in the present work. The Mata da Corda Group is composed by volcanic pyroclastic alkaline rocks and by proximal epiclastic sedimentary rocks. The Urucuia Group is composed of sandstones of eolian origin, as well as fluvial sandstones, conglomerates and pelites (Campos & Do Carmo 2005).

Figure 3
Chronostratigraphic column representing the Phanerozoic sequence of the São Francisco basin (Do Carmo et al. 2004, adapted according to Campos & Dardenne 1997a).

The Areado Group presents a broad lateral variation of lithofacies. The formations, from base to top, are: Abaeté, Quiricó and Três Barras. The Abaeté Formation presents two distinct sedimentary contexts, in the southern portion of the basin it consists of immature matrix-supported conglomerates and in the rest of the basin it consists of mature grain-supported conglomerates. The chronostratigraphic attribution of this formation relies on the fact that the Santa Fé Group represented an important source material for the conglomerates of the Abaeté Formation; therefore, it is superimposed on the Santa Fé Group and restricted to the base of the Areado succession, not being observed in superior stratigraphic portions (Fig. 2) (Campos & Do Carmo 2005). The distribution of this formation is horizontally broad, mainly in the central-south portion of the basin, but it is not continuous. In the southern portion of the basin, the Abaeté Formation was deposited by alluvial fans, while in the rest of the basin it was deposited by interlaced river systems (Campos & Dardenne 1997a, Campos & Do Carmo 2005).

The Quiricó Formation is composed of siltstones, which occur interstratified and predominant at the base of the sequence; fine, medium and coarse sandstones in the intermediate portion; and shales and micritic limestones, more frequent in the upper part of the sequence. This is the only formation of the Areado Group in which ostracod fossils have been recovered to date. Locally, in the Presidente Olegário County, Minas Gerais State, a black papyraceous shale occurs, rich in organic matter and with the occurrence of fossil fish and leaf impressions. The chronostratigraphic position of the Quiricó Formation will be discussed below. This formation occurs interdigitated with the Três Barras Formation in the upper part of the sequence and was deposited by a lacustrine system (Campos & Dardenne 1997a, Campos & Do Carmo 2005).

The Três Barras Formation presents the largest lithological diversity and the largest volume of rocks, composed of heterogeneous sandstones (Campos & Dardenne 1997a, Campos & Do Carmo 2005). This formation presents an unconformity, dated by Mescolotti et al. (2019) as Cenomanian to Coniacian, because the lower stratigraphic unit of the Três Barras Formation interdigitates with the upper portion of the Quiricó Formation, and the upper stratigraphic unit is overlaid by the Mata da Corda Group. This unconformity separates que sedimentary succession into a lower stratigraphic unit, representing a wet eolian system, and a upper stratigraphic unit, representing a dry eolian system (Mescolotti et al. 2019). The Três Barras Formation was deposited by fluvial-deltaic and eolian fluvial systems (Campos & Dardenne 1997a, Campos & Do Carmo 2005).

State of the art on stratigraphy of the Quiricó Formation

The term Areado was first used by Rimann (1917), while studying the region of Areado, near the Mata da Corda Mountain in Minas Gerais, to indicate a succession of sandstones from 40 to 100 m, called Areado sandstone. The base consisted of conglomerates or breccia of fluvial origin, with pebbles of granite, crystalline schist, and limestones and mudstones from the Bambuí sequence, and was attributed to the Permian-Carboniferous; followed by a red and white sandstone with eolian structures, attributed to the Triassic (Rimann 1917).

Barbosa (1965) while studying the region of the Triângulo Mineiro, specifically the Mata da Corda region, found Mesozoic layers superimposed on the Bambuí Group, and after further investigation, concluded that it was the Areado sequence mentioned by Rimann (1917). Barbosa (1965) assigned the Areado sandstone as Areado Formation, and divided it into three members, from base to top: Abaeté, Quiricó and Três Barras. The ages of members Abaeté and Três Barras were not assigned. For the Quiricó Member, a Cretaceous age was admitted due to the occurrence of Dastilbe moraesi Silva Santos 1955 registered by Scorza and Silva Santos (1955), which will be herein discussed.

Later Costa & Sad (1968) upgraded the Areado Formation to the Group rank and considered the three members as formations. The same nomenclature is used by Ladeira & Alves de Brito (1968), Ladeira et al. (1971) and Grossi Sad et al. (1971). Lima (1979) downgraded the Areado Group, considering the Areado as formation, and the Abaeté, Quiricó and Três Barras as members or facies. Seer et al. (1989) used the same scheme as Lima (1979). Since the publication of papers by Campos & Dardenne (1997 a, b) the designation by Costa & Sad (1968) has been consolidated and adopted.

Biostratigraphy is the main instrument for dating rocks of the Areado Group. However, U-Pb dating in volcanic rocks from the Mata da Corda Group, superimposed on the Areado Group, indicates an age of 75 to 81 Ma, Late Cretaceous (Sgarbi et al. 2004), therefore the Areado Group is older than 81 Ma (Campanian). Nevertheless, the Areado Group still lacks absolute dating.

The chronostratigraphic position of the Quiricó Formation was first mentioned by Scorza & Silva Santos (1955), with the identification of the fish Dastilbe moraesi Silva Santos 1955 in Scorza & Silva Santos (1955), recovered from the black papyraceous shale of the Presidente Olegário region. Dastilbe moraesi Silva Santos 1955 in Scorza & Silva Santos (1955) belongs to a genus with well-preserved occurrences from the Aptian of the Araripe basin, consisting as the starting point of the systematic study of fossils of the Phanerozoic from the São Francisco basin (Bittencourt et al. 2015). Cardoso (1971) discussed the position of the Areado Group within the Mesozoic, while studying conchostracans recovered in Carmo do Paranaíba, concluding that the unit was attributed to the Upper Jurassic or Lower Cretaceous.

Another important record regarding aquatic vertebrates was the discovery of coelacanths Mawsonia Woodward in Mawson & Woodward (1907), in the Tereza Farm, João Pinheiro. The genus is typically attributed to the interval Berriasian-Valanginian-Hauterivian, and it is recorded in the Recôncavo, Tucano, Almada, Sergipe-Alagoas, Araripe, Iguatu and São Luís do Grajaú basins (Carvalho 2002, Carvalho & Maisey 2008). The studied samples probably represent a single population belonging to Mawsonia gigas Woodward in Mawson & Woodward 1907 typical of the Candeias Formation, attributed to the Local Stage Rio da Serra (Caixeta et al. 1994, Carvalho 2002, Carvalho & Maisey 2008).

Terrestrial vertebrates were first identified in the form of footprints of herbivorous ornithischian dinosaurs, and carnivorous theropod dinosaurs, in outcrops in the João Pinheiro region, composed of typical deposits of eolian dunes and temporary rivers (Carvalho & Kattah 1998) corresponding to the Três Barras Formation (Bittencourt et al. 2015).

The fossil record of the Quiricó Formation was recently revised by Bittencourt et al. (2015), which is summed up in Table 1, with an update from 2015 to the present.

Table I
Fossils from the Quiricó Formation (adapted from Bittencourt et al. 2015).

TAXA		Authors to first recover the taxa
Gymnospermae – Coniferophyta – Brachyphyllaceae	Brachyphyllum obesum Heer 1881		In Duarte (1997)
Gymnospermae – Coniferophyta – Podozamitaceae	Podozamites lanceolatus (Lindley and Hutton 1936) Braun 1843		In Duarte (1997)
Angiospermae – Nymphaeales – Nymphaeaceae	Nymphaeites choffatii (Sap.) Teixeira 1947		In Duarte (1997)
Angiospermae – Poales – Poaceae	Paraleptaspis varjensis Duarte 1997		In Duarte (1997)
Angiospermae (palynomorphs)	Deltoidospora sp.		In Lima (1979)
	Punctatasporites sp.		In Lima (1979)
	Sergipea sp.		In Lima (1979)
	Transitoripollis crisopolensis (Regali et al. 1974) emend. Dino 1994		In Lima (1979)
	Inaperturopollenites sp.		In Lima (1979)
	Araucariacites australis Cookson 1947		In Lima (1979)
	Classopollis classoides Pflug 1953		In Lima (1979)
	Classopollis torosus (Reissinger 1950)		In Lima (1979)
	Monocolpopollenites sp. 1		In Lima (1979)
	Monocolpopollenites sp. 2		In Lima (1979)
	Cycadopites sp. 1		In Lima (1979)
	Cycadopites sp. 2		In Lima (1979)
	Clavattipollenites sp.		In Lima (1979)
	Retimonocolpites sp.		In Lima (1979)
	Eucommiidites minor Groot & Penny 1960		In Lima (1979)
	Psilatricolpites psilatus Pierce 1961		In Lima (1979)
	Exesipollenites tumulus Balme 1957		In Lima (1979)
	Afropollis spp.		In Arai et al. (1995)
	Araucariacites spp.		In Arai et al. (1995)
	Bennettitaepollenites regaliae Dino 1994		In Arai et al. (1995)
	Callialasporites sp.		In Arai et al. (1995)
	Cicatricosisporites spp.		In Arai et al. (1995)
	Cicatricosisporites microstriatus Jardine & Magloire 1965		In Arai et al. (1995)
	Classopollis spp.		In Arai et al. (1995)
	Eucommiidites spp.		In Arai et al. (1995)
	Gnetaceaepollenites barghoornii Pocock 1964		In Arai et al. (1995)
	Inaperturopollenites spp.		In Arai et al. (1995)
	Leiosphaeridia spp.		In Arai et al. (1995)
	Liliacidites kiowaensis Ward 1986		In Arai et al. (1995)
	Retimonocolpites sp.		In Arai et al. (1995)
	Sergipea cf. naviformis Regali et al. 1974		In Arai et al. (1995)
	Tricolpites cf. vulgaris Pierce in Srivastava 1969		In Arai et al. (1995)
Metazoa – Arthropoda – Insecta – Heteroptera	Saucrolus silvai Santos 1971		In Santos (1971)
Metazoa – Arthropoda - Spinicaudata	Platyestheria abaetensis Cardoso 1971		In Cardoso (1971)
	Cyzicus cf. barbosai (Almeida 1950)		In Cardoso (1971)
	Palaeolimnadiopsis freybergi Cardoso 1971		In Cardoso (1971)
	Palaeolimnadiopsis cf. reali (Teixeira 1960)		In Cardoso (1971)
Metazoa – Vertebrata – Chondrichthyes – Hybodontiformes	Hybodontiformes indet.		In Carvalho & Maisey (2008)
	?Tribodus sp.		In Fragoso et al. (2019)
	Hybodontiformes indet. Morphologies 2 to 8		In Fragoso et al. (2019)
Metazoa – Vertebrata – Osteichthyes – Actinopterygii - Seminotiformes	Semionotiformes indet.		In Carvalho & Maisey (2008)
Metazoa – Vertebrata – Osteichthyes – Actinopterygii – Amiiformes	Amiidae indet.		In Carvalho & Maisey (2008)
Metazoa – Vertebrata – Osteichthyes – Actinopterygii – Gonorynchiformes	Dastilbe moraesi Santos 1955		In Scorza & Silva Santos (1955)
Metazoa – Vertebrata – Osteichthyes – Actinopterygii - Neopterygii	Gen. et sp. indet.		In Bittencourt et al. (2017)
Metazoa – Vertebrata – Osteichthyes – Actinopterygii – Osteoglossiformes	Laeliichthys ancestralis Santos 1985		In Santos (1985)
Metazoa – Vertebrata – Osteichthyes – Sarcopterygii – Coelacanthiformes	Mawsonia gigas Woodward 1907		In Carvalho & Maisey (2008)
Metazoa – Vertebrata – Osteichthyes – Sarcopterygii – Dinosauria - Sauropoda	Tapuiasaurus macedoi Zaher et al. 2010		In Zaher et al. (2011)
	Rebbachisauridae		In Carvalho & Santucci (2018)
Metazoa – Vertebrata – Osteichthyes – Sarcopterygii – Dinosauria – Theropoda	Abelisauroidae indet.		In Zaher et al. (2011)
	Nosauridae		In Silva (2013)
	cf. Carcharodontosauridae		In Carvalho & Santucci (2018)
	Abelisauridae		In Carvalho & Santucci (2018)

Barbosa et al. (1970), while studying the occurrences of the Areado Group in the regions of Patos de Minas and Carmo do Paranaíba, Minas Gerais State, recovered ostracods, charophytes and bone fragments. They determined that the ostracod fauna corresponded to that found in the Santana Formation, attributing an Aptian-Albian chronostratigraphic interval to the Quiricó Formation. Additionally, palynological studies by PETROBRAS on the black papyraceous shale from the Presidente Olegário region indicated a lower Aptian age (Barbosa et al. 1970). Lima (1979) identified the Transitoripollis crisopolensis Palynozone, coded as P-230, corroborated by Arai et al. (1995), which attributed the papyraceous shale to the Barremian(Campos & Do Carmo 2005).

The detailed taxonomy of ostracods was first approached by Do Carmo et al. (2004), who identified 15 distinct species, all of them limnic. Wolburgiopsis plastica (Musacchio 1970) and Wolburgiopsis chinamuertensis (Musacchio 1970) recovered from the São Bento Farm (Carmo do Paranaíba County), occur in the Barremian of Argentina, attributing the base of the Quiricó Formation in this section to the Barremian and the Quiricó Formation to the Barremian-Aptian interval (Do Carmo et al. 2004).

Leite et al. (2018) detailed the ostracod taxonomy from the stratotype section of the Quiricó Formation and the Tereza Farm (Fig. 1), and identified 20 species, all limnic. Cypridea hystrix Krömmelbein 1962, recovered at the Tereza Farm, occurs in the Paracypridea brasiliensis Zone (NRT-O04), subzones Paracypridea bicallosa (NRT-O04.3) and Paracypridea maacki (NRT-O04.4) (Viana et al. 1971, Cunha & Moura 1979, Regali & Viana 1989), Rio da Serra Local Stage (Caixeta et al. 1994), attributing the base of the Tereza Farm to the Valanginian. Coimbra (2020), from the analysis of figures and descriptions from Leite et al. (2018), concluded that all Cypridea species were erroneously identified, and, therefore, the attribution of the base of the Quiricó Formation to the Valanginian would be incorrect. Additionally, to Coimbra (op. cit.), these Cypridea species would be new taxa. Considering Leite et al. (2018), position followed herein, if someone compared the original description of these four species, would observe that the material recovered from the Quiricó Formation yield all characteristics to identify Cypridea hystrix Krömmelbein 1962, Cypridea conjugata Krömmelbein & Weber 1971, Cypridea infima Krömmelbein & Weber 1971 and Cypridea jequiensis Krömmelbein & Weber 1971.

A total of 27 species were recovered for the Quiricó Formation so far (Tab. 2). Of those, 18 species occur in other basins from Brazil, South America and Africa. Especially Penthesilenula pintoi Leite et al. 2018, Alicenula longiformis Leite et al. 2018 and Timiriasevia sanfranciscanensis Leite et al. 2018, were proposed from the Quiricó Formation, and until now, seem to be restricted to this formation. Therefore, their stratigraphic distribution contemplates only their occurrence in the formation in question.

MATERIALS AND METHODS

The study in the São Francisco basin, aiming the description of stratotype section and hypostratotype section began in Leite (2017). Field campaigns were performed between the years of 2015 and 2018. From these fieldtrips, the main outcrops of the Quiricó Formation were identified (Fig. 1). Lithostratigraphic columns were elaborated for each section, presenting fossiliferous intervals and detailed sampling. The classification of lithofacies based on their primary depositional attributes follows Miall (1996), regarding bedding, grain size, texture and sedimentary structures, as well as biogenic structures and fossils.

The stratotype section of the Quiricó Formation was first studied on the taxonomy perspective by Leite et al. (2018), but was initially identified as the outcrop of the São José Farm by the banks of the São José creek. Later, it was concluded that this outcrop extends to the banks of the Quiricó creek, consisting of a complete section of the Areado Group and thus composing the stratotype section of the Quiricó Formation.

Description of the stratotype section

The stratotype section of the Quiricó Formation begins in the banks of the Quiricó creek, where the base of the section is, and after approximately 5 km extends to banks of the São José creek, where the top of the section is, Presidente Olegário County, Minas Gerais State, southeastern of Brazil (Fig. 1, 2). The coordinates of the section (UTM), Datum WGS84, are: for the base of the section, 23K, 382425.00 mE, 7972508.00 mN; for the top of the section, 23K, 387776.00 mE, 7968917.00 mN. The three formations of the Areado Group – Abaeté, Quiricó and Três Barras –, as well as the Santa Fé Group outcrop in this locality (Fig. 4, 5).

Figure 4
Lithostratigraphy of the Areado Group in the stratotype section of the Quiricó Formation, Presidente Olegário County, Minas Gerais State, Brazil. First part of the profile, from 0 m to 34 m. a) conglomerate of the Abaeté Formation. b) layers of fine sandstone intercalated with thin layers of calcite. c) layers of fine sandstone intercalated with thin layers of calcite. d) layers of fine sandstone with claystone lenses. e) surface with desert roses.

In this area, specifically in the banks of the Quiricó creek, the Quiricó Formation rests conformably over conglomerates and sandstones with limestone nodules (Fig 4a) of the Abaeté Formation, 5 m thick, which in turn is in erosional contact with friable red sandstones of the Permian-Carboniferous Santa Fé Group, formation unidentified, approximately 4 m thick. In the banks of the São José creek, the Quiricó Formation, about 63 m thick, is in conformable contact with fine/medium red sandstones, with thin layers of chert up to 1 cm thick, of the Três Barras Formation, at least 30 m thick.

As for the description of the Quiricó Formation, the lithostratigraphic sequence, from base to top, is: fine red sandstone with carbonate cement, intercalated with thin layers of limestone (Fig. 4b, 4c); red-yellow sandstone with carbonate cement, with claystone lenses (Fig. 4d), intercalated with layers of evaporite with desert roses and ostracod occurrence (Fig. 4e); layers of pelite; fine red sandstone with carbonate cement, with claystone lenses, intercalated with claystone layers, with ostracod occurrence; black shale, rich in organic matter; green laminated pelite with claystone lenses, intercalated with thin layers of evaporite and mud cracks (Fig. 5f); finely laminated sandstone with clay blades, intercalated with fine red sandstone with carbonate cement; rhythmite, composed by layers of sandstone and layers of pelite, with mud cracks, ostracod and conchostacans occurrence in the top portion (Fig. 5g).

Figure 5
Lithostratigraphy of the Areado Group in the stratotype of the Quiricó Formation, Presidente Olegário County, Minas Gerais State, Brazil Second part of the profile, from 34 m to 102 m. f) layer with mud cracks. g) rhythmite package.

Description hypostratotype section from the tereza farm

The hypostratotype section of the Tereza Farm is located near the Santa Luzia da Serra community, João Pinheiro County, Minas Gerais State, southeastern Brazil (Fig. 1). The coordinates of the section (UTM), Datum WGS84, are: 23K, 403859.00mE, 8050999.00mN. The three formations of the Areado Group – Abaeté, Quiricó and Três Barras –, as well as the Serra da Saudade Formation, Bambuí Group, outcrop in this locality (Fig. 6).

Figure 6
Lithology of the Areado Group in the hypostratotype section of the Tereza Farm, João Pinheiro County, Minas Gerais State, Brazil. a) microconglomerate overlaid by sandstone. b) very fine sandstone intercalated with laminated siltstone. c) bioturbation. d) sandstone with cross-bedding.

In this area, the Quiricó Formation rests conformably over matrix-supported conglomerates of the Abaeté Formation, a few centimeters thick, which in turn is in erosional contact (disconformity) with grey micaceous metasiltite of the Neoproterozoic Serra da Saudade Formation, with thickness undefined. In the upper portion of the outcrop, the Quiricó Formation, about 29 m thick, is in conformable contact with poorly selected, coarse/very coarse kaolinitic sandstones, of the Três Barras Formation (Fig. 6d).

As for the description of the Quiricó Formation, the lithostratigraphic sequence, from base to top, is: red-brown siltstones with grains of medium sand scattered on the matrix and lenses of fine sandstone, intercalated with a thin layer of poorly selected very fine/coarse sandstone, with ostracod occurrence; fine red sandstone with carbonate cement, with milimetric layers of grey sandstone, with conchostracans, ostracods, vertebrate bones and bioturbation; siltstone with carbonate cement, with scattered grains of sand; poorly selected, very fine/coarse sandstone, with vertebrate bones and mollusks, in erosive contact with a gray conglomerate; compact sandstone with trough cross-bedding; fine sandstone with cross-bedding (Fig. 6a); poorly selected, very fine/coarse sandstone, with carbonate cement, vertebrate bones, leaves, bioturbations and ostracods; microconglomerate with carbonate cement, with matrix of silt size, and pebbles, and a thin layer of fine gray fossiliferous sandstone with carbonate cement; red claystone, with conchostracans, ostracods, bioturbations and impressions of fish scales; finely laminated sandstone with carbonate cement, with milimetric layers of claystone, and very thin layers of very fine sandstone at the top, with ostracods and vertebrate bones; finely laminated siltstone, with milimetric to centimetric layers of fine sandstone, with ostracod occurrence; laminated sandstone with carbonate cement, with ripple marks (Fig. 6b); fine yellow sandstone with carbonate cement, with vertebrate bones and ostracods; red claystone with carbonate cement, rich in ostracods and bioturbations; fine red sandstone with carbonate cement, with centimetric calcite-filled bioturbations (Fig. 6c); compact yellow siltstone with carbonate cement, with sand grains scattered in the base and ostracod occurrence; finely laminated sandstone, with thin claystone layers, with stromatolites at the top; fine compact sandstone; siltstone with sand grains scattered; laminated sandstone with grains of coarse sand.

CONCLUSIONS

The stratotype section of the Quiricó Formation is herein formally described for the first time, along with a description of hypostratotype section, located in the Minas Gerais State, southeast Brazil: 1. Stratotype section located at the banks of the Quiricó and São José creeks, Presidente Olegário County; 2. hypostratotype section from the Tereza Farm, João Pinheiro County. The designation of the Tereza Farm section as hypostratotype section complements the lithostratigraphic and chronostratigraphic definition of the stratotype section, due to the abundant fossiliferous occurrence and well exposed and complete sedimentary sequence. With the biostratigraphic framework illustrated in Tables I and II, the description of the stratotype section originally designated by Barbosa (1965) and the formal proposal of a hypostratotype section, the complete characterization of the Quiricó Formation is achieved. The dating of the Quiricó Formation is based on biostratigraphy, and although fish and ostracod occurrences in the Tereza Farm seem to indicate a Valanginian age for the base of the section, due to controversies regarding ostracod taxonomy, the age of the Quiricó Formation remains to be reevaluated considering new fossil record and isotopic dating.

Table II
Geographic and stratigraphic distribution of ostracod species from the Quiricó Formation.

Specimen	Geographic distribution	Stratigraphic distribution
Harbinia sp. 1	São Francisco basin, Quiricó Formation (Do Carmo et al. 2004)	Barremian
Harbinia sp. 2	Africa, Gabon basin, Mediéla Formation (Grosdidier 1979) São Francisco basin, Quiricó Formation (Do Carmo et al. 2004)	Upper Aptian Barremian
Harbinia aff. Harbinia angulata (Krömmelbein & Weber 1971)	Sergipe-Alagoas basin, Riachuelo Formation (Krömmelbein & Weber 1971) Araripe basin, Santana Formation, Romualdo Formation (Poropat & Colin 2012) Cedro basin, in strata correlated to the Crato Formation (Tomé 2007) Jatobá basin, Serra Negra (Tomé et al. 2014) São Francisco basin, Quiricó Formation (Leite et al. 2018)	Upper Aptian Aptian Aptian Upper Aptian Barremian-Aptian
Harbinia symmetrica (Krömmelbein & Weber 1971)	Parnaíba basin, Codó Formation (Krömmelbein & Weber 1971, Ramos et al. 2006) Araripe basin, Santana Formation, Crato, Ipubi and Romualdo members, and Rio da Batateira Formation (Coimbra et al. 2002, Ramos et al. 2006, Antonietto 2010) África, Congo, Gabão and Angola basins (Bate 1999) São Francisco basin, Quiricó Formation (Leite et al. 2018)	Upper Aptian Aptian Barremian Aptian
Harbinia aff. Harbinia salitrensis (Krömmelbein & Weber 1971)	Araripe basin, Santana Formation, Romualdo Member (Krömmelbein & Weber 1971, Antonietto et al. 2012, Poropat & Colin 2012, Tomé et al. 2014) Grajaú basin, Codó Formation (Do Carmo et al. 2008) São Francisco basin, Quiricó Formation (Leite et al. 2018)	Aptian Aptian Aptian
Harbinia alta Antonietto et al. 2012	Grajaú basin, Codó Formation (Ramos et al. 2006, Do Carmo et al. 2008) Araripe basin, Santana Formation, Crato e Romualdo members (Viana et al. 1989, Silva-Telles Jr. & Viana 1990) Potiguar basin, Alagamar Formation (Do Carmo et al. 2013) Jatobá basin, Serra Negra (Tomé et al. 2014) São Francisco basin, Quiricó Formation (Leite et al. 2018)	Upper Aptian Aptian-Albian Medium-Upper Aptian Upper Aptian Aptian
Harbinia aff. Harbinia crepata Do Carmo et al. 2013	Araripe basin, Santana Formation, Crato Member (Silva-Telles Jr. & Viana 1990) Potiguar basin, Alagamar Formation (Do Carmo et al. 2013) São Francisco basin, Quiricó Formation (Leite et al. 2018)	Aptian Medium-upper Aptian Barremian-Aptian
Brasacypris sp. 1	São Francisco basin, Quiricó Formation (Do Carmo et al. 2004)	Barremian
Brasacypris ovum Krömmelbein 1965b emend. Leite et al. 2018	Tucano basin, Itaparica and Candeias Formation (Krömmelbein 1965) São Francisco basin, Quiricó Formation (Leite et al. 2018)	Lower Cretaceous, Berriasian Lower Cretaceous, Valanginian to Aptian
Brasacypris fulfaroi Dias-Brito et al. 2001	Paraná basin, Bauru Group, Adamantina Formation (Dias-Brito et al. 2001) São Francisco basin, Quiricó Formation (Leite et al. 2018)	Upper Cretaceous Lower Cretaceous, Valanginian to Barremian?
Ilyocypris sp. 1	São Francisco basin, Quiricó Formation (Do Carmo et al. 2004)	Barremian
Cypridea hystrix Krömmelbein 1962 emend . Leite et al. 2018	Recôncavo basin, Ilhas Formation, Rio da Serra Stage (Krömmelbein 1962, Poropat & Colin 2012) São Francisco basin, Quiricó Formation (Leite et al. 2018)	Lower Cretaceous, Berriasian to Valanginian Lower Cretaceous, Valanginian
Cypridea conjugata Krömmelbein & Weber 1971 emend . Leite et al. 2018	Recôncavo basin, São Sebastião Formation (Krömmelbein & Weber 1971, Poropat & Colin 2012) São Francisco basin, Quiricó Formation (Leite et al. 2018)	Lower Cretaceous, Barremian Lower Cretaceous, Valanginian
Cypridea infima Krömmelbein & Weber, 1971 emend . Leite et al. 2018	Recôncavo basin, Formação Candeias, porção média e inferior (Krömmelbein & Weber 1971, Poropat & Colin 2012) São Francisco basin, Formação Quiricó (Leite et al. 2018)	Lower Cretaceous, Berriasian Lower Cretaceous, Valanginian to Aptian?
Cypridea jequiensis Krömmelbein & Weber, 1971	Sergipe-Alagoas basin, Jiquiá Formation, Post Bahia Series (Krömmelbein & Weber 1971, Poropat & Colin 2012, Antonietto 2015) São Francisco basin, Quiricó Formation (Leite et al. 2018)	Lower Cretaceous, Barremian-Aptian Lower Cretaceous, Valanginian
Cypridea sp. 1	São Francisco basin, Quiricó Formation (Do Carmo et al. 2004)	Barremian
Bisulcocypridea ? sp. 1	São Francisco basin, Quiricó Formation (Do Carmo et al. 2004)	Barremian
Neuquenocypris ( Protoneuquenocypris ) antiqua Musacchio & Simeoni 1991	D-129 Formation, Chenques hill, Chubut Province (Musacchio & Simeoni 1991, Ballent et al. 2011) Austral basin, Piedra Clavada Formation, Santa Cruz (Ballent et al. 2011) São Francisco basin, Quiricó Formation (Leite et al. 2018)	Aptian Lower-upper Albian Valanginian
Darwinula sp. 1	Argentina, Chubut Group, Fortím hill Formation, Barcino hill Member (Musacchio & Chebli 1975) São Francisco basin, Quiricó Formation (Do Carmo et al. 2004)	Lower Cretaceous (Aptian?) Barremian
Darwinula sp. 2	São Francisco basin, Quiricó Formation (Do Carmo et al. 2004)	Barremian
Darwinula sp. 3	São Francisco basin, Quiricó Formation (Do Carmo et al. 2004)	Barremian
Penthesilenula martinsi (Silva 1978) emend. Do Carmo et al. 2004	Araripe basin, Santana Formation, Crato Member and base of the Ipubi Member (Silva 1978, Silva-Telles Jr. & Viana 1990, Colin & Dépêche 1997) Potiguar basin, Alagamar Formation (Do Carmo et al. 2013) São Francisco basin, Quiricó Formation (Leite et al. 2018)	Aptian Medium to upper Aptian Lower Cretaceous, Valanginian-Barremian
Penthesilenula pintoi Leite et al. 2018	São Francisco basin, Quiricó Formation (Leite et al. 2018)	Lower Cretaceous, Valanginian-Aptian
Alicenula longiformis Leite et al. 2018	São Francisco basin, Formação Quiricó (Leite et al. 2018)	Lower Cretaceous, Valanginian-Barremian?
Timiriasevia sanfranciscanensis Leite et al. 2018	São Francisco basin, Quiricó Formation (Leite et al. 2018)	Lower Cretaceous, Valanginian
Wolburgiopsis plastica (Musacchio 1970)	Argentina, Neuquén Province, La Amarga Formation (Musacchio 1970) São Francisco basin, Quiricó Formation (Do Carmo et al. 2004)	Barremian Barremian
Wolburgiopsis chinamuertensis (Musacchio 1970)	Argentina, Neuquén Province, La Amarga Formation, “Margas y Calizas” Member (Musacchio 1970) São Francisco basin, Quiricó Formation (Do Carmo et al. 2004)	Barremian Barremian

ACKNOWLEDGMENTS

The authors would like to thank Dr. Rodrigo R. Adorno, M.Sc. Matheus Denezine, M.Sc. Guilherme M. Caixeta, Lívio R. de Oliveira Gonçalves and Arthur S. Reis, for their great contribution during fieldtrips. Special thanks to M.Sc. Caio B. Ress, for his work on the localization map. Special thanks to Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq), for providing the Doctorate scholarship; to Coordenação de Aperfeiçoamento de Pessoal de Nível Superior – Brasil (CAPES), for the access to the periodical’s portal; to “Fundação de Apoio à Pesquisa do Distrito Federal” FAPDF, Project nº 0193.000.811/2015 and for the Masters’ Degree scholarship; and a special thanks to Mr. Edio Braga, from the Varjão County, for introducing the area of the stratotype section of the Quiricó Formation.

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Publication Dates

• Publication in this collection
  01 Dec 2021
• Date of issue
  2021

History

• Received
  19 Aug 2020
• Accepted
  8 Aug 2021