Ostracoda and foraminifera from Paleocene ( Olinda well ) , Paraíba Basin , Brazilian Northeast

Paleocene ostracods and planktonic foraminifera from the Maria Farinha Formation, Paraíba Basin, are herein presented. Eleven ostracod species were identified in the genera Cytherella Jones, Cytherelloidea Alexander, Eocytheropteron Alexander, Semicytherura Wagner, Paracosta Siddiqui, Buntonia Howe, Soudanella Apostolescu, Leguminocythereis Howe and, probably, Pataviella Liebau. The planktonic foraminifera are represented by the genera Guembelitria Cushman, Parvularugoglobigerina Hofker, Woodringina Loeblich and Tappan, Heterohelix Ehrenberg, Zeauvigerina Finlay, Muricohedbergella Huber and Leckie, and Praemurica Olsson, Hemleben, Berggren and Liu. The ostracods and foraminifera analyzed indicate an inner shelf paleoenvironment for the studied section. Blooms of Guembelitria spp., which indicate either shallow environments or upwelling zones, were also recorded reinforcing previous paleoenvironmental interpretations based on other fossil groups for this basin.


INTRODUCTION
The Paraíba Basin, located in northeastern Brazilian, is well known for its remarkable paleontological content, and by a rather continuous and exposed record of the Cretaceous-Paleogene (K-Pg) boundary.The Upper Cretaceous (Maastrichtian) deposits of this basin constitute the Gramame Formation, while the Paleogene ones are included in the Maria Farinha Formation.The Gramame Formation is characterized by deposits of both calcareous marl and marl without siliciclastic influence deposited in a high energy shallow platform environment under low to moderate action of periodic storms.The overlying Maria Farinha Formation is composed also of calcareous marl, as well as marls with more siliciclastic influence (see Barbosa et al. 2006 and references therein).
The interval between the end of Cretaceous and the beginning of Paleogene was characterized ENELISE K. PIOVESAN et al. by several catastrophic events that caused the extinction of a significant part of the biota and the emergence of new lineages.Many hypotheses have been proposed as the main triggers of those changes.According to one of them, the impact of an asteroid would have been the causal factor of the mass extinctions (Alvarez et al. 1980).In another hypothesis, proposed by Courtillot et al. (1986), the extinction would have been caused by the intense volcanism in Deccan, India (the so-called Deccan traps), which caused huge continental flows of basalt (CFB) associated with the large igneous regions.More recently Keller et al. (2003) and Keller (2014) sustained that these changes in the Earth were caused by several events acting simultaneously.
According to Birch et al. (2016), the coherence of terrestrial and marine proxy data is especially strong with regard to warming beginning near 65.9-66.0Ma, a peak of warming from 65.8 to 65.6 Ma, and cooling immediately before the K-Pg, and the authors interpret these as climate shifts of global extent.Based on paleontological data, Ashrof and Stinnesbeck (1989), suggested important climatic changes from tropical to subtropical conditions during the Maastrichtian to a subtropical to temperate conditions during the Paleocene in the Paraíba Basin.Oxygen isotope data corroborate this interpretation, showing a slight increase of temperature during the Cretaceous-Paleogene transition, followed by a slight temperature decrease in the Paraíba Basin (Nascimento et al. 2011).The Paleogene deposits of the Paraíba Basin are interpreted as shallow marine environments connected with a regressive event (lowstand system tract) (e.g., Mabesoone et al. 1991, Barbosa et al. 2003, 2006, Fauth et al. 2005, Córdoba et al. 2007).This event is interpreted as a regression forced by the combination of eustatic sea level fall (Haq 2014) and local rising tectonic processes (Barbosa et al. 2003).Due to the regression, the strata of the Maria Farinha Formation were preserved only in a narrow belt along the coast.
The Maria Farinha Formation holds abundant and well-preserved microfossil assemblages, including calcareous nannofossils, foraminifers, palynomorphs and ostracods.The first study on Paleogene ostracods of the Paraíba Basin was carried out by Tinoco (1967), who reported the occurrence of the marine genera Cytherella Jones, Costa Neviani, Cytheretta Muller, Bairdia M'Coy, Monoceratina Roth, Cytheropteron Sars, Pontocythere Dubowsky and Paracypris Sars.Stinnesbeck and Reyment (1988) reported that the ostracod assemblages in the Maria Farinha Formation contain rare but wellpreserved Brachycythere sp., Dahomeya sp. and Soudanella laciniosa Apostolescu 1961.A more comprehensive study, carried out by Fauth et al. (2005), reported abundant and diverse ostracod assemblages composed of 17 species, with three of them described as new.According to Fauth (2002), the Paleocene ostracod fauna has strong affinities with north, central and southern of South America, and west, north and central Africa.
The main purpose of this article is to present the microfossil assemblages (Foraminifera and Ostracoda) from the Olinda well, Paraíba Basin, in order to contribute to the taxonomic, stratigraphic and paleoenvironmental knowledge of the Maria Farinha Formation, and provide additional data on the geological evolution of this basin in the Paleocene.

STUDY AREA AND GEOLOGICAL SETTING
The geological evolution of eastern Brazilian sedimentary basins is related to the breakup of the western Gondwana supercontinent and development of the South Atlantic Ocean in the Late Jurassic-Early Cretaceous (Cainelli andMohriak 1999, Mohriak et al. 2008).The onshore and offshore areas of the Paraíba Basin comprise approximately 7600 km 2 and 31400 km 2 , respectively, extending to the isobath of 3000 m.The south limit of this basin in the coastal zone is the Pernambuco Shear Zone (ZCPE), and the north limit is the Patos Shear Zone (ZCPA) (Fig. 1).
The tectonism that originated and shaped the Paraíba Basin generated two depocenters that split the basin into the Olinda Sub-basin and the Alhandra/ Miriri Sub-basin.The first one is bordered in the south by the Pernambuco Shear Zone (ZCPE), and in the north with the Alhandra/Miriri Sub-basin by the Goiania High.The Alhandra/Miriri is limited in the north by the Mamanguape Fault (Mabesoone and Alheiros 1988, 1993, Barbosa et al. 2003).
The evolution of the Olinda Sub-basin is characterized by three tectonic phases.The first phase is represented by the opening and emergence of a rift (NW-SE) in the distal portion of the subbasin.Subsequently, a distensive phase (NE-SW) was set up with the formation of valleys and filled by clastic wedges.Finally, in the third phase (Paleogene), the NW-SE structures were reactivated, influencing the limestone deposits.
The sedimentary deposits of the Paraíba Basin consist of a continental-transitional sequence (Beberibe and Itamaracá formations) including the Coniacian?-Campanianinterval, a marine sequence (Itamaracá, Gramame and Maria Farinha formations) deposited in the Campanian-Paleocene (Lima Filho et al. 1998, Barbosa et al. 2003), a restricted reef-lagoon (Tambaba Formation), corresponding to the Eocene (Correia Filho et al. 2015), and finally the continental siliciclastic sequence (Miocene-Recent) represented by the Barreiras Formation and recent deposits.
The Maria Farinha Formation overlies the Gramame Formation and is underlain by an erosional contact (Albertão and Martins 1996).It was deposited in a deep-middle neritic environment, and its lithology changes from limestone in the base to siliciclastic (shales) in the upper portion.According to Barbosa et al. (2006) this lithostratigraphic unit is restricted to the Olinda Sub-basin (south part of the Paraíba Basin) due to the tectonically forced regression that influenced the deposition in the Paleocene in the north Alhandra/Miriri Sub-basin.

MATERIALS AND METHODS
The studied material consists of 16 samples collected along a stratigraphical interval of 8.05 m of the Olinda well.This core was drilled by the Universidade Federal de Pernambuco (UFPE) near the Poty quarry, in Olinda City, Pernambuco State (UTM 0296669E 9116303N) (Fig. 1).In the lower portion, it consists mostly of limestone and, in the upper, the incidence of siliciclastic rocks is higher.For this study, samples were chosen from the Paleocene, which was correlated using the distribution of the ostracod fauna of Fauth et al. (2005) and the international foraminiferal biostratigraphical framework by Gradstein et al. (2012).ENELISE K. PIOVESAN et al.
The analyzed section (39.15 m-31.35m) is represented by limestone with lithologic variations.In the base of the section (38.15m-38.05m),grayish conglomeratic limestone predominates and show the presence of bioturbation, sparse sedimentary structures and intraclasts.Near to the base (38.97 m), there is a thin clay layer.In the middle (38.05 m-33.96m) beige marl predominates and contain in the lower to middle part dark clay layers (37.1 m, 37.0 m, 36.7 m and 35.5 m), and in the middle to upper part the occurrence of convolution (postdepositional processes, slumps?) sparse intraclasts and bioclasts.The top of the section presents interspersed layers of grayish marly limestone and dark gray marl.There are records of sedimentary structures and intraclasts.At 33.1 m depth is a rich layer of bioclasts.Bioturbation was registered along all the section.
The samples were prepared according to the usual techniques for calcareous microfossils, which consist basically in an overnight soaking in hydrogen peroxide P.A. (H 2 O 2 ), washing over a 0.062 mm sieve and H 2 O 2 under heat for 2 hours.Afterwards, the samples were split into three meshes (0.250, 0.180 and 0.062 mm) and dried at 60°C.All ostracods and foraminifera from the three fractions were picked.Whenever necessary, the specimens were cleaned in ultrasonic baths for a few minutes before being imaged under a scanning electron microscope (SEM).The figured specimens are deposited at the collections of the Departamento de Geologia, Universidade Federal de Pernambuco, under the prefix DGEO-CTG-UFPE followed by their respective catalogue numbers.
Remarks: Cytherella piacabucuensis is a good stratigraphic marker for Paleogene strata in Brazilian and African Basins.Occurrence: Olinda well, 38.85-39.15m.Remarks: This species differs from other Cytherella species recorded in the Paraíba Basin in the more angular posterodorsal outline, in the punctuation pattern and in the stronger overlap of the RV, along all margins.Cytherella piacabucuensis Neufville 1973, recorded in the Middle Paleocene of Egypt (Bassiouni and Luger 1990), Danian of Sergipe-Alagoas Basin (Neufville 1973(Neufville , 1979) ) and Danian of the Paraíba Basin (Fauth et al. 2005) differs mainly in the more symmetrically rounded outline and lack of ornamentation.Occurrence: Olinda well, 36.15 m.Remarks: This species is typical from Danian of the Paraíba Basin (Fauth et al. 2005).The only specimen recorded is probably a juvenile, due to its smaller size compared to the holotype.

Subfamily Buntoniinae Apostolescu 1961
Genus Buntonia Howe 1935 Buntonia sp. Figure 3, d  Occurrence: Olinda well, 36.15 m, 37.35 m.Remarks: The genus Buntonia Howe is very common in the Paleocene of African basins (e.g., Apostolescu 1961, 1963, Reyment 1963, Foster et al. 1983, Okosun 1987, Carbonnel et al. 1990, Sarr 1999) and South America (e.g., Bertels 1973, Ceolin et al. 2011).This species differs from others by its rounded posterior outline and strong anteromarginal rib clearly seen in dorsal view.Compared to Buntonia tichittensis Apostolescu 1961, from the Paleocene of Senegal, our species is bigger, the punctuation is less prominent and the anterodorsal sulcus absent.Probably, it is a new species, but the scarcity and poor preservation of the material prevents its description.
Remarks: The genus Soudanella Apostolescu is a remarkable taxon that appears in the Paleocene of some African and South American basins.In Brazil, S. laciniosa is a Danian bioestratigraphical marker in the some Brazilian basins, including the Paraíba Basin.
Short description: Carapace large, subrectangular and elongate in lateral view.LV overlaps the RV along all margins, mainly in the anterodorsal and posterodorsal margins.Dorsal margin almost straight, ventral margin with a concavity at the middle part.Anterior outline broadly rounded and posterior subtriangular.Anteromarginal rib present.Surface reticulated and with well-developed longitudinal ribs.Anterior region with three ribs, parallel to the anterior margin; intercostal region coarsely reticulated.
Stratigraphical distribution: Paleocene of the Paraíba Basin (this work).
Occurrence: Olinda well, 37.05 m, 37.35 m.Remarks: This species is similar to Leguminocythereis senegalensis Apostolescu 1961, firstly recorded in Eocene of Senegal and later in the Paleocene-Eocene of Nigeria (Reyment 1963, Okosun 1987).The Brazilian species has a more acuminate and elongate posterior region and presents three ribs in the anterior region.
Occurrence: Olinda well, 38.25 m, 39.15 m.Remarks: A group of specimens showed morphological features that allowed include it in a Guembelitria genus.Due to the bad preservation and/or absence of diagnostic morphological features, it was not possible to determine the species.
Occurrence: Olinda well, 36.45 m.Remarks: The studied specimens are scarce, small (<125 µm) and resemble P. pseudoinconstans.According to Olsson et al. (1999), the first chambers of this species increase gradually in size, while the terminal ones increase abruptly; the last chamber slightly offsets towards the umbilicus in some specimens.Aperture is a high rounded arch, bordered by a narrow lip broadening towards umbilicus.It differs from Praemurica taurica by the moderately inflated chambers, which increase more abruptly in size in the last whorl.However, the smooth texture raises doubts about its identification.

RESULTS AND DISCUSSION
A total of 11 species of ostracods and nine planktonic foraminifera were identified in the Paleocene deposits of the Olinda well, Paraíba Basin.From the 16 analyzed samples, only 12 contained ostracod specimens and six, foraminifera.The stratigraphic distribution of the species is illustrated in Figure 5.
The Poty quarry bears more diverse and abundant ostracod assemblages compared with the Olinda well (Fauth et al. 2005).The species shared are Cytherella piacabucuensis, Soudanella laciniosa and Paracosta recifeiensis.The genera Cytherelloidea, Eocytheropteron, Semicytherura, Buntonia, Leguminocythereis and, probably, Pataviella are recorded for the first time in the Paraíba Basin.With the exception of the presumed occurrence of Pataviella, all the remaining genera had already been recorded in the Upper Cretaceous of the Potiguar and Sergipe basins (Neufville 1973, Delicio et al. 2000, Viviers et al. 2000, Piovesan et al. 2014).If confirmed, the record of Pataviella, also present in Paleocene of Senegal, would reinforce the similarities between the ostracofauna of the Brazilian northeast basins and the east African ones, as summarized by Fauth (2002).
In the lower part of the Olinda well (39.15-38.25 m) the ostracod assemblages are very poorly preserved and composed of Soudanella laciniosa and Cytherella sp. 2 along with a more diversified assemblage of the foraminifera, constituted by Zeauvigerina waiparaensis, Guembelitria cretacea, Heterohelix cf.globulosa and some unidentified species of Guembelitria, Muricohedbergella, Parvularugoglobigerina and Woodringina.The association is marked by the abundance of Guembelitria cretacea, Guembelitria spp.and the occurrence of Woodringina spp.This interval probably corresponds to the lower part of the Pα Zone, in accordance with bioevents recorded by Koutsoukos (2014) in the Campos Basin.The first occurrence of Soudanella laciniosa is also suggestive of the base of the Paleocene (Fauth et al. 2005).The blooms of Guembelitria (20-30%) are related either to shallow water environments or upwelling events.In the Danian, where the P0-P1a zones are recorded, Guembelitria (10-20%) and Z. waiparaensis are dominant in the low diversifity associations (Pardo and Keller 2008).These blooms of Guembelitria are commonly associated with a high influx of nutrients or continental runoff, upwelling along continental margins, or volcanic entry (Pardo and Keller 2008).In the Paraíba Basin blooms of Guembelitria have been identified by Stinnesbeck and Keller (1995), Keller and Stinnesbeck (1996), Koutsoukos (1996) and Pardo and Keller (2008).
The presence of the ostracod Soudanella laciniosa, a dominantly neritic species in the Poty quarry (Rodrigues et al. 2014), reinforces the interpretation of a neritic environment at the base of the well.The isotopic data show a substantial decrease of SiO 2 and Al 2 O 3 , a pattern associated with reduction of the siliciclastic input.The δ 18 O negative values in this interval suggest hotter seawater (Nascimento et al. 2011).
The superposed interval (38.25-37.35m) is marked by the decline in the abundance of planktonic foraminifera, with only Muricohedbergella monmouthensis present.According to Olsson et al. (1999), Paleocene species of Hedbergella, realocated in Muricohedbergella by Huber and Leckie (2011), are limited to the P0 zone.Thus, the specimen of Muricohedbergella monmouthensis recorded in this section could be reworked.This hypothesis is reinforced by its coincident occurrence with Woodringina?spp.that, according to Olsson et al. (1999), are restricted to the younger Pα zone.A notable change in the assemblage composition, with a decrease in diversity and abundance of Paleogene taxa and increase of reworked taxa is observed.A conspicuous change in the assemblage composition is seen in the interval 37. 35-35.25 m.From this level onwards, the ostracod diversity increases, in contrast to the planktonic foraminiferal diversity.The planktonic association in this range consists of Praemurica cf.pseudoinconstans, Woodringina hornerstownensis, Parvularugoglobigerina? spp., Woodringina?spp., and other unidentified specimens.In addition, the benthic foraminiferal association, represented mainly by Gavelinella and Cibicidoides (36.45 m and 35.55 m), also indicates a neritic environment.In the Poty quarry, Paraíba Basin, Koutsoukos (2006) reports the presence of Gavelinella coonensis and Cibicidoides alleni as indicative of a deep neritic environment.Another aspect of the ostracod fauna indicative of neritic environments is the presence of cytherurids (Semicytherura sp. and Eocytheropteron sp.).The Cytheruridae is a diverse and abundant family of marine/brackish water cytheracean Ostracoda (Ramos et al. 1999), and in the Mesozoic they seem to have been confined to shelfal depths, with many species also in marginal marine habitats (Ballent and Whatley 2009), a behavior that may have been extended to the Paleocene.Shallower waters in this interval could be inferred not only by the dominance of the benthic ostracods and reduction in plancktonic foraminifera, but also by the increase of SiO 2 and Al 2 O 3 (Nascimento et al. 2011).
Above 34.65 m begins 5.10 m thick interval composed predominantly of limestone where occurs only rare benthic foraminifera, fragmented planktonic specimens and the ostracod Cytherelloidea sp.occur.This noteworthy reduction in abundance and richness of both ostracods and foraminifera results possibly from preservational conditions related to the lowstand system tract, as proposed by Nascimento et al. (2011), based in the high SiO 2 and Al 2 O 3 content of the sediments.

CONCLUSIONS
Ostracods and foraminifera from the Olinda well seem to indicate environmental changes in the lower Paleocene of the Paraíba Basin.Nine planktonic foraminifer and eleven ostracod taxa were identified.
The lower Paleocene of Olinda Well can be subdivided in different faunal associations, probably related to changes in environmental conditions.The base of the well is characterized by blooms of Guembelitria spp., which constitutes important marker for shallow environments and upwelling zones in association with the ostracod Soudanella laciniosa, typical of neritic environments.The superimposed interval, in the median part of the studied well, presents associations indicative of shallower water based on the dominance of benthic foraminifera and cytherurid ostracods, associate with the reduction in the abundance of planktonic foraminifera.Finally, on the top of the section, the foraminifera and ostracods are rare and badly preserved, which could be related to the inception of the lowstand system tract.
The ostracod and foraminifera analyzed, therefore, permit the interpretation of neritic paleoenvironment in the studied section, ENELISE K. PIOVESAN et al. corroborating previous palaeoenvironmental interpretations for the Paleocene of the Paraíba Basin based on other fossil groups and isotopic data.

Figure 1 -
Figure 1 -The Paraíba Basin, showing the position of the studied well in Olinda city, Pernambuco State, Brazil (modified fromBarbosa et al. 2003 andGertsch et al. 2013).
-e Material: Seven specimens.Illustrated material: DGEO-CTG-UFPE-1426.Stratigraphical distribution (in the studied well): Lower Paleocene.Occurrence: Olinda well, 36.45 m, 39.15 m.Remarks: Due to the bad preservation and absence of diagnostic morphological features it was not possible to identify the specimens at specific level.Genus Woodringina Loeblich and Tappan 1957 Woodringina hornerstownensis Olsson 1960 Figure 4, f-g
Illustrated material: DGEO-CTG-UFPE-1427.Stratigraphical distribution (in the studied well): Lower Paleocene.Occurrence: Olinda well, 36.45 m.Remarks: The examined specimens are small and elongated, showing the biserial portion of the test distinctly twisted, although in lesser degree than Woodringina claytonensis Loeblich and Tappan 1957.According to Olsson et al. (1999), W. hornerstownensis differs from W. claytonensis by the elongate tapering test and the almost straight sutures.Woodringina?spp.(Not figured) Material: Five specimens.Stratigraphical distribution (in the studied well): Lower Paleocene.Occurrence: Olinda well, 36.45 m, 39.15 m.Remarks: The specimens examined are broken in the initial portion of the test, hampering the identification at specific level, though in the studied material there are possibly more than one species.Subfamily Heterohelicinae Cushman 1927 Genus Heterohelix Ehrenberg 1843 Heterohelix cf.globulosa (Ehrenberg 1840) Figure 4, h-i Material: One specimen.Illustrated material: DGEO-CTG-UFPE-1428.Stratigraphical distribution (in the studied well): Lower Paleocene.Occurrence: Olinda well, 38.25 m, 40.05 m,

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ENELISE K. PIOVESAN et al. two chambers above the previous pair becoming almost uniserial.According to Olsson et al.
Malz (1981)671982)aff.C. keijiMckenzie 1967from the Paleocene of Senegal(Diop et al. 1982), but presents two median ridges.Compared with Cytherelloidea keijiMckenzie 1967, recorded firstly in Recent deposits, the Brazilian specimens are shorter, with median ridges more sinuous and dorsal margin slightly concave.It is worthy to be mentioned thatMalz (1981)reassigned C. keiji to Keijcyoidea Malz, a genus proposed on Paleocene material from the Emperor Seamounts Ridge, in the Pacific Ocean.Bergue and Coimbra (2002) recorded the genus Keijcyoidea in Holocene deposits from Brazilian equatorial shelf.Therefore, Cytherelloidea sp.possibly constitutes the first fossil species of Keijcyoidea recorded in Brazil.Eocytheroteron sp.differs from E. trapezoidalis Carbonnel 1990, from the Paleocene of Niger, by the smaller size and smooth surface.Furthermore, E. trapezoidalis presents the caudal process more projected upward and acuminated.In the Upper Cretaceous from the Potiguar Basin, Piovesan et al. (2014) recorded two species of Eocytheropteron, both differing significantly from the species here recorded, especially in size, outline and ornamentation.
It differs from Mu. holmdelensis (Olsson 1964) because it presents more globular to subglobular chambers, while Mu.holmdelensis has ovate and compressed chambers.According to Olsson et al. (1999), only two species of Hedbergella (realocated in Muricohedbergella by Huber and Leckie 2011) cross the K-Pg boundary, Mu. monmouthensis and Mu.holmdelensis, both surviving up to the P0 zone.