This study evaluates Foraminiferal assemblages and their relation with grain size, calcium carbonate content, organic matter, and mineralogy of sediment samples collected at the sediment-water interface along a transect on the northern continental shelf of Rio Grande do Norte State, Brazil, adjacent to the city of Areia Branca. The sedimentary sequence of this shelf is represented by lithostratigraphic units of a marine regressive sequence dominated by four facies: Siliciclastic sand, Silicibioclastic Sand, carbonate mud, and Biosiliciclastic sand. The carbonate content ranged from 5.83% to 85% and the organic matter content from 1.16% to 27.05%. Mineralogical characters separated the predominant siliciclastic content (37% to 92%) from the bioclastic content (8% to 63%). We have identified 14 species out of 50 species of Foraminifera, associated to particular depths and sediment types as follows: (1)deeper-water sediments in the middle shelf contain Bolivina striatula, Bulimina marginata, Triloculina trigonula, Pyrgo ringens, Textularia gramen (2)the shallowest sediments in the inner shelf contain Ammonia tepida, Buccella peruviana, Miliolinella subrotunda, and Quinqueloculina patagonica, (3)the central parts of the transect, also in the inner shelf, provide habitats for Quinqueloculina lamarckiana, Textularia earlandi, Buliminella elegantissima, Discorbis peruvianus, and Pyrgo nasuta. The distribution of Uvigerina striata and Buccella peruviana is probably related to colder water temperatures and possibly the occurrence of an upwelling phenomenon for the deepest parts of the area rather than the sedimentological features discussed here.

 Keywords: habitats, inner and middle shelf, benthic foraminifera, upwelling

1. Species are associated with particular depths and sediment types.
2. Deeper-water sediments contain Bolivina striatula, Bulimina marginata, Triloculina trigonula, Pyrgo ringens, Textularia gramen
3. Shallower-water sediments contain Ammonia tepida, Buccella peruviana, Miliolinella subrotunda, and Quinqueloculina patagonica,
4. Inner shelf is habitat for Quinqueloculina lamarckiana, Textularia earlandi, Buliminella elegantissima, Discorbis peruvianus, and Pyrgo nasuta.
5. The distribution of Buccella peruviana is related to the upwelling of colder waters.

Foraminifera are excellent indicators of sea level change on continental margins and are useful in paleoenvironmental reconstructions.^1–4 While the distribution of each species is unique, groups of species (assemblages or communities) can be recognized as inhabiting particular areas such as mangroves, estuaries, bays, inner/outer shelves and deep basins. These natural habitats have particular geomorphologic and hydrographic characteristics, and may be further differentiated by variables such as depth, salinity, temperature, organic content, textural parameters, and oxygen supply.⁵

Poorly oxygenated bottom waters of other continental shelves and slopes often related to upwelling are known to support Foraminiferal habitats in which species of Bolivina and Bulimina are relatively abundant.⁶ We speculate that similar assemblages of benthic foraminifera in our inner and middle shelf are strongly affected by upwelling. For example, species of Buliminacea, Fursenkoina, and Nonionella, abundant in organic-rich, low-oxygen sediments in modern seas, increased in proportional abundance after world warming began. In addition, the offset in δ¹³C values between epifaunal to shallow infaunal taxa and a deeper infaunal species is greater in sediments with higher abundances of these taxa, further supporting increased organic carbon flux. An increase in laminated sediments coincident with these faunal and geochemical changes suggests dysoxic conditions accompanied by an increase in organic carbon. Taken together, this multiproxy record suggests that high-organic, low-oxygen, environments developed in shallow waters during Early Miocene warming, perhaps driven by similar upwelling mechanisms thought to drive hypoxia on the modern Oregon coast.^7,8

In spite of the great economic (petroleum, salt, marine production, fisheries), social (major cities) and historical (since the time of discovery) importance of tropical shelves in northeastern Brazil, we still do not have comparable data for bio-indicators of environmental changes such as sea level rise, water temperature rise, global warming, drill cutting disposal, contamination and pollution. The present investigation is an attempt to partly fill this gap; demonstrating that Foraminiferal biodiversity patterns show traceable responses to temporal environmental changes in this highly complex environment.

This multi-proxy study aims to evaluate Foraminiferal assemblages and their relation with grain size, carbonate content, organic matter and mineralogy on a transect on the northern continental shelf of Rio Grande do Norte State, adjacent to the city of Areia Branca (see Figure 1).

This continental shelf represents a modern, highly dynamic mixed carbonate-siliciclastic system characterized by reduced width (40 km) and shelf-break at a depth of around 60 m.^9–11

The study area is within the Potiguar Basin geological domain, which is within the Meso-Cenozoic basins of the Brazilian equatorial margin. The sedimentary packages that make up the platform in this sector are represented by the lithostratigraphic units of a marine regressive sequence (Early Campanian-Holocene) represented by the Ubarana Formation (marine shales), Guamaré Formation (carbonates) and Tibau Formation (sandstones and conglomerates), revealing a coastal-shelf-slope-basin environment.¹²

According to Dominguez et al.,¹³ winds predominantly from the northeast (Figure 1) reach the northern coast of Rio Grande do Norte, within the belt of trade winds controlled by the movements of the Intertropical Convergence Zone. The mean velocity of the winds, measured directly from the shoreface is 5m/s in April and 9m/s between August and October; it may reach up to 18 m/s during the month of August.¹⁴

According to Caldas,¹⁵ the Brazilian continental shelf adjacent to the Rio Grande do Norte state is dominated by the North Brazil Current (NBC). The NBC corresponds to the class of the southern equatorial current with a significant longshore current in an E-W direction. Within this context, our study area is part of a semidiurnal meso-tidal regime.^16,17

Considering the geomorphology and sedimentation, Vital et al.,¹⁸ and Gomes and Vital¹⁹ divided the continental shelf into three domains: 1. Inner shelf, dominantly siliciclastic sediments (up to 15m water depth), 2. Middle shelf, dominantly siliciclastic-carbonates (15 to 25m water depth), and 3. Outer shelf, dominantly carbonate sediments (25 to 40m water depth)

As shown in Figure 1, bed forms ranging from centimeters to kilometers are present on this shelf. The continental shelf is 35.5 km to 37 km wide toward 40 m isobaths. In front of Apodi Valley, it widens to 47 km. The outer shelf and the shelf edge start at 40 m water depth. In according to Lima and Vital,⁹ Gomes et al.,²⁰ and Vital et al.,²¹ five main features were recognized: (a) very large longitudinal dunes; (b) incised valleys; (c) reefs; (d) regions with a flat base, and (e) very large transversal dunes. Additional features were also identified: (f) two head canyons (C1 and C2) (Figure 1).

Seven sediment samples were collected along a transect (Figure 1) with a Van Veen grab and sub-sampled for analyses of Foraminifera, grain size, carbonate content, organic matter, and mineralogy. We usually collect the first cm (where we have a visual on the layer where bacterial activity is taking place) to estimate the population dynamics so we do not need to have equipment that preserves the structure.

Figure 1 Location map of the study area, the northern continental shelf in Rio Grande do Norte State, Brazil, and bedforms typical of this area. (a) very large longitudinal dunes, (b) incised valleys, (c) reefs, (d) regions with a flat base, (e) very large transversal dunes, (f) head canyons (C1 and C2). Red circles refer to the sediment sample transect used in this study.

The uppermost layer of the sediment (about 1 cm) was removed and stored in a mixture of 1 liter of alcohol and 1 gram of Bengal rose stain. After staining, a fixed volume of 50 cm³ of sediment was washed through a 0.063-mm sieve and dried in an oven at 70°C. This fraction was floated using trichloroethylene. The residues were examined for Foraminiferal tests. The procedure can be seen in Eichler et al.²²

Each sample for grain size analysis was washed with distilled water. Sand samples were then dried for 24h at (maximum) 65°C, and clay samples were lyophilized. Subsequently, samples were manually homogenized and classified according to grain size, by using a Ro-Tap sieve shaker or a laser particle-size analyzer (CILAS 1180L). Statistical parameters²³ were calculated, and sediments were classified.^18,24

To quantify the carbonate content, approximately 12 g of sediment was collected from each sample and transferred to a plastic tube. Subsamples were treated with a solution of 10% hydrochloric acid to dissolve their carbonate fraction. After dissolution, subsamples were washed repeatedly in freshwater to remove residues, dried, and weighed. Carbonate composition (%) was calculated by the difference between the pre-and post-treatment subsample weight.

Total organic matter was calculated by the difference between initial and subsequent weights after burning in a muffle furnace. The samples were heated for approximately 5 hours at a temperature of 600°C so that all organic material was eliminated.

Absolute and relative abundances of living Foraminifera species were recorded for each sediment sample. Relative abundance data were computed for foraminiferal species that contribute 10% or more to the assemblage in more than one sample, and subjected to Q-mode cluster analysis. The Bray-Curtis distance coefficient was used to measure differences between fourth-root transformed samples, and the group-average method was used to amalgamate samples into a hierarchical dendrogram.

Data from relative frequency were contoured on ARCGIS software and used to observe micro-faunal patterns. Species identification was done using an optical microscope and taxonomic determination of species was based on the Catalogue of Foraminifera;^25,26 scanning electron micrographs were taken to aid with occasional problematic identifications and for illustrative purposes. Similarity matrices were constructed to help differentiate sub-environments using PRIMER, a University of Plymouth software.²⁷

The mineralogical description of each sedimentary facies was done in the samples using optical microscopy at a magnification of 50x, noting mineralogy, color, structure and texture. Data on abiotic patterns were then integrated in GIS (Geographic information system) software and in electronic worksheets.

Table 1 illustrates the sedimentological features of collected samples. Sand dominates in the bottom sediment followed by mud and gravel. The percentage of grain size fraction indicates that medium, coarse, and very fine sand predominate. Silt is limited in station P55, which is localized inside the channel. The percentage of mud is higher in station P32. The degree of sorting in sediments alternated from moderately sorted (P12, P20, P25, P35) with values below 1, to poorly sorted (P5, P32, and P55) with values above 1. Carbonate content ranged between 5.83% to 85%. Samples P32, P35, and P55 had the highest concentration of carbonate (Table 1).

The TOM content ranged between 1.16% to 27.05% with an average of 13.23%. Organic matter concentration was the highest at station P32 (27.05%), followed by station P55 (7.15%), with the other stations showing concentrations of <7% (Table 1). The percentage of silt and very fine sand was higher at stations P32 (59.8%; 23.2%), P55 (9.7%; 10.0%), and P05 (9.6%; 59.6%).

The siliciclastic content ranged between 37% and 92%, and the bioclastic content was between 8% and 63% (Table 1). Station P55 showed high bioclastic content (63%) and rock fragments (25%).

The samples are grouped into four main sedimentary facies. According to classification based on Vital et al.,¹⁸ AS 1b: Siliciclastic sand (P5, P20, and P25 stations); AS 2b: Silicibioclastic Sand (P12 and P35 stations); LB 2: Carbonate mud (P32 station); AB 1b: Biosiliciclastic sand (P55 station), see Figure 2.

Figure 2 The distribution of sedimentary facies along the transect on the northern continental shelf of Rio Grande do Norte State.

Figure 3 shows samples of each sedimentary facies. The composition is comprised of quartz, biotite, rock fragments, and heavy minerals. The quartz is generally sub-rounded to round with sphericity ranging from medium to high. It can be easily recognized by its granular habit and vitreous luster. At station P12, individual fragments of quartz show moderate to weak selection. The smaller particles were more rounded, with sphericity ranging from medium to high, while the coarser particles tended to be more angular, with sphericity ranging from medium to low. At station P20, clean grains showed a degree of sorting ranging from moderate to high. The biotite exhibits a lamellar pattern, micaceous brightness, and color ranging from black to brown. Rock fragments and heavy minerals were present in significantly lower numbers. The rock fragments were composed of quartz, feldspar, and biotite. Heavy minerals were tourmaline and garnet.

Figure 3 Sediment facies along the transect on the northern continental shelf of Rio Grande do Norte State.

The bioclastic fraction consisted of echinoderms, mollusks, worm tubes, coralline algae, benthic foraminifera, and ostracods. Most of the grains were broken at stations P5 and P55 revealing a high hydrodynamic setting.

A total of 55 calcareous and 6 agglutinated foraminiferal species were found (Table 2). The miliolids of the genus Quinqueloculina, Miliolinella, and Pyrgo occurred in every sample and Textularia gramen was the only agglutinated that occurred in most of the samples.

Quantitative data on Foraminiferal assemblages are presented in Table 3, and Table 4 shows the relative frequency and absolute values of the total specimens in each sample, and their relation with geological data. Contour maps of the relative frequency of the more abundant species are presented in Figure 5.

Figure 4 Cluster analysis based on Foraminiferal abundance data.

Figure 5 Map of relative frequency of Foraminifera microfauna in a stretch on the northern continental shelf of Rio Grande do Norte.

As detailed in Table 4 and Figure 4 the following Foraminifera were observed in those stations (P32 and P55) where carbonate, organic matter and silt, clay, and very fine sand values are higher and grains are poorly sorted: Bolivina striatula, Bulimina marginata, Triloculina trigonula, Pyrgo ringens, Textularia gramen, Ammonia tepida, Buccella peruviana, Miliolinella subrotunda, and Quinqueloculina patagonica. The sediments at Station P35 contain high carbonate and organic matter content and are different from Stations P32 and P55, by a larger amount of medium-grained sand (46.14%). Station P35, where silt and medium sand predominate, is composed mainly of Bulimina striatula, Bulimina marginata, Triloculina trigonula, Pyrgo ringens and Textularia gramen.

Figure 6 The distribution of dominant foraminifera microfauna along the transect on the northern continental shelf of Rio Grande do Norte.

Quinqueloculina lamarckiana (an inner neritic to shelf indicator) and a coral reef endemic species (Amphistegina sp.) are found at the shallowest stations, P05 and P12, where the sediments are sandy. In contrast, Q. patagonica is typical of substrates with low organic matter and clay values, particularly at stations P12, P20, P35 (moderately sorted), and P55 (poorly sorted). The agglutinated species Textularia earlandi was found at stations where the sediment is moderately sorted (stations P12, P20, P25). Deeper-water sediments in the middle shelf contain Bolivina striatula, Bulimina marginata, Triloculina trigonula, Pyrgo ringens, and Textularia gramen. The shallowest sediments in the inner shelf contain Ammonia tepida, Buccella peruviana, Miliolinella subrotunda, and Quinqueloculina patagonica. The central parts of the transect along the inner shelf provide habitats for Q. lamarckiana, Textularia earlandi, Buliminella elegantissima, Discorbis peruvianus, and Pyrgo nasuta. The distribution of Uvigerina striata at two sedimentologically contrasting stations (P20 and P32) and the presence of Buccella peruviana at P05, P12, P32, P35, P55 indicates that their presence may be linked to water properties or other abiotic factors such as colder temperatures rather than the particular sedimentological features discussed above.

Cluster analysis applied to Foraminiferal abundances revealed three groups (Figure 4):

Group I: Stations P25 and P20 from the central parts of the transect located in the deeper inner shelf, with siliciclastic sediments and the following Foraminiferal assemblage; Q. lamarckiana, T. earlandi, B. elegantissima, D. peruvianus, and P. nasuta.

Group II: Stations P05 and P12 from the shallower inner shelf, with siliciclastic and silicibioclastic sediments associated with the Foraminiferal assemblage; A. tepida, B. peruviana, M. subrotunda, Q. patagonica.

Group III: Stations P32, P35, P55, with carbonate mud, silicibioclastic and biosiliciclastic sand sediments from channel, associated with the Foraminiferal assemblage; B. striatula, B. peruviana, B. marginata, T. trigonula, P. ringens, T. gramen.

Our results shows that with the exception of Station P05, the stations from deep (Stations P32, P35) and shallow (Station P55) channels contain the highest values of organic matter and calcium carbonate, as found by Pessoa Neto¹² and Vital et al.^18,28 The calcium carbonate content in the sediments in our study also correlates with siliciclastic composition in the inner shelf and carbonate-siliciclastic in the middle shelf. The significant presence of calcium carbonate is due to the occurrence of bioclastic material (shell fragments, calcareous algae, among others).

The TOM distribution appears directly related to sediment grain size; the smaller particle size correlates with the higher amount of TOM, particularly at Stations P05, P32, and P55. The poor sorting of sediments at these three stations indicates close proximity to the rock matrix source. Our results match those of the above-mentioned studies of siliciclastic, silicibioclastic and biosiliciclastic sands in the inner shelf that are replaced by silicibioclastic and carbonate mud in the middle shelf. We note the presence of carbonate mud inside the deep channel of the incised valley.

Figure 8 is a graphical abstract and summarizes data on abiotic and biological findings. Foraminiferal assemblages from Stations P12, P20, and P25 contain Q. lamarckiana, T. earlandi, B. elegantissima, D. peruvianus, and P. nasuta, which are characteristic of sediments with high TOM content. The occurrence of B. elegantissima is likely out of place, and probably due to organic contamination, see “Culver and Buzas”.²⁹ According to Eichler et al.,²² the polyhaline environment (18-30 PSU) of some parts of Bertioga Channel (SP, Brazil) contains both muddy and sandy sediments, with TOM varying from 1.2 to 9.5 mg/g and most stations have high sulfur content (>10 mg/g). It includes Foraminiferal assemblages dominated by Q. milletti, A. mexicana, P. cananeiaensis, A. beccarii, and B. elegantissima. The foraminiferal assemblage of poorly flushed marine bottom waters of inner parts of the bay Guanabara Bay, Rio de Janeiro,⁵ is composed by B. elegantissima, B. striatula, and B. elongata, which are known to dominate in organic-rich substrate beneath low-oxygen water columns. Thus, the species distribution in the northern continental shelf compare strongly to recent highly organic deposits at Stations P32 and P55 (and possibly others). The porcelaneous genus Quinqueloculina can also be associated with normal marine salinities, high water clarity, good circulation,³⁰ and intrusion of marine waters Eichler et al.²²

Depth and sediment type influenced the Foraminiferal assemblage, particularly at (a) the shallower inner shelf and in the shallow channel stations (Stations P5 and P55), where A. tepida, B. peruviana, M. subrotunda, and Q. patagonica are common, and (b) in the deep channel (Stations P32 and P35), with B. striatula, B. marginata, T. trigonula, P. ringens, and T. gramen. Buccella peruviana was described by Boltovskoy as a cold-water species from Malvinas current. Years later, in summer samples from the Brazilian continental shelf the presence of cold upwelled water masses was showed by the correlation between δ¹³C from benthic foraminifera and water depth weakens, reflecting a less stratified water mass associated with upwelling and the distribution of Buccella peruviana, indicator of the Sub Antartic Shelf Water.³¹

The presence of Buccella peruviana in the Northernmost part of Rio de Janeiro was described by Stevenson et al.,³² as a temperature water species typical to the Argentina province. In the South of Brazil, Eichler et al.,³³ has associated B. peruviana to upwelling of colder waters from Sub Antarctic shelf water. More recently, organically enriched sediments and foraminiferal species from the Açu Reef, have also indicated the presence of upwelling in NE Brazil.³⁴

Shallow (Station P55) and deep channels (Station P32 and P35) contain the highest values of carbonate content (more than 40%), with the shallow channels even showing oil impregnation in some Foraminiferal tests. In contrast, the two stations located in the deep channels of the mid continental shelf have low carbonate context and very abundant autochthonous microfauna. B. striatula, B. marginata, T. trigonula, P. ringens, and T. gramen inhabit sediments with medium mud and medium sand at Station P35 whereas Station P32 has the highest content of mud, organic matter, and silt. B. striatula, B. marginata, T. trigonula, P. ringens, and T. gramen inhabit sandy and muddy sediments inside the deep channel.

The Foraminiferal species B. striatula is present at locations where carbonate, organic matter, silt, and clay values are higher and grains are poorly sorted (Stations P32 and P55).

The presence of Amphistegina sp. (a coral reef endemic Foraminiferal species) at Stations P05 and P12 revealed that the shallower stations are comprised of allochthonous material from a not very distant coral reef.²⁶ Q. patagonica and Q. lamarckiana are characteristic of sediments with both low organic matter and clay values, such as those from Stations P12, P20, and P35 (moderately sorted) and Station P55 (poorly sorted). The agglutinated Foraminifera, T. earlandi was found at stations where the sediment is moderately sorted (Stations P12, P20, P25).

Following the geomorphology and sedimentation patterns, Vital et al.¹⁸ and Gomes and Vital¹⁹ divided this continental shelf into 1. Inner shelf, dominantly siliciclastic sediments (up to 15m isobath), 2. Middle shelf, with siliciclastic-carbonate sediments (15 to 25m deep), and 3. Outer shelf, formed by carbonate sediments (25 to 40m deep). The Foraminiferal distribution is distributed basic in shallow and deep sediments as follows: 1. the shallowest sediments in the inner shelf contain A. tepida, B. peruviana, M. subrotunda, and Q. patagonica. Central parts from the deepest inner shelf provide habitats for Q. lamarckiana, T. earlandi, B. elegantissima, D. peruvianus, and P. nasuta, 2. Deeper-water sediments in the middle shelf contain B. striatula, B. marginata, T. trigonula, P. ringens, and T. gramen. For a late Pliocene assemblage, Resig³⁵ concluded that a 33% frequency of B. elegantissima is characteristic of the middle shelf and are in agreement with our findings. Moreover, our results are in agreement with the distribution of Uvigerina striata at two stations with contrasting sedimentological features (Stations P20 and P32) indicating that its occurrence may be linked to water properties or other abiotic factors such as colder temperatures, instead of the studied sedimentological features discussed here. Further confirming our conclusions, the genus Uvigerina has been reported as a cold water-tracer suggesting the influence of South Atlantic Central Water (SACW) nutrients brought up by upwelling in the Brazilian Continental shelf³⁶ and U. striata has been shown to be indicative of current-generated deposition in the lower upper bathyal counter current regime of paleo environments off Peru³⁵. The distribution of U. striata in our work is also possibly linked to the occurrence of an upwelling phenomenon not yet described in the literature for the area. The cold waters would reach the shelf through the head canyons observed on the slope (Figure 1). Almeida et al.³⁷ mapped these canyons and identified that the Apodi canyon head reaches the shelf break at 106 m and suggested that Apodi-Mossoro canyons were probably connected to the incised valley and or shelf drainage system.³⁸

The results show that this transect is dominated by four facies: siliciclastic sand, silicibioclastic sand, carbonate mud and biosiliciclastic sand.

Siliciclastic sand encompasses P5, P20, and P25 stations. P5 is the shallowest station, comprised poorly sorted sediments, high percentage of silt and very fine sand, and allochthonous material from a not very distant coral reef and the presence of Buccella peruviana and A. tepida. M. subrotunda and Q. patagonica. P20 has Q. patagonica, Q. lamarckiana, Uvigerina striata, T. earlandi, B. elegantissima, D. peruvianus, and P. nasuta from low organic matter and clay values. P25 station has moderately sorted sediments with the presence of Q. lamarckiana. T. earlandi. B. elegantissima. D. peruvianus and P. nasuta.

Silicibioclastic sand groups P12 and P35 stations. Station P12 has Q. patagonica and Q. lamarckiana, T. earlandi. B. elegantissima. D. peruvianus and P. nasuta, sediment moderately sorted, low organic matter and clay values. P35 is also moderately sorted sediments with the high concentration of carbonate. Both have Buccella peruviana. P35 has B. striatula. B. marginata. T. trigonula. P. ringens, T. gramen, and Uvigerina striata.

Carbonate mud at P32 station has B. striatula. B. marginata. T. trigonula. P. ringens, T. gramen Uvigerina striata, and Buccella peruviana from poorly sorted sediments with high concentration of carbonate, organic matter, and high percentage of silt and very fine sand.

Biosiliciclastic sand at P55 station, poorly sorted sediments high concentration of carbonate and organic matter, high percentage of silt and very fine sand and the presence of B. peruviana, A. tepida, B. peruviana, M. subrotunda, and Q. patagonica. The carbonate content ranged between 5.83% to 85% and organic matter content 1.16% to 27.05%. The mineralogical description identified a predominance of siliciclastic content (37% to 92%) over bioclastic content (8% to 63%). These features are in accordance with the geomorphological divisions of northern continental shelf of Rio Grande do Norte State. The Foraminiferal distribution data show that the shallowest sediments in the inner shelf contain A. tepida, B. peruviana, M. subrotunda, and Q. patagonica. The central parts from the deepest inner shelf contain habitats for Q. lamarckiana, T. earlandi, B. elegantissima, D. peruvianus, and P. nasuta. Deeper sediments in the middle shelf contain B. striatula, B. marginata, T. trigonula, P. ringens, and T. gramen. The distribution of U. striata and B. peruviana are possibly linked to water properties or colder temperatures and upwelling rather than sedimentological features and should therefore be investigated. The sediment type, composition, and relation with the benthic biological community show that foraminifera are critical in coupling shelf systems with geological and hydrodynamic processes.

We gratefully thank the PRH-ANP 22 (Brazilian National  Oil Agency and PETROBRAS) and CAPES (Coordenação de Aperfeiçoamento de Pessoal de Nível Superior) for the scholarship to M.L.S.Nogueira and to CNPq by the productivity research grant to H.Vital. The second author is thankful for CAPES for the PostDoc Fellowship at the Laboratório de Geologia e Geofísica Marinha e Monitoramento Ambiental da Universidade Federal do Rio Grande do Norte (GGEMMA-UFRN-Brazil) through the Edital Ciências do Mar [207/2010], and to CNPq - Chamada MCTI/CNPq [Nº 23/2011], Apoio Técnico para Fortalecimento da Paleontologia Nacional). Thanks are also to GGEMMA (DG/PPGG /UFRN) group, in special Canindé for field assistance under rough sea environmental conditions. Authors are grateful for the English review done by Christofer Barker from EcoLogic project.

Financial support to field and laboratory works was provided by SISPLAT (REDE 05/FINEP/CTPETRO/ CNPq/ PETROBRAS), CAPES Ciências do Mar I (207-10) and TBEM IODP/CAPES-Brasil (88887.123925/2015-00). This is a contribution to INCT AmbTropic (CNPq/FAPESB/CAPES) and TBEM IODP/ CAPES-BRASIL.

The authors declare that there are no conflicts of interest.

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