Cretaceous - AGU Publications

PUBLICATIONS Paleoceanography RESEARCH ARTICLE 10.1002/2014PA002772 Key Points: • Upper Aptian samples from the South Atlantic Ocean are examined • Three dinocyst communities identified in late Aptian • The oceanographic fluctuations is matched by the changes in dinocyst communities

Correspondence to: M. A. Carvalho, [email protected]

Citation: Carvalho, M. A., P. Bengtson, and C. C. Lana (2016), Late Aptian (Cretaceous) paleoceanography of the South Atlantic Ocean inferred from dinocyst communities of the Sergipe Basin, Brazil, Paleoceanography, 31, 2–26, doi:10.1002/2014PA002772. Received 18 DEC 2014 Accepted 13 NOV 2015 Accepted article online 23 NOV 2015 Published online 9 JAN 2016

Late Aptian (Cretaceous) paleoceanography of the South Atlantic Ocean inferred from dinocyst communities of the Sergipe Basin, Brazil Marcelo de A. Carvalho1, Peter Bengtson2, and Cecília C. Lana3 1

Departamento de Geologia e Paleontologia, Museu Nacional, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil, Institut für Geowissenschaften, Universität Heidelberg, Heidelberg, Germany, 3Gerência de Bioestratigrafia e Paleoecologia, CENPES, PETROBRAS, Rio de Janeiro, Brazil

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Abstract The late Aptian (Early Cretaceous) is a crucial time interval for understanding the paleoceanographic changes in the Southern Hemisphere. Oceanographic changes in the emerging South Atlantic Ocean during this interval are reflected in the stratigraphic distribution of dinoflagellate communities recorded in the Muribeca and Riachuelo formations of the Sergipe Basin in northeastern Brazil. The Subtilisphaera community, in the lower and middle parts of the section, appears to be related to the Subtilisphaera Ecozone and suggests the onset of Tethyan influence in the central South Atlantic, in a restricted to inner-neritic environment. The succeeding Spiniferites community, in the middle part of the section, represents the first significant transgression, probably of eustatic origin. The Cyclonephelium-Exochosphaeridium community, in the upper part of the section, appears to be related to an oceanic event characterized by intermittent dysoxic-anoxic conditions. The uppermost part of the section is dominated by the Spiniferites community, related to a progressive regional transgression and culminating in an open-marine, fully Tethyan environment in the central part of the widening South Atlantic. 1. Introduction Cretaceous marine transgressions were caused by some of the most extensive sea level rises during the Phanerozoic. The floodings resulted in significant changes in the depositional environments of the South Atlantic continental-margin basins and may even have covered vast inland areas of the South American continent during the mid-Cretaceous [Arai, 1999, 2007, 2009, 2014], creating seaways that connected the Pacific Ocean with the North and South Atlantic oceans [Arai, 2009]. The Aptian transgression is recorded in carbonate platform deposits of tropical latitudes of South America (e.g., Venezuela and Colombia) and on the northern and southern margins of the Tethys, (e.g., Spain and France and from Algeria to Oman) [Arnaud-Vanneau et al., 2008]. In Brazilian continental-margin basins the upper Aptian is characterized by the first major flooding surface observed in the Cretaceous succession. Data from paleontological studies [Azevedo, 2004; Arai, 2005, 2007, 2009, 2014] support the view that the mid-Cretaceous South Atlantic was composed of a central and a southern part, separated by the Rio Grande Rise–Walvis Ridge (Figure 1). During the mid-Aptian to mid-Albian, the central South Atlantic, which contains the Sergipe Basin (Figure 2), communicated mainly with the equatorial Atlantic (“northern South Atlantic”), which in turn was connected to the Tethys [Bengtson et al., 2007; Koutsoukos and Bengtson, 2007]. However, the magnitude and the precise dating of Tethyan influence on the Brazilian continental-margin basins remain controversial. Azevedo [2004] characterizes the circulation in the central South Atlantic as lagoonal; however, the presence of foraminifers of “flysch type,” which are indicative of deeper-neritic to upper bathyal environments, suggests the existence of deeper waters in northeastern Brazil [Koutsoukos, 1992].

©2015. American Geophysical Union. All Rights Reserved.

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Musacchio [2000] and Arai [2009] suggested that although the Aptian transgression provided only restricted marine connections, it caused pandemic distribution of selected paralic and continental organisms, for example, ostracods and charophytes. Foraminifers and ammonites from the Sergipe Basin show conspicuous affinities with faunas of low latitudes of the Tethyan Realm [e.g., Bengtson and Koutsoukos, 1991, 1992; Koutsoukos et al., 1991; Koutsoukos, 1992; Koutsoukos and Bengtson, 1993; Bengtson and Souza-Lima, 2000; Bengtson et al., 2007]. The global Aptian transgression resulted in the initial connection of the central South Atlantic with the equatorial Atlantic. The shift from the transitional, evaporitic phase in the early Aptian to a fully marine drift phase was characterized by progressive crustal extension and thinning [Karner et al., 1992]. The gradual development of oceanic conditions in the central

LATE APTIAN SOUTH ATLANTIC, DINOCYST

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Figure 1. Idealized paleoceanographic setting for the late Aptian in the central and southern South Atlantic, after Koutsoukos et al. [1991]; Azevedo [2004], and Arai [2014] showing location of the studied well GTP-24-SE. Reconstruction at 119 Ma modified from ODSN Plate Tectonic Reconstruction Service. A–A′ section = interpretation of a longitudinal section extending from the equatorial region in the central to the southern South Atlantic.

South Atlantic established neritic-oceanic circulation patterns, and surface water was exchanged with the equatorial Atlantic (equivalent to the South Atlantic and central Atlantic oceans, respectively, of Bengtson and Koutsoukos [1992]), possibly even at intermediate epipelagic to mesopelagic water depths [Koutsoukos, 1992]. Dinocysts (dinoflagellate cysts) are frequently found in palynological samples from Cretaceous basins. However, there are few previous reports of Cretaceous dinocyst assemblages from the Sergipe Basin. The most relevant study is by Regali et al. [1974, 1975], who investigated several Brazilian basins, focusing mainly on biostratigraphic applications. Other studies, carried out by geologists of the Brazilian oil company Petrobras, remain unpublished. According to several studies [Wall et al., 1977; Goodman, 1979, 1987; Harland, 1983; Brinkhuis and Zachariasse, 1988; Brinkhuis, 1992; Courtinat, 1993; Wilpshaar and Leereveld, 1994; Pearce et al., 2003; Lebedeva, 2008], changes in physical and chemical features of water masses are reflected in the distribution patterns of

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Figure 2. Location map of the continental-margin basins of northeastern Brazil [from Seeling, 1999].

modern dinocysts. Therefore, quantitative analyses of dinocyst assemblages may provide information regarding depositional environment, sea level variations, sea surface temperature, productivity, and salinity. Significant progress in the development and application of dinocyst paleoecology has been made in the past decades, especially where quantitative approaches are employed. Dinocyst analysis is a powerful tool in paleoceanographic studies and particularly useful for linking inshore and offshore settings [Vandenberghe et al., 2003]. Goodman [1979] formulated the concept of “cyst communities,” the lateral and vertical distributions of which are attributed to the particular depositional environments. Thanks to the studies of Quaternary and Recent cyst distribution, inferences can be made about pre-Quaternary dinocysts. The present study aims at a better understanding of the origin and fluctuation of the vertical dinocyst distribution in the Sergipe Basin during the Aptian transgression, based on qualitative and quantitative stratigraphic analyses of core samples. It highlights the importance of sea level and oceanic circulation in controlling the distribution of dinocysts linked to the progressive separation of the African and South American continents.

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2. Geological Context The Sergipe Basin in northeastern Brazil contains one of the most extensive marine middle Cretaceous carbonate successions among the central South Atlantic basins. The basin, which forms the southern part of the Sergipe-Alagoas Basin [Souza-Lima et al., 2002], is an elongate continental-margin basin situated between latitudes 10°15′–11°30′S and longitudes 36°20′–37°30′W. Onshore the basin is 16–50 km wide, 170 km long, and covers an area of 6000 km2; the offshore portion comprises an area of ~5000 km2 (Figure 2). Structurally, the Sergipe Basin forms a half-graben with a regional dip averaging 10–15° to the southeast [Ojeda and Fugita, 1976]. The basin is bounded by faults with an overall NE-SW and NW-SE orientation. The faults were formed during rupture of the African-South American continent in the Early Cretaceous. The structural framework of the basin is characterized by large tilted fault blocks, which form structural lows and highs. The Sergipe Basin belongs to the class of sedimentary basins characteristic of passive continental margins. According to Ojeda and Fugita [1976] and Ojeda [1982], the evolution of the basin comprises five main tectono-sedimentary phases, viz., intracratonic, prerift, rift (earliest Cretaceous to early Aptian), transitional (Aptian), and an open-marine drift phase (late Aptian to Recent). The upper Aptian succession is represented by the upper part of the Muribeca Formation (Oiteirinhos Member) and the lower part of the Riachuelo Formation (Taquari Member).

3. Studied Succession The material for this study derives from well GTP-24-SE drilled by Petrobras/Petromisa in the TaquariVassouras area, between the towns of Rosário do Catete and Carmópolis (Figure 2). The cored succession has a thickness of 252.5 m, with samples taken at intervals of ~2.9 m. A total of 86 samples were analyzed. The stratigraphic succession comprises parts of the Muribeca and Riachuelo formations (Figure 3a). In general, the Muribeca Formation is composed of evaporites, clastics, and carbonate sediments laid down during the transitional phase. The Riachuelo Formation was deposited during the open-marine phase and consists of a carbonate-dominated sequence of calcareous mudstones and oolitic/oncolitic-bioclastic grainstones/packstones, with subordinate conglomerates, sandstones, marls, and shales [Koutsoukos et al., 1991]. In the studied samples, the Muribeca Formation is represented by the upper part of the Oiteirinhos Member (21.5 m), which consists of intercalations of grey to black bituminous shales, limestones, and siltstones. The Riachuelo Formation is represented by the lower part of the Taquari Member (231 m), composed of alternating calcareous mudstones and shales. The lower half of the cored section (270–125 m, lithofacies 1, 2a, and 2b) is dominated by calcareous mudstones and the upper half (125–10 m, lithofacies 2c) by shales (Figure 3b). Analyses for foraminifers and calcareous nannofossils were carried out on all samples. Planktonic foraminifers were found to be rare in the studied section. Samples analyzed between 249 m and 15 m revealed the presence of indeterminate hedbergellids and few specimens of Favusella washitensis (Marta Claudia Viviers, Petrobras, personal communication, 2015). These associations cannot be referred to global or local biozones or specific ages. Nevertheless, similar faunas are commonly recovered from the upper Aptian of the Sergipe Basin [Koutsoukos, 1989, 1992], corroborating the age inference based on palynological data (late Aptian, P-270 biozone). Available benthic foraminiferal data (samples from interval 277–19 m) point to an overall shallow-neritic environment with high terrigenous influx, the scarce microfauna being represented by agglutinant forms and locally by the genus Lenticulina (interval 79–42 m; Marta Claudia Viviers, Petrobras, personal communication, 2015). This calcareous-hyaline genus indicates the prevalence of dysoxic bottom-water conditions in this interval. Nannofossils were found in the section, but the analyses revealed no age-diagnostic species. The samples yielded an abundant and diverse palynoflora. The assemblages are typical of those reported from upper Aptian strata of Brazilian continental-margin basins and can be referred to the Sergipea variverrucata Zone [Regali et al., 1975]. In the studied section, the uppermost occurrence of S. variverrucata is recorded at 42.7 m. According to Regali and Santos [1999], in the Sergipe Basin the Sergipea variverrucata Zone is in part correlated with the Ap-1 planktonic foraminiferal zone of Koutsoukos [1989], which in turn is correlated with

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Figure 3. (a) Geological cross-section of the Muribeca and Riachuelo formations of the Sergipe Basin [adapted from Borchert, 1977]. D = discontinuity according to Mendes [1994]. Not to scale. (b) Lithostratigraphic scheme of well GTP-24-SE showing the gamma-ray curve and lithofacies [from Mendes, 1994]. Ts = transgressive surface and mfs = maximum flooding surface [from Carvalho et al., 2006a].

the global upper Aptian Hedbergella infracretacea Zone and part of the upper Aptian Globigerinelloides algerianus Zone [Koutsoukos and Bengtson, 1993] as presented in Figure 4. These correlations provide a late Aptian age for the studied section, estimated at 118–120(?) Ma.

4. Methods Samples were prepared at the Research Centre of Petrobras (CENPES), Rio de Janeiro, using the standard Petrobras method of palynological preparation compiled by Uesugui [1979] on the basis of methods developed by Erdtman [1943, 1969] and Faegri and Iversen [1966], among others. In this method, all mineral constituents are destroyed by hydrochloric and hydrofluoric acids before heavy-liquid separation. The remaining organic matter is sieved through a 10 μm mesh and mounted on slides. The samples were analyzed under a transmitted light microscope, and the analysis was based on the first 200 palynomorphs counted on each slide. The paleoenvironmental and paleoceanographic interpretation was based on the association of dinocysts (dinoflagellate cysts) revealed by cluster analysis to identify ecological similarities between palynomorph communities from different depositional settings. Cluster analysis based on abundance and composition was employed using the Ward method with Pearson-r similarity measure to establish groupings and recognize relationships between taxa. The cluster analysis forms discrete groupings based on abundances of the objects. The results are displayed in dendrograms. The Canonical Correspondence Analysis (CCA) [Legendre and Legendre, 1998] was performed using PAST software [Hammer et al., 2001]. This technique was chosen because the depths/species matrix is given for

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Figure 4. Biochronostratigraphic framework for the Aptian of the Sergipe Basin with the relationship between the Sergipea variverrucata pollen zone (shaded), local planktonic foraminiferal zones (modified from Koutsoukos [1989]), global planktonic foraminiferal zones, and Tethyan ammonoid zones [from Ogg and Hinnov, 2012].

environmental variables, herein ecological parameters (equitability, amorphous organic matter/phytoclasts ratio, productivity, and terrigenous input). Diversity and equitability indices were calculated for all samples using the PAST software [Hammer et al., 2001] to reconstruct paleoceanographic trends. The Shannon-Weaver diversity index [H(S)] takes into account the abundance of each species to characterize the diversity of assemblages. Equitability was calculated to describe evenness within assemblages. A value of 1 represents equal abundances of all species, whereas equitability approaches zero if one species dominates the assemblage. The dominance for each sample, expressed as a percentage, was determined on the basis of the formula D = (N1 + N2)/Nt, where N1 is the number of specimens of the most abundant species in a sample, N2 is the number of specimens of the second most abundance species in that sample, and Nt is the total number of specimens counted in the sample [Goodman, 1979]. The peridinioid to gonyaulacoid ratio (P/G) ratio, or heterotrophic/autotrophic ratio, introduced by Harland [1973], reveals changes in primary productivity in the geologic past [e.g., Eshet et al., 1992; Versteegh, 1994;

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Brinkhuis et al., 1998]. A peridinioid-dominated assemblage indicates nutrient-rich and low-salinity conditions related to freshwater influx into a marine environment [van Helmond et al., 2014]. By contrast, low values of the ratio, i.e., gonyaulacoid-dominated assemblages, indicate open-marine environments. The ratio used herein was described by Versteegh [1994] as P/G = nP/(nP + nG), where n is the number of specimens counted, P protoperidinioid dinoflagellate cysts (P-cysts), and G gonyaulacoid dinoflagellate cysts (G-cysts). The ratio of continental (terrestrial) to marine palynomorphs (C/M) was also described by Versteegh [1994], calculated as C/M = nC/(nC + nM), where n is the number of specimens counted, C spores + pollen grains, and M dinocysts + acritarchs. The C/M ratio was used herein to reconstruct changes in terrestrial input into the basin. The same procedure was applied for the ratio of amorphous organic matter (AOM) and phytoclasts (AOM/Phyto) to evaluate oxygen-depleted conditions in the environment, given that large amounts of AOM result from environments with high preservation potential and low energy [Carvalho et al., 2013]. An AOM-dominant percentage of total kerogen may be an indication of a reducing environment or at least a temporarily dysoxic to anoxic environment with high preservation potential. In low-energy, proximal, delta-top facies, some of the amorphous material present may be the product of degradation of higher plants [Tyson, 1989, 1993, 1995; Mendonça Filho et al., 2010; Pacton et al., 2011]. Total organic carbon (TOC) determinations and Rock-Eval pyrolysis data used herein are from Carvalho [2001] (http://archiv.ub.uni-heidelberg.de/volltextserver/1586/1/marcelo.pdf) and Carvalho et al. [2006a], respectively.

5. Dinocysts 5.1. General Characteristics Samples from the studied section yielded an abundant and diverse palynoflora. All samples contain dinocysts (Table 1), in most cases of moderate to high abundance, exceeding 100 individuals in ~50% of the slides (Appendix). The samples differ in taxonomic composition, abundance, and preservation of the palynomorphs, with dinocysts moderately to well preserved. Dinocysts are most abundant in the lower, mudstone-dominated part of the section (270–125 m; Figure 3b) but more diversified in the upper, shale-dominated part (125–10 m; Figure 3b). In terms of abundance, no significant differences between the two lithologies are observed. Twenty-nine species of dinocysts were identified in the samples (Table 1). The Shannon-Weaver diversity index varies from 0.28 to 2.14, with an average of 1.19, and dominance varies from 0.17 to 0.95, averaging 0.45. The species Subtilisphaera senegalensis, Spiniferites chebca, and Spiniferites ramosus dominate the samples. The first species comprises between 0 and 93.4% of all individuals on a slide, averaging 30.9%, with Spiniferites chebca and S. ramosus together reaching 30.3%. The tectonic phases and lithologic characteristics shown in Figure 3 indicate a transgressive trend, from transitional in the lower part to open marine in the upper part. The lower part of the section is dominated by peridinioids of the Subtilisphaera community (Table 1 and Figure 6) coincident with the nearshore conditions pointed out previously and suggested by previous studies [Vozzhennikova, 1965; Scull et al., 1966; Williams, 1977; Tappan, 1980; Sarjeant et al., 1987]. Higher in the section, where open-marine conditions are inferred, gonyaulacoid forms are more common. In this part, the Oligosphaeridium community also occurs and the Cyclonephelium-Exochosphaeridium community becomes predominant. 5.2. Dinocyst Communities Four dinocyst communities are recognized in the upper Aptian of the Sergipe Basin, viz., the Oligosphaeridium, Cyclonephelium-Exochosphaeridium, Spiniferites, and Subtilisphaera senegalensis communities. These were distinguished using cluster analysis (Figure 5) and named after their most dominant taxa (Figure 6). The cophenetic correlation coefficient of 0.83 demonstrates the utility of the method. 5.2.1. Oligosphaeridium Community The Oligosphaeridium community is the least abundant of the four dinocyst communities, represented by only 1.5% of the total occurrences. It is dominated by Oligosphaeridium complex (56.8% of this community) (Table 2) and also contains O. albertense, O. totum, O. poculum, O. pulcherrimum, and Systematophora spp.

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Table 1. Summary of Species and Suggested Paleoenvironments Based on Specialized References Species

References

Suggested Paleoenvironments Nearshore, shallow-marine; inner neritic

Oligosphaeridium albertense Oligosphaeridium complex Oligosphaeridium pocolum Oligosphaeridium pulcherrimum Oligosphaeridium totum Palaeoperidinium cretaceum

Millioud [1967], Lam and Porter [1977], Davey [1978], Burger [1982], Hedlund and Norris [1986], Helby and McMinn [1992], Duane [1994, 1996], Li and Habib [1996], and Skupien and Vašíček [2002] Brinkhuis and Zachariasse [1988], Lister and Batten [1988], Marshall and Batten [1988], Omran et al. [1990], Wilpshaar and Leereveld [1994], Gedl [1999], Pearce et al. [2003], and Mahmoud and Deaf [2007] Downie et al. [1971], Brinkhuis and Zachariasse [1988], Lister and Batten [1988], Marshall and Batten [1988], Omran et al. [1990], Harker et al. [1990], Wilpshaar and Leereveld [1994], Abdel-Kireem et al. [1996], Skupien and Vašíček [2002], and Mahmoud and Deaf [2007] Liengjarern et al. [1980], Brinkhuis and Zachariasse [1988], Marshall and Batten [1988], Courtinat and Schaaf [1990], Harker et al. [1990], Omran et al. [1990], Eshet et al. [1992], Abdel-Kireem et al. [1996], Li and Habib [1996], Lamolda and Mao [1999], Harris and Tocher [2003], Lignum et al. [2007], and Moustafa and Lashin [2012] Goodman [1979] and Barroso-Barcenilla et al. [2011]. Li and Habib [1996], Lamolda and Mao [1999], and Peyrot et al. [2012] Omran et al. [1990] Harker et al. [1990], Courtinat [1993], Wilpshaar and Leereveld [1994], Abdel-Kireem et al. [1996], Gedl [1999]; Prauss [2001], and Skupien and Vašíček [2002] Omran et al. [1990], Wilpshaar and Leereveld [1994], AbdelKireem et al. [1996], Duane [1996], Li and Habib [1996], Lamolda and Mao [1999], Prauss [2001], Skupien and Vašíček [2002], Harris and Tocher [2003], and Mahmoud and Deaf [2007] Harding [1990], Prauss [2001], and Harris and Tocher [2003];

Pervosphaeridium spp.

Courtinat [1993], Harris and Tocher [2003], and Lebedeva [2008]

Pseudoceratium securigerum

Gedl [1999], Prauss [2001], Skupien and Vašíček [2002], Mahmoud and Deaf [2007], and Moustafa and Lashin [2012] Downie et al. [1971], Davey and Rogers [1975], Brinkhuis and Zachariasse [1988], Marshall and Batten [1988], Courtinat and Schaaf [1990], Harker et al. [1990], Eshet et al. [1992], Courtinat [1993], Abdel-Kireem et al. [1996], Lamolda and Mao [1999], Prauss [2001], Skupien and Vašíček [2002], and Lignum et al. [2007] Davey and Rogers [1975], Jain and Millepied [1975], Wall et al. [1977], Regali [1989a], Omran et al. [1990], Arai et al. [1994], Brinkhuis [1994], Powell et al. [1996], Gedl [1999], Rochon et al. [1999], Arai et al. [2000], Antonioli [2001], Antonioli and Arai [2002], Skupien and Vašíček [2002], Harris and Tocher [2003], Arai [2007], Mahmoud and Deaf [2007], and Moustafa and Lashin [2012] Brinkhuis and Zachariasse [1988], Lister and Batten [1988], Marshall and Batten [1988], Omran et al. [1990], Wilpshaar and Leereveld [1994], Mahmoud and Deaf [2007] Brinkhuis et al. [1998] and Harris and Tocher [2003]. Courtinat and Schaaf [1990], Courtinat [1993], Abdel-Kireem et al. [1996], Harris and Tocher [2003], and Peyrot et al. [2011]

Apteodinium granulatum

Circulodinium distinctum

Cribroperidinium edwardsii

Cyclonephelium vannophorum

Dinopterygium cladoides Exochosphaeridium phragmites Florentinia mantellii Odontochitina operculata

Spiniferites ancorifer Spiniferites bejui Spiniferites chebca Spiniferites lenzi Spiniferites seghris Spiniferites ramosus Subtilisphaera cheit Subtilisphaera perlucida Subtilisphaera pirnaensis? Subtilisphaera senegalensis

Systematophora cretacea

Tanyosphaeridium sp. Trichodinium castanea

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Brackish and littoral; marginal-marine (deltaic); inner-neritic restricted marine

Most common in stable marine environments; inner-neritic and restricted marine; marginal-marine (deltaic); innerneritic

Marginal, brackish, coastal; nearshore, unstable environments; stressed environment; euryhaline

Relatively more inshore, marine restricted Nearshore, shallow-marine, associated with high carbonate content Open-marine mid-shelf Stable marine environments; normal salinity and oxygenation, brackish and littoral, salty marshy (restricted shallowmarine); restricted shallow-marine, reduced salinity Open-marine mid-shelf; euryhaline (O. pulcherrimum); stenohaline (O. totum); open-marine (inner-neritic), neritic; neritic to outer neritic; warmer and/or deeper shelf water

Euryhaline; brackish water; normal marine salinity to estuarine conditions ; enhanced primary productivity, estuarine circulation No environmental preferences; normal salinity and oxygenation; uniform habitat Brackish and littoral; marginal-marine; marginal-marine (deltaic); nearshore conditions Normal salinity and oxygenation, mid-shelf, stable marine environment; nearshore shallow-water environments and fall-off in an offshore direction; neritic; warmer and/or deeper shelf

Marginal, brackish, coastal; brackish and littoral in warmer water; stenohaline (S. pirnaensis); marginal-marine (deltaic) environment; salty marshy (restricted shallow-marine)

Inner-neritic and restricted-marine;, marginal-marine (deltaic)

No environmental preferences Paleoenvironments with high content of TOC; normal salinity and oxygenation; no environmental preferences; outerneritic preferences


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Figure 5. Ward Dendrogram (r-mode) of 15 dinocyst genera from the studied section showing the four communities.

The Oligosphaeridium community contains species with long processes, a feature assumed to be an indication of open-marine, neritic conditions (Table 1). Also, Oligosphaeridium pulcherrimum is euryhaline or able to adapt to a wide range of salinities [Harris and Tocher, 2003]. The Oligosphaeridium community occurs in only ~50% of the samples, mainly in the upper part of the section. At 65.9 m, this community displays a pronounced peak representing 37.5% of the total communities (Figure 7). It exceeds the general average of the community (1.5%) in only 15 samples. The community is rare in the lower part of the section, which is dominated by the Subtilisphaera community (Figure 7). 5.2.2. Cyclonephelium-Exochosphaeridium Community The Cyclonephelium-Exochosphaeridium community represents 31.6% of the dinocyst communities, making it the second most abundant. This community is composed of Cyclonephelium vannophorum, Exochosphaeridium phragmites, Circulodinium distinctum, Pervosphaeridium spp., Apteodinium granulatum, Tanyosphaeridium spp., Pseudoceratium securigerum, and Odontochitina operculata. Exochosphaeridium phragmites (46.4% of the community) and Cyclonephelium vannophorum (42.3% of the community) are the dominant species (Table 2). This community is present in 76 of the 86 samples and dominates the middle part of the section, where it shows three distinctive peaks, with the highest-abundance peak at 160.3 m (73.0%) (Figure 7). The community also shows two pronounced peaks in the upper part of the section (Figure 7). The relationship between the two most abundant genera, Cyclonephelium and Exochosphaeridium, has been discussed by other authors, specifically with respect to the Cenomanian-Turonian transition [Li and Habib, 1996; Harris and Tocher, 2003; Lignum et al., 2007; Peyrot et al., 2011; van Helmond et al., 2014]. Exochosphaeridium phragmites has been interpreted as typical of deeper water [Vozzhennikova, 1965; Scull et al., 1966; Williams, 1977; Tappan, 1980; Sarjeant et al., 1987] but has also been associated with proximal environments and in some cases even very restricted environments [Peyrot et al., 2011]. The species of the

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Figure 6. Dinocysts identified in the studied section: (A) Subtilisphaera senegalensis, (b) Spiniferites chebca, (c) Spiniferites ramosus, (d) Cyclonephelium vannophorum, (e) Exochosphaeridium phragmites, (f) Oligosphaeridium complex. Scale bar = 20 μm.

Cyclonephelium-Exochosphaeridium community are interpreted as indicative of shallow to bathyal conditions (Table 1). In some cases, Cyclonephelium is associated with more environmentally stressed conditions [e.g., Eshet et al., 1992; Courtinat, 1993; Lana, 1997, 1998; Lignum et al., 2007]. Most of the species composing the community are indicative of a shallow-marine environment, exceptions being Pervosphaeridium spp. and Tanyosphaeridium spp., which show very low abundances (0.1 and 0.3%, respectively) and no environmental preferences [Harris and Tocher, 2003]. The species Circulodinium spp., Apteodinium granulatum, Pseudoceratium securigerum, and Odontochitina operculata make up 11% of the CyclonepheliumExochosphaeridium community and are all indicative of nearshore conditions (Table 1). 5.2.3. Spiniferites Community The Spiniferites community is the most abundant community, comprising 38.2% of the total communities. The dominant species are Spiniferites chebca and Spiniferites ramosus (together 79.6% of this community).

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Table 2. Average Abundances (%) of Each Species and Its Respective Assemblages for the Studied Section Communities Oligosphaeridium community

Cyclonephelium-Exochosphaeridium community

Spiniferites community

Subtilisphaera community

Species

%

Oligosphaeridium complex Oligosphaeridium albertense Oligosphaeridium totum Systematophora cretacea Oligosphaeridium pulcherrimum Oligosphaeridium pocolum Exochosphaeridium phragmites Cyclonephelium vannophorum Pseudoceratium securigerum Apteodinium granulatum Circulodinium distinctum Tanyosphaeridium spp. Odontochitina operculata Pervosphaeridium spp. Spiniferites chebca Spiniferites ramosus Trichodinium castanea Spiniferites bejui Palaeoperidinium cretaceum Dinopterygium cladoides Florentina mantelli Spiniferites ancorifer Subtilisphaera senegalensis Spiniferites lenzi Spiniferites seghris Subtilisphaera cheit Subtilisphaera pirnaensis? Subtilisphaera perlucida? Cribroperidinium edwardsii Total of Oligosphaeridium community Total of Cyclonephelium-Exochosphaeridium community Total of Spiniferites community Total of Subtilisphaera community

56.8 25.3 7.4 4.2 4.2 2.1 46.4 42.3 5.3 4.4 1.0 0.3 0.3 0.1 41.0 38.6 17.4 1.4 0.9 0.5 0.2 0.04 92.9 5.6 0.6 0.4 0.3 0.2 0.1 1.5 31.6 38.2 28.6

The community also includes Trichodinium castanea, Palaeoperidinium cretaceum, Spiniferites ancorifer, Florentinia mantellii, Spiniferites bejui, and Dinopterygium cladoides (Table 2). Species of Spiniferites make up 81.0% of this community. The third most abundant species, Trichodinium castanea, is only moderately abundant (averaging 17.4% of the community). According to several studies (see Table 1), this species is indicative of normal salinity and oxygenation. Additionally, very low abundances of two species indicative of inshore conditions, Dinopterygium cladoides and Palaeoperidinium cretaceum [e.g., Courtinat and Schaaf, 1990; Courtinat, 1993; Abdel-Kireem et al., 1996; Harris and Tocher, 2003; Peyrot et al., 2011], are recorded in the community (together 1.4%). The Spiniferites community is particularly dominant in intervals characterized by low abundances of the Subtilisphaera community (Figure 7). The community is particularly abundant in the upper part of the section, where it reaches 79.2% of all communities (at 20.85 m), and is absent from the lower part of the section. However, the Spiniferites community shows conspicuous fluctuations in abundance (Figure 7). 5.2.4. Subtilisphaera Community The Subtilisphaera community represents 28.6% of the total communities and is dominated by Subtilisphaera senegalensis (92.9% of this community) (Table 2), which is the most abundant species in the whole section studied. It contains Subtilisphaera cheit, Subtilisphaera pirnaensis?, Subtilisphaera perlucida?, Spiniferites lenzi, Spiniferites seghris, and Cribroperidinium edwardsii. The Subtilisphaera community occurs in all samples and is the only community present in the lower part of the section (268.05 m) (Figure 7). Abundances show strong fluctuations from the middle to the upper part of the section, with lower values related to a high abundance of the Spiniferites community.

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Figure 7. Stratigraphic distribution of dinocyst assemblages, ecology indices (dominance, diversity, and equitability), P/G, C/M, AOM/Phyt ratios, and TOC. Abbreviations: P/G = peridinioid to gonyaulacoid dinoflagellate cysts; C/M = continental/marine palynomorphs; AOM/Phyt = amorphous organic matter to phytoclasts; TOC = total organic carbon. Dashed line = average values.

5.3. Dinocyst Ecology: Diversity, Equitability, and Dominance The values for dinocyst diversity and equitability in well GTP-24-SE generally increase upward in section (Figure 7); the lowest values are H(S) = 0.28 and E = 0.19. The maximum dinocyst diversity and equitability values occur in the upper part of the section, where average values of H(S) = 2.14 and E = 0.97 have been calculated. The lowest diversity and equitability values usually occur in intervals dominated by the Subtilisphaera community. High diversity and equitability values tend to coincide with high abundances of the Oligosphaeridium and Spiniferites communities (Figure 7). Dominance is inversely proportional to diversity and equitability, including minima (D = 19.1%) in the middle to upper part of the section. In general, high dominance values coincide with high abundances of the Subtilisphaera community (highest D = 93.5%). High values also occur where another community dominates the sample, whereas low values are correlated with a high abundance of the Oligosphaeridium community. The lowest dominance value coincides with the highest value for the Oligosphaeridium community (37.5% of total communities at 65.9 m). 5.4. Peridinioid/Gonyaulacoid Index In the studied section, only species of Subtilisphaera and Palaeoperidinium cretaceum are peridinioids. With the exception of the ceratioid cysts Odontochitina and Pseudoceratium, all other taxa are gonyaulacoids. Owing to the high abundance of Subtilisphaera senegalensis, the peridinioid/gonyaulacoid (P/G) ratio is controlled by this single species. The P/G values are plotted next to the values for diversity, equitability, dominance, and communities (Figure 7). Maximum P/G values (or dominance of peridinioids) occur in the lower part of the section, coinciding with the highest values of the Subtilisphaera community. Gonyaulacoids display strong fluctuations and become abundant from ~160 m upward. 5.5. Continental/Marine Index Changes in the co-occurrence of terrestrial palynomorphs (pollen and spores) and those of marine origin (dinocysts) in marine deposits can be used as an indicator of proximal-distal trends [Pellaton and Gorin,

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2005], thus providing a means for interpreting sea level changes and their impact on marine environments [Scott et al., 1984; Mudie, 1989; Versteegh and Zonneveld, 1994; Bombardiere and Gorin, 1998, 2000; McCarthy and Mudie, 1998; Carvalho et al., 2013]. In general, the ratio of terrestrial to marine palynomorphs decreases from nearshore to offshore environments. Terrestrial palynomorphs are present in all samples of the section. Usually, the terrestrial palynomorph curve coincides with the Subtilisphaera community and, consequently, with that of peridinioid cysts. Thus, the C/M ratio is highest in the lower part of the section (Figure 7). In the middle and upper parts of the section, this curve shows a decreasing trend, although with strong fluctuations.

Figure 8. Canonical correspondence analysis (CCA) plot showing the ordination direction of dinocyst communities and ecological parameters (equitability, AOM/Phyt, productivity and terrigenous input).

5.6. Amorphous Organic Matter/Phytoclasts Carvalho [2001] suggested that the AOM recorded in the GTP-24-SE section is primarily of marine origin, on the basis of moderate to high fluorescence, which is indicative of an aquatic origin and low oxygenation, in association with high abundance of marine palynomorphs. Thus, it is reasonable to assume that high values of the ratio indicate marine environments with low oxygenation, whereas low values reflect a higher degree of terrestrial input. The AOM/Phyto ratio, similarly to the C/M ratio, is slightly dominant in the lower part of the section (Figure 7). Above 110 m, the ratio shows an increasing trend with particularly high values between 75 and 55 m, corresponding to high abundances of the Cyclonephelium-Exochosphaeridium community. However, values of the C/M ratio decrease in the upper part of the section. The ratio of fern spores to xerophytic palynomorphs (Fs/X) was calculated by dividing the number of all in situ (non-reworked) fern spores by the number of xerophytic forms (Classopollis + Equisetosporites + Steevesipollenites + Gnetaceopollenites) (Figure 8). High values of Fs/X reflect humid conditions, as ferns depend on water to reproduce.

6. Discussion The upper Aptian succession of the Sergipe Basin is characterized by a transgressional trend, reflecting changes in environmental conditions over time. These changes are indicated by the lithologic characteristics of the column and coincide with interpretations based on vertical distribution patterns of the Oligosphaeridium, Cyclonephelium-Exochosphaeridium, Spiniferites, and Subtilisphaera dinocyst communities. The sharp break between the Oligosphaeridium and the Cyclonephelium-Exochosphaeridium communities shown in the dendrograms (Figure 5) reflects the separation of open-marine (e.g., Oligosphaeridium spp.) and nearshore or environmentally stressed dinocysts (e.g., Subtilisphaera spp., Cyclonephelium spp.). Three of the communities, the Cyclonephelium-Exochosphaeridium, Spiniferites, and Subtilisphaera communities, show stratigraphically characteristic occurrences (Figure 7). The Oligosphaeridium community is subordinate, with a very low abundance (1.5% of the total communities). 6.1. Subtilisphaera Community In the lower (268–180 m) and middle (112–72.25 m) parts of the section, the prominent feature is the dominance of the Subtilisphaera community, in particular of the species Subtilisphaera senegalensis. This community makes up an average of 79.2% of all communities in the lower part of the section, reaching 93.4% (183 cysts in 200 counted) at 190.75 m. In the middle part of the section the abundance is 41.8% (Figure 7).

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Table 3. Types of Subiltisphaera Ecozone Proposed by Arai et al. [1994] Ecozones

Characteristics

Subtilisphaera Ecozone (S. senegalensis) Subtilisphaera spp. Ecozone, with Spiniferites seghiris Subtilisphaera cheit Ecozone Subtilisphaera spp. Ecozone, diluted by other dinoflagellates Subtilisphaera spp. Ecozone, diluted by terrestrial palynomorphs

>70% of Subtilisphaera species Subtilisphaera species associated with Spiniferites seghiris Predominance of Subtilisphaera cheit High abundance of Subtilisphaera and other dinoflagellates High abundance of Subtilisphaera and terrestrial palynomorphs

Arai et al. [1994, 2000] proposed Subtilisphaera ecozones (Table 3) for the Early Cretaceous of the incipient South Atlantic. These ecozones were originally identified in the Aptian of the Ceará Basin [Regali, 1989b] and later in other continental margin basins of Brazil, including the Sergipe Basin [Carvalho, 2001, 2004]. According to Arai et al. [1994, 2000] the Subtilisphaera Ecozone is characterized by the predominance of Subtilisphaera cysts, forming a nearly monospecific community. On the basis of the very high abundance of Subtilisphaera, it can be concluded that the Subtilisphaera (S. senegalensis) Ecozone (Table 3) is present in this interval. Species of Subtilisphaera have been associated with restricted, low-salinity, marine environments [Jain and Millepied, 1975; van Helmond et al., 2014]. These species are common in low-diversity communities [Arai, 2001; Arai et al., 1994, 2000; Lana, 1997; Lana and Pedrão, 2000; Antonioli, 2001; Antonioli and Arai, 2002], reflecting an extensive bloom in mid-Cretaceous epicontinental seas. The distribution of Subtilisphaera strongly suggests connection with the Tethyan Realm [Arai, 2007, 2009, 2014; Arai et al., 2000], although there are reports of the genus also from the Southern Hemisphere [Morgan, 1980; Cookson and Eisenack, 1982]. The two intervals of the succession dominated by the Subtilisphaera community are characterized by low carbonate contents and a predominance of shales, suggesting that during these intervals a high source-area relief supplied large volumes of siliciclastic sediments [Koutsoukos et al., 1993]. This condition also explains the high content of terrestrial material, indicated by the high C/M ratios in this phase. Results of a canonical correspondence analysis (CCA) also suggest that the distribution of the Subtilisphaera community is mainly related to terrigenous input (high C/M; Figure 8). These results suggest a preferential distribution of this community in low-salinity conditions. The paleoceanographic model proposed by Pross [2001] and Pross and Schmiedl [2002] to interpret paleooxygenation based on the species Thalassiphora pelagica presents conditions similar to the intervals in the Sergipe succession, where Subtilisphaera senegalensis dominates. According to Pross [2001], horizons with high abundances of Thalassiphora pelagica are characterized by low diversity and equitability, high continental supply, high productivity, low salinity, a nearly monospecific occurrence, and inverse proportions of dinoflagellates characteristic of open-marine environments (e.g., Spiniferites spp.). These factors are supported by low values of diversity (H(S) = 0.3) and equitability (E = 0.2), very high values of P/G and C/M (Figure 7), high abundance of the Subtilisphaera community (79.2% of all communities), very low abundance of the Spiniferites community and absence of the Oligosphaeridium community (Figure 7). The high abundance of the Subtilisphaera community probably resulted from a more humid period, increased freshwater input, a high rate of nutrient supply, and the formation of a pycnocline separating slightly less saline surface waters from higher saline deeper waters. These conditions would have impeded vertical circulation, as suggested by Pross and Schmiedl [2002] for a dominance interval of Thalassiphora pelagica. Moreover, moderate to high AOM/Phyto ratios and moderate values of total organic carbon are recorded (TOC; Figure 7). A high AOM content is indicative of a more restricted environment far from terrigenous sources, unlike the environment indicated, where high abundance of Subtilisphaera community is recorded (Figure 7). Apparently, and despite the conditions of a restricted sea that allowed the accumulation of AOM, the Tethyan influence is confirmed by the presence of the Subtilisphaera Ecozone. In the following interval of the section studied, where the Subtilisphaera community is dominant (112–72.25 m), the relationship with the ecozone proposed by Arai et al. [1994] is also confirmed, including their “Subtilisphaera spp. Ecozone, diluted by other dinoflagellates” (Table 3). In this case, the Subtilisphaera community is associated predominantly with the Cyclonephelium-Exochosphaeridium community and shows moderate to high diversity indices. This association was also reported by Marshall and Batten [1988], supporting the view of a shallow-marine environment with episodes of terrestrial input.

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6.2. Spiniferites Community The Spiniferites community occurs in the middle (180–112 m) and uppermost (37.5–16 m) parts of the section, being more prominent in the middle interval (Figure 7), where it represents the first significant transgression recorded in the section (Figure 3). The community probably reflects the first important flooding surface observed in the section. In this part of the interval, there is a predominance of Spiniferites chebca. The high values of Spiniferites spp. coincide with the carbonate-dominated lithofacies 2b (e.g., calcareous mudstones). Koutsoukos et al. [1991] associated the deposition of calcareous mudstones with restricted shelf environments (pelmicrites) and offshore, open-shelf to upper-slope conditions (biomicrites) during peak carbonate deposition at maximum relative sea level rises. In the transition from the Subtilisphaera to the Spiniferites community, all measured parameters indicate an increase in water oxygenation, particularly in the productivity P/G (average 0.3) and AOM/Phyto ratios, whereas the terrestrial input (C/M) also decreases, though not significantly. This indicates a relative rise in sea level onto the shelf in this interval. However, the continuous input of terrestrial material in the marine environment created conditions for the formation of the Subtilisphaera community, as evidenced by three abundance peaks, at 167.3, 134.4, and 120.6 m. Moreover, these results show that the relative sea level rise probably occurred in pulses, with the changes causing replacement of the communities. This view is supported by the moderate values of the diversity and equitability indices and by the dominance values exceeding the general average (55.9%) in half of the samples (eight samples) from this interval. Conditions where the Spiniferites community is abundant in the uppermost part of the section (37.5–16 m) differ from those of the middle part (180–112 m). In the upper part, the community coexists primarily with the Cyclonephelium-Exochosphaeridium and Oligosphaeridium communities, with a predominance of Spiniferites ramosus. Here ecological parameters, such as diversity and equitability, show high values. The below-average values coincide with the predominance of the Subtilisphaera community, demonstrating that there were still episodes of terrestrial input into the basin, although of less intensity. In comparison with the other communities, the Spiniferites community tends to be more dominant in intervals characterized by low abundances of the Subtilisphaera community. CCA analysis (Figure 8) confirms that Spiniferites spp. tend to decrease in abundance in environments with high productivity and terrestrial input, where Subtilisphaera spp. are predominant. In summary, it appears that only Spiniferites spp. were able to adapt rapidly to the new conditions, i.e., a more open-marine environment with normal salinity. 6.3. Cyclonephelium-Exochosphaeridium Community The Cyclonephelium-Exochosphaeridium community is confined to the upper part of the section, with prominent abundance peaks in the interval 72.25–42.75 m (Figure 7). As mentioned above, this community already shows moderate to high values in the previous interval, where the Subtilisphaera community dominates. However, with increasing abundance, there was an abrupt decrease in the Subtilisphaera community, probably caused by a decrease or change in terrestrial input and/or a slight rise in sea level. The highest values of the Cyclonephelium-Exochosphaeridium community coincide with an interval of dark shales, the second highest TOC average (2.1%) and a moderate to high abundance of AOM. This combination is close to the suggested environmental characteristics of the Cyclonephelium and CyclonepheliumExochosphaeridium association [Li and Habib, 1996; Lamolda and Mao, 1999; Harris and Tocher, 2003; Barroso-Barcenilla et al., 2011; Peyrot et al., 2011; van Helmond et al., 2014]. As mentioned above, the Cyclonephelium-Exochosphaeridium community is interpreted as indicative of nearshore to bathyal conditions and in some cases of restricted marine environments (see Table 1). Furthermore, according to Lamolda and Mao [1999], Cyclonephelium typically occurs in organic-rich marls or “black shales,” indicating a stressed environment, as recorded by Lana [1997, 1998] for upper Cenomanian shales of the Potiguar Basin of Brazil, with low levels of oxygen throughout the water column. This evidence points to a dysoxic-anoxic event for this interval. On the basis of micropaleontological, geochemical, and sedimentological studies, Koutsoukos et al. [1991] suggested the occurrence of intermittent dysoxic-anoxic events on the shelf during deposition of the Riachuelo Formation. They associated the oxygen depletion with processes that restricted the free circulation of bottom

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Figure 9. (a) Stratigraphic column showing the Cyclonephelium-Exochosphaeridium community versus C/M, AOM/Phyto, TOC, and fern spores to xerophytes (Fs/X). Results of Rock-Eval pyrolysis for samples with high (orange dots) to moderate (yellow dots) content of Cyclonephelium, plotted in hydrogen index/oxygen index diagram distinguishing between two phases. Classification of kerogen according to Erbacher et al. [1996]. Abbreviations as in Figure 7. Dashed line = average values.

ocean waters including physiographic barriers in the earliest opening of the setentrional South Atlantic Ocean, salinity-stratified water masses, increased epipelagic primary productivity, and high sea levels. However, Koutsoukos et al. [1991] did not associate these events directly with an Oceanic Anoxic Event (OAE). Carvalho et al. [2006b] interpreted this part of the section as a highstand systems tract in the context of sequence stratigraphy. From the base of the sequence, marked by a flooding surface at 257 m (see Figure 3b), a clear decrease upward in dinocyst abundance and an increase in phytoclasts are observed. However, a maximum-flooding surface at 46.25 m recorded by Carvalho et al. [2006b] is located within the Cyclonephelium-Exochosphaeridium community interval and reflects the phase of deepest marine conditions, with low oxygenation values in of the studied section. This condition caused an increase in the TOC and AOM values (Figure 7). The interval of the Cyclonephelium-Exochosphaeridium community contains three pronounced peaks of the Oligosphaeridium community (Figure 7). This suggests that the oxygen-depleted condition was interrupted periodically during intervals of short-term oxygenation and normal salinity on the shelf during the initial stage of deposition of the Riachuelo Formation. Marshall and Batten [1988] differentiated the black shales of the Cenomanian-Turonian anoxic event from those of the Aptian and Albian, suggesting that the Albian in the North Atlantic was dominated by terrestrially derived plant detritus. Erbacher et al. [1996] designated the levels with black shales of marine origin “P-OAEs” (productivity oceanic anoxic events) and those of terrestrial origin “D-OAEs” (detrital oceanic anoxic events). Thus, P-OAEs are related to transgressive periods with type II kerogen, whereas D-OAEs are related to stillstands or falling sea levels and type III kerogen [Erbacher et al., 1996; Herrle et al., 2003]. The hydrogen-index/oxygen-index diagram for the Cyclonephelium-Exochosphaeridium community interval (Figure 9) shows that most samples are very close to the type III kerogen field, suggesting degradation of terrestrial organic matter. The stratigraphic distribution of the Cyclonephelium-Exochosphaeridium community and hydrogen-index/oxygen-index diagram (Figure 9) distinguishes two intervals. The first interval (112–72 m) is where the Cyclonephelium-Exochosphaeridium community becomes subordinate to the Subtilisphaera community, even with high values of terrestrial material (C/M and phytoclasts), here associated with high productivity. The second interval (72–36 m) occurs in association with the CyclonepheliumExochosphaeridium community, which shows high AOM and TOC.

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In the interval of high Cyclonephelium abundance and increased AOM/Phyto ratio, a conspicuous increase in the Fs/X ratio is observed (Figure 9). Humid conditions play an important role in dysoxic-anoxic events, especially those linked to D-OAEs, when runoff is enhanced [Erbacher et al., 1996]. According to Leckie et al. [2002], multiple discrete black shales of OAE 1b are recorded in Mexico, the North Atlantic basin (western Tethys) and the Mediterranean region (eastern Tethys). This late Aptian event has been linked to cooling and a eustatic sea level fall. Therefore, in the context of relative sea level fall, the nearshore and restricted-marine environments may have been formed as a result of structural physiographic highs and lows. The Cyclonephelium-Exochosphaeridium community typical of these environments increases accompanied by an increase in AOM abundance, significant TOC peaks and a decrease in C/M (Figure 9). However, the restricted environments periodically became more oxygenated (peaks of the Oligosphaeridium community), with a simultaneous decrease of the Cyclonephelium-Exochosphaeridium community and the TOC and AOM values. In summary, the Cyclonephelium-Exochosphaeridium community is possibly related to a dysoxic-anoxic event, although this community is of the D-OAE type of Erbacher et al. [1996]. This model is in agreement with the intermittent dysoxic-anoxic conditions proposed by Koutsoukos et al. [1991] for the Riachuelo Formation.

7. Conclusions Evaluation of the dinocyst assemblages of well GTP-24-SE reveals a paleoceanographic history for the late Aptian of the Sergipe Basin marked by a progressive regional transgression. The change from an onshore to open-marine environment was controlled by minor sea level fluctuations during deposition of the upper parts of the Muribeca Formation. This change was dominated by a progressive sea level rise at the onset of deposition of the Riachuelo Formation. 1. The dinoflagellate assemblages recorded in the studied section contain 28 moderately well preserved species dominated by Spiniferites chebca and Subtilisphaera senegalensis. Less abundant, but still common species are Cyclonephelium vannophorum, Spiniferites ramosus, and Exochosphaeridium phragmites. 2. Results from cluster analysis indicate the existence of four communities with distinct paleoecological and paleoceanographic preferences, viz., the Oligosphaeridium, Cyclonephelium-Exochosphaeridium, Spiniferites, and Subtilisphaera communities. 3. The Subtilisphaera community may be related to the Subtilisphaera Ecozone proposed by Arai et al. [1994], with the lower part of the section corresponding to the Subtilisphaera (S. senegalensis) Ecozone and the middle part to the “Subtilisphaera spp. Ecozone, diluted by other dinoflagellates,” suggesting a restricted to inner-neritic environment with Tethyan influence. 4. Statistical analyses (CCA and cluster analysis) show a strong, significant positive link between the contents of the Subtilisphaera community and terrestrial palynomorphs as well as the Cyclonephelium-Exochosphaeridium community; however, there is a significant negative correlation with the Spiniferites and Oligosphaeridium communities. 5. The first significant transgression recorded in the middle interval may reflect the onset of the global Aptian marine transgression, and is dominated by the Spiniferites community. The dark shales enriched with amorphous organic matter represent the deepest marine environments in the column. They are probably related to a dysoxic-anoxic event and are dominated by the CyclonepheliumExochosphaeridium community. The trends in the TOC and the Spiniferites/Cyclonephelium, AOM/Phyto, C/M, and Fs/X ratios indicate short-term oxygen depletion resulting from the topography of the area. However, most samples are classified as kerogen type III, suggesting a detrital origin (D-OAEs) for the dark shales layers. 6. The uppermost part represents the installation of a fully Tethyan, open-marine environment, evidenced by the dominant Spiniferites community.

Appendix A The succession studied yielded a rich dinocyst assemblage. A percentage count of the 29 species identified in the 87 palynological slides of well GTP-24-SE is given in the Appendix (Table A1).

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16.00 16.65 18.63 19.35 19.85 20.53 20.85 22.80 22.88 23.55 26.23 26.83 28.00 30.60 32.25 33.20 35.95 37.55 40.10 42.25 42.65 46.35 47.90 48.60 49.70 50.60 51.80 52.35 54.50 56.10 57.60 57.80 58.70 59.30 60.70 65.45 65.90 67.00 67.40 71.60 72.25 75.40 77.20 80.40 82.55 83.00 84.90 86.70 88.40 91.25 94.35 97.65 98.20

0.0 5.4 4.8 16.7 5.9 0.0 22.9 8.8 52.8 36.4 0.0 0.0 0.9 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.7 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 1.4 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0

0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 1.1 10.0 0.0 1.1 0.0 0.0

0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0

36.0 48.6 27.6 16.7 41.2 5.0 54.2 0.0 6.7 18.2 0.0 3.2 22.0 0.0 4.3 5.1 27.1 8.6 36.8 3.9 14.1 20.0 15.3 23.1 32.7 14.7 27.6 2.1 56.4 32.8 53.3 4.5 57.5 23.1 56.7 21.7 6.3 0.0 3.3 26.2 52.6 22.2 0.0 11.8 2.8 4.8 0.0 5.7 5.0 8.5 0.0 13.9 15.2

0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.7 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 11.3 0.0 0.0 0.0 0.0 0.0 0.0 0.0

0.0 2.7 0.0 0.0 0.0 0.0 2.1 0.0 0.0 0.0 0.0 3.2 0.0 0.0 18.4 0.0 45.8 0.0 0.0 2.0 63.5 44.0 43.1 5.5 25.2 60.3 24.1 16.7 10.3 34.5 23.3 37.3 3.4 11.5 15.9 42.2 6.3 14.3 36.7 52.4 12.6 3.7 8.3 23.7 34.7 11.3 36.6 70.1 2.5 40.7 11.5 20.8 15.2

0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.7 0.0 0.0 0.9 0.0 0.0 0.0 0.0 1.4 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0

0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 1.6 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 1.5 1.1 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 8.6 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0

0.0 0.0 0.0 5.6 0.0 0.0 0.0 1.5 0.0 0.0 0.0 0.0 0.9 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 11.5 0.0 0.0 0.0 0.0 4.6 0.0 0.0 1.7 12.5 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 1.0 0.0

2.0 16.2 0.0 0.0 5.9 0.0 0.0 0.0 0.0 0.0 4.0 0.0 1.8 4.8 0.0 0.0 2.1 0.0 0.0 1.0 0.6 0.0 2.8 0.0 0.0 0.0 0.0 11.5 0.0 2.5 0.0 4.5 6.9 0.0 1.2 5.6 12.5 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0

0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 1.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 6.3 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0

0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.6 0.0 0.0 0.0 0.0 0.0 0.0 1.0 0.0 0.8 0.0 0.0 0.0 0.0 0.0 0.0 6.3 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0

4.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 2.8 0.0 0.0 0.0 0.0 1.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 6.3 0.0 0.0 0.0 0.0 0.0 0.0 1.1 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0

DEPTH Apteodinium Circulodinium Cribroperidinium Cyclonephelium Dinopterigium Exochosphaeridium Florentina Odontochitina Oligosphaeridium Oligosphaeridium Oligosphaeridium Oligosphaeridium Oligosphaeridium (m) granulatum distinctum edwardsii vannophorum cladoides phragmites mantelli operculata albertense complex pocolum pulcherrimum totum

Table A1. Dinocyst Species Distribution (Percentages) of Well GTP-24-SE

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0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0

0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.6 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0

12.0 2.7 11.4 0.0 0.0 0.0 2.1 0.0 1.1 9.1 20.0 0.0 4.6 0.0 2.8 10.1 4.2 2.6 0.0 0.0 0.0 0.0 0.0 2.2 0.9 2.9 0.0 0.0 0.0 0.8 0.0 0.0 0.0 0.0 4.3 0.0 0.0 2.9 3.3 2.4 3.2 0.0 0.0 4.3 0.0 1.6 0.0 0.0 5.0 0.0 1.1 1.0 0.0

12.0 21.6 25.7 11.1 0.0 0.0 8.3 1.5 10.1 9.1 36.0 25.4 40.4 28.6 55.3 63.3 0.0 38.8 24.1 1.0 3.2 20.0 18.1 1.1 25.2 13.2 10.3 1.0 5.1 0.8 1.1 1.5 0.0 26.9 6.7 2.8 0.0 8.6 10.0 4.8 5.3 3.7 0.0 2.2 4.2 3.2 0.0 14.9 5.0 0.0 0.0 22.8 33.3

0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0

6.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 1.1 0.0 0.0 0.0 11.0 4.8 5.7 0.0 0.0 6.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0

20.0 2.7 8.6 38.9 11.8 5.0 0.0 13.2 16.9 18.2 8.0 1.6 15.6 57.1 0.0 17.7 8.3 25.0 24.1 4.9 16.0 6.0 12.5 59.3 11.2 7.4 23.0 18.8 15.4 21.0 20.0 9.0 25.3 0.0 10.4 23.3 6.3 11.4 36.7 7.1 25.3 1.9 0.0 16.1 9.7 53.2 2.4 8.0 0.0 13.6 0.0 27.7 27.3

0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 1.1 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0

0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0

0.0 0.0 0.0 0.0 0.0 0.0 0.0 2.9 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0

0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 2.4 0.0 0.0 0.0 2.3 0.0 0.0

0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0

8.0 0.0 2.9 11.1 35.3 90.0 10.4 72.1 10.1 9.1 32.0 65.1 0.0 4.8 12.1 3.8 12.5 18.1 6.0 87.3 0.6 0.7 0.0 7.7 2.8 0.0 4.6 34.4 12.8 5.0 2.2 43.3 2.3 38.5 4.3 2.2 31.3 54.3 10.0 7.1 1.1 68.5 91.7 40.9 47.2 4.8 58.5 0.0 72.5 37.3 83.9 1.0 6.1

0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 1.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.6 6.3 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0

0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 3.4 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.6 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0

0.0 0.0 19.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 2.8 0.0 0.0 0.0 0.0 0.0 9.0 0.0 0.6 8.7 4.2 1.1 1.9 0.0 5.7 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 9.7 0.0 0.0 0.0 0.0 0.0 11.9 3.0

Palaeoperidinium Pervosphaeridium Pseudoceratium Spiniferites Spiniferites Spiniferites Spiniferites Spiniferites Spiniferites Subtilisphaera Subtilisphaera Subtilisphaera Subtilisphaera Systematophora Tanyosphaeridium Trichodinium cretaceum spp. securigerum ramosus ancorifer bejuii chebca lenzi seghris cheit perlucida? pirnaensis? senegalensis cretacea spp. castanea

Table A1. (continued)

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99.20 101.70 103.15 108.10 109.40 110.60 112.70 119.50 120.60 122.85 124.40 124.67 128.10 130.55 134.45 135.75 146.10 157.15 160.35 167.25 170.43 178.56 182.06 189.8 190.75 202.37 205.35 214.75 227.10 240.65 256.10 259.05 268.05 268.50

6.5 0.0 0.0 4.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 1.6 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 7.5 0.0 0.0 0.0 0.0 0.0

0.0 10.8 25.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 4.8 0.0 0.0 0.0 0.0 0.0 0.0 0.0

0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.5 5.6 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0

0.0 18.9 2.8 2.0 1.4 4.8 0.0 0.0 0.9 0.0 0.0 0.0 2.8 0.5 0.8 15.6 0.0 0.0 0.0 0.0 0.6 0.0 0.0 0.0 0.0 0.0 0.0 5.7 0.0 0.0 0.0 0.0 0.0 0.0

0.0 0.0 0.0 0.0 0.0 0.0 2.7 0.0 0.9 0.0 2.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 2.7 0.0 0.0 0.0 0.0

0.0 13.5 0.0 0.0 27.8 23.8 5.4 6.9 0.0 1.4 7.0 19.3 0.0 1.6 0.0 10.2 1.2 0.0 0.0 5.8 16.0 11.1 1.2 0.0 0.0 0.0 0.0 13.2 0.0 0.0 0.0 0.0 0.0 0.0

0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 2.2 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0

0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0

0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0

0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0

0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0

0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0

0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0

DEPTH Apteodinium Circulodinium Cribroperidinium Cyclonephelium Dinopterigium Exochosphaeridium Florentina Odontochitina Oligosphaeridium Oligosphaeridium Oligosphaeridium Oligosphaeridium Oligosphaeridium (m) granulatum distinctum edwardsii vannophorum cladoides phragmites mantelli operculata albertense complex pocolum pulcherrimum totum


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0.0 5.4 0.0 0.0 0.0 0.0 0.0 3.4 0.0 0.0 18.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.5 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0

0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.6 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0

0.0 2.7 11.1 18.0 0.0 0.0 0.0 0.0 0.0 0.0 4.0 1.8 5.6 0.0 0.0 6.1 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0

12.9 16.2 19.4 6.0 26.4 0.0 67.6 20.7 0.9 4.2 8.0 17.4 22.2 7.9 0.0 10.2 11.9 4.8 15.9 14.4 46.9 51.1 12.3 8.7 0.0 5.6 9.5 5.7 0.0 10.8 4.4 0.0 14.8 87.0

0.0 0.0 0.0 0.0 0.0 0.0 2.7 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0

0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.5 0.0 0.0 0.0 0.0 0.0 0.0 0.6 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0

6.5 18.9 8.3 0.0 6.9 0.0 10.8 48.3 1.8 23.6 45.0 41.3 19.4 12.2 3.3 7.5 53.6 61.9 73.0 4.3 22.8 8.9 0.0 4.3 6.1 22.2 23.8 0.0 10.0 16.2 15.6 16.7 0.0 13.0

0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 22.2 0.0 0.0 0.0 0.0 0.0 0.0 72.6 0.0

0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 2.5 0.0 0.0 12.5 5.9 0.0

0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 2.5 0.0 0.0 0.0 0.0 0.0 7.5 0.0 0.0 0.0 0.0 0.0

0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0

0.0 0.0 0.0 0.0 0.0 2.4 0.0 0.0 2.8 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 2.5 0.0 0.0 0.0 0.0 0.0

74.2 13.5 33.3 70.0 1.4 66.7 2.7 20.7 92.7 70.8 6.0 0.9 13.9 0.5 93.4 0.0 1.2 33.3 9.5 74.8 0.6 2.2 82.7 87.0 92.9 44.4 57.1 75.5 70.0 70.3 80.0 70.8 6.7 0.0

0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 1.2 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0

0.0 0.0 0.0 0.0 0.0 2.4 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 1.2 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0

0.0 0.0 0.0 0.0 36.1 0.0 8.1 0.0 0.0 0.0 10.0 19.3 36.1 76.7 2.5 50.3 31.0 0.0 0.0 0.7 11.7 24.4 0.0 0.0 0.0 0.0 4.8 0.0 0.0 0.0 0.0 0.0 0.0 0.0

Palaeoperidinium Pervosphaeridium Pseudoceratium Spiniferites Spiniferites Spiniferites Spiniferites Spiniferites Spiniferites Subtilisphaera Subtilisphaera Subtilisphaera Subtilisphaera Systematophora Tanyosphaeridium Trichodinium cretaceum spp. securigerum ramosus ancorifer bejuii chebca lenzi seghris cheit perlucida? pirnaensis? senegalensis cretacea spp. castanea


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Paleoceanography Acknowledgments We are grateful to Javier Helenes Escamilla (CICESE, Ensenada, Mexico) and an anonymous reviewer, who improved this paper significantly with suggestions and critical comments. We also thank Susanne Feist-Burkhardt (SFB Geological Consulting and Services, Ober-Ramstadt, Germany) for additional palynological analyses of the GTP-24 well (unpublished Petrobras report), which provide a more precise age assessment for the section. We thank especially Marta Claudia Viviers (Petrobras, Rio de Janeiro, Brazil), who kindly analyzed the calcareous microfauna in several samples of the studied section. We express our thanks to Petrobras for giving M.A. Carvalho the opportunity to study the material. This study was funded mainly by the Brazilian National Council for Scientific and Technological Development (Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq), grant no. 302064/2010-9), the Research Support Foundation of Rio de Janeiro State (Fundação Carlos Chagas Filho de Amparo à Pesquisa do Rio de Janeiro (FAPERJ), grant no. E-26/103.028/2008), the Brazilian Research Funding Organization (Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES), grant no. BEX 11616/13-0), and the German Academic Exchange Service (DAAD), grant no. A/13/03339). The data used in this study can be accessed at http://archiv.ub.uniheidelberg.de/volltextserver/1586/1/ marcelo.pdf.

CARVALHO ET AL.

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