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27 October 2020 Neogene Palynostratigraphic Zonation of the Maranon Basin, Western Amazonia, Peru
F.J. Parra, R.E. Navarrete, M.M. di Pasquo, M. Roddaz, Y. Calderón, P. Baby
Author Affiliations +
Abstract

The palynology (150 species of pollen grains, 43 species of spores, eight species of dinoflagellate cysts, five genera of algae, two genera of fungal spores, foraminiferal linings, and copepod eggs) of the Neogene succession in the Marañon Basin, north Peru, was thoroughly investigated for the first time from six industrial wells (Arabela-1X, Maynas-1, Tucunare-1X, Tigrillo-30X, Nahuapa-24X, and La Frontera-1). Six palynozones spanning the Early Miocene to the Early Pliocene were defined. The zones in stratigraphically ascending order are as follows: the Mar-A Corsinipollenites oculusnoctis Zone (Aquitanian to early Burdigalian: 23.03–17.71 Ma), delimited by the appearance of Acaciapollenites myriosporites, Retitricolporites wijmstrae and/or Corsinipollenites oculusnoctis and/or the disappearance of Cicatricosisporites dorogensis at the base; the Mar-B Malvacipolloides (Echitricolporites) maristellae Zone (Burdigalian: 17.71–16.1 Ma), from Malvacipolloides maristellae at the base to the disappearance of Retitricolporites wijmstrae at the top; the Mar-C Mauritiidites crassibaculatus Zone (latest Burdigalian to Late Langhian: 16.1–14.2/13.9 Ma), from the appearance of Grimsdalea magnaclavata at the base to the disappearance of Retitriporites dubiosus and/or the appearance of Crassoretitriletes vanraadshooveni and/or Psilastephanoporites tesseroporus; the Mar-D Crassoretitriletes vanraadshooveni Zone (Late Serravallian: 14.2–11.62 Ma), from the appearance of Crassoretitriletes vanraadshooveni and/or Psilastephanoporites tesseroporus to the disappearances of Mauritiidites crassibaculatus, Bombacacidites nacimientoensis, and Cyathidites congoensis; and the Mar-E Psilastephanoporites tesseroporus Zone (Early Tortonian to Late Messinian: 11.62–5.48 Ma) from the disappearance of Corsinipollenites oculusnoctis and/or Cyathidites congoensis to the disappearance of Psilastephanoporites tesseroporus and/or Siltaria santaisabelensis. These zones were corroborated by means of events ordination demonstrated using graphic correlation. The Mar-F Ctenolophonidites suigeneris Zone (latest Messinian to Zanclean) is described only in the Frontera-1 well from the disappearance of Psilastephanoporites tesseroporus to the last record of Ctenolophonidites suigeneris and/or Siltaria hammenii. This study suggests that Pliocene sedimentation is also recorded in the Western Amazonia of Peru, and provides new palynological information compared with the Mio–Pliocene Solimões, Acre, and eastern Amazonas basins.

1. Introduction

The Marañon Basin is one of the most important basins in Peru in terms of hydrocarbon resources, but despite many decades of active exploration (Calderón et al. 2017a, 2017b; Baby et al. 2018), biostratigraphic research has not been conducted. The Marañon Basin contains Paleozoic and Mesozoic source rocks and Mesozoic reservoirs and subthrust traps. Recent studies by Calderón et al. 2017a, 2017b) have improved understanding and modeling of petroleum systems in this basin, especially regarding the formation and deformation of the subthrust traps. However, uncertainties remain concerning the timing and rate of Cenozoic burial, which forms part of the petroleum kitchen system. This is mainly because the Cenozoic deposits of the Marañon Basin are poorly dated (Roddaz et al. 2010).

The stratigraphic ages of Cenozoic units are generally based on different groups of fossils, including algae (Marocco et al. 1995) and invertebrates, such as mollusks and ostracods, from the Chambira, Pebas, and Solimões formations (Whatley et al. 1998; Muñoz-Torres et al. 2006; Ramos 2006; Wesselingh et al. 2006a; Wesselingh and Ramos 2010), and ostracods, foraminifera, and palynomorphs from the adjacent Solimões Basin (Linhares et al. 2011, 2017, 2019; Leandro et al. 2019), as well as vertebrates (Monsch 1998; Salas-Gismondi et al. 2007). The Pebas/Solimões and Nauta formations were palynologically dated from outcrops and wells in the Solimões and Acre basins (Hoorn 1993, 1994a, 1994b, 2006; Hoorn et al. 1996, 2010a, 2010b, 2017; Rebata et al. 2006a, 2006b; Leite et al. 2016; Leandro et al. 2019; Linhares et al. 2019). These units were also recognized from the Santa Lucia borehole drilled in the southern Marañon Basin (Hermoza 2004) and from three exploration wells (Jibaro 7/1AB-21-181, Huayuri Sur 15/1-AB-15-184D and Capahuari Norte 9/1AB-3-204) drilled in the westernmost part of the Marañon Basin (Hermoza 2004; Hermoza et al. 2005; Wesselingh et al. 2006a). These well sections were dated via mollusks by Wesselingh et al. (2006a) who also correlated them with palynozones (Hoorn 1993, 1994a).

Table 1.

Location of the six studied wells: Arabela-1X, Maynas-1, Tucunare-1X, Tigrillo-30X, Nahuapa-24X, and La Frontera-1 in the Marañon Basin. N: number of samples analyzed; UTM (18S) coordinates in meters; depth in feet (1 ft = 0.3 meters).

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The Neogene palynozones in South America have mainly been established in Colombian, Venezuelan, and Brazilian basins (Van der Hammen 1956; Germeraad et al. 1968; Regali et al. 1974a, 1974b; Lorente 1986; Hoorn 1993; Jaramillo et al. 2011). More specific palynostratigraphic works have been developed in the Solimões and Acre basins (Hoorn 1994a, 1994b; da Silva et al. 2010; Silveira and Souza 2015, 2016; Leite et al. 2016; Leandro et al. 2019; Linhares et al. 2019). Those paleontological studies have helped to establish correlations between Amazonian basins and to reconstruct Neogene biomass evolution (Wesselingh et al. 2006a; Hoorn and Wesselingh 2010; Jaramillo et al. 2010; Boonstra et al. 2015; Antoine et al. 2016; Jaramillo et al. 2017). However, to date, no detailed palynostratigraphic research has been carried out in the Marañon Basin, and the nature, evolution, and age range of the Neogene palynofloras of this basin remain poorly understood.

This study aims to establish a spore/pollen zonation for the Neogene sediments of the retroarc foreland (most subsiding area; Roddaz et al. 2010) of the Marañon Basin based on the identification of qualitative changes in palynomorphs (spores, pollen, and dinoflagellate cysts) through the intervals sampled in six exploration wells (Table 1 and Figure 1).

2. Geological setting

The Marañon Basin covers approximately 320,000km2 (Mathalone and Montoya 1995) and is located between 0°N and 7°30′S and 70 and 78°W in northeastern Peru (Figure 1). It is currently considered a foredeep depozone of the northern Amazonian retroarc foreland basin (Roddaz et al. 2005, 2010). The Huallaga and Santiago basins to the southwest and west, respectively, separate the Marañon Basin from the Subandean zone, and to the northeast the basin is bordered by the Iquitos forebulge (Roddaz et al. 2005, 2010). It continues as the Oriente Basin in Ecuador to the northwest and the Putumayo Basin in Colombia to the north. The Guyanese shield and Solimões Basin border the Marañon Basin to the east. To the south, the basin is bordered by the Ucayali and Acre basins, and to the southeast the Contaya arch separates it from the Ucayali Basin (Roddaz et al. 2005).

The Amazonian retroarc foreland basin system started to form between the late Maastrichtian and early Paleocene, during the first period of Amazonian Andes mountain building (Hurtado et al. 2018; Louterbach et al. 2018). This late Maastrichtian–Paleocene period of Andean tectonic loading was followed by an unloading stage during the Early–Middle Eocene (Roddaz et al. 2010). From the Middle–Late Eocene, the Amazonian retroarc foreland basin was subjected to continuous flexural subsidence driven by the continuous Andean tectonic loading, which promoted high sedimentation rates in the foredeep depozone (Roddaz et al. 2010). The formation and forward propagation of the eastern Amazonian orogenic thrust wedge began in the Oligocene (30–24 Ma) (Eude et al. 2015), causing flexural subsidence and high sedimentation rates in the Marañon foredeep (Roddaz et al. 2010).

The stratigraphy of Amazonian foreland basins has been synthesized by Roddaz et al. (2010). The Neogene sedimentary pile consists of late Oligocene–Miocene Chambira, Early–Late Miocene Pebas, Pliocene Marañon, and Quaternary Corrientes formations. These units are generally poorly dated. The Pebas Formation, with a thickness of approximately 1000 m (Wesselingh et al. 2006a), transitionally overlies the Chambira Formation (Oligocene) and is in underlying concordant contact with the Marañon Formation. The transition is characterized by blue clays, fine-grained lithic sandstones, and lignite layers rich in diverse and well-preserved invertebrate and vertebrate fossils; the base of this formation was dated around 22.5–23.9 Ma (Oligocene–Miocene boundary) (Wesselingh et al. 2006a).

3. Previous studies

Numerous studies have recorded the presence of palynomorph taxa in the Pebas and Solimões formations and other coeval units outcropping in Colombia, Brazil, and Peru (Hoorn 1993, 1994a, 1994b, 2006; Hoorn et al. 1995, 1996, 2010a, 2010b; Räsänen et al. 1995; Gingras et al. 2002a, 2002b; Hoorn and Ramos Feijó 2006; Rebata et al. 2006a, 2006b; Wesselingh 2006; Wesselingh et al. 2006a, 2006b, 2010; Hovikoski et al. 2007b; Latrubesse et al. 2007, 2010; da Silva et al. 2010; Gross et al. 2011; Leite et al. 2017; Leandro et al. 2019; Linhares et al. 2019). These formations generally date from the Early–Late Miocene (Hoorn and Wesselingh 2010; Latrubesse et al. 2010; Roddaz et al. 2010; Boonstra et al. 2015; Hoorn et al. 2017; Jaramillo et al. 2017; Leite et al. 2017). However, it is important to note that no palynological studies exist that deal with the Neogene sedimentary units of the Marañon Basin.

Figure 1.

Location of the six studied deep exploration wells (white-black circles). Structural boundaries of the Marañon Basin (after Roddaz et al. 2005).

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Neogene deposits of the Marañon Basin, to date, have been dated mainly based on palynozones defined by Hoorn (1993) for the Solimões and Acre basins, the Malacostraca zones defined by Wesselingh et al. (2006a), and the ostracod zones defined by Muñoz-Torres et al. (2006). Hoorn (1993) defined five palynozones for the Solimões Basin: the Verrutricolporites Acme Zone (Early Miocene), the Retitricolporites Acme Zone (Early Miocene), the PsiladiporitesCrototricolpites Concurrent Range Zone (late Early to early Middle Miocene), the Crassoretitriletes Interval Zone (Middle Miocene), and the Grimsdalea Interval Zone (late Middle to early Late Miocene), which correlated with those by Germeraad et al. (1968) and Lorente (1986). In the same basin, da Silva et al. (2010) defined the Asteraceae–Fenestrites Zone and recognized the Psilatricolporites caribbiensis palynozone of Lorente (1986). More recently, these zones in the Solimões Basin were recognized by (Leite et al. 2017; Linhares et al. 2017, 2019; Leandro et al. 2019), who further identified Lorente's (1986) palynozones: the Crassoretitriletes Interval Zone (Middle Miocene), the Asteraceae Interval Zone (Late Miocene), the Psilatricolporites caribbiensis Interval Subzone (latest Miocene–Pliocene), and the EchitricolporitesAlnipollenites Interval Subzone (Late Pliocene).

4. Sample material and procedures

A total of 77 ditch-cutting samples from six exploration wells (Arabela-1X, Maynas-1, Tucunare-1X, Tigrillo-30X, Nahuapa-24X, and La Frontera-1) located in the Marañon Basin were studied for their palynological content (Table 2 and Figure 1). The samples varied from silty shale to shale, claystone, sandy clay, and clayey, very fine sandstone. The palynological samples were prepared according to the standard procedure (Wood et al. 1996). The preparation of palynological slides was carried out in the Paleosedes Laboratory in Bogotá, Colombia ( http://www.paleosedes.tk). Samples were processed using hydrochloric acid, hydrofluoric acid, and zinc chloride solutions. The slides were analyzed at the Paleosedes Biostratigraphy Laboratory and the Palynostratigraphy and Paleobotany Laboratory of the institute CICYTTP-CONICET-ER-UADER ( http://www.cicyttp.org.ar) in Argentina. Slides and residues are housed at the Palynostratigraphy and Paleobotany Laboratory of the Centro de Investigaciones Científicas y Transferencia de Tecnología a la Producción (CICYTTP) and cataloged under CICYTTP acronyms; Table 2).

Table 2.

Analyzed intervals [depth in feet (1ft = 0.3 meters)] from Arabela-1X, Maynas-1, Tucunare-1X, Tigrillo-30X, Nahuapa-24X, and La Frontera-1 wells in the Marañon Basin and Centro de Investigaciones Científicas y Transferencia de Tecnología a la Producción (CICYTTP-Pl) collection number of each analyzed sample.

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Two slides per sample (oxidized and non-oxidized) were scanned for palynomorph identification using transmitted light microscopes with a digital camera (Leitz Labor Lux S and Labomed 10 in Colombia; Nikon E200 and Labomed 5 in Argentina). Well-preserved specimens were selected and illustrated in Plate 1 using England Finder coordinates. Palynomorph counting and logging were done by applying straight transects across each slide. Species names and abundance of taxa were recorded on data sheets. Six palynomorph distribution charts were prepared based on each palynomorph identified in the well sections, and the abundances of spores, pollen grains, fungal spores, algae, dinoflagellate cysts, acritarchs, foraminiferal linings, and copepod eggs were tabulated in the Tilia software (Grimm 2015) (Appendices 1–6). The recovered palynomorphs were gathered in seven morphogroups (Table 3) and percentages for the morphogroups in all wells were calculated (Table 4). Approximately 100–200 specimens were counted per sample. However, some samples with abundances lower than 100 identifications were also included in the qualitative analyses due to their biostratigraphic significance (see Appendices 1–6).

The qualitative vertical arrangement of taxa identified from the wells was used to interpret first downhole occurrence or last appearance datum (LAD) and last downhole occurrence or first appearance datum (FAD) data. Palynostratigraphic studies and online catalogues of species from northern South America (Van der Hammen 1956; Germeraad et al. 1968; Regali et al. 1974a, 1974b; Lorente 1986; Muller et al. 1987; Tryon and Lugardon 1991; Hoorn 1993, 1994a; da Silva et al. 2010; Jaramillo et al. 2011; Raine et al. 2011; Silveira and Souza 2015, 2016; Leite et al. 2017; Williams et al. 2017; Jaramillo and Rueda 2019) were consulted for taxonomic determinations (see the list of species with their authors below) and stratigraphic ranges of the species suitable for biostratigraphy (Table 5). Critical palynomorph taxa were selected according to their stratigraphic value, and the most biostratigraphically significant events are indicated in Figure 2. To validate these findings, the graphic correlation technique of Shaw (1964) was applied to the dataset using GraphCor: Interactive Graphic Correlation software (Hood 1998) to obtain a composite section (Table 6) that was reordered and plotted (Figure 3) according to the stratigraphic succession, thus revealing biostratigraphic units. Details of this method can be consulted in the extensive compilation of Mann and Lane (1995).

Plate 1.

Photographs of the main palynomorphs from the studied wells. 1. Laevigatosporites catanejensis CICYTTP-2005 Arabela 1X (610–640ft), EF M12/2; 2. Laevigatosporites granulatus CICYTTP-2014 Arabela 1X (1810–1840ft), EF L32/2-4; 3. Polypodiisporites usmensis CICYTTP-2007 Arabela 1X (910–940ft), EF H25/2; 4. Cyathidites congoensis CICYTTP-2074 Frontera 1 (1860–1880ft), EF N35/2; 5. Foveotriletes ornatus CICYTTP-2068 Nahuapa 24X (5720–5750ft), EF N32/1-2; 6. Osmundacidites ciliatus CICYTTP-2074 Frontera 1 (1860–1880ft), EF R35/1; 7. Retitriletes altimuratus CICYTTP-2061 Nahuapa 24X (3740–3770ft), EF W21/3-4; 8. Cicatricosisporites dorogensis CICYTTP-2017 Arabela 1X (3310–3340ft), EF E3/3-2; 9. Crassoretitriletes vanraadshooveni CICYTTP-2052 Nahuapa 24X (2210–2240ft), EF H43/1; 10. Magnastriatites grandiosus CICYTTP-2057 Nahuapa 24X (3110–3140ft), EF O43/2; 11. Grimsdalea magnaclavata CICYTTP-2053 Nahuapa 24X (2300–2330ft), EF W17/3; 12. Gomphrenipollis minimus CICYTTP-2061 Nahuapa 24X (3740–3770ft), EF T34/2-3; 13. Monoporopollenites annulatus CICYTTP-2058 Maynas 1 (3350–3400ft), EF P44/1; 14. Psilamonocolpites medius CICYTTP- 2046 Tigrillo 30X (8370–8400ft), EF Q11/4; 15. Mauritiidites franciscoi minutus CICYTTP-2014 Arabela 1X (1810–1840ft), EF S38/1; 16. Mauritiidites franciscoi franciscoi CICYTTP-2031 Tucunare 1X (6750–6800ft), EF H42/1; 17. Cyclusphaera scabrata CICYTTP-2020 Maynas 1 (4400–4450ft), EF E10/3; 18. Corsinipollenites psilatus CICYTTP-2014 Arabela 1X (1810–1840ft), EF N12; 19. Echitriporites cricotriporatiformis CICYTTP-2006 Arabela 1X (820–850ft), EF F44/3; 20. Proteacidites triangulatus CICYTTP-2061 Nahuapa 24X (3740–3770ft), EF Z33/1; 21. Retitricolpites simplex CICYTTP-2035 Tucunare 1X (7600–7650ft), EF P43/2; 22. Crassiectoapertites columbianus CICYTTP-2061 Nahuapa 24X (3740–3770ft), EF F38/1; 23. Bombacacidites nacimientoensis CICYTTP-2059 Nahuapa 24X (3560–3590ft), EF J35/1-3; 24. Bombacacidites brevis CICYTTP-2017 Arabela 1X (3310–3340ft), EF R40/3; 25. Malvacipolloides maristellae CICYTTP-2034 Tucunare 1X (7350–7400ft), EF N25/2; 26. Margocolporites vanwijhei CICYTTP-2046 Tigrillo 30X (8370–8400ft), EF M23/ 4; 27. Rhoipites guianensis CICYTTP-2014 Arabela 1X (1810–1840ft), EF H35/1; 28. Siltaria hammenii CICYTTP-2072 Frontera 1 (1180–1200ft), EF X48; 29. Ranunculacidites operculatus CICYTTP-2007 Arabela 1X (910–940ft), EF G23/3; 30. Psilastephanoporites tesseroporus CICYTTP-2077 Frontera 1 (2700–2720 ft), EF W34/3; 31. Perisyncolporites pokornyi CICYTTP-2011 Arabela 1X (1480–1510ft), EF V37/3; 32. Echiperiporites akanthos CICYTTP-2027 Tucunare 1X (5500–5550ft), EF U27/2; left high focus and right lowfocus; 33. Echiperiporites estelae CICYTTP-2016 Arabela 1X (2860-2890ft), EF G23/1. Scale bar is 20 µm for all pictures except for Figures 9 and 10 where it represents 30 µm.

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5. General characterization of the palynofloral assemblages

Seventy-seven samples from the Arabela-1X, Maynas-1, Tucunare-1X, Tigrillo-30X, Nahuapa-24X, and La Frontera-1 wells in the Marañon Basin (Table 2; Figure 1) yielded 6262 identifiable grains, as summarized in Table 3. Quantitative distribution of palynomorphs in the wells (Table 3 and 4; Appendices 1–6) reveals a total of 226 morphotypes, including 80 genera and 150 species of pollen grains, 24 genera and 43 species of spores, nine genera and eight species of dinoflagellate cysts, five genera of algae, four morphotypes, and two genera of fungal spores. Foraminiferal linings and copepod eggs (indeterminate copepods) were also identified. Of the identified palynomorphs, 75.1% belonged to pollen and spore groups, 14.3% were algae, and 7.8% included dinoflagellate cysts, acritarchs, foraminiferal linings, and other palynomorph remains. Fungal palynomorphs (2.8%) and abundant organic matter were recovered in all the samples.

Table 3.

Total grains counted per each analyzed well and percentage of each morphogroup from Arabela-1X, Maynas-1, Tucunare-1X, Tigrillo-30X, Nahuapa-24X, and La Frontera-1 wells in the Marañon Basin. NA: not applicable.

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Table 4.

Total grains counted per morphogroup in each analyzed well and percentage of each morphogroup from Arabela-1X, Maynas-1, Tucunare-1X, Tigrillo-30X, Nahuapa-24X, and La Frontera-1 wells in the Marañon Basin.

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Fairly well-preserved pteridophyte–bryophyte spores, angiosperm and gymnosperm pollen grains, phytoplankton (chlorophyceans, acritarchs, and dinoflagellate cysts) and miscellaneous groups (foraminifera, copepods, and fungal remains), characterize the palynoflora obtained from the six wells. The first group was mainly composed of spores such as Azolla, Cicatricosisporites, Crassoretitriletes, Cyathidites, Deltoidospora, Echinatisporis, Foveotriletes, Laevigatosporites, Magnastriatites, Polypodiisporites, Psilatriletes, Striatriletes, and VerrucosisporitesVerrutriletes.

Angiosperm pollen grains were frequent and more diverse, including Bombacacidites, Corsinipollenites, Crassiectoapertites, Cyclusphaera, Echiperiporites, Echipollenites, Echitriporites, Inaperturopollenites, Ladakhipollenites, Malvacipolloides, Mauritiidites, Paleosantalaceaepites, Perfotricolpites, Perisyncolporites, Proxapertites, Proteacidites, Psilamonocolpites, Psilastephanocolporites, Psilatricolporites, Retimonocolpites, Retipollenites, Retistephanoporites, Retitrescolpites, Retitricolpites, Retitricolporites, Scabrapollenites, Siltaria, Spinizonocolpites, and Striatopollis.

Gymnosperm pollen grains were rare and less diverse: Araucariacites, Cyclusphaera, Inaperturopollenites, Podocarpidites, and Striapollenites. Chlorophycean algae such as Botryococcus, Oedogonium, Pediastrum, and Pterospermella were obtained. Other phytoplankton, including acritarchs and dinoflagellate cysts, such as Apteodinium, Batiacasphaera, Bosedinia, aff. Ceratium, Cribroperidinium, Leiosphaeridia, Quadrina, Selenopemphix spp., and Operculodinium and Polysphaeridium groups, were common and always accompanied by foraminiferal linings, copepod eggs, and fungal palynomorphs, such as Fusiformisporites, Microthyraceae, and Tetraploa. The distribution of the palynomorphs in the abovementioned wells, their relative abundances (range charts), and extended Tilia diagrams are shown in Appendices 1–6, and key markers are illustrated in Plate 1.

6. Definition of palynozones

Fifty-two biostratigraphic marker species were recognized in the six boreholes (Table 5). Some occurred in all the wells, whereas others did not (Appendices 1–6), but all have a wide geographic distribution and well-known stratigraphic ranges given as FADs and LADs in millions of years ago for each taxon and/or based on stratigraphic ranges that have been used in biostratigraphic definitions in northern South America (Lorente 1986; Muller et al. 1987; Hoorn 1993; da Silva et al. 2010; Jaramillo et al. 2011) and elsewhere (Bujak and Williams 1985; Macphail 1999; Williams et al. 2017). Therefore, they are useful for dating the studied successions in this basin and for proposing regional correlations. Six palynozones named from the oldest to the youngest, namely Mar-A to Mar-F (‘Mar' is the abbreviation for ‘Marañon') are proposed considering the vertical distribution of the taxa (Figures 24; Appendices 1–6) based on the analysis of qualitative biostratigraphic events. A quantitative deterministic method of graphic correlation (Shaw 1964) in order to test this scheme was run in GraphCor: Interactive Correlation Software Hood (1998). Maximum stratigraphic ranges of species from previously known appearances and disappearances in each well (Table 6) allowed the construction of a biostratigraphic ordination in a composite section (Figure 3) according to last appearances of species. This method corroborates the proposed zonation based on a qualitative analysis, also evidenced by stratigraphically constrained cluster analysis (CONISS) in the Tilia software (Grimm, 2015) for each well (Appendices 1–6). The upper two zones are preliminarily characterized until further studies with more materials are carried out. The presence of well-known diagnostic species (FADs and LADs; Figures 24; Tables 5 and 6) supported the ages of the palynozones. In addition, seven timelines and a west–east and north–south correlation among the six wells were drawn (Figure 5), and a correlation of our palynozonation with other palynozones from northern South America (Figure 6) is also addressed below.

Table 5.

Marker age of palynomorphs recovered in the Arabela-1X, Maynas-1, Tucunare-1X, Tigrillo-30X, Nahuapa-24X, and La Frontera-1 boreholes in the in the Marañon Basin, in alphabetical order (occurrence levels are included; depth in meters). (1) da Silva-Caminha et al. (2010), (2) González-Guzmán (1968), (3) Hoorn (1993), (4) Jaramillo et al. (2011), (5) Eisawi and Schrank (2008), (6) Cole (1992); (7) De Verteuil et al. (1992), (8) Raine et al. (2011) and (9) Williams et al. (2017).

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Figure 2.

Range chart of taxa as used in this work, indicating the boundaries of the palynozones Mar-A to Mar-F.

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6.1. Mar-A Corsinipollenites oculusnoctis Interval Zone

  • Reference section. Arabela-1X interval 2890–1660ft (881–506m).

  • Distribution. This zone was recognized in all the wells: Arabela-1X interval 2890–1660ft (881–506m), Tigrillo-30X interval 10,680–7620ft (3255–2323m), Nahuapa-24X interval 4610–3230ft (1405–985m), Maynas-1 interval 8030–5250ft (2438–1600m), Tucunare-1X interval 7650–7400ft (2332–2255.5m) and La Frontera-1 interval 4420–4100ft (1347–1250m) (see Appendices 1–6 for details and Figures 26 for summary and correlation).

  • Description. We define the Mar-A Corsinipollenites oculusnoctis palynozone as occurring from the LAD of Cicatricosisporites dorogensis to the FAD of Malvacipolloides maristellae or, alternatively, it is from the FAD of Corsinipollenites oculusnoctis, the FAD of Retitricolporites wijmstrae, and/or the FAD of Acaciapollenites myriosporites to the FAD of Malvacipolloides maristellae as occurring respectively in the Maynas-1, Tigrillo-30X, and La Frontera-1 wells, to the FAD of Malvacipolloides maristellae.

  • Age. Aquitanian to Early Burdigalian (23.03–17.71Ma).

  • Characteristics. The presence of Paleogene taxa whose extinction occurred in the Neogene, such as Bombacacidites nacimientoensis, Corsinipollenites psilatus, Magnastriatites grandiosus, Mauritiidites franciscoi var. franciscoi, Mauritiidites franciscoi var. minutus, Retitricolpites simplex, and Spirosyncolpites spiralis, among others, is notable. This zone is characterized by the inception of other species, such as Apteodinium australiense, Leiosphaeridia, and Polysphaeridium groups (dinoflagellate cysts); the end of the acme of dinoflagellate cysts (Late Oligocene/Burdigalian); underlying Malvacipolloides maristellae (FAD); the first appearance of Acaciapollenites myriosporites, Corsinipollenites collaris, Corsinipollenites oculusnoctis, Corsinipollenites psilatus, Ctenolophonidites suigeneris, Multiporopollenites aff. pauciporatus/M. pauciporatus, Cyathidites congoensis, Retitricolporites wijmstrae, and Selenopemphix nephroides (dinoflagellate cysts); and the LAD of Bombacacidites gonzalezii. They frequently occur along with Clavainaperturites aff. clavatus, Laevigatosporites spp., Polypodiisporites specious, Polypodiisporites spp., and Psilamonocolpites spp., and seldom with Magnaperiporites spinosus (see Appendices 1–6 for details and Figures 26 for summary and correlations).

  • Comparison. The co-occurrence of several taxa (see Tables 56 and Figures 24) supports the correlation (summarized in Figure 6) of this zone with the palynostratigraphy of Venezuela (Lorente 1986), northern South America (Muller et al. 1987), and the Solimões Basin in Western Amazonia (Hoorn 1993). It is coeval with the T-12 Horniella lunarensis Zone from Llanos in Colombia (Jaramillo et al. 2011), the zonal boundaries of which are coeval with the Mar-A Zone. However, the T-12 taxon Horniella lunarensis is not present in the Mar-A Corsinipollenites oculusnoctis Zone (Figures 24)

  • Table 6.

    Maximum stratigraphic ranges of species among the studied wells, constructed in a composite section from previously known appearances and disappearances of species in each well obtained by means of graphic correlation.

    img-z9-2_675.gif

    6.2. Mar-B Malvacipolloides maristellae Interval Zone

  • Reference section. Arabela-1X 1660–1210 ft (506–369 m).

  • Distribution. This zone was recognized in the intermediate section of the six wells analyzed: Arabela-1X interval 1660–1180ft (506–360m), Maynas-1 interval 4450–3350ft (1356–1021m), Tucunare-1X interval 7400–5350ft (2255.5–1631m), Tigrillo 30X interval 7350–6450ft (2240–1966m), Nahuapa-24X interval 4430–2600ft (1350–792m), and La Frontera-1 interval 3220–3120ft (981–951m) (see Appendices 1–6 for details and Figures 26 for summary and correlation).

  • Description. We propose the Mar-B Malvacipolloides maristellae Zone as corresponding to the interval from the FAD of Malvacipolloides maristellae to the LAD of Retitricolporites wijmstrae and/or from the LADs of Retistephanoporites angelicus or Cyclusphaera scabrata to the FAD of Grimsdalea magnaclavata in the upper zone.

  • Age. Burdigalian (17.71–16.1Ma).

  • Characteristics. This zone is characterized by the first appearance and continuous presence upward of Malvacipolloides maristellae, often accompanied by Retistephanoporites angelicus, Corsinipollenites psilatus, and Retitricolporites wijmstrae; the rare occurrence of Bombacacidites nacimientoensis, Crototricolpites cf. annemariae, Ctenolophonidites suigeneris, Gomphrenipollis minima, and Retitriletes altimuratus; and the continued presence of Cyathidites congoensis. Furthermore, Clavainaperturites aff. clavatus, Laevigatosporites spp., Magnastriatites grandiosus, Mauritiidites franciscoi var. franciscoi, Mauritiidites franciscoi var. minutus, Perisyncolporites pokornyii, Polypodiisporites specious, Polypodiisporites spp., Polypodiisporites usmensis, Psilamonocolpites spp., Retipollenites spp., and Retitricolporites sp. are commonly present in moderate abundances. Acritarchs and dinoflagellate cysts, such as Batiacasphaera sp., Leiosphaeridia, Selenopemphix spp., and Operculodinium group, also occur. A peak abundance of Pterospermella spp. (prasinophycean algae) is noticeable (see Appendices 1–6 for details and Figures 26 for summary and correlations).

  • Comparison. The co-occurrence of taxa (see Tables 56 and Figures 24 for details) supports the correlation of this zone with others in South America (summarized in Figure 5; Lorente 1986; Muller et al. 1987; Hoorn 1993; Jaramillo et al. 2011). The record of the Early Miocene Malvacipolloides maristellae (Muller et al. 1987) in the six wells (Figures 3 and 5) reinforces the age assigned to this zone. The zonal limits of the T-13 Malvacipolloides maristellae Zone from Llanos in Colombia (Jaramillo et al. 2011) were identified in one of the six wells, the Nahuapa-24X (Figure 3), supporting their correlation (Figures 4 and 5).

  • Figure 3.

    Maximum stratigraphic ranges of species ordered by last appearance datum (LAD) among the studied wells, constructed in a composite section from previously known appearances and disappearances of species in each well obtained by means of graphic correlation.

    img-z10-1_675.jpg

    Figure 4.

    First palynological zonation for the Marañon Basin (this work) and correlation (time-lines). See Appendices 1–6 and Table 5 for details, and see Figures 23 and 56 for timeline correlation and correlation with other South American palynozones.

    img-z10-3_675.jpg

    Figure 5.

    First palynological zonation for the Marañon Basin (this work), and south–west and north–east correlation and timelines between boreholes of the six exploration wells Arabela-1X, Maynas-1, Tucunare-1X, Tigrillo-30X, Nahuapa-24X, and La Frontera-1 in the Marañon Basin.

    img-z11-1_675.jpg

    Figure 6.

    First palynological zonation for the Marañon Basin (this work) and its suggested correlation with other South American palynozones and the geological column.

    img-z12-1_675.jpg

    6.3. Mar-C Mauritiidites crassibaculatus Assemblage Zone

  • Reference sections. Arabela-1 interval 1180–910ft (360–277m) and Nahuapa-24X interval 2600–2240ft (792–683m).

  • Distribution. This zone was recognized in three wells, namely Arabela-1 interval 1180–910 (360–277 m), Tigrillo-30X interval 6450–6000 ft (1966–1829 m), and Nahuapa-24X interval 2600–2240 (792–683 m). Only the lower limit of this zone was recognized in the Maynas-1 and Tucunare-1X wells, and only the upper limit was recognized in the La Frontera-1 well (see Appendices 1–6 for details and Figures 26 for summary and correlations).

  • Description. The Mar-C Mauritiidites crassibaculatus Zone is defined as the interval with Mauritiidites crassibaculatus from the LAD of Retitricolporites wijmstrae (top of the lower zone) and/or the FADs of Grimsdalea magnaclavata to the LADs of Retitriporites dubiosus or FAD of Crassoretitriletes vanraadshooveni in the upper zone. Alternatively, the upper boundary may be defined by the FAD of Psilastephanoporites tesseroporus and/or that of Retipollenites crotonicolumellatus (in the upper zone), which should be used when Retitriporites dubiosus and Crassoretitriletes vanraadshooveni are absent.

  • Age. Latest Burdigalian to Late Langhian (16.1–14.2/13.9Ma).

  • Characteristics. This zone is characterized by the continuous presence of Ladakhipollenites simplex, Mauritiidites crassibaculatus, Bombacacidites nacimientoensis, Retitricolpites simplex and Cyathidites congoensis along with the frequent occurrence of Laevigatosporites spp., Magnastriatites grandiosus, Mauritiidites franciscoi var. franciscoi, Polypodiisporites spp., Polypodiisporites usmensis, Psilamonocolpites spp., and Retistephanoporites crassiannulatus. It also contains Leiosphaeridia spp., Selenopemphix spp., Selenopemphix nephroides, and other indeterminate dinoflagellate cysts (see Appendices 1–6 for details and Figures 26 for summary and correlations).

  • Comparison. The co-occurrence of taxa (see Tables 56 and Figures 24 for details) supports the correlation of this zone with others in South America (summarized in Figure 5; Lorente 1986; Muller et al. 1987; Hoorn 1993; Jaramillo et al. 2011). This zone, in the six wells, is coeval with the T-14 Grimsdalea magnaclavata Zone (Figure 5) from Llanos in Colombia (Jaramillo et al. 2011). The T-14 Zone was defined as extending from the FAD of G. magnaclavata to the FAD of Crassoretitriletes vanraadshooveni. These zonal boundaries identified in Nahuapa-24X (Figure 4) reinforce the age given to our zone and their correlation (Figures 46).

  • 6.4. Mar-D Crassoretitriletes vanraadshooveni Assemblage Zone

  • Reference section. Arabela-1 interval 850-610 ft (259–186 m) and La Frontera-1 interval 2720–2220 ft (829–677 m).

  • Distribution. This zone was recognized in the six wells analyzed: Arabela-1 interval 850–610ft (259–186m), Maynas-1 interval 2750–2700 (838–823m), Tucunare-1X interval 5000–5050 (1524–1539m), Tigrillo-30X interval 6000–5310 (1829–1618m), Nahuapa-24X interval 2240–2210ft (683–674m), and La Frontera-1 interval 2720–2220 (829–677m) (see Appendices 1–6 for details and Figures 26 for summary and correlations).

  • Description. The Mar-D Crassoretitriletes vanraadshooveni Zone is defined as the interval from the LADs of Retitriporites dubiosus (top of lower zone) and the FADs of the Crassoretitriletes vanraadshooveni, Psilastephanoporites tesseroporus, or Retipollenites crotonicolumellatus (which should be used when Crassoretitriletes vanraadshooveni and Retitriporites dubiosus are absent) to the LAD of Corsinipollenites oculusnoctis and/or the LAD of Cyathidites congoensis, and/or that of Bombacacidites araracuensis.

  • Age. Late Serravallian (14.2–11.62Ma).

  • Characteristics. This zone comprises the FADs of Crassoretitriletes vanraadshooveni, Paleosantalaceaepites cingulatus, Psilastephanoporites tesseroporus, and Retipollenites crotonicolumellatus and the last records of Bombacacidites araracuarensis, Bombacacidites nacimientoensis, Corsinipollenites oculusnoctis, Crototricolpites cf. annemariae, Ladakhipollenites simplex, Mauritiidites crassibaculatus, and Cyathidites congoensis. Also occurring in this zone are Ctenolophinidites suigeneris, Deltoidospora adriennis, Echitriporites cricotriporatiformis, Laevigatosporites spp., Laevigatosporites catanejensis, Magnastriatites grandiosus, Mauritiidites franciscoi var. franciscoi, Polypodiisporites spp., Polypodiisporites usmensis, Psilamonocolpites spp., and Retitricolpites simplex. Leiosphaeridia sp., prasinophyceans (algae), and indeterminate dinoflagellate cysts occur frequently (see Appendices 1–6 for details and Figures 26 for summary and correlations).

  • Comparison. The characteristic co-occurrence of taxa (see Tables 56 and Figures 24 for details) supports the correlation of this zone with other zones in South America (summarized in Figure 5; Lorente 1986; Muller et al. 1987; Hoorn 1993; Jaramillo et al. 2011). This zone is coeval with the T-15 Crassoretitriletes vanraadshooveni Zone and the lower part of the T-16 Zone from Llanos in Colombia (Jaramillo et al. 2011), where the LAD of Mauritiidites crassibaculatus (as in the Maynas-1 well) occurs. The upper boundary of our zone occurs in La Frontera-1 before the first record of Ladakhipollenites caribbiensis that is known from the Late Miocene (da Silva et al. 2010). The lower limit of the Mar-D Zone in the Nahuapa-24X well coincides with that of the T-15 Zone (Figure 6) of Jaramillo et al. (2011). Our zone comprises the FAD of Retipollenites crotonicolumellatus, which also occurs in the T-15 Zone, the FADs of both Paleosantalaceaepites cingulatus and Psilastephanoporites tesseroporus, and the LAD of Mauritiidites crassibaculatus, which also occurs in the T-16 Zone of Jaramillo et al. (2011). Therefore, these presences also emphasize the age given to our zone and their correlation (Figures 26).

  • 6.5. Mar-E Psilastephanoporites tesseroporus Interval Zone

  • Reference section. La Frontera-1 interval 2220–1540 (677–469 m).

  • Distribution. This zone was present only in the La Frontera-1 well, interval 2220–1540 ft (677–469 m). Note that in the other wells, samples were not analyzed above the top of the Mar-D zone (see Appendices 1–6 for details and Figures 26 for summary and correlations). Nevertheless, GraphCor confirmed this zone as defined here.

  • Description. We propose the Mar-E Psilastephanoporites tesseroporus Interval Zone as occurring from the LAD of Corsinipollenites oculusnoctis and/or that of Cyathidites congoensis (top of the lower zone) to the LAD of Psilastephanoporites tesseroporus and/or the LAD of Siltaria santaisabelensis.

  • Age. Early Tortonian to Late Messinian (11.62–5.48Ma).

  • Characteristics. This zone includes the inception and presence of pollen grains of Ctenolophonidites suigeneris, Foveotricolporites lenticuloides, Lanagiopollis crassa, Paleosantalaceaepites cingulatus, Nijssenosporites fossulatus, and Retimonocolpites maximus and the LADs of Acaciapollenites myriosporites, Deltoidospora adriennis, Ladakhipollenites caribbiensis, Psilastephanoporites tesseroporus, and Siltaria santaisabelensis. Other taxa such as Osmundacidites ciliatus and dinoflagellate cysts Bosedinia infragranulata, Quadrina? condita and Selenopemphix quanta along with Echiperiporites estelae, Magnastriatites grandiosus, and Rhoipites hispidus are common.

  • Comparison. This zone is coeval with the Echitricolporites spinosus Zone from northern South America (Muller et al. 1987) and can be compared with the upper part of the T-16 Fenestrites spinosus Zone of Jaramillo et al. (2011), where the LAD of Ladakhipollenites? caribbiensis occurs, and to the lower part of the T-17 Cyatheacidites annulatus Zone of Jaramillo et al. (2011), where the LAD of Psilastephanoporites tesseroporus occurs (upper boundary of our Mar-E zone) (Figures 26).

  • 6.6. Mar-F Ctenolophonidites suigeneris Zone

  • Reference section. La Frontera-1 interval 1560–1180 ft (475–360 m).

  • Distribution. This local zone was only identified in the La Frontera-1 well, interval 1540–1180 ft (469–360 m). Note that in the other wells, samples were not analyzed above the top of the Mar-D zone (see Appendices 1–6 for details and Figures 26 for summary and correlations).

  • Description. We propose the Mar-F Ctenolophonidites suigeneris Zone for the interval from the LAD of Psilastephanoporites tesseroporus (5.48Ma) to the LADs of Ctenolophonidites suigeneris (3.6Ma) and/or Cistacearumpollenites rotundiporus (LAD Pliocene). Note that samples above 1180ft (360m) were not analyzed.

  • Age. Latest Messinian to Zanclean (5.48–3.6Ma).

  • Characteristics. This zone comprises the inception or frequent presence of Deltoidospora spp., Echiperiporites akanthos, Echiperiporites estelae, Laevigatosporites ovatus, Lanagiopollis cf. crassa, Magnastriatites grandiosus, Mauritiidites franciscoi var. minutus, Monoporopollenites annulatus, Polypodiisporites usmensis, Retimonocolpites maximus, and Retitriletes sp. Fusiformisporites is common among the fungal spores. The last records of Siltaria hammenii (Neogene), Cistacearumpollenites rotundiporus (LAD Pliocene), and Crassoretitriletes vanraadshooveni (3.4 Ma) occur in this zone. Noticeable is the absence of Echitricolporites mcneillyi.

  • Comparison. This zone is coeval with the Psilatricolporites caribbiensis Subzone from Venezuela (Lorente 1986), due to the absence of Echitricolporites mcneillyi, and can be compared with the lower part of the Echitricolporites mcneillyi Zone of northern South America (Muller et al. 1987), where the LAD of Psilastephanoporites tesseroporus occurs (upper boundary of our Mar-E zone). The upper part of T-17 and the lower part of T-18 (Jaramillo et al. 2011) are also correlated (Figures 26).

  • 7. Correlation with other Western Amazonian basins and discussion

    The vertical succession of species in the six wells investigated from the Marañon Basin (see Appendices 1–6 for details) allowed us to propose the first palynozonation in a chronostratigraphic context (Figure 5). The presence of selected species in some or all of the boreholes and their stratigraphic ranges (FAD and LAD ages; Figures 23 and Tables 56) were used to date our zones and establish correlations with relatively coeval palynozones in South America (Figure 6). Some diachronisms exist between the ages of published palynozones from northern South America and ours. For instance, the Early Miocene to earliest Middle Miocene in Venezuela was characterized by the successive Verrutricolporites and PsiladiporitesEchitricolporites pollen zones (Lorente 1986). These zones are equivalent to the Verrutricolporites rotundiporusEchidiporites barbeitoensis and Echitricolporites maristellaePsiladiporites minimus zones defined by Muller et al. (1987). The Verrutricolporites Interval Zone and the Verrutricolporites rotundiporusEchidiporites barbeitoensis Zone are defined as extending from the first records of Verrutricolporites rotundiporus to the first occurrence of Psiladiporites minimus or Echitricolporites maristellae.

    Hence, the Verrutricolporites (Lorente 1986) and the Verrutricolporites rotundiporusEchidiporites barbeitoensis (Muller et al. 1987) zones can be correlated with our Mar-A Corsinipollenites oculusnoctis Interval Zone. In addition, the PsiladiporitesEchitricolporites Interval Zone (Lorente 1986) and the Echitricolporites maristellaePsiladiporites minimus Zone (Muller et al. 1987) are defined by the first occurrence of Psiladiporites minimus or Echitricolporites maristellae at the base, and the first occurrence of Crassoretitriletes vanraadshooveni at the top. These markers also correlate with our Mar-B Malvacipolloides (Echitricolporites) maristellae and Mar-C Mauritiidites crassibaculatus zones. Hence, our Mar-A, Mar-B, and Mar-C zones are within the Early Miocene to earliest Middle Miocene pollen zones of Lorente (1986) and Muller et al. (1987). Our Mar-A, Mar-B, and Mar-C zones are also coeval with the T-12 Horniella lunarensis, T-13 Echitricolporites maristellae, and T-14 Grimsdalea magnaclavata zones, respectively, of Jaramillo et al. (2011).

    The late Early Miocene in Venezuela and in Western Amazonia was characterized by Lorente (1986) and Hoorn (1993), respectively, by the Crassoretitriletes Interval Zone. This zone is defined from the first records of Crassoretitriletes vanraadshooveni and Trichotomocolpites sp. to the first occurrence of Grimsdalea magnaclavata in the latest Middle Miocene (Lorente 1986; Hoorn 1993). The top of this zone was defined by Muller et al. (1987) based on the first record of Echitricolporites spinosus in the earliest Tortonian. The FAD of Grimsdalea magnaclavata sensu Jaramillo et al. (2011) is the oldest at ca. 16.1 Ma, meaning that this FAD would occur before that of Crassoretitriletes vanraadshooveni.

    We have identified in Arabela-1X, Tigrillo-30X, Nahuapa-24X, and La Frontera-1 wells an interval similar to the Crassoretitriletes Interval Zone, by the presence of three biostratigraphic markers, Crassoretitriletes vanraadshooveni, Psilastephanoporites tesseroporus, and Retipollenites crotonicolumellatus (Tables 56) co-occurring at the base, which belong to the bases of both the T-15 Crassoretitriletes vanraadshooveni palynozone (Jaramillo et al. 2011) and the Crassoretitriletes palynozone (Lorente 1986). GraphCor indicated the FAD of Retipollenites crotonicolumellatus was slightly below the FADs of Crassoretitriletes vanraadshooveni and Psilastephanoporites tesseroporus. However, this might be explained by the quality of sampling. The top is identified by Corsinipollenites oculusnoctis, Cyathidites congoensis and Mauritiidites crassibaculatus at ca. 11.62 Ma (Serravallian/ Tortonian limit), as shown in the Crassoretitriletes vanraadshooveni Interval Zone of Muller et al. (1987). Therefore, the base of our Mar-D Crassoretitriletes vanraadshooveni Zone is coeval with the bases of the Crassoretitriletes vanraadshooveni zones of Hoorn (1993), Lorente (1986), and Jaramillo et al. (2011), whereas the top is coeval with the top of the Crassoretitriletes vanraadshooveni Interval Zone sensu Muller et al. (1987). Our Mar-D Crassoretitriletes vanraadshooveni Zone is also coeval with the Crassoretitriletes Interval Zone of Lorente (1986), recognized by Leite et al. (2017) in the Solimões Basin (Brazil).

    The late Miocene from northern South America is characterized by the Echitricolporites spinosus Zone (Muller et al. 1987), so our Mar-E zone is coeval and can be also compared with the upper part of the T-16 Fenestrites spinosus Zone of Jaramillo et al. (2011), where the LAD of Ladakhipollenites? caribbiensis occurs. It is also correlated to the lower part of the T-17 Cyatheacidites annulatus Zone of Jaramillo et al. (2011), in which the LAD of Psilastephanoporites tesseroporus occurs (upper boundary of our Mar-E zone: 5.48Ma). Although sediments referable to Mar-E and Mar-F zones were studied only in the Fontera-1 well, GraphCor displays the events limiting these zones. Furthermore, due to the abovementioned correlations this interval has a preliminary zonal character which can be improved with additional biostratigraphic studies above the upper section of the studied wells.

    Some authors have suggested that there is no record of Pliocene deposits in the Solimões Basin (Latrubesse et al. 2007, 2010). However, recent palynostratigraphic studies (da Silva et al. 2010; Silveira and Souza 2015, 2016; Leite et al. 2017) have documented Pliocene sedimentation in some areas of the Solimões Basin. These palynological studies are based on the presence of the Psilatricolporites caribbiensis Interval Subzone (Late Miocene to Early Pliocene: 5.6–3.7 Ma; Lorente 1986) and the Alnipollenites verus Interval Subzone (Late Pliocene to Holocene: 3.7 to present; Lorente 1986) found in the studied Solimões wells. Similarly, our study showed that Neogene sedimentation in the Marañon Basin continued during the Pliocene, where at least 360 ft (103 m) of the Marañon formation sediments were deposited (see La Frontera-1 well, Appendix 6 and Figures 46). We propose that the Mar-F Ctenolophonidites suigeneris Zone (Late Miocene to Early Pliocene, 5.48–3.6 Ma) comprises the youngest deposits dated here. However, since we did not analyze sediments above 1180 ft (356 m), we cannot exclude the possibility of the younger sediments belonging to the Alnipollenites verus Interval Subzone sensu Lorente (1986) or any coeval zone at depths over 1180 ft (356 m), and/or any coeval zone at depths over those of the last intervals from the other wells studied herein for the Marañon Basin.

    8. Conclusions

    This study of the Neogene biostratigraphic record obtained from six industrial wells in the Marañon Basin allowed us to define six palynozones (Mar-A to Mar-F); five of them (Mar-A to Mar-E) were validated by GraphCor. They range from the Aquitanian (Early Miocene) to the Messinian–Zanclean (latest Miocene to earliest Pliocene):

    • The Mar-A Corsinipollenites oculusnoctis Interval Zone (Aquitanian to early Burdigalian: 23.03–17.71 Ma) is defined as extending from the first occurrence of Retitricolporites wijmstrae, occurring immediately over the Cicatricosisporites dorogensis marker species (latest Oligocene), to the first appearance of Malvacipolloides maristellae.

    • The Mar-B Malvacipolloides maristellae Interval Zone (Burdigalian: 17.71–16.1 Ma) is recognized from the first appearance of Malvacipolloides maristellae to the last record of Retitricolporites wijmstrae.

    • The Mar-C Mauritiidites crassibaculatus Assemblage Zone (latest Burdigalian to Late Langhian: 16.1–14.2/13.9 Ma) is defined as occurring from the last record of Retitricolporites wijmstrae (top of the lower zone) or the first appearance of Grimsdalea magnaclavata (e.g. the Nahuapa-24X well) to the first occurrence of Crassoretitriletes vanraadshooveni or Psilastephanoporites tesseroporus.

    • The Mar-D Crassoretitriletes vanraadshooveni Assemblage Zone (Late Serravallian: 14.2–11.62 Ma) is defined by the first occurrence of Crassoretitriletes vanraadshooveni and or that of Psilastephanoporites tesseroporus at its base and by the last record of Cyathidites congoensis and Mauritiidites crassibaculatus or Corsinipollenites oculusnoctis at its top (e.g. La Frontera-1 well).

    • The Mar-E Psilastephanoporites tesseroporus local Interval Zone (Early Tortonian to Late Messinian: 11.62–5.48 Ma) represents the time interval with Psilastephanoporites tesseroporus from the last occurrence of Corsinipollenites oculusnoctis and/or Cyathidites congoensis to the last occurrence of Psilastephanoporites tesseroporus. It is dominated by Psilastephanoporites tesseroporus and Siltaria santaisabelensis.

    • The Mar-F Ctenolophonidites suigeneris local Zone (latest Messinian to Zanclean: 5.48–3.6 Ma) is defined at its base by the last appearance of Psilastephanoporites tesseroporus and at its top by the last occurrence of Ctenolophonidites suigeneris. Cistacearumpollenites rotundiporus and Siltaria hammenii dominate this zone.

    The biostratigraphic scheme proposed for the Marañon Basin is based on the presence of species in common with Miocene palynozones of northern South America (Colombia, Venezuela, and western Brazil), and a correlation between them is also established. Our study corroborates recent studies regarding the palynostratigraphy of the Miocene Solimões and Acre basins, and documents that Pliocene sedimentation occurred in Peru (western Amazonia). Future study of the interval above the analyzed wells may provide information to characterize the Pliocene palynofloras of the Marañon Basin. A comparison with Amazonia and elsewhere in northern South American basins will achieve new insights for the less well-known evolution of floras during the Pliocene.

    Acknowledgements

    This work was supported by the French Research Institute for Development (IRD) under Grant BTDR and by PALEOSEDES E.U. (Colombia) under Grant STU04-2016, as well as by collaboration and partnership with the Toulouse III Paul Sabatier University (France), National University (Colombia), and CICYTTP-CONICET (Argentina) under CONICET PIP 0812. The first author is a PhD candidate and IRD scholarship holder and received Graphic Correlation software training from Dr Jaramillo at STRI, Panama. We thank Perupetro for allowing us to study the ditch-cutting samples and their permission to publish this article. Special thanks are given to Dr C. Jaramillo and another, anonymous reviewer, for their suggestions that allowed us to substantially improve the manuscript.

    Disclosure statement

    In accordance with Taylor & Francis policy and our ethical obligation as researchers, all the authors state that there is no conflict of interest.

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    Appendices

    List of species with author citations Spores

    • Cicatricosisporites dorogensis Potonié & Gelletich, 1933

    • Crassoretitriletes vanraadshooveni Germeraad, Hopping & Müller, 1968

    • Cyathidites congoensis Sah, 1967

    • Cyathidites minor Couper, 1953

    • Deltoidospora adriennis (Potonié & Gelletich, 1933) Frederiksen, 1983

    • Echinatisporis muelleri (Regali, Uesugui & Santos, 1974) Silva-Caminha, Jaramillo & Absy, 2010

    • Foveotriletes ornatus Regali, Uesugui & Santos, 1974

    • Laevigatosporites catanegensis Muller, Di Giacomo & Van Erve, 1987

    • Laevigatosporites granulatus Jaramillo, Pardo, Rueda, Torres, Harrington, & Mora, 2007

    • Laevigatosporites ovatus Wilson & Webster, 1946

    • Magnastriatites grandiosus (Kedves & Sole de Porta, 1963) Dueñas, 1980

    • Nijssenosporites fossulatus Lorente, 1986

    • Osmundacidites ciliatus Sah, 1967

    • Polypodiisporites specious Sah, 1967

    • Polypodiisporites usmensis (Van der Hammen, 1956) Khan & Martin, 1972

    • Retitriletes altimuratus Silva-Caminha, Jaramillo & Absy, 2010

    • Striatriletes saccolomoides Jaramillo, Rueda & Torres, 2011

    • Verrutriletes virueloides Jaramillo, Pardo, Rueda, Torres, Harrington & Mora, 2007

    Pollen grains

    • Acaciapollenites myriosporites (Cookson, 1954) Mildenhall, 1972

    • Araliaceoipollenites Jussieu, 1789

    • Arecipites perfectus Silva-Caminha, Jaramillo & Absy, 2010

    • Bombacacidites soleaformis Muller, Di Giacomo & Van Erve, 1987

    • Bombacacidites annae (Van der Hammen, 1954) Leidelmeyer, 1966

    • Bombacacidites araracuarensis Hoorn, 1994

    • Bombacacidites brevis (Dueñas, 1980) Muller, Di Giacomo & Van Erve, 1987

    • Bombacacidites gonzalezi Jaramillo & Dilcher, 2001

    • Bombacacidites nacimientoensis (Anderson, 1960) Elsik, 1968

    • Bombacacidites psilatus Jaramillo & Dilcher, 2001

    • Catostemma type Bentham, 1843

    • Cistacearumpollenites rotundiporus Silva-Caminha, Jaramillo & Absy, 2010

    • Clavainaperturites clavatus Van der Hammen & Wymstra, 1964

    • Colombipollis tropicalis Sarmiento, 1992

    • Corsinipollenites psilatus Jaramillo & Dilcher, 2001

    • Corsinipollenites collaris Silva-Caminha, Jaramillo & Absy, 2010

    • Corsinipollenites oculusnoctis (Thiergart, 1940) Nakoman, 1965

    • Corsinipollenites psilatus Jaramillo & Dilcher, 2001

    • Crassiectoapertites columbianus (Dueñas, 1980) emend. Lorente, 1986

    • Crototricolpites annemariae Leidelmeyer, 1966

    • Ctenolophonidites suigeneris Silva-Caminha, Jaramillo & Absy, 2010

    • Cyclusphaera scabrata Jaramillo & Dilcher, 2001

    • Echiperiporites estelae Germeraad, Hopping & Müller, 1968

    • Echiperiporites jutaiensis Silva-Caminha, Jaramillo & Absy, 2010

    • Echiperiporites akanthos Van der Hammen & Wijmstra, 1964

    • Echiperiporites estelae Germeraad, Hopping & Müller, 1968

    • Echiperiporites lophatus Silva-Caminha, Jaramillo & Absy, 2010

    • Echitriporites trianguliformis van Hoeken-Klinkenberg, 1964

    • Echitriporites cricotriporatiformis Jaramillo, Rueda & Torres, 2011

    • Foveotricolporites lenticuloides Silva-Caminha, Jaramillo & Absy, 2010

    • Gomphrenipollis minimus Silva-Caminha, Jaramillo & Absy, 2010

    • Grimsdalea magnaclavata Germeraad, Hopping & Müller, 1968

    • Hedyosmum type Swartz, 1788

    • Ladakhipollenites simplex (González-Guzmán, 1967) Jaramillo & Dilcher, 2001

    • Ladakhipollenites? caribbiensis (Muller, Di Giacomo & Van Erve, 1987) Silva-Caminha, Jaramillo & Absy, 2010

    • Lanagiopollis crassa (Van der Hammen & Wymstra, 1964) Frederiksen, 1988

    • Magnaperiporites spinosus González-Guzmán, 1967

    • Malvacipolloides (Echitricolporites) maristellae (Muller, Di Giacomo & Van Erve, 1987) Silva-Caminha, Jaramillo & Absy, 2010

    • Margocolporites vanwijhei Germeraad, Hopping & Muller 1968

    • Mauritiidites crassibaculatus Van Hoeken-Klinkenberg, 1964

    • Mauritiidites franciscoi franciscoi (Van der Hammen, 1956) van Hoeken-Klinkenberg, 1964

    • Mauritiidites franciscoi minutus Van der Hammen & Garcia, 1966

    • Monocolpopollenites ovatus Jaramillo & Dilcher, 2001

    • Monoporopollenites annulatus (Van der Hammer, 1954) Jaramillo & Dilcher, 2001

    • Multiporopollenites pauciporatus Jaramillo & Dilcher, 2001

    • Paleosantalaceaepites cingulatus Jaramillo, Rueda & Torres, 2011

    • Perfotricolpites digitatus González-Guzmán, 1967

    • Perisyncolporites pokornyi Germeraad, Hooping & Müller, 1968

    • Polyadopollenites mariae Dueñas, 1980

    • Proteacidites triangulatus Lorente, 1986

    • Proxapertites tertiaria Van der Hammen & Garcia, 1966

    • Proxapertites minutus Dueñas, 1980

    • Proxapertites operculatus (Van der Hammen, 1954) Van der Hammen, 1956

    • Proxapertites psilatus Sarmiento, 1992

    • Proxapertites verrucatus Sarmiento, 1992

    • Psilamonocolpites medius (Van der Hammen, 1954) Van der Hammen & Garcia, 1966

    • Psilastephanocolporites fissilis Leidelmeyer, 1966

    • Psilastephanoporites tesseroporus Regali, Uesugui & Santos, 1974

    • Psilatricolpites papilioniformis Regali, Uesugui & Santos, 1974

    • Psilatricolporites garzoni Hoorn, 1993

    • Psilatricolporites operculatus Van der Hammen & Wijmstra, 1964

    • Psilatricolporites crassoexinatus Hoorn, 1993

    • Psilatricolportires operculatus minutus González-Guzmán, 1967

    • Ranunculacidites operculatus (van der Hammen & Wijmstra, 1964) Jaramillo & Dilcher, 2001

    • Retibrevitricolporites yavarensis (Hoorn, 1993) Silva-Caminha, Jaramillo & Absy, 2010

    • Retimonocolpites maximus Hoorn, 1993

    • Retimonocolpites retifossulatus Lorente, 1986

    • Retipollenites crotonicolumellatus Jaramillo, Rueda & Torres, 2011

    • Retistephanocolporites fossulatus Jaramillo & Dilcher, 2001

    • Retistephanoporites angelicus González-Guzmán, 1967

    • Retistephanoporites crassiannulatus Lorente, 1986

    • Retitrescolpites irregularis (Van der Hammen & Wymstra, 1964) Jaramillo & Dilcher, 2001

    • Retitrescolpites magnus (González-Guzmán, 1967) Jaramillo & Dilcher, 2001

    • Retitrescolpites saturum (González-Guzmán, 1967) Jaramillo & Dilcher, 2001

    • Retitricolpites simplex González-Guzmán, 1967

    • Retitricolpites colpiconstrictus Hoorn, 1994

    • Retitricolpites simplex González-Guzmán, 1967

    • Retitricolporites wijmstrae Hoorn, 1994

    • Retitriporites dubiosus González-Guzmán, 1967

    • Rhoipites guianensis (Van der Hammen & Wymstra, 1964) Jaramillo & Dilcher, 2001

    • Rhoipites hispidus (Van der Hammen & Wymstra, 1964) Jaramillo & Dilcher, 2001

    • Siltaria hammenii Silva-Caminha, Jaramillo & Absy, 2010

    • Siltaria santaisabelensis (Hoorn, 1994) Silva-Caminha, Jaramillo & Absy, 2010

    • Spirosyncolpites spiralis González-Guzmán, 1967

    • Tetracolporopollenites maculosus (Regali, Uesugui & Santos, 1974) Jaramillo & Dilcher, 2001

    Microplankton

    • Chomotriletes minor Pocock, 1970

    • Apteodinium australiense Williams, 1978

    • Selenopemphix quanta (Bradford, 1975) Matsuoka, 1985

    • Bosedinia infragranulata He, 1984

    • Operculodinium group Wall, 1967

    • Polysphaeridium group Davey & Williams, 1966b

    • Selenopemphix nephroides Benedek, 1972

    • Retitrescolpites? irregularis (Van der Hammen & Wymstra, 1964) Jaramillo & Dilcher, 2001

    • Quadrina? condita de Verteuil & Norris, 1992

    Appendix 1. Arabela

    img-AaBop_675.jpg

    Appendix 2. Maynas

    img-As94_675.jpg

    Appendix 3. Tacunare

    img-Av9C_675.jpg

    Appendix 4. Tigrillio

    img-Af-U_675.jpg

    Appendix 5. Nahuapa

    img-AdlKU_675.jpg

    Appendix 6. Frontera

    img-ATz3_675.jpg
    © 2019 AASP – The Palynological Society
    F.J. Parra, R.E. Navarrete, M.M. di Pasquo, M. Roddaz, Y. Calderón, and P. Baby "Neogene Palynostratigraphic Zonation of the Maranon Basin, Western Amazonia, Peru," Palynology 44(4), 675-695, (27 October 2020). https://doi.org/10.1080/01916122.2019.1674395
    Published: 27 October 2020
    JOURNAL ARTICLE
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