First record of Annonaceae wood for the Neogene of South America , Amazon Basin , Brazil Primeiro registro de madeira de Annonaceae para o Neógeno da América do Sul , Bacia do Amazonas , Brasil

Manuscript ID: 20160085. Received in: 07/14/2016. Approved in: 01/11/2017. ABSTRACT: The relief of the regions of Manaus and Itacoatiara, Central Amazon, is supported by Neogene siliciclastic rocks, bounded at the base and top by lateritic paleosols and covered by quaternary sedimentary deposits from the Solimões-Amazon river system. This unit is informally assigned to the Novo Remanso Formation, consists of usually reddish and ferruginized sandstones, conglomerates and pelites, with few identified fossil records, a fact that has hindered its stratigraphic position, and the paleoenvironmental reconstruction of the last phase of the Amazon Basin settling. This study describes, for the first time, the occurrence of fossil wood in outcroppings of the left bank of the Amazon River, where anatomical and morphological data has enabled its characterization to the species level. Thus, the data marks the record of the Annonaceae in South America, as well as the depositional processes related to incorporation of organic material in the sandy layer and the fossilization processes that allowed its preservation. In an unprecedented way, this study has described Duguetiaxylon amazonicum nov. gen and sp. and provided information on the anatomical and systematic character, as well as data on plant-insect interaction, and a better understanding of the family.

The present study has carried out the analysis of a fossilized wood collected in the Novo Remanso Formation, on the left bank of the Amazon River, in the Amazon Basin (Fig. 1).The anatomical and morphological data of the cellular structures allowed relating the fossil sample to the Annonaceae family, thus being the first record reported in South America.The Annonaceae Juss.family is currently distributed in the Neotropics.For South America, there is an average of 40 genera and about 650 species with distribution centers in the Brazilian Amazon and Guianas (Ribeiro et al. 1999).

GEOLOGICAL SETTING
The relief of the Central Amazon is supported by siliciclastic rocks from the Miocene unit -informally called Novo Remanso Formation -outcrops between the cities of Manaus and Itacoatiara.In the local stratigraphic context, this unit discordantly recovers the Cretaceous unit (Alter do Chão Formation), being delimited in the base, in the intermediate portion and on the top by lateritic paleosols and being partially covered by Quaternary fluvial deposits (Soares et al. 2010;Dino et al. 2012, Gonçalves Jr. et al. 2016) (Fig. 2).
The Alter do Chão Formation consists of sandstones, siltstones, mudstones and conglomerates (Caputo 1984, Soares et al. 2010, Dino et al. 2012), characteristic to a fluvial-lacustrine palaeoenvironment (Caputo et al. 1971;Cunha et al. 1994;Dino et al. 1999;Nogueira et al. 1999;Cunha et al. 2007, Mendes et al. 2012).In general, it displays silicified discontinuous-leaved variegated colors of red, yellow and white.Plant fossils are scarce in this formation, with angiosperm leaf debris standing out in sandstones of Serra da Paituna, municipality of Monte Alegre, Northwestern Pará state (Duarte 1987), in addition to fragmented, and much replaced fossilized woods, associated to paleosol levels in the vicinity of Manaus, Amazon (Vieira 1999;Nogueira et al. 1999;Horbe et al. 2006;Soares 2007), and amber -with spores and fungi included -in this Formation's voucher drillings (Dino et al. 1999;Pereira et al. 2006).et al. (2005) informally denominated the term Novo Remanso Formation for the essentially sandy deposits, which discordantly cover the cretaceous unit of the homonymous locality, eastward from Manaus (Amazonas).In general, this unit exhibits around 10 to 20 m outcropping thickness; it is made up of sandstones with subordinated pelites and conglomerates, characteristic to a meandering fluvial paleoenvironment, bounded in both bottom and top by discontinuity surfaces, marked by lateritic crust and/or erosive contact (Soares 2007;Dino et al. 2012;Soares et al. 2015).Locally, records of fossilized plant fragments have been cited in some regional studies of this formation outcrops on the banks of the Negro (in Paricatuba, Oliveira and Nogueira 2006), Solimões (in Manacapuru, Dino et al. 2012) and Amazonas (in Novo Remanso, Lima et al. 2013, Kloster et al. 2013) rivers.
Extensive deposits of pleistocene-holocene fluvial terraces constitute the alluvial plain of the Solimões-Amazonas system, partially covering the Miocene unit in canal and plain areas (Soares et al. 2010;Gonçalves Jr. et al. 2016).

METHODOLOGY
The fossil wood was recovered from a Novo Remanso site (03º15'02,2"S and 58º55'49,3"W) on the Amazon River's left bank during the receding water period (September 2011 and December 2013) (Fig. 1).Litotypes, geological contacts and stratigraphic position of fossils are shown in photo mosaic and columnar section (Fig. 3).
A fragment of silicified wood with external inlays of ferruginous sandstone, showing very good cellular preservation, was analyzed.Petrographic thin sections of 30−40 µm thick were prepared from the wood fragments; three thin sections were made, orientated along three sections: transverse section (ST), tangential longitudinal section (TLS), and radial longitudinal section (RLS), at the Geological Survey of Brazil (CPRM) Lamination Laboratory (Manaus Regional Superintendence).
Wood and rock portions were pulverized and subjected to an x-ray diffraction analysis, using the PANalytical Brand, X'PERT PRO MPD (PW 3040/60) model, x-ray difractometer of the CPRM/Laboratory of mineral analysis (LAMIN) Difraction Laboratory.
The collected fossil wood sample lied at the CPRM/ LAMIN Difraction Laboratory, under number BM-R-102B.These thin sections were thoroughly studied using a Leica DM500 microscope, with an attached EC2 (LM) camera, and some fragments were also observed using a Leitz M50 stereoscopic microscope.Observations were made using a Jeol5800 LV scanning electron microscope (SEM), at Universidad Nacional del Nordeste, Corrientes, Argentina.

Sedimentologic, stratigraphic and diagenetic data
The outcrop studied exhibits around 10 to 20 m outcropping thickness, divided into two portions in this study.The lower portion consists of whitish, reddish blended pinkish to brownish colored sandstone and pelite centimetric to metric interbedded layers, while the upper one is predominantly yellowish colored, clayey and massive, due to the intense pedogenesis (Fig. 3).It occurs discordantly on the cretaceous unit (Alter do Chão Formation), and is bounded in both bottom and top by lateritic ferruginous crusts, informally denominated here as S1 and S2 (Fig. 3).In general, crusts exhibit a massive and columnar aspect -at times seemingly fragmented -, up to 3 m thick and kilometric extension, covered by yellow latosol.
The layers of sandstones of the studied section exhibit massive aspect and/or cross-stratification with SE paleocurrent (Fig. 3, columnar section).They are mainly made up by quartz grains (monocrystalline and polycrystalline) and, more seldom, by rock fragments (sedimentary); they are fractured and exhibit weak to strong undulating extinction and corroded edges (Figs.4A and A1).Grains are poorly sorted (fine to coarse granulometry), they range from angular to rounded, and display low to average spherecity.The grain arrangement defines an open framework, with point and floating contacts, cemented by goethite (containing amorphous portions), according to x-ray diffraction data (Figs.4A, A1 and A2).
The basal -nearly 50 to 60 cm thick -Novo Remanso Formation's ferruginous sandstone layer, on the studied outcrop, lies discordantly on the ferruginous lateritic crust, developed from the overlying Alter do Chão Formation (Fig. 3, columnar section).There is concentration of fossilized woods in this layer, fragmented in varying sizes, arranged horizontally and randomly.The wood's inner structure was replaced by goethite, according to the petrographic and diffraction data (Figs.4B, B1 and B2).This study only analyzed sample BM-R-102B, which is 70 cm length and is partially compressed, according to data from the elipsoidal cross-section, which exhibits up to 30 cm on its largest axis (Fig. 5A).Dispersed in the same layer, there are smaller plant fragments, up to 7 cm long and 0.3 to 0.5 cm wide, as well as two portions resembling fruits and/or seeds of rounded to ellipsoidal external contour (2.0 × 1.5 cm), which need future morphological studies for further classification (Figure 5B, B1)

Systematic Palaeobotany
Order Magnoliales Bromhead Family Annonaceae Jussieu Genus Duguetiaxylon gen.nov.Type Specie Duguetiaxylon amazonicum sp.nov.(this work) Generic Diagnosis.Growth rings indistinct/not observed, diffuse porous, solitary and multiple vessels, numerous vessels per mm 2 , simple perforation plates, small and alternate pits, vessel-ray pits similar to intervessel pits, simple fibers not septated, axial parenchyma apotracheal in lines, high and homogeneous tending to heterogeneous rays.
Etymology.Nominis derivations from the extant genus Duguetia Augustin Saint-Hilaire.Their specific epithet derivates from the Amazon region.

DISCUSSION
Anatomical features described in the fossil wood -such as short-length, vessel elements, simple perforation plates, axial apotracheal parenchyma reticulate, multiseriate and high rays -are distinctive characters of the Annonaceae family (Metcalf and Chalk 1950).Our sample was further compared to the fossil and extant genus essential bibliography of Prakash (1978), Détienne and Jacquet (1983), Wheeler and Manchester (2002), Inside Wood (2004 onwards), León (2007) and Gregory et al. (2009).
Therefore, the absence of a fossil genus that shares all the characteristics with the fossil wood studied here justifies the creation of a new fossil genus.Current Duguetia Augustin Saint-Hilaire presents most similarities with the fossil sample, since Duguetia is the genus with small vessel diameter and intravascular pits inside the family (Détienne and Jacquet 1983;Léon 2007).A B

Comparison with fossil wood
Bande, most species from Africa, Asia and Europe, and only one record from North America, Annonoxylon bonesii (Wheeler and Manchester 2002).The sample studied here is compared to the eight fossil species of the Annonaceae family (Table 1), the sample differs from Annonoxylon striatum (Boureau 1950) by having major density of vessels by mm 2 , higher rays, less axial parenchyma and the presence of oil cells.It differs from Annonoxylon edegense (Boureau 1954) by having smaller diameter of vessels, less density of vessels by mm 2 and axial parenchyma.It differs from Annonoxylon bonesii (Wheeler and Manchester 2002) by having smaller diameter of vessels, higher density of vessels by mm 2 , rays with a major number of wide cells and the presence of crystal and oil cells.It differs from Polyalthioxylon parapaniense (Bande 1973), Polyalthioxylon platymitroides (Kramer 1974) and Polyalthioxylon oldhavenense by having smaller diameter of vessels, less parenchyma cells and the presence of crystal and oil cells.It differs from Polyalthioxylon stelechocarpoides (Kramer 1974) and Polyalthioxylon indicum (Prakash 1978) by having different diameter of vessels by mm 2 , smaller intervessel pits than P. indicum and the presence of crystals in ray cells (Table 1).

Comparisons with extant wood
Among modern species, the fossil wood described and denominated as Duguetiaxylon amazonicum strongly resembles the extant genus Duguetia Augustin Saint-Hilaire, and can be distinguished from others genera of Annonaceae by the presence of small vessels diameter (Figs.6A and 6B), the small size of intervasculary pits (Figs.6C, 6D, 7B and 7C), the high and multiseriate rays (Figs.6G and 6H) and the presence of oil and crystal in ray cells (Fig. 8E) (Détienne and Jacquet, 1983;León 2007).Léon (2007), in his paper about the wood anatomy of 26 species of Annonaceae from Venezuela, exposed a high xylem homogeneity, which makes difficult the differentiation between genera and species.Oil cells were found in only two species of Xylopia and Duguetia, while Oxandra and Duguetia are characterized by smaller diameters of vessels.Both rays' height and the length of their fibers and vessel elements also characters as rays, fiber lenth and vessels elements can show trends where genders can be differentiated (Table 2).Over all the characteristics presented by the fossil sample, the most similar extant genus is Duguetia, especially by the diameter of vessels, the small diameter of intervessel pits and the presence of oil cells in rays.

Palaeoecological inferences: organic evidence of fungi and insect-plant interactions
In the studied sample, evidence of fungal decay and hyphae of fungi, as well as related galleries insect activities are registered -Plates II (Fig. 7) and III (Fig. 8).The axial alignment of tracheids, vessels and fibers, and the radial arrangement of the xylem ray parenchyma facilitate access into the wood and allow a widespread distribution of hyphae within the xylem (Rayde and Boddy 1988 apud Schwarze 2007).The colonization of wood by hyphae is observed in the parenchyma cells and vessels (Figs.7D, 7E, 8A and 8B).The hyphae are septate, with simple branches and random arrangement within cellular elements (Figs. 7D,7E and 8B).It is possible to observe the formation of the secondary wall cavities in the fibers.These cavities have the form of T-branches or L-branching and are a result of the thin penetration of the hyphae (Schwarze 2007) (Figs. 8C to 8E).The structures of the cavities and the formation of multiple L-branching colonization, associated with hyphae, are typical of a soft rot, more precisely basidiomycete (Schwarze 2007, Schwarze et al. 2004).
Furthermore, the presence of circular-shaped galleries of about 1.3 mm in diameter, caused by insects which are likely to be the first ones to enter the wood, facilitates the invasion by fungi or vice versa (Schweingruber et al. 2006;Schweingruber 2007) (Figs. 8F to 8H).
This interaction occurs in current ecosystems, enabling us to infer an active plant/insect interaction, and the presence of fungi in Miocene as well confirms Novo Remanso Formation to have had hot and humid weather (typically tropical).

Novo Remanso Formation depositional paleoenvironment
Sedimentary facies (channel bottom, fluvial bars and crevasse splay deposits), described for the Novo Remanso Formation, by Dino et al. (2012) and Soares et al. (2015), are representative of the meandering fluvial paleoenvironment which implanted itself on the Amazon Basin in the Miocene.The characterization of this continental paleoenvironment is corroborated by the presence of algae (such as Botryococcus) indicating a fresh to brackish water environment, as well as the lack of elements of marine microphytoplankton, in which there was a predominance of paleovegetation of palm trees (Mauritia, Grimsdalea), (Grimineae, Bombacacae) and aquatic elements (Deltoidospora, Botryococcus).
Under this context, the presence of fragments of fossil plants on top and inside the sandy spit bars of this Miocene fluvial system is an indicative of alternating periods of subaerial exposure and sedimentation of the bar, which may be related to seasonal variations (receding and rising water levels of the Amazonian rivers, respectively), and persist up to now in Amazon.Furthermore, the fragmentation of the fossil plants along the studied layer indicates them to have been reworked and inserted into the fluvial bars during deposition, generating an autochthonous accumulation.However, the evidence of insect-plant interaction described in the studied sample shows plants to have been exposed to insect biotic activity prior to their burial.
The open framework of the studied sandstone layer is indicative of an incipient mechanical compactation, which characterizes a shallow diagenesis (eodiagenesis).This datum is consistent with the stratigraphic positioning of Novo Remanso Formation, which represents the Amazon Basin's sedimentary cover, and indicates this unit not to have undergone deep burial.
It appears that the cementation of goethite was precocious, preventing the advance of the mechanical compaction and also filling up gigantic and secondary pores (in some grain boundaries), formed by intra-stratified dissolution.These data indicate this unit to have undergone some changes on its framework's composition by the time it was subjected to the eodiagenesis field.This field is marked by an abundant presence of iron (goethite), which may have been originated while the just-deposited sediment was still in contact with the environment, according to the process suggested by Carvalho et al. (2010).

CONCLUSIONS
This study describes a new fossil wood occurrence in the Amazon Basin's Neogene unit, informally called Novo Remanso Formation.The sample was collected in an outcrop on the left bank of the Amazon River and, despite the absence of a precise stratigraphic positioning for the studied fossiliferous layer, it can be associated to the other occurrences in outcrops in the same formation, identified on the banks of the Negro (Paricatuba Town) and Solimões (Manacapuru Town) rivers.
The present study has analyzed a sample of a fossil wood and their anatomical characteristics -such as short length vessel elements, simple perforation plates, apotracheal reticulate axial parenchyma, multiseriate and high rays -have enabled it to be related to the Annonaceae family.This discovery becomes relevant, since it is the first record of this species in South America and may contribute to new paleofloristic studies in the Americas.
The preserved fungus inside the parenchyma cells and vessels, along with the presence of insect galleries, support the hypothesis of a hot and humid climate in Central Amazon during the Novo Remanso Formation's deposition in the Miocene, and therefore consistent with the paleoclimatic data obtained from the regional palynological studies conducted on this Formation by Dino et al. (2012) and Soares et al. (2015).
The fossil plants random arrangement and fragmentation degree in the studied sandy bar, as well as the described plant-insect interaction data, are indicative of -prior to deposition -subaerial exposure and reworking, for generating the autochthonous deposit.
The studied open sandstone layer framework may be related to the early development of ferruginous cement (goethite) between the grains, which prevented physical compaction advancement in a shallow silting zone (Eodiagenesis stage).This is consistent with the stratigraphic positioning of Novo Remanso Formation, which discordantly overlays the cretaceous unit and makes up most of the Central Amazon's relief.
The Novo Remanso Formation fossil wood study, despite its being a punctual analysis, has demonstrated its value as a paleoenvironmental indicator for the Amazon's Neogene.

Figure 1 .
Figure 1.Map of the location and access to the studied outcrop (Site BM-102), at the locality of Novo Remanso, on the left bank of the Amazon River (Modified from CPRM, 2006).

Figure 2 .
Figure 2. Stratigraphic chart illustrating the column of Cretaceous, Paleogene and Neogene of the central portion of the Amazon Basin (Modified from Dino et al. 2012).