Pg boundary in the Golfo San Jorge basin, Patagonia, Argentina

Journal Pre-proof A Maastrichtian terrestrial palaeoenvironment close to the K/Pg boundary in the Golfo San Jorge basin, Patagonia, Argentina Patricia Vallati, Andrea De Sosa Tomas, Gabriel Casal PII:

S0895-9811(19)30297-4

DOI:

https://doi.org/10.1016/j.jsames.2019.102401

Reference:

SAMES 102401

To appear in:

Journal of South American Earth Sciences

Received Date: 19 June 2019 Revised Date:

24 October 2019

Accepted Date: 24 October 2019

Please cite this article as: Vallati, P., De Sosa Tomas, A., Casal, G., A Maastrichtian terrestrial palaeoenvironment close to the K/Pg boundary in the Golfo San Jorge basin, Patagonia, Argentina, Journal of South American Earth Sciences (2019), doi: https://doi.org/10.1016/j.jsames.2019.102401. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2019 Published by Elsevier Ltd.

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A MAASTRICHTIAN TERRESTRIAL PALAEOENVIRONMENT CLOSE TO

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THE K/Pg BOUNDARY IN THE GOLFO SAN JORGE BASIN, PATAGONIA,

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ARGENTINA

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Patricia Vallati a, b *, Andrea De Sosa Tomasa,b, Gabriel Casala,b

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a. Laboratorio de Bioestratigrafía “Dr. Eduardo Musacchio”, Departamento de Geología,

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Universidad Nacional de la Patagonia San Juan Bosco, Ciudad Universitaria km 4 (9000)

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Comodoro Rivadavia, Argentina

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b. Laboratorio de Paleontología de Vertebrados, Departamento de Biología, Universidad

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Nacional de la Patagonia San Juan Bosco, Ciudad Universitaria km. 4 (9000) Comodoro

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Rivadavia, Argentina

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* Corresponding author. E-mail address: [email protected] (P. Vallati).

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Abstract:

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In this paper, we present new palaeontological data regarding plant remains (palynomorphs,

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mesofossils, and leaves) from the uppermost part of the Lago Colhué Huapi Formation

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(Maastrichtian), at the headwaters of the Río Chico, Golfo San Jorge Basin. We also

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suggest a palaeoenvironmental reconstruction of these deposits, taking into account the

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information reported herein and previous palaeontological and sedimentological studies.

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Several spores of bryophytes, lycophytes, and monilophytes (ferns) as well as zygospores

22

of Zygnemataceae form part of the freshwater aquatic ecosystem. The new species of

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Palmae affinity, Spinizonocolpites riochiquensis sp. nov. is described in this paper. Besides,

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we present the first record of leaf fragments with probable Palm-affinity in the Upper

25

Cretaceous of Patagonia, which could reassert the presence of the Arecaceae in the basin.

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The palaeoflora recognized in the upper Lago Colhué Huapi Formation contributes to

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interpreting palaeoecological and palaeoclimatic conditions of a stratigraphic interval close

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to the Cretaceous/Paleogene extinction event, at the latitude of Patagonia.

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Keywords: Palynomorphs, Mesofossils, Monocot leaves, Palaeoenvironment, Maastrichtian

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1. Introduction:

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This paper goes on with several studies developed in recent years in the uppermost deposits

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of the Lago Colhué Huapi Formation at the headwaters of the Río Chico in the Golfo San

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Jorge Basin (Fig. 1). Palaeontological studies carried out in different outcrops of these

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deposits reported dinosaur remains as well as palynomorphs, megaspores, angiosperm

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leaves and charcoal (Casal et al., 2015, 2016; Vallati et al., 2016; Vallati et al., 2017a, b;

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De Sosa Tomas et al., 2017; Vallati et al., 2018a, b).

38 39

---------------------------------------------Insert Fig 1 here---------------------------------------------

40 41

Angiosperm pollen grains with biostratigraphic and palaeoecological interest were

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previously recorded in a pelitic bed (PB) of the upper part of the Lago Colhué Huapi

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Formation at Cerro del Hadro (PB, Fig. 2A). Among them, we highlight the presence of

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Maastrichtian key species as Quadraplanus brossus Stover and Partridge, 1973 and

45

Tubulifloridites lilliei (Couper) Farabee and Canright,1986 as well as aquatic palynomorphs

46

representing a freshwater body (Vallati et al., 2016; Vallati et al., 2017a, b).

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Recently, several stromatolites were reported for the first time in the Lago Colhué Huapi

48

Formation (Casal et al., in press). The presence of these structures contributes to the

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understanding of the bioconstructions in non-marine environments, and provides

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palaeoecological information regarding the youngest chronostratigraphic interval of the

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Chubut Group.

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In this contribution, we present new palaeontological data (palynomorphs, leaves, and

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charcoal) from Cerro del Hadro (white marlstone bed, WM, Fig. 1C; Fig. 2), Corral de

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Piedra (Fig. 1C; Fig. 3) and Cerro Hoja Grande (Fig. 1C, Fig. 3), at the headwaters of the

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Río Chico. The new results alongside the previously reported information contributed to

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interpreting the palaeoenvironment represented by the deposits of the upper part of the

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Lago Colhué Huapi Formation.

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2. Geological setting

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The Golfo San Jorge Basin is a predominantly extensional basin developed during the Early

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Jurassic and Cretaceous interval in response to the displacement of the South American

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plate to the west (Barcat et al., 1989; Paredes et al., 2016). The Cretaceous of the Golfo San

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Jorge Basin is represented by the deposits of the Las Heras Group (Lesta et al., 1980),

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which are only registered in the subsurface of the basin, and the Chubut Group (Lesta,

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1968; Lesta and Ferello, 1972). The Chubut Group, of particular interest in this

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contribution, is characterized by lacustrine and fluvio-lacustrine systems with abundant

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volcanic ash from an explosive volcanism (Umazano et al., 2008, 2012; Paredes et al.,

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2015, 2016). It includes the following formations: Pozo D-129, Matasiete, Castillo, Bajo

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Barreal, Laguna Palacios and Lago Colhué Huapi. The outcrops of the Lago Colhué Huapi

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Formation (Coniacian-Maastrichtian) are widely extended in the basin (Casal et al., 2015).

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The basal levels of this lithostratigraphic unit are mainly recognized in the eastern flank of

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Sierra de San Bernardo and in Codo del Río Senguerr, while the younger levels outcrop in

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the eastern coast of Colhué Huapi lake (Casal et al., 2015; Casal et al., 2016). The upper

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deposits of the Lago Colhué Huapi Formation are characterized by the absence of

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pyroclastic material. These deposits include fine conglomerates and white and ocher

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sandstones deposited by fluvial channels of high sinuosity that alternate with red mudstones

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from well-drained distal floodplains (Casal et al., 2015).

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2.1 Study areas

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The outcrop known as Cerro del Hadro (Fig. 1C; Fig. 2) is well exposed on the southern

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margin of the Chico river. The sequence is 150 m thick and has the typical lithological

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alternation that characterizes the Lago Colhué Huapi Formation. It includes an irregular

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erosion surface (local unconformity) of concave geometry in the upper part (Fig. 2B). Its

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sedimentary filling is more than 20 m thick. It begins with a coarse intra-formational

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conglomerate, followed by thick to medium-grained sandstones of ocher and black color,

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with hadrosaurid remains and eggshells (Casal et al., 2016). Finally, it is overlaid by a dark

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and laminated pelitic bed, with abundant palynomorphs (Vallati et al., 2016). Immediately

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above the pelitic bed, a marlstone bed up to 0.20 m thick is laterally related to the

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stromatolite E1 (Fig. 2C, D). The sequence continues with yellowish sandstones and

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greyish-green and ocher-colored mudstones, followed by the characteristic reddish

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mudstones of the Lago Colhué Huapi Formation. A basalt flow (La Angostura Basalt),

91

present on top of the sedimentary sequence at Cerro del Hadro (Fig. 2A), was dated to 67.31

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± 0.55 Ma (Clyde et al., 2014).

93 94

-------------------------------------------Insert Fig 2 here-----------------------------------------------

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The sedimentary deposits that are partially outcropping in Corral de Piedra (Fig. 1C)

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include alternation of claystones, siltstones, and sandstones (Fig. 3). The mudstone deposits

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that include the palynomorphs are massive to horizontally laminated, 0.2 to 3.2 m thick,

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interpreted as the deposit of suspended particles in a dilute flow. The sandstones are

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medium to fine grain, gray-colored and with a diffuse horizontal lamination. This sandstone

101

bed has a flat base and top and is 0.18 to 0.9 m thick, being interpreted as a traction deposit

102

in low flow conditions.

103 104

--------------------------------------------Insert Fig. 3 here---------------------------------------------

105 106

The studied levels at Cerro Hoja Grande (Fig. 1C) consist of pelitic deposits dominated by

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reddish claystone, with tabular geometry, 50 cm thick, and with a lateral continuity of tens

108

of meters (Fig. 3). These deposits reflect the predominance of episodes of decantation, and

109

they are interpreted as a distal floodplain under oxidizing conditions (Retallack, 1988;

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Miall, 1996).

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3. Material and methods

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Nine out of the twenty samples collected in the newly studied deposits of the Lago Colhué

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Huapi Formation resulted fertile in palynomorphs, five from the marlstone bed of Cerro del

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Hadro and four from Corral de Piedra. The samples were processed using the standard

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palynological procedures, with dilute hydrochloric acid (19%) and hydrofluoric acid (70%)

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to remove respectively carbonate and silicate mineral components, followed by treatment in

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hot hydrochloric acid (37 %). Occasionally, a brief oxidation of the residue with nitric acid

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was necessary in order to improve the results. The palynological slides were studied under

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a Carl Zeiss KF 2 microscope, and the micrographs were taken with a digital Nikon

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Coolpix P2 camera at the Biostratigraphic Laboratory of the Universidad Nacional de la

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Patagonia San Juan Bosco (UNPSJB). The slides are housed in the micropalaeontological

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repository at the UNPSJB, under the

124

palynomorphs are cited according to the corresponding slide identification followed by the

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coordinates of the Vernier Scale in the Zeiss Microscope.

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The non-oxidized palynological residue from the white marlstone bed in Cerro del

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Hadro was wet sieved using mesh sizes 1.2 mm and 74 µm. Later, after being perfectly

128

dried, the charcoal particles were picked out under a stereomicroscope (Motic SMZ-

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168). Selected material was gold-coated (Quorum, Q150R ES) and photographed using

130

a JEOL JSM-6510LV Scanning Electron Microscope at the Universidad Nacional de la

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Patagonia San Juan Bosco (UNPSJB). The fragments of mesocharcoal are housed in the

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micropalaeontological collection of the Scientific and Didactic Repository “Dr.

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Eduardo A. Musacchio” at UNPSJB, Comodoro Rivadavia (catalogue numbers: UNPSJB-

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MF 168-180).

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Twenty-eight leaf fragments were recovered from Cerro Hoja Grande and are housed in the

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Palaeobotanical section at the UNPSJB Repository “Dr. Eduardo A. Musacchio” under the

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initials UNPSJB-PB 200-227.

initials UNPSJB-MFP-CV181-221. The

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4. Results

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4.1 Palynology

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In this topic, we present palynological data from new studied deposits in Cerro del Hadro

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(WM, Fig. 2) and Corral de Piedra (Fig. 3). A complete list of the taxa of palynomorphs

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recognized up to now in all the outcrops studied at the headwaters of the Río Chico (Fig.

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1C) is presented in Table 1.

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------------------------------------------------Insert Table 1 here---------------------------------------

147 148

The microflora from the marlstone bed at the headwaters of the Río Chico is dominated by

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Podocarpaceae (33% of the pollen assemblage), with several bisaccate and trisaccate pollen

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grains of the genera Podocarpidites, Phyllocladidites, Gamerroites, Dacrydiumites,

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Dacrycarpites, Microcachryidites and Trisaccites (Fig. 4I-P). The bisaccate species

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Dacrydiumites florinii Cookson and Pike, 1953 (Fig. 4M, N) and Dacrycarpites

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australiensis Cookson and Pike, 1953 (Fig 4P) as well as the asaccate Dilwynites

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granulatus Harris, 1965 are reported for the first time in the Late Cretaceous of Golfo San

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Jorge Basin. Other gymnosperm pollen grains represented in the assemblage reported

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herein are Araucariacites, Inaperturopollenites and few specimens of Classopollis and

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Cycadopites.

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The angiosperm pollen grains are dominated by the monosulcate pollen of Liliaceae,

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mainly represented by Liliacidites kaitangataensis Couper, 1953 (Fig. 4Q). Triporate grains

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of Proteacidites scaboratus Couper 1960 (Fig. 4X) represent the Proteaceae in these

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studied levels. A new taxon of the Arecaceae Family (Palmae), is described herein as

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Spinizonocolpites riochiquensis sp. nov. (Fig. 4R-W), taking into account distinctive

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ornamental characteristics. Tubulifloridites lilliei, representing the Asteraceae (Barreda et

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al., 2015) was recognized in samples from Cerro del Hadro and Corral de Piedra (Fig. 5H).

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It is a key Maastrichtian species of the southern Proteacidites/Nothofagidites Province

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(Herngreen et al., 1996) and became extinct at the Cretaceous/Paleogene boundary in

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Australia, New Zealand and Antarctica (Vajda and Bercovici, 2012, 2014).

168 169

-------------------------------------------Insert Fig. 4 here----------------------------------------------

170 171

Nonvascular plants are represented mainly by spores of Zlivisporis reticulatus (Pocock)

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Pacltová and Simoncsics, 1970 (Fig. 4G) and the Lycophyta by the spores Ceratosporites

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equalis Cookson and Dettmann, 1958 (Fig. 5E) and Retitriletes austroclavadites (Cookson)

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Potonié, 1956 (Fig. 5F). Among the Monilophyta, the assemblage includes Cibotiidites

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tuberculiformis (Cookson) Skarby, 1974 (Fig. 4E), which has an affinity to the Gondwanan

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tree fern family Dicksoniaceae. Besides, the present palynoflora includes spores of

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Concavisporites (Fig. 4C), Biretisporites (Fig. 4B), Gleicheniidites (Fig. 4D; Fig. 5D),

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Cicatricosisporites, Ariadnaesporites and massulae of Azolla (Fig. 4H).

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The non-pollen palynomorphs (NPP) recognized are mainly represented by zygospores of

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filamentous green algae as Catinipollis geiseltalensis Krutzch, 1966 (Fig. 4A) and

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Ovoidites spp. The species Ovoidites spriggi (Cookson and Dettmann) Zippi 1998 is well

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represented in the sample M9 from Corral de Piedra (Fig. 3; Fig. 5A-C).

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---------------------------------------------Insert Fig. 5 here---------------------------------------------

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Systematics

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We have considered the rules and recommendations of the International Code of

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Nomenclature for algae, fungi, and plants (Shenzhen Code) (Turland et al., 2018).

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Genus Spinizonocolpites Muller, 1968

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Type: Spinizonocolpites prominatus (McIntyre) Stover and Evans, 1973

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Spinizonocolpites riochiquensis Vallati and De Sosa Tomas sp. nov.

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Fig. 4R-W

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Spinizonocolpites cf. hialinus Vallati et al., 2016 (non Fig. 6.3)

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Spinizonocolpites cf. hialinus Vallati et al., 2017a

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Holotype. Fig. 4V (LM); UNPSJB-MFP-CV 187 12.5/91. Repository “Dr. Eduardo A.

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Musacchio” of the UNPSJB at Comodoro Rivadavia (this paper).

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Paratypes. Fig. 4T (LM), UNPSJB-MFP-CV 183 7/105 (this paper); Fig. 4R (LM),

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UNPSJB-MFP-CV 216 10/101 (this paper); Fig. 6.5 (LM), CR.P.CV CH 18/108 (Vallati et

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al., 2016).

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Type locality. Cerro del Hadro at the headwaters of the Río Chico in the Golfo San Jorge

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Basin (45°37'20.17"S, 68°26'35.42"W).

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Principal studied material: CR.P.CV CHx 24/100, CR.P.CV CH 18/108 (Vallati et al.,

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2016; Figs. 6.4 and 6.5 respectively); UNPSJB-MFP-CV 1C 14/98; UNPSJB-MFP-CV 216

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10/101 (Vallati et al., 2017a; Figs. 6H and 6I respectively); UNPSJB-MFP-CV 195 15/115;

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UNPSJB-MFP-CV 1C 22/95.5 (non-figured specimens).

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Stratigraphic horizon. Maastrichtian, based in a palynoflora studied in the pelitic bed in

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Cerro del Hadro (Fig. 2) (Vallati et al., 2016).

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Derivation of name. From the headwaters of the Río Chico, in the Golfo San Jorge Basin,

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where several outcrops provided the specimens of Spinizonocolpites riochiquensis sp. nov.

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Specific diagnosis. Spheroidal to sub-spheroidal pollen grains, up to 82.4 µm in diameter.

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The exine is hyaline and acolumellate. Zonosulcate, with a continuous zonosulcus that can

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divide the grain into two almost equal parts. The surface presents densely distributed

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baculate elements.

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Description. The pollen grains are spheroidal to sub-spheroidal when complete (Fig. 4V)

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and elliptical if they are split into two almost equal parts (Fig. 4R, T, this paper; Fig. 6H,

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Vallati et al., 2017a). The diameter in the measured specimens is 53.6 (58.2) 82.4 µm. The

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grains are zonosulcate with an aperture that encircles the grain (aperture type 16 in Harley

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and Baker, 2001). The exine is near 0.7 µm, hyaline, acolumellate and psilate, excepting for

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the ornamental elements. The sculpture consists of baculae 4.8 (7.6) 11.6 µm long and 1.6

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µm wide, scattered over the whole surface. The typically cylindrical baculae have rounded

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ends, and bases with a circular contour, in some cases swollen (Fig. 4S). Some baculae

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appear slightly curved (Fig. 4R, S). The complete specimen in Fig. 4V presents the baculae

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more densely distributed in the periphery of the grain, where they are 0.5 (0.8) 1.5 µm apart

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and more widely spaced (up to 6.4 µm) in the center.

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Remarks. A hyaline acolumellate exine, combined with densely distributed long baculae

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and a large size characterize this species of Spinizonocolpites.

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Archangelsky and Zamaloa (1986) included zonosulcate and sculptured pollen grains with

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a hyaline acolumellate exine, in the genus Spinizonocolpites. The latter was originally

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described by Muller (1968) as zonosulcate and finely reticulated with scattered sculpture

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elements. It was emphasized the coincidence of the aperture type and the sculpture

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elements (baculae, spines) for including the specimens with hyaline exine in the mentioned

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genus. The authors pointed out that the tectate-columellate or hyaline condition of the exine

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allows specific differentiation within the genus. Moreover, studies on extant pollen grains

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of the Family Arecaceae have shown a great variability of the exine ornamentation and

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structure even among species of a genus (Ferguson, 1986). Spinizonocolpites riochiquensis

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sp. nov. is similar to S. hialinus Archangelsky and Zamaloa, 1986 but the sculpture

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elements are more densely distributed in the new species. Besides, S. riochiquensis has a

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larger diameter (up to 82.4 µm) and longer baculae (up to 11.6 µm long) while S. hialinus

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has spines, cones or baculae up to 5 µm.

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Spinizonocolpites hialinus was recorded in the Maastrichtian deposits of La Irene and

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Monte Chico formations (Povilauskas et al., 2008; Povilauskas, 2013). The species

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Spinizonocolpites aff. baculatus Muller 1968, described and illustrated by Jaramillo and

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Dilcher (2001) from the middle Paleogene of Central Colombia, is similar to S.

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riochiquensis. The main differences are related to the presence of a thicker exine (2.5 to 3

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µm) and wider baculae (2 to 3 µm) in the Colombian specimens. The authors suggested the

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reworking of these specimens from Upper Cretaceous or lower Paleocene sedimentary

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rocks.

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Spinizonocolpites paleobaculatus is a species described by Caroprese (2000) from the

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Upper Cretaceous in Venezuela (South America). It has a hyaline exine and a very similar

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sculpture with long baculae up to 5.5 µm, but this species includes smaller oval specimens

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with fewer sculpture elements (up to 32 baculae per specimen). S. paleobaculatus is

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distributed only in the Upper Cretaceous and disappears in the K/Pg event, after which only

256

S. baculatus is reported (Caroprese, 2000).

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Povilauskas (2013) described Spinizonocolpites sp. 1 in the Maastrichtian of the Monte

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Chico Formation. This species includes grains with a hyaline exine, but they are smaller

259

(mean polar diameter of 31 µm) and sculptured with conical spines up to 3 µm long.

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Palaeobotanical affinity. The fossil form-genus Spinizonocolpites is compared to the pollen

261

of the extant palm Nypa fruticans Wurmb, 1779 (Arecaceae, subfamily Nypoidea). Harley

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and Barker (2001) considered that the mentioned affinity is strengthened by the finds of

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Nypa fruits associated with Spinizonocolpites pollen grains from the Eocene of Tasmania.

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The mentioned authors studied the morphological variability of pollen grains of the extant

265

Arecaceae. They pointed out that a spiny exine combined with the zonosulcate aperture and

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large size (55-70 µm) make the pollen of Nypa highly distinctive among the Arecacaceae.

267

Spiny pollen grains with completely zonosulcate apertures are also present in the Subfamily

268

Calamoidea (Salacca), but they are smaller, usually less than 30 µm in diameter (Harley

269

and Baker, 2001).

270

Nypa was formerly more diverse than at present, taking into account the considerable

271

diversity in fossil pollen compared to the uniformity of extant N. fruticans (Harley et al.,

272

1991; Dowe, 2010).

273

Stratigraphic distribution. The specimens of S. riochiquensis sp. nov. have been recognized

274

in the upper part of the Lago Colhué Huapi Formation at Cerro de los Fragmentos, Corral

275

de Piedra and Cerro del Hadro. In the overlying Danian Salamanca Formation,

276

Archangelsky and Zamaloa (1986) recognized the species Spinizonocolpites hialinus.

277

Besides, Scafati et al. (2009) reported the Spinizonocolpites-complex, with pollen grains

278

with processes of variable shape, in the lacustrine Danian palynoflora studied in the Cerro

279

Bororó Formation. We highlight the potential biostratigraphic interest of S. riochiquensis

280

sp. nov., considering that the species is restricted up to now to the Maastrichtian interval

281

prior to the Cretaceous/Paleogene global extinction event.

282 283

4.2 Monocot fragmentary leaves from Cerro Hoja Grande

284

Twenty-eight linear and symmetrical parallel-veined leaf fragments were recovered from

285

reddish claystone at Cerro Hoja Grande, southwest 1,5 km from Cerro del Hadro (Fig. 1C,

286

Fig. 6 A). The plant fossils are mainly impressions of leaf fragments, but some

287

compressions are also present. The isolated leaf fragments are unattached to a main rachis.

288

The base and apex are not preserved, and the margins are entire and unarmed (i.e., lacking

289

spines). The fragments are 5 to 13 cm long and 2.5 to 4 cm wide. The laminae present a

290

strong midvein up to 1mm in wide and many parallel veins 0.3-0.6 mm wide bounding it

291

(Fig. 6D-I). Some fragments clearly show two different orders of veins on each side of the

292

midvein (Fig. 6D-F). Transverse veins are not distinguished in the present material. The

293

leaves are mainly arranged according to the lamination. Some leaves are superimposed,

294

suggesting their deposition in a low energy environment. The presence of some distorted

295

leaf remains is interpreted herein as an effect of the lithostatic pressure when the sediment

296

was saturated by water.

297

The fragmentary condition of these fossils and their preservation precludes a more precise

298

botanical affinity. Despite this, the leaf segments show a strong, uniform midvein bounded

299

on either side by two orders of parallel veins. This criterion is considered one of the basic

300

characteristics of extant palm leaves that can be used to recognize fossil palm leaves (Read

301

and Hickey,1972; Harley, 2006). These palm-like fragmentary leaves recovered in the

302

upper part of the Lago Colhué Huapi Formation could strengthen the presence of the

303

Arecaceae in the Maastrichtian of the basin.

304 305

------------------------------------------------Insert Fig. 6---------------------------------------------

306 307

4.3 Fossil charcoal

308

Charcoalified plant material from the white marlstone bed in Cerro del Hadro includes

309

mesoscopic fragments of coniferous wood with uniseriate and biseriate bordered pits and

310

different types of cross-field pitting (Fig. 7B-F). The principal morphologies of the charred

311

wood are stem-like and elongate forms (Crawford, 2015). The homogenized cell walls of

312

the tracheids, that are diagnostic of charcoal, are evident in Fig. 7E. According to Brown et

313

al. (2012), these charcoalified fragments of the marlstone bed (180 to 800 µm in size) are

314

classified as mesocharcoal (fragments larger than 125 µm). Likewise, abundant small

315

particles of microcharcoal (less than 125 µm) were recognized in the palynological samples

316

from the marlstone bed (Fig. 7A) and Corral de Piedra (Table 1).

317 318

5. Discussion

319

The presence of zygospores of filamentous green algae in the deposits of the upper part of

320

the Lago Colhué Huapi Formation, suggests a freshwater body, with well-oxygenated warm

321

water and probable seasonality to stimulate the zygospore formation (Scafati et al., 2009;

322

Bowman et al., 2014).

323

The freshwater ferns (Salviniales) are represented in Cerro del Hadro by scarce massulae

324

and megaspore apparatuses of Azolla and microspores of Ariadnaesporites micromedusus

325

Stough, 1968. However, these aquatic plants are very abundant and diversified in the

326

previously studied deposits of Lago Colhué Huapi Formation in Cerro de los Fragmentos

327

(Fig. 1C), where leaves, megaspores, complete megaspore apparatuses and microspores of

328

the Marsileaceae and Salviniaceae were reported (Vallati et al., 2017; Table 1). The rich

329

assemblage of Azolla in these deposits is dominated by A. colhuehuapensis Vallati et al.,

330

2017. Collinson et al. (2010) pointed out that fossil water fern occurrences could be used as

331

an indicator of fresh open waters or wetlands.

332

The Podocarpaceae are very abundant in the upper levels of the Lago Colhué Huapi

333

Formation, with many taxa suggesting lowland to middle altitude vegetation as

334

Podocarpidites,

Phyllocladidites

and

Dacrydiumites.

Besides,

Microcachryidites

335

antarcticus and Araucariacites probably represent higher altitude vegetation.

336

The extant podocarpaceae Podocarpus, Microcachryis, Dacrydium, Dacrycarpus and the

337

araucariaceae Dilwynites are represented by several pollen grains in the marlstone bed of

338

Cerro del Hadro. In the present day, these conifers are essentially adapted to areas of wet,

339

equable, mesothermal climate (Morley, 2010; Macphail, 2007). Phyllocladidites mawsonii,

340

the pollen of Lagarostrobus franklinii (Huon Pine) is nowadays confined to very humid

341

habits in the southwest of Tasmania. It is a well-represented taxon in the palynological

342

assemblage from the pelitic bed of Cerro del Hadro, but it was not recognized up to now in

343

the samples studied from the immediately overlying marlstone bed. It is accepted that

344

Lagarostrobus franklinii has required high humidity levels during its evolution, making it a

345

useful modern analogue for palaeoenvironmental reconstructions (Bowman et al., 2014).

346

The characteristic wind-pollination mechanism of conifers involves the dispersion of a

347

significant number of pollen grains and could cause the overrepresentation of these plants

348

in the microflora (Bowman et al., 2014). Nevertheless, numerous coniferous wood

349

fragments recognized as mesocharcoal in the white marlstone bed studied herein constitutes

350

additional evidence of the abundance of this group of plants in the Maastrichtian

351

ecosystem. Mesocharcoal recovered in the upper part of the Lago Colhué Huapi Formation

352

suggests surface wildfire that affected the local vegetation (Scott, 2010; Brown et al.,

353

2012). The high levels of Oxygen during the Cretaceous account for widespread fires and

354

can even explain the fire of wet vegetation during this interval (Brown et al., 2012).

355 356

-------------------------------------------Insert Fig. 7----------------------------------------------------

357

-

358

359

The genera Spinizonocolpites, Arecipites, Mauritiidites?, and probably Proxapertites and

360

the fossil leaves recovered in the upper deposits of the Lago Colhué Huapi Formation have

361

an affinity with the Arecaceae (Palms). The extant Palm family is distributed widely in the

362

tropics and subtropics, with few species living in temperate regions (Eiserhardt et al.,

363

2011). In particular, the presence of Spinizonocolpites (Nypa-type pollen grain) in almost

364

every studied outcrop in the headwaters of the Río Chico, suggests a warm climate with at

365

least seasonal rainfall. Woelders et al. (2017) proposed such a climate for the Late

366

Maastrichtian and Danian in central and north Patagonia, probably related to the Late

367

Cretaceous Deccan Traps pouring phases. The extant Nypa has a restricted distribution in

368

brackish coastal swamps, in the Pacific and Indian Oceans. This mangrove palm occupies

369

estuarine floodplains of rivers, where it exhibits a colonial growth habit alongside the

370

coastlines (Tomlinson, 1986; Gee, 2001). The probable presence of coastal swamps in the

371

upper levels of the Lago Colhué Huapi Formation, where Nypa-like plants could thrive, is

372

suggested in Fig. 8. The first marine deposits in the basin are represented by the Salamanca

373

Formation, which overlies the Lago Colhué Huapi Formation. Some studies suggested a

374

Maastrichtian age for the beginning of this Atlantic transgression (Clyde et al., 2014, and

375

references therein). Of particular interest for this topic, is the suggestion that some

376

stratigraphic intervals of the Lago Colhué Huapi Formation could represent the lateral

377

relations between the uppermost part of the Chubut Group and the contemporaneous

378

deposits of the Salamanca Formation (Casal et al., 2015).

379

Plants of Asparagales/Liliales affinity represented in the present pollen assemblage by

380

Liliacidites spp. usually live in a marsh or a paludal environment (Scafati et al., 2009).

381

Particularly, Liliacidites kaitangataensis Couper, 1953 (Fig. 4Q), well represented in the

382

assemblage of the Lago Colhué Huapi Formation, has been compared by some authors to

383

pollen from Lilium. Regarding this topic, it is interesting to mention that extant plants of

384

Lilium prefer moderately acidic or lime-free soils, which suggest different environmental

385

conditions than those that prevailed during the deposition of the marl.

386

Even though the Proteaceae are scarcely represented in the new deposits studied (Figs. 4X,

387

5I), the family is well diversified in the palynoflora of the pelitic bed in Cerro del Hadro

388

(Table 1). This assemblage includes Peninsulapollis gilli (Cookson) Dettmann and Jarzen,

389

1988, Beaupreaidites orbiculatus Dettmann and Jarzen, 1988 and Beaupreaidites cf.

390

elegansiformis Cookson, 1950, all of which are Beauprea-type pollen grains (Vallati et al.,

391

2016). We highlight the presence of Beauprea-type plants in the upper part of the Lago

392

Colhué Huapi Formation, considering that the extant Beauprea is a thermophilic taxon,

393

nowadays represented by species confined to wet and warm habitats in the tropical New

394

Caledonia Island, in the southwest Pacific (Bowman et al., 2014; He et al., 2016).

395

Many of the taxa represented in the upper part of the Lago Colhué Huapi Formation, as

396

Dacrydium, Lagarostrobus, Beauprea and the Asteraceae (represented by Tubulifloridites

397

lilliei) have their origin center in Antarctica (He et al., 2016; Barreda et al., 2015). A

398

continental bridge linking Antarctica and South America at the end of the Cretaceous has

399

been suggested by Leppe (2017), considering the similarities in the Maastrichtian biota of

400

the northern part of Antarctica and the northern Magallanes Region.

401

Stromatolites are laminated microbialites that provide information on ancient habitats

402

(Reitner et al., 2011). These accretionary structures are traditionally interpreted as

403

biosedimentological

404

cyanobacteria

405

microorganisms such as methanogenic and sulfate-reducing bacteria can also be

406

components of these communities (Dupraz et al., 2008, and references therein). The

as

remains the

most

of

microbial

successful

mats,

building

that

include

organisms.

photosynthetic

However,

other

407

calcified stromatolite E1, present in the upper levels of the Lago Colhué Huapi

408

Formation in Cerro del Hadro (Fig. 2), presents a conspicuous lamination with an

409

alternation of dark and light color laminae. Its presence could suggest marginal areas of

410

the freshwater body (photic zone), with light availability for photosynthesis.

411

Taking into account the information previously discussed a palaeoenvironmental

412

reconstruction of the upper levels of the Lago Colhué Huapi Formation at the headwaters of

413

the Río Chico is proposed herein in Fig. 8. Well compared freshwater aquatic

414

palaeoenvironments in southern South America were reported in the Campanian–

415

Maastrichtian La Colonia Formation (Cúneo et al., 2014) and in the Danian Bororó

416

Formation (Scafati et al., 2009). These plant communities share with the Lago Colhué

417

Huapi Formation several taxa of Zygnematales, Salviniales, Coniferales, and Arecales. We

418

emphasize the close similarities in composition of the palynofloras of the Maastrichtian

419

Lago Colhué Huapi Formation and the Danian Bororó Formation. As noted by Cúneo et al.

420

(2014), the critical events around the Cretaceous/Paleogene boundary would not seem to

421

have affected the vegetation of these aquatic bodies and the surrounding environments. The

422

aquatic plant Azolla, abundant in some of the studied deposits of the Lago Colhué Huapi

423

Formation, includes many species that persist world-wide through the K/Pg boundary

424

(Kovach and Batten, 1989). Considering the characteristics of the extant Azolla, Vajda and

425

Mc Loughlin (2005) analyzed some probable mechanisms used by these plants to survive

426

the crisis. These authors suggested that the potential for vegetative regeneration and the

427

possible symbiotic relationship with Anabaena, a nitrogen-fixing cyanobacterium, could

428

have benefited the plants during the environmental changes related to the global crisis.

429 430

---------------------------------------------Insert Fig. 8-----------------------------------------------

431 432

6. Conclusions

433

The overall composition of the palynoflora of the upper levels of the Lago Colhué Huapi

434

Formation agrees with a freshwater aquatic palaeoenvironment and a warm and humid

435

climate.

436

Spinizonocolpites

437

morphologically different from the Danian taxa reported at present in the basin.

438

The record of Spinizonocolpites and several Palm-like leaf fragments in the upper part of

439

the studied unit reinforces the presence of the Arecaceae in the Cretaceous of Patagonia.

440

The presence of charcoal in these deposits suggests the existence of wildfires that affected

441

the vegetation in the Maastrichtian of the basin.

riochiquensis

sp.

nov.

is described

herein, including grains

442 443

Acknowledgments

444

The authors wish to thank Luis Insúa and Chiche Martínez, landowners in the headwaters

445

of the Río Chico for facilitating our work on their property. We also want to recognize the

446

students Leonardo Ovando, Francisco Oporto, and Enzo Vasquetto for their enthusiastic

447

collaboration in the field and Lab. We sincerely thank the careful review and suggestions of

448

two anonymous reviewers, and the editor José Matildo Paredes, that improved substantially

449

the original manuscript. This paper is a contribution to PICT-2016-0459 of the Agencia

450

Nacional de Promoción Científica y Tecnológica (ANPCyT).

451 452

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Vallati, P., De Sosa Tomas, A., Casal, G.A., Calo, M., 2017a. Salviniales from the Late

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Cretaceous of the Golfo San Jorge Basin. Cretaceous Research 74, 45–55.

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http://dx.doi.org/10.1016/j.cretres.2017.02.004

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Vallati, P., De Sosa Tomas, A., Casal, G.A., Calo, M., 2017b. El Bloom de Azolla (Helecho

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Mosquito) en el Cretácico Tardío de la Cuenca del Golfo San Jorge. In: Libro de

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Ciencias de la Tierra “Dr. Eduardo Musacchio”, Comodoro Rivadavia, Chubut, 77–

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78.

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Vallati, P., De Sosa Tomas, A., Casal, G., 2018a. Primer registro de un paleo-incendio en el

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Maastrichtiano de la Cuenca del Golfo San Jorge. In: Libro de Resúmenes (Eds. De

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Sosa Tomas, A. y Casal, G.A.), VI Jornadas de las Ciencias de la Tierra “Dr.

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Eduardo Musacchio”, Comodoro Rivadavia, Chubut, 51–52.

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Vallati, P., De Sosa Tomas, A., Casal, G., 2018b. Charcoalified plant remains from the

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Golfo San Jorge Basin, Argentine: evidence of wildfire during the Late Cretaceous.

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1stPalaeontological Virtual Congress. Book of abstracts, 170.

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Woelders, L., Vellekoop, J., Kroon, D., Smit, J., Casadío, S., Prámparo, M.B., Dinarès-

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Cretaceous climatic and environmental change in the South Atlantic region,

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Paleoceanography 32: 466–483.

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Wurmb, F., 1779. Nypa fructicans. Verhandelingen van het Bataviaasch Genootschap van Kunsten en Wetenschappen, 1–349.

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Zippi, P.A., 1998. Freshwater Algae from the Mattagami Formation (Albian), Ontario:

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Paleoecology, Botanical Affinities, and Systematic Taxonomy. Micropaleontology

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44, 1–78.

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Figure Captions

681

Fig.1. Location map showing the studied outcrops with plant remains in the Lago Colhué

682

Huapi Formation at the headwaters of the Río Chico, Golfo San Jorge Basin. A. Chubut

683

province. B. The black box represents the study area showed in 1C. C. Radar image

684

showing the location of the studied outcrops.

685 686

Fig. 2. A. Schematic section at Cerro del Hadro showing the white marlstone bed (WM)

687

with the associated stromatolite E1 and the pelitic bed (PB). Lithological references. Cl:

688

claystone; Sl: siltstone; Fs: fine sandstone; Ms: medium sandstone; Cs: coarse sandstone;

689

Fc: fine conglomerate; Mc: medium conglomerate; Cc: coarse conglomerate. The colors in

690

the stratigraphic section do not represent the field colors of the rocks. B. Panoramic view of

691

the outcrop. C. Enlarged image of the stromatolite E1. D. Detail of the laminated

692

stromatolite E1 and the associated white marlstone bed.

693 694

Fig. 3. Schematic sections of the Lago Colhué Huapi Formation outcropping at Cerro Hoja

695

Grande and Corral de Piedra, headwaters of the Río Chico, Golfo San Jorge Basin. The

696

position of the fertile levels is indicated in both sections. M9, M13, M14, M15: samples

697

fertile in palynomorphs. Lithological references. Cl: claystone; Sl: siltstone; Vfs: very fine

698

sandstone; Fs: fine sandstone; Ms: medium sandstone; Cs: coarse sandstone; Vcs: very

699

coarse sandstone; Fc: fine conglomerate; Mc: medium conglomerate; Cc: coarse

700

conglomerate.

701 702

Fig. 4. Selected zygospores, spores, gymnosperm and angiosperm pollen grains from the

703

white marlstone bed at Cerro del Hadro, Golfo San Jorge Basin. LM micrographs. A.

704

Catinipollis geiseltalensis, UNPSJB-MFP-CV 187 12/102. B. Biretisporites sp., UNPSJB-

705

MFP-CV 185 4/108. C. Concavisporites sp., UNPSJB-MFP-CV186 10/98. D.

706

Gleicheniidites senonicus, UNPSJB-MFP-CV 185 10/92. E. Cibotidiites tuberculiformis

707

UNPSJB-MFP-CV 185 10/100. F. Cibotiidites cf. auriculatus, UNPSJB-MFP-CV 189 16/

708

108. G. Zlivisporis reticulatus, UNPSJB-MFP-CV 182 3/109. H. Massula of Azolla sp. 3,

709

UNPSJB-MFP-CV 181 19/102. I. Gamerroites sp. UNPSJB-MFP-CV 197 4/120. J.

710

Podocarpidites sp., UNPSJB-MFP-CV 184 5/107. K. Podocarpidites ellipticus, UNPSJB-

711

MFP-CV 188 5/100. L. Phyllocladidites? sp. UNPSJB-MFP-CV 194 6/96. M, N.

712

Dacrydiumites florinii. M, UNPSJB-MFP-CV 181 8/107. N, UNPSJB-MFP-CV 181 17/92.

713

O. Microcachryidites antarcticus.

UNPSJB-MFP-CV 184 10/102. P. Dacrycarpites

714

australiensis, UNPSJB-MFP-CV 183 18/110. Q. Liliacidites kaitangataensis. UNPSJB-

715

MFP-CV 186 16/110. R-W. Spinizonocolpites riochiquensis sp. nov. R. Paratype.

716

UNPSJB-MFP-CV 216 10/101. S. Detail of the baculae and the exine in the specimen

717

illustrated in R. T. Paratype. UNPSJB-MFP-CV 183 7/105. U. Detail of the specimen

718

illustrated in T. V. Holotype. UNPSJB-MFP-CV 187 12.5/9, complete specimen showing

719

the distribution of the baculae. W. Detail of the baculae of the specimen illustrated in V. X.

720

Proteacidites scaboratus, UNPSJB-MFP-CV 182 17/104. Scale bars: A–E, I–O, Q–U, W–

721

X: 10 µm; F–H, P, V: 20 µm.

722 723

Fig. 5. Selected zygospores, spores, gymnosperm and angiosperm pollen grains from Corral

724

de Piedra, Golfo San Jorge Basin. LM micrographs. A–C. Ovoidites spriggi. A. UNPSJB-

725

MFP-CV 198 6/93. B. UNPSJB-MFP-CV 198 22/98. C. UNPSJB-MFP-CV 198 8/98. D.

726

Gleicheniidites senonicus, UNPSJB-MFP-CV 199 7/102. E. Ceratosporites equalis,

727

UNPSJB-MFP-CV 199 6.5/99. F. Retitriletes austroclavadites, UNPSJB-MFP-CV 200

728

13/99. G. Podocarpidites sp., UNPSJB-MFP-CV 199 13/102. H. Tubulifloridites lilliei,

729

UNPSJB-MFP-CV 199 5/93. I. Proteacidites scaboratus, UNPSJB-MFP-CV 221 21/102.

730

Scale bars: A–C, G: 20 µm; D–F, H–I: 10 µm.

731 732

Fig. 6.A. Panoramic view of Cerro Hoja Grande outcrop at the headwaters of the Río

733

Chico, Golfo San Jorge Basin. The yellow point indicates the plant level (see Fig. 3). Scale

734

bar: 5 m. B-C. Leaves and leaflets of Nypa, showing the morphology of an extant Palm

735

leaf. D-H. Monocot fragmentary leaves, D. UNPSJB-PB 200. E. UNPSJB-PB 201. F.

736

UNPSJB-PB 202. G. UNPSJB-PB 203. H. UNPSJB-PB 204. I. Detail of E, showing the

737

midvein and parallel longitudinal veins bounding it. White arrows indicate the robust

738

midveins of palm leaflets. Black arrows show parallel veins of a higher order. Scale bars: 1

739

cm.

740 741

Fig. 7. Micro and mesocharcoal from the white marlstone bed at Cerro del Hadro, Golfo

742

San Jorge Basin. A. Microcharcoal, LM micrograph. B-F. Mesocharcoal, SEM. B.

743

Charcoal fragment showing longitudinal tracheids with uniseriate radial pits. C. Detail of

744

the areolate pits, typical of coniferous wood. D. Charcoal fragment, with biseriate, sub-

745

opposite to alternate bordered pits on the longitudinal tracheids. E. Charcoal fragment

746

showing the detail of tracheids with homogenized cell walls. F. Charcoal fragment with

747

longitudinal tracheids and cross-field pitting in the rays. Scale bars: A: 100 µm; SEM B, D–

748

F:100 µm, C: 20 µm.

749 750

Fig. 8. Palaeoecological reconstruction of the upper levels of the Lago Colhué Huapi

751

Formation at the headwaters of the Río Chico, Golfo San Jorge Basin. Modern analogues of

752

the represented palynomorphs are included in brackets.

753 754

Table 1. Palynomorphs, mesofossils, and leaves from the different outcrops of the Lago

755

Colhué Huapi Formation at the headwaters of the Río Chico, Golfo San Jorge Basin. The

756

crosses indicate the presence of the taxa in the studied outcrops. The botanical affinity and

757

nearest living relatives after Raine et al., 2011; Harley, 2006; Bowman et al., 2014 and

758

references therein. The flowering plant classification follows the APG IV system (APG IV,

759

2016). References. PBCDH: Pelitic bed in Cerro del Hadro (Vallati et al., 2016); WMCDH:

760

White marlstone bed in Cerro del Hadro (This paper); CDF: Cerro de los Fragmentos

761

(Vallati et al., 2017); CHG: Cerro Hoja Grande (This paper); CDP: Corral de Piedra (This

762

paper).

•

Maastrichtian plant remains from the Golfo San Jorge Basin

•

A new species of Spinizonocolpites is described in the Lago Colhué Huapi

Formation •

Monocot fragmentary leaves are reported from the Maastrichtian of Patagonia

•

A reconstruction of a terrestrial environment close to the K/Pg boundary is proposed

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All authors have participated in (a) conception and design, or analysis and interpretation of the data; (b) drafting the article or revising it critically for important intellectual content; and (c) approval of the final version.

•

This manuscript has not been submitted to, nor is under review at, another journal or other publishing venue.

•

The authors have no affiliation with any organization with a direct or indirect financial interest in the subject matter discussed in the manuscript