Palynomorphs in Holocene sediments from a paleolagoon in the coastal plain of extreme southern Brazil

This paper presents the results of a qualitative palynological analysis of a 140 cm-thick section of Holocene sediments from a paleolagoon, representing the last 2600 years, taken from an outcrop at Hermenegildo Beach (33°42’S; 53°18’W), located in the municipality of Santa Vitória do Palmar, in the state of Rio Grande do Sul, Brazil. Samples were treated with hydrochloric acid, hydrofluoric acid and potassium hydroxide, after which they were subjected to acetolysis and mounted on glycerin-coated slides for light microscopy analysis. Among the 48 palynomorphs identified were 25 fungi, eight algae, three bryophytes, and 12 pteridophytes. Brief descriptions and illustrations of each palynomorph are presented, together with ecological data from the organism of origin when possible. Our findings will serve as reference material for paleoenvironmental studies in the coastal plain of southern Brazil.


Introduction
Little is known about sea-level oscillations and their effects on climate and vegetation dynamics in the southern coastal plain in the state of Rio Grande do Sul, Brazil, despite the contribution that such oscillations have made to shaping the current landscape of the region.Studies of plant succession can expand the understanding of the historic climate and vegetation dynamics responsible for the existing phytogeographic patterns.Palynological analysis of Quaternary sediment profiles with the associated chronological context is of great importance to plant succession studies because it elucidates vegetation changes over time.Archived catalogs are fundamental to the correct identification of palynomorphs in sediments.Few palynomorph descriptions exist for use in paleoenvironmental studies of the > 600 km-long coastal plain of Rio Grande do Sul, the southernmost Brazilian state (Lorscheitter 1988(Lorscheitter , 1989;;Neves & Lorscheitter 1992, 1995a;Neves & Bauermann 2003, 2004;Roth & Lorscheitter 2013), and there are no palynological references for the extreme southern portion of the region.
The purpose of the present study was to document the palynology of coastal plain sediments from the extreme south of Rio Grande do Sul, representing the last 2600 years, as reference material for paleoenvironmental research.We provide taxonomic descriptions and photomicrographs, as well as ecological information about the organism of origin when possible.

Materials and methods
A 140 cm-thick sediment profile of a paleolagoon was obtained from a Holocene outcrop at Hermenegildo Beach (33°42'S; 53°18'W), located in the municipality of Santa Vitória do Palmar, in the state of Rio Grande do Sul, in the coastal plain in the extreme south of Brazil (Fig. 1).Twenty-eight samples were taken at 5-cm intervals.Each was collected in an 8-cm 3 box, directly from the vertical slope.The radiocarbon date at the base of the profile was determined by Beta Analytic Inc. (Miami, FL, USA).
The samples were treated by hydrochloric acid, hydrofluoric acid and potassium hydroxide, after which they were subjected to acetolysis and filtered through a net with a 250μm mesh (Faegri & Iversen 1989).The samples were mounted on glycerin-coated slides (Salgado-Labouriau 1973;Faegri & Iversen 1989) and examined under light microscopy (DIA-PAN; Leica Microsystems, Wetzlar, Germany).We counted a minimum of 300 pollen grains per sample.In parallel counts, we identified spores and other palynomorphs, which were monitored by saturation curves.Photomicrographs were taken using a digital camera (DFC295; Leica Microsystems) connected to the microscope.

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The palynological description of each taxon is briefly presented, with nomenclature based on Punt et al. (2007) and Tryon & Lugardon (1990).In some cases, it was not possible to measure the polar axis of the grains due to their fixed position.Where possible, ecological data for the organisms of origin are included in order to facilitate future paleoenvironmental studies.

Conclusions
In this study, we identified 48 taxa, including 25 fungi, eight algae, three bryophytes and 12 pteridophytes.The morphological study of these distinct palynomorphs showed a diversity of taxa, corresponding to a variety of habitats.As the first palynological sedimentary study of the extreme southern of Brazilian coastal plain, this work provides reference materials for paleoenvironmental research in this region focusing on the last millennia in this region.

Figure 1 .
Figure 1. A. State of Rio Grande do Sul, in southern Brazil; B. Location of Hermenegildo Beach; C. Hermenegildo Beach and the Holocene paleolagoon outcrop studied, composed of dark-clay organic sediments covered by transgressive sands.