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288S. MEDEANIC & I. C. S. CORREAIntroductionPaleoclimatic changes during the Quaternary(approximately 2.5 Ma BP) were relatively rapidin the past as compared with past climate changesin the last 60 Ma. Understanding of climateoscillations during the Quaternary is importantto evaluate variability of the natural environmentsin the past and probably use of these data for abetter understanding of actual climate situationand prediction of the future climate. Climaticchanges occurred during the Holocene (10 ka BP tillpresent) were the main factors influencing on thecoastal plain evolution of the Rio Grande do Sulstate, Brazil. The oscillations of global temperaturescaused relatively high frequency changes on sealevel. The climatic modifications were alsoresponsible for the littoral sediments depositionin the coastal plains and palaeoenvironmentalevolution.There are many different methods (proxydata) for the Quaternary paleoclimate reconstructionsin the world (Bradley 1999). Palynologicalanalysis is one of the most important methods,providing information from continents tocomplement other proxy data about paleoclimates(Webb 1991, Bradshaw 1994, Ledru et al. 1998,Bradley 1999). In addition to pollen and spores ofvascular plants, sediments usually include differentnon-pollen palynomorphs, which are organic-walledmicrofossils composed of sporopollenin-like orchitin (pseudochitin) polymers (Traverse 1988).These palynomorphs as a rule are more resistant tocorrosion and oxidation than pollen and sporescomposed of sporopollenin (van Geel 1976,Komárek & Jankovská 2001). These palynomorphsare predominantly represented by cysts of Acritarcha(marine phytoplankton) and Dynophyta, zygospores,coenobiums and colonies of Chlorophyta, differentfungal palynomorphs, palynomicroforaminifers, andscolecodonts. The forms, usually classified bypalynologists as cysts of Acritarcha arePrasinophycean phycomata (Colbath & Grenfell1995). In spite of uncertainties, regarding of theirprecise biological affinities, acritarchs areconsidered as remains of cysts of algal protists(Tappan 1980, Strother 1996). Prasinophycean algaeare a class of green algae, which are known todayfrom freshwater to marine environments, although inrecent forms only the marine taxa produce afossilized phycomata. The vast majorities ofPrasinophycean phycomata are recovered frommarine sediments and/or are associated with marineorganisms. Furthermore, based on their distribution,morphology, and composition, most Prasinophyceanphycomata are assumed to be phytoplankton, andtherefore were the primary producers of the ancientmarine ecosystem during the Proterozoic andPaleozoic (Martin 1993).The study of non-pollen palynomorphsstarted at the early 1970s in the Netherlands, andsince then, the interest in their use for palaeoclimaticreconstructions is growing (van Geel 1976, van Geel& van Hammen 1978, van Geel et al. 1980/81, vanGeel & Aptroot 2006).In the Quaternary lagoon sediments ofcoastal plains, the palynomorph variability is morediverse than in continental deposits. In addition toalgal and fungal palynomorphs, there are frequentpalynoforaminifers (Zamora et al. 2007, Medeanicet al. 2009), Prasinophycean phycomata, and cystsof Dynophyta (Grill & Quatroccio 1996, Medeanicet al. 2001, Weschenfelder et al. 2008) indicative ofsediments deposited under sea water influence.Scolecodonts are palynomorphs, encountered insediments formed in shallow water environmentsnear the coast (Lorscheitter 1983, Cordeiro &Lorscheitter 1994).The different scientific projects regardingHolocene paleoclimate and palaeoenvironmentalreconstructions in the coastal Plain of the RioGrande do Sul State, Brazil based on palynomorphstudy started in 1980s (Lorscheitter 1983, Cordeiro& Lorscheitter 1994, Lorscheitter & Dillenburg1998, Medeanic et al. 2003, Medeanic 2006,Medeanic & Corrêa 2007). All obtained informationso far allowed us to make proxy evaluation ofclimatic oscillations occurred since the last Pleistoceneglaciations. The lowering of temperature thattime caused the regression of the ocean withnegative amplitude of 120-150 m. The temperaturerise at about 10 kyrs BP (the Early Holocene) wasthe reason of the beginning of the marinetransgression. The maximum of marine transgressionoccurred at about 5-6 kyrs BP (the MiddleHolocene) with positive amplitude of sea level riseat about 4-5 m. Posterior marine regression at about3-3.5 kyrs (the Late Holocene) was characterized bysea level fall at about 2 m. In this paper, we presenta revision of our previous published results, basedon palynomorph study focusing on the Holoceneclimatic paleoreconstructions.Materials and MethodsStudy areaThe study area is situated in the southernpart of the coastal plain of the Rio Grande do Sulstate (Fig. 1). The climate of this region is warmtemperate,due to the joint influence of the warmBrazil and cold Falkland currents (Vieira & RangelPan-American Journal of Aquatic Sciences (2010), 5(2): 287-297