Anais da Academia Brasileira de Ciências (2014) 86(4): 1573-1595 (Annals of the Brazilian Academy of Sciences) Printed version ISSN 0001-3765 / Online version ISSN 1678-2690 http://dx.doi.org/10.1590/0001-3765201420130274 www.scielo.br/aabc The sea-level highstand correlated to marine isotope stage (MIS) 7 in the coastal plain of the state of Rio Grande do Sul, Brazil RENATO P. LOPES1, SERGIO R. DILLENBURG1, CESAR L. SCHULTZ1, JORGE FERIGOLO1,2, ANA MARIA RIBEIRO1,2, JAMIL C. PEREIRA1,3, ELIZETE C. HOLANDA4, VANESSA G. PITANA1 and LEONARDO KERBER1 1Programa de Pós-Graduação em Geociências, Universidade Federal do Rio Grande do Sul/UFRGS, Av. Bento Gonçalves, 9500, Agronomia, 91540-000 Porto Alegre, RS, Brasil 2Fundação Zoobotânica do Rio Grande do Sul, Museu de Ciências Naturais, Seção de Paleontologia, Av. Salvador França, 1427, Jardim Botânico, 90690-000 Porto Alegre, RS, Brasil 3Museu Coronel Tancredo Fernandes de Mello, Rua Barão do Rio Branco, 467, 96230-000 Santa Vitória do Palmar, RS, Brasil 4Universidade Federal de Roraima, Instituto de Geociências, Departamento de Geologia, Av. Cap. Ene Garcez, 2413, Sala 11, Aeroporto, 69304-000 Boa Vista, RR, Brasil Manuscript received on August 8, 2013; accepted for publication on February 17, 2014 ABSTRACT The coastal plain of the state of Rio Grande do Sul, in southern Brazil, includes four barrier-lagoon depositional systems formed by successive Quaternary sea-level highstands that were correlated to marine isotope stages (MIS) 11, 9, 5 and 1, despite the scarcity of absolute ages. This study describes a sea-level highstand older than MIS 5, based on the stratigraphy, ages and fossils of the shallow marine facies found in coastal barrier (Barrier II). This facies outcrops along the banks of Chuí Creek, it is composed of fine, well-sorted quartz sand and contains ichnofossils Ophiomorpha nodosa and Rosselia sp., and molluscan shells. The sedimentary record indicates coastal aggradation followed by sea-level fall and progradation of the coastline. Thermoluminescence (TL) and electron spin resonance (ESR) ages from sediments and fossil shells point to an age of ~220 ka for the end of this marine transgression, thus correlating it to MIS 7 (substage 7e). Altimetric data point to a maximum amplitude of about 10 meters above present-day mean sea-level, but tectonic processes may be involved. Paleoceanographic conditions at the time of the highstand and correlations with other deposits in the Brazilian coasts are also discussed. Key words: Barrier II, Chuí Creek, MIS 7, Pleistocene, Paleoceanography. INTRODUCTION sheets, most notably in the Northern Hemisphere The Quaternary System encompasses the last (Pillans and Naish 2004, Head et al. 2008, 2.588 million years of Earth’s history, and has Gibbard et al. 2010). Besides affecting terrestrial been characterized by glacial-interglacial cycles environments due to changes in patterns of represented by the waxing and waning of ice atmospheric circulation and moisture supply, latitudinal displacement of ecosystems and cooling, Correspondence to: Renato Pereira Lopes E-mail: [email protected] another important effect of these cycles has been An Acad Bras Cienc (2014) 86 (4) 1574 RENATO P. LOPES et al. the oscillations of sea-level (eustasy). Although state Rio Grande do Sul (CPRS), in southern Brazil, regional isostasy, faulting and uplifting in coastal records of sea level oscillations prior to MIS 5 were areas also play an important role in relative sea- reported from microfossils in drilling cores (Closs level changes, the oscillations are directly linked 1970, Carreño et al. 1999) and geomorphological to variations in the volume of the ice sheets, thus features (Poupeau et al. 1988, Villwock and variations in the ratio of oxygen isotopes (16O/18O) Tomazelli 1995, Tomazelli et al. 2000). in microfossils and gases recovered from deep-sea The absolute chronologies and amplitudes and ice cores are used as proxies for changes in sea- of past sea-level oscillations in the coast of Rio levels, by assuming a relationship between these Grande do Sul, however, are not well defined yet. ratios and the ice volumes. This problem arises from the fact that most of Despite being recognized in coastal areas the geomorphological units formed by sea-level all around the globe since the XIX century (e.g. highstands represent the aeolian facies of coastal Darwin 1846), direct, reliable and well-preserved barriers; these deposits are usually reworked by indicators of past sea level highstands older than erosion, aeolian deflation and/or vegetation growth. the Pleistocene marine transgression of ~125 ka In addition, the CPRS is composed essentially BP correlated to marine isotope stage (MIS) 5, of siliciclastic sediments, devoid of consolidated are relatively scarce throughout the globe. While structures that could contain paleo sea-level oxygen isotope curves obtained from benthic indicators such as vermetids or erosion notches, foraminifera are used as indirect evidence of therefore the most reliable sea-level indicators would sea level oscillations through correlation with be found in well-preserved deposits representing the past ice volumes (Imbrie et al. 1984, Pisias et al. shallow marine facies of the barrier systems. These 1984, Martinson et al. 1987, Berger 2008), direct facies, however, are mostly covered by younger records in coastal areas are represented by paleo- sediments and coastal lakes; so far, the ~125 ka- shorelines that contain datable geomorphological old Barrier System III is the only Pleistocene unit features such as raised terraces, wave-cut notches whose marine facies is well-preserved and exposed and aeolianites (Pirazzoli et al. 1991, Hearty and (Tomazelli and Dillenburg 2007). Kindler 1995, Barreto et al. 2002) as well as other This study presents a description of the materials such as corals, vermetids or speleothems shallow marine facies of the Barrier System II, (Gallup et al. 1994, Angulo et al. 1999, 2006). from outcrops found in the southern sector of the In the Brazilian coast, the Holocene highstand CPRS, with information regarding the amplitude of ~6-5 ka BP (MIS 1) is well-represented by and chronology of the marine highstand that was several deposits, despite of some discrepancies responsible for the origin of this depositional system. regarding their timing and amplitude (Martin et Correlations with other deposits and paleoclimatic al. 2003, Angulo et al. 2006). Good records of the inferences from fossils and sedimentary features transgression correlated to MIS 5 are found in some are also presented. areas (Poupeau et al. 1988, Suguio et al. 2003, 2011, GEOLOGICAL SETTING Tomazelli and Dillenburg 2007) but the situation is complex for older transgressive events; so far, The CPRS (Figure 1) is located in the southern- only the northeastern Brazilian coast has provided most portion of the Brazilian coast. This features recognized as having been formed by the geomorphological unit is about 620 km-long marine transgression during MIS 7 (Barreto et al. and 100 km-wide, located between the latitudes 2002, Suguio et al. 2011). In the Coastal Plain of the 29°18’31”S and 33°43’17”S, and it is the An Acad Bras Cienc (2014) 86 (4) SEA-LEVEL HIGHSTAND DURING MIS7 IN SOUTHERN BRAZIL 1575 Figure 1 - a: location of the CPRS, in southern Brazil; b: geomor phologic subdivisions of the CPRS; c: west-east transect of the barrier (B) and lagoon (L) systems found in the southernmost CPRS (Modified from Villwock and Tomazelli 1995, Tomazelli and Villwock 2005, Rosa 2012). An Acad Bras Cienc (2014) 86 (4) 1576 RENATO P. LOPES et al. uppermost portion of the Pelotas Basin, the are usually covered by younger sediments. Precise southernmost marginal basin of the Brazilian coast. indicators of paleo sea-level highstands are scarce This basin is composed of terrigenous siliciclastic in these coastal barriers; the only reliable records of sediments eroded from older geological units Pleistocene sea levels known so far are ichnofossils located landwards, accumulated in the coastal area Ophiomorpha nodosa preserved some 5 to 7 meters since the split between South America and Africa a.s.l. in shallow marine facies of the Barrier System in the Late Cretaceous; its maximum thickness III (Tomazelli and Dillenburg 2007). is of approximately 10,000 meters (Closs 1970, The southernmost portion of CPRS is Bueno et al. 2007, Barboza et al. 2008). During dominated by two Pleistocene (II and III) and one the Quaternary, sea-level oscillations correlated to Holocene (IV) barrier-lagoon systems. Each system glacial cycles reworked the uppermost sediments of was chronologically correlated by Villwock and the Pelotas Basin, as evidenced by facies changes Tomazelli (1995) to the calibrated δ18O curves of and microfossil assemblages recovered from Imbrie et al. (1984), therefore attributing ages of drilling holes (Closs 1970, Carreño et al. 1999). ~450 ka (MIS 11) for system I, ~325 ka (MIS 9) for The first systematic geological survey of the system II, ~125 ka (MIS 5) for system III and ~6 CPRS was presented by Delaney (1965), who ka (MIS 1) for system IV. TL datings on sandstones followed the classical lithostratigraphy and proposed exposed on the shoreline beneath the Holocene the name “Itapoã Formation” for the aeolian deposits sediments of the Barrier IV System provided age of found along the coastal plain, while the marine 109 ± 7.5 ka BP, reinforcing the proposed age for deposits were named “Chuí Formation”; these Barrier System III (Buchmann and Tomazelli 2003). units were considered of Quaternary age because BARRIER SYSTEM II they overlay the Tertiary “Graxaim Formation”. During the 1980s, new geological surveys led to a This system is well-represented along the southern revision of the geology of the CPRS, and it became sector of the CPRS, stretching almost continuously clear that the units grouped together as “Itapoã” and for more than 200 km in the same SW-NE orientation “Chuí” formations were in fact several distinct units of the coastline.