Late Quaternary continental and marine sediments of northeastern Buenos Aires province (Argentina): Fossil content and paleoenvironmental interpretation

Journal of South American Earth Sciences 20 (2005) 45–56 www.elsevier.com/locate/jsames

Late Quaternary continental and marine sediments of northeastern Buenos Aires province (Argentina): Fossil content and paleoenvironmental interpretation Enrique Fucksa,*, Marina Aguirreb, Cecilia M. Deschampsc a

Facultad de Ciencias Naturales y Museo y Ciencias Agrarias y Forestales, Universidad Nacional de La Plata, Calle 64N3, CP 1900, Provincia de Buenos Aires, Argentina b CONICET, Ca´tedra de Geomorfologı´a y Geologı´a del Cuaternario, Museo de La Plata, Argentina c CIC, Departamento Paleontologı´a Vertebrados, Museo de La Plata, Argentina Received 1 April 2003; accepted 24 May 2005

Abstract Abundant invertebrate and vertebrate fossil remains that exhibit excellent preservation and were collected from deposits of both continental and marine origins at Pilar (Buenos Aires, Argentina) add paleoenvironmental data from the northeastern Buenos Aires province area linked to sea-level oscillations and climate variability since approximately 120 ka BP (marine oxygen isotope stage [MOIS] 5e). Two new fossiliferous localities discovered in the Luja´n River Valley allow for detailed geological studies and new dating of molluscan shells and bones. The studies suggest salinity changes during the Last Interglacial (8 m above m.s.l., min. 14CO40 ka) and the mid-Holocene transgression (5 m above m.s.l., 7–3 14C ka BP) compared with the modern pattern along the adjacent littoral (Rı´o de la Plata). The marine sequences represent the innermost boundary of the sea-level transgression in that area and contain a biogenic record (bivalves, gastropods, forams, ostracods) that indicates marginal marine environments (higher salinity than at present). Vertebrates and molluscs from the continental sequence suggest a freshwater habitat in which remains of marine fish must be allochthonous, probably incorporated by postmortem fluvial transport to the final depositional environment. q 2005 Published by Elsevier Ltd. Keywords: Late Pleistocene–mid-Holocene; Molluscs; Paleoenvironments; Vertebrates

1. Introduction The coastal area of the Buenos Aires province (‘Bonaerensian coastal area’) was affected during the Late Quaternary by sea-level invasions of different ages and magnitudes. The mid-Holocene transgression (7–3 14 C ka BP), with abundant fossils exhibiting excellent preservation (Aguirre and Farinati, 1999, 2000a,b), is best recorded between the Rı´o de la Plata margin and Bahı´a San Blas (Fig. 1A), as either extensive beach ridges or coastal lagoon and estuarine facies. In contrast, Late * Corresponding author. E-mail addresses: [email protected] (E. Fucks), maguirre@ museo.fcnym.unlp.edu.ar (M. Aguirre).

0895-9811/$ - see front matter q 2005 Published by Elsevier Ltd. doi:10.1016/j.jsames.2005.05.003

Pleistocene marine records (minimum 14C ages of 34– 43 ka BP, ca. 120 ka BP? or MOIS5e) are more discontinuous and contain fewer abundant fossils of poorer taphonomic signatures and comparatively lower faunal diversity. However, continental deposits of Late Pleistocene and Holocene age (Table 1) have provided the rich vertebrate fauna used for the definition of Land Mammal Ages and a local biostratigraphic pattern (Cione and Tonni, 1999) that, together with pollen records (e.g. Prieto, 1996; Prieto et al., 1998; Quattrocchio et al., 1995; Quattrocchio and Borromei, 1998), have shown paleoenvironmental fluctuations. A few examples of rich fossiliferous, Late Quaternary localities with both continental and marine remains are available in the literature pertaining to Argentina: mid-Holocene at Ensenada (Tonni and Cione, 1984), Las Brusquitas (Tonni and Fidalgo, 1983; Bonadona

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Fig. 1. (A) General location of the study area and localities mentioned in the text; (B) detailed map of the area showing Pleistocene and mid-Holocene transgression; (C) stratigraphic profile of the quarry with Late Pleistocene fluvial and marine deposits; and (D) cross-section of the Rı´o Luja´n valley with midHolocene sediments. Photographs a–e show details of the profiles.

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Table 1 Stratigraphic interpretation of the study area and correlation with other units known from the local literature with available dates

LP, Laboratorio de Tritio y Radiocarbono, Museo de La Plata, samples. Prieto et al., 1998, 2000; Figini, 1992; Carbonari et al., 1992; Figini et al., 1995; Politis et al., 1995, Figini et al., 1989.

et al., 1995), and Bahı´a Blanca surroundings (Aramayo et al., 2002) and Late Pleistocene at Rı´o Queque´n Salado (Pardin˜as et al., 1996). In addition, the Buenos Aires province still lacks updated information about and correlation of marine and continental paleoenvironmental and paleoclimatic changes since the Last Interglacial, especially those based on paleontological data from a single locality or area. This work is the first stage of a study designed to fill this gap and recognize variations in salinity, temperature, and energetic and general environmental conditions linked to sea-level oscillations

and global climate variability. This article reports the preliminary results of the doctoral thesis of one of the authors (EF).

2. General characteristics of the study area The area of study is located in northeastern Buenos Aires province, near Pilar (34827 0 20 00 S-58858 0 00 00 W) (Fig. 1A and B). The modern littoral in the vicinity of Pilar (Fig. 2) corresponds to the Rı´o de la Plata margin and

Fig. 2. Rı´o de la Plata. (A) Modern littoral; (B) interpretation of the northern horizontal (salinity) displacement during the marine transgressions; (a–c) displaced boundaries between estuarine zones (partly modified from Sprechmann, 1978). Modern zones: 1, inner fluvial; 2, intermediate fluvial; 3, fluviomarine; 4, marine. Salinity gradient: O, oligohaline (0–5‰); M, mesohaline (mixohaline) (5–18‰); P, polihaline (18–30‰); E, euhaline (O30‰).

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belongs to the oligohaline (limnic or inner fluvial) zone of the river (0–5% ppm salinity gradient; Sprechmann, 1978), though the limit between mixohaline and continental shelf waters depends on the season and dynamics of the estuary, with maximum freshwater discharge in winter and minimum in summer (Mianzan et al., 2001). Mean temperatures range from 10-15 8C in winter to 22–23 8C in summer (Guerrero et al., 1997), the substrate is mainly composed of muddy sediments, and a strong influence of the tidal regimes is drawn by the oceanic influence at the mouth (Punta Rasa). Winds are controlled by the position of the anticyclonic center of the South Atlantic, which brings westerlies responsible for precipitation in the area. The continental area is placed within the zoogeografic Pampasic dominion of the Guayano-Brazilian subregion (Ringuelet, 1961) and the phytogeographic Pampean province of the Chaquen˜o dominion (Cabrera, 1971).

3. Geological and paleontological background On the basis of the continental faunal content of Late Pleistocene and Holocene age near Luja´n, Ameghino (1889) proposed a ‘stages’ pattern still in use for the whole Pampean region. More recently, Dangaus and Blasi (1993) and Prieto et al. (1998) described the outcrops in this area on the basis of Ameghino’s work, providing new information on the geology, palynology, and microfossiliferous content. In a nearby basin (Rı´o Reconquista), Pardin˜as and Lezcano (1992), Lezcano et al. (1993), and Pardin˜as et al. (1995) have studied vertebrate fauna from continental units known in the local literature as Bonaerian and Lujanian (Middle– Late Pleistocene, w600–130 ka BP and 30 ka BP–Recent, respectively; Cione and Tonni, 1999) and described taphonomic, biostratigraphical, and paleoenvironmental aspects. Paleontological remains from the marine sediments also were mentioned earlier by Frenguelli (1957) and Camacho (1966). Previous geological and geomorphological studies in the Parana´ River delta area were carried out by Iriondo (1980), Parker and Marcolini (1992), and Violante and Parker (1993a). Three transgressions were proposed for the area by Gonza´lez and Ravizza (1989), though only two (Last Interglacial and mid-Holocene) are accepted by most local authors (Isla et al., 2000, references therein). Fucks and De Francesco (2000a,b, 2001) performed a detailed geomorphological study and the first lithological characterization of the continental and marine deposits in the area of Pilar, describing the innermost limit of the Holocene transgression in the Rı´o Luja´n Basin. The new sites considered in this study are very important because they: (1) show the exposure of continental and marine deposits in a single locality (Fig. 1C) that contains abundant invertebrate and vertebrate remains, quite an uncommon situation for the Bonaerensian area; (2) represent the innermost boundary for former high sea-

level episodes (Last Interglacial? and mid-Holocene transgression) in the area; and (3) allow documentation of the biogeographic response of invertebrate and vertebrate biotas to salinity changes driven by recent climate changes.

4. Geological setting The study of the sedimentology and paleontology of a quarry (Fig. 1B) resulted in the recognition of continental and littoral Pleistocene and marine (estuarine facies) Holocene deposits. Numerous well-preserved fossil remains, especially vertebrates associated with invertebrates (including microfossils), were recovered. Several detailed profiles show a regional substratum composed of Pampean sediments (‘Sedimentos Pampeanos’ Fidalgo et al., 1975). A marine-estuarine sequence overlays these sediments and is cut by a paleochannel of fluvial origin (Fig. 1C). These units are covered by the Sedimentos Pampeanos assigned to the Late Pleistocene. Invertebrate fauna were recovered from both marine (Pleistocene, Holocene) and continental (Pleistocene) sequences. The vertebrates were collected from the paleochannel. The macroinvertebrate fossil remains consist of abundant molluscan shells (bivalves, gastropods) that show excellent preservation and rather low diversity. A less abundant microfauna (forams, ostracods) was recovered from the marine Late Pleistocene. The vertebrates include remains of fish, turtles, and mammals and were recovered from the bottom of the channel deposit (Fig. 1C). 4.1. Pleistocene transgression The transgression is composed of green clay, 4 m thick in outcrop and 7 m in depth without reaching the base contact (Fig. 1A, level B). It passes laterally to sandy stratified sequences that are yellow with deep red areas (oxidation stains) (Fig. 1A, level C1). Shells of Ostrea sp., Mactra isabelleana, and T. plebeius are frequent, the latter generally as complete articulated valves, some of which appear in lifelike positions. Forams and ostracods also were recorded. A homogeneous, light brown, sandy-silty bed overlies these levels (Fig. 1A, level C2). The whole sedimentary sequence may represent an estuarine littoral environment, which begins with subtidal to intertidal facies and ends with aeolian sediments. Levels A and D of Fig. 1A represent disturbed materials. Fig. 1B represents T. plebeius in a lifelike position in level B (laboratory sample of Laboratorio de Tritio y Radiocarbono, Museo de La Plata (LP) 1217, O40.000 14C ka BP). On the basis of the geomorphological and stratigraphical relationships, the marine Late Pleistocene deposits, with only minimum radiocarbon ages available (LP 1217 O40 ka, T. plebeius), can be correlated with the marine units known as ‘Belgranense’ and the Pascua Formation in local literature (Fidalgo et al., 1973), which are exposed in

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different localities of the Bonaerensian coastal area (Isla Martı´n Garcı´a, Magdalena, Punta Indio, Pipinas, Punta Piedras, Samborombo´n Bay, Mar Chiquita surroundings, Santa Clara del Mar, Mar del Plata, Centinela del Mar, Claromeco´, Bahı´a Blanca) (Gonza´lez and Ravizza, 1989; Colado et al., 1995; Aguirre and Whatley, 1995; Etchichury et al., 1998; Isla et al., 2000; Cione et al., 2002). They also correlate with the Chuy Formation recognized in Uruguay (Nueva Palmira, La Coronilla; Martı´nez et al., 2001) and the Late Pleistocene transgression studied in Brazil (Suguio and Martin, 1978). Most authors have assigned similar marine sediments with synchronous minimum ages to the Last Interglacial maximum (MOIS5e). Recent studies, however, suggest that the ‘Belgranense’ stratotype (Barrancas de Belgrano, Argentina) originated by a pre-Wisconsin interglacial, younger than 0.78 Ma and probably during MOIS11 (w400 ka BP) rather than MOIS5e (120 ka BP), and that it is therefore older than the Pascua Formation (Violante and Parker, 1993b; Cione et al., 2002). To assess the paleosealevel position during interglacials of approximately 700– 140 ka BP and determine which was the warmest isotopic stage is neither simple nor unequivocal (Ortlieb et al., 1996). 4.2. Fluvial deposits A fining-upward deposit fills a channel 200 m wide and with a maximum thickness of 6.5 m (Fig. 1C). The sequence begins with 1.5 m of silty, dark brown, very tough Pampean sediments. A 1.5–2 m thick sequence of stratified beds overlies it unconformably. Each bed has a mean thickness of 0.30 m, is psephitic at the base, and is sharply sandy in the rest of the profile. The matrix-supported gravelly levels of the base have rounded clasts composed of CO3Ca2 (‘tosca’) and partially hardened brown-whitish sand and silts (‘Pampeano’), 0.05–0.06 m in diameter. Fig. 1C shows cross-bedding with Diplodon sp. shells (LP 1345 O40.000 14 C years BP). Fig. 1D shows a detail of the channel surfaces. Vertebrate fossils were recovered from this sequence. Although the clasts are well rounded, their scarce mechanic resistance suggests little transport. Approximately, 100 m east, this stratified sequence shows a high concentration of Diplodon shells, most of which are complete and articulated, and Ostrea sp. remains. Five meters of light yellowish, silty sand overlie the stratified section. It is massive, with channel surfaces and dispersed 2–3 cm thick lamentations. The lower sequence shows tabular and subordinate trough stratification, suggesting lateral meandering of the channel. The rest of the profile shows channel surfaces without inner stratification, which suggests the sudden silting of the paleochannel (Spalletti et al., 1987). A resistant brown-grayish brown bed, with scattered equidimensional carbonate concretions of Pampean sediments, lies at the top of the profile.

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Sedimentary sequences with these features have not been mentioned in the area, though fluvial pelitic intercalations are found commonly within the Pampean sediments. One Diplodon dating yielded O40.000 years 14C BP (LP 1345) (Table 1). 4.3. Holocene transgression This transgression is developed along the paleoestuary of the Luja´n River up to approximately Manzanares (34827 0 S– 59801 0 W) (Fig. 1A) and intercalated in the Luja´n Formation in its maximum extension, but it generally lies unconformably over the Pampean sediments and is covered by modern fluvial beds. It is composed of two facies: a black, very fluid, clayey one at the base and a silty-clayey, green to yellowish brown and light gray facies (Fig. 1D, photograph e). The measured thickness is approximately 1.80 m in the lower bed and 1.10 m in the upper. Both beds bear fossil invertebrates, commonly articulated and in lifelike positions, that would have been deposited in a low energy, subtidal to intertidal estuarine environment. Dating yields 3640G70 years 14C BP (LP 1347) and 6000–6370 years 14C BP (Figini, 1992). Therefore, it may be correlated with the Querandinense (Frenguelli 1957), Destacamento Rı´o Salado Formation, and the lower section of Las Escobas Formation (Fidalgo et al., 1972).

5. Faunal composition Within the marine Late Pleistocene sequence (Fig. 1C), the fossiliferous assemblage consists of abundant bivalves (dominant Ostrea, Tagelus, and Mactra), associated forams (Ammonia, Elphidium), and ostracods (Cytheracea, Cyprideis). These taxa also have been recovered in the midHolocene deposits from Samborombo´n Bay, Punta Rasa, and Mar Chiquita (Aguirre and Whatley, 1995; Aguirre, 1993a, b; Bertels-Psotka and Laprida, 1998; Laprida, 2001). The molluscan fauna (Table 2) and microfossils suggest a mixed paleoenvironment and moderate energetic conditions, though higher than at present in the modern fluvial area. Within the Late Pleistocene continental sequence at the paleochannel, the record consists of large shells of Diplodon sp. (Bivalvia), associated with scarce small specimens of Neocorbicula sp. (Bivalvia) and Ancylus sp. (Gastropoda), as well as fishes (pimelodids, Leporinus sp.) associated with brackish (Pogonias cromis) and marine (Carcharias taurus, Myliobatis sp.) (not living in the neighboring modern littoral) forms, freshwater turtles, and land mammals (see the Appendix). The dominance of continental vertebrates and exclusively freshwater molluscs suggests that the marine elements must have been incorporated by fluvial transport from the nearby marine beds. Vertebrate remains were found only in the paleochannel. Although the sample density is low, the diversity is

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Table 2 Paleoecology and distribution of the molluscan taxa

Full sources in Aguirre and Whatley (1995) and Aguirre and Farinati (2000a,b).

comparatively high. All the taxa are known from the Middle–Late Pleistocene in the Pampean area (Table 3). The freshwater fish record is outstanding because they are scarce in the fossil record of the area (Cione and Lo´pez Arbarello, 1995). Rodents (represented only by isolated teeth) and turtles belong to species related to warmtemperate environments near water. Megamammals (glyptodonts, toxodontids, Glossotherium, Morenelaphus) are represented by isolated fragments that suggest little transport because their fractures are not very abraded, which reinforces the sedimentological interpretation based on the mechanical resistance of some clasts. The marine mid-Holocene sequence is composed of gastropods (Littoridina) and bivalves (Mactra, Mytilus, Tagelus, and dominant Erodona), similar to the molluscan fauna characterizing the Destacamento Rı´o Salado Formation and the Canal 18 Member of the Las Escobas Formation proposed for the Salado Basin (Fidalgo et al., 1972; Fidalgo, 1979). A full list of the species recovered, paleoecological data, and distribution in space and time of the molluscan taxa and vertebrates appears in the Appendix and Tables 2 and 3.

6. Paleoenvironmental interpretation The molluscan taxa are well known from the marine Quaternary of Argentina and have modern representatives in the Argentine malacological province (Rı´o Grande do

Sul, Brazil-Golfo San Matı´as, Argentina), but not in the adjacent littoral area, except for Diplodon sp. and Erodona mactroides, which are typically oligo-mixohaline (not recorded in the Argentine Sea). These and the remaining molluscan taxa recovered in the paleochannel are common in Rı´o de la Plata. Salinity is probably the main factor responsible for the qualitative differences between the fossil molluscan assemblages and the modern taxa in the area surrounding Pilar (Rı´o Lujan, Rı´o de la Plata). During high sea-level stands that covered the area during the Late Pleistocene (MOIS5e?) and mid-Holocene, the mixing of oceanic and fluvial waters increased the salinity gradient, which caused a northward displacement of the horizontal zonation of the Rı´o de la Plata in comparison with the modern pattern. This claim is supported by the forams and ostracods recovered and in agreement with similar evidence documented for Uruguay and La Plata-Samborombo´n Bay (Sprechmann, 1978; Aguirre, 1993a; Martı´nez et al., 2001). A key observation regarding both marine units is the low diversity of the molluscan assemblages. This scarce number of taxa and specimens overall indicates a marginal marine environment of unstable conditions, perhaps polyeuhaline (Late Pleistocene) or mixohaline to mixo-polyhaline (midHolocene). The fish recovered from the Pleistocene sediments at the paleochannel, which supposedly were incorporated from the marine deposit, indicate mixohaline to marginal marine

Table 3 Stratigraphic distribution and environment of fossil vertebrates

E. Fucks et al. / Journal of South American Earth Sciences 20 (2005) 45–56 Pl, Pliocene; EP, Early Pleistocene; MP, Middle Pleistocene; LP, Late Pleistocene, H, Holocene; P, present. Tonni and Cione, 1984; Cione and Torno, 1988, Tonni and Cione, 1984, Cione and Lo´pez Arbarello, 1995; Lezcano et al., 1993, Lezcano et al., 1993; Tonni and Cione, 1984, Ringuelet and Ara´mburu, 1961, Pardin˜as et al., 1996, Broin and de la Fuente, 1993; Pardin˜as et al., 1996, Scillato Yane´ et al., 1995; Cione et al., 1999, Bond et al., 1995, Pardinas, 1995; Redford and Eisenberg, 1992, Vucetich and Verzi, 1995, Quintana, 1998; Vucetich and Verzi, 1995, Redford and Eisenberg, 1992; Deschamps et al., 2000, Menegaz and Ortiz Jaureguizar, 1995

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conditions in shallow warm-temperate waters, similar to evidence documented previously for the Holocene Las Escobas Formation (Tonni and Cione, 1984). Ostrea equestris is first recorded in the marine Bonaerensian Pleistocene. It and the record of Tagelus plebeius represent the northernmost boundary for both species in the marine Late Quaternary of Argentina. Both confirm salinity displacements since approximately 125 ka in the Rı´o de la Plata littoral. An overall comparison of the molluscan faunas suggests that the littoral water at Pilar was less saline than along the coastal area of La PlataSamborombon Bay at 2–6 ka BP. A warmer sea surface temperature (SST) during MOIS5e (e.g. Shackleton, 1987) in comparison with MOIS1 and modern conditions has been considered global in extent. The mid-Holocene climatic optimum has been recognized on the basis of different kinds of indicators in the southern hemisphere (6–7 ka BP; Iriondo, 1999) and worldwide. In the Bonaerensian coastal area, it has been documented by the mid-Holocene molluscan record (Aguirre, 1993b, 2002). In contrast, a paleobiogeographical analysis of the molluscs and microfossils recovered at Pilar (marine Pleistocene and mid-Holocene) does not support typically warmer water environments. During the Pleistocene transgression, the littoral environment was probably warm-temperate (O. equestris, T. plebeius, and M. isabelleana live within the warmtemperate range of shallow water masses) but not warmer than during the mid-Holocene. The SST cannot be assumed to have been much warmer; there is no evidence of latitudinal displacements in comparison with the modern geographical ranges, like those documented for other deposits with similar minimum 14C ages (e.g. Nueva Palmira and La Coronilla, Uruguay; Magdalena and Bahı´a Blanca, Bonaerensian area) (Weiler et al., 1988; Chaar et al., 1992; Martı´nez et al., 2001). No such displacement was documented for the Holocene transgression either. Substrate preferences of the invertebrate fauna are similar for both transgressions, though the energetic conditions of the oceanic waters probably were higher during deposition of the Pleistocene sediments. In this area, soft substrates in a shallow littoral (upper infralittoral-intertidal) paleoenvironment of moderate (Pleistocene) to low (mid-Holocene) energy probably were predominant. Land vertebrates represent temperate grasslands near water bodies, and freshwater fishes currently inhabit warmtemperate waters (Table 3).

7. Final remarks 7.1. Continental sequence (paleochannel) The vertebrate taxa recovered in the paleochannel are characteristic of the Middle–Late Pleistocene South

American megafauna (Table 3). On this basis and according to their stratigraphical position within the Pampean sediments and available radiocarbon dating, we interpret the continental unit as Middle–Late Pleistocene in age (Bonaerian–Lujanian). Some fish taxa represent the first mention of the Pleistocene (C. taurus, Myliobatis sp., Leporinus sp.) or of the fossil record (Serrasalminae). The dominance of continental vertebrates associated with typically freshwater molluscs supports a fluvial origin. The remains of marine fish and very scarce fragments of Ostrea sp. shells must have been incorporated through fluvial transport from the nearby marine unit to the final depositional environment. 7.2. Marine sediments The development and extension of the Late Pleistocene littoral deposits indicate a well-defined paleorelief, which suggests that a drainage basin had already settled before the sea-level rise. The older marine unit represents a shallow marginal marine environment, beginning with subtidal and intertidal facies and ending with aeolian sediments. This unit has poor chronological control (minimum w40 ka BP) but tentatively could be correlated with the Pascua Formation or Belgranense recognized in other Bonaerensian outcrops (Punta Piedras, Puente de Pascua, Queque´n Salado). The determination of whether the marine Late Pleistocene deposits at Pilar formed during MOIS5 or an older high sea-level stand requires further, more detailed studies, but apparently they do not correspond to the warmest peak accepted worldwide for substage 5e (MOIS5) of the oxygen deep-sea record. The Holocene marine deposits may correlate with the Las Escobas Formation and suggest subtidal to intertidal facies in a mixed environment. The fossiliferous content supports a paleoenvironment of muddy substrates, low energetic waters, and mixohaline salinity gradient. Our fauna and this scenario are similar to the Destacamento Rı´o Salado facies at Samborombo´n Bay (Las Escobas Formation). The molluscan assemblages from both transgressions are typical of estuarine rather than fully marine conditions and of higher salinity than the modern adjacent zone (Rı´o de la Plata). During both sea-level highstands, the mixohaline zone of the modern Rı´o de la Plata must have been displaced northward to at least the Pilar area (Fig. 2B), which demonstrates that rapid environmental changes (mainly salinity, substrate, and energetic conditions) occurred. The regressive trend displaced and restricted the optimum habitats for the molluscan species approximately 300 km southward, near the present Punta Rasa area. The northward latitudinal displacement in comparison with the modern malacological pattern represents a biogeographic response to the glacial cycles, thereby

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reinforcing the value of both molluscs and vertebrates as joint paleoenvironmental and paleoclimatic tools for the Late Quaternary. Our results support similar evidence for the area of Ensenada and Punta Indio-Samborombo´n Bay. The new marine sites substantially widen the geographical extension known for both transgressions during the Late Quaternary in the Bonaerensian coastal area and confirm the innermost boundary line for the sea level influence. C. taurus, Myliobatis sp., Leporinus sp., and Serrasalminae among the fish and Diplodon sp. among the molluscs represent the first records within the Argentinean Pleistocene.

Acknowledgements The authors thank Drs. M. Azpelicueta, A.L. Cione, U.F.J. Pardin˜as, S.F. Vizcaı´no, and G.J. Scillato Yane´ for their comments on the vertebrate assemblage and N. Landoni and M. Tassara for theirs on the continental molluscs. This study was partially funded by CONICET PEI 126/98 (M.L.A.) and PIP 4730/96 (M.G. Vucetich).

Appendix A. Invertebrate Systematic List Phylum MOLLUSCA Linne´, 1758 Class Gastropoda Cuvier, 1797 Order Mesogastropoda Thiele, 1925 Family Hydrobiidae Stimpson, 1865 Littoridina australis (d’ Orbigny, 1835) Family Ancylidae Dall Ancylus sp. Class Bivalvia (Buonanni, 1681) Linne´, 1758 Order Mytiloida Fe´rrussac, 1822 Family Mytilidae Rafinesque, 1815 Mytilus (Mytilus) edulis Linne´, 1758 Family Ostreidae Rafinesque, 1815 Ostrea (Ostrea) equestris Say, 1830 Order Veneroida H. Adams and A. Adams, 1856 Family Mactridae Lamarck, 1809 Mactra (Mactra) isabelleana d’Orbigny, 1846 Family Hyriidae Swainson, Diplodon sp. Family Corbiculidae Neocorbicula sp. Family Solecurtidae d’Orbigny, 1846 Tagelus (Tagelus) plebeius (Lightfoot, 1786) Order Myoida Stoliczka, 1870 Family Erodonidae Winckworth, 1932 Erodona mactroides Bosc, 1801 Microfossils Phylum PROTOZOA Order Foraminiferida

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Ammonia beccarii Linne´, 1758 Family Elphidiidae Elphidium sp Phylum CRUSTACEA Subclass Ostracoda Latreille, 1806 Superfamily Cytheraceae Baird, 1850 Cytheraceae indet. Cyprideis sp. Vertebrate List Pisces Order Lamniformes Bertin, 1939 Family Carchariidae Jordan and Gilbert, 1883 Carcharias taurus Rafinesque, 1810 Order RajiformesGoodrich, 1909 Family Myliobatidae Gu¨nther, 1870 Myliobatis sp. Order Siluriformes Fowler, 1951 Family Pimelodidae Eigenmann and Eigenmann, 1889 Pimelodidae indet. Order Characiformes Regan, 1911 Family Anostomatidae (Gu¨nther, 1864) Leporinus sp. Family Characidae (Eigenmann, 1910) Serrasalminae indet. Order Perciformes Ludwig, 1883 Family Sciaenidae Owen, 1846 Pogonias cromis (Linne´, 1766) Reptilia Order Chelonii Brongniart, 1800 Family Chelidae Gray, 1825 Chelidae indet. Mammalia Order Cingulata Illiger, 1811 Family Dasypodidae Bonaparte, 1838 Eutatus seguini Gervais, 1867 Zaedyus sp. Order Tardigrada Lathan y Davies, 1795 Family Mylodontidae Gill, 1872 cf. Glossotherium sp. Order Notoungulata Roth, 1903 Family Toxodontidae Owen, 1845 Toxodontinae indet. Order Rodentia Bowdich, 1821 Family Caviidae Gray, 1821 Cavia sp. Family Octodontidae Waterhouse, 1839 Ctenomys sp. Family Myocastoridae Miller and Gidley, 1918 Myocastor sp. Family Muridae Illiger, 1811 Lundomys sp. Calomys sp. Akodon cf. A. azarae (Fischer, 1829) Rheitrodon auritus (Fischer, 1814) Order Artiodactyla Owen, 1848

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Family Cervidae Goldfuss, 1820 Morenelaphus sp.

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