Interglacial sea levels

Quaternary International 55 (1999) 101—113

Interglacial sea levels Cari Zazo Museo Nal. de Ciencias Naturales, C.S.I.C. Jose& Gutierrez Abascal 2, 28040-Madrid, Spain

Abstract Isotopic curves have been used as approximative estimators of global sea level. Calculations of the amplitude of sea-level variations during Interglacials, especially for the last Interglacial, are based on the study of emerged coral terraces. The application of different dating methods shows great uncertainty about the length of each Interglacial and also about the number, chronology and altitude of the different highstands that occur during each Interglacial. Data of raised marine terraces from areas with different geodynamic behaviour (Bermudas, Bahamas, Peru´, Chile, Italy and Spain) are summarized in order to analyze the relationships between sea level and Interglacial stages. Two Interglacials have been identified for the early Pleistocene represented by two marine terraces with different highstands. During the early-middle Pleistocene, an Interglacial with several highstands is recorded in uplifted areas. During Isotopic Stage 11 at least one highstand with sea level equal or higher than present has been recorded. Similar sea-level behaviour can be suggested for Isotopic Stage 9. All the analyzed areas record two highstands during Isotopic Stage 7, when warm equatorial fauna migrate into the Mediterranean. During Isotopic Substage 5e at least two highstands took place with evidence of lowstands between them and at least one highstand during substage 5c with similar sea-level height above present MSL, except in Barbados and Bermuda. During Substage 5a at least one highstand has been recorded.  1999 INQUA/Elsevier Science Ltd. All rights reserved.

1. Introduction In the early twentieth century, the relations between climate and sea-level changes were established according to Penck and Bru¨ckner’s (1909) ‘‘classical model’’ which outlined the existence of four main Quaternary ice ages or glacial periods in Europe (Gu¨nz, Mindel, Riss and Wu¨rm) related to sea-level lowstands, alternating with interglacial periods coeval with highstands. Separate studies of marine terraces and deposits along the Italian and French coasts (De´pe´ret, 1918) showed the existence of different positions of sea level marked by variable elevations of these terraces and deposits. Further studies of marine terraces in Southern Italy allowed the definition of several marine stratotypes that outline the first chronostratigraphy of the Quaternary, from older to younger: Calabrian, Emilian, Sicilian, Milazzian and Tyrrhenian for the Pleistocene, and Versilian for the Holocene. The first appearance of ‘‘northern guests’’ in marinesediments in Italy refers to some cold-water marine organisms, particularly the mussel Arctica (Cyprina) islandica found in the basal Calabrian strata, on the basis of which it was proposed that the beginning of the Quat-

ernary was indicated. This was the criterion adopted in the International Geological Congress held in London in 1948. Later discussions about the validity of the current stratotypes led to disregarding the Calabrian Stage (Ruggieri and Sprovieri, 1975) and to the selection of the area of Vrica (Italy) for the Plio-Pleistocene boundary (Aguirre and Passini, 1985) where it has been dated at around 1.8 Ma. The aim of this paper is to analyze the Quaternary interglacials from the preserved records in coastal areas. It will focus on the number of highstands included in each interglacial, their duration, chronology, faunal content, and geomorphological and tectonic context. The first part of the paper resumes the evolution during the present century of ideas and theories about Quaternary sea-level changes, and it is essentially based on Pirazzoli’s (1993) excellent paper about ‘‘Global Sea-level Changes and their measurement’’. The second part is dedicated to the sea-level history deduced from the study of marine terraces, mostly based in the areas with more complete records in which we have worked, with the exception of Bahamas—Bermudas Islands and Italy.

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2. Oxygen isotope records, climate, interglacial/glacial periods and chronostratigraphy Extended oceanic studies after the 1960s allowed a major advance both in the determination of climatic changes for the end of the Cenozoic and in the general stratigraphy of the Quaternary. Emiliani (1955, 1966a, b) established the first isotopic curves based on changes in the O/O ratios recorded in foraminifera from deep sea cores in the Atlantic, Caribbean, and Pacific oceans. The oscillations of the isotopic curve led him to distinguish up to 16 Isotopic Stages, where even numbers were correlated with cold or glacial periods and those with odd numbers were linked to warm (interglacial) periods with the exception of Stage 3 (interstadial). Since the work of Shackleton and Opdyke (1973, 1976) on the deep sea cores V28-238 and V28-239, the chronostratigraphy of the Pleistocene has been closely linked to the oxygen-isotope stratigraphy (Bowen, 1978; Imbrie and Imbrie, 1980; Pisias et al., 1984; Ruddiman et al., 1986; Williams et al., 1988). This isotopic chronostratigraphy only provides approximate ages for the interglacials and glacials of the Pleistocene, although several time scales based on different mathematical treatments of deep-sea core data have been proposed (Shackleton and Opdyke, 1976; Imbrie et al., 1984; Williams et al., 1988; Ruddiman et al., 1989). In the isotopic curve of Shackleton et al., 1990 (Fig. 1) the lower Pleistocene time scale was reviewed on the basis of astronomical periodicities, shifting the last few reversals of the Earth’s magnetic field by about 5—7%.

Climatic oscillations show the predominance of the 41 ka cycle of orbital obliquity between 2.4 and 0.8—0.7 Ma, whereas during the mid-Pleistocene (0.9—0.4 Ma) a response at, or near, the 100 ka period is predominant, with however numerous superimposed glacial advances at periods of 41 and 23 ka (Ruddiman and Raymo, 1988; Shackleton et al., 1988). 2.1. Oxygen isotope records and sea level According to Shackleton and Opdyke (1973) ‘‘Ocean isotopic composition was never a linear function of ice volume and hence was never a linear function of sea levels, but it is generally agreed that by a first approximation the oxygen isotope record can give a rough approximation of global ice volume and therefore of global sea-level changes’’. These authors suggested the use of a change of about 10 m in the global sea level for a 0.1 change in the isotopic record. Later, Shackleton (1987) comparing detailed records of sea level during the last glacial cycle with highquality benthonic and planktonic isotopic records, reached some conclusions about the position of sea level during the different isotopic stages. During interglacial Isotopic Stages 7, 13, 15, 17, and 19, the sea may not have reached its present level, when Holocene isotope values were not attained, whereas during Isotopic Stages 1, 9, 11, and Substage 5e the sea levels are all so similar that it cannot be stated with any confidence that any one of these interglacials reached a significantly different level than another. Prior to Isotopic Stage 11, the warmer interglacial was Stage 25, at ca. 0.95 Ma.

Fig. 1. Oxygen isotope stratigraphy combining Holes 677 A and B: above, planktonic; below, benthonic. Selected isotope stages labelled for orientation (After Shackleton et al., 1990).

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The topographic height of sea level as related to present mean sea level (MSL) has not been calculated, except with relation to the Last Interglacial and particularly during Isotopic Substage 5e, at ca. 125 ka, for which Chappell and Shackleton (1986) assumed a level #6 m above present MSL. Later, Bard et al. (1990, 1993) suggested a#7 m figure. However, these figures, assumed as valid for many years and used in calculating rates of tectonic movements, are today open to question and are under discussion. 2.2. Chronology The models of climatic changes and position of the sea level during the isotopic stages, as deduced from deep-sea cores and ice cores, can hardly be applied to coastal outcrops. It is very difficult even to place records recovered from terrestrial or coastal-marine deposits in a common temporal framework. Most of these correlation problems arise from the age of the dated marine deposits, which usually is not beyond 300 ka, mainly as a result of the characteristics of the dating methods: The radiocarbon dating method offers good accuracy for deposits younger than 50 ka; the U-series methods using the new technique of TIMS (thermal ionization massspectrometry) reach only about 350 ka. Methods such as electron spin resonance (ESR) and amino-acid racemization (AAR) are suitable for older interglacial deposits. Coral reef areas have provided many datings by means of U-series techniques method, because corals are considered to behave as closed geochemical systems through time, in contrast to fossil molluscs. Unfortunately, corals are sparse around most of the world coastlines and attempts at dating other marine fossils, such as mollusc shells have been made. According to Hillaire-Marcel (1995): ‘‘There are geological situations allowing early diagenetic U-uptake to occur (i.e., within a few hundred years), and a fast closure of the radioactive system to follow. They include (a) early cementation of the embedding sediment (e.g. beach rocks), (b) rapid emergence under arid conditions of the fossiliferous deposits, (c) fossilization in reduced sediment (i.e., with minimum U mobility)’’. He concluded that the long term evolution of both mollusc and coral carbonates, with respect to U-Th systematics, is comparable. Asymptotic trends are often observed, resulting either in ‘‘final’’ ages for fossils beyond U-Th dating range, or increasing excesses in Th and U over their respective parent isotope.

3. Marine terraces: sea-level history The record of global sea level can be interpreted from the study of ancient shorelines that have been tectonically uplifted. However, as stated by Hearty and Kindler (1995), the reconstruction of paleo-sea levels in these

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cases requires several assumptions: constant uplift as in the case of New Guinea (Bloom et al., 1974) and Barbados (Bender et al., 1979) or temperature, ice-sea volume, and/or salinity calculations from oxygen isotopes measured on foraminifera in deep-sea cores (Shackleton and Opdyke, 1973; Chappell and Shackleton, 1986; Shackleton et al., 1988). Independently of the difficulty of dating the oldest interglacial deposits, records of Early Pleistocene highstands are extremely scarce, possibly because the shorelines of this period were almost entirely eroded during the subsequent transgressions of the Middle Pleistocene, and also because Early Pleistocene sea-level fluctuations had smaller amplitudes and frequencies than later Pleistocene fluctuations (Shackleton and Opdyke, 1976; Ruddiman et al., 1986). Whereas the knowledge of the marine terraces deposited prior to 0.4 Ma and after this age come from a most diverse set of data, we have separated the corresponding sea-level records into two large groups: Early Pleistocene and lower Middle Pleistocene, and Middle and Late Pleistocene. 3.1. Early and lower Middle Pleistocene sea-level records 3.1.1. Uplifted coasts 3.1.1.1. Mediterranean coast: Italy Five orders of marine terraces have been identified along the Tyrrhenian coast in Calabria (Carobene and Dai Pra, 1990). The chronological reconstruction of the sequence of terraces is based on the morphological and stratigraphical evidence, paleontological finding and Useries age measurements on Cladocora. It was also compared with the oxygen isotope curve (Williams et al., 1988), and sea-level highstands corresponding to interglacial peaks. The oldest terrace (1st-order terrace) is some 3 km wide and consists of several units deposited during highstands. It is correlated with the Emilian chronozone (Hyalinea balthica) in the middle-Early Pleistocene (1.3 to 0.8 Ma). The preserved remains of the oldest terrace occur at a maximum elevation of #550 m above MSL. The 2nd-order terrace includes three highstand deposits probably related to Isotopic Stages 21, 19 and 17. The 3rd-order terrace consists of two highstands (Isotopic Stages 15 and probably 13) deposited between 0.6 and 0.5 Ma. Spain The Plio-Pleistocene boundary is not accompanied by changes in climatic conditions in the southern Iberian Peninsula, if this limit is placed at ca. 1.6 Ma, as is shown by the absence of any record of the entrance of ‘‘northern guests’’ into the Mediterranean in emerged marine deposits. Detailed mapping and morphostratigraphic

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analysis of marine terraces together with chronostratigraphic data based on paleomagnetic sequences (Bardajı´ et al., 1995) and U-series measurements in the younger terraces allowed to deduce the Early-Middle Pleistocene sequence. There usually exists a large marine terrace (Goy and Zazo, 1986, 1988) considered as Lower Pleistocene in age, that consists of at least of two highstand units (Bardajı´ et al., 1995) separated by an erosional surface related to a sea-level fall. The inner edge of this terrace reaches a maximum elevation of #150 m above present MSL. This unit is followed by two terraces of assumed lower Middle Pleistocene, that include smaller-scale units related to shorter fluctuations of sea level. The Lower and Middle Pleistocene terraces are separated by alluvial fan sediments that indicate at least an episode of sea-level fall (lowstand). 3.1.1.2. Pacific coast: Peru and Chile Well-exposed, uplifted Quaternary marine terraces outcropping along the Pacific coast of Peru and Chile have been carefully studied using detailed geomorphological mapping of marine and coastal deposits, tectonic analysis and reconstruction of sedimentary environments (Ortlieb and Machare´, 1990; Goy et al., 1992; Zazo et al., 1994; Ortlieb et al., 1995a, b, 1996). The chronostratigraphy has been established by means of dating methods including U-series and amino acid racemization on mollusc shells (Ortlieb et al., 1990, 1992). Palaeontological studies made it possible to distinguish Pliocene and earliest Pleistocene marine deposits. At a regional scale (14° to 24°S) uplift rates did not exceed 150 mm/10 yr during the whole Quaternary period. However, the intensity of deformation tended to increase since the Middle Pleistocene in some sectors (Ortlieb et al., 1995b). In the most complete case study, Chala Bay (South of Peru), Goy et al. (1992) distinguished 27 individual terraces, corresponding to 27 successive highstands, at elevations ranging from present sea level to 274 m above MSL. These marine terraces are arranged in a staircase and separated from each other by escarpments. The terraces can be grouped into ten cycles which have been differentiated by the existence of well developed terrestrial, usually alluvial fan, deposits or by particularly high (10—20 m) escarpments between them. As a working hypothesis it is assumed that the individual terraces inside a single cycle were generated during individual highstands, and that cycles were deposited during interglacial periods. Some interglacial periods may generate more than one cycle. Goy et al. (1992) differentiated an Early Pleistocene cycle consisting of five terraces separated by small escarpments, and a lower Middle Pleistocene cycle with three individual terraces. However the boundary between Early-Middle Pleistocene remains somewhat unclear.

3.1.2. Less unstable coasts 3.1.2.1. Atlantic coast Hearty and Kindler (1995) assembled a history of sealevel highstands representing the past 1.2 Ma, from geological and geochronological data from Bermuda and the Bahamas. The chronology is derived from isotopic, Useries, palaeomagnetic and amino acid racemization data. An empirically-derived curve of Quaternary highstands correlated with the isotopic stages proposed by Shackleton et al. (1988) shows: Two positive sea levels in Bermuda during Early Pleistocene (ca. #5 and #22 m) at around 1 and 0.9 Ma, respectively. There is an evident hiatus in the Early-Middle Pleistocene that lasted several hundred thousand years (between 850 and 450 ka). During this period sea level did not reach its present MSL. Some conclusions about the evolution of sea level can be drafted from these regions, which are independent of their individual tectonic behaviour: There is a record of at least two interglacials with sea level higher or similar to the present MSL during the Early Pleistocene, and one more during the uppermost Early Pleistocene-lowermost Middle Pleistocene, prior to ca. 400 ka. However, it must be stressed that there is an hiatus affecting the Early-Middle Pleistocene, which lasted from 850 to 450 ka, and that has been observed in the less unstable region of Bermudas (Hearty et al., 1995) and also in South Carolina (Hollin and Hearty, 1990). Thus, interglacial periods include a variable, and still unknown, number of highstands, and there is no general agreement on the correspondence between a given interglacial period and the correlative isotopic stage, in spite of the proposals by Carobene and Dai Pra (1990), and Hearty and Kindler (1995). 3.2. Middle and Late Pleistocene sea-level record 3.2.1. Isotopic Stages 11, 9, and 7 During the interglacial maxima of the Middle Pleistocene, sea level was also probably close to present MSL. The deep-sea cores isotopic data suggest that the Isotopic Stage 7 lasted some 70 ka (Imbrie et al., 1984; Martinson et al., 1987; Williams et al., 1988) and that it included at least two major and one minor highstand. During Stage 7 highstands, sea level was probably below present datum (Shackleton, 1987). For Isotopic Stages 9 and 11, some core data show single major peaks that are high enough to suggest that the sea level attained a position similar to present MSL. However, many authors observe that most deep sea data covering the Late Quaternary indicate that Oxygen Isotope Stage 11 (423—362 ka) was warmer than the succeeding interglacials (Burckle, 1993). Some authors (Howard and Prell, 1992) even suggest that this Interglacial was the most prolonged and possibly warmest

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interglacial (in terms of sea surface temperature, and carbonate productivity) of the last 500 ka. 3.2.2. Uplifted coasts 3.2.2.1. Mediterranean Sea: Italy In the already mentioned sequence outcropping in southern Calabria, Carobene and Dai Pra (1990) described the so-called third order terrace, that is located between#12 and#20 m above present MSL, and characterized by Cladocora-bearing biocalcarenite deposits. Dating with the U-series method on Cladocora shells, yielded ages ranging from 250 to '360 ka, and the episode during which the marine terrace was deposited was thus referred to Isotope Stage 9, though the influence of highstand of sea levels in Stages 7 and 11 cannot be ruled out. Spain In the more complete sequences of marine terraces that outcrop in Almeria and Alicante-Murcia areas, Goy and Zazo (1986, 1988) related two marine terraces (placed at #40 and #30 m above present MSL), that occur separated by alluvial-fan deposits, to the middle part of the Middle Pleistocene. The sediments forming these two terraces were deposited before the entry of warm fauna into the Mediterranean Sea. A particular component of this warm fauna is the gastropod Strombus bubonius that arrived in the Mediterranean from the Atlantic Equatorial Africa at ca. 180 ka, during Isotopic Stage 7 (Hillaire-Marcel et al., 1986; Goy et al., 1986; Zazo and Goy, 1989; Zazo et al., 1993a). As the older terrace bearing the warm fauna (Isotopic Stage 7) immediately follows the two previously cited marine terraces, we assume that these can be correlated to Isotopic Stages 9 and 11. 3.2.2.2. Pacific coast: Peru A complete sequence of marine terraces crops out in Chala Bay (Ortlieb and Machare´, 1990; Ortlieb et al., 1990) but, unfortunately, the few U-series analyses on mollusc shells did not produce reliable ages. Thus, to reiterate the chronology is based on a detailed analysis of the distribution of the landforms and the associated major marine and terrestrial deposits. The last four interglacials (Isotopic Stages 5, 7, 9, and 11) are represented by the groups of marine terraces located between #20 and #200 m above present MSL (Goy et al., 1992). Two terraces have been associated to Isotopic Stage 11, and four individual terraces separated from both the previous and following ones by two large escarpments and alluvial-fan deposits are assimilated to Isotopic Stage 9. Isotopic Stage 7 is represented by four small terraces with alluvial-fan deposits separating them into two independent couples.

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South of Chala, in Pampa del Palo (Ilo), marine episodes younger than Isotopic Stage 7 occur vertically stacked because the Pampa is located in a faulted block that moved independently of the remaining southern Peruvian coast (Zazo et al., 1994). Abundant geochronological data, particularly amino acid razemization analyses, are available (Hsu, 1988; Hsu et al., 1989; Ortlieb et al., 1990). Combined U-series analyses (Th/U and U/U), allo/isoleucine data and measurements of the O composition on a series of marine mollusc shells (Ortlieb et al., 1992), together with morphostratigraphical and sedimentological analyses, allow the conclusion that the terrace of Pampa del Palo (#25 m) consists of a relatively-thick, vertical stack of shallow marine, coastal, and lagoonal deposits that are correlated with the successive marine highstands of Isotopic Stages 7 and 5. Isotopic Stage 7 includes two marine units (Ortlieb et al., 1996) that may correspond to Substages 7a and c. Chile The Hornitos area (North of Antofagasta) is becoming a classical site for the study of the marine Quaternary in Northern Chile. Radtke (1989) obtained some geochronological results using ESR and U-series dating and suggested that the youngest Pleistocene terrace was of Last Interglacial age, while the two older terraces could be assigned to the Middle and/or Early Pleistocene. Detailed morphostratigraphical and sedimentological studies of the area between Punta Yayes and Punta Chacaya, combined with photogeologic mapping as well as with 15 U-series measurements and some 115 amino acid racemization analyses, resulted in a more refined interpretation of the chronology of marine deposits associated with the last episodes of high sea-level stand. In most cases, the analytical results are internally consistent and coherent with the morphostratigraphical interpretation (Ortlieb et al., 1995a, b). In the most complete case, four raised morphological marine terraces can be distinguished. The lowest Pleistocene terrace is assimilated to Isotopic Stage 5. The elevation of the inner edge of this terrace ranges between #18 and #36 m. The second marine terrace occurs at about #65 m. Although it is poorly developed, its sediments comprise two episodes of highstand. Some allo/isoleucine results and a single U-series apparent age support the morphostratigraphic interpretation of an Isotopic Stage 7 (7a and c) age. The third, higher (#80 m) terrace is very wide and it consists of several marine units in an offlap pattern. A close cluster of allo/isoleucine favors an attribution to Isotopic Stage 9. The fourth, highest (#100 m) terrace is observed in some places only because it is covered by younger

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alluvial-fan deposits. It has been tentatively assigned to Isotopic Stage 11. In Pampa de Mejillones (North of Antofagasta, Chile) the whole plain is covered from #6 to #200 m above present MSL with beach ridges subparallel to the present coastline. Mapping and sedimentological analysis of the beach ridges allow to group them into several sets differentiated by means of the morphology of the surfaces limiting units, particularly erosional surfaces, the changes in geometry and orientation of sets of beach ridges, and their faunal content (Ortlieb et al., 1995a). The chronostratigraphy of the sets of beach ridges has not yet been established in spite of Radtke’s (1987a, b, 1989) geochronological data for the last four beach ridges that lie between #7 and #36 m above present MSL. Recently, numerous U-series and amino stratigraphic analyses were performed (Hillaire-Marcel et al., 1995). All papers conclude that the analyzed shells experienced late diagenetic U-uptake that resulted in ‘‘young’’ apparent U ages. The faunal content of the ridges and associated marine deposits varies across the ridges. Some of the most elevated deposits (#150 m above sea level) contain a molluscan fauna which includes warm loving [or water] taxa (Guzman et al., 1995), particularly ¹rachycardium pro-

cerum. Ortlieb (1995a) suggested that the age of the set of beach ridges containing the warm-loving fauna could be assigned to Isotopic Stage 11. 3.2.3. Less unstable coasts 3.2.3.1. Atlantic The sea-level highstand curve proposed by Hearty and Kindler (1995) for the Bermuda and Bahamas Islands suggests that at least three highstands occurred during the Middle Pleistocene reaching heights of #4 and #2.5 m above present MSL, that can be correlated with Isotopic Stages 11, 9 and 7a. During the Isotopic Substage 7c the sea level did not surpass the present datum. From the analyzed coasts it can be deduced (Table 1) that independently of the tectonic context, the sea level reached an elevation higher than the present during Isotopic Stage 11. In coasts with high uplift rates, this episode includes two highstands. Isotopic Stage 9 is well represented in all the described areas, and it consists of several highstands. In coasts with a continuous uplift trend, there is usually a conspicuous escarpment (i.e., a paleo-cliff ) separating the terraces deposited during Isotopic Stages 9 and 7.

Table 1 A synthesis of highstands deposited during Isotopic Stages 11 to 7, or Interglacials, in coasts with variable tectonic trends. Based on data by authors cited in the text, with the addition of some interesting geomorphologic and faunal data

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The Isotopic Stage 7 exhibits two highstands, the most important of which is the one corresponding to Isotopic Substage 7a. It is interesting to remark that in the Atlantic-Mediterranean linkage zone there is a record of the entrance in the Mediterranean realm of warm faunas (‘‘Senegalese fauna’’) coming from Equatorial Africa during Isotopic Stage 7. This phenomenon has been recorded not only in the south and southeastern coasts of Iberia but also in the Canary Islands (Zazo et al., 1993b) and it must be related to special paleo-oceanographic conditions. 3.2.4. Isotopic Stage 5. The Last Interglacial In marine stratigraphy, the Last Interglacial comprises the entire Isotopic Stage 5 (from 135 to 74 ka, Fig. 2), while in the continental stratigraphical division the stadials and interstadials forming Substage 5e (Eemian or Sangamonian) are included in the Weichselian Glaciation. During the Eemian optimum (125—120 ka) the climate was generally a few degrees warmer than during postglacial times (Mangerud, 1991a, b; Frenzel et al., 1992). Radiometric dating of Late Pleistocene coral reefs allowed calibration of the youngest part of the deep-sea core isotopic chronology (Shackleton and Opdyke, 1973,

Fig. 2. Oxygen isotope curve according to Martinson et al. (1987) for the last 130 ka.

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1976) and provided estimates of paleo-sea-level altitudes for each high sea-level stand of the last interglacial: Isotopic Substage 5e (125 ka), 5c (105 ka) and 5a (80 ka) (e.g. Chappell, 1974; Bloom et al., 1974). Most researchers agree that sea level reached a maximum elevation of about #6 m above present MSL at the beginning of the last interglacial (Substage 5e), and that during the ensuing Substages 5c and a sea level probably was close to present MSL, or at most a few metres below MSL (Chappell and Shackleton, 1986). 3.2.5. Climate instability during the Eemian (5e) There is some disagreement in the correlation between marine sedimentary records from the North Atlantic cores and the Greenland ice cores record. During the Eemian, marine records show a more stable climate than that implied by the GRIP Project. From the Greenland Ice Core Project (GRIP) the record implies that the peak Eemian period (130—110 ka) lasted nearly 20 ka and apparently it was interrupted several times by periods colder than present (Zhan, 1994). Shelf records from Northwest Europe indicate two cold events during substage 5e (Eemian) in two marine benthic foraminifera and suggest that these cooling events are a result of fluctuations in the strength of the North Atlantic surface-water circulation (Seidenkrantz et al., 1995). These two cooling events have been also detected by magnetic susceptibility, pollen and organic records from lake deposits in France’s Central Massif, supporting the idea that rapid climate changes extended to continental Europe (Thouveny et al., 1994). 3.2.6. The highstands during the Last Interglacial The time scale and regional specificities of sea-level changes during the Last Interglacial have been studied using U-series dating of coral reefs by TIMS method. Data from the Bahamas (Chen et al., 1991), Western Australia (Zhu et al., 1993), Hawaii (Szabo et al., 1994), Barbados and the New Hebrides (Edwards et al., 1987; Bard et al., 1990) show that high steady sea levels are observed between &134—131 and &116—114 ka at these localities (Zhu et al., 1993; Szabo et al., 1994). Hillaire-Marcel et al. (1996) used the same technique on mollusc shells of the Mediterranean Sea in the type section for the Tyrrhenian of the Balearic Islands (Campo de Tiro, Mallorca, Spain). They concluded that two highstands of sea level characterized the Last Interglacial (Isotopic Substage 5e) at about 135 and 117 ka. The age of 135 ka is consistent with the hypothesis of a sea rise at the transition of Isotopic Stages 6 and 5, much older than the isolation maximum in the northern hemisphere at about 128 ka (Stein et al., 1993). However, it disagrees (Bard et al., 1993) with the Milankovitch hypothesis since the tuned benthic dO record predicts a glacial maximum at about 135 ka.

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3.2.7. The highstand records in marine terraces 3.2.7.1. Mediterranean: Spain Zazo and Goy (1989) and Zazo et al. (1993a) synthesized the sea-level changes in the Iberian Peninsula during the last 200 ka, based on detailed geomorphological mapping, and sedimentological and neotectonic studies coupled with Th/U measurements (Hillaire-Marcel et al., 1986; Causse et al., 1993). In the Almeria and Alicante littorals there are three marine terraces containing warm fauna, particularly S. bubonius, the inner edges of which are located at maximum topographic elevations of about #15, #10 and #0.5 m. The average age of the two older, higher terraces is 128 ka (5e) and 95 ka (5c). No reliable results have been obtained for the lowermost, youngest terrace that only crops out in the coastal areas subjected to the highest uplift rates (Zazo et al., 1993a; Goy et al., 1993a) although it is certainly of pre-Holocene age and has been assimilated into Isotopic Substage 5a. The abundance and diversity of the Senegalese fauna is similar in the three episodes, but there is a larger content of ooliths in deposits of Isotopic Substage 5e. Nevertheless, the most laterally continuous and widespread marine episode is the one corresponding to Isotopic Substage 5c, with three independent marine oscillations, representing three different highstands, in the littoral of Almeria (Zazo et al., 1993). Many studies have been carried out in Campo de Tiro (Mallorca, Balearic Islands), (Butzer and Cuerda, 1962; Stearns and Thurber, 1965, 1967; Butzer, 1975). In this area, Hearty et al. (1986) and Hearty (1987) documented the chronology of the marine deposits from this section based on allo/isoleucine and Th/U measurements (by the alpha technique) concluded from the presence at Campo de Tiro of a ‘‘complex’’, that minor oscillations of sea level during Isotopic Stage 5 were represented. This littoral has been recently studied using a variety of techniques such as mapping and sedimentological analyses (Goy et al., 1993b) and U-series analyses by TIMS technique (Hillaire-Marcel et al., 1996). Three offlapping, independent, morphosedimentary marine units occur between#3 and the present MSL in Campo de Tiro section, because of the subsiding trend of the area. The oldest unit yields abundant warm Senegalese fauna including S. bubonius. A thin, laterally discontinuous reddish alluvial deposit interbedded in the marine deposits allows two subunits to be differentiated. The second, intermediate, marine unit lies on an erosional surface deeply cut into the former. It is a beach conglomerate with large boulders derived from the underlying older unit. The content in S. bubonius decreases considerably although it still bears abundant Senegalese fauna.

The youngest unit is an independent, partially cemented, beach deposit, but its faunal content is different from the others. Goy et al. (1993b) assimilated these three units to Isotopic Substages 5e (with two oscillations), 5c and a, but more recent dating (Hillaire-Marcel et al., 1996) yielded an age of 135 ka for the lowermost marine unit (below the reddish alluvial deposits), and 117 ka for the upper ‘‘subunit’’ 1 and the blocky unit. These results suggest two sea-level highstands during Isotopic Substage 5e. The youngest unit should be assimilated to Isotopic Substage 5c. 3.2.7.2. Pacific Coast: Peru In Chala Bay, the Last Interglacial is represented by four marine terraces (#31, #45, #54, #68 m above present MSL) with continuous outcropping along the whole Bay (Goy et al., 1992). The stratigraphy of this group of terraces shows that the alluvial episodes, coeval with low sea stands, alternate with episodes of marine terrace formation (highstands). The thickness and sedimentology of the continental deposits suggest that the alluvial phases were brief and did not correspond to entire glacial periods. On the contrary, two major seacliffs of comparable shape and height (ca. 20 m) form the physical boundaries of this set of four terraces. The two paleo-cliffs have been interpreted as carved during the sea-level maxima of Isotopic Substage 5e and Holocene respectively. Although U-series analyses of mollusc shells did not yield reliable ages (Ortlieb et al., 1990), the morphostratigraphical and sedimentological analyses suggest (Goy et al., 1992) that the two older terraces correspond to Isotopic Substage 5e whereas the more recent terraces should correspond to Isotopic Substages 5c and a. Hsu (1988) and Hsu et al. (1990) used the abundant available geochronological data in the marine terrace forming the Pampa del Palo (#25 m above MSL) in Ilo area to confirm its Late Pleistocene age, and interpreted two discrete units below the superficial sediment of the Pampa del Palo which could be assigned to Isotopic Stages 7 and 9. Goy et al. (1990), Ortlieb et al. (1992), and Zazo et al. (1994) confirmed the vertical stacking in Pampa del Palo of marine and lagoonal units deposited during successive episodes of highstand. Sedimentological and morphotectonic analyses lead to consider (Ortlieb et al., 1996) that the Last Interglacial deposits record at least two highstands separated by lagoonal deposits, both corresponding to Isotopic Stage 5e, partly eroded and covered by a younger marine unit (5c) that is the one capping the Pampa del Palo (#25 m). This apparently anomalous arrangement of units with Isotopic Substage 5c deposits lying on top of those of 5e age is caused by the differential movements of the Pampa del Palo tectonic block with respect to the surrounding

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areas during the Late Pleistocene (Zazo et al., 1994). Because of this, the two highstands of Isotopic Substage 5e are represented by two raised marine terraces whereas, just north of Ilo, there are two other terraces below these that are comparable to Isotopic Substages 5c and a. Chile Ortlieb et al. (1995) recognized at least two highstands of sea level for Isotopic Stage 5 in the Hornitos-Michilla area. In Hornitos they appear at the surface as one morphological terrace as a result of a later alluvial cover, this being the inner edge of the older marine unit located at #36m above present MSL. By contrast, in Michilla the two highstands occur as staircased marine terraces with an elevation of #40 m for the inner edge of the older one. According to Hillaire-Marcel et al. (1995) the morphostratigraphical and geochronological information leaves no doubt in assigning these marine units to the Last Interglacial, although unequivocal assignment to Isotopic Substages 5e or c is not possible. Assuming this designation to Isotopic Stage 5 as correct, and bearing in mind the uplifting tectonic trend of the area, the close topographic position of these two highstands seems to indicate that paleo-sea levels during these substages should have been very similar.

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3.2.8. Less unstable areas Hearty and Kindler (1995) drafted a detailed sea-level curve for the Last Interglacial of the Bermuda and Bahamas Islands. Two major and several minor sea-level oscillations characterized this period. The first oscillation (perhaps 135 to 128 ka) reached #4 m above present MSL. In the Bahamas, the interior of the ridge is of oolitic composition. The end of this oscillation is marked by a rubified protosol corresponding to a sea-level fall (?128—123 ka). During a second oscillation (at about 122—120 ka) the sea level rose to #2—4 m for some time, after which it rose abruptly to #8 m. By the end of the interglacial the sea level fell to !15 m. The cited authors place the sea level at !12 m during Isotopic Substage 5c (105 ka), but sea level rose progressively with minor oscillations almost to its present location during Isotopic Substage 5a (ca. 80 ka). Table 2 presents a synthesis of highstands assigned to the Last Interglacial. From these data it is deduced that during the peak of the Last Interglacial (5e) there were at least two highstands. The older one probably during the 6-5 transition (135 ka). From uplifting trending areas, except for the Bahamas and Bermudas, it is deduced that the topographic elevation reached by sea level in Isotopic Substages 5e and c was very close; however, deposits from 5a seem to record a lower sea level.

Table 2 A synthesis of marine terraces (highstand deposits) deposited during Isotopic Stage 5 in coasts with variable tectonic trends. Based on the data by authors cited in the text, with the addition of some interesting geomorphologic and faunal data

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The Senegalese warm-fauna assemblages, survived in some privileged areas of the Mediterranean (Almeria, Alicante), including even S. bubonius, during the whole Isotopic Stage 5. West of Gibraltar, in the Atlantic littoral, the only Last-Interglacial marine terrace bearing the Senegalese warm-fauna assemblages is the one deposited during Isotopic Substage 5c (Zazo and Goy, 1989).

4. Discussion and conclusions The reconstruction of global sea-level changes during the Quaternary involves great difficulty: the position of sea level at a certain moment is influenced not only by global factors, but mainly by regional ones which operate on different time, space and amplitude scales. There is also an added problem to locate the different sea-level oscillations within a precise temporal scale. In spite of the improvement experienced in the dating methods during recent years, there are still many difficulties to obtain accurate ages, derived not only from the problems inherent to the method but also from the nature of the dated materials. Since the 1970s, the variations of the oxygen isotope ratios in oceanic cores have been widely used as approximate estimations of global sea-level. One of the most generalized assumptions has been to consider the global eustatic sea level during the Isotopic Substage 5e (Eemian or Sangamonian) at #6 m above present MSL at ca. 125 ka (Chapell and Shackleton, 1986) or at #7m (Bard et al., 1990, Bard et al., 1993). Recent data from ice cores (GRIP, 1993) led to new interpretations about the consideration of a stable climate just a few degrees warmer than today, during the Eemian peak as had been widely assumed from the deep sea data. A great climatic instability during this peak (110—130 ka) is recorded both in ice cores and in emerged coastal records. In view of the existing problems, the geological analysis of the raised marine terraces can help in reconstructing Quaternary sea-level history. Nevertheless, the degree of uncertainty increases for the older Interglacials, specially regarding the chronology, number of highstands that compose a single Interglacial, amplitude of sea-level oscillations and, of course, the altitude of the different highstands in relation to the present MSL. The selected areas (the Bermudas and Bahamas Islands, Italy, Spain, Peru and Chile) are located in different geodynamic settings and they present a wide record of elevated marine terraces during the entire Quaternary. Most of these areas have been directly studied by us, and the rest of them present very complete synthetic references. During the Early Pleistocene, at least two interglacials are recorded with a sea level equal or higher

than present MSL, each one of them represented by a marine terrace and composed by several highstands. The number of terraces that represent the morphological expression of each one of these interglacials, depends mainly on the uplifting trend of the considered coast. During Early Pleistocene—Middle Pleistocene, another Interglacial with a sea level probably lower than present MSL took place. This Interglacial is represented in uplifted trending areas by a wide marine terrace where several highstands are recorded. Important development of alluvial fans between the most recent terraces of the Early Pleistocene and those from the Early-Middle Pleistocene, seems to indicate a long-lasting lowstand between these two Interglacials. The correlation between these Interglacials and the corresponding isotopic stages is still uncertain. Isotopic Stage 11 records at least one highstand with a sea level equal or higher than present MSL. Two marine terraces, representing two different highstands, have been recognized in areas with high uplifting rates (Peru), while on the northern coast of Chile, the warm fauna bearing deposits (¹rachycardium proceratum) have been associated with this Isotopic Stage. Isotopic Stage 9 is well represented in all the studied areas. Its topographic elevation above present MSL and the development of a morphological terrace with several highstands, suggest a behaviour of sea level quite similar to that during the previous Isotopic Stage or Interglacial. In uplifted trending coasts, either a great escarpment or paleocliff, or the development of alluvial fans, usually separates the marine terraces of Isotopic Stage 9 from those of Isotopic Stage 7. During Isotopic Stage 7, two highstands represented by two marine terraces are recorded in all the analyzed areas, although in stable areas the sea level during Isotopic Substage 7a was higher than present MSL. It is worthy of note that the migration of a warm fauna (Senegalese fauna) from Equatorial Africa towards the Mediterranean Sea took place during this Isotopic Stage. The record of this warm fauna (especially the Strombus bubonius) starts during Substage 7c in the Canary Islands whilst in the Mediterranean (South of Iberia, Almeria, Spain) the first appearance of S. bubonius is associated to Substage 7a. ¹he ¸ast Interglacial or Isotopic Stage 5 is usually represented by several highstands. Substage 5e records three highstands in the South of Iberia (ages around 128 ka); two highstands in the Balearic Islands (Spain) at 135 and 117 ka and three highstands in the Bermudas and the Bahamas (between 135 and 128 ka). On the coasts of Peru and Chile, two highstands are associated with this substage. There is always evidence of lowstands between the different highstands, which are recorded by interbedded terrestrial deposits, soils, wide erosional surfaces or escarpments.

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During the Isotopic Substage 5c at least one highstand is observed. The sea level could not be below the present sea level, as has always been assumed. According to the present topographic elevation of the deposits corresponding to Substages 5e and c, with the exception of Barbados and the Bermudas, together with the faunal content (South of Iberia, Mediterranean area) the sea level during these two substages was similar, and in both cases higher than present sea level. The deposits corresponding to the Substage 5a, usually show a single highstand of smaller amplitude than the previous substages, with the exception of Bermudas and Bahamas, outcropping only in the areas with high uplifting trend. Nevertheless, the Senegalese fauna with S. bubonius remains occur in several areas of the Mediterranean (Almerı´ a, Alicante, Spain) during this substage.

Acknowledgements This work has been supported by the Spanish DGICYT Projects PB95-0109, PB95-0946 and this is a part of the INQUA Shorelines Commission and the IGCP Project 367.

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