Marine Oxygen Isotope Stage 5e Research Articles

Coastal progradation associated with sea-level oscillations in the later phase of the Last Interglacial period, central Japan

Stratigraphic records of minor sea-level highstands in Marine Oxygen Isotope Stage (MIS) 5c and 5a are valuable archives of late Pleistocene sea levels and paleoenvironments, but have been identified less commonly in siliciclastic coastal systems than the highstand of MIS 5e. In the Kanto Plain, central Japan, the Iioka terrace comprises the seaward margin of the uplifted Last Interglacial (MIS 5) marine terrace. Sedimentological characterization, post-infrared infrared stimulated luminescence (pIRIR) dating, and tephra and paleontological analyses of the Iioka terrace allow identification of a wave-dominated coastal sedimentary system that prograded onto the Pliocene-Pleistocene basement during MIS 5c and 5a. The pIRIR ages of the coastal deposits range from ca. 80 to 112 ka and define a seaward younging trend, which is corroborated by the seaward lowering of the terrace surfaces. In an outcrop in the seaward part, two pIRIR ages were obtained above and below the tephra layer On-Pm1 (95.7 ka), supporting the general validity of the pIRIR chronology. The elevation of beach facies in the landward part (ca. 53 m above the present sea level) abruptly lowers (to ca. 37 m) and is further truncated by fluvial incision in the seaward part. The pIRIR ages include uncertainties that prevent distinction between MIS 5c and 5a. However, the abrupt and large gap in the beach levels between the central and seaward parts suggests the presence of a minor unconformity between MIS 5c and 5a; contemporary uplift may account for the gap. The Iioka terrace is thus interpreted as representing the successive downdip accretion of depositional sequences controlled by relative sea-level changes in the later Last Interglacial period. The refined characterization of the Iioka terrace allows reevaluation of the tectonic uplift rate of this area as ca. 0.7 mm/yr, twice the rate assuming correlation of the deposits with MIS 5e. Such refinement is likely elsewhere if marginal marine terraces are characterized in detail, as carried out here.

The Oyambre coastal terrace: a detailed sedimentary record of the Last Interglacial Stage in northern Iberia (Cantabrian coast, Spain).

ABSTRACTA detailed study is presented of a 15.3‐m‐thick Pleistocene coastal terrace located on the Cantabrian coast (northern Spain). Stratigraphic, sedimentological, topographic and micropalaeontological information is combined with a chronology based on luminescence dating to characterize the deposits. The sedimentary succession records: (i) a basal transgressive system, consisting of a wave‐cut surface covered by a lower layer of beach gravels and upper beach pebbly sands; and (ii) a thicker upper highstand system (aggrading), comprising medium to very fine aeolian sands interbedded with thin palustrine muds. Luminescence dating involved a detailed sampling strategy (36 samples and two modern analogues) and the use of both quartz optically stimulated luminescence (OSL) and feldspar post‐infrared infrared stimulated luminescence single aliquot regeneration protocols; feldspar results were used to confirm the completeness of bleaching of the quartz OSL signal. The quartz OSL luminescence age–depth relationship shows significant dispersion, but nevertheless two rapid phases of deposition can be clearly identified: one at ~130 ka [Marine Oxygen Isotope Stage (MIS) 5] and one at ~100 ka (MIS 5c). The top of the succession is dated to ~70 ka. The MIS 5e marine maximum flooding surface is identified at an elevation of 6.85 m above mean seal level. This elevation provides evidence of a regional sea‐level highstand for this sector of the Cantabrian coast.

Using Soil Stratigraphy and Tephrochronology to Understand the Origin, Age, and Classification of a Unique Late Quaternary Tephra-Derived Ultisol in Aotearoa New Zealand

In this article, I show how an Ultisol, representative of a globally-important group of soils with clay-rich subsoils, low base saturation, and low fertility, in the central Waikato region in northern North Island, can be evaluated using soil stratigraphy and tephrochronology to answer challenging questions about its genesis, age and classification. The Kainui soil, a Typic Kandiudult (Soil Taxonomy) and Buried-granular Yellow Ultic Soil (New Zealand Soil Classification), occurs on low rolling hills of Mid-Quaternary age mainly in the Hamilton lowlands in, and north and northeast of, Hamilton city. It is a composite, multi-layered tephra-derived soil consisting of two distinct parts, upper and lower. The upper part is a coverbed typically c. 0.4–0.7 m in thickness (c. 0.6 m on average) comprising numerous late Quaternary rhyolitic and andesitic tephras that have been accumulating incrementally since c. 50 ka (the age of Rotoehu Ash at the coverbed’s base) whilst simultaneously being pedogenically altered (i.e., forming soil horizons) via developmental upbuilding pedogenesis during Marine Oxygen Isotope Stages (MOIS) 3-1. Any original depositional (fall) bedding has been almost entirely masked by pedogenic alteration. Sediments in lakes aged c. 20 ka adjacent to the low hills have preserved around 40 separate, thin, macroscopic tephra-fall beds mainly rhyolitic in composition, and equivalent subaerial deposits together form the upper c. 30 cm of the coverbed. Okareka (c. 21.8 ka), Okaia (c. 28.6 ka), Tāhuna (c. 39.3 ka) and (especially) Rotoehu tephras make up the bulk of the lower c. 30 cm of the coverbed. Tephra admixing has occurred throughout the coverbed because of soil upbuilding processes. Moderately well drained, this upper profile is dominated by halloysite (not allophane) in the clay fraction because of limited desilication. In contrast, Otorohanga soils, on rolling hills to the south of Hamilton, are formed in equivalent but thicker (>c. 0.8 m) late Quaternary tephras ≤c. 50 ka that are somewhat more andesitic although predominantly rhyolitic overall. These deeper soils are well drained with strong desilication and thus are allophanic, generating Typic Hapludands. Ubiquitous redox features, together with short-lived contemporary reduction observed in the lower coverbed of a Kainui soil profile, indicate that the Kainui soil in general is likely to be saturated by perching for several days, or near saturation for several months, each year. The perching occurs because the coverbed overlies a slowly-permeable, buried, clay-rich paleosol on upper Hamilton Ash beds, >c. 50 ka in age, which makes up the lower part of the two-storeyed Kainui soil. The coverbed-paleosol boundary is a lithologic discontinuity (unconformity). Irregular in shape, it represents a tree-overturn paleosurface that may be c. 74 ka in age (MOIS 5/4 boundary). The buried paleosol is markedly altered and halloysitic with relict clay skins (forming paleo-argillic and/or paleo-kandic horizons) and redoximorphic features. It is inferred to have formed via developmental upbuilding pedogenesis during the Last Interglacial (MOIS 5e). The entire Hamilton Ash sequence, c. 3 m in thickness and overlain unconformably by Rotoehu Ash and underlain by c. 330-ka Rangitawa Tephra at the base, represents a thick composite (accretionary) set of clayey, welded paleosols developed by upbuilding pedogenesis from MOIS 10 to 5.

No evidence from the eastern Mediterranean for a MIS 5e double peak sea-level highstand

AbstractTo understand past and future sea-level variability, it is important to know if during an interglacial the eustatic sea level is constant or oscillates by several meters around an average value. Several field sites within and outside the tropics have been interpreted to suggest such oscillations during Marine Oxygen Isotope Stage (MIS) 5e (129–116 ka). Here, we present our analysis of one such non-tropical site, Hergla, where a facies succession indicates two foreshore deposits above each other, previously interpreted as MIS 5e sea-level highstand amplified by a second rise. Our study, based on field, microfacies, and optical age Bayesian statistics shows a sea-level rise forming the upper foreshore strata that coincided with the global sea-level rise of the MIS 5a interstadial. The site does therefore not provide evidence for the MIS 5e double peak. We conclude from our analysis that the facies-based proxy is insensitive to small-scale sea-level oscillation. Likewise, uncertainties associated with age estimates are too large to robustly infer a short-term sea-level change.

AMS-dated mollusks in beach ridges and berms document Holocene sea-level and coastal changes in northeastern Kuwait Bay

In northeastern Kuwait, ancient beach ridges and associated berms are separated from the present shoreline by a 4–6km-wide sabkha. A diverse mollusk fauna in the beach ridges attests to a former open marine environment. A total of 21 AMS dates were obtained in this study. Thirteen mollusk samples from beach ridges yielded AMS dates ranging from ~6990calyr BP in the southeast to ~3370calyr BP in the northwest, suggesting a southeast to northwest age progression during the Holocene transgression. In contrast, four samples from berms throughout the study area yielded AMS dates of 5195–3350calyr BP showing no age progression; these berms consist largely of Conomurex persicus gastropods that aggregated by storms during a highstand at ~5000–3500calyr BP. The berms are presently at ~+6m above sea level, 2–3m above the beach ridges. Human settlements were common on the ridge crests before and after the highstand. Regression to present-day sea level commenced after the highstand, which is when the sabkha began forming. A landward, marine-built terrace, which yielded AMS dates >43,500 14C yr BP, probably formed during Marine Oxygen Isotope Stage 5e and hence is not genetically related to the beach ridges.

Late Quaternary chronostratigraphic framework of terraces and alluvium along the lower Ohio River, southwestern Indiana and western Kentucky, USA

The lower Ohio River valley is a terraced fluvial landscape that has been profoundly influenced by Quaternary climate change and glaciation. A modern Quaternary chronostratigraphic framework was developed for the lower Ohio River valley using optically stimulated luminescence (OSL) dating and allostratigraphic mapping to gain insights into the nature of fluvial responses to glacial–interglacial/stadial–interstadial transitions and Holocene climate change. River deposits, T0 (youngest) to T7 (oldest), were mapped along a 75 km reach of the lower Ohio River and were dated using 46 OSL and 5 radiocarbon samples. The examination of cores combined with OSL and radiocarbon dating shows that fluvial sediments older than marine oxygen isotope stage (MIS) 2 are present only in the subsurface. Aggradation during MIS 6 (Illinoian glaciation) filled the valley to within ∼7 m of the modern floodplain, and by ∼114 ka (MIS 5e/Sangamon interglacial) the Ohio River had scoured the MIS 6 sediments to ∼22 m below the modern floodplain surface. There were no fluvial sediments in the valley with ages between MIS 5e and the middle of MIS 3. The MIS 3 ages (∼39 ka) and stratigraphic position of T5 deposits suggest the Ohio River aggraded 8–14 m during MIS 4 or MIS 3. Near the end of MIS 3, the Ohio River incised the mid Last Glacial (mid-Wisconsinan) deposits ∼10 m and began aggrading again by ∼30 ka. Aggradation continued into MIS 2, with maximum MIS 2 aggradation occurring before ∼21 ka, which is coincident with the global Last Glacial Maximum (LGM). As the Ohio River adjusted to changing fluxes in sediment load and discharge following the LGM, it formed a sequence of fill-cut terraces in the MIS 2 outwash that get progressively younger with decreasing elevation, ranging in age from ∼21 ka to ∼13 ka. From ∼14 ka to ∼13 ka the Ohio River rapidly incised ∼3 m to form a new terrace, and by ∼12 ka at the onset of the Holocene, the Ohio River established a meandering channel pattern. The river formed a broad floodplain surface from ∼12 ka to ∼6 ka, and then incised ∼1 m and formed a fill-cut terrace from ∼6 ka to ∼5 ka. After ∼5 ka, likely in response to mid-Holocene drought in North America, the Ohio River incised ∼5 m, and by ∼4 ka the river began aggrading again. The Ohio River has aggraded ∼4 m since aggradation began at ∼4 ka. The chronostratigraphic framework and reconstructed history developed here suggest that the lower Ohio River is highly sensitive to glacial–interglacial transitions and abrupt Holocene climate change and responds rapidly to these allogenic forcings.

A quantitative midge-based reconstruction of mean July air temperature from a high-elevation site in central Colorado, USA, for MIS 6 and 5

Sediments recovered from the Ziegler Reservoir fossil site (ZRFS) in Snowmass Village, Colorado (USA) were analyzed for subfossil chironomids (or midges). The midge stratigraphy spans ~140–77ka, which includes the end of Marine Oxygen Isotope Stage (MIS) 6 and all of MIS 5. Notable shifts in midge assemblages occurred during two discrete intervals: the transition from MIS 6 to MIS 5e and midway through MIS 5a. A regional calibration set, incorporating lakes from the Colorado Rockies, Sierra Nevada, and Uinta Mountains, was used to develop a midge-based mean July air temperature (MJAT) inference model (r2jack=0.61, RMSEP=0.97°C). Model results indicate that the transition from MIS 6 to MIS 5e at the ZRFS was characterized by an increase in MJAT from ~9.0 to 10.5°C. The results also indicate that temperatures gradually increased through MIS 5 before reaching a maximum of 13.3°C during MIS 5a. This study represents the first set of quantitative, midge-based MJAT estimates in the continental U.S. that spans the entirety of MIS 5. Overall, our results suggest that conditions in the Colorado Rockies throughout MIS 5 were cooler than today, as the upper limit of the reconstructed temperatures is ~2°C below modern July air temperatures.

High-elevation paleoenvironmental change during MIS 6–4 in the central Rockies of Colorado as determined from pollen analysis

Paleoecological studies from Rocky Mountain (USA) high elevations encompassing the previous interglacial (MIS 5e) are rare. The ~10-m composite profile from the Ziegler Reservoir fossil site (2705m asl) of central Colorado allows us to determine paleoenvironments from Marine Oxygen Isotope Stages (MIS) 6– 4 using pollen zones that are approximately equivalent to marine oxygen isotope stages. During Pollen Zone (PZ) 6 time, pollen assemblages dominated by Artemisia (sagebrush) suggest that alpine tundra or steppe occurred nearby. The transition to PZ 5e was characterized by a rapid increase in tree pollen, initially Picea (spruce) and Pinus (pine) but also Quercus (oak) and Pseudotsuga menziesii (Douglas-fir). Non-arboreal pollen (NAP) types increased during PZ 5d, while Abies (fir) and Juniperus (juniper) increased during PZ 5c. Pollen evidence suggests that temperatures during PZ 5b were as cold as during PZ 6, with the site again surrounded by alpine tundra. Picea dominated during PZ 5a before the onset of cooler conditions during PZ 4. The MIS 6–MIS 5e transition here was similar to the MIS 2–MIS 1 transition at other Rocky Mountain sites. However, the Ziegler Reservoir pollen record contains evidence suggesting unexpected climatic trends at this site, including a warmer-than-expected MIS 5d and cooler-than-expected MIS 5b.

An analysis and comparison of observed Pleistocene South Carolina (USA) shoreline elevations with predicted elevations derived from Marine Oxygen Isotope Stages

Geological maps of South Carolina, covering >6800km2, confirm the existence of eight preserved Pleistocene shorelines above current sea level: Marietta (+42.6m), Wicomico (+27.4m), Penholoway (+21.3m), Ladson (+17.4m), Ten Mile Hill (+10.7m), Pamlico (+6.7m), Princess Anne (+5.2m), and Silver Bluff (+3m). Current geochronologic data suggest that these eight shorelines correlate with Marine Oxygen Isotope Stages (MIS) as follows: Marietta—older than MIS 77; Wicomico—MIS 55–45; Penholoway—MIS 19 or 17; Ladson—MIS 11; Ten Mile Hill—MIS 7; Pamlico—MIS 5; Princess Anne—MIS 5; and Silver Bluff—MIS 5 or 3. Except for the MIS 5e Pamlico, and possibly the MIS 11 Ladson, the South Carolina elevations are higher than predicted by isotope proxy-based reconstructions. The <4m of total relief from the Pamlico to the Silver Bluff shoreline in South Carolina, for which other reconstructions suggest an expected relief of ~80m, illustrates the lack of match. Our results suggest that processes affecting either post-depositional changes in shoreline elevations or the creation of proxy sea-level estimates must be considered before using paleo sea-level position on continental margins.

The Palaeolithic occupation of Europe as revealed by evidence from the rivers: data from IGCP 449

AbstractIGCP 449 (2000–2004), seeking to correlate fluvial records globally, has compiled a dataset of archaeological records from Pleistocene fluvial sequences. Many terrace sequences can now be reliably dated and correlated with marine oxygen isotope stages (MIS), allowing potentially useful patterns in artefact distribution to be recognised. This review, based on evidence from northwest European and German sequences (Thames, Somme, Ilm, Neckar and Wipper), makes wider comparisons with rivers further east, particularly the Vltava, and with southern Europe, especially Iberia. The northwest and southern areas have early assemblages dominated by handaxes, in contrast with flake‐core industries in Germany and further east. Fluvial sequences can provide frameworks for correlation, based on markers within the Palaeolithic record. In northwest Europe the first appearance of artefacts in terrace staircases, the earliest such marker, dates from the mid–late Cromerian Complex. Flake‐core industries may have significantly preceded handaxe industries in southern Europe. An important technological innovation—Levallois technique—occurs at the Lower‐Middle Palaeolithic boundary, correlated with MIS 9–8. Humans deserted northern Europe during MIS 6, apparently returning to central Germany and northern France (Somme valley) by MIS 5e but not reaching southern England until the appearance of Mousterian culture during MIS 4–3. Copyright © 2006 John Wiley &amp; Sons, Ltd.

An OSL dated Middle and Late Quaternary sedimentary record in the Roer Valley Graben (southeastern Netherlands)

Well-dated terrestrial sedimentary sequences are important to evaluate the influence of Quaternary climate change on continental landscape evolution. The Roer Valley Graben (southeastern Netherlands) contains a 35 m thick sedimentary record of Middle and Late Quaternary fluvial, aeolian and organic deposits. Sediment provenance, depositional processes and the continuity and timing of deposition were reconstructed. Sedimentary and geochemical data reveal a change from a fluvial depositional environment to a dominance of aeolian deposits. This change may be related to increased tectonic uplift and the onset of large-scale volcanism in the Ardennes–Eifel region between 800 and 500 ka. The main source of aeolian sediments are Quaternary Rhine deposits that crop out to the northwest of the study area. Sedimentation and preservation in the Roer Valley Graben took place under humid surface conditions. These conditions occurred: (1) in a periglacial climate with permafrost; (2) at the transition from a warm-temperate to a cool climate. Dates from two internally consistent quartz Optically Stimulated Luminescence (OSL) age series in the Roer Valley Graben correspond well with the ages of related terrace deposits in the orbitally tuned Meuse river terrace flight. The OSL dates confirm the presence of organic deposits reflecting Marine Oxygen Isotope Stage (MIS) 9 or 11 and MIS 5e. This long terrestrial sequence thus provides input for the fragmentary Middle Pleistocene record of northwestern Europe and forms a possible link between the glacial history of northern Europe and the long lake and loess records of eastern and southern Europe.

Stratigraphy and timing of eolianite deposition on Rottnest Island, Western Australia

Over 100 whole-rock amino acid racemization (AAR) ratios from outcrops around Rottnest Island (32.0° S Latitude near Perth) indicate distinct pulses of eolian deposition during the late Quaternary. Whole-rock d-alloisoleucine/ l-isoleucine (A/I) ratios from bioclastic carbonate deposits fall into three distinct modal classes or “aminozones.” The oldest, Aminozone E, averages 0.33 ± 0.04 ( n = 21). Red palaeosol and thick calcrete generally cap the Aminozone E deposits. A younger Aminozone C averages 0.22 ± 0.03 ( n = 63); comprising two submodes at 0.26 ± 0.01 ( n = 14) and 0.21 ± 0.02 ( n = 49). Multiple dune sets of this interval are interrupted by relatively weak, brown to tan “protosols.” A dense, dark brown rendzina palaeosol caps the Aminozone C succession. Ratios from Holocene dune and marine deposits (“Aminozone A”) center on 0.11 ± 0.02 ( n = 15), comprising submodes of 0.13 ± 0.01 (9) and 0.09 ± 0.01 (6). Calibration of A/ I averages from Aminozones E and A are provided by U/Th and 14C radiometric ages of 125,000 yr (marine oxygen isotope stage (MIS) 5e and 2000–6000 14C yr B.P. (MIS 1), respectively. The whole-rock A/I results support periodic deposition initiated during MIS 5e, continuing through MIS 5c, and then peaking at the end of MIS 5a, about 70,000–80,000 yr ago. Oceanographic evidence indicates the area was subjected to much colder conditions during MIS 2–4 (10,000 to 70,000 yr ago), greatly slowing the epimerization rate. Eolianite deposition resumed in the mid Holocene (∼6000 yr ago) up to the present. The A/I epimerization pathway constructed from Rottnest Island shows remarkable similarity to that of Bermuda in the North Atlantic (32° N Latitude). These findings suggest that, like Bermuda, the eolian activity on Rottnest occurred primarily during or shortly after interglacial highstands when the shoreline was near the present datum, rather than during glacial lowstands when the coastline was positioned 10–20 km to the west.

Last interglacial beetle fauna from New Zealand

Fossil beetles from two last interglacial lake deposits from southern Wairarapa, central New Zealand are provisionally ascribed to marine oxygen isotope stages (MIS) 5a–e. Both assemblages represent ecological successions from lake margins to forest. The lower sample (MIS 5e) is characterized by species found today in northern New Zealand. These species, including Lorelus crassicornis, ‘Dasytes’ laticeps, Cryptobius nitidius, ‘Stenomalium’ sulcithorax, Psilocnaeia nana, and Microbrontes lineatus, represent a southward displacement from modern distributions by up to 700 km. Climate reconstruction indicates that temperatures at the time of deposition were 1.6–2.5°C warmer in the summer (January) and 2.3–3.2°C warmer in the winter (July) than at present. These results match local and regional pollen and phytolith findings of warmer, wetter conditions at the thermal maximum of the last interglaciation. In contrast, the upper sample is characterized by species that have widespread modern-day distributions. This indicates that modern conditions were attained later in MIS5, after the MIS 5e thermal maximum.

Pleistocene coastal stratigraphy, sea‐level highstands and neotectonism of the southern Australian passive continental margin—a review

AbstractLocated in a tectonically stable, intraplate setting and in the far field of former ice sheets, the southern Australian passive continental margin represents a globally important region for quantifying sea level during Pleistocene highstands. The stratigraphical record of the southern Australian margin is dominated by geographically extensive coastal barrier, estuarine and peritidal landforms of bioclastic, temperate carbonate affinity, a function of regional aridity. Siliciclastic successions dominate the eastern Australian coastline. Despite the generally high level of tectonic stability, regional contrasts are evident in the elevation of Pleistocene shoreline deposits that largely relate to pre‐Quaternary geotectonic setting. The most complete record of Pleistocene highstand deposits occurs in the Murray Basin–Coorong Coastal Plain region, and indicates that interglacial sea‐level highstands, for at least the past 11 interglacials, did not deviate by more than 6 m from present sea‐level. The Pleistocene marginal marine record of southern Australia is dominantly represented by coastal successions deposited during marine oxygen isotope stages 5e and 7, equating with relative sea‐level maxima of 2–6 m and greater than 1 m above present sea‐level (APSL) respectively. Intertidal facies of Late Pleistocene interstadial successions rarely occur above present sea level. The most reliable record of glacio‐eustatic (ice equivalent) sea level is registered on coastlines developed on stable Precambrian cratons such as the Gawler Craton (Eyre Peninsula), where a consistent elevation of 2 m APSL is registered for over 500 km for the last interglacial shoreline (125 ka). Copyright © 2002 John Wiley &amp; Sons, Ltd.

大磯丘陵下末吉埋没土層における腐植酸緑色画分Ｐｇの特性と生成環境

The use of humic acid green fraction (Pg) as a paleoenvironmental indicator still requires integrated case studies applied to tephra and loess soil sequences (Watanabe and Kado, 2000; Watanabe et al., 2001a), as well as biochemical studies on humic acid Pg (Watanabe et al., 2001b). The stability and the chemical transformation of humic acid Pg should be elucidated by investigating paleosols and terrestrial deposits.This study aims to clarify the properties of humic acid green fraction Pg in the Shimosueyoshi buried layer (SB layer), the buried humic soil originating from tephra supplies of Hakone Caldera, corresponding to Marine oxygen isotope stage 5e. Pg absorption strength (Pg abs), total carbon content (TC), carbon content of extracted humic acid (CHA), pH (NaF) value, major element compositions, and phytolith analyses, together with selective dissolution of Fe compounds, and color measurement according to CIE color system were conducted. The obtained results were : 1) Clear Pg absorption bands at around 450, 570, and 615 nm were detected from all the humic acid of paleosols, corresponding to > 100 ka, located at Oiso Hill, central Japan. The fluctuation of Pg abs of humic acid in the investigated profile showed a significant increase in the SB layer (ca. 130 ka), equivalent to the early stage of MIOS 5e.2) According to the measurement error of Pg abs determined through the profile, the significant level of Pg abs in this study is confirmed to be much lower than that of Pg abs in previous studies carried on younger tephra soil sequences. It is considered that humic acid Pg is transformed in paleosols over 100 ka.3) Although the relations among amorphous and crystalline iron hydroxides and Pg absorption strength were not clear in this profile, unlike the previous reports (Kawahigashi et al., 1999, Watanabe and Kobayashi, 2001), the SB layer was characterized by the existence of geothite-like iron hydroxides, suggesting a humid environment.

Palaeohydrology, vegetation, and climate since the late Illinois Episode (∼130 ka) in south-central Illinois

Our interpretation of pollen and ostracode successions from four basins in south-central Illinois provides a new synthesis of palaeovegetation, palaeohydrology, and palaeoclimate for the period from the late Illinois Episode (about 130,000 years ago) to near the end of the Wisconsin Episode (about 25,000 years ago). Correlations of pollen biozones between Raymond, Pittsburg, and Bald Knob basins are the basis for identifying the late Illinois glacial, Sangamon interglacial, Wisconsin glacial, and Hudson interglacial episodes. Glacial episodes were identified primarily by the presence of Picea pollen and the ostracode Limnocythere friabilis, whereas interglacial episodes were identified by Quercus pollen and by the ostracodes Candona caudata and Heterocypris punctata. Within interglacial and glacial episodes, pollen and ostracode assemblages varied with changes in moisture balance. Local palaeohydrology was assessed primarily on the basis of environmental tolerance indices of ostracodes and the stable isotope (C,O) stratigraphy of ostracodal calcite. Regional moisture balance was assessed from multivariate analyses of the pollen successions. Three climatic regimes occurred during the Sangamon Episode. (1) One regime was characterised by precipitation exceeding evaporation that promoted basin overflow. This climate was inferred from the high percentages (generally >80%) of deciduous-forest pollen. Peaks in the abundance of Liquidambar and Fagus pollen indicate that winters may have been slightly warmer, and effective moisture slightly greater, than at present. (2) The second climatic regime was continental, similar to the present climate of Illinois in which precipitation is equal to or just less than evaporation. This climate is inferred from abundant Ambrosia pollen (40 to 60%) and abundant nektic (swimming) ostracode valves which suggest a shallow lake. These conditions probably developed in association with a ‘heat-low’ over the interior of North America during marine oxygen isotope stages 5e and 5c. Associated with the transition between the first two climates are fossils of the subtropical ostracode Heterocypris punctata and the giant tortoise Geochelone crassiscutata that suggest short periods in winter when polar low-pressure systems did not extend into Illinois as they do today. (3) The third climatic regime occurred during the transition from the Sangamon interglacial episode to the Wisconsin glacial episode. A severely continental climate is indicated by the heat-tolerant ostracode Pelocypris tuberculatum, variable δ 18O values of ostracode valves, and high environmental tolerance index values for the ostracode assemblages. The weedy Chenopodiaceae and Amaranthaceae families grew on exposed mudflats. The tree pollen associated with this type of climate included low percentages of Picea and Liquidambar, an assemblage that has no modern analogue. We suggest that this transitional climatic regime was associated with the large-scale changes in the climate system during marine oxygen isotope stage 4.