Brunhes-Matuyama Research Articles

The Early Middle Pleistocene Site of Gombore II (Melka Kunture, Upper Awash, Ethiopia) and the Issue of Acheulean Bifacial Shaping Strategies

The Gombore II site dates to circa the Brunhes Matuyama Reversal and is one of the Acheulean localities of the Melka Kunture (Upper Awash, Ethiopia) archaeological complex, known since the 1970s. In 2001, this locality was selected as the site for an Open Air Museum and thus excavated. The excavation area has yielded an abundant Acheulean lithic assemblage manufactured on volcanic raw materials in close association with numerous paleontological remains. A technological analysis was carried out on a fraction of the bifacial tools (bifaces and cleavers) which could be temporarily removed from the displayed surface in the museum. This set of artefacts reveals new data about the bifacial shaping strategies adopted at the beginning of the Middle Pleistocene in Ethiopia. The use of obsidian and the systematic manufacturing of twisted bifaces are original features of the assemblage. These data are discussed in the framework of penecontemporaneous East African sites.

Human migration into Europe during the late Early Pleistocene climate transition

A critical assesment of the available magnetostratigraphic and/or radiometric age constraints on key sites bearing hominin remains and/or lithic industries from southern Europe (Italy, France, Spain) leads us to propose that the main window of early hominin presence in southern Europe is broadly comprised between the Jaramillo subchron and the Brunhes–Matuyama boundary (i.e., subchron C1r.1r, 0.99–0.78 Ma). Within the dating uncertainties, this ~ 200 ky time window broadly coincides with the late Early Pleistocene global climate transition that contains marine isotope stage (MIS) 22 (~ 0.87 Ma), the first prominent cold stage of the Pleistocene. We suggest that aridification in North Africa and Eastern Europe, particularly harsh during MIS 22 times, triggered migration pulses of large herbivores, particularly elephants, from these regions into southern European refugia, and that hominins migrated with them. Finally, we speculate on common pathways of late Early Pleistocene dispersal of elephants and hominins from their home in savannah Africa to southern Europe, elephant and hominin buen retiro. In particular, we stress the importance of the Po Valley of northern Italy that became largely and permanently exposed only since MIS 22, thus allowing possibly for the first time in the Pleistocene viable new migration routes for large mammals and hominins across northern Italy to southern France and Spain in the west.

10Be evidence for delayed acquisition of remanent magnetization in marine sediments: Implication for a new age for the Matuyama–Brunhes boundary

Fluxes of the meteoric cosmogenic radionuclide 10Be vary with changes in the incoming cosmic rays modulated by geomagnetic field intensity variations. The variability in the 10Be flux can be used to synchronize ice cores, as well as marine sediments, by comparison with the relative paleointensity variations of the geomagnetic field. However, lock-in of the paleomagnetic signal at some depth below the sediment–water interface in marine sediments through acquisition of a post-depositional remanent magnetization (PDRM) adds uncertainty to synchronization. Despite the long history of such studies, the magnitude of the PDRM lock-in depth remains controversial. In this article, we present clear evidence for a downward offset of the paleointensity minimum relative to the 10Be flux anomaly at the Matuyama–Brunhes (M–B) geomagnetic polarity boundary, which we interpret to result from a ∼ 15 cm PDRM lock in depth. This lock-in depth indicates that up to several tens of thousands years of age offset probably occurs when a paleomagnetic record is used for dating marine sediments, and the age of the M–B boundary should be revised to ca. 10 kyr younger, which is consistent with a younger ice core derived age of 770 ± 6 ka (2 σ). This cosmogenic age tuning strategy will contribute to refining paleomagnetic-based age models for marine sediments and identifying of lead-lag relationships for global abrupt environmental changes.

The Early–Middle Pleistocene environmental and climatic change and the human expansion in Western Europe: A case study with small vertebrates (Gran Dolina, Atapuerca, Spain)

The dispersal of hominins may have been favored by the opening of the landscape during the Early–Middle Pleistocene transition (EMP) in Western Europe. The structure of the small-vertebrate assemblages of the archaeo-paleontological karstic site of Gran Dolina in Atapuerca (Burgos, Spain) shows important environmental and climatic changes in the faunal succession, across the Matuyama–Brunhes boundary at 780 ka. These changes are interpreted to indicate impoverishment of the forests, along with an increase in dry meadows, and open lands in general that entailed a tendency towards the loss of diversity in small-vertebrate communities above the EMP. We evaluate variation in diversity of the faunal succession of Gran Dolina using Shannon’s Second Theorem as an index of ecosystem structure. The long cultural-stratigraphic sequence of Gran Dolina during the EMP is somewhat similar in its completeness and continuity to that in the locality of Gesher Benot Ya'aqov in the Upper Jordan Valley. We also evaluate related data including faunal and floral (pollen) succession. Both localities present cold, dry and humid, warm fluctuations at the transition between the Early and the Middle Pleistocene. Comparisons between these sites present opportunities to understand large-scale climatic changes.

Lentic Basommatophora molluscs and hygrophilous land snails as indicators of habitat and climate in the Early-Middle Pleistocene (0.78 Ma) at the site of Gesher Benot Ya‘aqov (GBY), Israel

The lentic Basommatophora molluscs and hygrophilous land snails of the Early-Middle Pleistocene site of Gesher Benot Ya‘aqov (GBY), 0.78 Ma, crossed by the Matuyama–Brunhes chron boundary [MBB] were studied in order to reconstruct their specific habitats and possible reactions to climate change along the site sequence. Samples of equal sizes from 27 of the 46 layers along the 100 k.yr. time-span of the site were examined. About 2000 specimens of 21 lentic and hygrophilous species belonging to five families: Planorbidae (11), Lymnaeidae (6), Acroloxidae (2), Carychiidae (1) and Succineidae (1) were identified. The family with the largest biodiversity is the Planorbidae and of these, the most abundant species include Gyraulus piscinarum (937), Planorbarius corneus (210) and Radix labiata (160). The recent known zoogeographic origin of 81% of the species is Palaearctic and Holarctic. The MBB coincides with remarkable environmental changes reflected in molluscs, other faunal and floral elements and stable isotopes. The Planorbidae and Lymnaeidae reach greater abundance (90% and 80% of their assemblages, respectively) pre-MBB, while Acroloxidae, Succineidae and Carychiidae are more abundant (74%, 64% and 90%) post-MBB. Our data indicate that GBY molluscs show a two-phase pattern (shallow and deep lake) in each of the five defined cycles. Their numbers increase during the shallow water phases, thus the site climate changes from cold and humid in the oldest layers, to dry and cold up to the MBB and few succeeding layers. Between cycles 2 and 3, post-MBB, we see a short period of warm and humid climate that enables the influx of African and Asian elements. At the same time, cold climate species of Euro-Siberian and Palaearctic origin disappear. The succeeding layers indicate a cooler and humid climate. Finally, the sequence indicates deep water in the oldest layers and desiccation towards MBB and deeper water post-MBB.

Multiple rapid polarity swings during the Matuyama‐Brunhes transition from two high‐resolution loess‐paleosol records

Two high‐resolution magnetic records of the Matuyama‐Brunhes (M‐B) transition have been obtained from Xifeng and Baoji loess‐paleosol sequences in the Chinese Loess Plateau. The results of stepwise thermal and alternating field (AF) demagnetizations confirm that both treatments are effective in isolating characteristic remanent magnetization (ChRM) from specimens of loess‐paleosol sediments which suffer from weak pedogenesis, and that AF demagnetization clearly fails to isolate ChRM from specimens of paleosol sediments which have undergone strong pedogenesis. On the basis of virtual geomagnetic pole latitudes crossing the virtual geomagnetic equator, the M‐B transition involves at least 15 rapid polarity swings. Rock magnetic experiments and anisotropy of low‐field magnetic susceptibility show that high‐frequency polarity swings during the M‐B transition cannot be attributed to rock‐magnetic and/or sedimentary causes. Extrapolating a constant accumulation rate between the Jaramillo‐Matuyama and M‐B boundary ages, the M‐B transition interval of both the Xifeng and Baoji sections is estimated to have a duration of more than 10 kyr. Durations of each short polarity interval are estimated to range from about 0.3 to 5.6 kyr. Our new results, combined with previous paleomagnetic observations from lavas and marine sediments, suggest that multiple rapid polarity swings occurred during the M‐B transition.

Reliability of the natural remanent magnetization recorded in Chinese loess

Chinese loess‐paleosol sequences undoubtedly have recorded geomagnetic events (both polarity reversals and excursions). However, the fidelity of the rapid paleomagnetic field oscillations during a polarity reversal remains uncertain. To test the reliability and consistency of the natural remanent magnetization records in Chinese loess, 10 subsets of parallel samples across the Matuyama‐Brunhes (MB) reversal boundary were obtained from the Luochuan region in the hinterland of the Chinese Loess Plateau. Our paleomagnetic results show diversified virtual geomagnetic poles (VGPs) during the MB transition but consistent VGPs outside of the transitional zone. The anisotropy of magnetic susceptibility and rock magnetism results indicate that the sampled interval is rather uniform and undisturbed. The discrepancies of the characteristic remanent magnetization within the MB transition are probably due to the low efficiency in aligning magnetic grains, mainly pseudo‐single‐domain magnetite, associated with the low field intensity. Nevertheless, the stratigraphic location of the MB boundary can be confidently defined. Therefore, we conclude that Chinese loess‐paleosol sequences can record geomagnetic reversal events, but the morphology within the polarity transition is rather questionable.

The oldest human traces north of the Carpathians (Kończyce Wielkie 4, Poland)

In the area of the Kończyce Wielkie quarry (middle-southern Poland), the Quaternary deposits of different genesis crop out. The lower fluvial series is overtopped with the glacigenic sediments occurring below the Matuyama–Brunhes boundary. This ice-sheet advance is correlated with the Günz and with the oldest traces of glaciations in Western Europe. Culture materials were located within layer of fluvial sands with fine-grained gravels, below the boulder pavement and diamicton – interpreted as till. Raw materials inventory are local flint and hornstone, also foreign flint, hornstone, quartzite, opalite and gneissose granite. The inventory contained macrolithic and microlithic cores, flakes and tools. The tools are made from pebbles, flakes and microlithic-flakes.

Comment on ‘Lower and Early Middle Pleistocene Acheulian in the Indian sub-continent’ by Gaillard et al. (2009) (Quaternary International)

This paper addresses the recent publication in this journal by Gaillard et al. (2010) who discuss several Early Acheulean occurrences from the Indian subcontinent in relation to their age, context and lithic assemblages. A critique of the associated data shows that their acquiescence of Acheulean occupation in the Indian Subcontinent as being older than the late Middle Pleistocene is based entirely on circumstantial and inconclusive evidence. Each of the sites discussed by them (Isampur, Bori, Morgaon, Chirki-Nevasa, Singi Talav, Atbarapur) have variably yielded limited contextual and chronometric data that is ambiguous, controversial or only preliminary at this stage. Although one or two occurrences may be as old as they claim, a more rigorous scientific approach is required to first address the problematic issues of stratigraphic interpretation, precise context and absolute age. The current temporal framework of the South Asian Paleolithic renders the earliest Acheulean assemblages simply as being older than ∼400 ka, due primarily to the limitations of the 230Th– 234U dating method used earlier. Whilst it is probable that future dating attempts will extend the earliest South Asian Acheulean occupation up to the Brunhes–Matuyama boundary or even beyond, convincing geochronological support for such a scenario is currently lacking at all of the ‘typologically-earliest’ sites.

Rock magnetism and palaeomagnetism of the Montalbano Jonico section (Italy): evidence for late diagenetic growth of greigite and implications for magnetostratigraphy

SUMMARY The Montalbano Jonico (MJ) section, cropping out in Southern Italy, represents a potential candidate to define the Lower/Middle Pleistocene boundary and it has been proposed as a suitable Global Stratotype Section and Point (GSSP) of the Ionian Stage (Middle Pleistocene). The MJ section is the only continuous benthic and planktonic δ18O on-land reference in the Mediterranean area for the Mid-Pleistocene transition, spanning an interval between about 1240 and 645 ka. Combined biostratigraphy and sapropel chronology, tephra stratigraphy and complete high-resolution benthic and planktonic foraminiferal stable oxygen isotope records already provide a firm chronostratigraphic framework for the MJ section. However, magnetostratigraphy was still required to precisely locate the Brunhes-Matuyama transition and to mark the GSSP for the Ionian stage. We carried out a palaeomagnetic study of a subsection (Ideale section) of the MJ composite section, sampling 61 oriented cores from 56 stratigraphic levels spread over a ca. 80-m-thick stratigraphic interval that correlates to the oxygen isotopic stage 19 and should therefore include the Brunhes-Matuyama reversal. The palaeomagnetic data indicate a stable and almost single-component natural remanent magnetization (NRM). A characteristic remanent magnetization (ChRM) was clearly identified by stepwise demagnetization of the NRM. The ChRM declination values vary around 0° and the ChRM inclination around the expected value (59°) for a geocentric axial dipole field at the sampling locality. This result indicates that the section has been remagnetized during the Brunhes Chron. A preliminary study of 27 additional not azimuthally oriented hand samples, collected at various levels from other parts of the MJ composite section, indicates that all the samples are of normal polarity and demonstrates that the remagnetization is widespread across the whole exposed stratigraphic sequence. A series of specific rock magnetic techniques were then applied to investigate the nature of the main magnetic carrier in the study sediments, and they suggest that the main magnetic mineral in the MJ section is the iron sulphide greigite (Fe3S4). Scanning electron microscope observations and elemental microanalysis reveal that greigite occurs both as individual euhedral crystals and in iron sulphides aggregates filling voids in the clay matrix. Therefore, we infer that the remagnetization of the section is due to the late-diagenetic growth of greigite under reducing conditions, most likely resulting in the almost complete dissolution of the original magnetic minerals. Iron sulphide formation in the MJ section can be linked to migration of mineralized fluids. Our inferred timing of the remagnetization associated with greigite growth represents the longest remanence acquisition delay documented in greigite-bearing clays of the Italian peninsula so far.

Relative geomagnetic paleointensity of the Brunhes Chron and the Matuyama–Brunhes precursor as recorded in sediment core from Wilkes Land Basin (Antarctica)

Paleomagnetic and rock magnetic investigation was performed on the 35-m long MD03-2595 CADO (Coring Adélie Diatom Oozes) piston core recovered on the continental rise of the Wilkes Land Basin (East Antarctica). Analysis of the characteristic remanent magnetization (ChRM) inclination record indicates a normal magnetic polarity for the uppermost 34 m of the sequence and a distinctive abrupt polarity change at the bottom of the core. This polarity change, which spans a 27 cm thick stratigraphic interval, represents a detailed record of the Matuyama–Brunhes (M–B) transition and it is preceded by a sharp oscillation in paleomagnetic directions that may correlate to the M–B precursor event. Paleomagnetic measurements enable reconstruction of geomagnetic relative paleointensity (RPI) variations, and a high-resolution age model was established by correlating the CADO RPI curve to the available global reference RPI stack, indicating that the studied sequence reaches back to ca. 800 ka with an average sedimentation rate of 4.4 cm/ka. Orbital periodicities (100 ka and 41 ka) were found in the ChRM inclination record, and a significant coherence of ChRM inclination and RPI record around 100 ka suggests that long-term geomagnetic secular variation in inclination is controlled by changes in the relative strength of the geocentric axial dipole and persistent non-dipole components. Moreover, even if the relatively homogeneous rock magnetic parameters and lithofacies throughout the recovered sequence indicates a substantial stability of the East Antarctic Ice Sheet during the middle and late Pleistocene, influence of the 100 ka and 41 ka orbital periodicities has been detected in some rock magnetic parameters, indicating subtle variations in the concentration and grain-size of the magnetic minerals linked to orbital forcing of the global climate.

The Lower Palaeolithic of Ukraine: Current evidence

For almost three decades, the only evidence of stratified and well-documented Lower Palaeolithic in Ukraine was reported for Korolevo, situated west of the Carpathian arch. This locality remains the most important in the country and provides four Lower Palaeolithic assemblages, of which two were recognised below the Brunhes–Matuyama boundary. Several new stratified localities were discovered recently: among these are Malyj Rakovets IV, situated in the Central European part of Ukraine, and Medzhybozh and Maslovo located in the western edge of the East European plain. All these localities are dated to the Middle Pleistocene, but only Medzhybozh has yielded rich and various biostratigraphic data. Some Ukrainian surface localities also provide assemblages of likely Lower Palaeolithic age; among these are Neporotovo IV in the Dniester area and Gaspra and Cape Mayachny in Crimea. Regardless of limited primary evidence, Lower Palaeolithic localities of Ukraine exhibit certain regularities, in particular concerning their spatial pattern.

Early Paleolithic of Korolevo site (Transcarpathia, Ukraine)

The most ancient in situ Palaeolithic industries in Ukraine are known from the multi-layer Palaeolithic site of Korolevo in Transcarpathia, along the Tisza River. The Korolevo site was excavated from 1974 to the early 1990s. The Palaeolithic artefacts were related to a complex loess–palaeosol succession on top of a volcanic mount above the present-day alluvial plain. In the eastern sector (Beyvar), abundant lithic implements were collected in various excavation areas, but the loess–palaeosol succession was often limited or discontinuous. In the northern sector (Gostry Verkh) the loess–palaesol sequence reached a total thickness of 14 m, although the Palaeolithic assemblages were poorly documented. Huge Middle and Early Palaeolithic collections were mainly produced on local raw material (andesite). At Gostry Verkh, the reference stratigraphic sequence of Korolevo encompasses a complex succession of loamy units alternating with seven palaeosols. The Brunhes–Matuyama boundary was fixed at the base of palaeosol VII. The 15 cultural-chronological complexes were further positioned within the pedosedimentary sequence, taking into account their inferred stratigraphic background as well as the degree of weathering of the lithics. The earliest assemblages were distributed respectively in the upper part of palaeosol VII (complex VI) and within the alluvial deposits prior to the Brunhes–Matuyama boundary (complexes VII and VIII). A new section opened at Gostry Verkh has allowed a complementary reading of the sequence. In this way, the reproducibility of the main pedosedimentary units previously described could be tested, as well as the presence of reversed magnetisation. Palaeoclimatic analysis of the sequence has been improved by micromorphological analysis of the main pedological units. The new research also aimed at providing better control of the stratigraphic positioning of the cultural assemblages. Consequently, five Middle and Early Paleolithic assemblages were discarded, including complex VIII, as their situation regarding the local pedosedimentary context is poorly documented. At present in Korolevo, only levels VI and VII were determined to be Early Paleolithic.

Chronology and the upper dating limit for loess samples from Luochuan section in the Chinese Loess Plateau using quartz OSL SAR protocol

Luminescence dating of loess older than 100 ka has long been a challenge. It has been recently reported that, using optically stimulated luminescence (OSL) of fine-grained quartz (4–11 μm) extracted from loess, the range of luminescence dating could be pushed to ∼0.6 Ma with OSL ages being in agreement with independent ages [Watanuki, T., Murray, A.S., Tsukamoto, S., 2005. Quartz and polymineral luminescence dating of Japanese loess over the last 0.6 Ma: comparison with an independent chronology. Earth and Planetary Science Letters 240, 774–789]. The aim of this study is to provide a luminescence chronology (20 samples) for the standard Luochuan loess section, and to further examine the upper limit of quartz OSL dating for Chinese loess. The growth curve does not saturate at 700 Gy, and should allow reliable equivalent dose ( D e) determination up to at least 400 Gy. However, when compared with independent chronological control, the D e that could be treated as reliable is less than ∼230 Gy (corresponding to ∼70 ka in age for Chinese loess), and the D e larger than ∼230 Gy should be underestimated. Ages for samples from the lower part of palaeosol S1 are severely underestimated, with the maximum age of 95 ka for a sample from the bottom of this palaeosol, much younger than the expected age of ∼128 ka. The maximum D e obtained for sample L9/M, collected from loess layer L9 which is below the Matuyama–Brunhes (B/M) boundary whose age is ∼780 ka, is only 403 Gy which corresponds to an age of 107 ka. The cause of underestimation is not yet clear. The previous results by Watunuki et al. (2005) on the extension of OSL dating of loess to 0.6 Ma is not confirmed. When evaluating the validity of OSL ages in S1, another possibility is to question the already established chronological frame for Luochuan section, which is based on the hypothesis of continuous dust deposition. The assumption of an erosion hiatus between L2 and S1 could make the OSL ages look reasonable. However, if this is the case, then it is difficult to explain why the age of sample L9/M is only 107 ka which could be treated as a saturation age, while the OSL can provide a correct age for loess as old as 94.9 ka for sample LC22 collected from the bottom of S1. Much work is required to clarify these confusions.

Climate variability in the Upper Jordan Valley around 0.78 Ma, inferences from time-series stable isotopes of Viviparidae, supported by mollusc and plant palaeoecology

The Early–Middle Pleistocene lacustrine sediments at Gesher Benot Ya'aqov (GBY) in the Upper Jordan Valley span ca. 100 Ka across the Matuyama–Brunhes Boundary (MBB) at 780 Ka and oxygen isotope stages (OISs) 20 to 18, provide a continuous record of their sedimentary history and prevailing climate. The lacustrine environment is investigated using ecological and stable isotope characteristics of gastropods belonging to the family Viviparidae supplemented by other molluscan and floral indicators. The sedimentary framework of the 34 m thick sequence is bounded by channel conglomerates at its base and top, and consists of six sedimentary cycles. Each one starts with shore sediments (coquina and sand) and ends with deeper water sediments (black mud or gray mud). Time series of δ 18O and δ 13C values were determined in individual shells belonging to two sympatric genera of viviparid gastropods: Viviparus apameae galileae and Bellamya sp. found in the sedimentary cycles 2 through 5. The total overall range of δ 18O in the time series of all the shells is from − 10.5‰ to − 5.2‰ (VPDB), and the δ 13C from − 9.2‰ to − 4.8‰ (VPDB). The δ 13C values of shells recovered from black mud are lower than those from the other sediment types suggesting a higher proportion of carbon of organic origin. The δ 18O values show only a weak relation with sediment type. The time series of the individual shells indicate a relative constancy in the water δ 18O and temperature whilst the variation in δ 13C could be related to the annual productivity cycle (growth and decay of aquatic plants) of the lake. The δ 13C patterns in the time series and winter rings indicate that the rate of growth of the individual snails was ca. 15–30 mm/year. The isotopic characteristics of the Viviparid shells from these beds indicate diverse sedimentary environments and suggest that above the MBB (cycles 2–5) the GBY lake received constant and isotopically consistent water inflow. Our integrated data, isotopic and ecological of molluscs, and ecological of plants, indicates that the geophysical-magnetic phenomenon of MBB coincides with an environmental change from a relatively cold dry climate towards a warmer temperate subtropical climate in this region. This change coincides with the occurrence of hominin artifacts, which were found mainly in layers of the sedimentary cycles 3–5.

Pleistocene magnetochronology of early hominin sites at Ceprano and Fontana Ranuccio, Italy

Paleomagnetic analyses were conducted on two cores drilled at Ceprano in central Italy where an incomplete hominin cranium was discovered in 1994, as well as on two additional cores from the nearby site of Fontana Ranuccio that yielded hominin remains associated with an Acheulean industry. No evidence for the 0.78 Ma Brunhes–Matuyama boundary was found at Ceprano down to 45 m below the level that yielded the hominin cranium. The Ceprano lithostratigraphy and the paleomagnetic age constraints are broadly consistent with the stratigraphy of the Liri lacustrine sequence of the Latina Valley, constrained by published K–Ar ages between ~ 0.6 and ~ 0.35 Ma, and according to an age model with magnetic susceptibility supported by pollen facies data, suggest that the level that yielded the hominin cranium has an age of ~ 0.45 (+ 0.05, − 0.10) Ma. Evidence for the Brunhes–Matuyama boundary was found at Fontana Ranuccio about 40 m below the hominin level, consistent with a K–Ar age of ~ 0.46 Ma reported for this level. Hence the Ceprano and Fontana Ranuccio hominin occurrences may be of very similar mid-Brunhes age.

Fossil embryos and adult Viviparidae from the Early–Middle Pleistocene of Gesher Benot Ya’aqov, Israel: ecology, longevity and fecundity

Ashkenazi, S., Klass, K., Mienis, H.K., Spiro, B. & Abel, R. 2010: Fossil embryos and adult Viviparidae from the Early–Middle Pleistocene of Gesher Benot Ya’aqov, Israel: ecology, longevity and fecundity. Lethaia, Vol. 43, pp. 116–127. A unique fossil assemblage of the extinct freshwater viviparids Viviparus apameae galileae and Bellamya sp. with intact embryos enabled the assessment of population ecology parameters applied so far only to recent living populations. The assemblage, from the Early Middle Pleistocene site of Gesher Benot Ya’aqov, occurs in the sedimentary sequence above the Matuyama Brunhes Boundary (MB boundary) at 0.78 Ma. This fossil assemblage is related to a shoreline habitat that was affected by desiccation during a sudden drop in water level. In both species, the youngest females with embryos had five or more whorls, with heights of >24.8 and >16.1 mm in Viviparus and Bellamya respectively. Comparison of shell height and width, aperture height and width and the ratio of shell height/width indicated that females are significantly longer and larger than the shells without embryos. Longevity was estimated as at least 9 years for Viviparus and 8 years for Bellamya and lifetime fecundity of female viviparids was estimated based on longevity and reproductive period. The high number of reproducing females and high number of embryos indicate favourable habitat and climate conditions for both Viviparidae. The fossil Viviparidae from GBY have the characteristics of organisms that are K-selected by natural selection forces. □Fecundity, fossil embryos, longevity, molluscs, Pleistocene, reproductive output, sexual dimorphism, viviparids.

Revised stratigraphy of the Blanchetown Clay, Murray Basin: age constraints on the evolution of paleo Lake Bungunnia

Paleo Lake Bungunnia covered more than 40 000 km2 of southern Australia during the Plio-Pleistocene, although the age and origin of the lake remain controversial. The Blanchetown Clay is the main depositional unit and outcrop at Nampoo Station in far-western New South Wales provides the most continuous lacustrine section preserved in the basin. Here the Blanchetown Clay represents the maximum lake fill and comprises: (i) a basal well-sorted sand with interbedded clay (Chowilla Sand), representing initial flooding at the time of lake formation; (ii) a thick sequence of green-grey clay comprised dominantly of kaolinite and illite, with the apparently cyclic occurrence of illite interpreted to represent cool and dry glacial climatic intervals; and (iii) a 2.6 m-thick sequence of finely laminated silt and silty clay, here defined as the Nampoo Member of the Blanchetown Clay. New magnetostratigraphic data constrain the age of the oldest lake sediments to be younger than 2.581 Ma (Matuyama–Gauss boundary) and probably as young as 2.4 Ma. This age is significantly younger than the age of 3.2 Ma previously suggested for lake formation. The youngest Blanchetown Clay is older than 0.781 Ma (Brunhes–Matuyama boundary) and probably as old as 1.2 Ma. The Nampoo Station section provides a framework for the construction of a regional Plio-Pleistocene stratigraphy in the Murray Basin.

High-resolution climate stratigraphy across the Matuyama–Brunhes transition from palynological data of Osaka Bay sediments in southwestern Japan

This study presents a high-resolution palynological analysis of a sedimentary core from Osaka Bay (Japan) straddling Marine Oxygen Isotope Stage (MIS) 19, i.e. across the Matuyama–Brunhes magnetic polarity Boundary (MBB). Comparison with the standard marine oxygen isotope curve ([Bassinot, F.C., Labeyrie, L.D., Vincent, E., Quidelleur, X., Shackleton, N.J., Lancelot, Y., 1994. The astronomical theory of climate and the age of the Brunhes–Matuyama magnetic reversal. Earth and Planetary Science Letters 126, 91–108.]) demonstrates that variations in vegetation and the basinal environment coincided with global ice volume changes. The late MIS 20 is characterized by boreal climate with coniferous forest. In MIS 19, the forest was generally dominated by Fagus and Quercus ( Lepidobalanus), suggesting onset of humid climatic conditions slightly cooler than the present. Excluding coastal vegetation components, climate during MIS 19 can be subdivided into three stages. The early stage, including substage 19.3, is characterized by high seasonality in precipitation. This contrasts with the very abundant, year-round precipitation that is inferred for the late stage, from substage 19.2 to substage 19.0, which is characterized by cool-temperate coniferous taxa including Cryptomeria. The very high precipitation rates of the latter persisted at least up to substage 18.4. There was no apparent vegetational response to the sea level highstand of 19.3. In contrast, a short-lived thermal maximum event took place ca. 6–7 kyr later, i.e. in middle MIS 19. This event is characterized by increases in the warm-temperate element Quercus ( Cyclobalanopsis). The MBB, the recommended criterion for defining the Lower–Middle Pleistocene boundary, took place in middle MIS 19. These lines of evidence indicate that the occurrence of the MBB corresponded with a shift towards warmer and wetter climatic conditions. Similar warming and wetting events across the MBB are also observed in pollen records from southern Italy and central Japan. This possibly provides long-distance correlation, and may suggest a connection between the Earth's magnetic field and climate.

Microwave palaeointensity results from the Matuyama–Brunhes geomagnetic field reversal

We present new palaeointensity and palaeodirectional results from the Matuyama–Brunhes geomagnetic field reversal. Volcanic sequences from La Palma and Guadeloupe record the Matuyama–Brunhes boundary, possible precursors, and fluctuations in the magnetic field prior to the main polarity reversal. Absolute palaeointensity was determined using the microwave technique and palaeodirectional results were obtained from thermal demagnetisation. Ten flows from the 29 flows studied gave reliable mean palaeointensities; however, only 1 of the 10 flows records a transitional direction. The VDM determined from this flow is 1.9±0.6(±σ)×1022Am2. Analysis of all Matuyama–Brunhes data suggests that the main directional changes occurred once the VDM was reduced below 3×1022Am2(∼35% of the present field value).