Pliocene-Pleistocene Boundary Research Articles

Climate and vegetation in southeastern Australia respond to Southern Hemisphere insolation forcing in the late Pliocene–early Pleistocene

Research Article| January 01, 2007 Climate and vegetation in southeastern Australia respond to Southern Hemisphere insolation forcing in the late Pliocene–early Pleistocene J.M. Kale Sniderman; J.M. Kale Sniderman 1School of Geography and Environmental Science, Monash University, Victoria 3800, Australia Search for other works by this author on: GSW Google Scholar Brad Pillans; Brad Pillans 2Research School of Earth Sciences, Australian National University, Canberra, ACT 0200, Australia Search for other works by this author on: GSW Google Scholar Paul B. O'Sullivan; Paul B. O'Sullivan 3Apatite to Zircon, Inc., 1075 Matson Road, Viola, Idaho 83872-9709, USA Search for other works by this author on: GSW Google Scholar A. Peter Kershaw A. Peter Kershaw 4School of Geography and Environmental Science, Monash University, Victoria 3800, Australia Search for other works by this author on: GSW Google Scholar Geology (2007) 35 (1): 41–44. https://doi.org/10.1130/G23247A.1 Article history received: 29 Jul 2006 rev-recd: 14 Aug 2006 accepted: 16 Aug 2006 first online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share MailTo Twitter LinkedIn Tools Icon Tools Get Permissions Search Site Citation J.M. Kale Sniderman, Brad Pillans, Paul B. O'Sullivan, A. Peter Kershaw; Climate and vegetation in southeastern Australia respond to Southern Hemisphere insolation forcing in the late Pliocene–early Pleistocene. Geology 2007;; 35 (1): 41–44. doi: https://doi.org/10.1130/G23247A.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract Terrestrial climate responses to orbital forcing during the late Pliocene–early Pleistocene are poorly understood, particularly in the Southern Hemisphere, but are important for determination of the timing of regional climate evolution early in the history of the glaciated Quaternary world. We present a pollen record from southeastern Australia that shows marked cyclic change over some 280,000 yr straddling the Pliocene-Pleistocene boundary. Rainforest communities responded to climate forcing primarily within the precession and eccentricity bands, suggesting that major vegetation changes were driven directly by summer insolation, rather than by obliquity-dominated glacial cycles. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Pliocene and earlier Pleistocene marsupial evolution in southeastern Australia

In recent years investigation of Australian Pliocene and earlier Pleistocene fossil occurrences and new methods for their dating has made it evident that there have been important changes in the mammal fauna during the past 5 million years. We review these data and believe they support the following general conclusions. By early Pliocene time (4–5 Ma) many marsupial genera characteristic of the late Cainozoic had appeared. Some species of extinct genera characteristic of the Pleistocene were also present in the late Pliocene (2 Ma). Megafaunal marsupials, notably Diprotodon, and the beginning of the spectacular radiation of a large sthenurine kangaroos, accompanied remnants of Miocene taxa (e.g. Ektopodontidae, and early macropodines like Prionotemnus and Kurrabi), into the early Pleistocene. This turnover, extending across the Pliocene-Pleistocene boundary, roughly corresponds with the time of northward withdrawal of rainforest from southeastern Australia and its replacement there by open Eucalyptus forest. Dust flux from the continent into the Tasman Sea and Indian Ocean increased in volume and frequency over the last four glacial cycles (400 ka) reflecting the progressive denudation of the Australian inland. Procoptodon sthenurines, the last megafaunal genus to appear, arose early in the Pleistocene near the initiation of 100 ka glacial cycling. During the last glacial cycle (120-20 ka) most of the megafauna including all sthenurine species became extinct.

Phylogeny of slug species of the genus Arion: evidence of monophyly of Iberian endemics and of the existence of relict species in Pyrenean refuges

The Iberian Peninsula contains the majority of the Paleartic land slug species of the genus Arion, which exhibits diverse taxonomic problems. The present study investigated Arion taxonomy on the basis of analyses of the mitochondrial ND1 gene and nuclear internal transcribed spacer 1 (ITS1) sequences. The Iberian endemic species were monophyletically clustered in two divergent sister clades. The topotype specimens of Arion lusitanicus and the closely related species Arion nobrei and Arion fuligineus, as well as Arion hispanicus and Arion flagellus, were grouped into an 'Atlantic' clade, whereas Arion baeticus, Arion gilvus, Arion anguloi, Arion wiktori and Arion paularensis were included in a 'Continental-Mediterranean' clade. Calibration of mutation rate in the ND1 gene suggested that the divergence of these two clades occurred around the Pliocene-Pleistocene boundary, with subsequent speciation events during the Pleistocene. A group of ancestral and divergent endemic species with distribution centred in the Pyrenean mountain range (Arion molinae, Arion lizarrusti, Arion antrhacius and Arion iratii) arose in the Pliocene and survived through the Pleistocene in geographically confined small populations. Arion lusitanicus showed up to be polyphyletic: specimens, sampled outside the geographic range of the topotype in the north-western Iberian Peninsula, were included in a non-monophyletic clade together with the widely distributed species Arion ater and Arion rufus. The divergent species with a wide European distribution (Arion subfuscus, Arion hortensis, Arion fagophilus and Arion intermedius) were located in basal positions in all topologies. The evolutionary history of these slug species (highly sensitive to climatic factors, with capacity for both outcrossing and selfing, and with low dispersal ability) appears to have been moulded by Pliocene-Pleistocene climate events and by the rugged topography of southern Europe, giving rise to repeated cycles of population isolation during periods of glaciation alternating with interglacial expansions limited by geographic barriers. © 2005 Blackwell Verlag.

秋田県海域および沿岸地域における鮮新世〜更新世の浮遊性有孔虫化石マーカーの出現パターンと集油構造形成時期

Planktonic foraminiferal marker beds such as Globorotalia ikebei bed, No.3 and No.2 Globorotalia inflata beds and Neogloboquadrina asanoi bed, have been useful for correlation and age determination of the marine Plio-Pleistocene formations along the coast of the Japan Sea in northeast Japan. All the marker beds are not necessarily found in the oil exploratory wells, however, although the formations are inferred to be deposited under the deep sea environment (the Uvigerina akitaensis Zone of benthic foraminifera). The N. asanoi and No.2 G. inflata beds are more occasionally missing at offshore wells, Akita Prefecture.The distribution maps of each marker bed were made based on biostratigraphic data of 80 wells, and they suggest that regional deep sea erosion and/or non-deposition occurred at topographic highs of anticlinal structures which had been formed in relation to compressional foldings since early Pliocene.The occurrence patterns of the marker beds were divided into five patterns based on their combination of existence and missing. The patterns could be closely related with the timing of structure growths. It is interpreted that major scaled erosions occurred at the Marker A and around the Pliocene-Pleistocene boundary, where they eroded the No.2 G. inflata bed and the N. asanoi bed, respectively. Structural uplift is considered to be the important factor for the deep sea erosion of the marker beds.

Changes in the fossil mammal faunas of Western Transbaikalia during the Pliocene–Pleistocene boundary and the Early–Middle Pleistocene transition

The faunal variations, sedimentary evolution and successive changes in vegetation during the Late Pliocene through the Middle Pleistocene of the Western Transbaikal area were analyzed to ascertain the main events on the Pliocene–Pleistocene boundary and to trace the Early–Middle Pleistocene transition. The evolutionary development of the main characteristic small mammals and their phyletic lineages involved replacement of the Itantsinian fauna by the Dodogolian assemblage. In the West Transbaikalia, the Pliocene–Pleistocene boundary is recognized between the Late Pliocene Itantsinian and the Early Pleistocene Dodogolian faunas. Biostratigraphic studies on small mammals have revealed that the Early–Middle Pleistocene transition can be placed at the Brunhes–Matuyama paleomagnetic boundary (0.78 Ma) which is determined in the middle sequence of the Tologoi key section, between the latest Early Pleistocene fauna of the Tologoi 2.1 and 2.2 and Middle Pleistocene fauna of Tologoi Complex (Tologoi 2.4 and 2.5).

Magnetostratigraphy of Miocene–Pliocene Zagros foreland deposits in the front of the Push-e Kush Arc (Lurestan Province, Iran)

The timing of the deformation in the Zagros Simply Folded Belt is poorly constrained because of the lack of an accurate absolute chronology of the syntectonic sedimentary sequences. The foreland basin infill at the front of the Push-e-Kush Arc is composed of fine-grained fluvial plain deposits (Agha Jari Fm.) and coarse conglomerates at the top of the section (Bakhtyari Fm.). A magnetostratigraphic study was carried out in a composite section spanning about 2800 m in order to date growth strata, and to constrain the timing of the deformation in the Mountain Front Flexure (MFF). Magnetostratigraphic correlation of the base of the Agha Jari Fm. with chron C5A yields an age of 12.8 to 12.3 Ma for this base. The transition to the conglomerates of the Bakhtyari Fm. correlates with the upper Gauss chron C2An at approximately 3 Ma. The deposition age of the top of the preserved Bakhtyari Fm. is extrapolated around the Pliocene–Pleistocene boundary. The base of the Agha Jari Fm. growth strata, and thus the beginning of the deformation in the front of the Push-e Kush Arc, is dated at 8.1–7.2 Ma. The topmost preserved Bakhtyari is folded in the NE flank of the Changuleh anticline and is unconformably overlying the SW flank of the Anaran anticline. This indicates that the tectonic deformation in the front of the Push-e-Kush Arc was active at least during 5 My. The MFF is a relatively long-lived structure active from 8.1 to 7.2 Ma to about the Pliocene–Pleistocene boundary, partly synchronous with the Changuleh anticline to the foreland. After MFF tectonic cessation, only the Changuleh anticline remained active.

Geochemical evidence for paleoclimatic variations during deposition of two Late Pliocene sapropels from the Vrica section, Calabria

The near-shore paleosetting of the Vrica Pliocene–Pleistocene boundary section provides an expanded sedimentary sequence that is ideal for investigating small-scale variations in sapropel deposition. We analyzed a suite of geochemical parameters in samples from a freshly drilled core that includes sapropelic layers c (1.851 Ma) and d (1.829 Ma) to characterize their depositional variation. Both sapropelic layers differ from background sediment by having higher total organic carbon (TOC) contents, lower δ 15N values, and higher contents of redox-sensitive and chalcophile elements. Layer c consists of a lower sub-layer in which TOC content is less than that of the upper sub-layer. Layer d exists as three sub-layers that are separated by low-TOC sediment. The lowermost sub-layer is weakly expressed and lacks chalcophile element enrichment. The other two sub-layers are strongly developed and illustrate that sapropel-forming conditions can be quickly established and interrupted. The two interruptions within layer d indicate a decrease in continental runoff, verifying the importance of humid conditions over continental borderlands and freshening of Mediterranean surface waters in forming sapropels. Although organic matter production was elevated during deposition of layers c and d, barium contents of sapropels and background sediment are similar, which shows that this paleoproductivity proxy is not suitable for shallow settings like Vrica. Our results confirm that considerable paleoclimatic variation can occur during deposition of an individual sapropel layer and in closely spaced sapropel events.

Paleoceanographic significance of sediment color on western North Atlantic Drifts: II. Late Pliocene–Pleistocene sedimentation

Color variations were interpreted in paleoceanographic terms for the late Pliocene–Pleistocene sediments recovered by ODP Leg 172 on deep-sea drifts at Blake–Bahama Outer Ridge and northeastern Bermuda Rise. The color-derived parameters used in interpretation included predicted carbonate content, terrigenous fluxes, and hematite content. Abundance of Upper Carboniferous spores indicates that the hematite is probably derived from the Permo-Carboniferous red beds of the Canadian Maritimes. In the last 800 kyr sedimentation pattern changes on the Blake–Bahama Outer Ridge were determined by the sediment delivery to the deep basin as well as circulation changes. Sediment delivery increased during glacials (especially during the last 500 kyr and particularly since Stage 6). A fundamental change in the thermohaline circulation occurred at about ∼500 ka corresponding to the end of the Mid-Pleistocene Transition period at the onset of the predominant 100-kyr climate cyclicity. Sedimentation related to WBUC had intensified at that time and had become more focused at depths below 3000 m. Changes in hematite content and sedimentation rate show a pulse of sediment via the St. Lawrence outlet at the Pliocene–Pleistocene boundary suggesting that a likely change in the hydrography/physiography of the Laurentide Ice Sheet could have been involved in the climatic and ocean circulation changes at that time.

Late Quaternary distributional stasis in the submediterranean mountain plant Anthyllis montana L. (Fabaceae) inferred from ITS sequences and amplified fragment length polymorphism markers.

Anthyllis montana is a submediterranean, herbaceous plant of the southern and central European mountains. The internal transcribed spacer (ITS) regions of nuclear ribosomal DNA were sequenced from multiple accessions of the species and several closely related taxa. In addition, amplified fragment length polymorphism (AFLP) was analysed from 71 individuals of A. montana collected in 20 localities, mainly in the Pyrenees, Alps, Italian Peninsula and Balkans. Our ITS phylogeny showed a sequential branching pattern in A. montana, implying a western Mediterranean origin followed by an eastward migration. ITS clock calibrations suggest that speciation of A. montana took place at the Pliocene-Pleistocene boundary, while intraspecific divergence dates to Late Quaternary times (i.e. 0.7 million years ago). The AFLP analyses revealed a major genetic (west/east) subdivision within A. montana, probably caused by the massive glaciation of the Alps during this latter time period. The present-day absence of A. montana from vast parts of the Alps, which appear ecologically suitable for the species, together with the finding of evenly distributed AFLP variability within each of the two western and eastern lineages identified, is taken as evidence for a largely static Late Quaternary history without large-scale migration. High levels of AFLP variation observed among populations, together with weak or absent patterns of isolation by distance, seem to be in accord with long-term population insularization and distributional stasis. However, recent small-scale migration and a narrow hybrid zone between western and eastern lineages need to be postulated to explain the intermediate genetic composition of individuals from the Maritime Alps, a well-known suture-zone for other plant and animal species.

Evidence for nearby supernova explosions.

Supernova (SN) explosions are one of the most energetic---and potentially lethal---phenomena in the Universe. We show that the Scorpius-Centaurus OB association, a group of young stars currently located at approximately 130 pc from the Sun, has generated 20 SN explosions during the last 11 Myr, some of them probably as close as 40 pc to our planet. The deposition on Earth of (60)Fe atoms produced by these explosions can explain the recent measurements of an excess of this isotope in deep ocean crust samples. We propose that approximately 2 Myr ago, one of the SNe exploded close enough to Earth to seriously damage the ozone layer, provoking or contributing to the Pliocene-Pleistocene boundary marine extinction.

Integrated paleontologic and paleomagnetic stratigraphy of the upper Neogene deposits around Limon, Costa Rica: A coastal emergence record of the Central American Isthmus

A chronostratigraphic study of mixed carbonate and siliciclastic sediments (Limon Group) along the Caribbean side of the Central American Isthmus was conducted to provide refined depositional ages on the uplifted, nearshore marine sequence exposed near Limon, Costa Rica. These upper Neogene sediments provide a rich faunal history that spanned the closure of the isthmus and cessation of marine circulation between the Pacific Ocean and Caribbean Sea. This faunal archive provides a critical link in regional assessment of evolutionary changes that resulted from the development of the Central American Isthmus. Results from this study have shown that integrated biostratigraphic and magnetostratigraphic techniques can be successfully combined to provide refined age dating in shallow-marine sediments, even where some microfossil reworking has occurred. We propose the new Quebrada Chocolate Formation to represent latest early–early late Pliocene mixed reefal and siliciclastic deposits that overlie the early Pliocene Rio Banano Formation. The superjacent Moin Formation is expanded to include a second reefal interval deposited near the late Pliocene-Pleistocene boundary as well as fine-grained, mollusk-rich deposits in the forereef and lagoon. The style of mixed-system reef geometry between the two units is distinct. The Quebrada Chocolate Formation reefs consist of a lower interval of alternating reefal units buried by siliciclastic sediment and an upper unit comprised of stacked, reefal buildups with relatively minor siliciclastic matrix. These stacked reefs formed on a rising sea level. In contrast, the Moin Formation reefs are isolated corals and patch reefs within a siliciclastic matrix that were deposited during the peak (maximum flooding) of the sea-level highstand. Our refined age model for the Limon Group sediments allows reassessment of Pleistocene uplift rates. We calculate a rate of about 50 m/m.y., slightly less than previous rate estimates, attributed to the shallow subduction in the Pacific of the Cocos Ridge beneath the Central American island-arc system. Development of similar high-resolution age models from other marine basins should provide the chronostratigraphic control necessary to assess environmental events and evolutionary trends in shallow-marine faunas separated and isolated by the Central American Isthmus.

Comparison of cosmogenic radionuclide production and geomagnetic field intensity over the last 200 000 years

The production rate of cosmogenic radionuclides such as 10Be or 14C is known to vary as a function of the geomagnetic field intensity. It should, therefore, be possible to extract a record of palaeofield intensity from the deposition record of these radionuclides in marine or terrestrial sediments and ice cores. Field intensity variations, however, are not the only factor that has influenced the cosmogenic radionuclide records. In the case of 14C, variations of the global carbon cycle, caused by reorganization of the ocean circulation patterns from the last glacial to the present interglacial, are superimposed. 10Be is not affected by these variations because it is not part of the carbon cycle, but its deposition rates in marine sediments vary as a function of lateral sediment redistribution and boundary scavenging intensity. A global stacked record of 10Be deposition rates, corrected for sediment redistribution by normalizing to 230Thex, was shown to remove most of the disturbances, and provides a record of 10Be production rate variations over the last 200 000 years, which translates into geomagnetic field intensity variations. This dataset is compared with palaeofield intensities reconstructed from marine sediments by palaeomagnetic methods, from variations in atmospheric 14C/12C derived from independent calibrations of 14C ages, such as U/Th dating and tree ring chronology, and from 36Cl and 10Be fluxes in polar ice cores. Potential influences of the Earth’s orbital parameters and insufficient correction for orbitally triggered climate variations on the palaeointensity reconstructions are assessed. It is argued that the palaeointensity records derived from marine sediments are not significantly affected by these factors.

The Plio-Pleistocene age of B�y�k Menderes and Gediz grabens and their tectonic significance on N-S extensional tectonics in West Anatolia: mammalian evidence from the continental deposits

The Büyük Menderes and Gediz grabens form the two main E–W trending structures in the western Anatolian extensional province. This paper concerns the dating of continental deposits within these grabens based on their small mammal content, and its implications for the stratigraphy and tectonics of the region. Four new small mammal localities yielded an Arvicolidae fauna including Mimomys cf. ostramosensis and Kalymnomys major, indicating a late Pliocene–early Pleistocene age for the deposits, related to the graben systems. The Plio-Pleistocene deposits in these localities have a discordant relationship with the older depositional systems revealing a regional disconformity in the Pliocene–Pleistocene boundary interval. The age of accessible sedimentary infills and their localization along the grabens suggest that the N–S extension produced significant effects in the Pliocene–Pleistocene boundary interval. The E–W normal faults chopped up and uplifted the late Pliocene–early Pleistocene deposits. This indicates that these grabens formed mainly during the Quaternary. Copyright © 2000 John Wiley & Sons, Ltd.

The Plio‐Pleistocene age of Büyük Menderes and Gediz grabens and their tectonic significance on N‐S extensional tectonics in West Anatolia: mammalian evidence from the continental deposits

The Büyük Menderes and Gediz grabens form the two main E–W trending structures in the western Anatolian extensional province. This paper concerns the dating of continental deposits within these grabens based on their small mammal content, and its implications for the stratigraphy and tectonics of the region. Four new small mammal localities yielded an Arvicolidae fauna including Mimomys cf. ostramosensis and Kalymnomys major, indicating a late Pliocene–early Pleistocene age for the deposits, related to the graben systems. The Plio-Pleistocene deposits in these localities have a discordant relationship with the older depositional systems revealing a regional disconformity in the Pliocene–Pleistocene boundary interval. The age of accessible sedimentary infills and their localization along the grabens suggest that the N–S extension produced significant effects in the Pliocene–Pleistocene boundary interval. The E–W normal faults chopped up and uplifted the late Pliocene–early Pleistocene deposits. This indicates that these grabens formed mainly during the Quaternary. Copyright © 2000 John Wiley & Sons, Ltd.

Stratigraphy of sediments from the Håkon Mosby Mud Volcano Area

Studies of four gravity cores from the Hakon Mosby Mud Volcano area have shown the existence of three lithologic–stratigraphic units: I – brown clay (0–10 ka), II – gray clay (10–30 ka) and III – gray silt (30–61 ka). The units reflect different paleographic sedimentation and conditions, including the influence of mud volcanic activity. Two periods of mud volcanic activity can probably be discerned: 10–30 ka and Recent. The coexistence of Pleistocene and Late Pliocene benthic foraminifera suggests that the source depth of the volcano is located below the Pliocene–Pleistocene boundary.

Sequence boundaries and salt diapirism in the Balearic abyssal plain, western Mediterranean

Unconformities and lapout structures in seismic profiles from the Balearic abyssal plain northeast of Menorca are apparently related to salt dome movements. Six sequence boundaries, observed around different salt structures, could be correlated throughout the area surveyed. The synchronous episodic movements are interpreted to be related to glacial/interglacial sea level fluctuations. During periods of low stand, more material is eroded from the continental shelf than during high stand, and it is deposited in the deep sea, in turn loading the Miocene salts and activating diapirism. DSDP site 372 and site survey seismic lines were used to define the Pliocene–Pleistocene boundary and to date the sequence boundaries.

Early Pliocene closing of the Indonesian Seaway: evidence from north-east Indian Ocean and Tropical Pacific deep sea cores

Deep sea cores from sites 214 and 758 A (Ninetyeast Ridge, north-east Indian Ocean), 761 B (Wombat Plateau, north-east Indian Ocean) and 586 B (Ontong Java Plateau, Tropical Pacific) are ideally located for comparison of late Neogene planktic foraminiferal biogeography and paleoceanographic records of tropical Indian and Pacific oceans to infer the timing of closing of the Indonesian Seaway. A consistent stratigraphy was developed between sites 214 and 586 B using graphic correlation and was integrated with the paleomagnetic time scale of Berggren et al. (1985) to provide an accurate chronology to compare interocean stratigraphic ranges of late Neogene planktic foraminifera. Tropical planktic foraminifera occur throughout each sequence at all sites. At each site the Miocene–Pliocene boundary is defined by the first appearance of Globorotalia tumida (5.2 Ma), the early/late Pliocene boundary by the first appearance of Globigerinoides fistulosus (3.2 Ma) and the Pliocene–Pleistocene boundary by the last appearance of G. fistulosus (1.6 Ma). Neogene planktic foraminiferal assemblages at sites 214, 758A, 761 B and 586B are generally similar until the beginning of the Pliocene (5.2 Ma) when the faunal record indicates divergence. A notable difference is complete absence of early Pliocene taxon Pulleniatina spectabilis from all the Indian Ocean sites. This difference suggests that the Indonesian Seaway became an effective biogeographic barrier to planktic foraminifera at the beginning of the Pliocene. However, there is still exchange of surface waters through this Seaway. Earlier studies suggested a Middle to Late Miocene occurrence for this biogeographic barrier. P. spectabilis evolved from P. primalis in the equatorial Pacific at about 5.2 Ma. It is a short-ranging early Pliocene species spanning about 1.3 my and occurred only in Pacific, unlike earlier suggestions of a broader distribution into the Indian Ocean.

Low-latitude Plio-Pleistocene temporal abundance variations in the radiolarian Cycladophora davisiana Ehrenberg: stratigraphic and palaeoceanographic significance

Abstract The abundance variation of the radiolarian Cycladophora davisiana was recorded throughout the Plio-Pleistocene Olduvai Time-slab of Ocean Drilling Program (ODP) Sites 677, 709, 847, 850 and 851, in the equatorial Pacific and Indian Oceans. Data were plotted on independently erected timescales. Twelve peak-abundance events were recognized, although not all events were recognized at all the sites. Most of the events, where they are recorded at different sites, were synchronous. However, events recorded at Site 709 in the Indian Ocean were found to be approximately 15 ka older than those events recorded at Pacific sites. This age difference may be due to either diachronous C. davisiana events or a slight inaccuracy in the erected timescale for ODP Site 709 compared with those of the eastern Pacific. The previously demonstrated synchroneity of C. davisiana events in the Late Quaternary leads us to believe that the ODP Site 709 timescale may be inaccurate. Thus, recognition of correlatable C. davisiana events in the equatorial Pacific and Indian Oceans permits the further evaluation and fine-tuning of high-resolution timescales, enabling accurate comparisons to be made of sediment sequences on a regional, and possibly oceanic and interoceanic scale. Of the 12 C. davisiana events recognized, only one event occurred at all the investigated sites. This event occurred at c. 1.8 Ma and immediately above the internationally defined Pliocene-Pleistocene boundary, and may thus prove to be a new useful biostratigraphic marker for the Tertiary/Quaternary boundary. C. davisiana is primarily characteristic of high-latitude water masses, therefore the cyclical abundance peaks of this species noted at the low-latitude sites investigated here, represent the injection of deep cold water of high-latitude origin.

Recurring global sea-level changes recorded in shelf deposits near the G/M polarity transition, Wanganui Basin, New Zealand: Implications for redefining the Pliocene-Pleistocene boundary

A well exposed 1 km-thick association of late Pliocene and early Pleistocene (ca. 2.6-1.7 Ma) strata in Wanganui Basin, New Zealand, contains a progradational stack of twenty, 5th order (41 ka duration) depositional sequences that accumulated in shelf to shoreface paleoenvironments in response to global glacioeustatic sea level fluctuations. The sequences are correlated with δ 18 O Isotope Stages 100-58, and each 41 ka glacial/interglacial stage couplet is represented by an individual sequence comprising transgressive (TST), highstand (HST) and regressive (RST) systems tracts that can be readily related to generic sequence stratigraphic models. In general, deposition of each of the sequences occurred during odd numbered (interglacial) isotope stages and the sequence boundaries developed during the maxima of even numbered (glacial) isotope stages. The key palaeomagnetic tiepoints used for pinning the isotope record to the section are the Gauss/Matuyama boundary (2.60 Ma in Stage 104) and the top of Olduvai Subchron (1.77 Ma in Stage 63). A deeply incised sequence boundary, with up to 30 m of relief, at the base of Te Rimu Sand, represents the first widespread subaerial exposure in Wanganui Basin during the Matuyama Chron; it is correlated with the high amplitude positive (glacial) δ 18 O shift in Isotope Stage 100, which is considered to mark the initiation of major northern hemisphere continental glaciations at ca. 2.52 Ma. The overlying Hautawa Shellbed, containing the subantarctic bivalve Chlamys delicatula , defines the base of the Nukumaruan Stage, and represents the earliest faunal evidence of climatic cooling in New Zealand Pliocene-Pleistocene marine sequences. The sequence boundary at the base of Hautawa Shellbed is correlated with Isotope Stage 98 (ca. 2.48 Ma). Traditionally, the Pliocene-Pleistocene boundary in New Zealand was located at the base of Hautawa Shellbed, but Beu and Edwards (1984) showed that the boundary, as defined in the Vrica stratotype (astronomically calibrated age ca. 1.81 Ma), actually lies in the upper part of the Nukumaruan Stage. The Hautawa Shellbed, which lies closer to the Gauss/Matuyama palaeomagnetic transition (2.60 Ma), is therefore much older than the currently defined Pliocene-Pleistocene boundary. From a New Zealand perspective, a more logical position for the Pliocene-Pleistocene boundary would be close to or just above the Gauss/Matuyama polarity transition. Such a position would take advantage of the boundaries proximity to a readily identifiable polarity reversal, and lie close to the time of initiation and development of major northern hemisphere ice sheets.

Twisting or stable quaternary boundary? A perspective on the glacial late Pliocene concept

There has been a long-running debate over the position of the Pliocene-Pleistocene boundary, i.e. 1.8 Ma versus 2.6 Ma. This study presents litho- and pedo-stratigraphic characteristics, grain size, magnetic susceptibility, and dust sedimentation rates for ‘red clay’-loess sequences over northern China, in order to assess the drastic climatic event(s) recorded in the quasi-continuous eolian deposits, and to readdress the position of the Pliocene-Pleistocene boundary. In complete Chinese loess sequences, 33 soil-loess couplets have been identified and labeled with Si-Li system. Traditionally, the base of Chinese loess has been designated at the bottom of loess unit L33. However, a typical loess layer within the uppermost ‘red clay’ is identified and formally designated here as L34 and the soil unit between L33 and L34 as S33, which lowers the basal age of Chinese loess from 2.6 Ma to ∼2.8 Ma. Although the Neogene ‘red clay’ and the overlying Quaternary loess are both of windblown origin, they have quite different pedogenic characteristics. The loess consists of alternating reddish soil and yellowish loess layers, while the ‘red clay’ is composed of soils with much redder colour and carbonate nodule layers. In general, the “red clay” has been subjected to stronger pedogenic processes than the overlying loess, and can be regarded as an extremely thick soil complex. The alternation of loess and soils reflects large-scale oscillations between glacial and interglacial conditions, whereas the well-developed ‘red clay’ deposition indicates a relatively stable climate condition. At ∼2.8 Ma, shortly before the Gauss/Matuyama boundary, the eolian sequences show a sedimentary transition from the well-weathered ‘red clay’ to the alternating loess and paleosol deposits, accompanied by coarser particle size, increased dust accumulation rates, and change of magnetic susceptibility signature. These indicate a large climatic shift from long-lasting warm-humid conditions to large-amplitude cold-dry and warm-humid fluctuations around 2.8 Ma, and a dramatic increase in aridity over the dust source region. In contrast, such a drastic event is not identified around the top of the Olduvai event or at any other time of the past 7.7 Ma. As the Gauss/Matuyama boundary offers a sound foundation for global time correlation and chronostratigraphic classification, these results still support the proposal of ICS and INQUA, that the conventional Pliocene-Pleistocene boundary should be lowered from 1.8 Ma to 2.6 Ma.