Olduvai Event Research Articles

Geochemical Features of the Olduvai Event in the Sediments of Lake El’gygytgyn (Anadyr Plateau, Chukchi Peninsula)

Geochemical Features of the Olduvai Event in the Sediments of Lake El’gygytgyn (Anadyr Plateau, Chukchi Peninsula)

The Kalahari sediments and hominins in southern Africa

The temporal coupling of the structural evolution of the Kalahari Basin and the accumulation of the Kalahari Group sediments has been an accepted paradigm leading to the assumption that the Kalahari group sediments have been accumulating gradually since the mid-Cretaceous. Here we review the first actual ages for the Kalahari Group based on cosmogenic ages from six geological localities. These results demonstrate that Kalahari Basin infill was a more dynamic process than previously thought and that the Kalahari Group sediments are mostly Plio-Pleistocene in age (∼4 Ma to 1–2 Ma). The hiatus between the initial structural subsidence of the basin, during the Cretaceous, and the general young age of the investigated sediments, implies a dynamic landscape in which significant phases of erosion occurred during the Mesozoic and Cenozoic. The magnitude of erosion is manifested by the fact that in many locations Kalahari Neogene to Quaternary sediments overlie Precambrian basement.The age of the present infill of the Kalahari thus falls within the temporal range of the genus Homo. In light of this new understanding, we provide a review of the archaeological evidence from the Kalahari Basin and along its southern fringe. Initial hominin presence is found at Wonderwerk Cave during the Olduvai Event and there is subsequent high-density occupation along the southern fringe of the Kalahari Basin during the Acheulean and the Fauresmith. Middle Stone Age occupation is limited to localities of limited size and small artifact counts and it appears that the focus of human occupation, particularly in the later stages of the Middle Stone Age, shifts southward, including along the coastal regions.

The geoheritage of Olduvai Gorge, Tanzania: providing geological answers to human origin questions

Abstract While Olduvai Gorge, Tanzania, is most famous for its impressive and formative record of early human technology, Pleistocene fauna and hominin fossils, its geological record is equally important. At Olduvai, palaeoanthropologically significant sites are often preserved in primary context (not redeposited), and they can be contextualized within the palaeoenvironments in which the hominins lived. This has provided an exceptional opportunity to assess not only hominin evolutionary changes over time, but also to understand their adaptive behaviour including toolmaking, foraging and sociality. Abundant volcanic material from the nearby Ngorongoro Volcanic Highlands, interspersed within and between archaeology-bearing deposits, made Olduvai a target for some of the earliest applications of radiometric dating using the K/Ar system. Ultimately, the 40 Ar/ 39 Ar dating system has produced ages with exceptional precision. Early radiometric dating at Olduvai helped establish the antiquity of the hominin lineage, and early palaeomagnetic studies (and the ‘Olduvai event,’ the longest normal subchron within the reversed Matuyama Chron) were critical in establishing the importance of Olduvai in the field of geochronology. More recently, high-resolution palaeoclimate studies of the palaeolake that once occupied the Olduvai Basin have helped to reconstruct the palaeoenvironments encountered by hominin species. Over a century of geological research has secured Olduvai's status as an important site for geoheritage.

Vegetation succession and climate change during the early pleistocene (2.2-1.8 Ma) in the Nihewan Basin, northern China

The Nihewan Formation, northern China is ideal for studying environmental changes during the early Pleistocene. In conjunction with palaeomagnetic measurements, pollen and grain-size analyses were conducted on 120 samples from a ~24 m long section (2.2-1.8 Ma) of core NHA from the Nihewan Basin, in order to reconstruct past vegetation and climatic changes. The pollen assemblages were dominated by Pinus, indicating that the vegetation was primarily pine forest and that the climate was relatively warm and wet. From 2.15-1.92 Ma, deciduous broad-leaved tree pollen significantly increased to >10% of the total, showing that more broad-leaved trees grew in the study area during the warmest and wettest period in the study section. From 1.92-1.78 Ma (coeval with the Olduvai event), Pinus and broad-leaved tree pollen types decreased. The percentages of Picea (>20%), Artemisia and Chenopodiaceae increased, indicating that spruce forests expanded, the openness of the forested areas increased and the climate became cold and dry. The vegetation changes reconstructed during the Olduvai period indicates that the climate in the Nihewan Basin was cold and dry, relating to global cooling facilitated by the uplift of the Tibetan Plateau and the strengthening of the winter monsoon.

Études stratigraphique, sédimentologique et paléomagnétique des travertins de Kocabaş, Bassin de Denizli, Anatolie, Turquie, contenant des restes fossiles quaternaires

Stratigraphic, sedimentological and paleomagnetic studies were conducted on the travertine from Denizli Basin, near Kocabas village, in the Denizli region in Turkey, following the paleontological discovery in 2002. The stratigraphic and sedimentological studies show at least two main cycles of mass travertine, separated by a fluvial deposit and overlain by a fluvio-lacustrine deposit. These travertines must have formed in environments with strong hydrodynamics (streams or waterfalls) and are preferentially located at breaks of slopes. The paleomagnetic study shows that all the quarry travertine presents reverse magnetic polarity. On the other hand, the detrital fluvio-lacustrine deposit above the travertine presents normal geomagnetic polarity, except at the top, where it is reversed. Given the presence of an archaic Homo erectus skull and Villafranchian paleontological remains in the upper travertine unit, the whole travertine dates from the upper Matuyama, and is more recent than the Olduvai event (1.78Ma). The normal polarity recorded in the upper fluvio-lacustrine deposit could correspond to the Cobb Mountain excursion, dated to 1.22Ma.

Age of the Tananwan Formation in Northern Taiwan: A Reexamination of the Magnetostratigraphy and Calcareous Nannofossil Biostratigraphy

Over the past two decades, the succession strata of the Tananwan Formation exposed horizontally on the Linkou Tableland in northwestern Taiwan has been either dated to a short time interval of 0.9-0.7 Ma or assigned to a vague long period within the Matuyama Epoch covering probably both the Olduvai and Jaramillo normal events. In this study, a reexamination of magnetostratigraphy and calcareous nannofossil biostratigraphy of this formation was carried out. The results show that the strata with stable remanent magnetizations have reversed magnetic polarities only, and the layers with marine sedimentary facies consistently contain specimens of large Gephyrocapsa. These updated results suggest that the Tananwan Formation was deposited within the interval of 1.46-1.24 Ma, corresponding to a short period of reversed magnetic polarity of the Matuyama Epoch.

Drastic climatic shift at ∼2.8 Ma as recorded in eolian deposits of China and its implications for redefining the Pliocene-Pleistocene boundary

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 S i-L i 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.

The Calabrian Stage redefined

The name Calabrian was introduced in the geological literature by the French stratigrapher Maurice Gignoux in 1910, and later described in his important monograph (633 pages) Les formations marines pliocenes et quaternaires de l'Italie du sud et de la Sicile published in 1913. Detailed data were provided on several sections (Santa Maria di Catanzaro, Caraffa, Monasterace, Palermo) and on their fossil content. The Calabrian Stage has commonly been used for over fifty years as the oldest subdivision of the Quaternary, notably in the time scales of Berggrenavan Couvering (1974) and HaqaEysinga (1987). However, after the GSSP for the Pliocene/Pleistocene boundary (P/P) was approved by INQUA in 1982 and ratified by IUGS in 1984 at the Vrica section of Calabria, there was a decline in the usage of the stage name, and an increasing tendency by many Quaternary workers to question the boundary stratotype. This was because there was increasing evidence that it did not correspond to the beginning of the ice age. In doing so, they were not complying with the recommendations presented at the 18th International Geological Congress (IGC) in London, 1948 (Oakley, 1950). The purpose of this paper is to clarify the current definition and usage of the Calabrian Stage, with a proper historical background and the presentation of several marine fossiliferous sections exposed on land that can be chronostratigraphically correlated with multiple criteria including biostratigraphy, magnetostratigraphy, isotopic stratigraphy, astrocyclostratigraphy and occasionally tephrastratigraphy. Other sections considered and equated with those from land are from the Mediterranean deep-sea record (Tyrrhenian Sea ODP Site 653, Ionian Sea ODP Site 964, Levantine Sea ODP Site 967, Balearic Sea ODP 975). The Calabrian Stage has a duration of approximately 1.1 Ma. Its base occurs in the latest part of the Olduvai Event; its top is coincident with the base of the following Ionian Stage. After a general agreement, the definition of the base of the Ionian Stage (in progress) will be proposed coincident with the Brunhes/Matuyama magnetic reversal. The choice of a physical parameter as a leading criterion for its identification facilitates its recognition in continental successions.

LATE NEOGENE PLANKTIC FORAMINIFERAL BIOCHRONOLOGY OF THE ODP SITE 763A, EXMOUTH PLATEAU, SOUTHEAST INDIAN OCEAN

Research Article| July 01, 2008 LATE NEOGENE PLANKTIC FORAMINIFERAL BIOCHRONOLOGY OF THE ODP SITE 763A, EXMOUTH PLATEAU, SOUTHEAST INDIAN OCEAN Devesh K. Sinha; Devesh K. Sinha 3 1Department of Geology, Centre of Advanced Studies, Delhi University, Delhi-110007, India. 3Correspondence author. E-mail: devasinha@yahoo.com Search for other works by this author on: GSW Google Scholar Ashutosh Kumar Singh Ashutosh Kumar Singh 2Planetary and Geosciences Division, Physical Research Laboratory, Ahmadabad 380 009, India. Search for other works by this author on: GSW Google Scholar Author and Article Information Devesh K. Sinha 3 1Department of Geology, Centre of Advanced Studies, Delhi University, Delhi-110007, India. Ashutosh Kumar Singh 2Planetary and Geosciences Division, Physical Research Laboratory, Ahmadabad 380 009, India. 3Correspondence author. E-mail: devasinha@yahoo.com Publisher: Cushman Foundation for Foraminiferal Research Received: 11 Oct 2006 Accepted: 23 Feb 2008 First Online: 03 Mar 2017 Online ISSN: 1943-264X Print ISSN: 0096-1191 © 2008 Journal of Foraminiferal Research Journal of Foraminiferal Research (2008) 38 (3): 251–270. https://doi.org/10.2113/gsjfr.38.3.251 Article history Received: 11 Oct 2006 Accepted: 23 Feb 2008 First Online: 03 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Devesh K. Sinha, Ashutosh Kumar Singh; LATE NEOGENE PLANKTIC FORAMINIFERAL BIOCHRONOLOGY OF THE ODP SITE 763A, EXMOUTH PLATEAU, SOUTHEAST INDIAN OCEAN. Journal of Foraminiferal Research 2008;; 38 (3): 251–270. doi: https://doi.org/10.2113/gsjfr.38.3.251 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 SocietyJournal of Foraminiferal Research Search Advanced Search Abstract The late Neogene section of ODP Hole 763A, Exmouth Plateau, southeast Indian Ocean, has been biostratigraphically subdivided into eight planktic foraminiferal zones. The zones are similar to those of the tropical northern Indian and tropical western Pacific Oceans. The sequential order of planktic foraminiferal events has been determined, and 32 late Neogene planktic foraminiferal events have been identified. A major faunal turnover (22 events) occurs between 80 and 45 meters below seafloor (mbsf), spanning 1.6 million years between 3.6 Ma and 2 Ma and may be related to the stresses transmitted to the upper ocean due to major cooling associated with Northern Hemisphere glaciation.Based on integration with magnetostratigraphy, numerical age estimates of planktic foraminiferal events have been determined for the first time from the southeast Indian Ocean. A comparison with the published dates for these events from other parts of the world suggests that 14 events are reliable for correlation over a wide geographic range. The useful synchronous events are the Globorotalia tosaensis FO (2.84 Ma), the Globorotalia tosaensis LO (0.59 Ma), the Globigerinoides extremus LO (1.87 Ma), the Globigerinoides fistulosus FO (3.26 Ma), the Globigerinoides fistulosus LO (1.73 Ma), the Dentoglobigerina altispira LO (3.05 Ma), the Dentoglobigerina globosa LO (3.18), the Neogloboquadrina dutertrei FO (2.77 Ma), the Sphaeroidinellopsis LO (3.35), the Globorotalia margaritae LO (3.38 Ma), the Globorotalia crassaformis FO (4.41 Ma), the Globoturborotalita nepenthes LO (3.44 Ma), the Globorotalia tumida tumida FO (5.10 Ma) and the Pulleniatina primalis FO (5.70 Ma). In contrast, the other events are diachronous and considered unsuitable for inter-oceanic correlation. The Pliocene-Pleistocene boundary is marked at ODP Hole 763A by the LO of Globigerinoides fistulosus, which is a synchronous event over a wide latitudinal range and occurs close to the top of the Olduvai Event (Chron C2n; 1.77 Ma). The Miocene-Pliocene boundary is approximated by the first evolutionary appearance of Globorotalia tumida tumida from its ancestor Globorotalia plesiotumida and occurs close to base of Thvera magnetic event (C3n.4n; 5.23 Ma). Recognition of both of these epoch boundaries is in accord with the International Commission on Stratigraphy. The detailed planktic foraminiferal biochronology developed for Hole 763A will aid correlation and dating of various paleoceanographic events over the last 6 million years in the southeast Indian Ocean. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Speleology and magnetobiostratigraphic chronology of the Buffalo Cave fossil site, Makapansgat, South Africa

Speleological, stratigraphic, paleomagnetic and faunal data is presented for the Buffalo Cave fossil site in the Limpopo Province of South Africa. Speleothems and clastic deposits were sampled for paleomagnetic and mineral magnetic analysis from the northern part of the site, where stratigraphic relationships could be more easily defined and a magnetostratigraphy could therefore be developed for the site. This is also where excavations recovered the fossil material described. A comparison of the east and South African first and last appearance data with the Buffalo Cave fauna was then used to constrain the magnetostratigraphy to produce a more secure age for the site. The magnetostratigraphy showed a change from normal to reversed polarity in the basal speleothems followed by a short normal polarity period in the base of the clastic deposits and a slow change to reversed directions for the remainder of the sequence. The biochronology suggested an optimal age range of between 1.0 Ma and 600,000 yr based on faunal correlation with eastern and southern Africa. A comparison of the magnetobiostratigraphy with the GPTS suggests that the sequence covers the time period from the Olduvai event between 1.95 and 1.78 Ma, through the Jaramillo event at 1.07 Ma to 990,000 yr, until the Bruhnes–Matuyama boundary at 780,000 yr. The faunal-bearing clastic deposits are thus dated between 1.07 Ma and 780,000 yr with the main faunal remains occurring in sediments dated to just after the end of the Jaramillo Event at 990,000 yr.

Sedimentary records of environmental evolution in the Sanmen Lake Basin and the Yellow River running through the Sanmenxia Gorge eastward into the sea

A series of independent faulted basins developed in the present middle reaches of the Yellow River during late Cenozoic, among which the Sanmen Lake Basin is located in the east edge of the Loess Plateau, a transitional zone between the second and third macromorphological step of China. The thick strata of the Sanmen Group deposited in the large basin. The Sanmen Group is a perfect place for the study on paleoenvironmental change, tectono-climatic cycles as well as the formation and evolution of the Yellow River. In this paper, the paleoenvironmental changes, regional tectonic movement and the evolutionary process of the Sanmen Lake Basin during the past 5 Ma were reconstructed based on the analysis of paleomagnetic stratigraphy, pollen, TOC and carbonate content from the Huangdigou outcrop near the Sanmenxia Reservoir, Pinglu County, Shanxi Province. The sedimentary records from the outcrop indicate that the basin was first formated by fault activity at about 5.4 MaBP, and after the strong tectonic movement at 3.6 MaBP the lake enlarged and the rainfall of summer monsoon increased. There was no great climatic transition near 2.6 MaBP, corresponding to the bottom age of loess in the Loess Plateau. After Olduvai event (about 1.77 MaBP) the Picea and Abies were presented in the sediments, which indicates a colder climate. The tectonic movement at 1.2 MaBP caused the light angular discordance between the upper and lower Sanmen Group. The sedimentary records show a cold and wet climate during the prosperous periods of loess accumulation such as L 15 , L 9 , L 6 . The tectonic intensification periods of the Sanmen Basin correspond with the tectonic movements in the Qinghai-Xizang Plateau chronologically. The earliest age of the outflow from the Paleo-Sanmen Lake or the partly cutting off of the Sanmenxia Gorge was about 0.41— 0.35 MaBP. The age of cutting thoroughly the Sanmenxia Gorge by the Yellow River and the disappearance of the Paleo-Sanmen Lake was about 0.15 MaBP, which symbolized the formation of the present Yellow River and had an important influence on the environmental and morphological evolution in the middle and lower reaches of the Yellow River.

The depositional history of the Bavarian Allgäu area at the turn of the Tertiary/Quaternary, Northern Alpine Foreland, Germany — a set of paleogeological maps

Abstract The Northern Alpine Foreland in southwestern Bavaria is characterized by Miocene Molasse overlain by deposits of glacial and glacifluvial origin. One peculiarity of this region is the occurrence of extended fluvial terraces of the Upper Pliocene/Lower Pleistocene, which can be subdivided into several distinct levels. From these sediments good information on the stratigraphy, palaeogeography and palaeoenvironment of the Illerglacier Foreland at the Plio-/Pleistocene transition as well as the influence of tectonics can be derived. Sediments of the OSM (Obere Suswassermolasse=Upper Freshwater Molasse) reflect the change of general flow direction from west to east during the Pannonien by tectonics causing the development of the easterly flowing Danubian river system. According to the general dip of the landscape the predecessors of the present day rivers Iller, Lech and Ammer flowed northeast. Initiated by cold climatic conditions at the onset of Pleistocene the changes in fluvial accumulation and vertical erosion resulted in a number of gravel deposits. Terraces of five Biber cold stages document the ancient course of the Iller running obliquely to the modern valley orientation. As the Danube–Iller Divide was cut by brooks, the Iller river shifted to the northwest at the end of Donau-complex. After this nontectonic change of the flow direction a huge area was covered by gravel deposits. As the river development can be reconstructed in detail, the preserved sediments are considered to document all Upper Pliocene/Lower Pleistocene fluvial accumulation and erosion phases in the area under discussion. Nine cold climatic terrace accumulations can be distinguished up to the end of the Olduvai event.

Fabric and origin of multiple diamictons within the pre-Illinoian Kennedy Drift east of Waterton-Glacier International Peace Park, Alberta, Canada, and Montana, USA

Pebble fabrics and sedimentological properties indicate a glacigenic origin for multiple, superposed diamictons within the (pre-Illinoian) Kennedy Drift east of Waterton-Glacier International Peace Park, Alberta, Canada, and Montana, USA. Determining the origin of these diamictons is particularly important in light of their antiquity. Eight diamictons on Mokowan Butte, Saint Mary Ridge, and Two Medicine Ridge have reversed magnetic polarity and are correlated with the Matuyama Chron (2.6–0.78 Ma). On Mokowan Butte, two diamictons with normal polarity underlying two reversed diamictons are correlated with the Gauss Chron (3.6–2.6 Ma) or possibly the Reunion or Olduvai events (2.23–2.20 and 1.93–1.76 Ma, respectively). Fabrics were taken from 17 units within the Kennedy Drift on five interfluves. On the basis of comparison of properties of these diamictons with those of modern glacial deposits, eight, including the uppermost one or two units on each interfluve, are probably undeformed lodgment tills. These are typically massive, matrix-supported bouldery sandy loam with strong unimodal fabric orientations, relatively high eigenvalue (S 1 /S 3 ) ratios, and striations on resistant clasts. Some include boulder pavements, bullet-shaped boulders, and weak fissility. Eight other units have weaker fabrics typical of either deformed lodgment tills or glacigenic sediment flows. Because these also include bullet-shaped boulders, stone pavements, and striated clasts, most are probably deformed lodgment tills. A colluvial or mudflow origin for the material is ruled out on the basis of the lateral and vertical extent of the diamictons (at least 300 m wide and 5–10 m thick), wide range of clast lithologies and sizes, and distance from the mountain front (2–10 km), as well as pebble fabrics and sedimentological properties.

Chronology of Neogene and Quaternary uplift and magmatism in the Caucasus: constraints from K–Ar dating of volcanism in Armenia

The Greater Caucasus is one of Earth's highest actively-uplifting mountain ranges; the adjoining Caspian Sea basin contains a substantial proportion of its hydrocarbon reserves. Like other parts of the former Soviet Union, the Neogene and Quaternary chronology of these important regions has not previously been well-defined. It has thus been impossible to obtain reliable estimates for rates of processes such as uplift of the Caucasus and sedimentation in the Caspian Sea. Previous studies have established the relative timings of events in the region, using correlation schemes between volcanism, glaciations, and the stratigraphy of the Caspian basin. However, a range of absolute chronologies has previously been proposed for these sediments and igneous rocks, based mainly on different interpretations of their magnetostratigraphic records. By K–Ar dating, we determine the ages of volcanism at three localities in Armenia as 1.1, 0.8 and 0.8 Ma. Using these data and other evidence, we propose a revision to the chronology of this region, in which a distinctive brief interval of normal magnetic polarity in the local sedimentary and volcanic magnetostratigraphic records is matched to the Cobb Mountain event in the global record rather than the Olduvai event or an earlier subchron as had previously been thought. We thus interpret a ∼1.5 Ma timing for the start of volcanism in the Lesser Caucasus, and also suggest a ∼1.2 Ma timing for the Late Akchagyl transgression of the Caspian Sea, a key event in the regional stratigraphy when this water body reached its greatest extent. We tentatively correlate this transgression with the melting event following glaciation during stage 36 of the oxygen isotope timescale, which was thus the first time during the Pleistocene when eastern Europe was covered by a lowland ice sheet. Time-averaged since ∼1 Ma, the flanks of the eastern Greater Caucasus mountains are shown to have uplifted at ∼0.6 mm a −1 and the Lesser Caucasus at ∼0.3 mm a −1. We show that the rate and spatial scale of this uplift are too great to be the result of plate convergence, and suggest instead that this uplift is caused by crustal thickening due to inward lower-crustal flow to beneath these mountain ranges. At the start of magmatism in both the Greater and Lesser Caucasus, the estimated crustal thickness was ∼45 km. We thus suggest that this magmatism has been caused by heating of the mantle lithosphere due to earlier crustal thickening, the temperature rise required to initiate magmatism being the same in both cases.

Magnetostratigraphy and sedimentologically derived geochronology of the Quaternary lacustrine deposits of a 3000 m thick sequence in the central Qaidam basin, western China

The Qaidam basin is a large basin in western China where the thickness of Quaternary deposits has a range of 2000–3000 m at its subsiding depocentre. This study investigated the chronology of the Quaternary deposits, including palaeomagnetics, biostratigraphic correlation, rates of sediment accumulation, seismic reflection surveys and electrical property correlations. The results give a full interpretation of ages for the sequence from bottom to top. The oldest sequence age was defined by the first appearance of Microlimnocythere sinensis Huang, and was placed in the Gauss Epoch, estimated at approximately 3 Ma by extrapolation of accumulation rates. The M/G boundary occurs at the base of the third fossil zone of Ostracoda (the first appearance of Qinghaicypris crassa Huang), or at the marker layer K 10 of the electrical log in the Sebei anticline area, considered here to be 2.48 Ma. The Olduvai event in the fifth fossil zone, spanning electrical layers K 4 and K 3 in the Sebei area, occurs at reflection layer T 0 −1 of seismic stratigraphy which could be stratigraphically correlated in the whole basin. The boundary of Early/Middle Pleistocene such as the Brunhes and Matsuyama (B/M) boundary, falls within the eighth fossil zone and coincides with electrical marker K 0 1. Two boundaries corresponding to Middle/Late Pleistocene and Pleistocene/Holocene occur at the bases of the 11th and 12th biozones respectively, neither of which can be correlated with seismic stratigraphy and electrical logs in the basin due to the lack of widely distributed lacustrine deposits since the Middle Pleistocene. The ages of the boundaries can be tested by deposition rates of different facies derived from the varves and synchronous deposits. As a result, geochronological sequences of subsurface stratigraphy could be established within a basin-wide area on the synchronology of seismic reflectors and correlations of electrical logs as well as biozones.

Cenozoic sedimentation and clay mineralogy in the northern part of the Magellan Trough, Central Pacific Basin

Assemblages of clay-sized minerals in twelve deep-sea cores from the northern part of the Magellan Trough in the Central Pacific Basin clearly show that authigenic smectite together with clinoptilolite formed subsea in situ and predominated throughout Palaeogene time. Clastic clay minerals such as chlorite, illite and kaolinite increased at the expense of smectite in sediments deposited since the Pliocene. Most of the authigenic smectites are of the di-octahedral, iron-rich type. The most probable origin of the authigenic smectites is formation from precursors such as volcanic glass. As part of this process biogenic silica evidently contributed to the formation of smectite and zeolites as clinoptilolite. The presence of a tri-octahedral saponite and the TEM morphology of some smectites, on the other hand, suggests that not all of the smectite studied was formed subsea in situ but that some had an allogenic origin. Systematic vertical changes in the assemblage of clay-sized minerals suggest that the authigenesis of submarine smectite and clinoptilolite prevailed in conditions of reduced aridity and weak wind activity throughout the Palaeogene in the study area. However, allogenic clay minerals such as chlorite and illite increased since the Olduvai event under conditions of severe aridity and strong wind activity caused by global climatic change. The west-northwest movement of the Pacific plate must have partly played a role in deposition of the clastic clay-sized minerals from the Asian continent by westerlies in the study area. The widespread occurrence of Cenozoic hiatuses in the study area is attributed to the influence of Antarctic Bottom Water (AABW). The latter must have influenced non-deposition of the clay-sized minerals at times during the Cenozoic.

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.

High-resolution stratigraphy and the response of biota to Late Cenozoic environmental changes in the central equatorial Pacific Ocean (Manihiki Plateau)

An undisturbed 16 m late Pliocene-Pleistocene sediment core spanning 2.6 Myr of deposition was recovered from the Manihiki Plateau by the German research vessel Sonne in 1990. This core 34KL complements the heavily disturbed late Pliocene-Pleistocene core sections of DSDP Site 317, and is well suited for stratigraphic correlation. The sediments consist of calcareous microfossils (93–97% CaCO 3), minor portions of siliceous microfossils and detrital minerals. All important calcareous microfossil zones could be identified and correlated with the magnetostratigraphic and isotope stratigraphic events, stages and periods. Due to the high degree of silica dissolution, the late Quaternary radiolarian Buccinosphaera invaginata Zone is the only siliceous fossil zone which could be identified. An interval with Globigerinoides gomitulus/pink was found within the middle Pleistocene which is clearly distinguished from the Globigerinoides ruber/pink interval of the late Pleistocene. The magnetostratigraphic Gauss-Matuyama and Matuyama-Brunhes boundaries as well as the Olduvai and Jaramillo events were clearly identified. The δ 180 curve displays the 100 kyr (Milankovitch) and the 41 kyr (Laplace) cyclicity periods. The beginning of the Laplace Period and the last occurrence of the calcareous nannofossil Discoaster brouweri, which marks the end of the Pliocene, fall within the base of the Olduvai Event. There is also a marked drop in sedimentation rates around this time, which seems to be a regional phenomenon. Prominent 3.5 kHz subbottom reflectors at 8 ms and 15 ms reflection time are related to lithologic changes near the Mid-Pleistocene Revolution (MPR) and the beginning of the Laplace Period or the Pleistocene, respectively. It is possible to trace these reflectors laterally to the eroded eastern edge of the Manihiki Plateau where they can be tied to older strata.

Magnetic anomoly patterns around the central rift area in the North Fiji Basin: Inversion approach for detailed structure

A detailed magnetic anomaly map around the central rift area in the North Fiji Basin was compiled from 6 starmer cruises. The data range is almost 800 km in length (between 22°S and 14°30′S), 100 km in width (between 173°E and 175°E). Detailed magnetic structure analysis was applied for the data around the rift axis, which revealed 5 or 6 segments along the 800 km long rift axis. Inversion trials were done on the grid data and good comparison with topographic features was obtained. The results of inversion indicate that the lineations which correspond to the Olduvai event were recognized in this area broadly, but not so common as those for the Gauss epoch. The central rift system seems to have started its spreading from around the end of the Gauss normal epoch or the beginning of the Matuyama reversed epoch (2.5 Ma).

An early pleistocene glacial-interglacial cycle in the breida vík group on Tjörnes, Iceland: Sedimentary facies, foraminifera, and molluscs

Sedimentary facies, foraminifera, and molluscs are used to reconstruct environmental conditions during the accumulation of the 1.5 Ma Svarthamar Member unit from the Tjörnes sequence, North Iceland. The Tjörnes sequence and the Breidavík Group in particular contains a unique record of Cainozoic glacier variations in the North Atlantic. This is reflected in lithological variations where marine and terrestrial sediments are intercalated between lava flows and pyroclastic rocks on Tjörnes Peninsula. Our results from the Svarthamar Member show that the lithological cycle from glacial to proglacial and then to shallow marine sedimentation coincide with faunal succession, reflecting a change from arctic to boreal arctic or even boreal conditions in the sea around Iceland just after the Olduvai event of the Matuyama. The amplitude of this climatic cycle is comparable to the Late Pleistocene glacial-interglacial cycles in the North Atlantic. This indicates that the North Atlantic current crossed the Greenland-Iceland and Iceland-Faroe ridges during interglacial periods resulting in a periodic northward shift of the polar front during at least a part of the Early Pleistocene.