Marine Oxygen Isotope Stratigraphy Research Articles

Local Differentiation in the Loess Deposition as a Function of Dust Source: Key Study Novo Orahovo Loess Paleosol Sequence (Vojvodina, Serbia)

Typical patterns of the Late Pleistocene loess–paleosol units are preserved in the Novo Orahovo brickyard, Northern Serbia. Presented preliminary luminescence chronology supports the chronostratigraphic interpretations of global isotopic marine climate reconstructions. Magnetic susceptibility and sedimentological evidence exhibit general similarities with the marine oxygen-isotope stratigraphy. These records provide new insights into the dust accumulation regimes over the eastern side of the Bačka loess plateau and offer new paleoenvironmental information for the region. They represent an important step forward towards the establishment of a catena from the thin loess-like sediments of the Banat foothills in the east towards the thicker and seemingly more complete loess sections of the southeastern and central Carpathian Basin. Grain-size data from the loess record of Nova Orahovo explain the regional differentiation in dust deposition.

Dryland dunes and other dryland environmental archives as proxies for Late Quaternary stratigraphy and environmental and climate change in southern Africa

AbstractThe Namib Desert and the Kalahari constitute the drylands of southern Africa, with the current relatively humid portions of the latter having experienced periodically drier conditions during the Late Quaternary. This study explores the range of dryland archives and proxies available for the past ~190 ka. These include classic dryland geomorphological proxies, such as sand dunes, as well as water-lain sediments within former lakes and ephemeral fluvial systems, lake shorelines, sand ramps, water-lain calcrete and tufa sediments at the interface of surface hydrological and hydrogeological, speleothems and groundwater hydrogeological records, and hyrax middens. Palaeoenvironmental evidence can also be contained within geoarchaeological archives in caves, overhangs and rockshelters. This integration of records is undertaken with the aim of identifying a (or a number of) terrestrial regional chronostratigraphic framework(s) for this time period within southern Africa, because this is missing from the Quaternary stratigraphy lexicon. Owing to a lack of long, near-continuous terrestrial sequences in these drylands, the correspondence between nearby terrestrial records are explored as a basis for parasequences to build this chronostratigraphy. Recognising the modern climatological diversity across the subcontinent, four broad spatial subdivisions are used to explore potential sub-regional parasequences, which capture current climatic gradients, including the hyper-arid west coast and the decrease in aridity from the southwest Kalahari toward the north and east. These are the Namib Desert, the northern Kalahari, the southern Kalahari and the eastern fringes of the southern Kalahari. Terrestrial chronostratigraphies must start from premise that climate-driven environmental shifts may have occurred independently to those in other terrestrial locations and may be diachronous compared to the marine oxygen isotope stratigraphy (MIS), which serves as a global-scale master climatostratigraphy relating to global ice volume. The fragmented nature of preserved evidence means that we are still some way from producing unambiguous parasequences. There is however, a rich record to consider, compile and compare, within which seven broad wetter intervals are identified, with breaks between these inferred to be relatively drier, and some also have proxy evidence for drying. The onset and cessation of these wetter intervals does not align with MIS: they occur with greater frequency, but not with regular periodicity. Precession-paced insolation forcing is often invoked as a key control on southern African climate, but this does not explain the pacing of all of the identified events. Overall, the pattern is complex with some corresponding wetter intervals across space and others with opposing west-east trends. The evidence for drying over the past 10 ka is pronounced in the west (Namib Desert), with ephemerally wet conditions in the south (southern Kalahari). The patterns identified here provide a framework to be scrutinised and to inspire refinements to proposed terrestrial chronostratigraphies for southern Africa. Considering changes across this large geographic area also highlights the complexity in environmental responses across space as we continue to test a range of hypotheses about the nature of climatic forcing in this region.

Terrestrial stratigraphical division in the Quaternary and its correlation

Initially, terrestrial evidence formed the foundation for the division of Quaternary time. However, since the 1970s there has been an abandonment of the terrestrial stage chronostratigraphy, which is based on locally dominated successions, in favour of the marine oxygen isotope stratigraphy which largely records global-scale changes in ice volume. However, it is now clear that glacial records around the world are asynchronous, even at the scale of the continental ice sheets which display marked contrasts in extent and timing in different glacial cycles. Consequently, the marine isotope record does not reflect global patterns of glaciation, or other terrestrial processes, on land. This has led to inappropriate correlation of terrestrial records with the marine isotopic record. The low resolution of the latter has led to a preferential shift towards high-resolution ice-core records for global correlation. However, even in the short term, most terrestrial records display spatial variation in response to global climate fluctuations, and changes recorded on land are often diachronous, asynchronous or both, leading to difficulties in global correlation. Thus, whilst the marine and the ice-core records are very useful in providing global frameworks through time, it must be recognized that there exist significant problems and challenges for terrestrial correlation.

Plio-Pleistocene transition in the continental record from Lake Baikal: Diatom biostratigraphy and age model

Lake Baikal basin in the continental interior Asia preserved a unique continuous sedimentary archive of the late Cenozoic; large-scale regional environmental changes of the past were recorded in the composition of fossil diatom flora. Here, the Lake Baikal planktonic diatom biostratigraphy is extended over the Plio-Pleistocene transition, it includes 11 new local diatom assemblage zones (LDAZ) for the time interval 1.25–3.6 Ma. The comparison of the parallel BDP-96-1 and BDP-98 drill core records allows constructing the complete diatom biostratigraphic record at the time of the inception of the Northern Hemisphere glaciations; diatom biostratigraphic zones around Matuyama/Gauss paleomagnetic reversal are correlated with individual stages of marine oxygen isotope stratigraphy. Contrary to previous assumptions, the period 2.8–2.6 Ma in Lake Baikal record was characterized not by a prolonged minimum in diatom abundance but by a distinct maximum in the abundance of small-celled diatom taxa Tertiarius baicalensis and Stephanodiscus binderanus et var. hyalinus, which proliferated in the lake during the interval of relatively warm and humid climate. The Lake Baikal diatom biostratigraphic change at around 1.8 Ma occurs only at a species level of the genus Cyclotella. By contrast, around 2.8–2.5 Ma, spectacular appearances and extinctions occurred at a high taxonomic level of genera (including the genera of Tertiarius, Thalassiobeckia and Stepahanopsis) making the biostratigraphic changes around Matuyama/Gauss reversal more prominent. At least three distinct biostratigraphic boundaries are observed: at 2.69 Ma, 2.65 Ma and at 2.46 Ma. None of these boundaries, however, coincides with the paleomagnetic reversal at 2.58 Ma. Thus the new well-resolved Lake Baikal biostratigraphic record points to the difficulty of assigning a single ‘golden spike’ biostratigraphic boundary around Matuyama/Gauss paleomagnetic reversal in continental Asia.

High resolution OSL dating back to MIS 5e in the central Sea of Okhotsk

Marine sediments contain important archives of past ocean and climate changes, but at high latitudes the absence of carbonate has prevented the construction of accurate chronological models. We have begun a study to (1) determine the accuracy of luminescence ages in deep-sea marine sediments, e.g. by comparison with marine oxygen isotope stratigraphy where possible, (2) describe changes in sedimentation rate through time, and (3) test whether it is possible to date back to marine isotope stage 5e (MIS 5e). We show here that optical dating of fine grains of quartz from the central Sea of Okhotsk is able to provide an accurate and precise chronology for the reconstruction of the palaeoceanic and palaeoclimatic environment at our site. The upper 6.5 m of the 18.42 m long core MR0604-PC07A is believed, based on its magnetic susceptibility and the oxygen isotope (δ 18O) records to contain the last ∼150 ka. Forty OSL samples were taken from this upper part of the core. The single-aliquot regenerative-dose (SAR) procedure is used for equivalent dose (D e) determination. The luminescence characteristics of fine-grained quartz (4–11 μm) extracted from the core are described. The OSL signal is dominated by the fast component and a dose recovery test shows that we can accurately measure a known dose given in the laboratory prior to any heat treatment. Dose rates were determined using high-resolution gamma spectrometry, and vary between 0.4 and 1.6 Gy/ka. The OSL ages from this section lie between ∼140 ka and ∼15 ka and are in very good agreement with the δ 18O stratigraphy up to MIS 5e. A clear change in sedimentation rate is identified: between ∼139 and 110 ka, the sedimentation rate was ∼0.09 m/ka, but then from ∼110 to 15 ka, the sedimentation rate decreases to a constant value of ∼0.04 m/ka. Our data confirm that OSL dating using widely distributed fine-grain quartz has great potential for dating deep-sea sediments. Because luminescence methods use clastic materials, they do not depend on the presence of biogenic carbonate. As a result it is now likely that we can establish a chronology in regions of the ocean that were previously undatable.

Diatom biostratigraphy of Lake Baikal during the past 1.25 Ma: new results from BDP-96-2 and BDP-99 drill cores

Detailed diatom zonation in the Lake Baikal holostratotype section BDP-96-2 is extended over the interval 0.85–1.25 Ma and compared with diatom assemblage composition from the new BDP-99 drill core. Interglacial diatom assemblages at these two sites over 220 km apart are of similar composition, and the same complete and continuous succession of diatom zones is observed in both drill cores over the 0–800 ka interval. We propose a correlation of Baikal diatomaceous intervals with the marine oxygen isotope stratigraphy and with European climato-stratigraphic divisions of the early Pleistocene. We then use the diatom succession in BDP-96-2 to demonstrate evidence for disconformity in BDP-99 and to establish an approximate age model for this section. Diatom assemblages characteristic of the top of the Matuyama reversed polarity interval and the upper part of the Jaramillo normal polarity subchron are not found in the BDP-99 section below the disconformity boundary. The lack of diatom zones corresponding to the MIS 21-27 of the marine oxygen isotope stratigraphy in BDP-99 section suggests that the estimated age span of missing sediment interval in BDP-99 is ca 150–160 ka. The unusual diatom assemblage of cosmopolitan species during MIS 33 in both BDP-96-2 and BDP-99 drill core sections is indicative of abrupt ecological changes in the time interval 1.12–1.08 Ma.

Stratigraphy and distribution of tephra layers in marine sediment cores from the Faeroe Islands, North Atlantic

The stratigraphical position of eight discrete tephra layers is investigated in four marine sediment cores from north and south of the Faeroe Islands. The tephras are correlated to the marine oxygen isotope stratigraphy and the interstadial/stadial cycles (Dansgaard–Oeschger cycles) of the Greenland ice cores. A very prominent volcanic event occurred during interstadial 23 in Marine oxygen Isotope Stage (MIS) 5c correlating with a cold event within this otherwise warm interval. Two tephra horizons in MIS 5a correlate with the beginning and end of interstadial 21, respectively. The most widely distributed ash is the well-known Ash Zone 2 from the lower part of MIS 3. In the two cores from north of the Faeroe Islands, it consists of two discrete layers, a lower one composed of rhyolitic and basaltic tephra and an upper layer composed exclusively of basaltic glass. The two tephra falls coincide with the two warm intervals of Dansgaard–Oeschger cycle No. 15. A hitherto unknown basaltic tephra was recorded just above Heinrich event H4 in the lower part of the warm interstadial 8 and dated to ca. 33 14C ka BP. Another frequently recorded layer termed the Fugloyarbanki Tephra is likewise basaltic. It is dated to 23.1 14C ka BP. It was deposited after the peak warm phase of interstadial 3 at the MIS 3/2 transition. Finally, a tephra dated ca. 15.4 14C ka BP was found in two cores from north of the ridge. It was deposited at the beginning of the deglaciation between the Last Glacial Maximum and Heinrich event H1.

Luminescence dating of loess–palaeosol sequences and coversands: methodological aspects and palaeoclimatic implications

Of the terrestrial archives, loess–palaeosol sequences provide a most complete record of climatic change. This may be compared with the Marine oxygen isotope stratigraphy, and may help in the reconstruction of past atmospheric circulation patterns. Numerical chronometry of loess–palaeosol sequences has generally been based on correlation of variations in climatic proxies (such as magnetic susceptibility and particle sizes) with Marine isotopic data. Such chronometric assignments involve implicit assumptions about the constancy of sedimentation rates and particle fluxes through time. This review presents a brief survey of the present status, methodology, outstanding problems and interpretational aspects of luminescence techniques, and discusses the import of luminescence ages on global land–sea correlations. Statistical analysis of the ages suggests episodicity of loess accumulation with extended periods of quiescence. Recent luminescence dating studies on closely spaced samples also lead to a similar inference. Luminescence ages imply high variability in loess sedimentation rates. This conflicts with the assumption, made in some current attempts to correlate loess records with marine records, of almost constant particle fluxes. A review of source-proximal coversand deposits of northwest Europe is also presented. Evidence of the onset of coversand deposition at 15 ka, with a peak in accretion during the Younger Dryas and subsequent minor reactivation episodes, is discussed.

A global perspective of the European chronostratigraphy for the past 650 ka

Characteristic global climatic events are employed to interpret the regional, land-based European stratigraphy. The Chinese loess record shows well expressed, continuous and reliably dated climatic signals of worldwide significance, which are well correlated with the marine oxygen isotope stratigraphy. The sequence in the surroundings of Ferdinandow in Poland plays a key role in the correlation of the European stratigraphy with the loess record and the oxygen isotope record. In particular, the complex but well-expressed Ferdinandowian Interglacial is a key marker because it shows striking similarities with the most pronounced soil complex of the last 700 ka years of the Chinese loess sequence (S5) and, by correlation, Oxygen isotope stages (OIS) 13–15. It follows that the Holsteinian Interglacial corresponds with the S4-soil and OIS 11. This appears to be confirmed by sequences deposited in the craters of the Central Massif, France. Problems of regional stratigraphical correlation in Europe persist, but is suggested that a general framework is now established.

Chronostratigraphy and correlation of the Pliocene and Quaternary of Colombia

Abstract Names for the chronostratigraphic units of the Pliocene and Quaternary of Colombia are defined and formalized based on studies of outcrops and deep bore holes in the area of the high plain of Bogota. Chronostratigraphic, biostratigraphic and lithostratigraphic sequences have been correlated as far as possible. A tentative correlation with the marine oxygen isotope stratigraphy is indicated. Pliocene chronostratigraphic units are provisionally characterized by abundance/first appearance in the pollen record of specific floral elements: Mauritia zone (Tequendamian: ca. 5.5-4.2 Ma), Hedyosmum zone (Facatativanian: ca. 4.2-3.5 Ma), Myrica zone (Sisganian: ca. 3.5-3.1 Ma), Borreria zone (Chocontanian: ca. 3.1-2.7 Ma and Engativanian: ca. 2.7-2.4/2.2 Ma), although precise boundaries cannot yet be established. The Engativanian is a transitional phase, characterized by a continuous temperature decrease in successive cold episodes, and may include the latest part of the Pliocene and the earliest part of the Quaternary. Quaternary chronostratigraphic units are precisely limited by levels of pronounced climatic change; these boundaries are near to the first appearance/abundance of Juglans-Plantago (Funzanian: ca. 2.4/2.2-1.0 Ma), Alnus (Fuchanian: ca. 1000-660 ka and Cotanian: ca. 660-335 ka), and Quercus (Subanian: ca. 335-128 ka, Bacatanian: ca. 128-73 ka, Fuquenian: ca. 73-10 ka, and the Holocene). The relationship with the officially defined position of the base of the Quaternary, at ca. 1.80 Ma, is shown. The last glaciation in Colombia is named the Cocuy glaciation.

Orbital forced frequencies in the 975 000 year pollen record from Tenagi Philippon (Greece)

Frequency analysis was applied to different time series obtained from the 975 ka pollen record of Tenagi Philippon (Macedonia, Greece). These time series are characteristic of different vegetation types related to specific climatic conditions. Time control of the 196 m deep core was based on 11 finite C-14 dates in the upper 17 m, magnetostratigraphy and correlation with the marine oxygen isotope stratigraphy. Maximum entropy spectrum analyses and thomson multi-taper spectrum analysis were applied using the complete time series. Periods of 95-99, 40-45, 24.0-25.5 and 19-21 ka which can be related to orbital forcing, as well as periods of about 68, 30 ka and of about 15.5, 13.5, 12 and 10.5 ka were detected. The detected periods of about 68, 30 ka and 16, 14, 12, 10.5 ka are likely to be harmonics and combination tones of the periods related to orbital forcing. The period of around 30 ka is possibly a secondary peak of obliquity. To study the stability of the detected periods through time, analysis with a moving window was employed. Signals in the eccentricity band were detected clearly during the last 650 ka. In the precession band, detected periods of about 24 ka show an increase in amplitude during the last 650 ka. The evolution of orbital frequencies during the last 1.0 Ma is in general agreement with the results of other marine and continental time series. Time series related to different climatic settings showed a different response to orbital forcing. Time series of vegetational elements sensitive to changes in net precipitation were forced in the precession and obliquity bands. Changes in precession caused changes in the monsoon system, which indirectly had a strong influence on the climatic history of Greece. Time series of vegetational elements which are more indicative of changes in annual temperature are forced in the eccentricity band.

The last full glacial cycle in the Australian region

A broad regional reconstruction of climate in the eastern half of Australia through the last full glacial cycle is attempted incorporating a diversity of evidence from a wide range of environments. The critical climatic feature over much of the continent has been variation in precipitation. The majority of studies indicate that cool phases have been dry, and warm phases, wet. Recent, well-dated sequences combined with the refinement and reinterpretation of some existing records strongly suggest, however, that temperature and effective precipitation have not been in phase. Instead, wettest conditions appear to correspond with the interstadials within the latter part of Stage 5 of the marine oxygen isotope stratigraphy rather than with the Last (full) Interglacial or with the Holocene. Driest conditions most likely occured during the transition from the peak of the Last Glacial to the Holocene. The use of this period, however, as a model for cyclical climatic variation for the late Quaternary in Australia is limited to some extent by the likely impact of Aboriginal people on the landscape.