Marine Oxygen Isotope Substage Research Articles

Arquitetura deposicional e datação absoluta das cristas de praia pleistocênicas no complexo deltaico do Paraíba do Sul (RJ)

Beach ridges are depositional features associated with prograding coasts, where each ridge represents an ancient shoreline. These features store records of coastal evolution during the Quaternary, especially when investigated with geochronological and morphostratigraphical methods. The Rio Paraiba do Sul delta complex has two extensive plains of of Holocene and Pleistocene beach ridges, the latter of which still insufficiently known. Therefore, the aim of this work is to characterize the sedimentary architecture of the Pleistocene ridges using GPR profiles, vibracores and absolute ages obtained by OSL and AMS. A radar facies was identified comprising a sequence of regressive or prograded barriers, with a depositional thickness of around oito meters. Beach ridges showed absolute ages of marine oxygen-isotope substage 5a (~85.000 ka), although some samples require analysis of more aliquots using the SAR protocol. The integration of GPR and OSL methods allowed identification of depositional units of the dated samples as well as the boundary between aeolian and foreshore radar facies, regarded as an indicator of mean sea level. This research resulted in the discussions about the genesis and evolution of beach ridges and the potentialities and limitations in association methods for investigation of Quaternary coastal plains.

ORIGINAL ARTICLE: Mass extinctions in the Azores during the last glaciation: fact or myth?

AbstractAim The influence of the last glaciation on the shallow‐water marine malacofauna of the Azores Islands is reviewed. We test, for this fauna, the ‘Pleistocene temperature theory’ of J.C. Briggs, which hypothesizes that a (supposed) lack of endemics in the older (Azorean endemic) fauna resulted from extinctions caused by a severe drop in sea surface temperatures during the Pleistocene.Location Santa Maria Island, Azores, Portugal.Methods We compare the fossil mollusc fauna of Prainha, Praia do Calhau and Lagoinhas Pleistocene outcrops with the recent mollusc fauna of the Azores Islands. We dated the fossil fauna, using shells of Patella aspera Röding, 1798, by standard U/Th methodology at the GEOTOP laboratory (Université du Québec à Montreal, Canada).Results Dating of the shells of P. aspera indicates that the deposition of the lower unit of the Prainha outcrop corresponded to Marine Oxygen Isotope Substage 5e (MISS 5e). Not a single endemic Azorean species of mollusc that is present in the Pleistocene fossil record has since become extinct, and we found no signs of ‘mass extinctions’ in the littoral marine molluscs of the Azores. The only species that were extirpated from these islands were thermophilic molluscs and littoral bivalves living in fine sand.Main conclusions Our results do not support Briggs’‘Pleistocene temperature theory’. Nor did we find evidence supporting the hypothesis that most of the marine organisms now present in the Azores recolonized the islands after the last glacial maximum.

Vegetation and climate changes during the Eemian and Early Weichselian in the Upper Volga region (Russia)

Ples is the key-section that represents the Mikulino (Eemian) interglaciation and early part of the Valdai (Weichselian) glacial epoch in the north-central Russia. Pollen profile of this section reflects spread of the broad-leaved forest dominated by Quercus, Ulmus, and Tilia with participation of Acer, Fraxinus and Carpinus in the optimum phase of the interglaciation. A gradual cooling and increasing humidity of climate brought about a decline in the broad-leaved forest and development of dark-coniferous communities ( Picea-Abies-Pinus sibirica) in the end of the interglaciation. It was followed by Scots pine and birch forest, and then replaced by communities of tundra shrubs with patches of the open birch forest. During the first post-Eemian cooling the climatic conditions were not uniform, as a short climatic amelioration separated it into two stages. This minor warming is indicated by an increase in birch woodland in complex plant cover. This first Early Weichselian cold stage was followed by a warm interstade, when mixed spruce-birch, and later larch-pine and spruce-pine forests occupied the region. This interstade, known as Verkhnevolzhskiy (Upper Volga) in the climatostratigraphic subdivision of the Late Pleistocene in the Russian Plain (after Grichuk [1961. Fossil floras as the basis for the Quaternary stratigraphy. In: Markov, K.K. (Ed.), Rel`ef i Stratigrafiya Chetvertichnykh Otlozheniy Severo-zapada Russkoi Ravniny, Izdatel'stvo AN SSSR, Moscow, pp. 25–71]), corresponds to the Brörup interstade in the northern Europe, or to Marine Oxygen Isotope Substage (MIS) 5c (e.g. Mangerud [1989. Correlation of the Eemian and the Weichselian with deep sea oxygen isotope stratigraphy. Quaternary International 3, 1–4.]). On the whole, we correlate the sediment sequence at Ples to the MIS from 5e to 5c.

The environment of Venice area in the past two million years

A ca. 950 m thick succession that was continuously cored in 1971 in Venice has been revisited, in order to reconstruct the environmental history of the Venice area since about 2.15 Ma. Magnetic polarity stratigraphy, integrated with refined calcareous nannofossil biostratigraphy, provides a firm chronostratigraphic framing of the succession. In order to improve the chronological resolution, we derived astrochronological refinements in the lower Pleistocene sapropel-bearing interval by a comparison with other time-correlative sections in the Mediterranean. The pollen record is used as a proxy of climatic changes and as an indirect tool in the chronological reconstruction in the upper part of the succession. The following history has been inferred: (1) in the late Gelasian (late Pliocene), the depositional area was a strongly subsiding shelf which shoaled to near sea level; (2) following a hiatus of a minimum duration of 0.2 Myr, encompassing most of the Olduvai Subchron, the shelf rapidly drowned to bathyal depths over the early Pleistocene (biozones MNN 19a to 19e: from 1.947 Ma to 0.96 Ma). This interval was characterized by starved sedimentation (less than 10 cm/kyr), represented by hemipelagic muds interbedded with sapropel layers; (3) during most of biozone MNN19f ( Pseudoemiliania lacunosa Zone, 0.96–0.42 Ma) a thick package of turbidites was laid down as a result of massive terrigenous input from the eastern Southern Alps; (4) later, in the middle part of Chron 1n (Brunhes), deltaic sedimentation, primarily related to the progradation of the paleo-Po system, led to the progressive infill of the basin. This progradational episode was a major building phase, and ended with the first appearance of continental sediments, tentatively correlated with marine oxygen isotope substage 8.4; (5) the upper part of the succession shows a cyclic organization, with an upward increasing amount of marginal-marine and subaerial deposits. In this interval the Venice area was below sea level during glacioeustatic highstands but became emergent during subsequent major glacioeustatic lowstands. Pollen data support an overall good correspondence of continental sediment packages of sequences with glacial conditions and of maximum flooding intervals with interglacial conditions.

The marine Eemian of the Baltic: new pollen and diatom data from Peski, Russia, and Põhja‐Uhtju, Estonia

AbstractSeveral relatively well‐preserved last interglacial (Eemian, marine oxygen isotope substage 5e; ca. 130–116 ka) deposits containing marine diatom flora have been found in Finland. In addition to these Finnish sites, more numerous Eemian (Mikulino) marine deposits are known from the northwestern part of Russia and from Estonia.Two new clayey and silty deposits covered by till, one at Peski, Russia, and the other Põhja‐Uhtju, Estonia, were studied for pollen and diatom content. At Peski, the deposit representing the Eemian interglacial is 3.8 m thick. The polyhalobous diatom flora in the Corylus and Carpinus zones indicates the maximum of the marine transgression during the climatic optimum. Later, the increasing proportion of brackish water diatom flora indicates a lowering in the relative sea‐level, and finally, during a very late phase of the Eemian, the sharply increasing proportion of freshwater species indicates the isolation of the sedimentary basin from the Eemian Sea.At Põhja‐Uhtju, according to the pollen, the Eemian deposit is 3.5 m thick. Diatoms occur only in a layer 1.6 m thick, which represents the period of Corylus and Carpinus zones, and thus the period of the climatic optimum. The brackish–marine diatom flora consists mainly of littoral, shallow‐water species.Although Peski is situated at a higher altitude than Põhja‐Uhtju at present, the diatom stratigraphy at Peski indicates deeper and more saline conditions than at Põhja‐Uhtju during the Eemian. This probably is the result of variations in glacio‐isostatic rebound between these sites, which can be accounted for by differences of the ice load during the final phase of the Saalian glaciation. Copyright © 2002 John Wiley & Sons, Ltd.

Middle Pleistocene interglacial deposits at Barling, Essex, England: evidence for a longer chronology for the Thames terrace sequence

AbstractResults are presented from a multidisciplinary study of fossiliferous interglacial deposits on the northern side of the Thames estuary. These fill a channel cut into London Clay bedrock and overlain by the Barling Gravel, a Thames–Medway deposit equivalent to the Lynch Hill and Corbets Tey Gravels of the Middle and Lower Thames, respectively. The channel sediments yielded diverse molluscan and ostracod assemblages, both implying fully interglacial conditions and a slight brackish influence. Pollen analysis has shown that the deposits accumulated during the early part of an interglacial. Plant macrofossils, particularly the abundance of Trapa natans, reinforce the interglacial character of the palaeontological evidence. A beetle fauna, which includes four taxa unknown in Britain at present, has allowed quantification of palaeotemperature using the mutual climatic range method (Tmax 17 to 26 °C; Tmin −11 to 13 °C). A few vertebrate remains have been recovered from the interglacial deposits, but a much larger fauna, as well as Palaeolithic artefacts, is known from the overlying Barling Gravel.The age of the interglacial deposits is inferential. The geological context suggests a late Middle Pleistocene interglacial, part of the post‐diversion Thames system and therefore clearly post‐Anglian. This conclusion is supported by amino acid ratios from the shells of freshwater molluscs. The correlation of the overlying Barling Gravel with the Lynch Hill/Corbets Tey aggradation of the Thames valley constrains the age of the Barling interglacial to marine oxygen isotope stages 11 or 9. The presence of Corbicula fluminalis and Pisidium clessini confirms a pre‐Ipswichian (marine oxygen isotope substage 5e) age and their occurrence in the early part of the interglacial cycle at Barling precludes correlation with marine oxygen isotope stage 11, as these taxa occur only later in that interglacial at sites such as Swanscombe and Clacton. Thus by process of elimination a marine oxygen isotope stage 9 age would appear probable. Copyright © 2001 John Wiley & Sons, Ltd.

Last Interglacial (isotope stage 5) glacial and sea-level history of coastal Chukotka Peninsula and St. Lawrence Island, Western Beringia

Study of glacial and marine sequences along the outer coast of Chukotka Peninsula, Bering Strait, is the basis for major revisions of the regional stratigraphy. The Val’katlen Suite at its type section at the mouth of the Enmelen River records the youngest high sea stand of the last interglaciation on Chukotka Peninsula. Marine deposits and glacial diamicton stratigraphically below the type section record, respectfully, the peak of the last interglacial (marine oxygen-isotope substage 5e) and rapid glacierization of the coastal mountains probably during substage 5d or 5b. Correlative deposits recording a similar sequence of intra-stage 5 events, but once thought to be of early and middle Pleistocene age, include the Upper and Lower Pinakul’ Suite at Cape Pinakul’ and marine deposits near the Nunyamo River on the Gulf of Anadyr, based upon amino-acid analyses, biostratigraphy, and supporting geochronology. These deposits enclose warmer-than-present faunas and floras comparible to last interglacial Pelukian marine deposits found along the coast of Alaska. The last major advance of glacial ice from Chukotka Peninsula across Anadyr Strait and onto St. Lawrence Island was likely initiated during the later part of stage 5 based on our reinterpretaion of the stratigraphy at Cape Pinakul’, near the Nunyamo River, and on northwestern St. Lawrence Island. Chukotkan ice probably reached St. Lawrence Island sometime during oxygen-isotope stage 4. Ice extend across Chukotka during the LGM was very imited.

Marine late Saalian to Eemian environments and climatic variability in the Danish shelf area

AbstractThe marine Eemian (marine oxygen-isotope substage 5e: MIS 5e) is represented by shallow-water deposits in southern and western Denmark, while relatively deep-water environments occurred to the north and north-east, where complete interglacial successions seem to be present. We present an overview of the marine Eemian deposits in Denmark, and discuss in more detail indications of climate variability, both for the late Saalian and within the Eemian.

Paleontological evidence of a brief global sea‐level event during the last interglacial

A gently undulating to flat erosion surface with shallow-water borings and burrows is present in the midst of a Sangamonian (Eemian; marine oxygen isotope substage 5e) reefal facies on the islands of San Salvador and Great Inagua, Bahamas. Precise U/Th dating of corals above and below this surface show that it formed around 125-124 ka, and that the sea-level regressive-transgressive cycle which produced it lasted for 1500 years or less. The surface occurs on entirely carbonate rocks and has a low relief punctuated by erosional channels and karstic caves formed during the sea-level lowstand. A terra rossa paleosol, developed during that lowstand, partially fills a set of large lithophagid bivalve borings (Gastrochaenolites torpedo), showing that they were excavated during the regression. Rhizomorphs formed by plant roots occur on the erosion surface at Great Inagua. Extensive boring of the upward-facing surfaces occurred during the ensuing transgression, including a smaller G. torpedo and a clionid sponge boring (Entobia ovula). The bored surface is encrusted by a variety of shallow-water corals and, eventually, the re-established bank-barrier coral reefs. A sparse assemblage of serpulid worm and vermicularid gastropod tubes encrusted the channel and cave walls. Robust Ophiomorpha burrow systems occur within pockets of sediment in the coral facies both below and above the erosion surface. The channels and caves are filled with transgressive calcarenitic sediments in which occur numerous Ophiomorpha and Skolithos burrows. The ichnofossils on, below, and above this erosion surface are prominent indicators of a short-lived but significant global sea-level event.

Absence of Glaciation in Illinois during Marine Isotope Stages 3 through 5

A10Be inventory and14C ages of material from a core from northernmost Illinois support previous interpretations that this area was ice free from ca. 155,000 to 25,000 yr ago. During much of this period, from about 155,000 to 55,000 yr ago,10Be accumulated in the argillic horizon of the Sangamon Geosol. Wisconsinan loess, containing inherited10Be, was deposited above the Sangamon Geosol from ca. 55,000 to 25,000 yr ago and was subsequently buried by late Wisconsinan till deposited by the Lake Michigan Lobe of the Laurentide Ice Sheet. The Sangamonian interglacial stage has been correlated narrowly to marine oxygen isotope substage 5e; our data indicate instead that the Sangamon Geosol developed during late stage 6, all of stages 5 and 4, and early stage 3.

Suborbital timescale variability of North Atlantic Deep Water during the past 200,000 years

We generated ∼200‐kyr‐long proxy records of surface and deepwater variability from a subpolar North Atlantic core (V29–202), enabling us to assess the linkage between surface and deepwater changes on suborbital timescales. In particular, we used a benthic δ13C record to evaluate the deep water response to Dansgaard‐Oeschger temperature oscillations and to Heinrich events, times of massive iceberg delivery to the North Atlantic. We found that the reduction of North Atlantic Deep Water (NADW) production was generally associated with cold or dropping sea surface temperatures (SSTs) as indicated by planktonic foraminiferal assemblages. The NADW contribution to the site did not drop appreciably during Heinrich events H4 through H2, probably because these events followed intervals of prolonged surface cooling already characterized by low rates of NADW production. By contrast NADW reduction appears to have been synchronous with H5. SST rise associated with both Dansgaard‐Oeschger oscillations and Heinrich events was usually accompanied by increasing NADW strength. In a few cases the NADW recovery appeared to lag the SST rise; however, the apparent delay is most likely an artefact of the sedimentary record (low concentrations of benthic foraminifera). As a result of low benthic foraminiferal abundances during stage 6, the stage 6 benthic foraminiferal δ13C record is of lower resolution than the younger part of the record. The stage 6 proxy records for surface hydrography nevertheless reveal millennial‐scale oscillations similar to those seen in stage 3. The available δ13C data suggest that NADW weakened in association with the cold portions of stage 6 SST oscillations. We also sought to confirm a recent study which concluded that there was little NADW variability during the peak of the last interglaciation, marine oxygen isotope substage 5e (Eemian). Isotope stage 5 was marked by a trend of increasing benthic δ13C in V29‐202. Rising δ13C through isotope stage 5 is also seen in tropical surface water records and at some deep Atlantic sites and may reflect the common derivation of these water masses. Variations of ≥ 0.5 ‰ superimposed on this rising δ13C trend within substage 5e in V29‐202 are so far not evident in tropical feed waters and may therefore indicate that NADW production was weaker during the late than mid‐Eemian.An electronic supplement of this material may be obtained on a diskette or Anonymous FTP from KOSMOS.AGU.ORG. (LOGIN to AGU's FTP account using ANONYMOUS as the username and GUEST as the password. Go to the right directory by typing CD APEND. Type LS to see what files are available. Type GET and the name of the file to get it. Finally, type QUIT to leave the system.) (Paper 95PA02089, Suborbital timescale variability of North Atlantic Deep Water during the past 200,000 years, by D. W. Oppo and S. J. Lehman) Diskette may be ordered from American Geophysical Union, 2000 Florida Avenue, N.W., Washington, DC 20009; $15.00. Payment must accompany order.

Stratigraphic Evidence of a Pre-Wisconsinan Interglaciation in the Adirondack Mountains, New York

Multiple tills separated by interbedded lake sediments were temporarily exposed during open-pit mining at Sanford Hill, near Newcomb, in the central Adirondack Mountains of northeastern New York. Radiocarbon ages of wood fragments from brown clay between two tills at that site indicate an age older than 55,000 yr B.P. A pollen profile in the brown pond clay (Tahawus clay) records a transition from initial domination by pine, spruce, and birch to an oak pollen zone. The upward disappearance of spruce and decrease of pine and birch are accompanied by diversification and increase in hardwood pollen. This assemblage includes several warm-climate hardwood species that are not represented in the postglacial flora of the region, suggesting that the biota existed during an interglacial or interstadial interval that was warmer and/or longer than postglacial time. Accordingly, the Tahawus clay is tentatively assigned to the Sangamon interglaciation, and probably to marine oxygen isotope substage 5e. Truncation of the Tahawus clay by glacial erosion may account for the absence of a Sangamon paleosol.

Quaternary glacial and marine stratigraphy of the Qivitu Peninsula, northern Cumberland Peninsula, Baffin Island, Canada: Summary

Sediments exposed along the outer coast of the Qivitu Peninsula record the advances and retreats of glaciers in the fiords bordering the peninsula and accompanying sea-level fluctuations during the Quaternary. Seven main lithofacies and 21 subfacies are recognized, based on texture, color, bed thickness and lateral extent, internal structures, and abundance of macrofossils. In contrast to earlier work in the area, the interpretation of lithofacies genesis using a model of fiord glaciomarine sedimentation suggests that all lithofacies are of marine or glaciomarine origin with no evidence of grounded ice extending seaward of the peninsula. The abundance and diversity of benthic foraminifera in selected samples and in situ subarctic molluscs shows that relatively warm water was present along the east Baffin Island coast during several periods of extensive fiord glaciers. Analysis of upward facies transitions in 54 stratigraphic sections suggests that facies sequences are cyclical. These sedimentation cycles are interpreted in terms of glacier-sea-level responses during glacial/interglacial cycles. Detailed relative time control for the lithofacies sequence is provided by time-dependent amino-acid ratios on the common shell fragments in many stratigraphic units. Because the stratigraphic sequence is marked by significant unconformities due to relative sea-level regressions near the end of each glacial sedimentation cycle, amino-acid ratios on molluscs contemporaneous with particular cycles are statistically similar and distinct from ratios for older and younger cycles. Thus, although few stratigraphic units can be physically traced for more than 0.5 km, aminozones based on groups of animo-acid ratios allow chronocorrelation and relative dating of units in each sedimentation cycle. The Qivitu stratigraphic sequence is divided into two formations consisting of a total of seven members for which formal names are proposed. Sediments predating the two most recent interglacials are lithologically similar to later beds, suggesting that events during these earlier periods were of the same character as those of later glacial/interglacial cycles. Biostratigraphic evidence suggests that a relatively mild climate prevailed in this region during the Clyde and Ayr Lake glaciations and intervening Cape Broughton aquatherm. The Quajon interstade is correlative With the marine sediments deposited near the end of the Ayr Lake glaciation rather than the Cape Broughton aquatherm. Soil horizons indicate regressions at the end of the Cape Broughton aquatherm and Ayr Lake glaciation, and pollen assemblages suggest that the terrestrial climate may have been warmer than the present climate. A reinterpretation of U-series dates and amino-acid ratios on shells suggests that the Cape Broughton aquatherm and earlier events predate marine oxygen-isotope substage 5e. The Ayr Lake glaciation may have occurred well before the major interglacial-glacial transition in more temperate latitudes, but evidence from ocean cores in the North Atlantic and ice cores from Greenland and Devon Island supports the interpretation of warm-water incursions into Baffin Bay during this ice advance following substage 5e. By inference, relative sea level during the period following the Ary Lake glaciation was lower than present sea level, and glacier extent was restricted; no evidence of an exceptionally cold, dry climate has been found, however. Distal glaciomarine sediments in the upper coastal cliffs suggest a limited readvance of fiord glaciers prior to the Holocene. Near the beginning of the Holocene (10,000 yr B.P.), warmer water extended into the area as relative sea level fell and subsequently rose again to 15 m about 8,200 yr B.P. Pollen assemblages in peat horizons suggest that during the earliest Holocene, a climate milder than that of the present day existed. Local deposition of eolian and soliflucted sediment may indicat deteriorating climate in late Holocene time.