1,721,023 research outputs found
Extracting a detailed magnetostratigraphy from weakly magnetized, Oligocene to early Miocene sediment drifts recovered at IODP Site U1406 (Newfoundland margin, northwest Atlantic Ocean)
No full textFine-grained magnetic particles in deep-sea sediments often statistically align with the ambient magnetic field during (and shortly after) deposition and can therefore record geomagnetic reversals. Correlation of these reversals to a geomagnetic polarity time scale is an important geochronological tool that facilitates precise stratigraphic correlation and dating of geological records globally. Sediments often carry a remanence strong enough for confident identification of polarity reversals, but in some cases a low signal-to-noise ratio prevents the construction of a reliable and robust magnetostratigraphy. Here we implement a data-filtering protocol, which can be integrated with the UPmag software package, to automatically reduce the maximum angular deviation and statistically mask noisy data and outliers deemed unsuitable for magnetostratigraphic interpretation. This protocol thus extracts a clearer signal from weakly magnetized sediments recovered at Integrated Ocean Drilling Program (IODP) Expedition 342 Site U1406 (Newfoundland margin, northwest Atlantic Ocean). The resulting magnetostratigraphy, in combination with shipboard and shore-based biostratigraphy, provides an age model for the study interval from IODP Site U1406 between Chrons C6Ar and C9n (∼21-27 Ma). We identify rarely observed geomagnetic directional changes within Chrons C6Br, C7r, and C7Ar, and perhaps within Subchron C8n.1n. Our magnetostratigraphy dates three intervals of unusual stratigraphic behavior within the sediment drifts at IODP Site U1406 on the Newfoundland margin. These lithostratigraphic changes are broadly concurrent with the coldest climatic phases of the middle Oligocene to early Miocene and we hypothesize that they reflect changes in bottom-water circulation
Oligo-Miocene oxygen isotope and carbon record from IODP Site 342-U1406
No full textThese data contain a new high-resolution benthic foraminiferal oxygen isotope (d18Ob) record spanning ~26-22 Ma from Integrated Ocean Drilling Program Expedition 342 Site U1406 (Newfoundland Margin, Northwest Atlantic Ocean, ~40°N, 51°W; 3.8 km water depth). Oxygen isotopes of Cibicidoides mundulus (size range 125-250 micrometer) were generated using a Thermo Fisher Scientific MAT 253 mass-spectrometer coupled to a Thermo-Finnigan Kiel IV Carbonate Device in Southampton, Heidelberg, and Leipzig, and coupled to a Gasbench II in Frankfurt. International standards (NBS-18 and NBS-19) and in-house quality control standards were used to calibrate d18Ob. The record was astronomically tuned by recognising obliquity cycles in the X-ray fluorescence based CaCO3 record using newly generated coulometric carbonate content data (wt.% CaCO3), generated at the University of Southampton's Waterfront Campus, National Oceanography Centre Southampton (UoS-NOCS), using a CM5015 coulometer equipped with an AutoMate automated analysis devic
Evaluation of geomagnetic relative palaeointensity as a chronostratigraphic tool in the Southern Ocean: Refined Plio-/Pleistocene chronology of IODP Site U1533 (Amundsen Sea, West Antarctica)
No full textInternational Ocean Discovery Program (IODP) Expedition 379 to the Amundsen Sea margin of West Antarctica recovered drill cores at two sites spanning the Latest Miocene–Holocene interval with the aim of reconstructing past West Antarctic Ice Sheet dynamics. The recovered Plio-/Pleistocene sediment sequences offer an opportunity to apply and test different dating approaches in an Antarctic deep-sea drift setting, where the records are nearly continuous and unaffected by scouring of icebergs or grounded ice. Here, through palaeomagnetic analysis of continuous u-channel samples and application of X-ray fluorescence (XRF) scanning, we revise the IODP Exp. 379 Site U1533 age model for the uppermost Pliocene and Pleistocene composite interval (0.0–2.9 Ma). We first refine the magnetostratigraphic age model with high-resolution u-channel analysis and interpreted directional data. Consistent with shipboard results, all major geomagnetic polarity chrons and subchrons are identified in the Pleistocene section. The new high-resolution u-channel dataset also allows us to identify a geomagnetic polarity excursion at ∼884 ka (interpreted as the Kamikatsura excursion) and another excursion at ∼2734 ka with confidence (potentially the Porcupine excursion). Based on the improved polarity stratigraphy, we then develop two new highly resolved age models for Site U1533 using: (i) barium enrichment cycles identified in XRF scanning data, and (ii) geomagnetic relative palaeointensity (RPI). In our first age model, we correlate cyclic variations in sedimentary barium enrichment, inferred to represent changes in export productivity, to glacial‒interglacial cycles of the Lisiecki and Raymo (2005) benthic foraminiferal oxygen isotope (δ18O) stack (LR04). Nearly all Pleistocene Marine Isotope Stages (MIS) are interpreted to be present in the barium enrichment record of Site U1533, assuming simultaneous changes in Antarctic sea-ice extent/local export productivity and global oxygen isotope stratigraphy. We then construct the second, independent age model using the Plio-/Pleistocene RPI record developed for Site U1533, which represents the longest (nearly) continuous RPI record currently available for the Antarctic margin. Comparison of the two, independently derived age models shows a variable offset, on average ± 12 kyr, with the RPI-based ages consistently older than the barium-based ages in the interval from 1.9 to 2.9 Ma and then consistently younger from 0.0 to 1.9 Ma. We interpret these offsets to result from a combination of lock-in depth effects in the younger interval (due to the relatively low sedimentation rates at this site, ∼2 cm/kyr), temporal offsets between global δ18O changes in the deep ocean and productivity response on the Antarctic margin, and/or systematic miscorrelation in the construction of the two age models. Finally, we construct a hybrid age model for the Pleistocene section of Site U1533 by combining a mixture of RPI- and barium-based age tie points that are deemed to be robust. The Site U1533 RPI record is then used, together with other Southern Ocean RPI records, to construct an Antarctic RPI stack (designated as ‘ANT-1600’) for the interval 0.0–1.6 Ma. Although sedimentation rates at two-thirds of the sites selected for the stack are lower than 10 cm/kyr, the new ANT-1600 stack is strongly coherent with the SINT-2000 RPI stack (Valet et al., 2005) on time scales of ∼20–200 kyr, allowing for its use as a regional RPI reference curve in future studies. Overall, we demonstrate that RPI at Antarctic margin/Southern Ocean sites provides a viable and valuable independent dating method for application to Plio-/Pleistocene Antarctic sediments
Extracting a Detailed Magnetostratigraphy From Weakly Magnetized, Oligocene to Early Miocene Sediment Drifts Recovered at IODP Site U1406 (Newfoundland Margin, Northwest Atlantic Ocean)
Get PDFFine-grained magnetic particles in deep-sea sediments often statistically align with the ambient magnetic field during (and shortly after) deposition and can therefore record geomagnetic reversals. Correlation of these reversals to a geomagnetic polarity time scale is an important geochronological tool that facilitates precise stratigraphic correlation and dating of geological records globally. Sediments often carry a remanence strong enough for confident identification of polarity reversals, but in some cases a low signal-to-noise ratio prevents the construction of a reliable and robust magnetostratigraphy. Here we implement a data-filtering protocol, which can be integrated with the UPmag software package, to automatically reduce the maximum angular deviation and statistically mask noisy data and outliers deemed unsuitable for magnetostratigraphic interpretation. This protocol thus extracts a clearer signal from weakly magnetized sediments recovered at Integrated Ocean Drilling Program (IODP) Expedition 342 Site U1406 (Newfoundland margin, northwest Atlantic Ocean). The resulting magnetostratigraphy, in combination with shipboard and shore-based biostratigraphy, provides an age model for the study interval from IODP Site U1406 between Chrons C6Ar and C9n (approximate to 21-27 Ma). We identify rarely observed geomagnetic directional changes within Chrons C6Br, C7r, and C7Ar, and perhaps within Subchron C8n.1n. Our magnetostratigraphy dates three intervals of unusual stratigraphic behavior within the sediment drifts at IODP Site U1406 on the Newfoundland margin. These lithostratigraphic changes are broadly concurrent with the coldest climatic phases of the middle Oligocene to early Miocene and we hypothesize that they reflect changes in bottom water circulation.</p
Large obliquity-paced Antarctic ice-volume fluctuations suggest melting by atmospheric and ocean warming during late Oligocene
No full textAbstract The late Oligocene (~27.8–23 My ago) offers an opportunity to study past climate variability under high-CO2, warmer-than-present and the unipolar (Antarctic) glaciated state. Here, we present new high-resolution geochemical records from exquisitely well-preserved benthic foraminifera for the late Oligocene, an interval for which Antarctic ice-sheet size and stability are debated. Our records indicate four obliquity-paced glacial-interglacial cycles with ice-volume changes of up to ~70% of the modern Antarctic ice-sheet. The amplitude of ice-volume change during these late Oligocene glacial-interglacial cycles is comparable to that of the late Pliocene and early Pleistocene. Ice-volume estimates for interglacials are small enough to be accommodated by a land-based Antarctic ice-sheet but, for three of the four glacials studied, our calculations imply that ice sheets likely advanced beyond the Antarctic coastline onto the shelves. Our findings suggest an Antarctic ice-sheet vulnerable to melting driven by both bottom-up (ocean) and top-down (atmospheric) warming under late Oligocene warmer-than-present climate conditions
Eccentricity pacing and rapid termination of the early Antarctic ice ages
No full textEarth’s obliquity and eccentricity cycles are strongly imprinted on Earth’s climate and widely used to measure geological time. However, the record of these imprints on the oxygen isotope record in deep-sea benthic foraminifera (δ18Ob) shows contradictory signals that violate isotopic principles and cause controversy over climate-ice sheet interactions. Here, we present a δ18Ob record of high fidelity from International Ocean Drilling Program (IODP) Site U1406 in the northwest Atlantic Ocean. We compare our record to other records for the time interval between 28 and 20 million years ago, when Earth was warmer than today, and only Antarctic ice sheets existed. The imprint of eccentricity on δ18Ob is remarkably consistent globally whereas the obliquity signal is inconsistent between sites, indicating that eccentricity was the primary pacemaker of land ice volume. The larger eccentricity-paced early Antarctic ice ages were vulnerable to rapid termination. These findings imply that the self-stabilizing hysteresis effects of large land-based early Antarctic ice sheets were strong enough to maintain ice growth despite consecutive insolation-induced polar warming episodes. However, rapid ice age terminations indicate that resistance to melting was weaker than simulated by numerical models and regularly overpowered, sometimes abruptly
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