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  • 1
    Publikationsdatum: 2017-04-04
    Beschreibung: The Cenozoic evolution of the Antarctic cryosphere and fluctuations in its ice sheet cover are considered to be one of the major influences on low- and mid-latitude deep-sea sedimentary records. Long-term Cenozoic trends and short-term climate fluctuations (≤40 ka) alike are inferred to have been driven or modulated by changes in Antarctic ice sheet volume (Kennett, 1977; Imbrie and Imbrie, 1980; Zachos et al., 1997, 2001; Shackleton et al., 1999; Lear et al., 2000; Naish et al., 2001). Similarly, changes in sea level elevations at continental margins are also inferred to result from growth and decay in Antarctic ice sheet volume throughout the Cenozoic (Barrett et al., 1987; Haq et al., 1987). Yet, direct records of the Antarctic cryosphere and its ice sheets are sparse at best, and much of the inference remains untested. Recent efforts have begun to change this, and the last decade has seen several expeditions to the Antarctic and Southern Oceans, which have recovered new high-quality sedimentary core and seismic reflection records of Southern high-latitude Cenozoic ice sheets and climate. These include the Cape Roberts Project (CRP) (Cape Roberts Science Team, 1998; Hambrey et al., 1998; Cape Roberts Science Team, 1999; Barrett et al., 2000; Cape Roberts Science Team, 2000; Barrett et al., 2001; Davey et al., 2001), ODP Leg 177 (Gersonde et al., 1999, 2003), Leg 178 (Barker et al., 1999, 2002), Leg 182 (Feary et al., 2000; Hine et al., 2004), Leg 188 (O’Brien et al., 2001; Cooper et al., 2004), and Leg 189 (Exon et al., 2001, in press), and various RVIB NB Palmer and Polarstern cruises. Recent results from these expeditions were presented at a special session of the EGS–AGU Joint assembly held in Nice, France, in April 2003. The focus of the session was the many orders and scales of variation of Antarctic ice sheets and climate from Antarctic and sub-Antarctic records derived from outcrop studies, deep sea and continental margin drilling, and seismic reflection investigations. The session also included new modelling results utilizing new data from these recent expeditions and preliminary results of geophysical surveys defining sub-ice shelf and sea ice sedimentary basins identified as drilling targets in the near future under the ANDRILL program (Harwood et al., 2002; Florindo et al., 2003a).
    Beschreibung: Published
    Beschreibung: 1-7
    Beschreibung: 3.8. Geofisica per l'ambiente
    Beschreibung: JCR Journal
    Beschreibung: reserved
    Schlagwort(e): Antarctic climate evolution ; 03. Hydrosphere::03.01. General::03.01.06. Paleoceanography and paleoclimatology
    Repository-Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Materialart: article
    Standort Signatur Erwartet Verfügbarkeit
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  • 2
    Publikationsdatum: 2017-04-03
    Beschreibung: Ocean Drilling Program holes 744Aand 748B represent key sections for calibration of Southern Ocean Eocene-Oligocene biostratigraphic zonations. Sites 744 and 748 were above the carbonate compensation depth throughout this time interval and contain good planktonic foraminiferal, calcareous nannofossil, and diatom biostratigraphic records. In particular, the Southern Ocean diatom biostratigraphic zonation for the Oligocene critically hinges on calibration of these two holes. Previous low-resolution magnetostratigraphic studies at these sites were hampered by limited sampling and technical difficulties, which prompted our high-resolution reinvestigation of the magnetostratigraphy. Magnetic polarity zonations for holes 744Aand 748B were constructed after inspection of vector component plots at 1-cm stratigraphic intervals from continuous u-channel measurements. The magnetizations are generally stable and a robust polarity stratigraphy has been obtained for both holes. The increased resolution of our study and identification of persistent secondary overprints, which were not recognised in previous studies, suggests that the previously published interpretations need to be revised. Our magnetostratigraphic interpretations for both holes are constrained by foraminiferal and calcareous nannofossil datums, as well as by Sr isotope ages. We have calibrated four diatom datums, which are synchronous at the two studied sites, to the geomagnetic polarity timescale, including the first occurrence (FO) of Lisitzinia ornata (27.8 Ma), the FO of Rocella vigilans var. B (27.8 Ma), the FO of Cavitatus jouseanus (30.9 Ma) and the FO of Rhizosolenia oligocaenica (33.8 Ma). The synchroneity of these datums suggests that diatom biostratigraphy has considerable potential for Palaeogene biostratigraphic correlation in the Southern Ocean. Although the ages of some datums are obscured by an unconformity in Hole 744A, our age model from Hole 748B suggests age estimates for the last common occurrence of Rocella vigilans var. A(~29.0 Ma), the FO of Rocella vigilans var. A(30.0 Ma) and the FO of Rhizosolenia antarctica (33.2 Ma). It should also be noted that the last occurrence of the calcareous nannofossil Chiasmolithus altus occurs in Chron C8r rather than C8n in our revised magnetostratigraphic interpretation, which indicates that this datum is not diachronous between low and mid latitudes as had previously been suggested. Significant unconformities are documented in both holes, in the middle Oligocene and in the middle late Oligocene, respectively, which probably resulted from periods of enhanced circumpolar deep-water circulation.
    Beschreibung: Published
    Beschreibung: 145-168
    Beschreibung: 2.2. Laboratorio di paleomagnetismo
    Beschreibung: JCR Journal
    Beschreibung: reserved
    Schlagwort(e): Eocene ; Oligocene ; Ocean Drilling Program ; holes 744A and 748B ; Kerguelen Plateau ; Antarctica ; magnetostratigraphy ; biostratigraphy ; diatoms ; foraminifera ; calcareous nannofossils ; 03. Hydrosphere::03.01. General::03.01.06. Paleoceanography and paleoclimatology ; 04. Solid Earth::04.05. Geomagnetism::04.05.06. Paleomagnetism
    Repository-Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Materialart: article
    Standort Signatur Erwartet Verfügbarkeit
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  • 3
    Publikationsdatum: 2017-04-04
    Beschreibung: Present understanding of Antarctic climate change during the Early to Mid-Miocene, including major cycles of glacial expansion and contraction, relies in large part on stable isotope proxies from deep sea core drilling. Here, we summarize the lithostratigraphy of the ANDRILL Southern McMurdo Sound Project drillcore AND- 2A. This core offers a hitherto unavailable ice-proximal stratigraphic archive from a high-accommodation continental margin setting, and provides clear evidence of repeated fluctuations in climate, ice expansion/ contraction and attendant sea-level change over the period c. 20.2–14.2 Ma, with a more fragmentary record of Late Miocene and Pliocene time. The core is divided into seventy-four high-frequency (fourth- or fifthorder) glacimarine sequences recording repeated advances and retreats of glaciers into and out of the Victoria Land Basin. The section can be resolved into thirteen longer-term, composite (third-order) sequences, which comprise packages of higher frequency sequences that show a consistent stratigraphic stacking pattern (Stratigraphic Motif). The distribution of the six recognized motifs indicates intervals of less and more iceproximal, and temperate to subpolar/polar climate, through the Miocene period. The core demonstrates a dynamic climate regime throughout the Early to Mid-Miocene that may be correlated to some previouslyrecognized events such as the Mid-Miocene Climatic Optimum, and provides a detailed reference point from which to evaluate stable isotope proxy records from the deep-sea.
    Beschreibung: Published
    Beschreibung: 337-351
    Beschreibung: 1.8. Osservazioni di geofisica ambientale
    Beschreibung: 2.2. Laboratorio di paleomagnetismo
    Beschreibung: JCR Journal
    Beschreibung: restricted
    Schlagwort(e): Miocene ; Antarctica ; Sequence stratigraphy ; Cyclicity ; Mid-Miocene Climatic Optimum ; ANDRILL SMS project ; 04. Solid Earth::04.05. Geomagnetism::04.05.06. Paleomagnetism ; 04. Solid Earth::04.05. Geomagnetism::04.05.07. Rock magnetism ; 04. Solid Earth::04.05. Geomagnetism::04.05.09. Environmental magnetism
    Repository-Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Materialart: article
    Standort Signatur Erwartet Verfügbarkeit
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  • 4
    Publikationsdatum: 2022-06-08
    Beschreibung: We use all available chronostratigraphic constraints – biostratigraphy, magnetostratigraphy, radioisotopic dates, strontium-isotope stratigraphy, and correlation of compositional and physical properties to well-dated global or regional records – to construct a preliminary age model for ANDRILL SMS Project’s AND-2A drillcore (77°45.488’S, 165°16.605’E, 383.57 m water depth). These diverse chronostratigraphic constraints are consistent with each other and are distributed throughout the 1138.54 m-thick section, resulting in a well-constrained age model. The sedimentary succession comprises a thick early and middle Miocene section below 224.82 mbsf and a condensed middle/late Miocene to Recent section above this. The youngest sediments are Brunhes age (〈0.781 Ma), as confirmed by a radioisotopic age of 0.691±0.049 Ma at 10.23 mbsf and the occurrence of sediments that have normal magnetic polarity down to ~31.1 mbsf, which is interpreted to be the Brunhes/Matuyama reversal (0.781 Ma). The upper section is punctuated by disconformities resulting from both discontinuous deposition and periods of extensive erosion typical of sedimentary environments at the margin of a dynamic ice sheet. Additional breaks in the section may be due to the influence of tectonic processes. The age model incorporates several major hiatuses but their precise depths are still somewhat uncertain, as there are a large number of erosional surfaces identified within the stratigraphic section. One or more hiatuses, which represent a total 7 to 8 million years of time missing from the sedimentary record, occur between about 50 mbsf and the base of Lithostratigraphic Unit (LSU) 3 at 122.86 mbsf. Similarly, between about 145 mbsf and the base of LSU 4 at 224.82 mbsf, one or more hiatuses occur on which another 2 to 3 million years of the sedimentary record is missing. Support for the presence of these hiatuses comes from a diatom assemblage that constrains the age of the core from 44 to 50 mbsf to 2.06-2.84 Ma, two radioisotopic dates (11.4 Ma) and a Sr‑isotope date (11.7 Ma) that indicate the interval from 127 to 145 mbsf was deposited between 11.4 and 11.7 Ma, and three diatom occurrence datums from between 225.38 and 278.55 mbsf that constrain the age of this upper part of Lithostratigraphic Unit (LSU) 5 to 14.29 - 15.89 Ma. Below the boundary between LSU 5 and 6 sedimentation was relatively continuous and rapid and the age model is well-constrained by 9 diatom datums, seven 40Ar-39Ar dates, one Sr-isotope date, and 19 magnetozones. Even so, short hiatuses (less than a few hundred thousand years) undoubtedly occur but are beyond the resolution of current chronostratigraphic age constraints. Diatom first and last occurrence datums provide particularly good age control from the top of LSU 6 down to 771.5 mbsf (in LSU 10), where the First Occurrence (FO) of Thalassiosira praefraga (18.85 Ma) is observed. The diatom datum ages are supported by radioisotopic dates of 17.30±0.31 Ma at 640.14 mbsf (in LSU 9) and 18.15±0.35 and 17.93±0.40 Ma for samples from 709.15 and 709.18 mbsf (in LSU 10), respectively, and 18.71±0.33 Ma for a sample from 831.67 mbsf (in LSU 11). The sediments from 783.69 mbsf to the base of the hole comprise two thick normal polarity magnetozones that bound a thinner reversed polarity magnetozone (958.59 - 985.64 mbsf). This polarity sequence most likely encompasses Chrons C5En, C5Er, and C6n (18.056 - 19.772 Ma or slightly older given uncertainties in this section of the geomagnetic polarity timescale), but could be also be Chrons C6n, C6r, and C6An.1n (18.748 - 20.213 Ma). Either polarity sequence is compatible with the 40Ar–39Ar age of 20.01±0.35 Ma obtained from single-grain analyses of alkali feldspar from a tephra sample from a depth of 1093.02 mbsf, although the younger interpretation allows a better fit with chronostratigraphic data up-core. Given this age model, the mean sedimentation rate is about 18 cm/k.y. from the top of LSU 6 to the base of the hole.
    Beschreibung: Published
    Beschreibung: 221-220
    Beschreibung: 2.2. Laboratorio di paleomagnetismo
    Beschreibung: N/A or not JCR
    Beschreibung: reserved
    Schlagwort(e): ANDRILL ; Antarctica ; Stratigraphy ; 04. Solid Earth::04.04. Geology::04.04.10. Stratigraphy ; 04. Solid Earth::04.05. Geomagnetism::04.05.06. Paleomagnetism
    Repository-Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Materialart: article
    Standort Signatur Erwartet Verfügbarkeit
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  • 5
    Publikationsdatum: 2022-06-14
    Beschreibung: Stratigraphic drilling from the McMurdo Ice Shelf in the 2006/2007 austral summer recovered a 1284.87 m sedimentary succession from beneath the sea floor. Key age data for the core include magnetic polarity stratigraphy for the entire succession, diatom biostratigraphy for the upper 600 m and 40Ar/39Ar ages for in-situ volcanic deposits as well as reworked volcanic clasts. A vertical seismic profile for the drill hole allows correlation between the drill hole and a regional seismic network and inference of age constraint by correlation with well‐dated regional volcanic events through direct recognition of interlayered volcanic deposits as well as by inference from flexural loading of pre‐existing strata. The combined age model implies relatively rapid (1 m/2–5 ky) accumulation of sediment punctuated by hiatuses, which account for approximately 50% of the record. Three of the longer hiatuses coincide with basin‐wide seismic reflectors and, along with two thick volcanic intervals, they subdivide the succession into seven chronostratigraphic intervals with characteristic facies: 1. The base of the cored succession (1275–1220 mbsf) comprises middle Miocene volcaniclastic sandstone dated at approx 13.5 Ma by several reworked volcanic clasts; 2. A late-Miocene sub-polar orbitally controlled glacial–interglacial succession (1220–760 mbsf) bounded by two unconformities correlated with basin‐wide reflectors associated with early development of the terror rift; 3. A late Miocene volcanigenic succession (760–596 mbsf) terminating with a ~1 my hiatus at 596.35 mbsf which spans the Miocene–Pliocene boundary and is not recognised in regional seismic data; 4. An early Pliocene obliquity-controlled alternating diamictite and diatomite glacial–interglacial succession(590–440 mbsf), separated from; 5. A late Pliocene obliquity-controlled alternating diamictite and diatomite glacial–interglacial succession (440–150 mbsf) by a 750 ky unconformity interpreted to represent a major sequence boundary at other locations; 6. An early Pleistocene interbedded volcanic, diamictite and diatomite succession (150–80 mbsf), and; 7. A late Pleistocene glacigene succession (80–0 mbsf) comprising diamictite dominated sedimentary cycles deposited in a polar environment.
    Beschreibung: Published
    Beschreibung: 189-203
    Beschreibung: 2.2. Laboratorio di paleomagnetismo
    Beschreibung: JCR Journal
    Beschreibung: restricted
    Schlagwort(e): Stratigraphic Drilling ; McMurdo Ice Shelf ; Chronostratigraphy ; Neogene ; Tectonics ; Ice Sheet history ; 02. Cryosphere::02.03. Ice cores::02.03.05. Paleoclimate ; 04. Solid Earth::04.04. Geology::04.04.10. Stratigraphy ; 04. Solid Earth::04.05. Geomagnetism::04.05.06. Paleomagnetism
    Repository-Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Materialart: article
    Standort Signatur Erwartet Verfügbarkeit
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