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Summary of 40Ar/39Ar results from core sediment CRP-1 (Table 1)

McIntosh, W C ; McIntosh, Bill

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In: Supplement to: McIntosh, W C (1998): 40Ar/39Ar geochronology of volcanic clasts and pumice in CRP-1 core, Cape Roberts, Antarctica. Terra Antartica, 5(3), 683-690, hdl:10013/epic.28322.d001

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Publication Date: 2023-06-27

Description: 40Ar/39Ar dating of volcanic clasts and pumice provide constraints for depositional ages of the CRP-1 core. Laser-fusion analyses of anorthoclase phenocrysts from pumice clasts concentrated near 116 mbsf suggest a depositional age of 18.40 ± 1.12 Ma (± 2). Results from anorthoclase phenocrysts and groundmass concentrates from five clasts of reworked lava provide maximum depositional ages of 19.73 ± 0.86 Ma to 17.15 ± 0.80 Ma for the 61 to 114 mbsf interval of CRP-1. The most precise age determination is 19.32 ± 0.14 Ma for the trachytic clasts near 105 mbsf. Taken together, the 40Ar/39Ar results from the lower part of CRP-1 suggest that none of the sediment above 116 mbsf is older than 19.5 Ma, and the data are most compatible with rapid accumulation of the 61 to 116 mbsf segment of CRP-1 near 18 Ma. 40AR/39Ar results from a basaltic clast from the carbonate-rich layer at 33 mbsf provide a maximum depositional age of 1.2 ± 0.1 Ma for this horizon.

Keywords: 16 km ENE Cape Roberts; Age, 40Ar/39Ar Argon-Argon; Age, dated; Age, dated standard deviation; Cape Roberts Project; Comment; Core wireline system; CRP; CRP-1; CWS; Depth, bottom/max; DEPTH, sediment/rock; Depth, top/min; Lithology/composition/facies; off Cape Roberts, Ross Sea, Antarctica; Sample code/label; Sampling/drilling ice; Visual description; Yield

Type: Dataset

Format: text/tab-separated-values, 80 data points

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Summary of 40Ar/39Ar results from sediment core CRP-2A (Table 1) (2004)

McIntosh, W C

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In: Supplement to: McIntosh, W C (2000): 40Ar/39Ar geochronology of tephra and volcanic clasts in CRP-2A, Victoria Land Basin, Antarctica. Terra Antartica, 7(4), 621-630, hdl:10013/epic.28247.d001

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Publication Date: 2023-06-27

Description: 40Ar/39Ar analyses of tephra and clasts of volcanic rock provide age constraints for upper parts of the CRP-2A core. Single-crystal laser-fusion analyses of anorthoclase phenocrysts from three tephra-bearing layers yielded the most precise age constraints for CRP-2A. The dated tephra layers are: 1) a 2.7-m-thick interval of pumice and ash layers between 111.5 and 114.2 meters below sea floor (mbsf) (weighted mean age = 21.44 ± 0.05 Ma, +2.2); 2) a concentration of pumice near 193.4 mbsf (23.98 ± 0.13 Ma): and 3) a concentration of pumice near 280 mbsf (24,22 ± 0.03 Ma) (all ages are calibrated relative to Fish Canyon Tuff sanidine at 27.84 Ma). The 111 to 114 mbsf tephra is almost entirely non-reworked, and the 193 mbsf and 280 mbsf tephra concentrations are interpreted as being reworked and redeposited soon after eruption. All three of the tephra ages are therefore considered to be equivalent to depositional ages. The variation in precision of these three age determinations is largely a function of phenocryst size and abundance. The accuracy of these ages is equal to the accuracy of the current calibration of the 40Ar/39Ar methode (about ± 1 %). 40Ar/39Ar results from volcanic clasts provide three additional maximum age constraints for the CRP-2A core. Single-crystal laser-fusion of sanidine phenocrysts from a rhyolitic clast from 294 mbsf yielded a precise maximum depositional age of 24.98 ± 0.08 Ma, and plateau ages of groundmass concentrates from basaltic clasts near 36.02 mbsf and 125.92 mbsf yielded maximum depositional ages of 19.18 ± 0.12 Ma, and 22.56 ± 0.14 Ma, respectively. The 40Ar/39Ar data, in association with biostratigraphic, paleomagnetic, and isotopic age constraints for CRP-2A, confirm interpretation for rapid sedimentation rates in the 36 to 280 mbsf interval, particularly in the 193 to 280 mbsf interval where they support interpretations for sedimentation cycles spanning 100 k.y. intervals. In addition to the 19 to 25 Ma ages measured from thephra layers and clasts, provenance-related ages ranging from 150 to 450 Ma were determined from clasts and individual detrital or xenocrystic crystals from CRP-2A.

Keywords: 14.2 km at 096° true from Cape Roberts; Age, dated; Age, dated material; Age, error; Argon-39; Calcium/Potassium ratio; Cape Roberts Project; Comment; Core wireline system; CRP; CRP-2; CRP-2A; CWS; DEPTH, sediment/rock; Isotope ratio mass spectrometry; Number; off Cape Roberts, Ross Sea, Antarctica; Sample comment; Sample ID; Sample method; Sampling/drilling from ice; see comment

Type: Dataset

Format: text/tab-separated-values, 103 data points

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Chronostratigraphy of sediment core CRP-2/2A (Table 1) (2000)

Wilson, Gary S ; Bohaty, Steven M ; Fielding, Christopher R ; [et al.]

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In: Supplement to: Wilson, Gary S; Bohaty, Steven M; Fielding, Christopher R; Florindo, Fabio; Hannah, Mike J; Harwood, David M; McIntosh, W C; Naish, Tim R; Roberts, Andrew P; Sagnotti, Leonardo; Scherer, Reed P; Strong, C Percy; Versub, K L; Villa, Giuliana; Watkins, David K; Webb, Peter-Noel; Woolfe, Ken (2000): Chronostratigraphy of CRP-2/2A, Victoria Land Basin, Antarctica. Terra Antartica, 7(4), 647-654, hdl:10013/epic.28244.d001

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Publication Date: 2024-01-20

Description: The 624.15 m glaciomarine sedimentary succession recovered in the CRP-2/2A drillcore comprises lower Oligocene (〈c. 31 Ma) to lower Miocene (18.5 Ma) strata that are overlain by a thin succession of Pliocene and Pleistocene strata. The age model for the CRP-2/2A drillhole, as presented in this paper, is based on combined microfossil biostratigraphy. 40Ar/39Ar age on volcanic material, 87Sr/86Sr analyses on mollusc shells, and correlation of a magnetic polarity zonation to the magnetic polarity time scale (MPTS). Between 25.92 and 109.05 metres below sea floor (mbsf), several alternative correlations to the MPTS are possible, all of which suggest that sediment accumulation rates averaged ~180 m/m.y. between unconformities, although actual sedimentation rates may have been higher. Between 109.05 and 306.65 mbsf, the age model is straightforward and average sedimentation rates were much higher (〉1000 m/m.y.). Between 306.65 mbsf and the bottom of the drillcore (624.15 mbsf), fewer datums are available to constrain the age model and unique correlation with the MPTS is not possible, although high average sediment accumulation rates are likely. A significant unconformity is identified at 306.65 mbsf, which may represent as much as 5 m.y. of missing time. Additional unconformities at 25.92 and 130.27 mbsf account for c. 16 and 2.5 m.y. of missing time, respectively. The Oligocene-lower Miocene interval documented in the CRP-2/2A drillcore spans about 13 million years, however, it is possible that more time is missing in sequence-bounding unconformities than is represented in the stratigraphic record recovered in the CRP-2/2A drillcore.

Keywords: 14.2 km at 096° true from Cape Roberts; Age, comment; Age, dated; Age, dated, error to older; Age, dated, error to younger; Age, dated material; Cape Roberts Project; Core wireline system; CRP; CRP-2; CRP-2A; CWS; Depth, bottom/max; DEPTH, sediment/rock; Depth, top/min; off Cape Roberts, Ross Sea, Antarctica; Sample code/label; Sampling/drilling from ice

Type: Dataset

Format: text/tab-separated-values, 199 data points

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(Table S1) Chronostratigraphic constrains for sediment core AND1-1B (2009)

Naish, Tim R ; Powell, Ross ; Levy, Richard H ; [et al.]

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In: Supplement to: Naish, Tim R; Powell, Ross; Levy, Richard H; Wilson, Gary S; Scherer, Reed P; Talarico, Franco M; Krissek, Lawrence A; Niessen, Frank; Pompilio, Massimo; Wilson, Terry; Carter, Lionel; DeConto, Robert M; Huybers, Peter; McKay, Robert M; Pollard, David; Ross, J; Winter, Diane M; Barrett, Peter J; Browne, G; Cody, Rosemary; Cowan, Ellen A; Crampton, James; Dunbar, Gavin B; Dunbar, Nelia W; Florindo, Fabio; Gebhardt, Catalina; Graham, I J; Hannah, Mike J; Hansaraj, D; Harwood, David M; Helling, D; Henrys, Stuart A; Hinnov, Linda A; Kuhn, Gerhard; Kyle, Philip R; Läufer, Andreas; Maffioli, P; Magens, Diana; Mandernack, Kevin W; McIntosh, W C; Millan, C; Morin, Roger H; Ohneiser, Christian; Paulsen, Timothy S; Persico, Davide; Raine, J Ian; Reed, J; Riesselman, Christina R; Sagnotti, Leonardo; Schmitt, Douglas R; Sjunneskog, Charlotte; Strong, P; Taviani, Marco; Vogel, Stefan; Wilch, T; Williams, Trevor J (2009): Obliquity-paced Pliocene West Antarctic ice sheet oscillations. Nature, 458(7236), 322-329, https://doi.org/10.1038/nature07867

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Publication Date: 2024-05-06

Description: Thirty years after oxygen isotope records from microfossils deposited in ocean sediments confirmed the hypothesis that variations in the Earth's orbital geometry control the ice ages (Hays et al., 1976, doi:10.1126/science.194.4270.1121), fundamental questions remain over the response of the Antarctic ice sheets to orbital cycles (Raymo and Huybers, 2008, doi:10.1038/nature06589). Furthermore, an understanding of the behaviour of the marine-based West Antarctic ice sheet (WAIS) during the 'warmer-than-present' early-Pliocene epoch (~5-3 Myr ago) is needed to better constrain the possible range of ice-sheet behaviour in the context of future global warming (Solomon et al., 2007). Here we present a marine glacial record from the upper 600 m of the AND-1B sediment core recovered from beneath the northwest part of the Ross ice shelf by the ANDRILL programme and demonstrate well-dated, ~40-kyr cyclic variations in ice-sheet extent linked to cycles in insolation influenced by changes in the Earth's axial tilt (obliquity) during the Pliocene. Our data provide direct evidence for orbitally induced oscillations in the WAIS, which periodically collapsed, resulting in a switch from grounded ice, or ice shelves, to open waters in the Ross embayment when planetary temperatures were up to ~3° C warmer than today ( Kim and Crowley, 2000, doi:10.1029/1999PA000459) and atmospheric CO2 concentration was as high as ~400 p.p.m.v. (van der Burgh et al., 1993, doi:10.1126/science.260.5115.1788, Raymo et al., 1996, doi:10.1016/0377-8398(95)00048-8). The evidence is consistent with a new ice-sheet/ice-shelf model (Pollard and DeConto, 2009, doi:10.1038/nature07809) that simulates fluctuations in Antarctic ice volume of up to +7 m in equivalent sea level associated with the loss of the WAIS and up to +3 m in equivalent sea level from the East Antarctic ice sheet, in response to ocean-induced melting paced by obliquity. During interglacial times, diatomaceous sediments indicate high surface-water productivity, minimal summer sea ice and air temperatures above freezing, suggesting an additional influence of surface melt (Huybers, 2006, doi:10.1126/science.1125249) under conditions of elevated CO2.

Keywords: Age, comment; Age, error; Age model; Age model, optional; Ageprofile Datum Description; AND1-1B; AND-1B; ANDRILL; Antarctic Geological Drilling; D-ANDRILL; Datum level; Depth, bottom/max; DEPTH, sediment/rock; Depth, top/min; DRILL; Drilling/drill rig; McMurdo Ice Shelf; McMurdo Station; Method comment; MIS; Priority Programme 1158 Antarctic Research with Comparable Investigations in Arctic Sea Ice Areas; SPP1158

Type: Dataset

Format: text/tab-separated-values, 129 data points

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Preliminary Integrated Chronostratigraphy of the AND-1B Core, ANDRILL McMurdo Ice Shelf Project, Antarctica (2008)

Wilson, G. ; Levy, R. ; Browne, G. ; [et al.]

Terra Antartica

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Publication Date: 2017-04-04

Description: Chronostratigraphic data available for the preliminary age model for the upper 700 m for the AND-1B drill core include diatom biostratigraphy, magnetostratigraphy, 40Ar/39Ar ages on volcanic material, 87Sr/86Sr ages on calcareous fossil material, and surfaces of erosion identified from physical appearance and facies relationships recognised in the AND-1B drill core. The available age data allow a relatively well-constrained age model to be constructed for the upper 700 m of the drill core. Available diatom biostratigraphic constraints and 40Ar/39Ar ages allow a unique correlation of ~70% of the AND-1B magnetic polarity stratigraphy with the Geomagnetic Polar Time Scale (GPTS). Unique correlation is not possible in several coarse diamictite intervals with closely spaced glacial surfaces of erosion and sparse microflora. However, the age model indicates relatively rapid (up to 1 m/k.y.) and continuous accumulation of intervening finer grained diatomaceous intervals punctuated by several half- to million-years hiatuses representing more than half of the last 7 m.y. in the AND-1B record. The mid- to late Pleistocene is represented by superimposed diamictite units separated from upper Pliocene alternating diamictites/diatomites by a ~1 m.y. hiatus co-incident with a regionally correlated seismic reflection surface. A c. 100 m-thick diatomite represents a significant portion of the early Pliocene record in the AND-1B drill core. Strata below ~620 m are late Miocene in age; however, biostratigraphic constraints are absent below 586 m and correlation with the GPTS is relatively unconstrained. At the the of writing, the only chronostratigraphic data available below 700 mbsf include three 40Ar/39Ar ages on volcanic clasts from near 1280 mbsf affording a maximum depositional age of 13.57 Ma for the base of the AND-1B drill core.

Description: Published

Description: 297-316

Description: 2.2. Laboratorio di paleomagnetismo

Description: 3.8. Geofisica per l'ambiente

Description: N/A or not JCR

Description: reserved

Keywords: Chronostratigraphy, ANDRILL, Antarctica ; 04. Solid Earth::04.05. Geomagnetism::04.05.06. Paleomagnetism

Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)

Type: article

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