Publikationsdatum:
2022-06-14
Beschreibung:
In 2007, the Antarctic Geological Drilling
Program (ANDRILL) drilled 1138.54 m of
strata ~10 km off the East Antarctic coast,
includ ing an expanded early to middle Miocene succession not previously recovered
from the Antarctic continental shelf. Here,
we pre sent a facies model, distribution, and
paleoclimatic interpretation for the AND-2A
drill hole, which enable us, for the fi rst time, to reconstruct periods of early and middle Miocene glacial advance and retreat and paleo environmental changes at an ice-proximal site. Three types of facies associations can be recognized that imply signifi cantly different paleoclimatic interpretations. (1) A diamictite-dominated facies association represents glacially dominated depositional environments,
including subglacial environments, with only brief intervals where ice-free coasts existed, and periods when the ice sheet was
periodically larger than the modern ice sheet.
(2) A stratified diamictite and mudstone facies association includes facies characteristic of open-marine to iceberg-infl uenced depositional environments and is more consistent with a very dynamic ice sheet, with a grounding line south of the modern position. (3) A mudstone-dominated facies association generally lacks diamictites and was produced in a
glacially infl uenced hemipelagic depositional environment. Based on the distribution of these facies associations, we can conclude that the Antarctic ice sheets were dynamic, with grounding lines south of the modern location at ca. 20.1–19.6 Ma and ca. 19.3–18.7 Ma and during the Miocene climatic optimum, ca. 17.6–15.4 Ma, with ice-sheet and sea-ice minima at ca. 16.5–16.3 Ma and ca. 15.7–15.6 Ma.
While glacial minima at ca. 20.1–19.6 Ma
and ca. 19.3–18.7 Ma were characterized by
temperate margins, an increased abundance
of gravelly facies and diatomaceous siltstone
and a lack of meltwater plume deposits suggest a cooler and drier climate with polythermal conditions for the Miocene climatic optimum (ca. 17.6–15.4 Ma). Several periods of major ice growth with a grounding line traversing the drill site are recognized between ca. 20.2 and 17.6 Ma, and after ca. 15.4 Ma, with evidence of cold polar glaciers with ice shelves. The AND-2A core provides proximal evidence that during the middle Miocene climate transition, an ice sheet larger than the modern ice sheet was already present by ca. 14.7 Ma, ~1 m.y. earlier than generally inferred from deep-sea oxygen isotope records.
These fi ndings highlight the importance of
high-latitude ice-proximal records for the interpretation of far-fi eld proxies across major climate transitions.
Beschreibung:
Published
Beschreibung:
2352-2365
Beschreibung:
1.8. Osservazioni di geofisica ambientale
Beschreibung:
2.2. Laboratorio di paleomagnetismo
Beschreibung:
3.8. Geofisica per l'ambiente
Beschreibung:
JCR Journal
Beschreibung:
reserved
Schlagwort(e):
ANDRILL-SMS
;
Miocene
;
Ross Sea
;
Antarctica
;
03. Hydrosphere::03.01. General::03.01.06. Paleoceanography and paleoclimatology
;
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
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